Research On Key Technologies Of Coherent Combination For High-energy Short Pulse Lasers

The development of high-energy short pulse laser(HESPL)technology provides conditions for the research on material properties under extreme conditions and strongfield physics experiments.Many countries are planning to develop laser systems that can produce tens of petawatt,hundreds of petawatt,and even exawatt-class pulses.However,the output power of single laser beam is difficult to be further improved due to the limits of physical properties of operation material,nonlinear effect and pump technology.By coherently focusing multiple beams in far field,the coherent beam combination technology can exponentially raise the power density of focal spot despite of the limits of single beam output capability,which makes it one of the effective approach to obtain higher power short pulse laser output and has been adopted in many HESPL facilities over the world.This paper focuses on the key technologies of coherent combination for HESPL.The theory and system of coherent combination of multiple HESPLs are analyzed.The coherent combination of two ultrashort pulse lasers are realized based on stochastic parallel gradient descent(SPGD)algorithm.A new method of tilling error compensation based on a small-size mirror for large aperture array grating is proposed.The influence of wavefront error on the spatial-temporal property of output pulse for array grating compressor has been analyzed.The main research contents in this paper are as follows:1.The theory of coherent combination of HESPL has been studied.The influences of amplitude,synchronization error,pointing error,wavefront aberration,fill factor,polarization direction,and dispersion on the effect of coherent combination are analyzed.The system analysis of coherent combination of HESPL facility is carried out based on the theory.2.According to the characteristics of HESPL facility,coherent combination of multiple short pulses using SPGD algorithm is realized.The evaluation function,the perturbation mode and the distribution character of perturbation are optimized by using numerical simulation.Coherent combination of two beams with the pulse width of 30 fs is experimentally achieved combined with the cross-correlation signal.Finally,the applicable conditions of SPGD algorithm for multi-channel HESPL coherent combination are discussed.3.For the problem of tiling array gratings coherently in coherent combination of HESPL,a novel method for error compensation of large-aperture array grating compressor by using a small-aperture mirror is presented and the feasibility of the high frequency and high precision tiling error compensation is proved thought experiment.Combining the theory of coherently tiling and the property of array grating,the system analysis of array grating compressor is carried out.The advantages of the novel method compared with the conventional tiling method are investigated based on the theory of system stability and rapid movement.The relationships between the amount of mirror compensation and tiling error are analyzed.The influence of the compensated tiling error on the focus energy is quantitatively compared with numerical simulations,which combined with the ray-tracing method and principle of Fraunhofer far field diffraction.The correctness of the method principle is proved theoretically.Finally,an array grating compressor experimental platform is built to verify the correctness.4.The effects of wavefront error of input pulse,deformation and wave aberration of grating on the spatial-temporal property of the far-field focal plane of the compressor's output pulse are analyzed combined with the theoretical model of array grating compressor.Their corresponding error tolerances are presented based on Monte-Carlo simulation method.The probability of wavefront error correction using deformable mirror is investigated and the mirror location relative to compressor is analyzed.HESPL coherent combination technology is still in the exploration and design period so far.This paper analyzes,calculates and verifies some of the key technologies from both theoretical and experimental aspects,and has important reference significance for the engineering realization of coherent combination in HESPL facility.