New methods for growing large aperture water soluble monocrystals

A unique laboratory technique for producing large-size nonlinear optical elements from water soluble crystals has been created. It includes high-rate growth of profiled large-aperture crystals and their precision finishing by the method of diamond micromilling. Development of new technologies of growing large-size nonlinear optical crystals was stimulated by the demands of the systems for Laser Fusion Synthesis (LFS) elaborated in a number of countries: in Russia (the family of Iskra facilities, Sarov), USA (NIF, Omega upgrade), France (LMJ laser), Japan (Gekko XII). Each such complex demands up to 103 crystal elements with the aperture of about 4040 m that are used in electrooptic shutters and frequency multipliers of laser radiation. It takes more than a year to grow a single KDP crystal of such size by traditional methods.

Researchers in IAP RAS developed the theory and elaborated the technology of growing large-size KDP crystals with growth rate ten times that achieved by traditional techniques. At the present, the growth rate amounts up to ~2 m, and the aperture of grown crystals has almost reached 4040 m.

Specific features of the technology allow growing profiled crystals of needed orientation, thus making production almost wasteless. Absence of inter-sector borders and a lower level of trapping of heavy metal impurities as compared to traditional techniques provide crystals of better optical quality.

Nonlinear optical elements for controlling high-power laser radiation made of such crystals (frequency conversion elements, optical modulators) meet the demands of the element crystal base of powerful laser systems. High-rate crystal growth substantially saves costs and resources on formation of element base. The developed technology of crystal processing, especially the method of diamond micromilling of crystal surface, allow fabricating optical elements meeting the requirements of LFS systems.

IAP RAS is an active participant of the Russian LFS program (Iskra-5, Iskra-6, Luch projects) and collaborates with a number of laboratories in the USA, France, China, and the Czech Republic

Fig. 1. Diamond micromilling of a crystal surface
Fig. 2. DKDP frequency doubling element for Iskra-5 laser