Photoexcited Carrier Lifetime and Refractive Nonlinearity in Direct and Indirect Band Gap Crystals on the Z-Scan Technique

The photoexcited carrier lifetime ( tau) and peak to valley transmission difference (delta/ t p-v) in direct and indirect band gap crystals has been investigated by the use of single beam open and closed aperture z-scan technique using frequency doubled nd:yag laser. the peak to valley transmission difference (delta/ t p-v) is found to be of the order of 102 in case of direct band gap crystals and of the order of 10-3 in case of indirect band gap crystals. the carrier life time ( tau) is found to be in nanoseconds range in case of direct band gap crystals and picoseconds range in case of indirect band gap crystals. lower value of ( tau) and (delta/ t p-v) in case of indirect band gap crystals can be attributed to the reduction in the value of carrier density (n) and small value of nonlinear phase shift (delta/ varphi), respectively.