Research On Raman Properties Of YVO₄ Crystals

Diode-end-pump all-solid-state lasers have many advantages,such as compactness,high efficiency,steadiness,long service time,controllable and so on.Stimulated Raman scattering(SRS)is the strong power density collides strongly of the pumped laser with the material molecules in Raman medium.It is an important method of laser wavelength conversion.We can obtain the wavelengths that can't be directly radiation from the crystal.It has high conversion efficiency and the spectrum ranges from ultraviolet to mid-infrared.Laser Raman materials include gas,liquid and solid Raman materials.Compared with traditional gas and liquid Raman materials,solid Raman materials have the advantages of high Raman gain coefficient,good thermal conductivity(high thermal conductivity coefficient)and compact construction.At present,most solid-state Raman lasers are mainly studied in the visible light and near infrared spectrum.Because the Raman coefficient decreases as the wavelength increases,Raman materials have not been widely used at longer wavelengths.The main contents of this thesis are as follows:1.Based on standing wave resonator theory,we use MATLAB to simulate and analyze the Joule-heat power density,effect of the thermal focal length on resonator,the thermal distribution model and comparative analysis of spot radius in optical resonator by output coupling mirrors with different curvatures.2.A diode end pumped Tm:YLF/YVO₄ Raman laser with linear cavity structure was fabricated.The stability of the cavity and the size of the fundamental mode spot radius at different positions in the cavity were compared.Finally,the concave-concave resonator was selected according to the experimental conditions and theoretical analysis.We try out the pulse repetition frequency(PRF)from 1.1 k Hz to 1.6 k Hz.A maximum average output power of 234 m W for the first-Stokes laser at 2250 nm was obtained under the incident pump power of 30 W with the pulse repetition rate of 1.1 k Hz,corresponding to optical-optical efficiency,the pulse width,the single pulse energy and the peak power is0.8%,15.53 ns,0.21 m J and 13.76 k W,respectively.3.A diode-end-pumped composite crystal based on YVO₄/Nd:YVO₄/YVO₄ with linear cavity structure first-Stokes self-Raman laser has been achieved.According to the experimental conditions and theoretical analysis,the flat-concave resonator with straight structure was selected.We compared the influence of transmittance of output coupling mirror on output power.Under a first-Stokes Raman transmittance of 35%output coupling mirror,we obtained the maximum average output power of 1.34 W for the first-Stokes Raman laser of 1176 nm with the pump power of 38 W and the pulse repetition frequency of 50 k Hz.Corresponding to optical-optical efficiency of 3.6%,the shortest mode-locked pulse is 300 ps.With the pump power of 38 W and the pulse repetition frequency of 30 k Hz,the maximum Q switched pulse envelope energy and the peak power is 35?J,10.5 k W,respectively.