Compact High Repetition-Rate Infrared Countermeasure System

Abstract

In the presented countermeasure system a pulsed optical generator with a periodically poled lithium niobate crystal as frequency converter is used to generate mid-infrared radiation between 2 and 5 µm. The system is compact and easy to operate due to the absence of resonator mirrors. The average output power of the mid-infrared radiation is expected to reach the multi Watt-level for repetition rates up to 20 kHz. The spectrum of the OPG idler wave is broadened near 3.2 µm due to the occurrence of line broadening degeneracy in the OPG-waves for a domain period of 30.5 µm. The position of the line broadening degeneracy can be recognized e.g. by the intersection of the second harmonic OPG signal and a difference frequency mixing wave. The mixing line is made-up by the second harmonic pump wave and the signal wave near 0.8 µm. In the vicinity of the degenerate signal and idler state, which is close to 2 µm, the spectrum is broadened with lower output intensities and therefore lower average output powers. The longer wavelength range above 4 µm is limited by absorption of the idler wave in the lithium niobate crystal. Numerical results of the optical parametric generation in the crystal as well as experimental propagation characteristics of the idler beam will be shown.