Far-infrared raman laser with high intensity laser pumping

Theoretical and experimental results are presented for a pulsed far-infrared (FIR) molecular gas laser with high intensity laser pumping. In these FIR lasers, high intensity pumping is found to produce stimulated Raman emission at very large offsets (up to 30 GHz) from resonance with the intermediate state. A theoretical, density matrix model is developed for these lasers to account for simultaneous Raman emission on rotational levels in the ground and excited vibrational states (double Raman resonance). This theoretical approach is necessary in the case of off-resonant, high intensity pumping. Theory predicts the FIR emission frequency, the FIR laser gain, and the pump threshold intensity as a function of pump laser frequency. Experimental results are obtained on
P
-,
Q
-, and
R
-branch transitions in
¹²
CH
3
F and
¹³
CH
3
F using a single-mode, grating tuned CO
2
TEA pump laser with an intensity of up to 40 MW/cm
²
. Good agreement is obtained between theory and experiment for the observed values of FIR emission frequency and pump threshold intensity. These results indicate that a widely tunable (
150-1200 \mu
m), pulsed FIR CH
3
F laser could be constructed with a tunable, multiatmospheric CO
2
pump laser of modest power (about 2-5 MW).