| Single longitudinal mode visible light laser has extremely high spectral responsivity and signal-to-noise ratio,in precision measurement,laser holography,laser display and other fields are widely used.At present,the common way of obtaining single longitudinal mode(SLM)visible laser is achieved by double the frequency of the near infrared band of Nd:YAG or Nd:YVO4 lasers once or more.So the optical and optical efficiency of the system is very low.The output bands of the Pr: YLF laser are all in the visible light range.Therefore,the combination of the mode selection technique and the Pr:YLF laser is an effective way to obtain the high efficiency SLM visible light.In this paper,the prelase theory is used as the starting point,examined the internal working principle of Pr: YLF laser and the influence of different parameters on the output characteristics of prelase Pr:YLF laser.At the same time,the single longitudinal mode pulse laser output at 639 nm is realized by the combination of prelase technology and prelase F-P etalon.The research work is as follows:In theoretical research,by introducing step function into the four-level rate equations,a mathematical model is established to describe the behavior of prelase,and the particle number evolution process of prelase Pr:YLF laser is simulated.The evolution law of inversion population and photon number with time is obtained.On this basis,the multi-mode competition theory is introduced to simulate the mode evolution process in prelaser technology,and the mode evolution law in Pr:YLF pre-laser process is obtained.At the same time,the rate equation of prelase technology is solved by Lagrange multiplier method,and its analytic expression is derived.The output characteristics of prelase Pr:YLF laser with different parameters(cavity length,single longitudinal mode modulation depth and introducing F-P etalon)are obtained by solving transcendental equation with step loss and quasi-steady operation time.In the aspect of experimental research,the continuous laser experiment of Pr:YLF laser is carried out firstly.The resonator adopts plane-concave cavit,the maximum output power of 639 nm red light is 1W,and the optical efficiency is 53%.Using the structure of the resonator above,conducted experiments in the pulse laser of Pr:YLF laser.A 639 nm red laser with 10 kHz repetition frequency is obtained.The threshold value is 0.56 A,single pulse energy is 4.5μJ,the pulse width is 110 ns,and the output power is 45 mW.By analyzing the experimental results at different repetition frequencies,it is found that the laser has "insufficient gain" when the repetition rate is 10 kHz.On this basis,the experimental study of pre-laser mode selection is carried out,and the experimental study of F-P etalon,prelase and combination technique are carried out.In the prelase mode selection experiment,the pump current is 0.72 A.A single longitudinal mode laser with a repetition frequency of 10 kHz at 639 nm is obtained,the single pulse energy is 30 nJ and the pulse width is 232 ns.It is found that when the pump current is greater than 0.72 A,the single longitudinal mode pulse laser can not be obtained by prelase technique.The experimental results show that the prelase technique has an upper limit of energy injection.In F-P etalon mode selection experiment,when pump current is 1.6 A,639 nm single longitudinal mode laser with repetition frequency of 10 kHz is obtained,the threshold value is 0.9A and the maximum single pulse energy is 0.25μJ,pulse width is 144.6ns,output power is 2.5mW,and SLM conversion efficiency is 5.6%.In the experiment of combination technique,when pump current is 1.6A,SLM laser with repetition frequency of 10 kHz is obtained,the threshold value is 0.60 A and the single pulse energy is 0.75 μJ,pulse width is 123 ns,output power is 7.5 mW,and the SLM conversion efficiency is 16.7%.Compared with the experimental results,it is found that the combination technique overcomes the energy injection problem compared with pre-laser technology,and its SLM conversion efficiency is three times higher than the F-P etalon.Compared with the experimental results with the theoretical results,it is found that the experimental results are almost the same as the theory,which indicates that the theoretical model established in this paper can reasonably describe and explain the internal operating mechanism of prelase Pr:YLF lasers. |
