Optimization Of The Ld Resonantly Pumped GdVO₄Based Raman Shifting Laser

All-solid-state yellow lasers are of great value to the applications of medicaltreatment, information storage, underwater detecting, etc. However, it is verydifficult to directly obtain laser radiations in such band from the solid-state gainmedium. Raman shifting is one of the effective ways to expand the wavelengths ofsolid-state lasers. By using the first-order Stokes effect, the Nd3+laser at1.06μm canbe shifted to1.17μm wavelength, and further be frequency converted to yellow laseroutputs in the band of560~600nm by means of frequency doubling or sumfrequency mixing techniques. Therefore, it is very significant to study thesolid-state Raman lasers at1.17μm. In this thesis, the design of the intracavityRaman laser at1.17μm based on GdVO4crystal is optimized. The specific researchis as follows:Firstly, with the concentration quenching effect being neglected, the resonantpumping theory is deduced based on the rate equation theory. Therefore, theexpressions of pumping threshold and output power are obtained, which providetheoretical foundations for the optimization of the laser crystal and optical cavity.Besides, with the consideration of the stimulated Raman scattering, the intracavityRaman laser is theoretically analyzed, and the impacts of the loss ratio, normalizedRaman gain coefficient and the fundamental to Raman spot ratio on the number ofRaman photons are simulated.Secondly, thermal effects of the Nd:KGW crystal is analyzed. According to thecrystal shape, the practical thermal model is established, and the heat conductionequations under the thermal balance condition are solved by means of finitedifference method. Furthermore, the temperature distributions under the conditionsof indirect and direct pumping at808nm and880nm, respectively, are simulated,and the impacts of crystal concentration and pump spot size to the temperature distribution are discussed, and also the impacts of refractive index variation and endface deformation on the thermal focal length are investigated.Thirdly, component units of the Raman shifting laser are optimized, whichincludes the parameters of concentration and length of the Nd:KGW crystal, pumpspot size and cavity length. On the other hand, the impacts of the confocal lengthand space of the double lens optical coupling system are analyzed.At last, by using the Nd:LuVO4and Nd:KGW crystal as the active medium andthe un-doped GdVO4crystal as the Raman gain medium, the output properties ofthe intracavity Raman laser at1.17μm are investigated. Raman laser pulses as shortas5ns are obtained, and the output beam quality is near the diffraction limit.