用于激光冷却与原子布居数探测的激光光源是冷原子钟的重要组成部分,选用工业技术成熟的1560 nm光纤激光器和光纤放大器分别作为种子源和光放大器,经非线性倍频晶体对放大后的激光进行倍频,得到较大功率的780 nm的激光,通过饱和吸收稳频得到冷却激光,一部分冷却激光利用电光调制器和声光调制器移频6.8 GHz得到重泵浦激光,对上述激光进行适当的功率分配后提供给冷原子钟。对该套激光装置关键器件进行了特性测试,将稳频后的倍频激光与锁定在超稳激光上的光学频率梳进行拍频,得到的激光的线宽在74 kHz左右,其短期稳定度比外腔半导体激光器提高半个多数量级。将这样的激光光源应用于冷原子钟,可以减小探测激光频率噪声对喷泉钟稳定度的限制。

The laser source is an important part of a cold atomic clock for laser cooling and atomic population detection. This study selects a 1560-nm fiber laser and a fiber amplifier as the seed laser and the amplifier laser, respectively, in a rubidium cold atomic clock system because of the technical maturity of the industrial products. The cooling laser is obtained at 780 nm by doubling the frequency of the amplified laser using a nonlinear frequency doubling crystal. Further, the laser frequency is locked to the rubidium transition line via the saturation absorption frequency stabilization technique. A part of the cooling laser passes through an electro-optic modulator and an acousto-optic modulator with a frequency shift of 6.8 GHz to obtain the repumping laser. The lasers are provided to the cold atomic clock after ensuring appropriate power distribution. The amplifying, frequency doubling, and noise characteristics of the key components in the laser device are verified. Subsequently, the beating signal between the cooling laser after frequency doubling and the optical frequency comb locked to an ultra-stable laser denotes that the line width of the cooling laser is approximately 74 kHz and that the short-term stability is half an order of magnitude higher than that of the external cavity semiconductor laser which is used in our laboratory. Furthermore, the application of such a laser light source to the cold atomic clock can reduce the limitation of fountain clock stability which can be attributed to the detection of the laser frequency noise.