Backward stimulated Bragg scattering in multiphoton active CdTe_x Se_1-x quantum dots system

The backward stimulated Bragg scattering (SBgS) of CdTe_x Se _1-x quantum dots in chloroform is investigated at three pump laser wavelengths (532, 816, and 1064 nm) in nanosecond regime. The spectral and temporal structures of the backward stimulated scattering and pump threshold dependence on the concentration are presented in this paper. The energy conversion efficiency from input pump pulse to SBgS pulse was measured to be ≥ 14%. In addition, the samples exhibit multi- (two-, three-)photon absorption capability over the spectral range we investigated. More importantly, both mechanisms of SBgS and multiphoton absorption provided an enhanced optical limiting performance. The measured nonlinear transmissivity was changed from ∼0.73 to ∼0.17 for 532 nm laser pulses and from ∼0.9 to ∼0.35 for 816 nm laser pulses when the input pulse energy was changed from 10 to ∼1500 μJ.