Theoretical And Experimental Study On Multi Frequency Shift Oscillating Nd:YVO₄/GdVO₄ Composite Raman Laser

Stimulated Raman scattering in crystals has become an important way of frequency conversion of solid-state lasers,and has been a hot spot in the field of laser research in recent 30 years with the vigorous development of crystal materials.Solid state Raman lasers have rich diversity in laser structure,operation mode and output wavelength.LD pumped Q-switched intracavity Raman laser integrates laser crystal,Q-switched crystal and Raman crystal into one laser cavity.The conversion from LD to Raman light in one laser cavity has the advantages of high efficiency and small volume.It has always been the focus of solid-state Raman laser research.In recent year,integrating a self-Raman crystal and a Raman crystal in a lase cavity has become an effective way to obtain synchronous pulse multi-wavelength laser output.In recent years,a self-Raman crystal and a Raman crystal are integrated in a laser cavity had become an effective way to obtain synchronous pulse multi wavelength laser output.In this paper,a diode-end-pumped,a c-cut Nd:YVO₄crystal as a self-Raman crystal,and a Gd VO₄crystal as a Raman crystal,acousto-optic Q-switched,three frequency shifts(890cm^-1for YVO₄,882cm^-1for Gd VO₄and 259cm^-1for both)composite Raman laser is studied theoretically and experimentally.In terms of theoretical research,a theoretical model of three frequency shift synchronous oscillation pulse Raman laser based on laser rate equations is constructed.In this theoretical model,the inversion population distribution is defined to be Top-Hat distribution,and the intracavity lasers are defined to be TEM₀₀fundamental mode with Gaussian distribution.The generation of cascaded Stokes light with secondary Raman-shift(259cm^-1)shared by the two crystals is considered,the influence of thermal effect on laser operation is considered,and different pulse repetition rates are simulated,The pulse waveform and average output power of the laser output at different wavelengths under the pump power.In terms of experimental research,the fiber coupled808nm semiconductor laser is used as the pump source,c-cut Nd:YVO4 is the self-Raman gain medium,c-cut Nd:Gd VO₄is the Raman gain medium,acoustooptic Q-switching,and the fundamental frequency wavelength of the laser is 1066nm.The synchronous operation of 1097nm,1177nm and 1178nm of the first-order Stokes light corresponding to 259 cm^-1,882 cm-1 and 890cm-1 is realized.Due to the different reflectivity of the coating of the output mirror to different wavelengths,the second-and third-Stokes output with 259 cm^-1Raman-shift are obtained in experiment.The average output power,output spectrum and pulse waveform of the laser output are measured under different pulse repetition rate and pump power.At the pulse repetition rate of 10k Hz,the incident pump power is 7.72w.The maximum total average output power of cascaded Stokes light corresponding to 259cm^-1Raman frequency shift is 938mw and the pulse width is 13.6ns.