New phenomena related to pulsed far-infrared superradiant and Raman emissions

We report on new effects in relation to optical pumping of far-infrared (FIR) superradiance and Raman emissions in CH₃F, CH₃CN, D₂O, NH₃ by rapidly truncated 10 μm CO₂ laser pulses and optical-free-induction decay (OFID) 30 ps-10μm-CO₂ laser pulses. Thus, we have found a drastic reduction of the FIR-pulse duration which is closely related to the fast truncation of about 10 ps of the plasma shutter used in our OFID 10 μm-CO₂ laser system. The forward emissions exhibit the on-set of swept-gain superradiance and the appearance of Raman emission with increasing pressure in the FIR cell. This implies line competition between the superradiant and Raman emissions and thus results in different emission regimes which we have investigated systematically. The backward emissions are superradiant over the whole range of our investigations and show high quality with respect to stability and reproducibility which is important for applications.

Furthermore, we have found that the CO₂-pump radiation and the generated FIR Raman emission interact mutually which results in anticorrelated fluctuations of the two fields. We have been able to interpret this effect as a result of periodic back-and-forth fluctuations of the Λ-like three-level molecular systems.

Finally, we have observed the development of OFID of the truncated CO₂-pump pulses in the FIR-laser gases. This effect has been thoroughly investigated and as a result we have generated for the first time ps-10 μm-CO₂-OFID pulses with FIR-laser gases as spectral filters instead of the usual hot CO₂ gas. New phenomena and advantages of our new OFID system based on FIR laser gases are discussed.