Experimental observation of simultaneous oscillation at the Raman frequency and a cascade frequency in a broadly tunable
13CH
3F far-infrared laser is reported. Oscillation on both components persists over the full 25 GHz separation between the

and

lines. This observation is in marked contrast to the behavior of the tunable
12CH
3F FIR laser which produces only the Raman frequency when it is optically pumped at lower

values in the same branch. A marked qualitative difference in the large-scale emission spectra for the two lasers is also discussed.