Study On The Nonlinear Absorption Uniformity Of KDP Crystals

KH2PO4(KDP)crystal has been studied for more than 80 years,and it is a kind of multi-functional water-soluble crystal material with long flourishing and excellent performance.It has excellent piezoelectric,electro-optic,ferroelectric and nonlinear effects.It has long been widely used in high tech fields,such as laser frequency conversion,parametric oscillation,electro-optic modulation,high speed Q switch and piezoelectric transducer.KDP crystal has become the only nonlinear optical material available in Inertial Confinement Fusion Engineering(ICF)for high power laser systems due to its excellent electro-optical properties and nonlinear optical properties.When the high power laser passes through the KDP crystal,the nonlinear absorption of the crystal will limit the output energy density of the laser and reduce the efficiency of the laser conversion.On the other hand,it will cause the damage of the crystal itself.It is very necessary to study the influence of the homogeneity of KDP crystal on the nonlinear absorption,and explore the rules and characteristics of it,which is helpful to the application and preparation of crystals.Using picosecond laser Z-scan technique,the characteristics of nonlinear absorption in traditional growth and rapid growth of KDP crystals at different locations are explored and studied.The main contents of this paper are as follows:1,a KDP crystal was grown by the traditional method.The influence of different parts of the crystal on the nonlinear absorption was studied by picosecond Z-scan technique.The results show that the crystal samples show obvious nonlinear absorption effect at 532 nm,and the nonlinear absorption effect of II-direction wafers in the similar parts is less than that of z-direction,which is related to the crystal orientation.The nearer the bottom of the cap is,the nonlinear absorption coefficient of the sample is larger,and the II and Z-direction samples all conform to this rule,which indicates that the crystal quality is different,that is,the nonlinear absorption of the different parts of the crystal is different.2,four KDP crystals with different supersaturation(3%,5%,7%,9%respectively)were grown by rapid growth method,and compared with the traditional method of KDP crystal growth.Picosecond laser Z-scan technique was used to study the influence of different locations of crystal sector sector on nonlinear absorption.The study shows that the different positions of the sector of KDP crystal show obvious nonlinear absorption phenomena at ?= 532 nm;compared with the ?-direction,z-direction samples has a larger nonlinear absorption coefficient to the sample.The nonlinear absorption of the fan-shaped region shows a certain difference.The nonlinear absorption coefficient trend of the sector area is that the nonlinear absorption coefficient of the interface is the largest,the cone is the second and the smallest is the column region,and the nonlinear absorption coefficient decreases with the increase of the supersaturation.3,four Fe3+ ions doped KDP crystals(doping concentration of 5ppm,10ppm,15ppm and 20ppm)were grown by rapid method.The effects of different positions on the nonlinear absorption of the sector region of the crystal sector were studied by picosecond laser Z-scan technique.The study shows that the different positions of Fe3+ ions doped KDP crystal sector show obvious nonlinear absorption phenomena when ?= 532 nm,and the phase matching direction has smaller nonlinear absorption effect;Fe3+ ions have significant influence on the nonlinear absorption effect of KDP sector region,and the effect of Fe3+ separation on the inner column region of the sector region is greater than that of the cone region.This indicates that the nonlinear absorption effect of KDP crystal is related to the crystal quality.