Zhang J, Shi X H, Zeng X Y, Lü X L, Deng K, Lu Z H
MOE Key Laboratory of Fundamental Physical Quantities Measurement, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.
Rev Sci Instrum. 2016 Dec;87(12):123105. doi: 10.1063/1.4971852.
We demonstrate thermal noise limited and shot noise limited performance of ultra-stable diode laser systems. The measured heterodyne beat linewidth between such two independent diode lasers reaches 0.74 Hz. The frequency instability of one single laser approaches 1.0 × 10 for averaging time between 0.3 s and 10 s, which is close to the thermal noise limit of the reference cavity. Taking advantage of these two ultra-stable laser systems, we systematically investigate the ultimate electrical noise contributions, and derive expressions for the closed-loop spectral density of laser frequency noise. The measured power spectral density of the beat frequency is compared with the theoretically calculated closed-loop spectral density of the laser frequency noise, and they agree very well. It illustrates the power and generality of the derived closed-loop spectral density formula of the laser frequency noise. Our result demonstrates that a 10 level locking in a wide frequency range is feasible with careful design.
我们展示了超稳定二极管激光系统的热噪声限制和散粒噪声限制性能。测量得到的两个独立二极管激光器之间的外差拍频线宽达到0.74赫兹。对于平均时间在0.3秒至10秒之间，单个激光器的频率不稳定性接近1.0×10 ，这接近参考腔的热噪声极限。利用这两个超稳定激光系统，我们系统地研究了最终的电噪声贡献，并推导了激光频率噪声闭环谱密度的表达式。将拍频的测量功率谱密度与理论计算的激光频率噪声闭环谱密度进行比较，二者吻合得非常好。这说明了所推导的激光频率噪声闭环谱密度公式的有效性和通用性。我们的结果表明，通过精心设计，在宽频率范围内实现10级锁定是可行的。
