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 Zeeman 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 and separated by precisely 250 kHz. The sensitivity of the system was found to be 0.77 nm. This Value is larger than the theoretical resolution limit of 0.065 nm because of the noise associated with the vibrations. The critical factors of the heterodyne technique far the monitoring of solution crystal growth have been studied. The growth rate of L-arginine phosphate crystal was 6.15+/-0.13 nm/s (0.53 mm/day) at the solution temperature of 28.2 degrees C and seed crystal temperature of 26.0 degrees C. This is the first experiment in which the heterodyne technique has been applied for real-time in situ measurement of crystal growth rate. (C) 1998 Society of Photo-Optical instrumentation Engineers.