光学相位锁定激光在原子玻色-爱因斯坦凝聚中实现拉曼耦合

采用光学相位锁定环路技术将外腔反馈式半导体激光器锁定到与钛宝石激光器输出激光频率上. 锁定后两束激光的差频线宽从MHz降低到Hz量级, 同时两束激光的频率差可实现几百兆赫兹到7 GHz的精密调节. 锁定的两束激光作用在铷原子玻色-爱因斯坦凝聚的两个基态超精细态F=2, 1, 观测到在两个超精细态之间的拉曼跃迁. 该技术可用于超冷原子两个超精细态之间自旋轨道耦合.

Raman coupling in atomic Bose-Einstein condensed with phase-locked laser system

We present a simple, versatile and reliable phase-locked laser system. The system consists of an external cavity diode laser, Ti: Sapphire laser, fast detector, phase frequency detector (PFD) and loop filters. The beat signal of the laser is detected with a detector. From the PFD, we can obtain an error signal. The loop filter converts the output of the PFD into a control voltage and thus drives piezoelectric ceramic transducer (PZT) and current of diode laser. After locking, the bandwidth of the beat signal is reduced form MHz to Hz. So the line-width of the diode laser is almost close to that of Ti: Sapphire laser. The locking range is from sub-MHz to 10 GHz. So it is used for the ground hyperfine state transition of ⁸⁷Rb. Through the use of the phase-locked loop system, we can drive the transition of ⁸⁷Rb atoms between two ground hyperfine states F=2 and 1. The system is used to demonstrate Raman transition between two states through changing the detuning of the beat signal. From this, we can obtain Rabi frequency Ω = 10 kHz. So, this system can be used to induce an effective vector gauge potential for ⁸⁷Rb Bose-Einstein condensed and realize the spin-orbit coupling.