OPTICAL HETERODYNE INTERFEROMETRY TECHNIQUE FOR SOLUTION CRYSTAL-GROWTH RATE MEASUREMENT

A noncontact optical heterodyne technique was implemented for in situ measurement of crystal growth rate from solutions. A two-frequency Zee man laser with a total output power of 1 mW (each polarized component is 0.5 mW) was used at 633 nm and is composed of two frequencies v(1) and v(2) that are collinear but polarized orthogonally to each other a nd separated by precisely 250 kHz. The sensitivity of the system was f ound to be 0.77 nm. This Value is larger than the theoretical resoluti on limit of 0.065 nm because of the noise associated with the vibratio ns. The critical factors of the heterodyne technique far the monitorin g of solution crystal growth have been studied. The growth rate of L-a rginine phosphate crystal was 6.15+/-0.13 nm/s (0.53 mm/day) at the so lution temperature of 28.2 degrees C and seed crystal temperature of 2 6.0 degrees C. This is the first experiment in which the heterodyne te chnique has been applied for real-time in situ measurement of crystal growth rate. (C) 1998 Society of Photo-Optical instrumentation Enginee rs.