Research On The Thin Disk Laser Multi-pass Amplifier

In the solid laser gain medium,thin disk crystal has the high surface-volume ratio,which can improve the cooling effect,reduce the thermal stress and weaken the thermal lens effect of thin disk.All these characteristics will guarantee both good beam quality and high output power.The single pass gain of thin disk is small due to the thickness of thin disk.A multi-pass structure is proposed to improve the power and energy of output laser.Thin disk laser multi-pass amplifier is to make a seed laser with good beam quality passes through thin disk crystal with inversed population many times to make the output laser with both good beam quality and high output power.Thin disk laser multi-pass amplification structure can accept laser pulses range from continue wave to femtosecond wave.In this paper,a thin disk multi-pass amplification system is designed based on the conjugated double parabolic mirror pumping module for thin disk.The related theoretical and experiment research have been analyzed minutely.The detail contents are:Firstly,a continue wave and a short-pulse amplification model is established.The output optical intensity can be calculated according to the steady rate equation with and without ASE.As for the short-pulse amplification,the total output energy is obtained by the transform equation and iteration.Secondly,a thin disk laser multi-pass amplifier is designed by a method of“Three Steps”,which include the design of the laser cavity,the expansion of the cavity and the design of the coupling system.A 20 or more passes thin disk amplifier is realized considering the advantage and disadvantage of foreign amplifier structure.And the distortion characteristics of the ideal Gaussian beam have been concluded.In a word,the thin disk laser multi-pass amplifier has good stability and high feasibility,which lays strong foundation for the experimental research.Thirdly,a 20-pass thin disk amplifier is built through three-stage experiment.On the basis of the experimental result,this amplifier can realize 20-pass amplification when the pump power density is less than 847.6W/cm~2 for the existing thin disk crystal.However,with the increase of the pump power density,the aspherical surface of thin disk can be worse,which will break the balance of the amplifier.Fourthly,combined with the theoretical analysis and experimental results,this paper obtains the small signal gain coefficient for different pumping power density.When the small seed pass through thin disk 2 times,the experimental results and the theoretical results are in good agreement.