Phase-coherent multi-tone lasers play a critical role in atomic, molecular, and optical physics. Among them, the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence. Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise, which limits their performance in practical applications. In this work, we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator (VCO) to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain, where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop (PLL). The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches -80dBc/Hz@5kHz with a 20 kHz loop bandwidth. Furthermore, this compact and robust scheme effectively reduces the system’s complexity and cost, which is promising for extensive application in atomic, molecular, and optical physics.

研究了基于光学锁相环技术的Raman光系统，系统包含参考光、主激光和从激光三束激光，其中参考光采用调制转移光谱稳频后用做频率基准，主激光相对于参考光频差1 GHz实现相对于激发态远红失谐以避免激光与原子的直接作用，从激光相对于主激光频差6.8 GHz用于激发⁸⁷Rb原子基态超精细能级之间的跃迁，采用两套光学锁相环分别实现主、从激光的锁频锁相。测量结果表明，两套光学锁相环的相位噪声在100 Hz~1 MHz频段分别低于-70 dBc/Hz和-65 dBc/Hz，因此相位噪声对单次原子干涉重力测量的影响为5.3×10^-7。采用两台锥形放大器分别对主、从激光进行功率放大以保证主、从激光功率比严格为1∶2，采用光纤传输与空间光传输相结合的设计实现主、从激光的合束、偏振统一及频率调制，最终获得的Raman光总功率为180 mW。持续功率测量结果显示，在没有额外增加功率稳定元件的条件下Raman光的总功率最大起伏小于5%，满足原子干涉测量实验需求。