Optical free induction decay (OFID) 10 μm co 2 laser systems

Abstract

This paper describes new unproved and reliable optical free induction decay (OFID) picosecond-pulse CO 2-10 μm laser systems, differing mainly in the pump laser and in the peak power of the generated pulses. In this context a single-mode TEA-CO 2-10 μm laser preionized by a novel surfacecorona discharge was developed. Our improved plasma shutters operate as optical switches at variable gas pressures. They are triggered either by a laser-produced surface plasma or by an electrical high voltage discharge. With respect to the first trigger scheme we found new target materials for the surface plasma generation, i.e. metallized graphites. In the second scheme the electrical discharge is initiated by the TEA-laser pulse via a new laser-triggered spark gap. Single-mode TEA-CO 2-10 μm laser, plasma shutter plus a spectral filter form the OFID laser system, which generates the picosecond pulses. An electronic control completes the system as reliable working tool. Each of the OFID laser systems developed is capable to produce 10 μm pulses with a duration of 30–300 ps. Numerical calculations are performed to estimate the influence of various parameters on pulse shape and duration. Since a direct measurement of the time variation of the short pulses by fast IR detectors is not possible, we measure the picosecond pulses by means of an optical autocorrelation method with optical second harmonic generation. For the first time this is performed with polycrystalline material, e.g. GaAs or ZnSe, instead of a single crystal, e.g. GaAs or Te.