In-band Pumped All-solid-state YVO₄ Raman Lasers And The Raman Beam Cleanup

Research on Raman lasers is of significance in the field of all-solid-state lasers.By means of shifting the fundamental laser to required wavelengths,Raman lasers provide varieties of suitable laser sources for laser communications,laser remote sensing,biomedicine and other areas.As an efficient third-order nonlinear optical frequency conversion technique,stimulated Raman scattering?SRS?has several unique properties such as cascading characteristic and Raman beam cleanup effect,which makes it potentially promising in more application fields.Therefore,with optimizing the thermal effect and the resonator structure for YVO₄ Raman lasers,we conduct researches concerning the output performance of cascaded Stokes waves and the Raman beam cleanup effect.The application of Raman lasers in optical parametric oscillators is also studied.A series of original results are achieved and as follows:1.The thermally-boosted in-band pumping scheme at 914 nm is employed to actively Q-switched Nd:YVO₄ self-Raman laser for the first time.By virtue of further reduction of quantum defect and consequent lower thermal load,efficient Raman output at 1176 nm and 1525 nm is achieved,respectively,with the conversion efficiency to be47.6%and 25.3%from absorbed pump power to Stokes output.2.Based on an actively Q-switched Nd:YVO₄/YVO₄ intracavity Raman laser,a folded coupled cavity is designed to make full use of the high pump intensity on the Raman crystal.The first-order Stokes output of 10.32 W at 1176 nm and the second-order Stokes output of 5.16 W at 1313 nm is achieved,respectively,which are higher than the ever-reported 1.17-?m end-pumped intracavity Raman lasers and 1.3-?m second-Stokes intracavity Raman lasers.3.The mechanism of Raman beam cleanup is illustrated based on four-wave mixing interaction.With a Nd:YVO₄ self-Raman laser and a Nd:YVO₄/YVO₄ coupled-cavity Raman laser,we found that the beam quality of the Raman scattering light at1176 nm?M²=1.69?is better than that of the fundamental laser at 1064 nm?M²=3.08?,and the Raman beam quality?M²=1.21-1.69?is capable of maintaining quasi-Gaussion distribution along with increasing gain.4.A tunable MgO:PPLN OPO pumped by Raman scattering light is demonstrated for the first time.Compared to the MgO:PPLN OPO pumped by the fundamental laser at 1064 nm,higher conversion efficiency of 44.9%and narrower linewidth of⁰.3 nm are achieved with the OPO pumped by the Raman light at 1176 nm.With increasing pump power,the degradation of the OPO beam quality is smaller with the Raman pumping source.5.A tunable MgO:PPLN OPG pumped with dual wavelengths at 1064 nm and1176 nm is presented for the first time.By changing the crystal temperature,continuously-tunable dual-wavelength output around 1.7?m with small frequency differences is achieved at the grating period of 31.59?m.We came up with a new solution for dual-wavelength output with frequency difference locating in THz band,which is compact in structure,convenient in tunning and economical in cost.