Rapid Growth of KDP Crystals in the [101] Direction

Mengfei Qin,Wenyong Cheng,Bo Wang,Xinguang Xu,Guangwei Yu

doi:10.3390/cryst10020108

Abstract

KDP crystals have important applications in inertial confinement fusion. However, during the rapid growth of large-sized KDP crystals, inclusion is prone to occur. The existence of inclusion will lead to the reduction of crystal quality and utilization and even the end of the growth process. The generation of inclusion is related to the interaction between the crystal and the liquid flow. In this paper, we changed the hydrodynamic condition around the crystal by changing the crystal growth direction and achieve the rapid growth of [101] direction KDP crystals without inclusion at a low rotation rate. The utilization of the crystal was improved and the crystal has good optical transmittance, crystalline perfection and laser damage threshold. Meanwhile, atomic force microscopy was used to study the characteristics and changes of the micromorphology on (100) and (101) faces under different levels of supersaturation. The analysis results show that under high supersaturation, the uneven distribution of solutes and insufficient flow rate cause local macrosteps, two-dimensional step platforms and two-dimensional cores to form irregular structures with large slopes, thereby reducing the stability of the interface. This study will help to better understand the effect of the interaction between liquid flow and crystals on the formation of inclusion and guide the growth of KDP crystals.

Highlights

Potassium dihydrogen phosphate (KH2 PO4, KDP) crystal is a representative electro-optical conversion and nonlinear optical material which could be grown into large size in aqueous solution.With the development of laser fusion, KDP crystal is used in the inner confinement fusion (ICF) project for pockels cell and frequency conversion
To investigate the causes of inclusion and avoid the formation of it more effectively under low rotation rate, the hydrodynamic condition near the crystal was changed by changing the growth orientation of the crystal, [101] direction KDP crystals were grown by the point seed rapid growth method, growth of inclusion-free crystals was achieved at low rotation speed and the crystals can withstand higher supersaturation without inclusions generation
The optical performance characterization of crystals grown under high supersaturation shows that the crystals have good optical transmittance, crystalline perfection, and laser damage threshold is as good as the z-cut KDP

Summary

Introduction

Potassium dihydrogen phosphate (KH2 PO4 , KDP) crystal is a representative electro-optical conversion and nonlinear optical material which could be grown into large size in aqueous solution.With the development of laser fusion, KDP crystal is used in the inner confinement fusion (ICF) project for pockels cell and frequency conversion. Potassium dihydrogen phosphate (KH2 PO4 , KDP) crystal is a representative electro-optical conversion and nonlinear optical material which could be grown into large size in aqueous solution. N.P. Zaitseva developed the point seed rapid growth method and achieved the growth of large-type (400–550 mm) KDP crystals [3]. As the crystal size increases, solution inclusion frequently occurs inside, which limit the optical performance and yield. The development of macrosteps may cause the instability of surface morphology and result in the solution inclusion [9].

Methods

Results

Conclusion