Optical EngineeringIntensity dependence of two-photon absorption in CdS measured by photoluminescence excited by femtosecond laser pulses
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Two-photon absorption is evoked in a CdS crystal by laser excitation up to almost 200 GW/cm2 at 804 nm. Pulses with duration of 200 fs are used to achieve this high intensity. By means of a z-scan technique, the nonlinear absorption coefficient (?) is measured and the constant value of p= 6.9 cm/GW was found. Simultaneously, the two- photon excited emission is recorded. Examination of the photoluminescence data reveals that ? is not constant but decreases from 6.9 to 2.9 cm/GW with increasing excitation. The crossover between the ? values takes place at approximately 70% of the maximum intensity. The result shows that the two-photon excited photoluminescence is a very sensitive method to show saturation and intensity dependence of the nonlinear absorption coefficient.