# Talk:Laser

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## Indigo laser pointer?

File:Laser pointers.jpg This image is near the top. Nice image, probably the most familiar sort of laser for most readers. However what colour is that "indigo" laser? It seems (across several articles and the Commons image) to see-saw between blue and violet/blue-violet, and 445nm and 405nm. Also watch out for caching effects, as there seem to be any number of different versions circulating under the same filename.

IMHO, it's a 405nm violet. But then my eyeballs aren't gamma-corrected, so what do I know?

However we should be describing this as either blue if it's 445 or violet / blue-violet if it's 405nm. 445nm is a blue, not a blue-violet (as currently labelled). Andy Dingley (talk) 20:00, 22 March 2012 (UTC)

Yep. "Indigo" is more violet than blue, and there are really only two lasers types in that range. The 405nm's really are purple/violet, and not at all blue. If you shine them on fluorescent white paper, you see actual blue, but that's blue fluorescense. Comparing the two reminds you how different violet and blue are, visually. The 445 lasers put out a beam that is as dead-on blue, and much the same color as the blue fluorescence from white paper from a violet laser. Nobody would call them indigo. So I think, like you, that the "indigo" is just a poor terminology for the standard 405. The one that is used (ironically enough) in Blu-ray Disc technology. I guess somebody didn't like "violet ray." SBHarris 20:31, 22 March 2012 (UTC)
If you shine them on wood (many hardwood species, at least), you also get a surprisingly white spot. I think there must be some reddish-orange fluorescence going on that's just right to balance out the reflected beam colour. Recently I built myself a 'nocturnal indoor sundial' using one, with a fixed laser, swivelling mirror and an oval ring of 48 uranium glass marbles. When you hit a marble, the lime-green fluorescence is dazzling. Andy Dingley (talk) 20:47, 22 March 2012 (UTC)
I've seen that white on wood-- are you sure it's not a wax effect? I have never seen U glass (though I knew making it was the most common use for U before, er, 1945). Cool. Another fun thing to do with a violet laser is point it at a leaf at night. The chlorophyll gives you a nice red fluorescent secondary spot that is in a slightly different place and looks spooky. And my cats seem to like to chase the violet spot even more than green or red. SBHarris 21:03, 22 March 2012 (UTC)
I make furniture, so I shone a violet laser pointer across my wood rack. Most darker hardwoods do it. You need a smooth surface to see it, rather than rough sawn, but it's not just the finish doing it. Andy Dingley (talk) 22:26, 22 March 2012 (UTC)
I've gone back and tested my 405 nm pointer on a number of dark woods, and it is as you say-- the fluorescence is indeed nearly white. It must represent a large spectral range of fluorescent processes in wood chemicals, and your eye puts all these wavelengths together as "white." It's a testiment and direct demonstration of how chemically complex a wood surface must be. Thanks for helping me "see" what I'd been looking at for a long time. Interesting! SBHarris 23:21, 10 April 2012 (UTC)
I believe the current image in the article is the 445 nm laser. The original version of File:Lasers.jpg showed two lasers, one of which was 405 nm and clearly violet. Another user (possibly the creator of the original photo, but not the person who uploaded it) replaced the photograph with a new one in 2010, but did not change the image description or licensing info, nor fix the caption in this article. The other day, that same user uploaded yet another photograph to the same filename.
According to Violet (color), 445 nm is violet (and there is a reliable source for this). I wrote "blue-violet" because this wavelength is right in the borderline between the two colors. I would not recommend relying on how the image appears to you on your RGB screen. Color rendering is not that accurate on a typical monitor. I don't believe in indigo. It was included in the visible spectrum for rather poor reasons.--Srleffler (talk) 00:27, 23 March 2012 (UTC)
You might have a RS that "violet" includes 445nm, however laser diode manufacturers (and more RS if you want) generally term this as "blue" and 405nm as "violet". After all, these are the two wavelengths available and they have to call them something to distinguish them. My point is that our current label of "445 blue-violet" is contradictory to equally good and relevant sources from laser makers, no maker how the makers of paints and pigments might describe violet.
I would agree that it's impossible to judge the actual wavelength from an image that has passed through the interweb (although the maker is cited, so you might yet find the original source image and the original caption). My concern is over consistency between wavelength, description here, and description by the laser makers.
As to indigo, then that was a deliberate choice. I'm familiar with Newton's foibles. Andy Dingley (talk) 00:44, 23 March 2012 (UTC)

## simplified overview?

This is way too complicated for the average reader, is there somebody who can describe the operation in a readable summary, maybe one or two paragraphs? I can take a stab at it, but I'm not a laser expert and would probably get yelled at for oversimplifying things. Nerfer (talk) 21:08, 10 April 2012 (UTC)

I'll take a stab at it. I don't mind people yelling at me when I simplify. Or at least, not much. SBHarris 23:25, 10 April 2012 (UTC)
It appears not much has been done here, so I added a notice on the article. Keep in mind schoolkids are coming here for help with their homework, an 8th grader shouldn't need college physics to read the opening paragraphs (I can slog thru it, but I have a B.S. in Computer Engineering). It might be worthwhile to split some things off into separate pages also, as this article is tremendously long. Thanks. Nerfer (talk) 05:58, 10 January 2013 (UTC)
Just so you know, there is a whole separate version of Wikipedia called "Simple English Wikipedia" that provides dumbed-down explanations for the less educated. 8th graders are not the target audience of the normal Wikipedia. They should be going to the simplified version. Over-simplifying an inherently complex topic simply makes the explanation wrong and misleading. 129.63.129.196 (talk) 18:39, 31 January 2013 (UTC)
That interpretation of simple WP is somewhat contested - it's also seen (and this could be seen as the predominant view) as content that's just as sophisticated as any other WP, except that it's expressed so that those with lesser English language skills, or who are learning English, can still read it. Andy Dingley (talk) 22:58, 31 January 2013 (UTC)
While that might be a good goal to strive for, it's probably not realistic. I don't think it is possible to convey technical content in full detail while remaining within the constraints of the Simple English Wikipedia. Big words exist for a reason: they allow a lot of information to be packed into a much smaller volume of writing. Presenting technical material without technical terms makes for text that is very long, and hard to read because too many concepts have to be explained before one can get to the actual content to be conveyed.--Srleffler (talk) 02:31, 1 February 2013 (UTC)
I'm not saying the whole article should be "dumbed down". I'm saying the lead paragraphs could give an overview without diving into highly technical terminology. It can be done, and there are right ways and wrong ways to do it. Something like lasers appeal to a wide group of people, not just people with a PhD in physics. I never heard of the Simple English Wikipedia, I'll check it out, but I wonder how many people know about it and would go there as a resource (especially if they're going to use it in their report). But thanks for the feedback. Nerfer (talk) 05:43, 5 February 2013 (UTC)
That's still pretty funny - "dumbed-down, less-educated, Over-simplifying an inherently complex topic simply makes the explanation wrong and misleading". I'm guessing this person has never explained why the sky is blue to a 1st-grader. It's not easy, but if you're prepared and can think like they do, it takes no more time than doing it with complex words that only a select few understand. Okay, it looks like my services are best used at the simplified English site. Unfortunately most people automatically come here and probably (like me) don't even know that site exists. Nerfer (talk) 04:07, 8 February 2013 (UTC)
http://xkcd.com/1133/ http://splasho.com/upgoer5/ Andy Dingley (talk) 09:48, 1 February 2013 (UTC)

## Gordon Gould's confiscated lab notebook

My father was a physicist and at one point a friend and colleague of Gordon Gould. He was one of a small group of people who signed a statement to the U.S. Government stating that Gordon Gould was not a communist and was not developing a weapon to use against the U.S. Because Gould's wife was a registered communist his lab equipment and his lab notebooks were confiscated by the U.S. Government. Later, as the family story goes, the lab notebooks were released to Bell Labs, and presumably Townes and Schawlow, who of course later got credit for the invention of the LASER. Growing up, we were aware of the Gordon Gould lawsuit and I remember seeing the newspaper article when he won the lawsuit. The Wikipedia article doesn't mention anything about the confiscation of his lab notebook and their release to Bell Labs. I wonder if anyone has any further information about this, with proper documentation that would allow its inclusion in the Wikipedia article. It's a colorful part of the history. I have no documentation for this. SanJoseRobert (talk) 01:07, 7 May 2012 (UTC)

Taylor's biography of Gould doesn't mention anything about this incident, as far as I recall. Gould did have troubles as a result of his membership in a communist organization as a young man, and there was some leakage of his ideas to Townes while they were both at Columbia. The incident you describe sounds apocryphal, though.
What did really hurt Gould, was that while he was working for TRG he was pulled off of their attempts to make the first laser because he couldn't get a security clearance because of his communist past. Taylor suggests that had Gould been allowed to work directly on the project, TRG's team might have succeeded in making the first laser.
• Taylor, Nick (2000). LASER: The inventor, the Nobel laureate, and the thirty-year patent war. New York: Simon & Schuster. ISBN 0-684-83515-0. OCLC 122973716.
--Srleffler (talk) 02:13, 7 May 2012 (UTC)

## Laser cavities

I undid some edits, that changed the definition of what a laser is. The issue is whether a "laser" requires an optical resonator. By conventional definition, a laser is a gain medium based on stimulated emission, inside a resonant optical cavity. There are a few cases where the term "laser" is applied to systems that are superradiant, producing optical emission via stimulated emission without feedback from a cavity. Such uses of the term are relatively uncommon, and not unambiguously correct. These uncommon usages should not be given undue weight in the article.

The edits seem to have been partly based on misunderstanding. The editor mentions laser fusion systems like Nova. These systems are not resonator-free lasers as the editor thinks. Rather, these are master oscillator power amplifier systems: a small laser oscillator (consisting of a gain medium inside a cavity) produces the initial laser beam. This beam then passes through a chain of optical amplifiers, e.g. pumped slabs of neodymium-doped glass. It's the oscillator that makes it a laser system. An optical amplifier is not a laser.

The editor also mentions nitrogen lasers, and the article on those does claim that they are commonly built as superluminescent devices, not depending on a resonant cavity. I have added a request for citation on this claim, as I suspect it to be a misunderstanding. An optical cavity does not always imply mirrors as one would normally think about them. For a system with high enough gain, stray reflections off of nearby surfaces (particularly windows or other optical elements along the beam path) are enough to function as a cavity, producing "self-lasing". This is a common problem in high-gain optical amplifiers, sometimes requiring a variety of countermeasures to prevent accidental formation of optical cavities. A system that can emit light on its own via stimulated emission is well into the regime where any reflection back along the length of the device will create true lasing. One would have to work very hard to make a device exhibit superradiant emission rather than self-lasing, by ensuring that reflections back into the cavity are at exceptionally low levels.--Srleffler (talk) 02:47, 8 May 2012 (UTC)

An optical amplifier (by stimulated emission) DOES make it a laser. That's what LASER means, don't you know. Your highly artificial requirement that there be no light reflected accidentally into the gain medium is bizarre, since no gain medium is totally transparent, so there will be some reflection internally even if all light DOES escapes externally. If that's your argument, it's designed to be self-defining. I think that what makes an optical resonator, however, is not the accidental presense of photons that don't make it out. An optical resonator is an artifact, something that is added to the gain medium by techology. It is a deliberately-placed mirror somewhere, otherwise the term is meaningless (otherwise you define "optical cavity" by whether or not lasing occurs in it, you having presumed some kind of accidental reflection, which is a No True Scotsman syllogism). An optical resonator is a thing that is designed to work as an optical resonator for the frequency you chose. It is not an accident.

Amplified spontaneous emission systems like pumped optical fibers are identified as lasers in standard texts. Perhaps the most common “mirrorless lasers” which use no optical cavity and only a single pass of light through a high-gain medium, include “amplified spontaneous emission” systems such as pumped optical fibers (one class of fiber lasers) see below). Other examples are many types of high gain dye lasers and pulsed excimer lasers. Also high-gain semiconductor laser diodes may be operated so that the mirror reflection at the end of the laser is deliberately spoiled. Molecular lasers such as the nitrogen molecular laser at 337 nm and the hydrogen molecular laser at 120 nm, especially when pumped by fast transverse electric discharges or electron beams, operate without an optical resonator. Mirrorless lasing occurs in infrared lines with high gain, such as the 3.39 micron line in He-Ne lasers, and the 3.51 micron mode in He-Xe lasers. The many natural high power lasers and masers in astronomical sources also operate without mirrors. See Lasers. pp. 550-551 (mirrorless lasers section) Anthony E. Siegman. Stanford University. ISBN 978-0-935702-11-8, 1986. [1] An astronomical source example is MWC 349. Finally, X-ray lasers of various types (nuclear weapon pumped lasers, and free electron lasers) operating in frequency regions in which mirroring is impossible, require no optical cavity. Finally, those nuclear fusion lasers need a master oscillator only for pulse shaping. If you charged up all those flash lamps and fired them without an input signal, you'd still get a lot of laser power out the other end-- it just wouldn't be coordinated. But you still wouldn't want to stand in front of it (or have your pinkie in it, or whatever). SBHarris 03:42, 8 May 2012 (UTC)

Is it just me, or did we used to call these things superradiant lasers, rather than superluminescent? As it is now, the superradiant laser seems to be a highly esoteric form only of interest to cosmologists. The superluminescent though is the common or garden nitrogen laser, from the old 1960s SciAm plans. There must be loads of these things around and they're still a popular home-build project for the pyrosparkie - easier even than a Tesla coil, and less workshop needs than a Wimshurst. Andy Dingley (talk) 09:16, 8 May 2012 (UTC)
Yes, I saw one myself in those years, built off the Sci Am plans. It put out pulses of UV light about the size and shape of a broomstick, which was about as long as the gain medium gas filled space between the flat capacitor plates, since there was NO internal reflection in this 3-level laser (and no time for one, and no need for one). The problem with defining lasers as having need for an optical resonator cavity, which by definition is a cavity through which light traverses more than one-pass, is that it conflicts with the definition of "laser" given in standard texts, one of which I quote above. Evidently, Srleffler has his own personal definition of "laser" which he would like to foist on the rest of us, and which conflicts with the texts on the subject. I think he should write his own text containing his own eccentric view, and leave us alone. Meanwhile, I'm going to "cite tag" the article on the idea that a laser needs a resonator, and see what kind of sorry-ass amateur sources people have to come up with, if they attempt to comply. Two can play at this game. SBHarris 18:01, 8 May 2012 (UTC)
Andy: See page 551 in Siegman's book (cited above). These things have often been called "superradiant" in the past, but Siegman (and others) now recommend a narrower application of that term.--Srleffler (talk) 02:24, 9 May 2012 (UTC)
On the definition: Siegman seems to agree with you, which is good enough for me. I'll see what my other books say when I'm at work tomorrow, but Siegman's book is certainly an important text in the field. On page 2, he does define "suitable optical feedback elements" as "essential elements" of a laser, however he goes on to say that these elements may allow a beam of radiation to pass once through the device "as in a laser amplifier". It's clear from the context that he considers laser amplifiers to be a type of laser, contrary to my usage. I'm familiar with ASE systems such as those you mention (quoting from Siegman); I would not have classed them as "lasers", and am surprised that Siegman does so.
I notice that in the "mirrorless lasers" section, Siegman several times refers to lasers with mirrors as "true lasers". In modifying the article's definition to be inclusive of mirrorless lasers, it will be important not to give undue weight to them; even Siegman treats these as special cases, not "true" lasers.
I think you are mistaken about systems like Nova. I guarantee you that every amplification section in those systems is isolated with saturable absorbers and spatial filters, which ensure that the amplifiers will not lase on their own. (For the reasons why, see Siegman, p.556, 1st para.)--Srleffler (talk) 02:20, 9 May 2012 (UTC)

I reworked the Design section as a result of the discussion above, relying on Siegman's definition that "optical feedback" is required, and moving discussion of optical resonators down a bit in the section and describing it as common, rather than a mandatory element. I also reworked the comment about an amplifier in a cavity being a laser by saying instead that it is a laser oscillator. I don't think anyone here will dispute that putting an amplifier in a cavity makes a laser oscillator (and Siegman supports that statement). The disagreement is just over whether the amplifier is a "laser" in its own right, which the text no longer addresses one way or the other.

A side note: the edit comment on the request for citation regarding amplifiers read "[A]n optical amplifier that produces coherent light by stimulated emission, is not a laser until you add an optical cavity? Give the cite." While I take the point seriously, as phrased the question seems to include a misunderstanding. An optical amplifier does not produce coherent light by itself. It might emit amplified spontaneous emission ("superluminescence"), but that is not coherent. An amplifier can of course produce coherent output by amplifying a coherent input beam. If it produces coherent light on its own, then it is a laser, but except for rare and odd cases, this requires some kind of optical feedback. --Srleffler (talk) 03:02, 10 May 2012 (UTC)

• This has always been a poor article, and it's also a broad-scope article. I make a point of never worrying about the quality of broad wiki articles, as the open wiki editing model just doesn't work for them. However this absolutist attitude that "if it doesn't have an etalon, it's not a laser" is nonsense. At most it's over-interpreting the phrasing of one source, so as to infer far too much from one short piece of text.
Lasers are called LASERs because the obvious acronym for self-oscillators would have made them "LOSERs". They developed from masers, which were used and intended originally as low-noise amplifiers, not as self-oscillators. There's no reason at all to exclude those that amplify without oscillating, or those that don't express all of the distinctive features of a laser. It's common knowledge that lasers are coherent, monochromatic, self-oscillators with parallel output beams, built around a reflective cavity. Yet anything beyond the simplest study shows that they're certainly not monochromatic, aren't necessarily coherent and that there are plenty of types without resonant cavities. We've mentioned simple nitrogen lasers, but there are also the X ray lasers, the fibre optic comms amplifiers and many other superluminescent types. Whilst agreeing that systems like Herald, Nova etc have master oscillators, their gain chains, in isolation, don't stop being lasers either. Andy Dingley (talk) 07:52, 10 May 2012 (UTC)
You seem to have missed the fact that you have already won this argument.--Srleffler (talk) 03:27, 11 May 2012 (UTC)
So where's my goldfish? I haven't "won" anything. Reality might have won something, I'm just quoting it. Andy Dingley (talk) 08:52, 11 May 2012 (UTC)
We're waiting to hash this out, because it's impossible to rewrite the horrid lede without a consensus. It might be well (for example) to mention laser oscillators (defined by cavity) vs. laser amplifiers (no cavity) in the lede. And we can say that some people consider the first as "true lasers" but there is no clear distinction. The cavity is only a crutch. The oscillator which has self-feedback (like most of not all oscillators in nature and technology) is more apt to produce CW radiation of some degee of coherence using the LASER mechanism. However, the laser amplifier (any laser amplifier) DOES produce coherent light out with no deliberate input, since there's always a spontaneous input to the thing some excited atom spontaneously emitting. A laser amp could not function as an amplifier if it did not amplify, and it could not amplify without being pumped to the laser threshhold degree of population inversion for it, and be capable of lasing. One spontaneously emitted photon emitted into the medium once it's pumped, will be amplified in its passage down the gain medium, and emerge with a larger amplitude, and this radiation will in general have some degree of coherence, since it was (after all) produced by the laser mechanism. There is no getting away from that (a laser amplifier does not have some threshhold input, below which it will not function).

A gain medium pumped into being able to produce amplification is like a fissile mass that is supercritical. All it needs is a neutron, and there's always a neutron. Of course, amplifiers with no cavities are more apt to produce pulses, and these pulses are not as good as if they were managed (same with nuclear weapons, which give much better explosions if radiated with neutrons at just the right time). In a few cases, the gain is so high in the medium and the pumping input is so large and effective, that a CW is emitted. Astronomical laser sources seem to be in this category. In most cases, an amplifier set up to amplify with no input is not as efficient or powerful at producing laser radiation, but it will produce laser radiation and that makes it a laser. I would be willing to bet this is true of Nova as well (how could it not be?).

I would be willing to bet it's true of simple helium-neon laser, so long as the tube is long enough that it could indeed BE used as a laser amplifier. See the discussion at the end of chapter 4 on lasing theshholds [2] It takes about 30 cm of plasma in an He-Ne laser before you get first pass-amplification of light (gains exceed loses in the the pumped medium). You can make a He-Ne laser shorter than this, but it wouldn't function as a amplifier because it is too lossy to do so. But with a longer tube, capable of one-pass amplication, now you really don't need mirrors to see some laser light. You'd get far, far weaker laser light with a mirrorless amplifier. But not NONE. SBHarris 19:50, 11 May 2012 (UTC)

Don't forget distributed feedback lasers. Coherent, self-oscillators, but no mirrors and the "cavity" is therefore questionable. Andy Dingley (talk) 23:24, 11 May 2012 (UTC)
You are correct that defining a laser as requiring a cavity with mirrors is much too narrow. There are many kinds of optical resonator that are used to make lasers. What is essential is optical feedback.--Srleffler (talk) 03:48, 12 May 2012 (UTC)
SB: I agree that if we are going to consider amplifiers to be lasers too, then we need to discuss and distinguish between laser oscillators and laser amplifiers.
The cavity is more than a "crutch". To produce spatial or temporal coherence, some kind of feedback is required, whether this comes from a cavity or some other source. An amplifier will not produce coherent light from spontaneous emission. If you started with a single photon in an amplifier, it would be amplified coherently. You don't start with a single photon, however. You start with a population of photons produced by spontaneous emission, which are incoherent with each other. The output of an amplifier that is amplifying spontaneous emission is no more coherent than the spontaneous emission was. It is the selective effect of feedback, combined with coherent amplification, that produces coherent output from a laser oscillator.
You are correct that an amplifier doesn't have a lower limit: if it has gain it amplifies any signal, no matter how small. In a device that is intended to function as an amplifier, the system is designed such that when spontaneous emission is amplified, it does not reach levels where it can significantly deplete the gain. An amplifier that produced significant output from spontaneous emission would be a badly designed amplifier (but a good ASE source).
In very powerful systems, with multiple amplifiers, the amplifiers are isolated from one another by saturable absorbers. Signals below a certain level are blocked, but once that level is surpassed the absorber becomes transparent. Amplified spontaneous emission from one amplifier (or one part of an amplifier) is absorbed by the saturable absorber, so that it cannot be further amplified by the next amplifier in the chain. When the pulse from the master oscillator passes through the first amplifier it is amplified to a level that is sufficient to saturate the saturable absorber, so the amplified pulse passes through unattenuated and continues down through the chain of amplifiers. By design, the system cannot produce significant output without the pulse from the master oscillator. (Other mechanisms also aid in preventing the amplifier chain from lasing on its own.)
If you make a HeNe laser without the mirrors you will of course get amplified spontaneous emission out, but the intensity will be orders of magnitude lower than from the same laser with the cavity, and the output will not be coherent. Anyone who has built conventional lasers (not high gain systems like the nitrogen laser) on an optical bench has experienced this. If your mirrors are not aligned, you get essentially no output. There is weak ASE there, of course, but it is negligible. Adjusting the mirrors, when you find the correct alignment the output of the device rises by a huge factor (Thousands? Tens of thousands? More, perhaps.) One says that the device has begun to lase.--Srleffler (talk) 03:48, 12 May 2012 (UTC)
Okay, I think we are making progress. If the difference between an ASE mirrorless laser and one with mirrors (or some other type of feedback) is simply efficiency and degree of temporal coherence (for ASEs often have resonable spatial coherence), then we're down to looking at things that weren't part of our definition of "laser." Nothing says a laser must have both temporal and spatial coherence (or indeed any coherence at all), or that it have high power, or that it be efficient. Our definition of "laser" is that it operate by amplifying EMR by stimulated emission. A laser amplifier fits that definition, even when amplfying nothing but spontaneous emission "noise." The rest is bells and whistles to give you a cleaner signal or one that you want.

If the article says this, then it will agree with the texts, and I'll be happy. And we can then explain nuclear X-ray lasers without too much difficulty, and the operation of many "free electron lasers" (FELs). Although for the terms of stimulated emission, in FELs I suppose one has to interpret it rather loosely to include all processes that tend to bunch electrons into groups that radiate together, and not just quantum processes like fluorescence. (Some of the same processes as in FELs happen in some traveling wave tubes, but with non-relativistic electrons). However, interestingly, FELs are often started off with "noise" rather than a seed signal, and they then progress from there to lasing with no feedback. Which is good, since some FELs must operate in the UV or X-ray where there is no way to have feedback. See self-amplified stimulated emission. How are you going to explain "laser emission" from such a beast, using the arguments that you insist on using? SBHarris 03:42, 16 May 2012 (UTC)

It all comes down to definition. My definition of "laser" is essentially synonymous with what Siegman would call a "laser oscillator". Some things that are commonly called "lasers" don't fit my definition. Some of those things don't fit your definition either. Besides FELs there are things like atom lasers. As commonly used, "laser" is not a very strictly defined term. There is a wide grey area around the edges. For the article, I'm fine with using Siegman's definition.
Something to think about: If Theodore Maiman had only succeeded in obtaining ASE from his ruby crystal, would he still be credited as having made the first laser?--Srleffler (talk) 03:46, 18 May 2012 (UTC)

## Expanded laser applications section?

The section on laser uses is very cursory. I propose expanding it somewhat to give a better overview of laser applications. We could do it by regrouping and adding a short paragraph on each of the following topics:

• Manufacturing and materials processing
• Medical and cosmetic
• Military
• Sensors and spectroscopy
• Research and Development
• Entertainment (e.g. laser projectors, light shows, etc.)

What do you think of these broad categories?— Preceding unsigned comment added by Davisonkirby (talkcontribs) 12:50, 3 July 2012‎

The section is cursory because it is a summary of the main article on that topic. Check out the main article on laser applications and see if you have material to add there first. The summary in this article should not be expanded, but if there are key application areas missing the content could be adjusted a bit.--Srleffler (talk) 04:25, 4 July 2012 (UTC)

## Lasers as weapons?

Here it says that lasers have not been successfully developed as weapons. However the article MIRACL describes just such a weapon. So why is this not mentioned here? — Preceding unsigned comment added by Samsite (talkcontribs) 12:39, 25 September 2012 (UTC)

This article says that "actual laser weapons are still in the experimental stage". MIRACL appears to be an experimental system. I don't see the contradiction. I don't see anything in a quick skim through the sources cited in the MIRACL article, that would suggest that it has been deployed as a weapons system. It looks, in fact, like the system is stationary, located at the White Sands test range.
Making an actual (as opposed to experimental) weapon requires a lot more than just making a laser that can blow things up. To be useful as a weapon, you have to be able to transport it and power it in the field, and it has to be robust enough and easy enough to maintain, to keep it operating for an extended period under combat conditions.--Srleffler (talk) 01:35, 26 September 2012 (UTC)

## Laser that destroys unmanned spacecraft

Croatian writer Giancarlo Kravar: German company Rheinmetall AG, which manufactures weapons and auto parts, introduced a system of laser weapons that can knock down two unmanned spacecraft at a distance of over 1.5 km, the BBC reported Tuesday. The demonstration of laser weapons, unmanned aircraft that are assembled at a speed of 50 meters per second, were ruined when they were in the programmed sector of fire. The company tested the system in various weather conditions, including snow, sun and rain, and the weapon system uses radar to roughly target drones, while for fine tracking targets include optical system. The company plans to produce mobile laser weapon system and integrate it into automatic gun.78.3.219.240 (talk) 17:58, 9 January 2013 (UTC)

Sources? Cheers!-- Allied Rangoontalk 23:40, 10 May 2014 (UTC)

## Section on lasers as a hobby is useless

The short section that discusses lasers as a hobby is mostly useless because it doesn't say what hobbyists do with the laser. Telescope hobbyists build telescopes to look at the stars. HAM radio hobbyists use their devices to communicate. What exactly do laser hobbyists do with the lasers? The article should say. Simply saying some people play with lasers is pointless. Every article in Wikipedia could have a similar section saying that some people play with the article's subject. Either erase this section or give it some details to make it useful. Is there s laser hobbyist magazine? Are the laser hobbyist conferences? 129.63.129.196 (talk) 18:34, 31 January 2013 (UTC)

## Spelling Edit War

See spelling of disc. For optical devices, the spelling is disc. If this spelling edit war continues, then, I will slap the British English tag on this talk page, and I am in Washington, DC. Stop the edit war and use the agreed spelling. Robert McClenon (talk) 01:33, 2 July 2013 (UTC)

Wow, one revert, one restore, nothing since, and it's an edit war? I saw that Soap (talk · contribs) was right. The only drama is your tone. -- Scray (talk) 01:53, 2 July 2013 (UTC)
Okay. Robert McClenon (talk) 01:57, 2 July 2013 (UTC)
Attending the conference was Gordon Gould. Gould suggested that, by pulsing the laser, peak outputs as high as a megawatt could be produced.[10]

## Components of original ruby laser

Text copied from Ruby laser:

As time went on, many scientists began to doubt the usefulness of ruby as a laser medium. Maiman, too, felt his own doubts, but, being a very "single-minded person," he kept working on his project in secret. He searched to find a light source that would be intense enough to pump the rod, and an elliptical pumping cavity of high reflectivity, to direct the energy into the rod. He found his light source when a salesman from General Electric showed him a few xenon flashtubes, claiming that the largest could ignite steel wool if placed near the tube. Maiman realized that, with such intensity, he did not need such a highly reflective pumping cavity, and, with the helical lamp, would not need it to have an elliptical shape. Maiman constructed his ruby laser at Hughes Research Laboratories, in Malibu, California.[11] He used a pink ruby rod, measuring 1 cm by 1.5 cm, and, on May 16, 1960, fired the device, producing the first beam of laser light.[12]
Theodore Maiman's original ruby laser is still operational.[13] It was demonstrated on May 15, 2010 at a symposium co-hosted in Vancouver, British Columbia by the Dr. Theodore Maiman Memorial Foundation and Simon Fraser University, where Dr. Maiman was Adjunct Professor at the School of Engineering Science. Maiman's original laser was fired at a projector screen in a darkened room. In the center of a white flash (leakage from the xenon flashtube), a red spot was briefly visible.
The ruby lasers did not deliver a single pulse, but rather delivered a series of pulses, consisting of a series of irregular spikes within the pulse duration. In 1961, R.W. Hellwarth invented a method of q-switching, to concentrate the output into a single pulse.[14] — Preceding unsigned comment added by 103.15.55.108 (talk) 14:50, 27 August 2013 (UTC)
Did you have a question or comment?--Srleffler (talk) 17:09, 27 August 2013 (UTC)

## Improper use of the word LASER

LASER is an acronym which should always be capitalized. — Preceding unsigned comment added by N0ty (talkcontribs) 12:44, 6 September 2013 (UTC)

No. While it started out as an acronym, it has become a word. It is now more common to spell it in lower case, like any other word.--Srleffler (talk) 05:15, 7 September 2013 (UTC)
Agreed. The current article already does a good job of explaining this origin. I don't see any need for changes in this regard. ronningt (talk) 13:42, 8 September 2013 (UTC)

Whether an acronym (the meaning of which I prefer to limit to any abbreviation that is pronounceable) is capitalized or not is mostly (but not always) an easy determination and merely has to do with whether the acronym refers to an organization. So "NATO" is all caps because it is the acronymic abbreviation for "North Atlantic Treaty Organization." The word "laser" is entirely lower case (except, obviously, if it begins a sentence) because it refers to the phrase "light amplification by stimulated emission of radiation," as it states in the article under heading 1.1 "Terminology." Military organizations idiosyncratically use all caps in their acronyms, such as "CDRUSPACOM" (Commander, U.S. Pacific Command) [which prior to 2002 was "CINCPAC" (Commander-in-Chief, U.S. Pacific Command), considerably more pronounceable but changed probably because of possible confusion with the real Commander-in-Chief, the President of the US], but any further discussion of this matter belongs elsewhere in Wikipedia.

In my opinion it is also incorrect, and possibly confusing, to capitalize the initial letters of the words of this phrase in the introductory paragraph of this article: "...The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation.[1]...." The reason it is presented this way, I suspect, is an artifact caused by the writer's having copied the phrase as it is presented in the reference given, reference [1], in which the phrase is shown this way. But the only reason it is shown this way is surely merely because the phrase is part of the title of an article: "Gould, R. Gordon (1959). 'The LASER, Light Amplification by Stimulated Emission of Radiation'. In Franken, P.A. and Sands, R.H. (Eds.). The Ann Arbor Conference on Optical Pumping, the University of Michigan, 15 June through 18 June 1959. p. 128. OCLC 02460155." I, therefore, urge the writer to change to lower case those words of this phrase in the introductory paragraph now beginning with capital letters.Wikifan2744 (talk) 07:51, 11 December 2013 (UTC)

You may find the article Acronym interesting. Your suggestion that capitalization of acronyms should be used only for organizations is unfamiliar to me. Perhaps this orthography is idiosyncratic?
I personally like your proposal to not capitalize the letters in the expansion of the acronym. Our article Acronym says that this is typical in professional publishing, but that nonprofessionals tend to capitalize expansions of acronyms. On Wikipedia, capitalization of expansions is a compromise between people like you and I, and the many editors who would like to see the initial letters in the expansion not only capitalized but also bold face. --Srleffler (talk) 05:09, 12 December 2013 (UTC)

## Thoughts on how to improve?

I'm happy to see that the laser has been denoted as a significant technology, and I'm willing to invest effort in improving the article, but I'd like other editors thoughts on what key changes would help the article.

I feel the overall tone, and certainly the introduction, is tilted towards what makes the laser scientifically interesting rather than what makes it a valuable technology. I feel shifting that balance by providing a greater emphasis on applications and people's daily encounters with lasers would be beneficial.

Several of the current section feel like they would be better served by being distinct articles that were not trying to serve as broad an audience. Could the Laser Physics section be largely moved into laser science? How about limiting the discussion of laser types to one paragraph here and creating a separate article for anything more detailed than that?

To reconsider the overall structure of the article, I went searching for analogous topics that have an article with a higher rating. The three I found were steel, camera and telescope. I'm going to review these as potential guides. Do you have thoughts on other analogous articles?

Thanks for any thoughts and suggestions you can offer. I hope we can work together to raise the quality of this article. ronningt (talk) 13:14, 8 December 2013 (UTC)

Wikipedia:Summary style may provide some useful guidance on how to spin off material into other articles and simplify this one.
This article, particularly its early sections, should be aimed at a general audience not the technical reader. The article does need to explain clearly to a general audience what a laser is, what it is composed of, and how it works. I think these things are best explained before covering applications, but I'm open to trying other arrangements of the material. --Srleffler (talk) 18:43, 8 December 2013 (UTC)

## Navy laser weapon

• Headline: US Navy ready to deploy laser system this summer; rail guns aren't far behind.

"It fundamentally changes the way we fight," said Capt. Mike Ziv, program manager for directed energy and electric weapon systems for the Naval Sea Systems Command.

• Headline: 'Star Wars' at sea: Navy ready to deploy laser system this summer.

"The Navy plans to deploy its first laser on a ship later this year, and it intends to test an electromagnetic rail gun prototype aboard a vessel within two years." — FYI, Charles Edwin Shipp (talk) 15:23, 18 February 2014 (UTC) PS: There are some nice pictures.

• Headline: The Future Is Now: U.S. Navy Ready to Deploy Laser on Ship for First Time.

More pictures, same AP story, February 17, 2014. FYI, Charles Edwin Shipp (talk) 16:15, 18 February 2014 (UTC)

## Dark magic

Really? 80.2.87.59 (talk) 21:35, 19 March 2014 (UTC)

That was vandalism. It has been fixed.--Srleffler (talk) 05:21, 20 March 2014 (UTC)

## Ability to focus and columnate

I am coming to laser optics from imaging with incoherent light and I'm trying to clarify a few things. First, I was surprised to learn that laser diodes spray light out over a wide angle—that they need a lens to produce a beam. This raises the question: is it their coherence that makes a laser diode well-suited to producing a beam or is it something about the area and angle over which light is emitted?

Specifically:

• If I had a laser diode and a conventional diode both of which had a 0.1 mm square face and emitted over a range of ±30° with Gaussian intensity profile across the face and angle space, would I be able to get basically the same beam out of both?
• If not, would they be basically the same up to a large M2 factor?
• Do laser diodes have intrinsically lower beam parameter product? That is, is it easier to make laser diode to produce a small and/or small-angle source than it is with a conventional diode for a given power?

Thanks. —Ben FrantzDale (talk) 03:16, 3 April 2014 (UTC)

It's the spatial coherence of a laser diode that defines its ability to be collimated into a beam with low divergence. A singlemode laser diode, in particular, can be collimated into a beam that is just as nice as that from any other singlemode laser, even though the output of the laser diode is highly divergent.
You can't have a singlemode diode and an LED with the same emitter size and the same far-field divergence. Diffraction won't allow that. The LED will either have a much larger emitter, or a much larger far-field divergence. This is equivalent to saying that it has high M2.
No, a laser and an LED are not "basically the same up to a large M2 factor". The M2 describes the ratio of divergence to waist size for a beam; it does not completely characterize the beam (except for the case where M2 = 1.)
Yes, the lower beam parameter product from a typical laser diode is an intrinsic characteristic of that type of device. Lasing increases coherence. Not all laser diodes have good beam quality, however. Many types are multimode, and in particular ones designed for optical pumping may have very poor beam quality.--Srleffler (talk) 05:25, 3 April 2014 (UTC)
Thanks for the response; I'm starting to get it (and once I do I'll make an effort to add what I've been missing to the appropriate articles). A few more questions:
• It sounds like you are saying that an ideal singlemode laser diode can be focused to the smallest possible spot at a given NA regardless of the size and emission angle of the the emitter. Is that right? That would go against my ray-optics intuition that (assuming the emitting surface is a waist) if I relay that surface the imaged waist size will go by the ratio of the distance from the image to the exit pupil over the distance from the emitter to the entrance pupil. (Or is it that from a distance, the beam waist looks like it was a point source regardless of its actual diameter (in that at at a distance you have a spherical wavefront emanating from the center of the waist)?)
• I'm having trouble understanding why multimode (and incoherent light) aren't as focusable. Certainly the Gaussian-mode component of a multimode beam is still focusing like it would alone; is it that the modes other than 00 are each bigger (shown)?
• Is singlemode really shorthand for "just the 00 mode"? (In principle you could have a singlemode beam with just the 30 mode which I'm guessing wouldn't be as focusable as a 00 singlemode beam.)
Thanks again. —Ben FrantzDale (talk) 12:49, 3 April 2014 (UTC)
Starting with the last question: Yes, when people say "singlemode" they mean a Gaussian beam—TEM00, not a single isolated higher-order mode. There is only one TEM00 mode. This means that all Gaussian beams of a given wavelength are in some sense the same. You can image any Gaussian beam into any other with simple optics. So, if a laser diode is singlemode, it doesn't matter how big the emitter is or how wide the divergence. With the right optics you can in principle perfectly match it to any other singlemode beam. (In practice, the high emission angle of laser diodes makes them very sensitive to optical aberrations. It's hard to image that wide an angle with perfect fidelity.) Yes, any singlemode beam can be focused to the smallest possible spot with a given NA regardless of the size or emission angle of the source.
Ray-optics intuition is not always right with Gaussian beams. In many cases, one can almost correctly determine the image waist location and size by imagining imaging the source using conventional ray optics. In other cases this fails spectacularly. In particular, ray optics will give very wrong answers for large conjugate-ratio imaging. It's actually quite surprising that ray optics often does work. Fundamentally, it's not obvious that it should. Ray optics envisions rays spreading from a point source and being imaged to a point. An extended source is just a collection of point sources. A Gaussian beam waist is not a collection of point sources. Its size is governed by diffraction, which is outside the scope of ray optics. There are rays, but they do not propagate in straight lines in the vicinity of the waist. Given this, it is quite surprising that in many cases one can treat a Gaussian waist as a classical extended source and get the right answer from a simple paraxial ray-optics calculation.
Yes, the TEM00 component of a multimode beam behaves just the same as it would if it were alone. The other modes are "bigger" in the sense that for any given size they have higher divergence than a TEM00 mode of that size would. (The correct definition of "size" here is the D4σ width of the beam.)--Srleffler (talk) 02:01, 5 April 2014 (UTC)
Ah! That clarifies a lot! One book I'm looking at, Laser Diode Beam Basics by Sun, has an example of large-conjugate-ratio imaging that was making me scratch my head: It showed a high-NA beam with its waist imaged by a lens at distance f. Obviously ray optics tells us that the image of the waist is columnated so the rays are parallel, yet the example shows the second waist at f to the right of the lens(!). That agrees with the answer I get using the complex beam parameter. I suspect that looking over Ray_transfer_matrix_analysis#Ray_transfer_matrices_for_Gaussian_beams will show why for near-unity conjugate ratios ray optics work pretty well. Thanks again. —Ben FrantzDale (talk) 18:54, 7 April 2014 (UTC)
Yes, if you put a lens one focal length from a waist the image is at f not at infinity. Intriguingly, if you image that waist again with a second lens, putting the second lens one focal length from the first lens's image, the resulting image is one focal length past the second lens, and the image has just the size and location you would predict by naively applying ray optics.--Srleffler (talk) 05:18, 8 April 2014 (UTC)
Crazy. The baffling part of that for me is that it appears applying Ray_transfer_matrix_analysis#Ray_transfer_matrices_for_Gaussian_beams to the situation that the wavefront emerging from the first lens is planar as it leaves the (thin) lens, which would suggest that the waist is at that first lens. For the first relayed waist to be f to the right of the lens, then it would seem that the wavefront would have to have a radius very close to ${\displaystyle R=-f}$ at the lens. I don't understand what the wavefront looks like that puts a waist at f before and f after the lens, since the lens should be getting a spherical wavefront of radius f I can't see how that lens is putting out a converging front.
Also, I'm still not seeing how to connect the dots between multimode laser behavior and regular incoherent behavior. It seems that in a sense a single-mode TEM00 laser looks a lot like a diffraction-limited point source (where diffraction gives it its finite waist), so it makes some sense that the area of a diode face doesn't act quite like a regular incoherent area source that can be imaged. However, my understanding is that the wavefront from an incoherent area source could be recreated by the right combination of laser modes. I still don't see where we'd get something looking like a pencil of rays coming from near the edge of the emission surface. —Ben FrantzDale (talk) 02:58, 10 April 2014 (UTC)

## Semi-protected edit request on 19 May 2014

Please edit "A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation." so that when hovering above the word "laser" the full meaning should appear. This would be good for people viewing as the word is already bold and it provides an easier way to show the meaning of "laser" The following code can be used (the first is the original followed by the edited code: Original: A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Edited: A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. RahulSanthosh (talk) 08:55, 19 May 2014 (UTC)

Not done: please establish a consensus for this alteration before using the `{{edit semi-protected}}` template. I believe there is a current consensus in place against hovering definitions of words. I also believe there "may" be a userscript or gadget that will allow you to see some words like that. — {{U|Technical 13}} (tec) 12:25, 19 May 2014 (UTC)

## Semi-protected edit request on 12 July 2014

This article omits one of the most prominent and impactful applications of the laser - optical fiber communications.

At a BARE minimum, the 2nd paragraph should be edited from its current form:

Lasers have many important applications. They are used in common consumer devices such as optical disk drives, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. NASA has been experimenting with lasers for the purpose of transmitting data from space.[3] Lasers also have many important applications in scientific research.

to the following:

Lasers have many important applications. They are used in common consumer devices such as optical disk drives, laser printers, and barcode scanners. They are used in optical fiber communications to enable the internet. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. NASA has been experimenting with lasers for the purpose of transmitting data from space.[3] Lasers also have many important applications in scientific research.

Optoeng (talk) 21:50, 12 July 2014 (UTC)

Done Wow, yes. I'm not sure how we missed that. Thanks for pointing it out.--Srleffler (talk) 04:44, 14 July 2014 (UTC)

## Semi-protected edit request on 23 July 2014

I was taught in physics that it meant "linear amplification of spectral emission radiation" which is far more correct. When one examines the mode of operation this def'n is much more accurate. The gas is excited by a current causing an electron to raise to a higher orbital. When the field is collapsed the excited electrons all fall back simultaneously, giving off a photon at a characteristic wavelength, or spectrum. This is called "spectral emission radiation". The nature of the tube and window cause the linear amplification. Thank you 122.109.51.141 (talk) 10:07, 23 July 2014 (UTC)

Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format. —cyberpower ChatOnline 10:38, 23 July 2014 (UTC)
Not done:The proposed change is clear enough, but is complete nonsense. Assuming good faith, the requestor has perhaps misremembered what was learned in class.--Srleffler (talk) 00:05, 24 July 2014 (UTC)

## LASER

LASER is an acronym, why is the article name laser? 202.123.130.53 (talk) 12:03, 25 August 2014 (UTC)

Becuase laser has evolved into a word. It's not merely an acronym anymore. You can find discussion of this issue above, and in the archives linked at the top of this page.--Srleffler (talk) 08:21, 24 August 2014 (UTC)

## Semi-protected edit request on 26 September 2014

In the Semiconductor lasers section it's written:

Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm.

Here is a good overview of commercially available wavelength that can be used as a reference.

This part

In 2012, Nichia and OSRAM developed and manufactured commercial high-power green laser diodes (515/520 nm), which compete with traditional diode-pumped solid-state lasers.[25][26]

can be removed. These wavelength and particular diodes are listed in the reference above.

In general I would distinguish between laser diodes and diode lasers. This section is about laser diodes. External-cavity semiconductor lasers are diode lasers, i.e. systems. I would open a seperate section for diode lasers and write an article about diode lasers, unfortunately English is not my mother tongue. But is somebody know German, the respective article is here — Preceding unsigned comment added by 141.89.75.210 (talk) 17:05, 26 September 2014 (UTC)

Partly done: Thanks for the reference. It's an interesting page. I'm not sure why you think the line about the development of green laser diodes should be removed. Can you explain further?
In English, "laser diode" and "diode laser" are used interchangeably. While it would make sense to use "diode laser" to refer to systems such as ECLs, that is not the typical usage. --Srleffler (talk) 02:05, 27 September 2014 (UTC)
Hi Srleffler, the diodes from Nichia and Osram at 515/520 nm are just two of hundrets. They are included in the overview here. I don't understand, why they shoudl be mentioned seprately. — Preceding unsigned comment added by 188.100.65.197 (talk) 18:25, 27 September 2014 (UTC)
The implication of the sentence is that these were the first commercial high-power green laser diodes, which is worthy of mention.--Srleffler (talk) 20:59, 27 September 2014 (UTC)

## Semi-protected edit request on 12 January 2015

85.189.149.201 (talk) 08:44, 12 January 2015 (UTC) lasers are a bright light which can blind people and are banned in the uk and many other countries.

Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format.  B E C K Y S A Y L E 09:34, 12 January 2015 (UTC)

## "laserlight"

The usage and primary topic of laserlight is under discussion, see talk:LaserLight -- 65.94.43.89 (talk) 10:16, 29 April 2015 (UTC)

## edit request

```{{redirect|Laser light|the song|LaserLight}}
```

to

```{{redirect|Laser light|the song|LaserLight|laser light show|laser lighting display}}
```
"Laser light" redirects here. For the song, see LaserLight. For laser light show, see laser lighting display.

-- 65.94.43.89 (talk) 10:22, 29 April 2015 (UTC)

Partly done: by another user, linking to the disambiguation is best Kharkiv07Talk 12:05, 29 April 2015 (UTC)
Done Alakzi (talk) 19:44, 29 April 2015 (UTC)

## Semi-protected edit request on 8 June 2015

Experimentation in ultra violet laser technology has demonstrated the short burst potential of a laser can be reduced to attosecond length bursts.

Shirtbrigade (talk) 12:43, 8 June 2015 (UTC)

Not done: as you have not cited reliable sources to back up your request, without which no information should be added to, or changed in, any article. - Arjayay (talk) 13:01, 8 June 2015 (UTC)

## Early reception

Around the time of its invention, the laser was famously labelled 'a solution in need of a problem', but now it has penetrated so many aspects of industry, science and our daily lives that the number of applications are countless.

My emphasis. With a better source, that should become part of the history section. 85.178.192.101 (talk) 13:16, 13 August 2015 (UTC)

## What does "monomode" mean?

I read something about a "monomode laser". Could someone define that term, please? Equinox (talk) 13:46, 15 January 2016 (UTC)

It could refer either to a singlemode laser, or to a single-frequency laser. A singlemode laser is one whose transverse intensity pattern corresponds to a single transverse mode of the laser's resonator; the output of the laser is then typically a Gaussian beam. A single-frequency laser is a singlemode laser whose resonator is designed such that only a single frequency of light lases; the light in the laser is a single longitudinal and transverse mode of the laser resonator.--Srleffler (talk) 07:31, 16 January 2016 (UTC)
Circular TEM mode patterns
• It's a comparison of monomode vs multimode. It applies to anything with waves in a large waveguide, so lasers are one thing but it's maybe more common as a term in relation to fibre optics. Lasers will use terms like TEM00 / TEM01.
It's "well known" (but in the real word turns out to be only an approximation) that lasers are coherent. They (ideal textbook lasers) achieve this by a single wave passing through their etalon or cavity and the "lasing" emission aspect happening in phase with this. The cavity is somewhere between a waveguide and an etalon between two mirrors. Textbook lasers are simple monomodes.
Consider microwave radio for a moment. That uses waveguides and it uses minimally small waveguides in relation to their wavelengths. They're monomode because only a single mode will "fit" into the waveguide (the condition for a conductive waveguide is that the nodes are on the walls). If the waveguide gets bigger for the same wavelength, then its Q first drops (waves don't fit exactly) then rises again as integer numbers of waves will fit. Now imagine doing that with light (tiny wavelength) in a physically larger waveguide. You can get almost anything to fit in there: whatever the wavelength, there's some path that meets the waveguide condition. This is the situation in optical fibres - the paths taken aren't simple, so the overall behaviour becomes more of an averaging to a Gaussian profile. There will be dispersion in the fibre, owing to the different path lengths, and eventually that starts to limit bandwidth. This multimode fibre represents pretty much all "short" fibres. For "long" fibres (telecoms) it was realised a long time ago (1980ish) that a monomode fibre would be an advantage. Single mode, single path, much less dispersion, better bandwidth for further. So telco fibres have thinner active cores to favour only monomode transmission.
Back to lasers. Unless you're talking about tiny diode lasers coupled into fibres the monomode / multimode distinction above isn't the one that laser people are talking about. The issue of interest with lasers is mostly about transverse mode and beam profiling, with terms like TEM00. Inside the laser cavity there is a distribution of intensity that's again derived from the waveguide conditions. There are several modes (sorry! - it's the termed used, but it's not used in the same way as for fibres) that this can settle into: one (TEM00) has a single lobe (lobe, not mode) whilst a rectangular TEM11 mode has four lobes. Generally (especially for high power lasers) a lot of effort goes into achieving the simplest TEM00 mode as this gives the most effective{[sic}} beam for the cost of the laser capacity. This might be termed a "single mode" laser, but that's really a misnomer - lasers just have one mode in this sense, it's a single lobe. Andy Dingley (talk) 12:07, 16 January 2016 (UTC)

## Should Weber's contributions be summarized in section 5.2?

See http://www.eng.umd.edu/html/ihof/inductees/weber.html for a summary of Joseph Weber's contributions to the development of the maser.

Added.EAWH (talk) 02:28, 16 March 2016 (UTC)

## Semi-protected edit request on 11 May 2016

The title of the page is currently 'Laser' which is incorrect grammar for the topic presented. I request for a change of all words in/on page '(Laser -or- laser)' to be changed to 'LASER' due to the correct term being 'Light Amplification by Stimulated Emission of Radiation' Which is stated in the page on line 4 (line 3 if not including blank line) or the second sentence in the first paragraph. WTLM2013 (talk) 14:20, 11 May 2016 (UTC)

Not done as policy mentioned above, and because, although derived from "Light Amplification by the Stimulated Emission of Radiation", as an acronym, laser is now a stand alone word in its own right.

## Relation of narrow spectrum and narrow beam

Perhaps someone could add to the first section that some lasers emit only one color of light because different colors will refract differently, and having a single wavelength keeps the beam narrow.

50.5.106.186 (talk) 15:19, 11 August 2016 (UTC)

Not done Not a "complete and specific description of the request." Meters (talk) 17:14, 11 August 2016 (UTC)

Nor is the statement correct. --Srleffler (talk) 23:51, 11 August 2016 (UTC)

I've set "answered" to no because while the first section states that lasers emit a narrow spectrum, it is not clear to a person of mediocre intelligence that it allows the beam to stay narrow despite refraction.— Preceding unsigned comment added by 50.5.105.58 (talkcontribs) 16:49, 9 October 2016 (UTC)

Not done for now: I'm not sure what exactly you have in mind here. The fact that many lasers produce narrow, collimated beams is not particularly related to the narrowness of the laser's spectrum. There are lasers with broad spectra, which yet can produce narrow beams. There are lasers with narrow spectra that are spatially incoherent and can't be collimated well. The two properties are not very much related to one another.
If you're using a lens or prism that has significant dispersion, it will of course spread or smear the beam if the beam is not monochromatic. I can't see how that detail is worth mentioning early in the article, though. It's not something one typically has to worry about.--Srleffler (talk) 01:16, 10 October 2016 (UTC)