| In recent years,low-dimensional nanomaterials have received extensive attention from researchers due to their excellent mechanical,thermal,and optoelectronic properties,especially in the fields of condensed matter physics,materials science,chemistry,optoelectronics,and nanotechnology.Shows an exponential growth.In the field of nonlinear optics,the exploration of the nonlinear optical properties of low-dimensional nanomaterials has become a hot research direction.The development of photonic devices based on the nonlinear optical properties of low-dimensional nanomaterials are also in full swing,such as photodetectors,optical modulators,optical limiting devices.Among them,saturable absorbers made with their nonlinear absorption properties are the key components of all solid-state,fiber pulse lasers.With the continuous improvement of pulsed lasers in terms of short pulse,high energy,and tunable performance,the requirements for saturable absorber materials are getting higher and higher.Traditional materials are extremely shortcomings due to their slow recovery time,narrow working bandwidth,and complex integration.Greatly restricts the development of pulsed lasers.Saturated absorption devices based on low-dimensional materials possess ultra-fast response time,broadband nonlinear absorption,low loss,inexpensive and high scalability.Thus,research on the nonlinear optical properties of nanomaterials has important significance and value for enriching kinds of saturable absorbers and improving the pulsed lasers performance.Taking this as a starting point,this paper studies the wide-band nonlinear optical properties of a variety of new low-dimensional nanomaterials in the near-infrared region,preliminarily explains the physical mechanisms and laws of different nonlinear absorption and refraction phenomena,and explores the effects The main factors of its nonlinear optical performance have determined many key nonlinear optical parameters and explored its application potential as saturable absorption devices and optical limiting devices.Finally,based on the saturated absorption characteristics of these new nanomaterials,the stable output of pulsed lasers with multiple wavelengths was realized and the influence of different systems of nanomaterials on the output characteristics of pulsed lasers with different wavelengths was analyzed.By comparing and summarizing the pulsed laser modulation characteristics of many systems of low-dimensional nanomaterials at different wavelengths,we have obtained some regularity indicators and guidance for subsequent application research.The main research contents of this paper are as follows:1.The CdSe/ZnS core-shell quantum dots composite film based on polymethyl methacrylate(polymethyl methacrylate,PMMA)substrate was successfully prepared.The nonlinear optical properties of the sample in the near-infrared band(including 1 and 1.3 μm)are studied,and the influence of factors such as pump power and doping concentration on its nonlinear optical performance is explored.It is found that with the increase of excitation light intensity,a process of transition from saturable absorption to anti-saturable absorption occurs.With the enhanced excitation light intensities,the nonlinear optical properties of the samples increase,which are also affected by the quantum dots doping concentration.According to the comparison of the experimental results of samples with different doping concentrations,it is proved that it is a feasible route to improve the nonlinear optical performance of the quantum dot material composite sample by optimizing the concentration ratio.In addition,the non-linear refraction characteristics of the sample.were also explored.Under the excitation of strong light,it showed self-defocusing phenomenon.Through experimental data fitting,many key parameters such as modulation depth,nonlinear absorption coefficient,nonlinear refractive index and so on are determined.Finally,based on the saturable absorption characteristics of CdSe/ZnS core-shell quantum dots,stable output of Q-switched pulsed lasers with pulse widths of 233 and 196 ns at 1 and 1.3 μm were achieved,and the effect of doping concentration on quantum dots was verified again.The influence of the saturation absorption performance of the composite sample.2.Two-dimensional bismuth ene quantum dots(Bi quantum dots,BiQDs)with uniform size were prepared by liquid phase exfoliation(liquid phase exfoliation,LPE),and the morphology and structure were characterized.The saturable absorption characteristics of BiQDs in the 2 μm band were explored,and the modulation depth was determined to be about 15.4%.Based on its excellent saturable absorption characteristics,BiQDs saturable absorbers were prepared and applied to 2 μm Tm:YLF solid-state Q-switched lasers,and three couplers with different output transmittances were used to study the output characteristics of the lasers.Finally,a pulsed laser output with the highest peak power of 8.1 W and the narrowest pulse width of 440 ns was obtained.The experiment proved the laser modulation ability of BiQDs in the 2 μm band.3.The InSe nanosheets with 8-9 layers were prepared by LPE method.Using first-principles calculations based.on density functional theory(density functional theory,DFT)theory,the relationship between the electronic band structure and layers of InSe nanosheets is studied.The results show that as the layers of nanosheets gradually decreases from bulk to single layer,a transition from direct band gap to indirect band gap is happened.At the same time,the bandgap increases.The band gap of single-layer InSe nanosheets reaches 2.1 eV.It is determined that the 8-9 layer nanosheets prepared in this paper have a direct band gap structure,and the band gap width is about 1.5 eV.The nonlinear optical performance of InSe nanosheets in the 1-2 μm band was studied,and its good broadband saturable absorption characteristics were found.Based on this,using it as a saturable absorber,solid-state Q-switched lasers with operating wavelengths of 1.06,1.34,and 1.91 μm were built,and stable output of pulsed lasers with pulse widths of 599,520,and 210 ns were achieved.4.The high-quality MoSe2 nanosheets were prepared by LPE method and their nonlinear optical properties in the 1 μm band were measured.The results show that as the excitation light intensity increases,the few-layer MoSe2 nanosheets exhibit a transition from saturated absorption to anti-saturated absorption.According to the results of fitting experimental data,related parameters such as its nonlinear absorption coefficient,nonlinear refractive index and third-order nonlinear polarizability are determined.Using few-layer MoSe2 nanosheets as a saturable absorption device,a Q-switched Nd:CNGG pulsed laser output with a pulse width of 772 ns in the 1 μm band was realized.5.A single-layer MoS2 nano-film with a large size and uniform thickness was grown on a sapphire substrate by physical vapor phase epitaxy(physical vapour deposition,PVD).The nonlinear optical response in the 1 and 2 μm bands was explored,and the modulation depth,two-photon absorption coefficient,nonlinear refractive index and other parameters were determined.Based on its broadband saturable absorption properties,a 1 μm all-solid-state mode-locked laser and 2 μm Q-switched laser were set up.The mode-locked lasers with pulse width of 438 ps and the Q-switched laser with pulse width of 765 ns were obtained.6.The dodecahedral cobalt dimethylimidazole material(ZIF-67)with a particle size in the range of hundreds of nanometers,a smooth surface and a relatively uniform size distribution was prepared by liquid phase synthesis.According to first-principles calculations and experimental characterization results,it is determined that the band gap width of the metal-organic framework ZIF-67 is about 1.9 eV.The broadband nonlinear optical characteristics of ZIF-67 in the 1～2 um spectral band and its nonlinear absorption change phenomenon with the excitation intensity are studied.The nonlinear optical parameters such as nonlinear absorption index,two-photon absorption cross-section and nonlinear refractive index are determined.Especially the large two-photon absorption cross-section in the near-infrared region makes it very promising for optical limiting equipment.Based on the broadband saturable absorption characteristics of ZIF-67,1,1.3 and 2 μm solid-state Q-switched lasers with ZIF-67 as the saturable absorber were successfully built,and short-pulse laser output of 120,108 and 278 ns was obtained respectively. |
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