Talk:Laser/Archive 2

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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. —Ben Brockert (42) UE News 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 [1] 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) (What k1, k2 are for selected wavelengths)

(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. (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. 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. 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. 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. 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. 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)