Nonlinear Optical Properties Of Two-Dimensional Layered Materials And Their Applications In Pulsed Lasers

Two-dimensional layered materials represented by graphene have developed rapidly in the fields of materials,information,optoelectronics,energy and have become one of the hotspots of current research because of its excellent mechanical,optical and electrical properties.It provides a new material basis for the application of science and technology,which greatly stimulates people to explore and develop the properties of two-dimensional layered materials.Nonlinear optics is a new branch of optics with the development of laser technology,which studies the new phenomena and laws of the interaction between light and matter.With the development of nonlinear optics,nonlinear optical materials have gradually evolved from macro-materials to micro-materials.The study of the nonlinear optical properties of two-dimensional materials has become a new research direction.Saturable absorber based on saturable absorption characteristics of nonlinear optical materials is the key component of pulse laser.With the development of laser towards short pulse,high energy and tunable,the requirement for nonlinear optical materials is increased.The development of pulse laser is greatly limited by the disadvantages of traditional nonlinear materials,such as slow recovery time,narrow working bandwidth and complex integration.Therefore,people turn their attention to two-dimensional nonlinear optical materials with ultra-fast response time,broadband non-linear absorption,low loss,low cost and easy compatibility.The research on the nonlinear optical properties of two-dimensional materials and their applications in solid-state lasers have important guiding significance and practical value for the preparation of saturable absorbers and the improvement of the performance of pulsed lasers.In this paper,the third-order non-linear optical properties of carbon nitride materials,unitary nanomaterials,binary nanomaterials,ternary nanomaterials and two-dimensional crystal were studied.Their third-order non-linear optical parameters were measured and the multi-band nonlinear absorption law was found.Using the wideband saturable absorption characteristics of these materials,passively Q-switched pulsed lasers at various wavelengths were realized.The output characteristics,regularities and reasons at different wavelengths were analyzed.The main contents are as follows:1.The third-order nonlinear absorption and refraction of carbon nitride materials,g-C3N4 and F-C3N4,were studied with the change of incident laser intensity,laser wavelength and sample concentration.Their excellent saturable absorption characteristics in visible band were found.The characteristics of the transition from saturable absorption to reverse saturable absorption in near infrared band were explained by using the theory of excited state nonlinear absorption.It was found that the conjugate system of F-C3N4 nanosheets was partially destroyed due to the introduction of fluorine atoms,resulting in the increase of bandgap,the decrease of saturable absorption and the enhancement of reverse saturable absorption.2.Saturable absorption properties of antimonene,silicon nanosheets and boron nanosheets at 532 and 1064 nm were found.Saturation intensity and modulation depth were obtained.All-solid-state passively Q-switched pulsed lasers were realized at 0.9,1.06 and 1.34 μm through a flat-concave laser resonator.Due to the influence of strong non-linear absorption at short wavelength,the material has more stable pulse output in short wavelength Q-switched experiments.Among them,antimonene has a band gap width close to 0 eV,and its saturable absorption performance was stronger,and the Q-switched output laser parameters were better.3.The saturable absorption properties of two elements nanomaterials,SnSe2,SnTe2 and SnSe were studied in the range of 0.5-2.0 μm.The parameters such as the nonlinear absorption coefficient,saturation intensity and modulation depth were obtained.Among them,SnSe2 has larger nonlinear absorption coefficient,lower saturation intensity and better saturable absorption performance,which is more conducive to Q-switched laser output.Using the saturable absorption properties of the three materials,the all-solid-state passively Q-switched pulsed lasers has been achieved in the range of 0.9-2.0 μm.The results show that the intrinsic absorption of these materials has a significant effect on their Q-switching performance.Their intrinsic absorption were stronger and the Q-switching laser performances were better in short wavelength band.At the same time,the nonlinear absorption coefficient increased with the decrease of wavelength,which also contributed positively to the short wavelength laser modulation.4.The non-linear absorption properties of ternary nanomaterials PbSnS2 nanosheets were studied.Based on its broadband nonlinear absorption characteristics,all-solid-state passively Q-switched lasers of 1.06,1.3 and 1.87 μm were constructed.Because of its stronger intrinsic absorption and higher nonlinear absorption in short wavelength,the experimental results of Q-switching at short wavelength were better.5.The electrical and optical properties of CrOCl crystal have been studied by density functional theory and experiments,and the bandgap width of CrOCl crystals was got as 1.4 eV.Linear optical measurements show that the ultrawide transmission band of 0.8-18 μm.Z-scan experiments verified its wideband saturable absorption characteristics and high damage threshold.It was applied to Q-switched lasers at various wavelengths.The results show that CrOCl crystal is a kind of infrared band nonlinear optical material with great potential.