Implementation of side-fringe locking in an SHG cavity

Abstract

An alternative method for locking a second-harmonic generation (SHG) cavity on resonance is described and implemented. The usual method, Pound-Drever-Hall locking, is prone to long-term power fluctuations from power variations in the incident laser. When using the second harmonic field for squeezing, these power fluctuations need to be stabilized with an additional control loop (usually a Mach-Zender interferometer). The alternative method, side-fringe locking, involves a simple DC offset on the second-harmonic signal at the desired power to generate the error signal. This thesis demonstrates the insensitivity of side-fringe locking to such long-term power fluctuations and that the noise spectrum is comparable to PDH locking-explained largely due to PZT noise length fluctuations off-resonance..