Theoretical And Experimental Study On HF Chemical Laser Systems With MOPA Configuration

Master oscillator-power amplifier (MOPA) technology is one of the importanttechnical approaches to obtain high power and high beam quality output laser, and it isan important direction for future research in the field of high-energy laser. The energyextraction efficiency of the amplifier, the amplification ratio of coherent laser and theproblem of stray light caused by amplified spontaneous emission (ASE) in single strainMOPA structure HF chemical laser systems are studed. A complete theoretical modelabout MOPA structure HF chemical laser is established. Basing on this model, it canprovide important reference to developed and optimized for the high-power HF/DFlasers which using MOPA structure.The high-power HF chemical laser device which using MOPA structure is mainlycomposed by the master oscillator and the amplifier, the spontaneous emission is alsoamplified in the amplifier when the coherent laser is amplified. The ASE is not only animportant factor to affect the energy abstraction of the coherent laser, but also the mainfactor of the stray light in the amplifer. In order to analyzed the influence of ASE effectson energy abstraction efficiency in amplifier and in order to bring guidance to themanagement of stray light, a physical model which coupling the coherent laser and theASE in the MOPA structure HF chemical laser is established. This model used the smallsignal gain coefficient to coupled the coherent laser flow equation and the ASE flowequation, through iterative computation, it can obtained the magnitude of the coherentlaser and the ASE in any position of the amplifier. Because made the multi-line spectralconvert to single-line spectral, it is the simplified the HF chemical amplifier and it iseasy to calculation.In order to bring inlet parameters for the established physical model, the researchon the mearsuremt methods of inlet parameters are carried out. And the integrated smallsignal gain coefficient, the integrated upper state population density and the saturationlight intensity is mearsrued. The integrated small signal gain coefficient is gained by themethod of amplification of the input laser, and in this method, the distribution of theintegrated small signal gain coefficient is measured by scanning mirror. The integratedupper state population density is measured by the ASE light which normal incidence outof the amplifier. The saturation light intensity is measured by the results of theintegrated small signal gain coefficient to restrict the results of variable couplingmethod, it can avoid the error due to the power fluctuations in variable coupling methodand can improve the accuracy of the measurement results. Bring these inlet parametersinto the physical model of amplifier and into the model of master oscillator, wesimulated the electrical discharge HF/DF chemical laser which using MOPA structure.The output power and the laser beam shape of the master oscillator under different conditions, the energy extracted in the amplifier by output laser of oscillator, the energyextraction efficiency in the amplifier and the amplified ratio of input laser, thedistribution of ASE in the amplifier under different conditions are simulated. And theASE that propagated outside the amplifier when there is no input laser is also simulated.By comparison these simulation results with the experiment results, it can found that thedifference between the calculation results and the experiment results is less than15%,the correctness of simulation models are verified.The high-power MOPA structure HF chemical laser systems were simulated afterverified the correctness of the simulation model. The influence of the gain mediumlength, the gain medium length-to-height ratio, and the saturation light intensity onmaster oscillator’s output power is analyzed. And also the influence of the gain mediumlength, the gain medium length-to-height ratio, the saturation light intensity, the powerof input laser, and the beam shape of input laser on energy extraction efficiency and onASE in the amplifier are analyzed. It can be drawn from the simulation results, for theHF chemical lasers which using MOPA structure, in order to obtain greater outputpower, the following measures can be used. The distance between the gain module withthe unstable resonator concave mirror should be as small as possible; increase the of thegain medium length-to-height ratio can not improve the output power of the masteroscillator, but it can reduce the amplified spontaneous emission in amplifier; it cansignificantly suppress ASE when the input laser’s average power density is muchgreater than the gain medium’s saturation light intensity.