Talk:Laser/Archive 7

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Lase

I noticed that somebody had written that there was a verb "to lase" which means to shine a laser or to be shined on by a laser. This definition sounded too broad (since it was talking about the transmitter and the receiver) and didn't sound like a real word, so I checked the source and it was recorded as Dictionary.com. This site is one of the least credible on the net, I think that in order for "lase" to still be recorded here as a legitimate verb, it should be listed by a more credible source. Since lasers emit light, surely the existing verbs describing light can already be used to describe lasers as well. —Preceding unsigned comment added by Owen214 (talk • contribs) 09:00, 13 December 2009 (UTC)

I have frequently encountered the verb 'to lase' but it has a different meaning. In the contexts that I have encountered it, the verb refers to the ability of a particular material to be excited to produce laser light. Thus:

Many suitable materials can be made to lase.

Means that many substances can be made to emit laser light. 20.133.0.13 (talk) 14:05, 14 January 2010 (UTC)

See e.g. thisMattyp9999 (talk) 10:51, 5 August 2010 (UTC)

There are many aspects of modern science that are oral traditions or customs within the scientific community. Among these is the use of the verb, "to lase". Probably not in the dictionary. Correct use is "to oscillate" or "to resonate", but this is somewhat clumsy because many things can oscillate or resonate, but when a laser physicist gets coherent radiation out of his device, he means to oscillate or resonate optically. It is an artifact of the acronym LASER ending in -ER which makes it natural to use the first part of the word as a verb. If we look at the grammar of the acronym LASER - Light Amplification by Stimulated Emission of Radiation, we see it refers to a process or an end result, not a device, thus, if you amplify light by a stimulated emission process, you have produced LASER. In spite of this, the acronym LASER is in common use as a noun referring to a device, not the process nor the product. I recommend that we not try to correct the grammatical inconsistencies in using LASER as a noun referring to a physical device, nor the use of LASE as a verb meaning to produce coherent radiation by the LASER process. — Preceding unsigned comment added by Seanross (talk • contribs) 02:05, 4 August 2011 (UTC)

Coherence

The key property of a laser is the coherence of its output. The article makes this clear, but does not explain coherence (and the link is to a very general treatment of the concept). Do our experts think it would be appropriate to give a brief explanation of coherence (just a phrase) for the benefit of non-expert readers, many of whom evidently think that coherence is the same as monochromacity. Dbfirs 20:21, 16 June 2008 (UTC)

Sure, go for it.--Srleffler (talk) 23:09, 16 June 2008 (UTC)

Thanks, have done, though I've put it at the end of the intro to distinguish laser from other light sources. Is this OK? Dbfirs 08:41, 17 June 2008 (UTC)

It's a start. People will tinker with the wording I'm sure. I don't know if "out of phase with itself" is clear enough. Temporally incoherent light is such because its phase shifts randomly with time. This is fundamentally the same thing as lack of (due to the magic of Fourier transforms) a slightly broadened spectrum. There is an inverse relationship between the width of the spectrum and the coherence time of the beam. A spatially incoherent beam, on the other hand, is one where different parts of the same beam are out of phase with one another, in some random pattern.--Srleffler (talk) 17:00, 17 June 2008 (UTC)

I see two key points. Firstly, without an understanding of "coherence" there can be little valid understanding of what constitutes a "laser" or more particularly laser light i.e. the special light emitted by the laser. Inter alia the greatest interest on the part of a casual reader would be in laser light, and to a lesser degree in the laser per se. So the Wikipedia page on lasers is really itself about coherent light and how it is generated by the devices or systems called "lasers." Secondly, the reference to a separate Wikipedia entry on "coherence" is superfluous if that entry does not serve the need of explaining (to the casual - but, yes, minimally qualified - reader willing and able to devote some thought) "laser light."Jabeles (talk) 16:13, 29 July 2008 (UTC)

Quite separately, there is another little problem with respect to defining lasers by "coherence." It so happens that another sizable class of diode lasers, the so-called "pump lasers," are not coherent - neither temporally nor spatially. They do emit light that is spatially coherent along one axis, but that is not sufficient to allow their light to be low-divergence overall. They are called "lasers" because they share many features and properties with other lasers: Even along the non-coherent axis, the light emitted from these lasers can be somewhat directional, and the spectrum can be somewhat narrow (certainly more directional and more narrow overall than LEDs or other incoherent light sources). Importantly, too, the efficiency of these lasers can be quite high (equally high or even higher than other diode lasers). Indeed, a key aspect of diode lasers heretofore un-discussed in the main article is their capability for incredible electrical-to-optical power conversion efficiency.

In any event, it may be a serious omission should the main article not allow for and explain the fact that there exists a class of light-emitting semiconductor devices commonly called pump lasers that in fact are not lasers per se (though some might dispute that -- see below) but share many of the properties of conventional diode lasers. Why, one may query, is anyone interested in pump lasers? Because they can be configured in large quantities to generate light (kilowatts of raw light power) efficiently such that this light can be utilized to pump other (solid state) laser media such as neodymium-doped glasses or crystals. In turn the solid state (or other) media do in fact generate coherent light.

Now, as I mentioned, there is room for disagreement regarding whether these pump lasers are, or are not, pump lasers. The approach currently taken by the main article insists on "coherence" as the sine qua non of lasers. This definition while not incorrect (!) is not the only possible definition. In the research community consisting of workers striving to demonstrate new types of diode lasers (e.g. those made of different materials such as silicon, or those emitting light at new wavelengths in the IR, THz, green, or UV) it is not at all unusual to use different criteria to specify the presence or absence of bona fide lasing. These different criteria are (1) existence of a threshold, (2) narrowing of the spectrum, and (3) increase in intensity of the narrowed portion of the spectrum with increased input power whilst the remainder of the spectrum remains susbstantially at the threshold-defined intensity level.

In the above sense, indeed, pump lasers do qualify as lasers. This is an interesting discussion and would require the participation of experts holding the latter point of view to really determine. My personal preference is to not include pump lasers in the strictly defined classification (taxonomy) of "laser." Jabeles (talk) 16:13, 29 July 2008 (UTC)

You've raised a good issue. In my view pump diodes are unquestionably lasers. I hadn't thought about their lack of coherence when discussing this here before. Other examples come to mind. Large diameter VCSELs may lack spatial coherence altogether, for example. What is fundamental in my opinion is that a laser is a device where stimulated emission and feedback from an optical resonator produces net gain (oscillation). --Srleffler (talk) 17:06, 29 July 2008 (UTC)

I guess I can endorse that point-of-view. But the Introduction as it stands is at odds with these fundamentals of lasers. Indeed, "pump lasers" seem to be excluded from the classification of "laser" according to the intro — as it now stands.Jabeles (talk) 19:58, 4 August 2008 (UTC)

Most common usage

The article gives optical reading (in CD/DVD) players as the most common use, I would have thought indicator devices - LEDs - were far more widespread applications. Apepper (talk) 09:24, 22 June 2008 (UTC)

LEDs are not lasers.--Srleffler (talk) 14:39, 22 June 2008 (UTC)

Well, most LEDs aren't lasers. Laser diodes are lasers, of course. —Ben FrantzDale (talk) 15:51, 22 June 2008 (UTC)

Laser diodes are not LEDs. (Yes, they emit light and are diodes. Nevertheless, they are not LEDs.) --Srleffler (talk) 19:32, 22 June 2008 (UTC)

Really? Interesting. I just assumed. Could you explain the difference? Does a light emitting diode use a different mechanism than a laser diode? —Ben FrantzDale (talk) 21:24, 22 June 2008 (UTC)

It's basically a semantic issue. We don't call laser diodes LEDs even though they are diodes that emit light. The mode of operation is different: laser diodes lase (emit light via stimulated emission), while LEDs emit via spontaneous emission. There are obviously structural differences between the devices that explain this difference in operation, but I don't know what they are.--Srleffler (talk) 17:08, 26 June 2008 (UTC)

The difference between LEDs and laser diodes is simply the absence of a suitable resonant cavity in the LED structure preventing the LED from emitting stimulated emission. N.B.: {laser} = {stimulated emission} + {suitable resonant cavity}. The difference between stimulated and spontaneous emission for a typical LED structure (but not for all structures exhibiting spontaneous emission) is the absence of the "suitable resonant cavity."Jabeles (talk) 22:02, 28 July 2008 (UTC)

I think you are mistaken. The resonant cavity is the easy part. A Fabry-Perot laser diode simply uses the uncoated cleaved edges of the chip as reflecting surfaces. An LED with uncoated edges will not lase, nor can you make one lase by adding an external cavity. External cavity semiconductor lasers use a "gain chip" (a semiconductor optical amplifier), which is an F-P laser diode with antireflection coatings on one or both facets. These gain chips are distinct from LEDs.

My informed guess is that LEDs have much lower gain, and cannot get above the lasing threshold even with a highly reflecting external cavity. I don't offhand know what the structural differences are that cause them to have lower gain. Typical laser diodes use a waveguide on the chip to confine the light in the transverse direction, and have structures to confine the current so that it overlaps the waveguide. I'm guessing that LEDs lack these structures, but perhaps the lower gain is instead due to some difference in the junction structure or something else I'm not aware of. --Srleffler (talk) 04:26, 6 August 2008 (UTC)

Revert

I reverted, removing the following:

William R. Bennett and Donald Herriot, made the first gas laser using helium and neon in 1958. Iranian physicist Ali Javan, later received the Albert Einstein Award in 1993 for their work. William R. Bennett (born January 30, 1930) is an American physicist. He was co-inventor of the first gas laser (the helium-neon laser), discovered the argon ion laser, was first to observe spectral hole burning effects in gas lasers, and created a theory of hole burning effects on laser oscillation. He was co-discoverer of lasers using electron impact excitation in each of the noble gases, dissociative excitation transfer in the neon-oxygen laser (the first chemical laser), and collision excitation in several metal vapor lasers.

I am aware that there are accusations that Javan stole credit from Bennett and Herriot. I'm not sure if it's true that they did the work entirely on their own and Javan got the credit for it. A citation is required to support this claim. I know Taylor's book (LASER: The inventor, the Nobel laureate, and the thirty-year patent war) discusses this, but I no longer have a copy.--Srleffler (talk) 18:29, 29 June 2008 (UTC)

Intensity is used incorrectly herein

The term Intensity is used incorrectly in this article. Intensity is measured in W/(m^2 ster) not W/m^2. What the authors of this article are confusing Intensity with is Irradiance. Irradiance is W/m^2. This is understandable in that a small number of old optics engineers very wrongly misuse the word "intensity" when they are discussing W/m^2. Saying "optical intesity" is sometimes used as a fix but it is still incorrect. The scientific community uses Irradiance. So, the graphic discussing "Intensity" is labled incorrectly and a bit suspect.

Dr. Travis S. Taylor —Preceding unsigned comment added by 12.202.220.217 (talk) 04:08, 9 July 2008 (UTC)

This usage is, unfortunately, widespread in laser physics/engineering, even among young engineers. Even those of us who know better more or less have to go along. See Intensity (physics) for a discussion of this. Ironically, your correction is also incorrect. Radiant intensity is W/sr, not W/(m^2 ster). The latter is properly called radiance. You wouldn't happen to be an astronomer or astrophysicist, would you? The misuse of the term "intensity" as a substitute for "radiance" is common in those fields.--Srleffler (talk) 17:51, 28 July 2008 (UTC)

The term "radiance" (as Srleffler states) is the thermodynamically conserved quantity whose units are [power]/([area]×[solid angle]). Note that the quantity whose units are ([area]×[solid angle]) is known as etendue. So radiance is power per etendue. Another definition of a transverse single-mode light source is one having the minimum etendue, or equivalently the maximum brightness for a given power. The term "brightness" is technically analogous to "radiance" but the latter is a photometric quantity, i.e., referenced to the efficiency of human sight by substituting lumens for watts. Nonetheless, the term "brightness" and even "brilliance" have been used as synonyms for "radiance" (in my understanding incorrectly). One can refer to the RCA Electro-Optics Handbook available at the burle.com website for the historically accurate terminology.Jabeles (talk) 23:10, 4 August 2008 (UTC)

The term "brightness" is now deprecated in scientific use, except as a non-quantitative description of the subjective perception of light. The photometric analog to radiance is luminance in modern terminology. --Srleffler (talk) 02:05, 5 August 2008 (UTC)

SI radiometry units

Quantity		Unit		Dimension	Notes
Name	Symbol	Name	Symbol
Radiant energy	Qe	joule	J	M⋅L2⋅T−2	Energy of electromagnetic radiation.
Radiant energy density	we	joule per cubic metre	J/m3	M⋅L−1⋅T−2	Radiant energy per unit volume.
Radiant flux	Φe	watt	W = J/s	M⋅L2⋅T−3	Radiant energy emitted, reflected, transmitted or received, per unit time. This is sometimes also called "radiant power", and called luminosity in Astronomy.
Spectral flux	Φe,ν	watt per hertz	W/Hz	M⋅L2⋅T −2	Radiant flux per unit frequency or wavelength. The latter is commonly measured in W⋅nm−1.
	Φe,λ	watt per metre	W/m	M⋅L⋅T−3
Radiant intensity	Ie,Ω	watt per steradian	W/sr	M⋅L2⋅T−3	Radiant flux emitted, reflected, transmitted or received, per unit solid angle. This is a directional quantity.
Spectral intensity	Ie,Ω,ν	watt per steradian per hertz	W⋅sr−1⋅Hz−1	M⋅L2⋅T−2	Radiant intensity per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅nm−1. This is a directional quantity.
	Ie,Ω,λ	watt per steradian per metre	W⋅sr−1⋅m−1	M⋅L⋅T−3
Radiance	Le,Ω	watt per steradian per square metre	W⋅sr−1⋅m−2	M⋅T−3	Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. This is a directional quantity. This is sometimes also confusingly called "intensity".
Spectral radiance Specific intensity	Le,Ω,ν	watt per steradian per square metre per hertz	W⋅sr−1⋅m−2⋅Hz−1	M⋅T−2	Radiance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅sr−1⋅m−2⋅nm−1. This is a directional quantity. This is sometimes also confusingly called "spectral intensity".
	Le,Ω,λ	watt per steradian per square metre, per metre	W⋅sr−1⋅m−3	M⋅L−1⋅T−3
Irradiance Flux density	Ee	watt per square metre	W/m2	M⋅T−3	Radiant flux received by a surface per unit area. This is sometimes also confusingly called "intensity".
Spectral irradiance Spectral flux density	Ee,ν	watt per square metre per hertz	W⋅m−2⋅Hz−1	M⋅T−2	Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include jansky (1 Jy = 10−26 W⋅m−2⋅Hz−1) and solar flux unit (1 sfu = 10−22 W⋅m−2⋅Hz−1 = 104 Jy).
	Ee,λ	watt per square metre, per metre	W/m3	M⋅L−1⋅T−3
Radiosity	Je	watt per square metre	W/m2	M⋅T−3	Radiant flux leaving (emitted, reflected and transmitted by) a surface per unit area. This is sometimes also confusingly called "intensity".
Spectral radiosity	Je,ν	watt per square metre per hertz	W⋅m−2⋅Hz−1	M⋅T−2	Radiosity of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. This is sometimes also confusingly called "spectral intensity".
	Je,λ	watt per square metre, per metre	W/m3	M⋅L−1⋅T−3
Radiant exitance	Me	watt per square metre	W/m2	M⋅T−3	Radiant flux emitted by a surface per unit area. This is the emitted component of radiosity. "Radiant emittance" is an old term for this quantity. This is sometimes also confusingly called "intensity".
Spectral exitance	Me,ν	watt per square metre per hertz	W⋅m−2⋅Hz−1	M⋅T−2	Radiant exitance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m−2⋅nm−1. "Spectral emittance" is an old term for this quantity. This is sometimes also confusingly called "spectral intensity".
	Me,λ	watt per square metre, per metre	W/m3	M⋅L−1⋅T−3
Radiant exposure	He	joule per square metre	J/m2	M⋅T−2	Radiant energy received by a surface per unit area, or equivalently irradiance of a surface integrated over time of irradiation. This is sometimes also called "radiant fluence".
Spectral exposure	He,ν	joule per square metre per hertz	J⋅m−2⋅Hz−1	M⋅T−1	Radiant exposure of a surface per unit frequency or wavelength. The latter is commonly measured in J⋅m−2⋅nm−1. This is sometimes also called "spectral fluence".
	He,λ	joule per square metre, per metre	J/m3	M⋅L−1⋅T−2
See also: SI Radiometry Photometry

SI photometry quantities

Quantity		Unit		Dimension	Notes
Name	Symbol	Name	Symbol
Luminous energy	Qv	lumen second	lm⋅s	T⋅J	The lumen second is sometimes called the talbot.
Luminous flux, luminous power	Φv	lumen (= candela steradian)	lm (= cd⋅sr)	J	Luminous energy per unit time
Luminous intensity	Iv	candela (= lumen per steradian)	cd (= lm/sr)	J	Luminous flux per unit solid angle
Luminance	Lv	candela per square metre	cd/m2 (= lm/(sr⋅m2))	L−2⋅J	Luminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit.
Illuminance	Ev	lux (= lumen per square metre)	lx (= lm/m2)	L−2⋅J	Luminous flux incident on a surface
Luminous exitance, luminous emittance	Mv	lumen per square metre	lm/m2	L−2⋅J	Luminous flux emitted from a surface
Luminous exposure	Hv	lux second	lx⋅s	L−2⋅T⋅J	Time-integrated illuminance
Luminous energy density	ωv	lumen second per cubic metre	lm⋅s/m3	L−3⋅T⋅J
Luminous efficacy (of radiation)	K	lumen per watt	lm/W	M−1⋅L−2⋅T3⋅J	Ratio of luminous flux to radiant flux
Luminous efficacy (of a source)	η	lumen per watt	lm/W	M−1⋅L−2⋅T3⋅J	Ratio of luminous flux to power consumption
Luminous efficiency, luminous coefficient	V			1	Luminous efficacy normalized by the maximum possible efficacy
See also: SI Photometry Radiometry

Notwithstanding the above remarks, the term "brightness" is frequently -- as of the year 2008 -- used in scientific meetings. Accordingly I am not sure what Srleffler intends using the term "deprecated..." (seems to me it's a $10 word that somewhat obfuscates the discussion). In order to follow this discussion correctly, once again, I must refer interested readers to the RCA Electro-Optics Handbook available on-line at burle.com (specifically http://www.burle.com/techrefs.htm). I am quite in agreement that "radiance" is the correct term - as stated in the RCA reference I cite in the August 4th entry (above). Here's the problem: Despite "brightness" being unequivocally defined by the RCA reference as the photometric equivalent of radiance, that's not how the term is being used. For at least the last 10 years, researchers presenting their most recent work on high-radiance laser diodes have referred to them as "high-brightness." Their work has been published in reputable journals. Evidently, these researchers and their editors believe that the term "high-brightness" is preferable to "high-radiance" despite the fact that brightness has been used as a photometric quantity. The fact remains that radiance is the only unequivocal term to describe radiated power per etendue, the thermodynamically conserved quantity of interest for delivery of power through any optical system.Jabeles (talk) 02:14, 30 November 2008 (UTC)

Introduction changes

I've undone these for now. I don't dispute that the new text was more precise and included detail on things that the previous intro omitted, but this came at a cost of a serious loss in general readability, especially for readers with a non-professional scientific background. Many of the points added should be re-added, but it'd probably be better to do so on an individual basis rather than by a significant one-off rewrite. Chris Cunningham (not at work) - talk 17:11, 28 July 2008 (UTC)

The previous introduction was incorrect and misleading. But as soon as I made changes to fix the problem, another Editor saw fit to reverse my corrections(!).

As far the newer version I edited being less understandable to the average reader, one could only agree with that evaluation if the knowledge being imparted by the original version were correct. I.e., the word "understandable" perforce must refer to valid knowledge or meaning - not to dumbed-down drivel that would lead the average high-school student with an interest in technology astray!!!

In particular, it is simply not true that a laser must emit a highly directional beam; indeed the most numerous by far lasers in existence (those employed in CD players) emit light over a 35° (full-width at half maximum) or so pattern -- very far indeed from the highly directional lasers suggested by the original introduction. Nor is it true that a laser must emit in a narrow optical spectrum (ultrashort pulsed lasers do not)!!!

I am not going to invest more effort right now into explaining the other changes I had made but they are all made with careful thought and should not be arbitrarily removed by a non-expert.

Jabeles (talk) 17:20, 28 July 2008 (UTC)

I didn't revert your edits, but I'll add my opinion. This is often a difficult issue on Wikipedia. Articles on technical topics need to be both technically correct, and accessible to a general audience (such as the high-school student you mentioned). This is particularly true of the introduction to an article. Achieving this difficult balance typically involves some back-and-forth editing to reach a wording that achieves both goals. So, don't be offended that Thumperward reverted you. As his edit comment indicated, this was just a temporary measure to give us all a chance to discuss the issues. Hopefully we can come up with wording that satisfies you and is readable.

Many of us here are aware that laser beams need not be narrow in either divergence or spectrum. The introduction very carefully does not say that lasers must emit that way. It says that a typical laser emits light in a narrow beam, with a narrow spectrum. This wording implies that in fact not all lasers have these characteristics. One might, of course, debate the meaning of the word "typical" here, given that laser diodes by far dominate the laser market, probably both in number and in dollars. "Archetypical" might be more correct.--Srleffler (talk) 17:35, 28 July 2008 (UTC)

As to the last Editor's comment, yes! It is true that the previously worded introduction used the term "typical." So it was not categorical in excluding non-narrow-divergence-beam lasers. But it misled by suggesting that typical lasers indeed are narrow-beam-divergence lasers. In fact they are not. As already mentioned, the vast majority of lasers in world today do not satisfy the description of having a narrow-divergence beam. In short my earlier comment already refuted the previous introduction even taking into account the use of the term "typical."

As to being both technically correct, and accessible to a general audience, this condition is not satisfied by a description that is not technically correct. I hope this makes the point.

To explain other purposes of my edit: They dealt with applications (many had been omitted, incorrectly classified, or described using terminology that is not standard and would not support e.g., a Google search) and the origins of lasers that do belong in the introduction.

I cannot agree that my edit was not understandable by a high school student -- unless one is referring to one who has little interest in physics or poor academic skills. It is not at all surprising that a reader lacking mathematical skills might have trouble visualizing what is meant by "coherent." Unfortunately such a person would also not be able to understand how a laser functions. One cannot escape that conundrum and calling it a low-divergence-angle light beam with narrow spectrum will not rectify that situation.

To reiterate, and in sum, what possible intent can underlie misinforming readers of Wikipedia in order simply to avoid confusing them? If someone else can devise a better means of informing these readers regarding the basics of what is a laser, where did it come from, where is it found, and what is it used for that does a better job of not confusing them, that would be great! But please do not dumb it down by making it incorrect.

I therefore propose reverting my edit as the standing introduction. Unless there are persuasive reasons otherwise not yet brought forth, I request your support in taking that action.

Jabeles (talk) 21:50, 28 July 2008 (UTC)

Thanks for the heap of condescension, but neither am I disinterested in physics nor do I have "poor academic skills". I am, however, experienced in bringing Wikipedia articles up to the standards expected of Featured and Good Article status. As I said before, I don't have a problem with the content changes insofar as they increase the accuracy of the prose; I do have a problem with plodding, academic prose such as this:

Typically, lasers are thought of as emitting light in a narrow, low-divergence beam, with a narrow wavelength spectrum ("monochromatic" light). However, narrow beam-divergence and narrow spectrum should be considered manifestations of the underlying spatial and temporal coherence which constitute the complete (i.e., necessary and sufficient) defining characteristics of laser light (which in special cases may be neither narrow spectrum nor narrow divergence). Indeed, laser light differs from broad-band and/or incoherent light sources such as lamps (e.g., the incandescent light bulb or light emitting diodes), or the sun.

Count the parentheses in there! While all those asides might be technically proper interruptions which avoid giving the reader incorrect information for a moment, they serve to make the sentence disjointed and difficult to follow coherently.

Invective and personal attacks aren't an appropriate way to gain consensus for the changes you've made. Discussing the content is. That's why I brought the issue to talk. Chris Cunningham (not at work) - talk 22:05, 28 July 2008 (UTC)

The introduction as it now stands contains errors that my version corrected, as well as significant omissions which are highly misleading. As far as I can understand, the Wikipedia system is not working in this instance. Instead of consensus by knowledgeable experts, I am afraid we are witnessing incorrect edits approved by consensus. Oh, and oversensitivity on the part of Editors. I am resigned to it -- and it helps me to understand "What Wikipedia Is Not" is not. Jabeles (talk) 22:11, 28 July 2008 (UTC)

The edits in question are less than five hours old. Srleffler has already incorporated some of your changes into the old version. The system will work perfectly well so long as you are prepared to embrace it rather than attacking it because other editors have failed to instantly submit to your authority. Chris Cunningham (not at work) - talk 22:25, 28 July 2008 (UTC)

Actually, the introduction to an article as important as Laser must be comprehensible to a high school student with little interest in physics and perhaps poor academic skills too. Lasers are an important technology. The article should not immediately dissuade readers who just want some basic information. The intro must be technically correct, but it is equally important that it not be overly technical. Nobody has said that the reversion to the prior version is permanent. We're all quite open to your ideas, and many of them will end up in the intro. Griping about the process is just going to slow that down, however.--Srleffler (talk) 03:42, 29 July 2008 (UTC)

History in intro?

Jabeles has proposed increasing the amount of laser history in the introduction. I'm not sure this is a good idea. I prefer articles on technical and scientific topics to focus first on "what it is" and "what it's used for", before moving on to the history of the subject. The current introduction's brief mention of the first working laser seems like the appropriate amount of history for the intro to me, with the details covered fully in the "history" section. What do others think about this issue?--Srleffler (talk) 03:48, 29 July 2008 (UTC)

Agreed. In presenting a summary, the introduction must omit some detail for the sake of being concise, and less important historical information is a good candidate. Chris Cunningham (not at work) - talk 07:52, 29 July 2008 (UTC)

Agreed, but shouldn't the last sentence of the first paragraph read "time or position". I think it is possible to have monochrome (non-laser) incoherent light that varies only in position phase (or have I misunderstood the technicalities?). Dbfirs 10:08, 29 July 2008 (UTC)

I'm not quite sure I follow you, but if light is coherent either in time or in transverse position, we usually call it "coherent". Incoherent light is light that has neither characteristic. "Monochrome" is also kind of an ambiguous term. Truly monochromatic light has perfect temporal coherence, and vice versa. Single-frequency lasers have very narrow spectra because they have a high degree of temporal coherence. Lasers that are less temporally coherent (shorter coherence time) have broader spectra. Incoherent sources have broader spectra than sources that are temporally coherent. --Srleffler (talk) 22:59, 4 August 2008 (UTC)

More intro changes: coherence does not define a laser

I think the intro did not properly define a laser. Coherence is nice, but letting monochromatic light from a gas discharge lamp pass through a pinhole will alno produce coherent light. Light from an optical parametric amplifier is also coherent and narrow-banded, but an OPA is not a laser, and neither is the frequency-doubling crystal in a typical green laser. A generation mechanism involving stimulated emission is really essential for a laser. Some degree of coherence is only a result of the generation mechanism.

I've also tried to clarify the term coherence a bit more, since our non-academic high school pupil who looks up laser out of curiosity should not be deterred more than necessary by a term as complicated and vague as coherence. With 12 years of research in spectroscopy and lasers behind me, I am still not able to give a proper general definition of coherence without looking it up, so we shouldn't expect the high school pupil to understand it. Han-Kwang (t) 15:30, 5 August 2008 (UTC)

Furthermore, as noted above, some lasers emit light that is neither temporally nor spatially coherent. I've refined the intro further.--Srleffler (talk) 16:20, 5 August 2008 (UTC)

Getting better. I would like to direct your attention to the phrase on directed energy weapons starting to be "used." I do not think that is correct. Despite hoopla directed energy is only in the research and development.

I also agree as discussed above that it should not be coherence that defines a laser but stimulated emission combined with optical feedback in a suitable cavity.

Next nit-pick: A laser is an "optical device." Is a light bulb an "optical device"? No, I would not think that terminology proper. These are electro-optic devices or electrical-optical devices if that terminology would be more appropriate for the high-school student you are targeting.Jabeles (talk) 20:17, 6 August 2008 (UTC)

You're probably right about directed energy weapons not being in use yet, although there are some systems that are clearly in the development (rather than research) stage. A light bulb isn't an optical device because the design of a bulb does not involve any real optics. Perhaps we can come up with a better description of a laser, however. The trouble with "electro-optic" and the like is that not all lasers operate on electricity. The intro formerly used "electronic-optical", which I think was an attempt to dodge the issue by relying on the fact that lasing does involve electrons. I didn't like that term, in that it either dumbs down something that should be expressed in more words, or it misleads. For now, I'll try just deleting "optical": "A laser is a device that emits..." The "optical" was kind of redundant anyway. It doesn't really provide any new or useful context information.--Srleffler (talk) 02:05, 7 August 2008 (UTC)

I agree that coherence is not a necessary property for defining a laser. However, the presence of a cavity and feedback is entirely unnecessary as well. While most lasers do incorporate some form of feedback, the only requirement for defining something as a laser is that Light is Amplified by Spontaneous Emission. Single- and multi-pass laser amplifiers with no cavity/feedback are commonly used to amplify light from other sources. Amplified spontaneous emission lasers have no cavity or feedback either. The seed in an ASE laser is the spontaneous emission inside the inverted medium itself, but the gain is provided by the same stimulated emission mechanism as any other form of laser. Even naturally occurring population inversions in astrophysical bodies have been investigated as sources of lasing action [H. A. Smith, Astrophysical Journal 158, 371 (1969)]. I think it's appropriate to discuss common properties of lasers (e.g. coherence) and typical designs (e.g. two-mirror cavities), but the article should make it clear that the defining feature of a laser is amplification by stimulated emission. --Zeaster (talk) 19:24, 14 September 2008 (UTC)

I would opine that a laser amplifier should be distinguished as separate from, and not included in, the class of laser, and that a laser amplifier (lacking feedback) is not commonly (within the electro-optics community, astrophysics notwithstanding) thought of as a laser, per se. The original demonstrations of lasing action depended upon feedback. The sine qua non of lasing action is a threshold beyond which the growth of one portion of the optical spectrum occurs with increasing energy input (electrical, optical, or chemical) while other portions remain relatively constant. In general this "gain clamping" effect does not obtain in a laser amplifier.Jabeles (talk) 20:13, 22 October 2008 (UTC)

Acronym

Anacronym rather than acronym. 220.255.147.62 (talk) 14:04, 1 October 2008 (UTC)

What? Han-Kwang (t) 11:06, 4 October 2008 (UTC)

i'm not sure about the guy who noted the laser was "Light osscillation by stimulated emmission of radiation, so the correct acronym should be LOSER...". Check it again, please. KEVINOESEF (talk) 10:30, 6 November 2010 (UTC)

Well I added that, and thought it was certainly an appropriate remark in a discussion of terminology considering that LASER is indeed an "anacronym" (if that's a real designation!). An historical reference is included in the preview of this article in New Scientist (I don't have the full article) at: http://www.newscientist.com/article/mg18925442.000-the-word-loser.html Interferometrist (talk) 11:00, 8 November 2010 (UTC)

Minor edits

The "Solid-state lasers" section begins with the sentence:

Solid-state laser materials are commonly made by "doping" a crystalline solid host "doped" with ions that provide the required energy states.

Unless I'm reading it wrong, someone might want to change that. --Subversive.sound (talk) 00:48, 4 October 2008 (UTC)

Fixed, but next time be bold! Han-Kwang (t) 11:06, 4 October 2008 (UTC) -- O wait, it is semiprotected. Han-Kwang (t) 11:08, 4 October 2008 (UTC)

Please add the link to Diode-pumped solid-state laser —Preceding unsigned comment added by 203.155.125.178 (talk) 01:29, 17 June 2009 (UTC)

The link color center in the last paragraph of the section "Fiber-hosted lasers" now leads to an article on the color-processing regions of the brain. It should probably be replaced with f-center. Josh Hernandez —Preceding undated comment added 23:50, 5 October 2010 (UTC).

---

The phrase "Near the beam "waist" (or focal region) it is highly collimated: the wavefronts are planer," uses planer incorrectly, it should be spelled _planar_ (in a plane) vs the wood shop device that planes/smooths a plank of wood (planer).— Preceding unsigned comment added by 76.6.213.117 (talk • contribs) 23:06, 29 November 2010

Fixed. Thanks for the suggestion.--Srleffler (talk) 05:22, 30 November 2010 (UTC)

brief section

Later on (currently I'm rather busy), I might add a short section noting this [1] apparently there has been recent development in the world's largest laser.

After more than a decade of work and $US3.5 billion ($A5.15 billion), US engineers have completed the world's most powerful laser, capable of simulating the energy force of a hydrogen bomb and the sun itself.

The federal Energy Department will announce on Tuesday that it has officially certified the National Ignition Facility at the Lawrence Livermore National Laboratory in California, clearing the way for a series of experiments over the next year that eventually is hoped will mimic the heat and pressure found at the centre of the sun.

I'll find more information as I come across it. -- 李博杰  | —Talk contribs 04:08, 31 March 2009 (UTC)

Why locked?

I've been a user on Wikipedia for some time, but decided to creat an account today to make a few minor modifications. I was intending adding some material about dye lasers, but see the page is locked. Why should this be? I can't believe this is the sort of page that would attract vandels. —Preceding unsigned comment added by MightyBig (talk • contribs) 14:38, 22 June 2009 (UTC)

I agree that it's a shame that the article is protected, but unfortunately it is always heavily targeted by vandals. Take a look at the history for January when the article was unprotected! You might not be able to edit the article for a couple of days until your account is autoconfirmed. Until then, just write {{editsemiprotected}} on this talk page and write your list of changes underneath. Papa November (talk) 15:04, 22 June 2009 (UTC)

Semiconductor Lasers - wavelength coverage

The sentence "Commercial laser diodes emit at wavelengths from 375 nm to 1800 nm" does not seem correct to me since it misses the green-yellow gap. Depending where one sees commercial products this gap starts at 488 (515) nm and ends at about 635 nm.

91.13.31.123 (talk) 07:32, 28 September 2009 (UTC)TR

Commercial laser diodes emit at wavelength from 375 nm to 2900 nm since MANY years now, and since shortly to 3500 nm, I hope there will be a change of this mistake in WIKI. (See: [2] (760nm to 16000nm (this is including quantum cascade lasers, which are NO diode lasers) and [3] by company nanoplus. I recomment to write:"Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm..." — Preceding unsigned comment added by Laser-jok (talk • contribs) 10:36, 9 December 2011 (UTC)

x ray laser

I saw a report in Sciencenews (April 2009) about dramatic progress in x ray lasers.Rich (talk) 22:49, 20 October 2009 (UTC)

Wow someone beat me to the punch. The section of X-ray laser is pretty poor. It should be broken out and separate the hard X-rays for weapons research (Peter H's work) from the soft X-ray work for cellular holographic imaging. 143.232.210.38 (talk) 23:00, 22 October 2009 (UTC)

Protocol on Blinding Laser Weapons

Shouldn't the section on Lasers as Weapons include a sentence on the Protocol on Blinding Laser Weapons? Synook (talk) 09:56, 13 November 2009 (UTC)

First sentence

I think this is badly written;

"within the electromagnetic radiation region of the spectrum"

as it is normally the visible light region of the electromagnetic radiation spectrum. I don't normally get involved in wiki, just thought I would say my peace here.

72.240.84.146 (talk) 22:13, 15 January 2010 (UTC)Todd

 Done[4]. Is that any better? This is of course a Wiki, so it's possible just to press Edit and see if you have a better wording—remember that the first sentence should be high-level and not go into too many details and that LASERs are not always in the visible light range. —Sladen (talk) 23:06, 15 January 2010 (UTC)

Okay, thank you for responding! The sentence is better, but could be a little more precise. It is now:

"Light amplification by stimulated emission of radiation (LASER or laser) is a mechanism for emitting light within the electromagnetic radiation spectrum via the process of stimulated emission."

I think a better version would be

"Light amplification by stimulated emission of radiation (LASER or laser) is a mechanism for emitting electromagnetic radiation, typically light, via the process of stimulated emission."

I had a wordier version, but I think the above is better for simplicity sake. To clarify, my concern was that the original wording made it seem like em radiation was a portion of some larger spectrum of radiation, while in fact the em spectrum only contains em radiation with a "spectrum" of wavelengths/energies.

Thanks for your courtesy, I won't be as hesitant to contribute in the future, and will have to register! —Preceding unsigned comment added by 24.53.175.220 (talk) 23:54, 18 January 2010 (UTC)

 Done[5]. I tweaked it slightly to also get a link to visible light in to the WP:LEAD. Thank you for your input—with a user account it would be much easier to keep track and follow-up with you, and of course, you'd have a record of your contributions in one place! —Sladen (talk) 00:41, 19 January 2010 (UTC)

request to add link

{{editsemiprotected}} please change

• Website on Lasers 50th anniversary by APS, OSA, SPIE

to

• Website on Lasers 50th anniversary by APS, OSA, SPIE
• Bright Idea: The First Lasers (history with interviews)

PS: With the 50th-anniversary celebrations of the laser coming up, I suggest that these links be put up near the top of the links list, as the history will be getting a lot of attention. The sites, in particular the laserfest one, also give excellent introductions to laser stuff in general. Spencerweart (talk) 13:10, 29 April 2010 (UTC)

Spencerweart (talk) 19:38, 10 February 2010 (UTC)spencerweart 2/10/2010

I prefer http://www.aip.org/history/exhibits/laser/sections/raydevices.html over http://www.aip.org/history/exhibits/laser which leads to some kind of flash page, which isn't a desirable external link. Josh Parris 11:32, 11 February 2010 (UTC)

After this was raised, I accessed http://www.aip.org/history/exhibits/laser with Adobe Flash disabled. The page says "skip intro" and the rest of the content can be accessed normally. This shows why it is not a good idea to have a lot of Flash content on the front page of a website, but it is compatible with non-Flash browsers. http://www.aip.org/history/exhibits/laser/sections/raydevices.html is the page that it leads to, so the link may as well give this.--♦IanMacM♦ ^{(talk to me)} 13:17, 11 February 2010 (UTC)

Done per consensus --Shirik (Questions or Comments?) 15:41, 11 February 2010 (UTC)

please can I request that the following link also be added

http://visions.iop.org/

This provides a paper put together by the institute of physics about lasers, it includes information on the latest research developments in the field.

Many thanks — Preceding unsigned comment added by IOPhysics (talk • contribs) 11:19, 21 January 2011 (UTC)

Unfortunately, the link does not take the reader directly to the paper. There is an article about lasers there, but it's buried two clicks down in a list of articles on unrelated topics, and the server seems to be set up not to allow direct linking to the articles. We can't link to that.--Srleffler (talk) 02:04, 22 January 2011 (UTC)

Laser operation

This is almost certainly above and beyond what is required in a wikipedia article. However, the description of population inversions and stimulated emmision causing gain in a laser cavity given in the article is technically incorrect. Is it worth noting this somewhere? Mattyp9999 (talk) 13:45, 24 February 2010 (UTC)

Ultra-high power lasers

Should there be added a classification for those ?! The term was not found in the article as of the time of this writing , yet they seem to be the ones to play big role in the future FUSION research and other fields ... See: [[6]] [[7]] —Preceding unsigned comment added by YordanGeorgiev (talk • contribs) 07:53, 25 March 2010 (UTC)

History/Laser Patent controversy

I suggest ADD TO THE FOLLOWING: "it was not until 1987 that he won the first, significant patent lawsuit victory, when a Federal judge ordered the US Patent Office to issue patents to Gould for the optically pumped and the gas discharge laser devices." THIS TEXT: The question of just how to assign credit for inventing the laser remains unresolved by historians. Spencerweart (talk) 13:58, 29 April 2010 (UTC)

Done →Στc. 07:48, 3 December 2011 (UTC)

Fix Me.

On picture with wavelengths of different types of radiation right side of visible spector is 700 μM, whereas it should be 700 nM. —Preceding unsigned comment added by 91.76.229.18 (talk) 19:00, 14 May 2010 (UTC)

Yes, it looks like Spectre visible light.svg is wrong here. Unfortunately, this would require editing the svg image, which is not as easy as editing text. Any help here?--♦IanMacM♦ ^{(talk to me)} 19:11, 14 May 2010 (UTC)

 Done with a new PNG version.--♦IanMacM♦ ^{(talk to me)} 17:54, 15 May 2010 (UTC)

vediov added

vedio for cosmetic laser uses http://www.youtube.com/watch?v=RTVsZGkyJWM http://www.youtube.com/watch?v=OFoBG3tj1cQ

http://www.youtube.com/watch?v=Nimfcgg9Eis

http://www.youtube.com/watch?v=BUNxzvqDegY —Preceding unsigned comment added by Drkhsh2001 (talk • contribs) 14:37, 14 June 2010 (UTC)

Article needs to cover physics

If you read http://science.howstuffworks.com/laser3.htm they discuss how lasers work. I think at minimum the article needs to cover this level of explanation. Right now the article is restricting itself to talking about lasers, rather than discussing lasers. In other words, it's discussing lasers in terms of their properties, but a good encyclopedia article would be explaining them in terms of how they work, rather than just listing their properties with no explanation.- Wolfkeeper 00:51, 16 June 2010 (UTC)

Wicked Lasers' Spyder III Pro Arctic: Should this be mentioned?

This laser was released early this month and has been marketed as "the world's most powerful portable laser." Does this warrant inclusion in this article, as it stands out in terms of today's available-to-consumer lasers? DeadlyMETAL (talk) 20:04, 21 June 2010 (UTC)

This has picked up a fair amount of media coverage, eg [8], but there is also an element of WP:NOTNEWS. Not sure if this has enough long term notability for the article.--♦IanMacM♦ ^{(talk to me)} 20:08, 21 June 2010 (UTC)

Since WP has no article on simple portable visible lasers, we've been dumping all this in the laser pointer article so far. Wicked lasers produces green pointers with powers of 300 mW, and hand lasers with powers of 1000 mW (1 watt visible), all by very similar means (see the DPSS wiki). What's new is the price, which is now down significantly (the rule for DPSS green lasers last year was you paid about $1 per mW at high powers). It may be time to split off a portable laser wiki for all those portable lasers that aren't in the laser pointer packages. SBHarris 21:26, 21 June 2010 (UTC)

Thanks for the information and feedback, everyone. DeadlyMETAL (talk) 00:54, 22 June 2010 (UTC)

Spelling mistakes

1st paragraph under "Solid-state lasers": "[...] are caller fiber lasers." -> "[...] are called fiber lasers." —Preceding unsigned comment added by 94.218.251.123 (talk) 22:00, 1 September 2010 (UTC)

Nice catch! Fixed. -- Scray (talk) 03:24, 2 September 2010 (UTC)

Misspelling Additions

I have noticed very often people will mispell laser as "lazer", "lasor", and "lazor". I suggest changing "Light Amplification by Stimulated Emission of Radiation (LASER or laser) is [...]" to "Light Amplification by Stimulated Emission of Radiation (LASER or laser, also often mispelled as "lazer", "lasor", and "lazor") is [...]"

I disagree. There are many important things that can be written about lasers. The fact that some people can't spell is not one of them! Papa November (talk) 01:29, 17 October 2010 (UTC)

Proposed merging of "Laser construction" into Laser section "Design"

If there is no objection, I intend to transform the article "Laser construction" into a redirect to the "Laser" article, section "Design." The current "Laser construction" article is not very comprehensive but includes material that should be (and largely is) in the "Laser" article; I will insure that any unique material in it winds up in the "Laser" article, mainly in the section "Design."

Furthermore I intend to rename the "Design" section as "Principle of operation" and will also reorganize some of the material in the following section ("Laser physics") into that section (and clean up the latter section so it really has to do with the physics). Also, the subsections under Laser physics are not really physics and "Modes of operation" should become a main section.

Please comment if you dis/agree with these changes before I begin working on this (in the near future). Interferometrist (talk) 18:55, 24 October 2010 (UTC)

I object. That material was spun off to keep this article from getting too long.--Srleffler (talk) 01:46, 9 November 2010 (UTC)

See Wikipedia:Manual of Style (summary style). What we need is for this article to contain a nice, concise summary of how lasers work (which could encompass information on laser physics and design, together) and more technical articles on Laser construction and laser physics to cover the subjects in more depth.--Srleffler (talk) 03:16, 9 November 2010 (UTC)

don't send roung ok. —Preceding unsigned comment added by 218.248.5.222 (talk) 16:07, 5 March 2011 (UTC)

Princinple of lasing not dependent on quantum physics??

I believe the following paragraph within the article is in error:

"Although the laser phenomenon was discovered with the help of quantum physics, it is not essentially more quantum mechanical than other light sources. The operation of a free electron laser can be explained without reference to quantum mechanics."

The defining element of a laser is the use of stimulated emission. Every other light source depends primarily on spontaneous emission. Stimulated emission was discovered by Einstein (defining the A and B coefficients) in order for the transitions of atoms absorbing and emiting photons to be consistent with the Planck radiation function. It doesn't have a classical explanation, period.

I will remove that paragraph unless someone can argue that it is valid. Interferometrist (talk) 11:33, 25 October 2010 (UTC)

Playing devil's advocate, the writer is technically correct. A free electron laser (FEL) with wiggler magnets doesn't have electrons in quantum orbitals in atoms. It produces a laser beam in exactly the same way a radio antenna produces an automatically coherent radio beam. It's a field effect on electrons, which naturally bunch up and radiate into the field in synch with the field. Presumably they do much the same in atoms, as well (quantum effects produce population inversions and bunches of electrons in high energy states). Einstein's spontaneous emission coefficients had to be deduced from first principles with QFT, but AFAIR the transition probabilities for stimulated emission are not a quantum property. SBHarris 11:41, 25 October 2010 (UTC)

Thanks for your reply. Part of my hesitance in this regard is that I am not familiar with free-electron lasers, and don't want to research them JUST in order to judge this paragraph. However I would conjecture that if the free electron laser does NOT involve optical amplification through stimulated emission (not necessarily involving atomic orbitals), then calling it a laser is a misnomer.

On the other hand, I believe you are wrong in saying that stimulated emission has any classical explanation at all. If you're right then I absolutely withdraw my point and apologize for taking your time. But I feel rather sure of this. Classical explanations of light did not identify quanta (photons) and the absorbtion of quanta by atoms which raises them into a higher energy level. (Einstein won the noble prize for explaining the photo-electric effect, dependent on the concentration of energy in photons, unexplainable by classical physics). Stimulated emission (and spontaneous emission too) involves the opposite process, and is thus a quantum phenomenon. If you disagree, then one of us can go look this up elsewhere. What do you think? Interferometrist (talk) 14:24, 25 October 2010 (UTC)

Obviously I need to do some reading. However, WP has an article on free electron lasers. They rely in bunching of electrons in a relativistic beam, which then radiate coherently, tapping the potentials from their velocity and the magnetic potentials of wiggler magnets. They amplify EM coherrently, so they are lasers/masers by any definition. They need an input "seed" signal to bunch the electrons initially, after which the amplification is self-reinforcing, from which a tap can be run. I can't think of any quantum effects necessary to explain this. FELs in the microwave region work a lot like a traveling-wave tube amplifier with a self-feedback (to make it an oscillator), and in fact the latter can be made with cavities which make them look a lot like high power klystron tubes, which are also sources of high power microwaves from electron bunches. All these things put out coherent radiation, and that's no accident. Quantum effects are only necessary when the scale becomes so small that there is no natural clumping of radiators, but instead they need to independently radiate into the field. Also, when the frequency of the field becomes very high so that again there seems to no "room" for radiating changes to act in physical concert. This is one of those many cases where the the classical fades into the quantum world, as per the correspondance principle. For example, an electon in a very large hydrogen orbital radiates at its orbital frequency, very classically. Only in the very smallest orbitals does it start to behave non-classically and radiate at the mathematical mean of starting and ending orbital "frequencies." A fact that puzzled Bohr a lot. SBHarris 02:06, 26 October 2010 (UTC)

I looked more into this, more out of curiousity than the issue of this one entry in Wikipedia. And I appreciate your understanding of physics and discussion of cases where the quantum or classical picture is of greatest value in understanding a phenomenon (and the tricky regions where one has to combine both understandings at the same time, where intuition generally fails). On the other hand, you must agree that any quantum mechanical explanation for a physical principle must apply at ALL scales (distance, frequency, energy...) even if some results in some regimes can be obtained with high precision using classical physics. For instance, the energy of radio waves IS quantized in photons, but those tiny tiny energy packets need not be considered in any practical problem. Even the 50Hz power line is accompanied by an EM wave whose energy is quantized in photons having a ridiculously small energy.

With respect to the Wikipedia article, the questions are 1) Whether the FEL relies on stimulated emission; and 2) Whether stimulated emission is a quantum phenomenon. I wasn't sure about (1), but according to references I have located both are true. Thus the paragraph is incorrect and should be removed. (It would be alright to point out that stimulated emission need not only result from transitions in atomic electron states or molecular excitational states, like "normal" lasers).

I agree that synchrotron radiation can be explained classically, but the use of the synchrotron radiation mechanism in a FEL appears (in all respects) to be stimulated emission. This webpage: http://www.sjsu.edu/faculty/watkins/stimem.htm also mentions that in the 5th paragraph, though I can find no trace of Riyoupoulos who is cited. And for (2), I am still quite sure what I said is right: stimulated emission can only be understood as a quantum phenomenon. It also states that in the very first line ("definition") of http://www.rp-photonics.com/stimulated_emission.html and anyway I could just repeat my argument above (without quantum mechanics, atoms don't have energy levels that COULD be population-inverted, though admittedly that doesn't address free electrons). I can't believe we're just arguing about semantics! But even if we are, then is the sentence in Wikipedia really useful to anyone? Interferometrist (talk) 17:33, 26 October 2010 (UTC)

Well after ALL that discussion, and looking further into it, I finally DO believe that the FEL can be explained classically! Sorry for wasting your time with this. But the article indeed was misleading since this is an exception among lasers. I changed the paragraph to improve it in that respect (please see if you accept what I wrote). I still do NOT know if it should be called "stimulated emission" or not, but that is just a matter of definition which I won't worry about. You have convinced me (in conjunction with the literature) regarding the FEL. Cheers, Interferometrist (talk) 17:13, 27 October 2010 (UTC)

"The plain and simple truth is rarely plain and never simple." (Oscar Wilde). FELs can be described either completely classically or as a two state system (Rabi system) with a population inversion.

There's been much arguing about it Apparently the population inversion can be a momentum-inversion of the electron bunches. Personally, however, I don't even see why a two-state system with a population inversion (necesary for a laser, supposedly) MUST be a quantum system. Usually it is, but here's a perfect example of where it isn't (or doesn't have to be-- more on that in a minute). Most articles on stimulated emission, SE (including WP's article) describe SE it as "quantum process" but I THINK it's no more a quantum process than anything else in life (some things can ONLY be described as quantum processes, but macro-classical things can ALSO be described as macro-resonant processes, by the correspondance principle). Remember what we mean by "quantum" is that under the circumstances, the wave-nature of matter forces us to use wave-equations for matter! So, bound matter-particles like electrons have resonances and energy levels and so on, due to their wave natures. OTOH, when we have to use wave equations for EM waves or sound waves or whatever (non matter-waves), we call that "classical." Thus, whistles and cavity magnetrons and traveling wave amplifiers all have tuned cavities, but since the mode-locked waves are EM waves, we don't invoke QM.

But now, think of how any (classical) electronic EM amplifier works-- say a vacuum tube or transistor. You have a population inversion (a bunch of electrons that would like to go someplace and are prevented) and thus a two-state system. The electrons can either be on base or emitter, or anode or cathode. It has a lot of energy built up in a potential, just waiting for a signal to come along and release it, and thus, "gain." Naturally, the amplified signal is coherent and in phase with the signal amplified. Why can't this be viewed as a non-QM type of stimulated emission? The only thing that makes SE in atomic lasers "QM" is that the potential energy is stored in some type of QM system (like an excited atom) before release. But in that case it's not the SE process that is QM (I mean describe-able only by QM), but merely the storage process of the potential energy being tapped to make the amplified signal [To describe which, you need QM for, because the energy is stored in a single excited electron-wave bound in an atom, which spontaneously decays only by QM laws-- for all that you DO need QM]. Do you see what I'm driving at? People have been scratching their heads at the non-QM nature of FELs at least since 1979, I find on Googling this, so we shouldn't be too embarassed here. But at the same time, it may be time to think about the real nature of "stimulated emission," from two-state non-QM systems, and get it right. We might be near the borders of physics here, but somebody out there must see this clearly by now. I very much doubt that I personally have stumbled on some new insight in physics, as a non-physicist whose math is so-so. SBHarris 21:05, 6 November 2010 (UTC)

Well, this is an interesting discussion and I will briefly reply to your latest conjectures. However -- just to get this straight -- I trust we are no longer arguing about the wording of the Wikipedia article (are we?) which I tried to make as accurate as possible without going into excessive depth for a general article about lasers (in fact I don't think the issue of whether a laser relies on QM is even needed in this article, but I wanted to replace the paragraph that someone else had already introduced at that point which I really DID think was misleading).....

FELs can be described either completely classically or .... There's been much arguing about it

Alright, but for the sake of the discussion let us ignore the FEL for the time being (which I admit I haven't investigated and have no business lecturing about) and just deal with every other instance of stimulated emission or amplification of EM signals. I still believe that stimulated emission is a quantum phenomenon and has no classical counterpart (remember: ignore the FEL!). It obeys the same law as atomic absorption (same Einstein B coefficient) but was never even predicted until Einstein showed that it was neccessary in order for the Planck function to describe black body radiation in a closed system in thermal equilibrium (and derived the relation between B and A). There hadn't been, and still isn't (to the best of my knowledge) a classical explanation even valid at very low frequencies (where h nu -> 0).

Remember what we mean by "quantum" is that under the circumstances, the wave-nature of matter forces us to use wave-equations for matter!

Well I see quantum mechanics in various contexts as dealing with the following non-classical phenomena: 1) That electrons and other particles of matter consists of waves which can be solved to determine the likelihood of that particle appearing in a state (position, momentum, etc.); 2) That light waves transfer their energy and momentum in quanta, photons, which act like a particle (are discrete units rather than a continuous function); and 3) That because of the wave nature of matter, electrons (for instance) subject to boundary conditions can only take on discrete energy levels, with the transitions between them defining "quantum" states in a different sense again. Stimulated emission in the normal sense has to do with (2) and (3), but even if you take away (3) I still see (2) as qualifying it as a "quantum phenomenon" unless there is a classical explanation of the energy transfered from the electron to the photon (yes, I realize there is for SPONTANEOUS emission: the classical decaying orbit of the electron which radiates due to its centripetal acceleration). But you have tried to do that:

But now, think of how any (classical) electronic EM amplifier works-- say a vacuum tube or transistor. You have a population inversion (a bunch of electrons that would like to go someplace and are prevented) and thus a two-state system.

That's a seductive argument but I don't know that it's accurate to call the electrons on the negative terminal of a battery in a different "state" than when they arive at the + terminal. (Anyway "state" is a QM term!) I wouldn't know how to formalize that if it were case.

It has a lot of energy built up in a potential, just waiting for a signal to come along and release it

Well not exactly. Most amplifiers are "class A" devices which use just as much power (same current drawn from the power supply) whether there is a signal there or not (contrary to stimulated emission in a laser). I will admit that all electric and magnetic fields (except perhaps at DC) are mediated by "photons," even at low frequencies where the photons are of almost negligible energy, and there is a superposition of photons that can account for any travelling wave, standing wave, or even the oscillation in an LC circuit. But quantifying that correspondence would be a nightmare, and pointless since (practically) the only time you need to talk about "photons" is when there is a transfer of energy (when a photon is created or destroyed) and otherwise you NEED to use Maxwells equations (thus classical physics) to describe electromagnetism.

The other aspect of electronic amplifiers which is totally unlike stimulated emission is this: in a laser the transition of an electron from one state to another corresponds to the creation of ONE photon (as is also true for spontaneous emission and for absorption in the reverse direction). But in an RF amplifier, the transition of one electron from the - to + battery terminal (as you have called a "2 state system") can produce millions or billions of radio photons (just figuring out from conservation of energy). That can't be explained in terms of the 2 states you posited. I just don't see the parallels. I don't deny that there will be a correspondence between quantum and classical theory -- in fact there must be. But I can't see how an electronic amplifier can be described in terms of electrons going from a higher populated to a lower populated state OR an anolog to the simulataneous process of atomic absorption which RAISES the electron's energy from a higher populated lower state to a higher state (as happens in a laser or elsewhere when the population inversion reverses, or all the time, depending on how you look at it: see the middle of section "Mathematical Model" that I wrote: http://en.wikipedia.org/wiki/Stimulated_emission#Mathematical_Model).

So I still stand by saying that stimulated emission (or at least what goes on in a laser BESIDES the FEL) is a quantum phenomenon. And I left the explanation of the FEL somewhat ambiguous in the article because I don't know exactly what to think in that particular case (or whether the term "stimulated emission" correctly applies). But thanks for your interesting thoughts on the matter! Interferometrist (talk) 00:27, 10 November 2010 (UTC)

Recent changes to introduction.

Srleffler wrote:

The first sentence from Nov. 6 2009 was better. I'm tempted to revert the whole introduction. The version from a year ago was carefully worded and avoided false claims present in this version.

I'm not sure about all of the changes in the last year, but I'm pretty sure that I didn't add any "false claims" in the lede (nor can I find any, or I would have removed them myself!). Don't be "tempted" to revert: if you think it is right then DO it, but be prepared to explain yourself in detail. Or use this talk page to propose any change back, or in particular to point out ANY misstatement (particularly a "false claim") in the lede. Of course wording can always be improved (which you did in several other places) but that isn't done by reverting unless you can show where the new wording is inferior. I'm happy to work with you on this. Interferometrist (talk) 14:07, 9 November 2010 (UTC)

My opinion softened some once I started looking at how to rephrase it. I was annoyed not so much about the current text as about the process by which we got here. A lot of effort and discussion (see above) went into the previous intro. When I came to this article, I was struck by how bad the first sentence was. Looking at the history to find out how it got that way, I found that the article went through repeated cycles of text being mangled by inexperienced editors, and then subsequent editors starting with the mangled text and improving on it rather than checking to see if there was a better version in the history to revert to. I've seen this cycle before; it happens when an article isn't being watched by any experienced editors.

"False claim" was probably too strong. The current intro is overly focused on lasers producing coherent light and narrow beams, though. Most lasers do not produce narrow beams. The ability to produce a diffraction-limited beam is not a defining characteristic of a laser. (It is, however, a notable characteristic of the lasers that do have this property.) There is a discussion above about whether coherence is an essential characteristic of lasers. I'll have to re-read it, though.--Srleffler (talk) 01:07, 10 November 2010 (UTC)

Alright, I realize that I got into this rather late and should have looked a little into the history of the article before (as you say) repeating a cycle. To answer your specific concern, though, I would say that the defining aspect of a laser is that it relies on stimulated emission and I had meant to write those exact words but now see that it doesn't say that.

However because stimulated (rather than spontaneous) emission generates the light, it is POSSIBLE for a laser to have a high degree of temporal coherence (defined by the optical resonator) and spatial coherence (created by restricting the spatial extent of the beam in conjunction with the resonator geometry). The vast majority of lasers are single-spatial-mode and that means that their beams will be (approximately) diffraction limited and I'd say that the majority of laser applications are dependent more than anything else on that spatial coherence, particularly where a large photometric flux is desired (many applications) or a very small spot (many other applications) or a small divergence in a beam, just to name a few consequences of spatial coherence. Temporal coherence (at various degrees obtainable from different lasers) is important in many (but fewer) applications with some overlap.

So in summary I don't think the coherence of typical lasers DEFINES what is a laser (for instance, they call this superluminscent noncoherent device a "nitrogen laser") but spatial and temporal coherence are the aspects of laser light that are key to most applications. That's my take. But yes, I should really look up the older discussion and edits, if this is going over familiar territory! Oh, I also wanted to respond regarding the merger, but I'll write that another time -- it's late now. Interferometrist (talk) 01:47, 10 November 2010 (UTC)

I agree with you that one of the defining aspects of a laser is amplification by stimulated emission. What you say above about coherence is exactly right: not all lasers are coherent (either temporally or spatially) but lasers are unique in that it is possible for them to have high temporal or spatial coherence. I'm not so sure about your statement "The vast majority of lasers are single-spatial-mode..." The vast majority of lasers are diode lasers, with high divergence and astigmatism. Diode lasers can be single transverse mode, but I'm not sure whether the majority are. Similarly, the statement in the current lede, "Spatial coherence typically is expressed through the output being a narrow beam..." is wrong: singlemode diode lasers are spatially coherent, but do not by themselves produce a narrow beam. Their coherence is expressed in the fact that you can reform them into a narrow beam with optics. The intro used to say this, but it got mangled and then the mangled text got edited into oblivion.--Srleffler (talk) 03:34, 10 November 2010 (UTC)

Well, we're largely in agreement but let's sort out the small issues here. I do indeed believe that the vast majority of lasers (whether counting the number produced or the number of catalog items) are single-spatial mode, though the beams may not be perfect gaussian TEM00 shapes (thus the M^2 parameter which is cited is greater than 1. I see there is a WP page defining that parameter: http://en.wikipedia.org/wiki/Beam_parameter_product). And this is because of the reasons I cited for using a laser in the first place related to its spatial coherence. High intensity at the focus: nonlinear optics, welding, laser ablation, CD writers, among others. Or wanting a precise focus: CD players, optical tweezers, lithography, etc. Also, regardless of the specific focussing used: interferometry, coupling into single mode fiber, best illumination of a (standard) hologram. Some of these applications are less dependent on temporal coherence (or not at all) but use a laser because it's the only way to get so much light into such a tiny focussed spot or into a single mode in general. I really don't think you can argue this being the most important aspect of laser light with respect to APPLICATIONS. Temporal coherence is second in importance. But beyond that, what is a laser good for anyway??

Now you stated/asked:

The vast majority of lasers are diode lasers, with high divergence and astigmatism. Diode lasers can be single transverse mode, but I'm not sure whether the majority are.

Well yes, I believe most are. A laser pointer must be single mode or reasonably close to it, or its beam would diverge more than one would desire. And above all, the laser diodes in CD players is absolutely single mode since it is the small focused spot size that defines the information capacity of the media (and the reason they had to go to red and now violet lasers for DVD and Blueray, since they were already at the diffraction limit). And as for He-Ne lasers (the laser I use the most) at least 99% are designed to be single mode though it is POSSIBLE to buy one (made for higher power) which is multimode but that is undesired for most applications. Anyway making a single spatial mode laser isn't extremely difficult, it just involves matching the resonator characteristics with the size of an internal aperture (the internal capillary tube in a He-Ne laser, or the width of the chip itself in a diode laser). I'm pretty sure that single spatial mode lasers dominate the market and the applications.

Similarly, the statement in the current lede, "Spatial coherence typically is expressed through the output being a narrow beam..." is wrong: singlemode diode lasers are spatially coherent, but do not by themselves produce a narrow beam. Their coherence is expressed in the fact that you can reform them into a narrow beam with optics.

Well, I totally agree with the last part you wrote: that a single mode beam can be focused into a small spot or into a pencil beam. Yes you are right that the "raw" output from a laser diode usually has a large divergence due to the small width of the chip, but it is indeed "narrow" (just not "collimated") at that point. It is so narrow (in cross sectional width) that it is MUCH brighter than the sun, for instance. And even more so when it is focused to a tiny spot in a CD player (although you can argue that's not the laser itself doing it). And the "narrow beam" (in both aspects) coming out of a laser pointer is an indication of the single mode nature so when I wrote "Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam."" of course I'm talking about the beam AS it comes out of the optical system, if you will, but that illustrates the spatial coherence of the laser and I think adding wording about the necessity of a couple additional lenses detracts from the point. Also, in practice a "laser" is a box with a beam coming out of it, not just a resonator and gain medium. Even when you talk about the output of a He-Ne laser you are including refraction at the second surface of the front mirror which isn't technically part of the laser cavity if you want to be really picky. So we probably agree on the technical description, but the only issue is expressing this in English at the level of the article that would be expected for Wikipedia. Interferometrist (talk) 15:20, 10 November 2010 (UTC)

Previous addition:

You know what, looking at the lede again, I can see a few things in perspective. I rewrote it a couple weeks back but the second paragraph (about temporal coherence) I hadn't changed much. But it could use a little work. And indeed I DID say, as I had thought, that the defining characteristic of the laser was stimulated emission:

However all such devices are classified as "lasers" based on their method of producing that light

But I can see now that it isn't a very strong statement. I should have repeated "stimulated emission" so that it was very clear what "their method" meant. I will change that (unless you do first!). And in line with what I wrote just before, I think that there should be a little less concentration on temporal coherence and more on spatial coherence (mentioning high intensities and focussing to a diffraction limited spot). Interferometrist (talk) 01:58, 10 November 2010 (UTC)

RGV Laser, please add/discuss

Could someone who is more knowledgeable about it please add information about RGV Lasers? (Red-Green-Violet) LP-mn (talk) 02:42, 22 December 2010 (UTC)

Too many facts, not enough explanation

I was trying to learn about the principles of lasers for a lab but instead of reading how lasers work I keep reading how they do not work and how that or the other is misnomered or often mis taught. It would be a good idea to go over this article and change its focus to how lasers DO work. 79.179.192.22 (talk) 14:52, 5 March 2011 (UTC)

"Gillette" Measurement

In the safety section, a "Gillete" is mentioned, which links to a List of unusual units of measurement. This page does not actually contain any information regarding such measurement. That said, should I remove the link or add the information regarding a "Gillette" to the appropriate page? I'm leaning toward removing the link. BTech United (talk) 05:06, 16 May 2011 (UTC)

You can't add information about it to the list of unusual units unless you can cite a reliable source, because the entry for Gillettes was removed in March for lack of proper sourcing. If you can find a source, restore the information to the linked page. If not, just remove the link.--Srleffler (talk) 16:37, 16 May 2011 (UTC)

Cheers, I'll remove the link. BTech United (talk) 22:42, 16 May 2011 (UTC)

Edit request from Dirkcline, 23 May 2011

Hello --

I would like to have the following paragraphs added to the Laser wiki:

Argon-Ion Commercialization

Following the discovery of the helium-neon laser at Bell Labs, research conducted by Hughes Research Laboratories (William Bridges et. al) stumbled onto the argon-ion laser while adding argon as a buffer gas to a pulsed helium-mercury laser in 1964. Shortly after this finding, Bridges helped develop the continuous wave argon laser. The USAF contracted Hughes to further develop the argon-ion laser for their night reconnaissance system. This research developed methods, materials and optical configurations that helped lead to the successful commercialization of the argon-ion laser.

The discovery of the argon laser wavelengths opened doors to a wide range of commercial applications such as florescence (i.e., flow cytometry, DNA sequencing and confocal microscopy), image-setting, photo masking, inspection, image recording, research and medical procedures. Spectra Physics started marketing glass-beryllia structured argon lasers in the late 1960’s. American Laser introduced the metal-beryllia structured argon lasers in the early 1970’s. These and other continuous wave gas lasers laid the foundation for today’s laser industry.

Until recently, the argon laser was the main method for producing blue and green laser light. Longevity and power efficiency have made the solid state and semiconductor lasers more desirable over the older gas lasers. However, since argon lasers produce multiple wavelengths with robust designs, they are still a preferred laser in certain applications.

By G. Nelson, National Laser Company <www.national-laser.com>

Please contact me with questions about this submission.

Best regards,

Dirkcline (talk) 18:07, 23 May 2011 (UTC) Dirk Cline dirkcline@gmail.com

Question: This looks like a good contribution to the discussion of laser history, but the byline at the end concerns me. Are you "G. Nelson", or do you have the right to contribute this to the encyclopedia (and release the text for use under the licenses specified on the edit page)? Wikipedia takes copyrights very seriously, so unless you are the author or copyright owner of this text, or have the permission of the copyright owner, we cannot accept this contribution.--Srleffler (talk) 00:28, 24 May 2011 (UTC)

Selfmade Megawatt Pulse Laser weapons

Are there really Megawatt Pulse Laser weapons or are they just 1000 miliwatt (1 watt) lasers found in eveything objects? Space Commander Plasma (talk) 04:30, 24 July 2011 (UTC)

You're probably thinking of the Boeing YAL-1. It exists. It can shoot down missiles. It's not really viable, though, and the military isn't planning to deploy it.--Srleffler (talk) 16:56, 24 July 2011 (UTC)

Actually I was referring to the ones on youtube, one user by the name of AnselmoFanZero claims he has created a Megawatt Pulse Laser Weapon. Space Commander Plasma (talk) 06:43, 7 August 2011 (UTC)

I see. Megawatt pulse, yes. Weapon, no. It doesn't take much energy to get a megawatt of peak power in a single short pulse. If it's a 10 ns pulse, you only need about 10 mJ. That's enough to pop a balloon or make a nice burn mark on flammable material. If the beam quality is good, one might succeed in making a small hole in a piece of very thin metal by hitting the same spot over and over with many shots.--Srleffler (talk) 23:07, 7 August 2011 (UTC)

So he lied about it being a weapon and calls me stupid, he also said that it would not burn a hole in any kind of metal no matter how many times he would fire at it, thanks. Space Commander Plasma (talk) 10:16, 20 August 2011 (UTC)

Edit Request - No such thing as electrically powered CO2 Laser

The claim that Northrup Grumman announced a 100kW electrically powered CO2 laser is false. The referenced article from the LA times says it is an electrically powered solid state laser, not CO2. Seanross (talk) 02:16, 4 August 2011 (UTC)

You are right. The article does say solid-state; it's probably just a huge rack of diodes pumping a big YAG cylinder. There do exist electrical CO2 lasers (they all are) but not at 100 kW. I've fixed the article. SBHarris 03:00, 4 August 2011 (UTC)

Beautiful pic, but why is it there?

What is the relevance to this article of the image "Spectre_visible_light.svg" in the Terminology section? Old_Wombat (talk) 12:02, 14 December 2011 (UTC)

There's little relevant on Commons, so editors looking for images to add tend to grab things that are pretty instead. There are certain images on Commons, just like this, that are "vaguely relevant" to a whole range of articles, so they're used far too widely. I'd support removing it - as you say, it adds little. Andy Dingley (talk) 13:57, 14 December 2011 (UTC)

Removed. You are right; it is not really relevant to that section, even though the section does talk about different bands in the EM spectrum.--Srleffler (talk) 01:53, 15 December 2011 (UTC)

Natural Laser

It was first observed by scientists on board NASA's Kuiper Airborne Observatory in 1995 from the star MWC 349.[9] - 142.150.48.218 (talk) 00:40, 20 December 2011 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Laser/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

the article is informative.. thanks to theproviders. topians@hotmail.com I nominate this article for good article status. —Preceding unsigned comment added by Funky jo (talk • contribs) 11:43, 11 October 2008 (UTC)

Last edited at 05:28, 22 January 2009 (UTC). Substituted at 20:41, 3 May 2016 (UTC)