The Nonlinear Optical Properties Of High Power Ultraviolet Materials Under Intense Laser Radiation

KDP crystal is a nonlinear optical crystal with excellent optical properties and has been widely applied in electro-optic modulation,laser frequency conversion etc.Under intense laser irradiation,the KDP crystals will be induced nonlinear absorption and self-focus effect,which decreases the laser damage thresholds at some extent.Z-scan technique has been extensively used in nonlinear optical properties research due to the easy operation and high accuracy.In this paper,picosecond Z-scan technique was applied to investigate the nonlinear absorption and nonlinear refraction of KDP crystals under different laser energy,wavelength and thickness,the relation of nonlinear absorption induced by impurities with laser damage thresholds and the nonlinear optical properties of KDP crystal irradiated by pumping laser had been investigated as well.The Main research work and results are shown below:(1)The influences of thickness of samples,wavelength and optical power density on nonlinear optical properties of KDP crystals were investigated based on Z-scan theory of thick and thin medium.Results shown that thick samples had strongly nonlinear optical properties than the thin samples at same laser fluence,KDP crystals exhibited obviously resaturable absorption and self-focus effect at 355 nm and532nm wavelength and two-photon absorption was the main nonlinear absorption mechanism in KDP crystals,but the KDP crystals didn’t have any nonlinear optical properties at 1064 nm wavelength.(2)The relationship between nonlinear absorption of impurities in KDP crystals and laser damage threshold,the effects of growth sectors and orientation of KDP crystal and the content of deuterium on nonlinear optical properties had been investigated.Results shown that KDP samples with more impurity contents had stronger nonlinear absorption and lower damage threshold,for the nonlinear optical properties of rapidly grown KDP crystal: z> Ⅱ orientation and prismsector>pyramid sector,The nonlinear optical properties of DKDP crystal decreased with the increasing of the content of deuterium.(3)The nonlinear optical properties of KDP crystal after irradiation with different nanosecond laser pulses of 355 nm was investigated under probe picosecond laser of 532 nm,and the nonlinear properties of KDP crystals probed by 532 nm picoecond laser with 355 nm nanosecond laser irradiation at the same time.Results shown that the nonlinear absorption of KDP crystals increased with the increasing of laser pulses and fluence,however the variation of nonlinear refraction was not obvious.