A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) wavelength
dependent of Kerr type nonlinear refraction in direct and indirect band gap crystals has been
reported in the present work. The Z-scan measurements are recorded for both ZnO and CdI2 with femtosecond
laser pulses while the wavelength dependent of the Kerr nonlinearity are in agreement with a two
band model. The wavelength dependence of the 3PA is determined by [(3Ephoton/Eg)–1]5/2[(3Ephoton/Eg)]9
in the case of direct band gap crystal and ½ð3Ephoton hX=EgÞ 1
5=2
½ð3Ephoton hX=EgÞ9 in the case of
indirect band gap crystal. In the present investigation the value of 3PA in the case of indirect band gap
crystal is lower than the direct band gap crystal which is due to the phonon assisted transition. The materials
of large band gap with optical nonlinearity and fast response speed should be dominating factor for
further photonic devices such as optical limiters, optical switches and optical modulators. The higher
order nonlinear optical effects have also been determined in the present study.
2012