Study On Generation And Application Of High Energy DUV Lasers

Deep-ultraviolet(DUV)laser are extensively required for science,medical,and industrial application,since the shorter wavelength and higher single photo energy.In the context of Inertial Confinement Fusion(ICF),powerful laser facilities have inspired the development of precise physics experiments,as well as expose unprecedented problems especially the laser plasma instabilities problem.This brings new opportunities and challenges for the development and application of high-energy deep ultraviolet lasers,since the laser-target coupling efficiency and the square of wavelength are inversely proportional,and the shorter laser wavelength increases the instability intensity thresholds.Thus,by driving the target by 4ω laser instead of 3ω laser,the ability of laser driver for physics experiments can be improved,and the LPI problem can be mitigated.However,damage to the optical elements becomes worse as wavelength decreases,as the optics damage threshold drops severely as the single-photon energy increases.Concurrently,the gain of nonlinear effects,such as small-scale self-focusing and stimulated scatterings,increases dramatically.New technologies are urgent with breakthrough,which is also the focus of this paper.On the other hand,Physicists believe that large deviations are exist in the understanding of plasma physics processed under extreme conditions,so obtaining accurate plasma state parameters and their evolutionary properties is the basis for understanding plasma physics,which is of great significance.Thomson scattering diagnosis is the most accurate diagnosis methods for extreme plasma state.With a high-energy DUV probe laser,higher plasma density can be penetrated,and the single-noise-ratio can be significantly improved.The research on DUV probe beam can promote the development of Thomson scattering diagnosis technology,as well as accumulating experiences for high energy application.Based on the significant requirement in ICF field,this paper mainly focuses on the research of high energy fourth and fifth harmonic generations and applications,the main context and innovation points are as follows:1)A novel fourth harmonic generation(FHG)scheme in focusing beams is proposed for large aperture laser facilities.By placing the focusing lens before the FHG crystal,the desperate ultraviolet damage problem can be released,while the FHG conversion efficiency is almost unaffected owing to the large angular acceptance of non-critical phase matching(NCPM)technique.Numerical simulation to the FHG process indicates that,the angular acceptance can be appropriately increased by lowering the working temperature and jointing the two adjacent compensating angles,so that the focusing beam with relatively small F numbers turn feasible.2)Since the 4ω and the residual 2ω focal spot are strictly con-focal in this configuration,the target can be driven by dual-wavelength lasers simultaneously,which provides a novel and interesting idea for laser-target coupling.For dual-wavelength driving,more energy could be coupled to target.Besides,the focal spot smoothing would also be more favorable.Due to the mode mixing mechanism during frequency conversion,the size of the 4ω and 2ω focal spots are almost the same but there are much more high-frequency components in the 4ω spot.Since the two spots are completely incoherent,the spatial uniformity of the target irradiation can be improved.For pure 4ω beam driving,the residual light can be easily dispersed by making the DS to be a small-angle wedge,since the con-focal characteristic makes beam separation more efficient by spot-to-spot rather than spot-to-near field.3)High precision and large aperture temperature controlling system with two layers of recycling water and vacuum isolation have been developed,and a precision beam focusing and pointing technique method was proposed with 3ω indicating light and compensating lens have been verified.Large aperture and NCPM FHG has been experimentally demonstrated in the focusing beam,and 182 J of 4ω laser energy was generated and 82%of FHG efficiency(2ω-4ω)was realized.4)Fifth harmonic generation of Nd:glass laser with ADP and CLBO crystals were investigated,and maximum conversion efficiency of 15%and 19%were demonstrated respectively.Since the temperature sensitivity of ADP crystal would hinder its high-energy application,based on the complementary relationship of angular and temperature in the phase-matching condition,an upgraded focusing 5thHG design coupled with cylindrical temperature distribution scheme was proposed.By this upgraded focusing design,more than the improving of the conversion efficiency,the output 5ω near-field intensity distribution turns to be insensitive to the temperature gradient.Potentially,this idea can be provided for many other frequency conversion schemes such as high-repetition frequency lasers which have similar temperature gradient problems.