Sodium Vapor Lamps (low pressure) for spectral calibration and diffraction work

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Discussion Overview

The discussion centers around the use of low pressure sodium vapor lamps for spectral calibration and diffraction work, particularly in the context of finding suitable substitutes for these lamps after their discontinuation by manufacturers. Participants explore the characteristics and requirements for a quasi-coherent visible light source with closely spaced spectral lines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express curiosity about the lack of available low pressure sodium vapor lamps for laboratory use and seek alternatives.
  • One participant questions the definition of a "reasonable substitute" and challenges the effectiveness of typical discharge tubes used in physics labs.
  • Cost, simplicity of implementation, and ease of use are highlighted as important factors in selecting a suitable light source.
  • Participants mention the sodium lines at 588.9950 nm and 589.5924 nm as ideal for testing spectrometers due to their intensity and close spacing.
  • There is a discussion about the coherence length of non-laser sources and the specific requirements for the light source in relation to a heterodyne spatial spectrometer design.
  • Some participants suggest high-pressure sodium lamps, mercury, and neon lamps as potential alternatives, while noting the limitations of each option, such as Lorentz broadening in high-pressure lamps.
  • One participant mentions finding a neon lamp with intense lines around 533 nm and expresses interest in the coherency of arc sources.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a suitable substitute for low pressure sodium vapor lamps, with multiple competing views and suggestions remaining unresolved.

Contextual Notes

Participants express uncertainty regarding the coherence properties of various lamp types and the implications of spectral line separation on instrument resolution. There are also references to the limitations of available sources and the need for further exploration of spectral characteristics.

fsonnichsen
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Just curious if anyone out there is using the old low pressure sodium vapor lamps for spectral calibration and diffraction work. I was surprised that I do not see any bench ready laboratory lamps from the usual vendors. I understand that the last manufacturer of the low pressure bulbs, Philips, has discontinued them.
They were quite handy for testing spectrometers splitting the two Na peaks at about 0.6nm.

Does anyone know a reasonable substitute for a quasi-coherent VIS, double peak source without a lot of clutter on either side of the peaks?
thanks
fritz
 
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Define "reasonable substitute".

What's wrong with the typical discharge tubes that are often used in physics labs?

Zz.
 
Cost. simplicity of implementation. Ease of use. There are probably some HV discharge lamps out there with a closely spaced and intense pair of lines in the VIS regions separated by less than a few nm. I have used deuterium and mercury for single lines.
I don't quite grasp the coherence length for non-laser source but I do know the sodium worked well here. Not sure of the others.

fs
 
fsonnichsen said:
Cost. simplicity of implementation. Ease of use.

Er... yeah, they're not that expensive. They are simple to use. And you flick a switch, it glows! How much more "ease of use" than that?

There are probably some HV discharge lamps out there with a closely spaced and intense pair of lines in the VIS regions separated by less than a few nm. I have used deuterium and mercury for single lines.

I have no idea what you are talking about here. What "lines"? If these are the spectral lines, the line separation depends on the resolution of your instrument! I mean, if I want the lines to be more separated, I can crudely use a diffraction grating with more lines/mm. There, larger separation.

Zz.
 
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By sodium lines I mean the pair of lines at 588.9950 and 589.5924 . (Yep-i always have to look that up!)
That is a great spacing because it is only 0.5nm----a good test for a spectrometer and they are intense, isolated from other lines, and nearly equal in height.

I am working with a "heterodyne spatial" spectrometer design--basically a form or interferometer---and the bandwidth is very narrow but the optical throughput is comparatively high and one--apparently-can get great resolution.

So I am seeking an intense pair of VIS lines at such a spacing for my source. And-drat--the source needs to be quazi-coherent. :frown: I am guessing a few mm.

I don't really want to get crazy with setting up some type of emission experiment for the lines--just want a reliable source so I can spend my time worrying about the spectrometer design. (feel like I am acting spoiled here ).:smile: Unfortunately I don't usually think much about sources-until now. Of course that is the fun of it. Amazing the important things that never appear in the textbooks.

thanks
fritz
 
ZapperZ said:
Er... yeah, they're not that expensive. They are simple to use. And you flick a switch, it glows! How much more "ease of use" than that?

I don't think you are going to find anything cheaper and easier to use.
 
fsonnichsen said:
By sodium lines I mean the pair of lines at 588.9950 and 589.5924 . (Yep-i always have to look that up!)
That is a great spacing because it is only 0.5nm----a good test for a spectrometer and they are intense, isolated from other lines, and nearly equal in height.
I am working with a "heterodyne spatial" spectrometer design--basically a form or interferometer---and the bandwidth is very narrow but the optical throughput is comparatively high and one--apparently-can get great resolution.
So I am seeking an intense pair of VIS lines at such a spacing for my source. And-drat--the source needs to be quazi-coherent. :frown: I am guessing a few mm.
I don't really want to get crazy with setting up some type of emission experiment for the lines--just want a reliable source so I can spend my time worrying about the spectrometer design. (feel like I am acting spoiled here ).:smile: Unfortunately I don't usually think much about sources-until now. Of course that is the fun of it. Amazing the important things that never appear in the textbooks.

thanks
fritz

Not sure why you can't just switch to a high-pressure Sodium lamp, but Hg I spectra also has a doublet candidate around 579 nm. Neon also has a lot of closely spaced lines in the region you are interested in (https://physics.nist.gov/cgi-bin/AS...=on&enrg_out=on&J_out=on&submit=Retrieve+Data).

Short arc sources are in general reasonably spatially coherent, but if you have special requirements you will probably have to spatial filter the source beam.
 
Andy
I think the high pressure lamps have a lot of Lorentz broadening. However I was able to locate a Ne lamp this weekend and will try it today. There are a couple of intense lines around 533nm.
I have not worked with arc sources but your comment on the coherency is interesting--I will read up on them.
Thanks!
Fritz
 
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Yes-their spectra for the Ne lamp shows peaks starting at 533.06.
I assume it has a reasonable coherency given that it is a gas lamp.

I guess the Na lamp is history save for a few bulbs left in old inventory.

Thanks
fritz
 

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