Effects of foreign gases on the degenerate four-wave-mixing in I-2

The effects of laser fluence and foreign gas (N-2, CO2, NO2) pressure on th e degenerate four -wave-mixing (DFWM) spectrum and signal intensity of I-2 have been studied. The dependence of DFWM saturation intensity on foreign g as pressure is measured and found to be I-sat proportional to p(0.7). Resul ts show that the foreign gas has little effect an the DFWM spectrum structu re but has great effect on the signal intensity, which depends on the laser fluence. At high laser fluence, the addition of foreign gas can enhance th e DFWM signal, and thermal grating contribution dominates. Using the relati onship of I-2 proportional to p(0.7) and the two- level model, the dependen ce of I-2 DFWM intensity on foreign gas pressure can be well fitted.