Growth technique to increase the device purpose yield of a KDP crystal and assessment of its quality using X-ray and optical techniques

Abstract

A methodology to increase the device purpose yield of a KDP crystal is reported in this paper. The method is based on increasing the cross-section of the prismatic sector {100} of the growing KDP crystal at the expense of the unusable pyramidal cap portion by restricting the growth of the crystal up to a particular height, decided by the solution–air interface in the crystallizer. Due to the lack of solution above the interface, the crystal ceases to grow in the upward direction whereas it continues to grow laterally. This leads to an increase in the usable volume of the grown crystal for the fabrication of crystal elements required for electro-optic switching and frequency conversion applications. An empirical relationship has been introduced as a condition to grow flat-top shaped KDP crystals. It relates the growth parameters with the apparatus design parameters. Several flat-top shaped crystals have been grown as a validation of the growth methodology and the empirical relationship. The influence of the growth methodology on the crystalline quality of the grown crystal was assessed by measuring the defect structure of different sectors of the grown crystal by X-ray topography (XRT). The crystalline perfection was estimated by recording the rocking curve widths using high resolution X-ray diffraction (HRXRD). The optical quality was assessed by measuring the UV-vis-NIR transmission of the different sectors of the crystal and the refractive index homogeneity using interferometric techniques of conoscopy. It is found that restricting the growth of the crystal in the [001] direction by the solution–air interface does not have any detrimental effect on the crystalline and optical qualities of the grown crystal.