HeNe through a diffraction grating...

[Trevor]

I got curious tonight and decided to take a picture of my bare-tube HeNe while it was running - through a diffraction grating. It yielded quite an interesting photo that includes all of the wavelengths that HeNe's lase at (632.8, 611.8, 604, 594, and 543) represented as rather bright lines, plus quite a few extras that I assume are just emissions from the plasma.

It's a fun illustration of how all those wavelengths are present in the cavity, but the optics and cavity length determine what wavelength the HeNe actually lases at. Interesting.

The original high resolution version can be had here:

http://www.safelasers.org/photos/HeNe/IMG_2883.JPG

-Trevor

 

[532 with Envy]

Very cool picture! I knew that the optics helped determine the wavelength but hadn't read that the cavity length made a difference. So could you just take the optics off a 632.8 tube and replace the optics to get another wavelength or does the cavity have to be a certain length as well?