Theoretical And Experimental Study Of 560nm Solid-state Raman Sum-frequency Yellow-green Laser

The yellow laser in the wavelength range of 560⁶00nm has important applications in the areas of biological genetics,clinical medicine,atmospheric detection,and information storage and so on.The 560nm yellow-green laser is the most sensitive visible light wavelength of the human eyes,and has special significance in clinical medical treatment,image and data display,spatial detection and identification,geographic survey,and signal transmission,etc.Currently,the yellow-green laser has been applied to the specific clinical treatment of skin.Stimulated Raman Scattering?SRS?is an effective method for obtaining new laser lines.In recent years,with the development of excellent Raman crystals,all-solid-state Raman lasers have become a hot spot in current research and have developed rapidly with their advantages of simple and compact structures,good mechanical properties and thermal properties.To use fundamental frequency laser and Raman laser to get the output of sum-frequency laser with sum-frequency crystal is an important way to obtain yellow-green laser at present.Sum-frequency Raman yellow-green laser has the advantages of compact structure,high conversion efficiency and stable performance.Sum-frequency laser has the characteristics of narrow pulse width and high energy.With these advantages,560nm sum-frequency Raman yellow-green laser have got extensive attention and have made great progress in recent years.In the aspect of theory,the rate equations of actively Q-switched intracavity sum-frequency Raman laser were derived and seven general parameters included k_ls,?,K_sp,N,M,F and K were obtained after normalization.Numerical simulations were performed to calculate the influences of different general parameters on the peak power of the output pulse,the energy of the single pulse,and the pulse width.The result was that the normalized initial population density N,the sum-frequency factor F,the normalized Raman gain coefficient M,and the loss factor K were bound and there was an optimal matching value of every general parameter in the certain numerical range.In order to achieve the maximum pulsed peak power and the maximum single pulse energy,matching relationships between F and M,F and K,M and K were fitted.The results showed a linear matching relationship among them,which was mainly reflected the matching relationship of the length of sum-frequency crystal,the length of Raman crystal and the reflectivity of the Raman output mirror in the experiment.This conclusion can be used for numerical analysis of specific experiments to optimize experimental settings to obtain the best output of sum-frequency laser.In terms of experiments,the output performance of the passively Q-switched intracavity Raman laser was studied.The flat-concave cavity structure was used with Nd:YAG as the laser crystal,SrWO₄ crystal as the Raman medium,and Cr⁴⁺:YAG as the passively Q-switched crystal.Under the guidance of theoretical calculations,the parameters such as the initial transmittance of the saturable absorber,the reflectivity of the output mirror to the Raman laser and the cavity length were continuously optimized.With a pump power of 3.92W and the initial transmittance of Cr⁴⁺:YAG of 96%,a maximum Raman output power of 0.79W was achieved,corresponding to an Raman conversion efficiency of 20.4%,and the corresponding repetition rate and pulse width was 38.6kHz and 20ns,respectively.This is the maximum conversion efficiency of the currently known LD-pumped passively Q-switched Nd:YAG/Cr⁴⁺:YAG/SrWO₄ Raman laser.Then,on the basis of previous experiments,a corresponding study was conducted on LD-pumped passively Q-switched intracavity sum-frequency Raman yellow-green laser with KTP as the sum-frequency crystal.The polarization relationship of the fundamental frequency laser and the Raman laser,energy relations and pulse synchronization issues were considered to set reasonable cavity parameters,560nm passively Q-switched sum-frequency Raman yellow-green laser was achieved.when the input pump power was4.18W,the maximum output sum-frequency optical power reached 0.101W with 2.4%of the optical-to-optical conversion efficiency,and the pulse width was about 10ns after adjusting the resonant cavity and polarization angle.