Research And Application On Flow Heat Management In Liquid Laser

The thermal effect of the laser gain media is the main bottleneck restricting the development of high average power laser. Liquid flowing provides a new method solving the thermal problem in high average power laser, which results in high-power liquid laser absorbing more attention gradually. In general opinion, liquid can take out the heat from the gain area by flowing, which is helpful to reducing the influence of laser beam quality by thermal effect. But the influence of laser beam quality by thermal effect during the pumping period is not worked out. In this dissertation, by the aid of the principle of hydrodynamics and the energy equation method, the design of the construction of liquid circulation and flowing heat management are studied. The feasibility of flowing heat management using in high energy liquid laser is discussed. On the base of the semiclassical theory, the theoretical and experimental investigation of mode competition in short pulse pumped broad spectrum dye laser are studied.It is the most important for shrinkage segment design in the design of the construction of fluid circulation. This decides the flowing state in gain area. In this section, witozinsky curve and double cubic curve are applied. Through the numerical simulation by Fluent Software, the result shows that the good flowing quality is achieved, avoiding the separation of boundary layer. By means of promoting the entrance speed, the thickness of boundary layer is declined. The wave-front of He-Ne probe laser influenced by the flow of Rh6G dissolved in ethanol is experimental studied. Under three kinds of speed conditions, the strehl ratios of the probe laser are bigger than 0.99 all. Flow influences the beam quality sightly.On the base of the analysis of thermal effect mechanism in liquid laser media, the main factor is decided. The nonuniform distribution of the refractive index induced by nonuniform temperature distribution lead the undulation of the optical path distance along the laser path. The temperature equation is deduced. The model of flow heat management and the thermal effect of liquid laser media are both investigated under the pulse mode and the continuous wave mode conditions. Although the heat cumulation can be eliminated between the pulses, but the heat can not be ignored during the pulse. The working condition shows no difference with the stand singer pulse laser.Under the continuous wave mode condition, the optical power density is declined, and the lasing time is increased. Therefore, there is no break in the distribution of the temperature and the optical path distance. The promotion of the temperature is smaller than that in pulse mode. The laser beam quality is enhanced. As to Guassian nonuniform pumping, when the flow speed is constant, the strehl ratio descends distinctly while theκlessening. Heat efficiencyηand flow speed u y influence the laser beam quality. The uniformity of the phase can be improved by lessening u y and promotingη. By the aid of the curvature sensor and the Green's function algorithm, liquid thermal effect with small scale and pumping power is researched experimentally. Under the slow flow speed condition, the purpose of promoting the laser beam quality by flow heat management is not distinctive, the laser beam quality becomes worse while the power is bigger. Along with the improvement of the flow speed, the uniformity of the probe laser phase is ameliorated. But because of the nonuniformity of pumping, the influence of thermal effect can not be eliminated.The feasibility of flow heat management using in high energy liquid laser is researched. Because of the request of output power, it is difficult to reducing the heat in gain area by shorten the distance in flow direction. On the other hand, the improvement of flow speed will induce the"Gas Cavity"phenomenon, which could lessen the efficiency of laser. For the sake of avoiding the"Gas Cavity"phenomenon, the cumulation system demands high request for the pressure. Therefore under the engineering technology condition at present, it's very difficult to eliminate the thermal effect only by flow heat management.Under the middle or small pumping power condition, the flow heat management make a good use for many applications. When the pumping pulse is very short, mode competition is very serious, so the numerical resolution must be used. In the two spectrum competition condition, both of the spectrum will export approximate power, by adjust the waste of one spectrum. the tunning range broaden. It make consistent which the experimental result. Through the numerical modification and the experiment, the mode competition in the broad spectrum is discussed, and the spectrum character of broad spectrum dye laser is concluded.