Sub-mK Temperature Control For Ultrastable Laser Systems

With much higher accuracy and precision, it is highly possible that optical clocks will replace microwave clocks as new second definition. Optical clock consists of three parts: ultrastable laser oscillator, ion/atom trap system and femtosecond frequency comb. Narrow linewidth ultrastable laser system works as a local oscillator for the optical clock, which is the core of the optical clock.In the narrow linewidth ultrastable laser system, we use Pound-Drever-Hall(PDH) technique to lock a diode laser to a Fabry-Perot(FP) cavity. The FP cavity is the core of the ultrastabel laser system, and the noise of FP cavity is the dominate noise source in the system. Temperature fluctuation of the FP cavity is one of the major contributions. Therefore, my thesis focuses on high performance temperature control of FP cavities.We will first introduce an analog temperature controller in detail, from the choice of electronic components to its function realization. Since we cannot measure the temperature of an FP cavity directly, we use its vacuum chamber as the controlling object in our experiment. When temperature set point is 25 oC, the temperature standard deviation of the vacuum chamber which houses the FP cavity reaches 40?K within 12 hours and reaches 80?K in more than 46 hours.In order to reduce the controlled temperature set point fluctuation due to environmental temperature fluctuations, we then investigate a two-stage temperature control system using the help of two digital temperature control systems and discuss some key issues in a temperature control system such as temperature gradient of a thermostat, mounting mechanism of a vacuum chamber, and so on. In the two-stage temperature control system, when the inner temperature is set to 36 oC, and the outer temperature is set to 35 oC, the temperature standard deviation can reach 80?K within 2 hours and 0.5mK in more than 14 hours; when the inner temperature is set to near room temperature(the inner temperature is set to 25.5oC, the outer temperature is set to 24.5oC), the temperature standard deviation can reach 70?K within 20 hours and 110?K in more than 45 hours. The temperature stability of the vacuum chamber has a significant improvement compared with our former result.At last, the thesis introduces the temperature control of an Electro-Optical Modulator(EOM). With special thermal isolation and mounting design, the temperature standard deviation of EOM can reach 0.24 mK within 3 hours and 1.21 mK in more than 14 hours, which can meet the experiment requirement.