Talk:Laser

These properties have many uses in science and technology. (Please list some here as links.) Alternative light sources with all these properties are typically weak and cumbersome. Lasers are widely used by the armed forces in many applications. Lasers can be set to specific, pre-determined frequencies to correspond with a bomb or missile's tracking system. Because the frequency can be set to a range not normally found in natural light settings it is easy for a homing device to find and home in on the signal. Also, lasers can be mounted to weapons and collumated to line up properly with the barrel for targeting purposes. This is especially useful in night combat environments. Some lasers are not in the visible spectrum, and can only be seen using devices that can see infrared, allowing easy targeting for users utilizing night vision devices.

-- DrBob 2001-09-25

Rewritten, to remove redundencies and improve flow -- DrBob

Thanks DrBob. The whole rewriting process in the last few weeks has been great. Geronimo Jones (original author).

Radio lasers?

Can you enlarge on the early "radio lasers" prior to masers? Have you got a reference, a name, anything? This sounds fascinating... The Anome

Ho:YAG/Nd:YAG

The hospital I work at uses Holium YAG in the OR for laser surgery (cutting/coag). Is this the same as Nd:YAG or similar? If it is a seperate type of laser, should it be included in the list? Perhaps even in Laser Applications since it is used for surgery? We use other lasers in the OR as well, but the YAG/Holium is the newest. Nurses like it better then the others because it is smaller, easier to transport and can take more abuse without decalibration issues. Appearantly the larger lasers we use can be decalibrated easily if bumped. I'd love to see a section or article on comparisons of lasers and their characteristics. Specifically regarding application. And diagrams would also be a place for improvement. Keep up the good work. Robert Lee

Ho:YAG is has the same host material as Nd:YAG (YAG=yttrium aluminium garnet), but a different dopant material (holmium instead of neodymium), see information about this in laser construction. This makes it operate at a longer wavelength (2.1 microns instead of 1.06 microns). Probably the best place to add stuff like this is in laser applications. Specific laser information has been on my "To-do in my copious free time" list for a while. -- DrBob 2002-11-17

Laser safety

A while ago, an anomymous user made a number of changes (http://en.wikipedia.org/w/wiki.phtml?title=Laser&diff=2911031&oldid=2909803) in the laser safety classification. The result sounds professional with lots of numbers, but does not agree with what I remember learning in laser-safety instructions. The previous version is what I originally wrote, mostly based on my memory and what I could find on the web.

class I: laser pointers? I was pretty sure that laser pointers are Class II or IIIb, though the latter is controversial because of the associated eye hazard. Class I would give a spot that noone[sic] can see and class IIIa would be too big a spot size.
class II: the lower end of the power range, .39 uW, sounds way too low for visible light (400-700 nm).
class IIIb: it should be "unsafe for the eyes if the beam enters the eye". The phrase frequencies 315 nm to 1 million nanometer (sic) does not sound very scientific. The upper limit of 500 mW is also unrealistic it would be more like 5 mW.

I will revert.

-- Hankwang 09:40, 23 Apr 2004 (UTC)

PS, can everybody please timestamp comments? I added a few.

Definition of a laser

Someone want to elaborate on the reason for using collimated as part of the description of what constitutes a laser—the output from a laser diode is not generally regarded as collimated but everyone agrees they are lasers :-) --lidarman 05:37, 28 Apr 2004 (UTC)

Likewise there are other lasers that aren't particularly coherent or monochromatic, but everyone agrees they are lasers. The problem comes with fitting a one-line common definition to all the variety of the real thing. I'd say leave the description intact but if neccessary clarify further down -- DrBob 15:57, 28 Apr 2004 (UTC)

As I see Hankwang has already done, thanks -- DrBob 16:01, 28 Apr 2004 (UTC)

Even HeNe classroom lasers naturally produce spreading light (due to confocal resonator.) Manufacturers typically add a lens to the output end of the laser tube in order to collimate the beam. Hmmm. Do ANY modern lasers produce collimated light (i.e., use large parallel flat mirrors?)

So what IS a laser? An optical oscillator using a gain-medium? Winston Kock called lasers "sharp tools," since lasers differ from other sources in that their light can be focused to nearly a geometrical point. --Wjbeaty 06:11, Mar 31, 2005 (UTC)

Diffraction?

The beam will eventually spread due to the effect of diffraction but much less than a beam of light generated by other means.

I don't see how this could be diffraction, since it would occur in empty space. anthony (see warning) 03:41, 20 Aug 2004 (UTC)

Diffraction is usually thought of as happening when light hits a slit or some other obstruction, but it also occurs for any beam of finite size propagating in free space. For this reason, you can't focus a beam of light into a spot of infinitly small size, or make a beam which is perfectly collimated.

If you don't like the idea of diffraction in free space, you can think of the laser beam's inevitible[sic] spreading as occurring due to diffraction from the last aperture the beam passes through (e.g. the output coupler mirror of the laser). -- DrBob 15:59, 20 Aug 2004 (UTC)

Well, yeah, I certainly agree that the phenomenon happens I just never heard it referred to as diffraction. Maybe the problem is the term "eventually"? I mean, yes at some point there is diffraction occurring, but this happens at the beginning, not at some point in the future. I'll try to reword without "eventually" I guess. anthony (see warning) 19:26, 20 Aug 2004 (UTC)

The word "eventually" should probably still be used. A collimated beam is not immediately changed to diverging at a certain angle after leaving the lens... there is transition distance in which beam waist varies non-linearly. At the lens, a collimated beam actually is collimated, with an infinite radius of curvature. Then the radius of curvature drops quickly over a relatively short distance, then approaches a fixed constant angle asymptotically. The radius is always positive anywhere away from the lens for a collimated beam, so the beam waist is expanding with distance from the lens, but right at the lens it is infinite.

A perfectly collimated beam cannot be created, due to the effect of diffraction, but a laser beam will spread much less than a beam of light generated by other means.

I think that's more clear. But feel free to reword further. anthony (see warning) 19:32, 20 Aug 2004 (UTC)

Safety issues

Re RPaschotta's addition, safety issues (even knowledgeable operators should not breach safety regulations!)

On paper these regulations sound wonderful, but I wonder whether you have ever tried aligning a Ti:sapphire laser or parametric amplifier with "adequate protection". I dare to say that that is impossible.

These devices are designed such that you cannot get any unexpected reflections during normal alignment, except if you remove parts that have big yellow stickers on them warning you that they are there for protecting you.

Han-Kwang (talk) 20:11, 20 Oct 2004 (UTC)

Severe or permanent eye damage my arse. I shone a laser pointer into my eye for half a minute, on two occasions, without suffering harm. I saw a yellow spot for a while, and had a little dizziness, but they disappeared. Though I wonder if astigmatism had to do with it... What happens when the dopant is removed from the laser? Why aren't there any diamond lasers? lysdexia 02:59, 21 Oct 2004 (UTC)

If it was a class I or II laser pointer, you're not likely to do that much damage (though deliberately staring at a class II is a very bad idea.) Class III and above, I assure you that permanent damage is quite possible (I know people who've suffered retina damage from less than a second of exposure to a class IV beam). Note the human eye and brain is quite adept at glossing over holes in your visual field, so you can be damaged and not know it.

If you remove the dopant from a solid-state laser, you don't have a laser anymore, since it's (usually) electronic transitions in the dopant ions that cause the laser action. If you remove the erbium from Er:glass, you're left with just glass. If you remove the Nd from Nd:YAG, you're left with a fairly boring transparent garnet (YAG) crystal.

Diamond, I believe, isn't very suitable as a host material because it consists of strongly-bonded light atoms (carbon). That tends to cause fast non-radiative (non-light producing) decays from higher energy states, which isn't good for efficient laser action. -- DrBob 04:37, 21 Oct 2004 (UTC)

Nope, I don't know of any class I or II pointers. They come at IIIa and IIIb, and the one I used was the commoner (guess). A physicist saying "quite possible" doesn't give one any brownie points with me. Anyway, you're probably wrong. IIIa's are <5mW. Even Sam's Laser FAQ cites a study that no permanent eye damage occurred from staring at IIIa's for half an hour. My eyes are more damaged—sometimes-dehydrated, I guess—from long hours at modern, large computer screens than any puny laser. *sigh* I could look at my old 11.5" screen almost forever. Can you give a test for hole blindness? There are diamond LEDs. Ooh, can one make a sonic aser from a diamond sample? :) lysdexia 21:25, 20 Dec 2004 (UTC)

I edited the safety stuff again in the new article laser safety and also gave some explanations on the corresponding talk page.

Following the comments by Han-Kwang: Indeed I have aligned Ti:sapphire lasers. Only during the very first stage where the fluorescence is used for a sort of pre-alignment, I had to take the glasses off. This was with the cavity blocked (so for sure no Ti:sapphire lasing) and after checking that no pump light was leaving the case. Concerning parametric amplifiers and oscillators, we have built quite a few of those in my research group at ETH Zürich, partially with very high output powers, and never had to use unsafe practices for that.

Anyway, physicists are used to solve many technical problems, so why shouldn't they be able to solve safety problems as well? With a little thinking, and sometimes some investment of time and money, one normally finds reasonably safe methods.

Besides, anyone is free to accept additional risks for himself. Recommending unsafe practices to others is another thing, which for obvious reasons I strongly recommend to avoid.

RPaschotta 12:16, 30 Oct 2004 (UTC)

Removed parts

I removed this:

A new state of energy, called liquid light, has been found in intense beams propagating through nonlinear optical media, whose electric and magnetic fields alter the refractive index of the medium, an effect called self-focusing, to condense the photons into an ultralow- divergence beam. Such a beam may have an indefinite range, and may eventually be focused to extragalactic distances without significant loss.

Liquid light sounds like pseudoscience and is not documented (nonexistant[sic] article). Self-focusing is a true effect but it only happens while propagating through certain materials, not while propagating through empty space. Focusing and losses are two completely independent things.

Also removed (context: laser projectiles in Star Wars):

Of course, this assumes that what we see is the actual laser beam, rather than a second, retarded effect such as turbulent atmospheric fluorescence or phosphorescence, or particle creation and decay.

The issue is whether you would see a flash of laser light propagating at a few 100 km per hour. The effects above would only affect the duration of the afterglow.

It's only nonexistent on Wikipedia. If that's your criterion for determining what exists, then maybe you should be out of work. I pulled the material back and rewrote it, bulldozing over your ignorance of new physics. (I'm occasionally amazed at how professionals and other authorities are so out of the loop.) Loss can apply to intensity as well: Being able to send a small-enough wavelength beam of enough intensity, one can—I suspect—still maintain a nondiverging beam in space, which is NOT EMPTY!

Laser light can propagate at any velocity. Get with it. Oh, and I'm not too happy about the people who downplayed laser projectiles. After I wrote my rough essay Making Stargate a Reality, I enjoyed finding news stories that confirmed my wishes, dreams, and claims, especially published after my essay was written. If Stargate is fiction, then why do images from the articles I just put in the laser article look just like zat beams or Asgard transporter beams and Gou'ald ring transporter beams? :) I need to get back to that message board to rewrite that essay, deleting a couple of calcuotypos and putting in real isotope decay chains with their outputs... I think substituting the kilometre there for a metre makes the temperature make a lot more sense. :D

For interested parties, here are a few of my feedbacks to Sam's Laser FAQ (I've posted on Scitoys too, and corrected the host a few times!):

Pressure of Light http://repairfaq.ece.drexel.edu/sam/laserioi.htm#ioipol

About your brief pressure of light section, I'll let you in on a little secret to make dreaming funner. The tiny force from a given energy or power light is only due to light's huge speed: That from a massive object at a normal speed would be much larger. People forget that when light is absorbed by any medium (diaelectret, conductor, superconductor, etc.) it acquires a mass and a noncelerity speed given by the medium's refractive index multiplied by celerity. So find a substance with a high-enough refractance, and absorbance, and it will experience a much larger force. With the "infinite" refractive index of atomic- or partonic-degenerate condensates, or black holes, an object may behave like it's reacting off an infinite-mass propellant to be effectively "pushing off space" as some bogus propulsion designs claim. I don't have the equations for this, but I suspect it's right. In order to make a more efficient tractor beam, the subject then must be put into a "condensate sabot". This is only one of dozens upon dozens of breakthrough ideas I've had in the past three years, along with those that allow futuristic scifi devices to work or be understood today.

Ring Lasers http://repairfaq.ece.drexel.edu/sam/laserioi.htm#ioiring

Why must resonators have integer half-waves? Like, couldn't one eliminate the regular minima and nodes by adding a large, high negative harmonic and antiwave, storing /that/ in the resonator, then removing the antiwave when the output is needed?

Wavelength versus Frequency http://repairfaq.ece.drexel.edu/sam/laserioi.htm#ioicav5

Maybe light is given in wavelengths instead of frequencies because the former is easier to grasp and the latter is quite large, not to mention a derived property. At RF, more attention is given to the oscillator than its dimension, though both are common. Hmm, I think I want to abolish frequency from all kinds of serious conversation or discussion: We don't talk about the reciprocal of wavelength, or resolution, do we? (Extending this proposal I'd get rid of gauge, mesh, fine, and grit.) It makes more sense to talk in fundamental properties, so instead one would give the period—the stint—of the wave as a little time for most wavelengths. Now that the frequency f or nu is gotten rid of, light's equation becomes simply and easily c = (l/t)_c. Most times may be tiny, but that's how they are. Because I also want to spurn (abolish!) Latin, the terms in English become swiftness = span/stint, or w = p/t.

-Aut lysdexia 21:25, 20 Dec 2004 (UTC)

Mist

"Some action movies depict security systems using red lasers (and being foiled by the hero, typically using mirrors); the hero may see the path of the beam by sprinkling some flour in the air. It is actually easier to build infrared laser diodes than visible light laser diodes, therefore such systems have no reason to work in visible light."

I've seen this done (in movies) with mist (a fine mist from a spray bottle)---where the laser was 'supposedly' not infrared. Is there a liquid that can glow in the presence of infrared which will make a fine mist like water can?

Anon (207.65.110.121) 13 Nov 2004

There are (expensive) dyes that you can "charge" with visible light (like the hands on your watch) that will light up when illuminated with near-IR light. You'd have to charge the contents of the spray bottle a few minutes beforehand and I doubt that the light would be bright enough to see. Han-Kwang (talk) 19:33, 14 Nov 2004 (UTC)

- I would really like to see these dyes. Are they multiple photon absorbing? I guess they'd have to be otherwise you're creating energy; light emission is always red-shifted (lower in energy) from the excitation. It can theoretically be the same wavelength, but every lumophor I've seen has a stokes shift. By implication they are also phosphorescent (like the hands of a watch) which can not emit light that is not red-shifted because the process involes an exothermic internal conversion to the triplet state. At any rate, can you provide a link or something? I'm very curious how you can convert near-IR light into visible light by phosphorescence... Fearofcarpet 18:06, 18 Mar 2005 (UTC)

I haven't actually encountered this sort of dye, but I would imagine that the "charging" operation is to put the dye in an meta-stable excited state such that absorbing an infrared photon causes the state to decay and emit a visible photon. --Carnildo 21:00, 18 Mar 2005 (UTC)

"Needs attention"

I listed this article on Wikipedia:Pages needing attention because I think the most recent round of edits could be better integrated into the article. Nothing horribly wrong, but some more eyes looking at it couldn't hurt. Gwimpey 04:50, Dec 21, 2004 (UTC)

Sorry but don't like this "liquid light" stuff

I removed the paragraph[] "In 2002, a Spanish research team led by Humberto Michinel came up with computer simulations showing intense beams sent through special nonlinear optics, whose electric and magnetic fields made a concentric refractive index gradient in the medium as seen in normal self-focusing, but were slightly slacked in the beam's core to prevent a convergent-divergent beam from forming. The result was their discovery of a new state of energy, liquid light or light condensate, obeying viscous fluid properties such as surface tension and vorticity, whereby the beam could be split into drops and droplets if it hit a surface. [1] (http://www.aip.org/pnu/2002/596.html) [2] (http://www.newscientist.com/article.ns?id=dn2497)"

from the article for 2 reasons. First, it is an entirely theoretical hypothesis and has never been observed in a laboratory experiment. Second, this is a general article on lasers and a buzzwordy unproven cutting edge hypothesis does not belong here. Also, I tend to strongly doubt its relevance and or importance; it's been like three years since this paper came out and I've heard nothing else about it. That, to me, = dead end minor curiosity in a backwater of laser research not "fundamental breakthrough". --Deglr6328 19:49, 21 Dec 2004 (UTC)

I did not word it to claim that it was a shown and known entity. Read more carefully. It was part of the beginning sections supposing the properties of different light beams. The idea to put in liquid light followed from the filament which was found much earlier, yet you kept that in. Why? Different forms of a laser beam are relevant. The discoveries that inversions weren't needed to lase were much longer ago, and I doubt that you heard anything about it; if so, why wouldn't you or other laser experts write about it, and keep claiming that inversion is part of lasing operation? Whether or not you heard of something doesn't determine whether you keep something in an article. And it's only been two-and-a-half years, not three. More time passed before the second time noninversion lasing was seen and reported again, which you apparently missed also. lysdexia 22:43, 21 Dec 2004 (UTC)

Stop editing the talk pages with your grammar "corrections"! You've been warned about this many times and I've added my name to the consenting opinion on the request for comment page about you. --Deglr6328 22:21, 21 Dec 2004 (UTC)

The page includes the Wikipedia variance that talk pages are fair game. If you were more familiar with reality, you wouldn't be complaining. If you don't want to be corrected, write correctly. lysdexia 22:43, 21 Dec 2004 (UTC)

I see now you're in the habit of removing my comments from the talk page? --> "The filament mentions are experimentally proven phenomena and are commonly known and used. The "liquid light" term dubbed by press release phenomenon is not even proven. It dosen't belong here. Also to call it a "new form of energy" is insanely pseudoscientific."--Deglr6328 22:21, 21 Dec 2004 (UTC)"

I've had enough of dealing with your nonsense. You're so close to being listed on an arbitration page.--Deglr6328 22:51, 21 Dec 2004 (UTC)

What did I remove? You didn't even finish that quotation. I never called it a new form of energy. Why can't you read right? Why don't you ever try to argue back instead of making threats that have no bearing? lysdexia 23:47, 21 Dec 2004 (UTC)

That was a slip of the cursor, an accident. I'm still waiting for you to answer my above. lysdexia 23:59, 21 Dec 2004 (UTC)

YOU deleted the answer! And now you're ignoring it! I think we're done here. Also there is nothing "choppy" about the way the article was left relative to what it was before, I've merely consolidated sections talking about quantum effects etc. --Deglr6328 01:01, 22 Dec 2004 (UTC)

I expanded the above just after your answer. Don't you notice it's a lot longer? Both parts of your "answer" weren't enough. If the filaments were known, why was there never any mention of them with divergence? Yes, it's choppy now. The starts and ends of those paragraphs no longer match or flow, your image is in the wrong place, you removed emphasis on nonlinear exceptions, chirping and filamenting are unrelated, you removed the fact of a turnaround, you put needless emphasis on higher powers and a personal assumption of deadliness, you left the lie and red herring that shows always and definitely used lasers, you left the false assumptions in the same section, you detracted from the stated purpose of the section, you orphaned references, and most importantly you degeneralised your "general article" claim. lysdexia 03:51, 22 Dec 2004 (UTC)

What are you talking about!?! Ugh, you're so incomprehensible most of the time I can't even decipher your complaints. CPA and filamentation ARE related, you NEED to use CPA to achieve the fluences necessary to start kerr lensing and 'filamentation' in air, again if you knew something about lasers you'd know this. And the image is in exactly the right place, right next to talk of CPA which introduced a huge increase in pulse powers. And how did I "orphan refrences"? --Deglr6328 05:29, 22 Dec 2004 (UTC)

I'm only "incomprehensible" to you. This is your only excuse for not answering me. You pasted lines from other paragraphs into new paragraphs, where they didn't belong. Do you not understand what start and end mean? My main problem with your change, in the beginning section, was that you didn't allow or played down the qualification that light beams behave differently than that commonly claimed in popular or even technical literature. What you said here wasn't written there, but they are still unrelated because chirping is only one way of filamenting, just like how I needed to write in that inversion is only one way of lasing. You have problems understanding causality and necessity. You cannot find anything to support your "NEED"ed claim. Look where I put the image in my edit. It belongs there with all the lasers. You tell absolutely no connection between that image and section, and only a minor part of the image is relevant there. I think you also removed where I put 30 GW as the air threshold, and you put in terawatts twice, still being unrelated to the filament section, which was fine when I put it in. The article is very choppy now; it's top- and bottom-heavy. The references no longer correspond with the article's content. In your edit summary, you thought I wrote reverting when I wrote rewriting. You put in a wholly-needless section on uses when there already was a separate article for them. With all of your misspellings and understanding problems, maybe you've spent enough time with bright lasers. lysdexia 03:39, 29 Dec 2004 (UTC)

Put the disputed paragraph on a new page called 'liquid light', and put the rider on it that there's no practical experimental evidence for it. Dan100 15:35, Dec 22, 2004 (UTC)

Laser article not really the place to validate/vet childhood comic book laser fantasies

I removed the section

"Many assumptions are made when criticising an effect in a fictional, future, or alternate universe: Not all elements and conditions of the effect are given or known, and as follows it is unwise to apply one's limited knowledge and prejudices to what is seen as new, strange, or different. For example, most viewers are unaware of nonlinear and nonconservative physical processes: an intense beam increases its medium's refractive index, slowing itself down; a medium has resonant or absorptive peak wavelengths (or frequencies), causing a phase change to materialise from certain applied energies; an intense beam's EM fields polarise nearby materials, drawing them in—the mysterious beam with unknown boundary conditions on Earth would be influenced by the ubiquitous amounts of silicate and aluminate dust floating in the air, perhaps giving rise to ball lightning. Interstellar and intergalactic space are not even perfect vacua as beams have hydrogen, the microwave background, cosmic rays, dark matter, and virtual particles to interact with. In other words, if a particular influence is invisible, its collisions with other invisible or less-visible influences may give rise to visible influences which are hard to explain without knowing what they were. Criticism about known implementations of radiating systems is safer."

Why did I remove it? It's horrible. A small section on popular misconceptions of lasers does not at all need an overly pedantic, grasping and rediculous[sic] discussion of all the possible caveats which might allow the misconceptions to be true (ball lightning and ubiquitous silicate and aluminate? virtual particles? you're kidding right?)--Deglr6328 20:30, 21 Dec 2004 (UTC)

I never wrote anything to allow misconceptions to be true! It was an NPOV exposition of common and uncommon interferences to directed energy, which may or may not actually be a laser beam, which was in response to misconceptions surrounding a laser beam. If you want to make the article more relevant, fine, but you're showing the stupid behaviour that so many other "authoritative" editors have: not rewriting, making, or splitting articles, but deleting from them entirely when they are relevant and interesting. lysdexia 22:43, 21 Dec 2004 (UTC)

Not only is the paragraph NOT relevant or interesting, it's factually incorrect and a bit crankish too. Let's look at the line "an intense beam's EM fields polarise nearby materials, drawing them in—the mysterious beam with unknown boundary conditions on Earth would be influenced by the ubiquitous amounts of silicate and aluminate dust floating in the air, perhaps giving rise to ball lightning." I can't even tell what you're trying to say there and it looks like crazy rambling with some scientific words thrown in to lend an air of plausibility so far as I can see. Now let's take the sentence "Interstellar and intergalactic space are not even perfect vacua as beams have hydrogen, the microwave background, cosmic rays, dark matter, and virtual particles to interact with." Now, anyone who knows anything about lasers could spot this for the kookery that it is. Firstly the concentration of H in interstellar space is phenomenally low. Like, 2-3 atoms/m^3 low. Far below what is needed to make a beam visible. Second, cosmic rays are even fewer. Third, dark matter?!? We dont even know what it is let alone the intensity of a laser it would take to interact with it. Fourth, virtual particles are created and destroyed on the Plank scale; we have no lasers in existence which are powerful enough to be capable of forcing virtual particles out of the vacuum (this takes something like 10^28 W/cm^2 if I recall, an insanely high power). Now, if you think I'm showing "stupid behaviour that so many other 'authoritative' editors have" been removing the factually incorrect and ludicrous additions you've made to the article then I'm awfully sorry for that, but it's what should be done. Oh by the way, I work here, and while that sure doesn't automatically make me some all knowing laser guru, I do think I know a thing or two about them.--Deglr6328 22:44, 21 Dec 2004 (UTC)

Okay, bub, if you don't know what a sentence is trying to say, then have you tried using a question? It's when you put out your confusion in words so you can get rid of it. Your next complaint is again your missing the point of the misconceptions section, especially that of my additions which I already wrote to you earlier on this page. I wrote nothing about a light beam scattering off space debris to become visible solely; I wrote nothing about a light or laser beam having to hit such debris to become visible. Reread that sentence. It was about a so-called vacuum for laser beams, and it was about so-called laser beams. What does it take to know anything about dark matter or anything else in space? Based on how larger systems behave against known gravitic and inertial forces, the concentration of dark matter is projected to increase from the stellar to the extragalactic scale. Are you forgetting what section you're talking about? It was about supposed lasers in the media. You haven't yet made an argument against talking about anything related to lasers, media included, and that is what a general article about lasers should have. lysdexia 23:47, 21 Dec 2004 (UTC)

That paragraph is pretty much nonsense. Has no place on wikipedia. Dan100 15:39, Dec 22, 2004 (UTC)

I know much about lasers and optics, and I fully agree with that. RPaschotta 16:14, 25 Dec 2004 (UTC)

I've been busy with other things than Wikipedia but I fully support Deglr6328 and I think that the contributions by Lysdexia have no place here since they do not represent common consensus in the field. The "article needs work" tag is not necessary in this version. Han-Kwang (talk) 21:12, 25 Dec 2004 (UTC) (Ph.D. in laser spectroscopy and nonlinear optics)

Support and elaborate on your accusations. Common consensus was never a prerequisite for articles' content. It's not nonsense, and it's self-explanatory. The material was important and relevant to popular misconceptions, and removing it is like neutering the article. He left my clause about criticisms of depictions in the media, yet there isn't an explanation any more. I made many contributions to the article which were kept or edited, which were against the knowledge of laser experts throughout this talk page and which could not be argued against. And here, there are no arguments to support removing the rest. Ye are merely making stuff up. I'll put the attention tag back up. lysdexia 03:39, 29 Dec 2004 (UTC)

Discussing with you is like explaining to a 4-year old why an orange is not a pear. I am not going to waste my time with that. Han-Kwang (talk) 20:50, 31 Dec 2004 (UTC)

It doesn't even read like original research -- more like original speculation by someone with a strong grasp of scientific buzzwords. --Carnildo 01:27, 5 Jan 2005 (UTC)

Laser applications

Laser applications needs a lot of work. It currently has three small sections on the normal applications of lasers, and a bunch of sections on the military uses of lasers. The average reader is much more likely to come into contact with a laser when it's used to scan their groceries than on the receiving end of a Death ray, and it would be good for the article to reflect that. The scientific section only lists four applications. User:Brockert/sig 22:24, Jan 2, 2005 (UTC)

3 or 4 quantum levels

From article:

...those which involve three or four energy levels rather than two make better lasers because the electrons are kept above the ground state...

The given reason for using 3 or 4 quantum level systems for lasers does not agree with my understanding of the physics. AFAIK, the idea is that lasing occurs when there is population inversion (of electrons) between two energy levels whose separation is equal to the energy of one photon of the light in question. If you only have 2 levels, then when a photon is emitted, an electron is moved from the higher level to the lower level, which reduced the population inversion. With 3 levels, the lower level can itself then decay quickly to the ground state below, which removed population from the level at the bottom of the optical-wavelength gap. Reducing the population in the lower level increses the populatino inversion, increasing the gain of the lasing material. Having electrons in the ground state is not itself a problem, unless the ground state is also the lower state of the optical-transition involving in lasing, in which cases population in the lower (ground) state reduced the population inversion and thus reduces the gain. Having more electrons in the ground state is actually good in some cases, as it makes pumping more effective, wheras having all the population in a relatively stable upper level that did not increase population inversion would be bad, if the pumping did not promote electrons from that level.

I fully concur. Go ahead and change it. (ps. sign your edits plz. :o)--Deglr6328 21:32, 18 Mar 2005 (UTC)

coherent/incoherent

I'm going to do something about "coherence," particularly the diagrams. But first a nitpicker question. Suppose we sequentially reflect some laser light from several frosted screens. Should we call the resulting wave "coherent?" After all, the phase difference between any two sampled points in the wave is not changing with time. But the wave itself is a mess, and doesn't really fall under the description of "coherent light" that most people use. Does that make it incoherent, or is there a more appropriate term? --Wjbeaty 02:10, Mar 23, 2005 (UTC)

I think the diagrams there are quite lovely actually. What is wrong with them exactly?--Deglr6328 05:57, 23 Mar 2005 (UTC)

The object of a diagram is to educate, not decorate. I'd rather have a non-lovely diagram which gives me insights into the physics.

Back in school, when I finally understood the nature of spatial/temporal laser coherence, I realized that my original misunderstandings had mostly been caused by these exact diagrams, and they misled me because they purport to explain coherence, but instead they only explained phase difference.

Also, neither light waves nor water waves look anything like these transverse waves on strings. The "parallel pieces of string" concept leads us away from understanding coherence, so the diagrams form a learning barrier, not a learning aid.

To explain coherence, the waves in the diagram must superpose, rather than existing on separate pieces of string, i.e. they must all be added together to become one single wave on one single string.

Now the real question is: can I come up with a "coherence" diagram without resorting to mpeg movies.--Wjbeaty 23:52, Mar 23, 2005 (UTC)

It's called "abstraction".--Deglr6328 00:52, 24 Mar 2005 (UTC)

Rinky-dink

Okay, I've mildly tinkered with part of one section of the article, whilst also reading this bit about lasers [3] (http://www.vectorsite.net/v2005m04.html) on Greg Goebel's wonderful site. With regards to the cliche about cat burglars spraying mist in the path of 'security lasers' - and I assume the writer was thinking about the tightly-clad buttocks of Catherine Zeta Jones, in her 1999 film "Entrapment" - I believe this gag was first used in one of the early Pink Panther films, specifically the 1963 original. However, I'm not sure if it wasn't the 1975 "The Return of the Pink Panther" or the 1976 "The Pink Panther Strikes Back". It's only a short, juvenile trivia point, which I would enter as a dashed aside - like this - but it would be nice to be sure. Short of spending a week downloading the films with Emule or paying money to rent the films, something which I am not prepared to do, I have no way to verify this for definite, i.e. to see it with my own eyes. I pass the torch on, to you. Yes, you.-Ashley Pomeroy

Great picture, by the way; nothing says science more than earnest-looking young men wearing goggles whilst staring at frickin' laser beams. They're so Devo!-Ashley Pomeroy 11:54, 6 Apr 2005 (UTC)

Laser Classification Reference

For anyone that would like to revise/improve the laser classifications, here's the source with some comments:

Excerpts from the Center for Devices and Radiological Health (CDRH) regulation 21 CFR 1040.10 and 21 CFR 1040.11, verbatim, comments italicized: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?FR=1040.10

TITLE 21--FOOD AND DRUGS

CHAPTER I--FOOD AND DRUG ADMINISTRATION

DEPARTMENT OF HEALTH AND HUMAN SERVICES

SUBCHAPTER J - RADIOLOGICAL HEALTH

Sec. 1040.10 Laser products.

[...]

(What the parameters k1 and k2 are for any wavelength) (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.034.pdf) (What k1, k2 are for selected wavelengths) (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.035.pdf)

(5) Class I laser product means any laser product that does not permit access during the operation to levels of laser radiation in excess of the accessible emission limits contained in table I of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.031.pdf) (4 wavelength ranges spanning 180nm-1000um, divided up into exposure durations, then limited based on radient energy, power, exposure, radiance, or integrated radience)

1 Class I levels of laser radiation are not considered to be hazardous.

(6) Class IIa laser product means any laser product that permits human access during operation to levels of visible laser radiation in excess of the accessible emission limits contained in table I, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in table II-A of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.032.pdf) more-or-less says: all the same as class I, except visible (400-710nm), where the emission limits are 3.9 uW (over >1000 s)

2 Class IIa levels of laser radiation are not considered to be hazardous if viewed for any period of time less than or equal to 1×10 3 seconds but are considered to be a chronic viewing hazard for any period of time greater than 1×10 3 seconds.

(7) Class II laser product means any laser product that permits human access during operation to levels of visible laser radiation in excess of the accessible emission limits contained in table II-A, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in table II of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.032.pdf) more-or-less says: all the same as class I, except visible (400-710nm), where the emission limits are 1.0 mW (over >250 ms)

3 Class II levels of laser radiation are considered to be a chronic viewing hazard.

(8) Class IIIa laser product means any laser product that permits human access during operation to levels of visible laser radiation in excess of the accessible emission limits contained in table II, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in table III-A of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.033.pdf) more-or-less says: all the same as class I, except visible (400-710nm), where the emission limits are 5.0 mW (over >3.8 × 10⁻⁴ s)

4 Class IIIa levels of laser radiation are considered to be, depending upon the irradiance, either an acute intrabeam viewing hazard or chronic viewing hazard, and an acute viewing hazard if viewed directly with optical instruments.

(9) Class IIIb laser product means any laser product that permits human access during operation to levels of laser radiation in excess of the accessible emission limits of table III-A, but does not permit human access during operation to levels of laser radiation in excess of the accessible emission limits contained in table III-B of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.033.pdf) lots-o-parameters, but says for >400nm, 500mW is the limit; 315-400nm, 495mW limit; 302.4-315nm, 1.5mW × 10^{(λ−302.4)/5} limit; 180-302.4nm, 1.5mW limit

5 Class IIIb levels of laser radiation are considered to be an acute hazard to the skin and eyes from direct radiation. e.g. w/o collimating optics like IIIa

(10) Class III laser product means any Class IIIa or Class IIIb laser product.

(11) Class IV laser product means any laser that permits human access during operation to levels of laser radiation in excess of the accessible emission limits contained in table III-B of paragraph (d) of this section. (http://www.access.gpo.gov/ecfr/graphics/pdfs/er01fe93.033.pdf) anything beyond a IIIb

6 Class IV levels of laser radiation are considered to be an acute hazard to the skin and eyes from direct and scattered radiation.

Prometheus235 15:16, 31 May 2005 (UTC)

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