Nonlinear optical characterization of the metal oxide and metal sulfide thin films
Abstract
The TiO2 and CdS nanocrystallite films prepared by thermal deposition are characterized using different morphological and optical methods. The nonlinear optical absorption of 1030 nm and 515 nm, 200 fs radiation in the films is determined. The competition between saturable absorption, reverse saturable absorption, and two-photon absorption is demonstrated with variation of the pulse energies of the visible and infrared radiation used. We show the overlap of positive and negative nonlinear absorption in different energy ranges of the probe pulses. The saturated intensities of the CdS film are determined to be 1.7 × 10^12 W cm−2 for 1030 nm probe pulses and 1.3 × 10^11 W cm−2 for 515 nm probe pulses. The two-photon absorption coefficient for 1030 nm pulses is calculated to be 4.7 × 10−8 cm W−1. The reverse saturable absorption coefficient for 515 nm probe pulses is determined to be 8 × 10−8 cm W−1. We analyze the original TiO2 films and the films irradiated by an electron beam. The photon energy at 1030 nm does not allow nonlinear absorption in the unirradiated film, while in the irradiated film two-photon absorption is observed.