Abstract

SUMMARY Apart from many technical and scientific applications, mid- and far-infrared gas lasers are suited for the study of a large variety of basic phenomena. This paper reviews lasers and phenomena which have been discovered and/or investigated at our laboratory. They can be separated into two groups. The first group concerns distributed-feedback (DFB) lasers, helical-feedback (HFB) lasers and related soliton formation, while the second comprises extremely fast plasma shutters for mid- and far-infrared laser radiation which permit the production of ultrashort mid- and far- infrared pulses on one hand and the observation of interesting phenomena on the other hand. The ultrashort mid- and far infrared pulses arc predestinated for studies e.g. of fast detectors, nanometer thin-film diodes and high-T_c superconductors. Apart from many technical and scientific applications, mid- and far-infrared gas lasers are suited for the study of a large variety of basic phenomena. This paper reviews lasers and phenomena which have been discovered and/or investigated at our laboratory. They can be separated into two groups. The first group concerns distributed-feedback (DFB) lasers, helical-feedback (HFB) lasers and related soliton formation, while the second comprises extremely fast plasma shutters for mid- and far-infrared laser radiation which permit the production of ultrashort mid- and far- infrared pulses on one hand and the observation of interesting phenomena on the other hand. The ultrashort mid- and far infrared pulses arc predestinated for studies e.g. of fast detectors, nanometer thin-film diodes and high-T_c superconductors. The development of a plasma shutter with a laser-triggered spark gap which cuts off 10 pm TEA CO₂ laser radiation within 10 ps permits the generation of reproducible 30 ps 10 pm pulses by optical free induction decay (OFID). In addition, it was demonstrated that far-infrared emitting molecular gases, such as CHjF, can be applied as OFID filter as well as the usual hot CO2. A combination of a high-pressure TEA CO2 laser with the plasma shutter mentioned allows us the generation of frequency-tunable truncated and .30 ps OFID 10 pm pulses. A modification of this plasma shutter also works for far-infrared laser radiation. Pumping far-infrared emission with 10 pm TEA CO2 laser pulses truncated by the plasma shutter already discussed provided a wealth of exciting phenomena: stimulated Raman emission with anucorrelated fluctuations of 10 pm pump beam and far-infrared emission, forward standard and swept-gain superradiance, backward superradiance. 10 pm OFID related to far-infrared emission as well as the generation of mid-infrared solitons in far-infrared Raman scattering. Optical pumping of far-infrared emissions was the clue for the realization of distributed and helical feedback gas lasers. Because of their long wavelengths and periods, these far-infrared DFB and HFB lasers represent an excellent tool to test the various theories on all kinds of DFB and HFB. Whilst the theories on cw DFB and HFB lasers are generally approved, those on the pulsed DFB and HFB lasers need considerable improvement to explain experimental facts. Presumably, this will be achieved by the theory on solitons in periodic laser structures without, and with cw or pulsed gain. Characteristic phenomena involved are in- and out-gap solitons, transitions to chaos, pulse formation, stabilization and decay.

© 1996 IEEE