| The high-power ultra-fast and ultra-intense lasers are being extensively employed in the research field of biology,chemistry,as well as physics,especially in the highfield physics.This state-of-the-art lasers have also started to play critical roles in the industrial and medical areas,such as precise machining,surface processing,material modification,imaging and medical diagnostics.The pulse temporal quality is one of the key properties of high-peak-power laser systems,which includes pulse contrast ratio and the pulse duration of the compressed pulses.The former has impacts on the interaction process between the laser and the matter,while the latter determines the peak-power of the laser system.This thesis is focusing on the manipulations and diagnostics of fore-mentioned two key parameters: temporal contrast and pulse duration.The key technologies to control and enhance temporal quality in a CPA laser system was systematically studied.The main research topics and innovative results are demonstrated as follows:1.Dispersion managements in chirped pulse amplification systems are theoretically investigated,including the origin of different orders of dispersion,as well as their effects on the temporal pulse shape of the ultrafast lasers.Principles and alignment procedures of typical dispersion-management device and instruments,such as bulk materials,prism-pairs,Martinez stretchers,Offner stretchers,grating-pair compressors,as well as AOPDF are studied systematically.This study provides theoretical and experimental references to the dispersion managements of CPA laser systems.2.A temporal filter based on cross-polarized wave generation(XPW)was designed and implemented to enhance the temporal contrast and extend the bandwidth of our high-power ultrafast laser system.A double-CPA(DCPA)structure was utilized.In the first CPA stage,the regenerative laser cavity was designed by taking the thermal lensing effects into account.AOPDF was inserted before the amplifier to precisely control the dispersions.A high-contrast seed pulse for the second CPA was generated with 20% XPW conversion efficiency and 70nm(FWHM)bandwidth.Two repetitionrate modes of 10 Hz and 1Hz can be freely switched to each other in the second CPA stage.Output of 40 mJ,18.9fs pulses under 10 Hz and 400 mJ,<20fs pulses under 1Hz were demonstrated.Plans for further energy boost and vacuum pulse compression were proposed.3.The characteristics of XPW fundamental pulses affection to the XPW pulses was theoretically and experimentally investigated.First,we studied the impacts from the pulse duration and linear chirp of the driving pulses on XPW pulse duration and linear chirps.We compared the discrepancies under different parametric conditions.A femtosecond Ti:sapphire laser system(central wavelength 800nm;pulse energy 1.4mJ;Pulse repetition rate 1k Hz)was deployed to drive the XPW filter.An AOPDF was employed to precisely control the second-order dispersion.We have found that the XPW spectral bandwidth was expanded by more than?3 times,which could support a pulse duration more than?3 times shorter than the original drive pulses.There existed dramatic differences if same absolute amount of negative and positive dispersions were loaded.4.The investigation of the gain-narrowing effects in our CPA laser system has been conducted.We have experimentally demonstrated anti-gain-narrowing,in which FWHM bandwidth was extended from 30 nm to 60 nm,which could potentially reduce the pulse duration from 31 fs to 16 fs.This will dramatically enhance our capability to get higher peak-power from our ultra-fast and ultra-intense laser pulses. |
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