Study On Key Technologies For Quasi-parametric Chirped Pulse Amplification For High Average Power Applications

The peak power of ultra-short lasers has been significantly enhanced since its infancy,and the focused intensity(W/cm)generated by extremely strong electric field makes strong-field experimental physics into the area of relativity.However,the repetition rates of current high-peak-power lasers still remain quite low(single-shot or ? 10Hz),limiting the average power of high-peak-power laser to only tens of watts,which cannot meets the experimental requirements,for example laser acceleration.On the other hand,although diode-pumped technology can be applied to generate lasers with an average power exceeding 10,000 watts,its pulse durations are generally restricted to the level of nanosecond,which means the infeasibility to achieve extremely high peak power.Such dilemma of ensuring either high peak power or high average power is caused by limitations of various laser amplification methods and state-of-the-art technology.Chirped-pulse amplification(CPA)with high repetition rate is often constrained by thermal effect due to absorption of pump light over gain medium.Moreover,optical parametric chirped-pulse amplification(OPCPA)can effectively alleviate energy deposition,yet its saturation amplification is faced with intractable parametric back conversion problem,damming the energy conversion efficiency(only about 10-20%).Quasi-parametric chirped-pulse amplification(QPCPA)is an emerging technology designed to restrict the back conversion problem that besets OPCPA.Both theoretical and experimental study has proven that QPCPA can achieve extremely high peak power.Nevertheless,relevant analyses and researches about its average power are still in shortage worldwide.To address these problems,this paper has carried out two pieces of researches:1.Study on QPCPA's Characteristics of High Average PowerUnder the condition of high average power,the temperature rise of crystal will change its refractive index,thereby resulting in thermal dephasing,and its space distribution is unevenly distorted.However,QPCPA itself has excellent robustness and is insensitive to phase mismatching.Hence,the two contradictory conditions are bound to be mutually constrained,and eventually a balance will be reached.In the Chapter 3,we apply iterative algorithms to conduct theoretical simulations for such situation,which takes into account absorption,thermal dephasing and spatiotemporal modulation including first to third-order dispersion,beam walk-off and diffraction.In order to study the thermal effects on QPCPA,we gradually increased the pulse repetition rates and single pulse energy in simulation,and observed spatiotemporal characteristics and temperature distribution of crystals.The simulations show the amplification of 5 k Hz-3 TW and 1 Hz-13.5 PW.The average powers of both exceed 150 W.In addition,to reduce the impact of thermal dephasing,we also offer simulations of using temperature-insensitive configuration at the end of the chapter.It turns out that the configuration can effectively restrain the thermal dephasing on QPCPA with high average power.2.Study on SHG-QPCPA and SFG-QPCPAQPCPA can work steadily with high average power(>100 W)and high peak power.However,thermal dephasing problem still besets its amplification,making it necessary to study a new QPCPA technology which aviods obvious thermal effects.In Chapter 4,we propose two new configurations of QPCPA,which are consuming idler by second-harmonic generation(SHG)and sum frequency generation(SFG).They have some advantages: First,thermal effects in both SHG and SFG are insignificant.Second,these two parametric processes can be used to deplete idler and suppress back conversion as QPCPA does,thus further promoting the average power and high peak power.Third,phase matching could be easily achieved in SHG and SFG,which means it can be applied to visible light,near infrared and middle infrared directly.In Chapter4,we solve phase matching solutions for both SHG-QPCPA and SFG-QPCPA in various crystals and simulate the amplifications.The simulations have proven that both of them are able to suppress back conversion and enjoy a promising prospect for future applications of higher-average-power laser.