Photoinduced nonlinear optical effects in ZnS nanocrystallites incorporated within the photopolymer polyvinyl alcohol matrices were studied. As a basic method we have used photoinduced optical second harmonic generation (SHG). The Q-switched HF-laser (λ=2.64 μm; pulse duration 30-40 ps) was used as a source of probing (fundamental) light beam and the pulsed nitrogen (λ=337.7 nm) was applied as a source of the photoinducing pump light. With increasing photoinducing beam power, the output SHG signal (at λ=1.32 μm) increases. The maximal second-order non-linear optical susceptibility corresponds to tensor component d₁₂₃=d₁₄=3.8∓0.2 pm/V at a photoinducing power density equal to about 1.25 GW/cm². With decreasing temperature, the SHG signal increases within the temperature range 25-30 K. Time-dependent pump-probe measurements of the SHG indicate an existence of the SHG maximum for a pump-probe delaying time 20 ps. The ZnS hexagonal structural components play a crucial role in the observed photoinduced second-order non-linear optical effects. Large values of the non-linear optical constants as well the good technological parameters open a possibility to enhance the non-linear optical susceptibilities of the investigated ZnS nanocrystallites

Keywords: ZnS, nanocrystals, optical properties

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