Investigation On Passively Q-switched Self-Raman Laser And Frequency Doubled Yellow Laser

The yellow lasers at 550-600 nm have been specially applied in biological mark,eye treatment,astronomical exploration,visible display and so on.Based on nonlinear effect,all solid-state yellow lasers can be generated through the following two main methods:one is obtained by sum-frequency generation?SFG?of 1.06?m and 1.30?m emissions.But most of the SFG lasers have large sizes and complex structures.Another way is via second harmonic generation?SHG?of 1.1-1.2?m near infrared?NIR?laser.However,there are few gain mediums that can directly emit efficient NIR lasers.Based on third-order nonlinear effects,the stimulated Raman scattering?SRS?can convert the common laser at 1.0-1.1?m to 1.1-1.2?m.SRS have the advantages of no need for phase matching,pulse compression,high energy,beam clean-up,et al.When doped with rare earth ions,some materials with Raman active can achieve both lasing and frequency conversion.Thus,the appearance of the self-Raman crystals promotes the yellow lasers which based on SRS and SHG to be more compact and simpler.In this paper,passively Q-switched?PQS?self-Raman laser and frequency-doubled yellow laser based on Nd:YVO₄ crystal were demonstrated.The main achievements are manifested as follows:1.To alleviate the influence of thermal effect in self-Raman crystal,both in-band pumping technique and diffusion-bonded crystals are used.For 880 nm LD pumping c-cut Nd:YVO₄composite crystal,the quantum effect was about 29.2%decrease and the focal length of thermal lens was increased by 3.6 times than the device of 808 nm LD pumping a Nd:YVO₄ crystal.Therefore,these two methods of thermal management technology were verified to be benefit to improve the output power and efficiency.2.A concave-plane resonator was utilized to deliver PQS fundamental and Raman lasers.i.When the absorbed pump power increased to 27.5 W,9.0 W-output power of 1066 nm laser with a slope efficiency of 43.6%was obtained,corresponding to the diode-to-fundamental conversion efficiency of 32.8%.ii.Under the absorbed pump power of 20.6 W,the maximum average output power of first Stokes laser was up to 2.53 W,corresponding to the diode-to-Raman conversion efficiency of 12.3%.The pulse repetition frequency and pulse width were measured to be 39.1 k Hz and 20.4 ns,and the corresponding pulse energy and peak power were calculated to be 64.7?J and 3.2 k W.To the best of our knowledge,this is the highest output power ever obtained from PQS self-Raman laser.3.A type-?non-critical phase-matching LBO crystal was adopted to generate yellow laser at589 nm.When the absorbed pump power reached 17.5 W,the maximum output power was 0.66W with a slope efficiency of 8.1%,corresponding to a diode-to-yellow conversion efficiency of3.8%.The pulse properties of yellow laser were 2.8 ns/16 k Hz/41.3?J/14.7 k W.The M² factor was measured to be better than 1.5.To our knowledge,this is the highest average output power,single pulse energy and peak power of PQS yellow laser via frequency doubling self-Raman laser.