赫兹线宽光学频率合成器研究

Frequency synthesizers from audio frequency to the microwave region are widely used in both high-technology scientific research and daily life. Spectroscopists have been long-dreaming of such kind of frequency synthesizers in the optical domain, which can generate optical light with high precision at any moment and at any wavelength over a wide range according to the requirement of precision spectroscopy and measurement. Based on the developments of narrow-linewidth lasers with high frequency stability and a femtosecond laser optical frequency comb in our group, in this proposal we will precisely transfer the frequency stability and high coherece of the narrow-linewidth lasers to a frequency-tunable, single frequency Ti:sapphire laser via the optical frequency comb. We will explore the key techniques of narrow-linewidth optical frequency synthesizer. The goal of this proposal is to develop an optical frequency synthesizer from 730 nm to 970 nm with a linewidth of 1 Hz and frequency stability of 1E-15. It will open entirely new fields in optics with this optical frequency synthesizer.

目前的频率合成器已很成熟，它可覆盖音频到微波频段，已在高科技、科学研究和日常生活中得到了广泛应用。光谱学家也长期梦想在光学波段建立频率合成器，可在宽调谐波长范围内，根据精密光谱和精密测量的需要，高精度地在所需要的频率处产生激光输出。该课题将在已研制成的亚赫兹线宽稳频激光和飞秒激光光梳的基础上，进一步将亚赫兹线宽稳频激光的频率稳定性和相干性高保真地传递到单频可调谐钛宝石激光，重点研究窄线宽光学频率合成器的关键技术。研究团队将在730-970 nm波长范围，实现激光线宽为1 Hz和频率稳定性为1E-15的光学频率合成器，为开拓光学频率合成器研究新领域做贡献。

光谱学家长期梦想在光学波段建立频率合成器，可在宽调谐波长范围内，根据精密光谱和精密测量的需要，高精度地在所需要的频率处产生激光输出。原子光钟在过去十年获得了飞速发展，其频率不确定度已达到E-18，频率不稳定度可达到E-19。如何将如此高精度的光钟信号高精度地转换到其他光学波段和微波波段，而不破坏光钟信号的精度和相干性是必须解决的关键技术。光学频率梳的诞生为建立光学频率合成器铺平了道路，但由于光梳的全部梳齿都在同一个光束里，而且每一个梳齿的功率非常微小，它还不是一个完善的光学频率合成器。该研究课题通过精密光学锁相技术将光学频率梳受控于赫兹线宽的YAG激光，将光梳的每一个梳齿的线宽都压缩到1赫兹，并采用多项光梳频率噪声免疫技术和光频下转换自参考频率基准技术，其分频不确定度达到1.4E-21。采用该分频器实现了1064nm赫兹线宽激光在700-990nm范围对可调谐钛宝石连续激光的精密控制，其频率不稳定度达到1.5E-15(1 秒平均时间)，线宽达到1.2 Hz。