Intensity dependence of two-photon absorption in CdS measured by photoluminescence excited by femtosecond laser pulses

Abstract

Two-photon absorption is evoked in a CdS crystal by laser excitation up to almost 200 GW/cm 2 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 ␤ϭ6.9 cm/GW was found. Simultaneously, the twophoton 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.

Intramolecular charge transfer enhanced optical limiting in novel hydrazone derivatives with a D1–D–Ai–π–A structure

“…The photons with those wavelengths of the RSA window can only be absorbed through the multi-photon absorption process which only occurs for light with high intensity. 57 The following 2PA and 3PA calculations for the lowest six singlet excited states of the BTH molecule confirm this conjecture. Based on the numerical results given in Table 1, it is seen that there are obvious two-photon and three-photon absorption for the wavelengths within 513-619 nm (2.01-2.42 eV) and 779-1224 nm (1.01-1.59 eV) respectively.…”

Green emission and bandgap narrowing due to two-photon excitation in thin film CdS formed by spray pyrolysis

“…In figures 1 and 2, I = 200 GW cm −2 . At such high intensities β of CdS is 2.9 cm GW −1 [12] resulting in d p = 30 µm. As a consequence, the fs-laser pulses penetrate the sample without attenuation and the TPL corresponds to the integrated bulk emission of the film.…”