Suppression of residual amplitude modulation of ADP electro-optical modulator in Pound-Drever-Hall laser frequency stabilization

Abstract

We report a simple and robust approach to reduce the residual amplitude modulation (RAM) by employing an ammonium dihydrogen phosphate (ADP) crystal to provide optical phase modulation in the Pound-Drever-Hall frequency stabilization system. The birefringence-related amplitude modulation can be suppressed due to the insensitivity to the ambient temperature of the crystal. The proposed RAM can be significantly reduced to 20 ppm level, which is comparable with the electro-optic modulator (EOM) under critical active temperature and bias voltage control. The RAM-induced frequency instability is below 2 × 10−17 for integration times from 1 to 1000 s, which is lower than the fundamental thermal noise limit of the reference cavity and meets the requirements for realization of the ultra-stable laser and high-precision measurement.