Theoretical And Experimental Study Of The Multi-raman-modes Solid-state Raman Lasers

Stimulated Raman Scattering(SRS)in crystal is one of the important frequency conversion techniques in the field of solid-state lasers.The SRS of the strongest symmetrically breathing vibration mode is suppressed,and coherent lights of different frequency and different wavelength can be obtained through the SRS of the Raman mode with relatively lower gain.The emergence of new wavelength is of great significance to the research of laser field.In this paper,the normalized rate equations of actively Q-switched Raman lasers with two Raman modes are deduced under the plane wave approximation.The values of normalized variables are calculated with typical experimental parameters.The rate equations are solved numerically,and the reasonable value range of the normalized parameters are obtained to achieve the SRS of the Raman mode with relatively lower gain.Based on the theoretical simulation results,the optimization scheme of experiments can be given.In this paper,assuming that photon densities and initial population inversion densities have Gaussian spatial distributions,the space-dependent rate equations of actively Q-switched Raman lasers with two Raman modes are deduced theoretically.The rate equations are solved numerically to explore the experimental conditions to achieve the SRS of Raman mode with relatively lower gain,and the numerical simulation results are used to optimize the experiments.In the paper,the laser experiment with c-cut Nd:YVO₄ crystal is carried out.Under continuous wave condition,the absorption characteristics of Nd:YVO₄ crystal are tested,and the fundamental conversion efficiency under different output mirror conditions is compared.With an absorbed diode pump power of 4W,the highest fundamental laser output power of 1.852W is obtained,corresponding to an optical-to-optical conversion efficiency of 46.3%.The saturable absorber is added into the resonator to perform the passively Q-switched laser experiment,and the initial transmission of Cr⁴⁺:YAG saturable absorber is 85%,89%and 92%,respectively.With an absorbed diode pump power of 4W and initial transmission of 92%,the highest fundamental output power of 0.83W is obtained,corresponding to an optical-to-optical conversion efficiency of 21.5%.Meanwhile,the c-cut Nd:YVO₄/Cr⁴⁺:YAG intracavity Raman laser is operated.By adopting the suitable cavity mirror,the high conversion efficiency of the Raman mode with relatively lower gain 266cm^-1 is realized.With Cr⁴⁺:YAG of the initial transmission of 89%,the highest Raman output power of 0.521W is obtained,corresponding to an optical-to-optical conversion efficiency of 13.03%,and it is the highest conversion efficiency of the SRS of Raman mode with relatively lower gain currently.In experiment,there are nine wavelengths can be observed in the spectra at most,1020nm,1050nm,1066nm,1085nm,1097nm,1110nm,1130nm,1140nm and 1178nm.