Spatial Structure and Simulations of Midwave Infrared Ultrashort Pulse Laser Frequency Conversion in Polycrystalline Chalcogenide Optical Materials

We experimentally and theoretically investigate the nonlinear frequency conversion of transparent chalcogenide optical materials using ultrashort midwave infrared laser pulses at 3.6 microns. Evidence of the structure of second through sixth harmonic generation demonstrates different levels of filamentation related to laser intensity, sample thickness, and sample position. Simulations using a (3+1)D model with experimentally measured n(2) values and random quasi phase matching provide good qualitative agreement with experimental data. Together, the data suggests that focusing geometry and material structure play a significant role in harmonic generation in these materials.