Strategies for noise reduction of a dual-frequency VECSEL dedicated to cesium CPT clocks

We investigate the strategies to reduce the noise of a class-A dual-frequency vertical external cavity surface emitting laser (VECSEL) operating at Cesium clock wavelength. We focus mainly on the beatnote phase noise of the two orthogonally polarized modes emitted. Within the framework of coupled rate equations, we show that the phase noise spectrum of the beatnote is well described by considering both the phase–amplitude coupling and the thermal effects. The spearhead of this study consists in first theoretically evidencing reduction strategies for the phase noise beatnote by optimizing the physical parameters of the model and then experimentally demonstrating its feasibility by using two in-phase fully–correlated beams pumping each mode separately. Possible ways to decrease the intensity noises are also identified.