Talk:Helium-neon laser
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I have added references and removed a lot of erroneous material from this article. In particular, the original article described the various electron configurations (2s, 3p, etc...) as states, and talked about transitions INTO the 1s, 2s, and other sub-valence levels. I have removed these incorrect statements and their accompanying figure, and replaced them with proper state descriptions for the 633nm line. I did not have time to look up which states are actually involved in the IR and other transitions, and encourage such additions in the future.
Please visit the NIST atomic spectra database if interested in finding real atomic transitions with appropriate labels. In particular, look up Ne 0, for the NIST energy for the HeNe transition, 2s22p5(2P1/2)3p - 2s22p5(2P1/2)5s).
I have also added scholarly articles and web links where appropriate. Future edits should perhaps move Sam's FAQ link to be featured earlier in the article, due to it's excellent, detailed description of HeNe lasers. Also, the article is getting long and may warrant some organizational editing. Az7997 19:08, 14 August 2006 (UTC)
The references are nice but they will be more appropriate for an article about stabilized lasers. It's on my to-do list if someone else doesn't beat me to it. Paul Koning
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- The references are for stabilized HeNe lasers, and are quite appropriate. The use of stabilized HeNe lasers is so common, mention in this article is warranted. It is also important to note that HeNe lasers are used for stabilized sources, which considerably improve upon the (already narrow) HeNe frequency spread. Az7997 18:54, 9 October 2006 (UTC)
- What I meant is that stabilized lasers are a large enough topic to justify an article of its own, in which case the references that talk about stabilized lasers would fit there. Paul Koning 23:00, 9 February 2007 (UTC)
- The references are for stabilized HeNe lasers, and are quite appropriate. The use of stabilized HeNe lasers is so common, mention in this article is warranted. It is also important to note that HeNe lasers are used for stabilized sources, which considerably improve upon the (already narrow) HeNe frequency spread. Az7997 18:54, 9 October 2006 (UTC)
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[edit] Jan 2007 updates
I fixed what were, according to my references, some errors in the energy level nomenclature. This could be a case of differences between physicist and chemist notation, so let me know and we can do both. I also added some refs and firmed up some of the numbers on the laser construction itself as well as moved the pics around to line up and removed thumb sizing per MOS. --Patrick Berry 19:59, 30 January 2007 (UTC)
[edit] Stability
There are many causes of frequency error; temperature change is one of them. The recently added cross-reference to Frequency_drift isn't all that appropriate for "frequency stabilized" because the referenced article doesn't contain anything that applies to stabilized lasers. Paul Koning 21:47, 9 March 2007 (UTC)
[edit] The typical 633 nm wavelength red output of a HeNe laser actually has a much lower gain compared to other wavelengths..
The article states:
The typical 633 nm wavelength red output of a HeNe laser actually has a much lower gain compared to other wavelengths such as the 1.15 μm and 3.39 μm lines, but these can be suppressed by choosing cavity mirrors with optical coatings that reflect only the desired wavelengths.
If the red (633nm) emission has lower gain, why HeNe lasers, by default, emit red and not infra-red?
May be, it should be written
".., but these are usually suppressed by selective cavity mirrors.."
dima 00:04, 2 April 2007 (UTC)
- Coated mirrors (dielectric mirrors) are "selective mirrors", they typically reflect well just around the desired wavelength. Even broadband dielectric mirrors reflect just perhaps 100 nm around the centre wavelength.--Danh 06:51, 3 April 2007 (UTC)
[edit] Pressure a function of cavity length?
I'm puzzled by the assertion that the gas pressure depends on cavity length. It doesn't match what I read in my favorite reference (thesis by Schellekens on stabilized lasers) though admittedly he only talks about it briefly and specifically mentions optimal pressure for a particular cavity length. But the numbers he quotes are in the 260 to 400 Pa range for a 13 cm cavity, i.e., substantially lower. I'm also wondering what physical mechanism justifies having pressure proportional to the length. Finally, if that's really true, is it cavity length or discharge tube length? They are quite different for iodine-stabilized lasers. Paul Koning 21:12, 4 June 2007 (UTC)
- From looking at the reference given, I would say that it is the discharge tube length as thats where the gas is. I think that one could probably find references for a range of 'optimal' pressures, each for different situations. --Chuck Sirloin 21:16, 4 June 2007 (UTC)
[edit] Gain bandwidth
The article states: "The gain bandwidth of the laser is dominated by Doppler broadening, and is quite narrow at around 1.5 GHz for the 633nm transition[5][7] lasing on a single longitudinal mode." I am not so sure that the phrase "lasing on a single longitudinal mode" belongs here, because the gain bandwidth should be about 1.5 GHz whether it is lasing on one mode or several. Or are you implying that mode competition will, in effect, change the gain bandwidth? It will turn the smooth gain profile into something else, but I was under the impression that this is not part of the usual definition of the gain bandwidth. Any comments? --JckS 01:40, 19 September 2007 (UTC)
