Improvement Of 698nm Ultrastable Laser

With high frequency stability lasers have important applications in high-resolution spectroscopy, optical clocks, quantum information science, and other fields to detect gravitational waves. Especially in the time and frequency domain, strontium atomic clock is expected to become the next generation of time and frequency standards, due to its superior performance and remarkable progress. Strontium atomic clock reference light natural linewidth of the transition line is in m Hz magnitude. In order to achieve accurate measurements of strontium atomic reference transition line, we need to develop a 698 nm laser with very high frequency stability.In this experiment, the frequency of a 698 nm external cavity semiconductor laser is locked to an optical reference cavity with Pound-Drever-Hall technique. In 2013, the researchers in our laboratory obtained a ultra-stable laser with a fractional instability of less 1.4×10^-14/s. There may be some deficiency via analyzing the Allan Deviation of the beat frequency. So I will carry out the research work on the optimization of the control system of servo reference, cavity temperature control, residual amplitude modulation and laser power stabilization in the 698 nm stabilized laser system in this paper.The bias-set frequency technique is first used to measure simultaneously cavity linewidth and error signal voltage frequency conversion relationship in the experiment of measuring finesse of optical reference cavity. This method provides a new way for the measurement of cavity linewidth, and greatly improves the measurement accuracy of error signal slope of stabled lasers based on high finesse cavity. In the residual amplitude suppression experiments, that the crystal temperature is controlled at the point which the residual amplitude is biggest to reducing the affection of temperature on laser frequency is proposed, and it has been proved.After a series of optimization measures in this paper, we measure the frequency stability of the stabled laser. The optical heterodyne beat between two independent lasers shows that the frequency instability of one laser reaches 1.87×10^-15/s.