Growth and Characterization of KDP and Its Analogs

Abstract

Crystals of potassium dihydrogen phosphate (KDP, KH 2 PO 4) and its deuterated analogs (DKDP, K(D x H 1−x) 2 PO 4) have been studied for their interesting electrical and optical properties, structural phase transitions, and ease of crys-tallization. They are the only nonlinear crystals currently applied in inertial confinement fusion (ICF), which has made them a hot topic of research for decades. To yield enough large crystals exceeding 50 cm in all three dimensions , the point-seed technique was recently developed. This method can grow crystals one order of magnitude faster than conventional methods. Recent developments in both the techniques and science of growth phenomena and defect formation under various conditions are described in this chapter, which also reviews significant advances in understanding of the fundamentals of KDP crystal growth, other growth methods to yield large high-quality crystals, growth defects and optical performance, and evaluations of crystal quality. Crystals of potassium dihydrogen phosphate (KDP) and its isomorphs have been the subject of a wide variety of investigations for over half a century owing to their interesting electrical and optical properties, structural phase transitions, and ease of crystallization [22.1-4]. Today, these crystals are widely used in both laboratory and industrial settings to control the parameters of laser light, such as pulse width, polarization, and frequency, through first-and second-order electrooptic effects [22.4, 5]. Their application in inertial confinement fusion (ICF) research [22.6] has made them a hot topic of research for decades. The very high-energy Nd-glass lasers used for ICF research need large plates of nonlinear crystals for elec-trooptic switches and frequency converters (Fig. 22.1). The lasers under construction in the USA and France with about 40 × 40 cm 2 aperture require single-crystal boules with linear dimensions in the 50-100 cm range. KDP (KH 2 PO 4) and its deuterated analogs DKDP (K(D x H 1−x) 2 PO 4) are the only nonlinear crystals currently used for these applications due to their unique physical properties, which include transparency over a wide region of the optical spectrum, resistance to damage by laser radiation, and relatively high nonlin-Part C 22