| Narrow linewidth laser has the characteristics of high spectral purity,large peak spectral density,long coherence length and low phase noise.Therefore,it can be used as the core light source in cold atomic physics,optical precision measurement,coherent optical communication and clock.The visible light band deep red narrow linewidth laser can be applied in biological detection and used as a two-photon fluorescent dye excitation light source in some live cell imaging experiments.The common method to obtain visible narrow linewidth laser output is to perform nonlinear frequency conversion in the near-infrared band,combined with short cavity,ring cavity,volume Bragg grating,and Fabry-Perot etalon method(F-P)and other mode selection methods.However,multiple nonlinear conversions seriously affect the laser’s conversion efficiency and output power.The emergence of Pr:YLF crystal can directly lasing visible light(390-780 nm)laser at different wavelengths.Compared with the method of nonlinear frequency conversion to obtain visible light,the laser conversion efficiency and output power are significantly improved.At the same time,the crystal has low phonon energy and low thermal lens effect,which has attracted much attention.For the selection of mode selection method,the mode selection method of F-P etalon group has strong linewidth compression ability and simple structure,which has become an important means to realize visible light narrow linewidth laser.This paper studies and discusses the Pr:YLF deep red narrow linewidth laser based on double F-P etalons theoretically and experimentally.Theoretical part: Based on the physical model of Pr:YLF four-level rate equation,a theoretical model of narrow linewidth deep red laser with double F-P loss term and output mirror transmission loss is established.The output characteristics of Pr:YLF narrow linewidth deep red laser are simulated and analyzed by solving the model.At the same time,the related principle of the mode selection technology of the double F-P etalon group is described,and the influence of the different parameters of the double F-P etalon group on the output characteristics of the laser is analyzed.The insertion angle of the F-P etalon is particularly important.Finally,the F-P etalon of 0.5 mm and 1 mm thickness is selected and coupled.The insertion angle of 1 mm F-P etalon is 1.54°,and the insertion angle of 0.5 mm F-P etalon is 0.92°.Finally,the ABCD transfer matrix is used to simulate the resonator’s stable range when the output mirror’s curvature radius is different,which lays a theoretical foundation for the experimental research.Experimental part: Through theoretical analysis and experimental design,the experimental study of Pr:YLF deep red laser output and Pr:YLF narrow linewidth deep red laser output based on double F-P etalon group were carried out respectively.Firstly,the output mirrors with different radius of curvature and different transmittance are selected for comparative experiments.Finally,it is concluded that the laser output performance is optimal when the radius of curvature of the output mirror R = 100 mm and the transmittance T = 3 %.Then,the F-P etalon group with thickness of 0.5 mm and 1 mm is placed in the resonator to adjust its angle.The output characteristics of the narrow-linewidth deep red laser are as follows: when the pump power is 2605 m W,the maximum output power of 509 m W is obtained.The slope efficiency is 20.8 %,the optical-to-optical conversion efficiency is 19.5 %,and the center wavelength of the deep red laser is 720.9 nm.The Fabry-Perot interferometer was used to measure the single longitudinal mode output of the laser with a linewidth of 50 MHz. |
PDF Full Text Request