Study On Characteristics Of LD End-Pumped And Side-Pumped Nd-Doped Solid-State Raman Lasers

Solid-state Raman laser can realize laser frequency conversion,and generate new wavelengths based on stimulated Raman scattering processes.The output power,temporal characteristics,polarization characteristics,spectral characteristics and beam spatial distribution of Stokes laser are needed to be investigated by using different types of laser materials,Raman media,modulation methods and resonator types.Theoretical and experimental schemes are further optimized to achieve stable output in the range of visible,near infrared and middle infrared spectra.Solid-state Raman lasers have been used in industrial processing,medical treatment,military applications,optical communication,scientific research and other fields,promoting the development of laser technology.The main works of this paper are as follows:（1）In this thesis,experimental and theoretical studies have been carried out on the multiple transverse modes output of LD side-pumped acousto-optically Q-switched Nd:YAG solid-state Raman lasers.By studying the temporal distribution and spatial distribution of Q-switched pulses,multiple transverse modes are observed,i.e.TEM₀₀,TEM₁₀,TEM₂₀ and etc.The rate equations of acousto-optically Q-switching of two transverse modes are derived.Through numerical simulation of photon number densities of two modes in the resonator,the photon number density of TEM₀₀ is found to be relatively stable,and the higher-order mode shows a trend of pulses flunctuating regualary.The simulation results are consistent with the experimental ones.（2）Output characteristics of LD side-pumped acousto-optically Q-switched Nd:YAG/Sr WO₄ solid-state Raman laser are studied with straight resonator and folded resonator in this thesis,respectively.The output of 1180nm 1st Stokes laser with high power,high single-pulse energy,high conversion efficiency and low stimulated Raman scattering threshold is realized.For the experiment of folded resonator,the distribution of beam size in the folded resonator is calculated by using ABCD matrix and resonator mode theory.Combined with the influence of thermal focal length and resonator length on the resonator mode,the folded resonator is designed to achive low threshold stimulated Raman scattering.The maximum output power of 1180nm 1st Stokes laser is 2.89W,the conversion efficiency of pumping laser to Stokes laser is 4%,the single pulse energy is 0.96m J,and the shortest pulse is 35.5ns.（3）The output characteristics of continuous wave and acousto-optically Q-switched Nd:YLF solid-state lasers are studied.In these experiments,the output power,temporal characteristics,polarization characteristics and spectral characteristics are investigated to generate linear polarization fundamental laser at 1047 nm.（4）In this thesis,for LD end-pumped Nd:YLF/YVO₄ passively Q-switched solid-state laser,stimulated Raman scattering conversions of A_1g 893cm^-1,B_1g 817cm^-1 and B_2g 262cm^-1have been realized in c-cut YVO₄ crystals.The fundamental laser is 1047nm.1st Stokes laser is1145nm and 1155nm for 817 cm^-1 and 893 cm^-1 Raman modes,respectively.For 262 cm^-1Raman shift,the 1st Stokes laser is 1077nm,and the 2nd Stokes laser is 1108nm.Two c-cut YVO₄ crystals with different cutting accuracy are experimentally investigated,and characteristics of Raman laser output for different orientations of c-cut YVO₄ crystals are carried out.YVO₄ crystal with higher cutting accuracy of c-axis has higher output power,higher conversion efficiency and narrower pulse width.The maximum output power of Stokes laser is317m W,the maximum conversion efficiency of pumping laser to Stokes laser is 13.47%,and the average narrowest pulse width is 6.95ns.