title: Active sub-Rayleigh alignment of parallel or antiparallel laser beams.
abstract: We measure and stabilize the relative angle of parallel and antiparallel laser beams to 5 nrad/(square root of)Hz resolution by comparing the phases of radio frequency beat notes on a quadrant photodetector. The absolute accuracy is 5.1 and 2.1 microrad for antiparallel and parallel beams, respectively, which is more than 6 and 16 times below the Rayleigh criterion.
authors.affiliation: Physics Department, Stanford University, Stanford, California 94305, USA. holgerm@stanford.edu
authors.forename: Holger
authors.initials: H
authors.lastname: Müller
authors.forename: Sheng-Wey
authors.initials: SW
authors.lastname: Chiow
authors.forename: Quan
authors.initials: Q
authors.lastname: Long
authors.forename: Christoph
authors.initials: C
authors.lastname: Vo
authors.forename: Steven
authors.initials: S
authors.lastname: Chu