# Spectrum of generic $\mathrm{CO_2}$ laser

It is often quoted, that it's emission is 10.6um. But we also know that CO2 lasers have huge number of possible emission lines in 2 main bands: 10.6um and 9.6/9.4um.

But what is emission spectra of generic sealed tube CO2 laser (let's say ~1m long, ~40W CW) without any line selection devices?

Should I expect single line with highest gain, jumps between 2 neighbor lines, or simultaneous emission from all of them from ether single or both bands?

I need this for optimization of CO2 laser collimation optics.

It sounds like you have a particular laser, and you don't know what spectrum it's emitting? The best way to answer this question would be to measure your emission with a spectrometer, but if you're asking here, that implies you don't have one.

Let's pretend you got your laser from Coherent. You'll notice that different cavity designs can pick out different emission lines (9.2 $\mu$m, 10.2 $\mu$m, 10.6 $\mu$m, etc), so just knowing that it's a CO$_2$ laser isn't enough to tell you which line(s) are emitted. The spectrum emitted by any one of these models is roughly specified in its datasheet. For example, the GEM-100A 10.6 $\mu$m model is specified to emit from 10.55-10.63 $\mu$m, whereas the 9.6 $\mu$m model is specified to emit from 9.5 to 9.7 $\mu$m.

Where did you get your laser? Can you really not get a datasheet for it? Can you get a spectrometer? Can you build a spectrometer? I've built spectrometers for the visible with gratings and lenses, do you have gratings, lenses, mirrors, and sensors available for ~10 $\mu$m?

• This is Chinese glass sealed 40W CO2 laser. Building spectrometer for 10um range might be quite challenging task ) – BarsMonster Nov 23 '14 at 14:45
• What optics/budget do you have access to? – Andrew Nov 23 '14 at 14:59
• Oh, that reminds me. Do you know any other specifications of the tube? Assuming your tube only lases on one line, we might be able to say something about the linewidth based on the tube pressure. – Andrew Nov 24 '14 at 16:05
• I only have few ZnSe lenses. So for a rough spectrometer I still need suitable diffraction grating and detector. Regarding the specs - there are nothing else, Chinese manufacturers only care about raw output power, that's it. If it is only one line - that would already answer my question, but I am not sure it supposed to be 1 line without line selection. – BarsMonster Nov 25 '14 at 7:50
• What are you planning to use the laser for? Cutting? I ask, because whatever it is used for might function as a "detector" while you align the collimation optics. Are you trying to design better lenses, or just determine where to put them to collimate your beam? – Andrew Nov 29 '14 at 18:32

You should stimulate emission from the entire ro-vibrational spectrum. There are a few modes in the P branch that will dominate, just because they have the largest oscillator strength. They're close enough in frequency that your output should be a homogeneously broadened peak centered around 10.6 $\mu$m. If you wanted to put an etalon or diffraction grating with 1 cm$^{-1}$ resolution at the output of the cavity, then you could pick out any of the transitions.

• Also, your cavity should obviously be aligned to support the modes from the part of the spectrum you want. – Nick Nov 21 '14 at 20:28
• It's a sealed tube - if I put anything at the output I'll loose power. The question is "how broad" could it be? Is it 0.1um wide? 1um wide? – BarsMonster Nov 22 '14 at 2:19