Study On Ultrafast Nonlinear Optical Properties Of TlGaS₂

TlGaS2 is a novel quasi-two-dimensional layered material.Due to its unique energy band structure,TlGaS2 has a high photosensitivity in the range of visible light and X-ray,which makes it have an important application prospect in optoelectronic devices.At present,the optical and electrical properties of TlGaS2 have been widely studied,but the study on its ultrafast nonlinear optical properties has not yet been carried out.For the application of TlGaS2 in optoelectronic devices,it is necessary to deeply study the ultrafast nonlinear optical properties of TlGaS2.Therefore,we carried out the study on ultrafast nonlinear optical properties of TlGaS2,The detailed contents are shown as follows:Firstly,the ultrafast nonlinear absorption properties of bulk TlGaS2 is measured by intensity dependent transmission technique.TlGaS2 exhibits obvious nonlinear absorption response under the excitation of 800 nm femtosecond laser pulse.By fitting the results with the two-photon absorption model,we determined that the nonlinear absorption is two-photon absorption,and calculated the two-photon absorption coefficient of TlGaS2 to be ?lin=7.4×10-10 cm/W for linearly polarized beam.We further confirmed its two-photon absorption characteristics by time-resolved transient absorption measurement.The two-photon absorption is the third-order nonlinear optical effect,and the two-photon absorption coefficient is directly related to the imaginary part of the third-order nonlinear susceptibility tensor elements,so we calculated the values of the imaginary part of the third-order susceptibility tensor elements by combining the intensity dependent transmission measurement with the polarization dependent measurement of transient absorption signal.Finally,the third-order nonlinear optical properties were further studied by time-resolved optical heterodyned detection of optical Kerr effect measurement,the real and imaginary parts of the third order susceptibility tensor x(3)xyxy+x(3)xyxy are obtained.A fast temporal response within the limit of resolution was manifested,indicating that its nonlinear refraction is derived from non-resonant electronic nonlinearities.Combining the relation of the third-order susceptibility tensor under Kleinman symmetry of the non-resonant electronic nonlinearities,we calculated the values of the real part of the independent susceptibility tensor elements and further calculated the nonlinear refractive index.The results show that TlGaS2 has a large ultrafast optical nonlinearities,which makes it a promising material for application in photonic techniques.