研究目的
Investigating strategies to reduce the noise of a class-A dual-frequency vertical external cavity surface emitting laser (VECSEL) operating at Cesium clock wavelength, focusing on the beatnote phase noise of the two orthogonally polarized modes emitted.
研究成果
The study demonstrates a significant reduction in the beatnote phase noise by using two fully in–phase correlated pump beams, highlighting the importance of optimizing the correlation between the pump noises and minimizing the mode coupling constant. Future work will focus on further reducing the residual noise through balanced excitation ratios, increased mode splitting, and the use of low-noise pump lasers.
研究不足
The study identifies the need for further efforts to decrease the noise to meet the stringent requirements of CPT atomic clocks, including the use of a servo loop on the pump laser driver and the insertion of an electro-optic crystal inside the cavity for phase locking.
1：Experimental Design and Method Selection:
The study uses a dual-frequency VECSEL device with a semiconductor chip and a birefringent crystal inserted inside the cavity to separate the extraordinary polarization from the ordinary one. The model for the phase noise of the beatnote is developed within the framework of coupled rate equations, considering both the phase–amplitude coupling and the thermal effects.
2：Sample Selection and Data Sources:
The semiconductor chip is a multi-layered structure grown on a GaAs substrate, containing a distributed Bragg reflector and active layers with quantum wells.
3：List of Experimental Equipment and Materials:
The setup includes a Peltier cooler, a concave mirror as the output coupler, a 673 nm laser diode for pumping, and a YVO4 birefringent crystal.
4：Experimental Procedures and Operational Workflow:
The experiment involves measuring the beatnote phase noise spectra under different pumping schemes, including a simple pumping scheme and a two fully in–phase correlated pump-beams scheme.
5：Data Analysis Methods:
The phase noise power spectral density is analyzed using the developed model, considering the contributions from phase-amplitude coupling and thermal effects.
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