| Nonlinear optical frequency conversion technology is always a research hotspot in the field of laser, and frequency doubling is its most typically and most widely used technology. KBBF crystal is a type of negative biaxial crystal and belongs to orthogonal point group of D3, KBBF crystal has wide bandwidth, the phase of moderate refractive index and a wide range of phase matching values. At present, KBBF crystal is the only can in theory and experiment to achieve the following200nm laser frequency doubling output crystal. So study KBBF crystal frequency conversion in DUV region is very popular.In this dissertation, we comprehensively summarize the research status of KBBF crystal’s nonlinear character at home and abroad. Based on this analysis, the theoretical study and numerical calculation on frequency doubling of KBBF crystal are presented. The main achievements are as follows.First、From non-collinear optics and electromagnetic field theory, drive the frequency doubling formulas of negative crystal’s type I is,and the type II isSecond、Type I and type II nonlinear frequency-doubling phase-matching angle of KBBF crystal whose fundamental frequency wavelength is at1064nm,532nm and under400nm to320nm is calculated with numerical method.Take the wavelength is400nm, the range of type I two groups non-collinear phase-matching angle in the first quadrant are about:θ1(51.00°～90.00°),θ2(50.83°～66.32°),θ3(52.68°～78.16°) and θ1(51.00°～66.00°),θ2(60.41°～89.59°),θ3(55.71°～77.79°).Take the wavelength is532nm, the range of type II phase-matching angle in the first quadrant are about:θ1(49.50°～54.50°),θ2(53.68°～55.03),θ3(53.05°～54.75°) and θ1(52.00°～69.00°),θ2(60.82°～86.69°),θ3(56.49°～78.08°), and so on.Arbitrary wavelength with a fundamental frequency of two groups of matched angular range is very different. Third、Type I effective non-collinear coefficient°f KBBF crystal whose fundamentalfrequency wavelength is at1064nm,532nm and400-320nm is calculated with numericalmethod.In any fundamental wavelength, the two groups were matched direction°f theeffective non-collinear coefficient are different, and the difference is very big. Because theSHG conversion efficiency is proportional to the square°f the effective non-collinearcoefficient, should choose effective nonlinear coefficient matching angle.Fourth、In anisotropic°ptical material, each beam°f light has walk-off angle, so evenif the two fundamental frequency waves have the same wave vector direction, thedirection°f energy flow will still have deviation. Numerical calculation°f KBBF crystalthe acceptance angle and walk-off angle under type I and type II non-collinear phasematching.In the range°f non-collinear walk-off angle, the angle range between the e light°f1064nm and thee ’light°f532nm i（s3.14265o，3.31432o）and（3.35481o，3.44275o）,another group°f the walk-off angle: e light range is（2.17475o，3.24019°）and thee ’light range is（1.39850°，3.27663°）. KBBF crystals have larger walk-off angle,therefore in the calculation°f frequency conversion efficiency should be considered whenthe walk-off angle effect.Fifth、Numerical calculation°f the crystal KBBF type I and type II non-collinearphase matching acceptance angle.In the ultraviolet and deep ultraviolet region, tape I non-collinear phase matchingacceptance angle with fundamental wavelength increases linearly. The fundamentalfrequency light wavelength is400nm, the acceptance angle is0.135mrad; the fundamentalfrequency light wavelength is325nm, the acceptance angle is0.108mrad.The above results have an important guidance to improve type I and type IIphase-matching frequency doubling conversion efficiency°f KBBF crystal in eachwavelength. At the same time, the research approach and numerical method provide somereferences to the study°f similar non-linear°ptical materials’°ptical properties. |
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