title: Utilizing weak pump depletion to stabilize squeezed vacuum states.
abstract: We propose and demonstrate a pump-phase locking technique that makes use of weak pump depletion (WPD) - an unavoidable effect that is usually neglected - in a sub-threshold optical parametric oscillator (OPO). We show that the phase difference between seed and pump beam is imprinted on both light fields by the non-linear interaction in the crystal and can be read out without disturbing the squeezed output. In our experimental setup we observe squeezing levels of 1.96 ± 0.01 dB, with an anti-squeezing level of 3.78 ± 0.02 dB (for a 0.55 mW seed beam at 1064 nm and 67.8 mW of pump light at 532 nm). Our new locking technique allows for the first experimental realization of a pump-phase lock by reading out the pre-existing phase information in the pump field. There is no degradation of the detected squeezed states required to implement this scheme.
authors.forename: T
authors.initials: T
authors.lastname: Denker
authors.forename: D
authors.initials: D
authors.lastname: Schütte
authors.forename: M H
authors.initials: MH
authors.lastname: Wimmer
authors.forename: T A
authors.initials: TA
authors.lastname: Wheatley
authors.forename: E H
authors.initials: EH
authors.lastname: Huntington
authors.forename: M
authors.initials: M
authors.lastname: Heurs