Noncollinear Noncritical Phase-matching For Sum Frequency Generation In KDP Crystal

As the driver of the inertial confinement fusion,the transmission of high-energy laser would cause obvious nonlinear effects,which might lead to the damage of optical element and impose restrictions on the operation and capability of a high-power laser facility.Study shows that the damage of short wavelength laser to fused silica is much greater than that of longer wavelength laser.In large laser systems,such as the National Ignition Facility in America,focusing third-harmonic ultraviolet wave for ignition target experiment might damage the lenses or other optical components of the system.Aiming at the above problems,this thesis proposed the scheme of prefocusing and noncollinear noncritical phase-matching configuration.By using lenses to focus the incident fundamental wave k₁ and second-harmonic wave k₂ before KDP crystal for sum frequency generation,the third-harmonic generation k₃ could focus automatically without a lens,which could overcome the problem of lenses damage during the focusing of high-energy ultraviolet light.For realization of prefocusing,the angular acceptance for KDP crystal is supposed to be large.In collinear configuration,noncritical phase-matching has the advantages of large angular bandwidth,large effective nonlinear optical coefficient,and no beam walk-off.However,for different crystal and different phase-matching types,collinear noncritical phase-matching corresponds to different specific fundamental wavelength.For example,in National Ignition Facility of America,the fundamental wavelength is 1053nm,while the sum frequency generation type-I noncritical phase-matching wavelength for KDP crystal is 738 nm.Therefore,we proposed noncollinear noncritical phase-matching configuration.By setting k₃ along?=90°direction,noncollinear phase-matching configuration could achieve broad angular acceptance such as in collinear noncritical phase-matching configuration.This kind of phase-matching configuration has no limitation for fundamental wavelength,thus we do not need to regulate doping ration or temperature in crystal to satisfy the specific fundamental wavelength.In this thesis,we have fully explained the principle of broadband sum frequency generation for noncollinear noncritical phase-matching configuration.At the same time,the noncollinear effective nonlinear optical coefficient,angular bandwidth,and up-conversion efficiency have been calculated in theory and verified in experiments,giving the basis for the scheme of prefocusing and a convergent third-harmonic generation.Calculation shows that thinner crystal could bring about larger angular bandwidth but have lower conversion efficiency as well.Actual crystal thickness is determined by the tradeoff between conversion efficiency and angle tolerance.