Generation of ultra-broadband, mid-IR radiation in gallium arsenide pumped by picosecond 10 micron laser pulses

Production of ultra-broadband radiation in the "molecular fingerprint region", from 2 -- 20 mum is of practical interest for applications in optical coherence tomography, broadband spectroscopy and LIDAR measurements of gases. To date, supercontinuum generation in optical fibers has been limited to ∼ 4.5 microm in the mid-IR range. In this thesis we describe an experiment in which supercontinuum radiation from 2 -- 20 mum is generated using a 67 mm GaAs crystal pumped with a train of picosecond CO2 laser pulses. In addition to spectral measurements, we have measured the temporal profile of the laser pulse after the interaction and observed splitting of the picosecond pulses into finer structure. Simulation show that such temporal structure may arise from modulational instability. Simulations further indicate that the observed spectral width is strongly influenced by stimulated Raman scattering and the use of a train of picosecond CO2 laser pulses.