title: External cavity beam combining of 21 semiconductor lasers using SPGD.
abstract: Active coherent beam combining of laser oscillators is an attractive way to achieve high output power in a diffraction limited beam. Here we describe an active beam combining system used to coherently combine 21 semiconductor laser elements with an 81% beam combining efficiency in an external cavity configuration compared with an upper limit of 90% efficiency in the particular configuration of the experiment. Our beam combining system utilizes a stochastic parallel gradient descent (SPGD) algorithm for active phase control. This work demonstrates that active beam combining is not subject to the scaling limits imposed on passive-phasing systems.
authors.affiliation: MIT Lincoln Laboratory, Lexington, Massachusetts 01810, USA. juan.montoya@ll.mit.edu
authors.forename: Juan
authors.initials: J
authors.lastname: Montoya
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Augst
authors.forename: Kevin
authors.initials: K
authors.lastname: Creedon
authors.forename: Jan
authors.initials: J
authors.lastname: Kansky
authors.forename: Tso Yee
authors.initials: TY
authors.lastname: Fan
authors.forename: Antonio
authors.initials: A
authors.lastname: Sanchez-Rubio