Determination of nonlinear absorption and refraction in direct and indirect band gap crystals by Z-scan method

摘要

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 CdI _2 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 [(3E photon/E _g)-1] ~(5/2)[(3E _(photon)/E _g)] ~(-9) in the case of direct band gap crystal and [(3E _(photon)±?Ω/E _g)-1] 5/2[(3E _(photon)±?Ω/E _g)] ~(-9) 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.