Study On Performance Of QCW LD Pumped Yb:YAG Raman Laser

Stimulated Raman Scattering(SRS)effect is a third-order nonlinear process and is an effective and important method for achieving frequency conversion in solid-state lasers.The solid-state lasers based on SRS effect dramatically expands the laser wavelengths which are difficult to obtain by using traditional laser crystals.And multi-wavelength laser oscillation is easily achieved in Raman lasers.Solid-state Raman lasers have potential applications in medical surgery,optical communications,measurement,military,and so on.Compact integrated passively Q-switched solid-state Raman lasers have many advantages such as free of phase-matching condition,high beam quality,high conversion efficiency,and high peak power.In this paper,the performance of continuous-wave(CW)and passively Q-switched Raman lasers have been studied in Yb:YAG/YVO4 Raman microchip laser and Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman microchip laser pumped with a quasi-continuous-wave(QCW)laser diode.Lasers with optical frequency comb(OFC)has been widely used in many fields,however,compact and miniature lasers for generating OFC are challengeable.The miniature solid-state Raman laser with broadband comb-like laser spectrum not only can realize multi-wavelength laser with wide spectrum range and stable longitudinal modes interval,but also provide a new idea for realizing broadband OFC in microchip laser.In this paper,the broadband comb-like laser spectrum has been generated in a QCW laser diode pumped Yb:YAG/YVO4 Raman microchip laser.The highly doped Yb:YAG crystal with low quantum defect,long storage lifetime,broad emission bandwidth is used as gain medium to generate 1.03 ?m and 1.05 ?m multi-longitudinal modes fundamental laser.A comb-like first-order stokes laser spectrum including 44 longitudinal modes with a bandwidth of 22.5 nm is generated by utilizing Raman shift 155cm-1 and 259 cm-1 of the YVO4 crystal converted from the fundamental laser around 1.05 ?m.It is the first time to our best knowledge that Raman conversion has been demonstrated in solid-state lasers by utilizing the 155 cm-1 Raman shift of YVO4 Raman crystal.Meanwhile,the highest slope efficiency of 35.3%is obtained,which is the highest optical conversion efficiency achieved in microchip Raman lasers,to our best knowledge.A coupled Raman microchip laser cavity with two output coupling mirrors has been designed to balance the intracavity losses of 1.03?m and 1.05?m fundamental laser.And the comb-like laser spectrum is obtained,which covers from 1041 nm and 1096 nm with a spectral bandwidth of 55 nm and 112 equidistant longitudinal modes.It is a major challenge for achieving stable high peak power Raman laser pulses in a passively Q-switched solid-state Raman laser.In order to improve the stability of Raman laser pulses and enhance the peak power of Raman laser in a passively Q-switched Raman microchip laser,a 940 nm QCW laser diode was used as pump source and a Yb:YAG/Cr4+:YAG composite crystal was used as working medium to alleviate thermal accumulation.By utilizing the 890 cm-1 Raman shift of the YVO4 crystal,the 1030 nm fundamental laser is converted to 1134 nm first-Stokes laser and 1261 nm cascaded Raman laser in Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman laser.And stable laser pulse trains and high peak power have been achieved.Meanwhile,the effects of the pump pulse duration and the reflectivity of output coupling mirror on the performance of the Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman laser have been investigated experimentally.The highest Raman laser pulse energy is 50 ?J,the peak power is 57 kW.And the stable Q-switched Raman laser pulse train is achieved with an amplitude fluctuation less than 6%at different pump powers.This work provide a new idea and method for developing stable and high peak power Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman microchip lasers.