Research progress of 698nm narrow-linewidth lasers applied for Sr atom optical clocks at NTSC

Narrow linewidth frequency-stabilized lasers are crucial in the research of optical clocks, precision spectroscopy, and tests of fundamental physics. Narrow linewidth laser with the wavelength of 698nm is essential in the development of Sr atom optical clocks that will be used for the frequency standards in the future. Here we report the recent development of ultra-stable lasers at national time service center, Chinese academy of sciences (NTSC). In the experiment, the frequency of an extended cavity diode laser at the wavelength of 698nm is stabilized to a reference cavity with a finesse of ~130000 using the Pound-Drever-Hall methods. The optical heterodyne beat between two independent lasers shows that the linewidth of one diode laser reaches 0.88Hz. The fractional frequency stability removed linear frequency shift is better than 2×10-15.