Optical Frequency Synthesis And Automatic Control

Nowadays,the frequency instability and uncertainty of the best optical clocks have reached 10^-18,surpassing the current time/frequency standard-the Cs fountain clock.The unprecedented frequency accuracy and stability provided by optical clocks enable us to test the constancy of fundamental constants and fundamental physics,to search dark matter,to detect gravitational wave,and to perform ultra-precision spectroscopy.However,all these applications of optical clocks rely on accurate optical frequency synthesis,which can convert the signal of optical clocks at specific frequencies to any desired frequency in the optical or radio frequency?RF?region without degrading the laser frequency stability and accuracy.Over the last decade,efforts have been made to develop optical frequency synthesizers with wide tuning range,high precision or on a chip.In this thesis,we make a step towards practical and popular situation,and automatic control of an optical frequency synthesizer.?1?Since a few combs based on fiber or chip cannot be tightly phase-locked to narrow-linewidth lasers,such as those from optical clocks,due to limited dynamic response,we demonstrate that even a comb with 10^-11 frequency instability when phase-locking to an RF frequency standard can realize optical frequency synthesis at the 10^-16 level by using the technique of transfer oscillator scheme to reduce the comb frequency noise.Using this technique,the coherence of a1064 nm narrow-linewidth laser with a frequency instability of 1.2×10^-15 at 1 s averaging time is transferred to a 578 nm laser.By comparing against an independent578 nm narrow-linewidth laser,the frequency instability of the synthesized 578 nm laser is 1.3×10^-1515 at 1 s averaging time,limited by the reference laser.?2?Based on the improvement of optics and signal processing,we realize fine frequency set of the optical frequency synthesizer to the target frequency,setting of RF electronics and automatic signal processing with a Labview program.The error signal for phase-locking the output laser can be obtained within 1 minute.In the near future,with digital phase lock loops,the optical frequency synthesizer can be automatically controlled in ful.