LASER-INDUCED MULTIPHOTON PHOTOCONDUCTIVITY IN DIRECT AND INDIRECT BAND GAP CRYSTALS USING Z-SCAN TECHNIQUE

摘要

Nanosecond laser pulses have employed the photoconductive Z-scan technique. Photo-conductivity traces measured by moving the sample across the laser beam waist wereused for measuring two and three-photon absorption processes. The value of the three-photon absorption coefficient β_3 = 9.6 × 10~(-10)cm~3/GW~2in the case of direct, and8.96 × 10~(-12)cm~3/GW~2and 5.0 × 10~(-2in the case of indirect band gapcrystals have been estimated from a comparison of traces measured by exciting the sam-ple with the first and second harmonics of Nd:YAG laser. The low value of β_3in thecase of indirect band gap crystals compared to direct band gap crystals is attributed tophonon-assisted transitions.