Formation of “hair” inclusions and growth optimization for large aperture KDP crystals based on the numerical simulation method

Abstract

“Hair” inclusion defects in large-aperture KDP/DKDP crystals degrade the performance of high-power laser systems because they adversely modulate the laser beam. This study investigates the formation mechanism of these defects and optimizes the growth parameters through numerical simulation of the solution circulating growth system. A self-consistent crystal growth rate model coupling fluid dynamics, heat transfer, and solute transport is developed. The results reveal that crystal rotation-induced centrifugal flow generates vortex structures, forming localized low-supersaturation regions near the pyramidal face edges. Subsequently, growth step aggregation and mother liquor entrapment may promote the formation of “hair” inclusion. In addition, orthogonal experiments quantified the impact of growth parameters, showing that the inlet temperature differential predominantly governs surface thermal uniformity, while the equilibrium temperature critically influences solute distribution. Further, an optimal parameter combination (inlet temperature differential of 2 °C, inlet flow velocity of 0.36 cm s⁻¹, crystal rotation rate of 8 rpm, and equilibrium temperature of 40 °C) was proposed, which significantly improved thermal uniformity and solute transport on crystal surfaces, thereby being expected to reduce the likelihood of “hair” inclusion formation. An optimization strategy for achieving high-efficiency, low-defect growth of large-aperture KDP-type crystals has been developed, providing important support for the precise control of crystal growth.