We measure and stabilize the relative angle of parallel and antiparallel laser beams to 5 nrad/Hz resolution by comparing the phases of radio frequency beat notes on a quadrant photodetector. The absolute accuracy is 5.1 and 2.1 µrad for antiparallel and parallel beams, respectively, which is more than 6 and 16 times below the Rayleigh criterion.
© 2005 Optical Society of America
Instrumentation, Measurement, and Metrology
Holger Müller, Sheng-wey Chiow, Quan Long, Christoph Vo, and Steven Chu, "Active sub-Rayleigh alignment of parallel or antiparallel laser beams," Opt. Lett. 30, 3323-3325 (2005)