CH3F Laser Pumped with a Continuously Tunable, Multi-Atmosphere CO2 Laser

While very powerful, narrow bandwidth, pulsed FIR lasers are being constructed for plasma diagnosis it is striking to observe that a very small number of rotational transitions of very few molecules are under investigation. This comes from the fact that many conditions must be fulfilled to obtain efficient pulsed FIR laser emission [1]. One of the most important is that the molecule used must be quite simple in order that the ground absorbing state contains a good fraction of the population of the molecules and that FIR reabsorption from rotational transitions of the ground state be negligible. Furthermore, a near coincidence is required between an absorption line of the molecule and an emission line of the CO2-TEA laser. If the first condition is unavoidable the second one might be circumvented by using a continuously tunable multi-atmosphere CO2 laser. Then it should be possible to pump a molecule which would be a good candidate on most of its vibrational rotational absorption lines. Let us take for example the CH3F molecule which has only been pumped via two of its absorption lines by the CO2-TEA laser (the Q (12) and P (32) of the C-F strech mode). The Q branch of CH3F is situated in a part of the spectrum contained between the 9P18 and 9P36 line of the CO2 molecule. In this branch, there are nearly forty CH3F absorption lines which could produce as much efficient millimeter and submillimeter lines. Some other lines in the P and R branches are also accessible with other parts of the CO2 laser spectrum, but they would lead to the same FIR lines.