Investigation On Third-order Nonlinear Optical Properties And Plasma High-order Harmonic Generation Of Micro-structure Optoelectronics Materials

With the improving of laser technology,the research interests on nonlinear optical materials has been growing rapidly.The development and research of materials with greater nonlinear optical effects are valuable for the application of optoelectronic devices such as lasers,optical modulators,and optical switches.Due to quantum size effect,the nonlinear optical properties of metal nanoparticles and metallic compound quantum dot are different from that of the same materials in the form of bulk materials caused by their nanostructures,such differences are of great interest to researchers,and are particularly important for the development of micro-nano optoelectronic devices.On the other hand,the non-linear optical properties of the interaction of metals and metal compounds with intense lasers have opened up a new branch of scientific research.When high-intensity femtosecond laser pulses interact with the plasma generated by laser ablation,high-order harmonic occur due to higher-order nonlinear polarization.In this dissertation,Z-scan technology and pump-probe technology are used to research the nonlinear optical properties and dynamics combined with the theoretical system under femtoseconds and picoseconds laser for three types of typical micro-nano optoelectronic materials:gold nanoparticles,silver sulfide?Ag₂S?quantum dots,organic-inorganic and all inorganic hybrids perovskite thin films.Laser ablation of three types of materials are used to generate plasma-induced harmonic emission,and the phenomenon of harmonic generation is analyzed and discussed.Specific research work includes the following aspects:1.The effect of particle size on the third-order nonlinear optical properties of gold nanoparticles was systematically studied.Gold nanoparticle suspensions of different sizes were prepared by controlling the amount of reducing agent,and the samples were characterized.As the size of the nanoparticles increases,the absorption peaks show a significant red shift.The relationship between the particle size of gold nanoparticle solution and nonlinear absorption and nonlinear refraction was studied by Z-scan technique.With the change of incident energy,gold nanoparticles have a light limiting effect in the 800 nm band due to their reverse saturable absorption.The light limiting threshold is 2?J,indicating there are good application prospects in eye protection,pulse shaping and active mode-locking.The high-order harmonic emission of the plasma plume generated by the ablation of gold nanoparticles produced strong harmonics up to the 25^th order,with the overall intensity five times higher than that generated from the plasma of bulk materials under the same experimental conditions,proving that plasma of gold nanoparticles is an effective medium for high harmonic generation.2.Strong nonlinear optical properties of quantum dots?QDs?dispersions and films made of quantum dots due to quantum confinement effects.We prepared silver sulfide?Ag₂S?QD dispersions with an average size of 4 nm and its solution with concentration of 0.375 mg ml^-1 and 0.125 mg ml^-1.Optical absorption,nonlinear refraction characteristics influence of the laser pulse width on the positive and negative nonlinear refraction coefficients of the dispersion were studied under 800 and 400 nm,200 ps and60 fs pulses,the dispersion with a low Ag₂S QD content exhibited a light limiting effect when the incident energy in the range of 0.8 to 2.5?J.The carrier kinetics of Ag₂S QD dispersion is studied at 400 nm,60 fs pulses.The results indicate that the main kinetic processes are the electron-phonon and phonon-phonon interactions with corresponding relaxation time constants of 1.7 and 6.9 ps.3.80 and 500 nm Ag₂S QD films were prepared,and the effects of film thickness on nonlinear optical properties were investigated using open-and closed-hole Z-scans.Compared with Ag₂S QD dispersion samples,the nonlinear optical coefficients are increased by three to six orders of magnitude.The transient absorptions of 80 nm and500 nm films were studied under 400 nm,30 fs pulses,and the decay times of the two films were found to be 150 and 245 fs,respectively.High-harmonic up to the 23^th order were generated from the plasma from laser ablation of Ag₂S QD film.By analyzing the kinetics of diffusion of QD containing plasma,the time delay between the heating pulse and the driving pulse,thus the harmonic conversion efficiency,can be optimized.4.The nonlinear optical properties of organic-inorganic hybrid perovskite and all-inorganic perovskite?MAPbX₃,X=Cl,Br,I?films were studied.A MAPbI₃ thin film was prepared and basic characterization was performed.A photodetector with a doubling effect was prepared to characterize its photoelectric properties.The non-linear absorption process of MAPbCl₃ and MAPbBr₃ thin films obtained by using open-hole Z-scanning at 800 nm and 40 fs is mainly due to two-photon absorption,and the non-linear absorption coefficient?was found to be?1.5±0.4?×10^-8 cm W^-1 and?5±1.2?×10^-8 cm W^-1,respectively,As for MAPbI₃ film,the process is dominated by saturated absorption:the saturation absorption intensity was found to be 8×10¹¹ W cm^-2,and the nonlinear absorption coefficient was found to be?5±1.2?×10^-7 cm W^-1.The preparation method of all-inorganic perovskite?CsPbX₃?thin film was optimized,and the nonlinear absorption and nonlinear refraction of the precursor solution and the thin film were studied with 400 nm,35 fs pulses.5.High harmonic generation from the plasma of the laser ablated organic-inorganic hybrid perovskite MAPbCl₃ single crystal were studied,up to the 23^thh harmonic was observed.To investigate the mechanism of polyatomic target generation of higher harmonics,single crystal samples prepared with MACl,PbCl₂ powders and MACl/PbCl₂ equivalent mixed powders were studied.Regulated the time delay between the heating pulse and the driving pulse,the high harmonic generation from plasma containing multi-particles to enhance the intensity of the harmonics is studied.