Investigation On Nonlinear Dynamics Of ZnO Using Time-resolved Pump-probe Technique With Phase Object

Recently, People pay more attention to broadband semiconductors. Among thosebroadband semiconductors Zinc oxide (ZnO) because of its significant characteristics like:larger band gap and higher excited gain are becoming the promising candidate in opticalinformation processing, optical storage and the development of short wavelength laserdiode. A time-resolved pump-probe system based on the PO Z-scan technique and thestandard pump-probe system is employed for the investigation of optical nonlinearities of asemiconductor. This system is suitable for both degenerate and non-degenerate laser beams.With this method the refraction and absorption dynamics of nonlinear materials can beobtained simultaneously. According to the fact that different nonlinear mechanisms havedifferent response time, we can separate each nonlinear mechanism from another, andobtain the optical parameters in the meantime:2PA coefficient,2PA coefficient, boundelectronic nonlinear refractive index, free-carrier absorption cross section, free-carrierrefractive coefficient and the life time of the free-carrier.In our research, both the degenerate and non-degenerate situations are observed. Inthe non-degenerate situation, the pump and probe beam are from the same laser beam withthe help of beam splitter. The wavelength of the laser beam is532nm and21ps (FWHM).In the picoseconhd domain the nonlinear response of a semi-conductor is a combination ofthe bund-electron effects and2PA induced free-carrier effects. The result of the openapertures curve is related to the2PA, free-carrier absorption, free-carrier absorption crosssection, and the life time of the free-carrier.In order to observe the different absorptions and refractions of ZnO under differentwavelengths, we consider the non-degenerate situation. In the non-degenerate pump-probetechnique, the probe beam is from the optical parameter generator (OPG), whosewavelength is600nm and10ps (FWHM). The pump beam is532nm (wavelength) and 19ps (FWHM). For non-degenerate results, the nonlinear absorption is compound ofnon-degenerate2PA and2PA induced free-carrier absorption. While the nonlinearrefractions is both related to the bound-electron Kerr effect and the free-carrier refraction.