Study On The High Quality Of Femtosecond Pulse Amplification

Amplification of femtosecond laser pulses is an important step to get high energy in ultrashort time scale.With the advent of chirped-pulse amplication(CPA),the energy of femtosecond laser pulses was improved to multi-Joule or tens of Joule,which corresponds to more than petawatt(1015W,PW).Due to the applications in high-field physics and ultrafast phenomenon,the amplified laser pulses must have very high beam quality with high temporal contrast ratio.The development of high quality amplified fs laser pulses is significant to interaction of laser and plasma in both laser technology and high-field physics.In this thesis,the researches focuse attention on the improvement of temporal and spatial qualities of amplified femtosecond laser pulses.The main researches and innovative results are summarized as follows:1.High contrast temporal ratio of laser pulses is realized by two aspects:(1)well conpensation of high-order dispersion,(2)cross-polarized-wave technology(XPW).As for conpensation of high order dispersion,by using the ray-tracing method,the dispersions arisen from grating stretcher and grating pair compressor are calculated,with consideration of all the material's dispersion in the amplifier,the compensation of dispersion of whole system is realized by optimization of grating's angle and distance between the gratings.The temporal contrast ratio will be improved.Furthermore,cross-polarized-wave technology(XPW)was employed to improvement of contrast ratio from 10-6to 10-9,meanwhile,the spectral bandwidth of laser pulses was broadened and compressed down to 16.7 fs by chirped mirrors.2.High beam quality in high energy terawatt(TW)amplified laser pulses was realized by large-mode regenerative amplifier.A new large-mode regenerative cavity was designed.Output laser energy up to 17.4mJ was achieved under the pump energy of 60 mJ,which corresponds to the efficiency of 29%.Based on this large mode size regenerative amplifier,1.9TW laser system which compressed pulse energy of 81.4mJ in 43 fs was also obtained by following a stage of multipass amplifier.The beam quality of compressed laser beam is less than 1.5 and energy stability is 2.15%(RMS).