Evaluation Of The Transportable Strontium Optical Clock And Pre-research Of The Optical Clock For Space Station

As one of the candidates of the next generation time frequency standard,optical clock has great significance in scientific research and engineering application.Due to its large size and complex systerm,the stationary optical clock is only used in the laboratory,which limits its application in science and technology.The transportable optical clock with small volume,good portability and high adaptability to the environment makes the frequency comparison of different systems free from the restriction of distance.The special microgravity environment in space is very beneficial to improve the optical clock’s performance,so the space optical clock has great potential and broad application prospect.For all these purposes,the National Time Service Center has successively carried out the development of stationary optical clock,transportable optical clock and optical clock for space station based on strontium atoms.Based on transportable strontium clock and optical clock for space station in National Time Service Center,this thesis’s main works include:research for transportable narrow-linewidth laser,development of the transportable strontium clock,the evaluation of instability and uncertainty for the transportable strontium optical clock,and the pre-research of the optical clock for space station.（1）In the development of transportable narrow-linewidth laser,the Pound-Derever-Hall（PDH）technology was used to develop the transportable narrow-linewidth 689nm laser for the second cooling and 698 nm laser for probe of transition spectrum probe light source.The 689 nm laser source was locked on a25 mm cubic cavity.Then the linewidth of 689 nm laser is better than 135 Hz and the second stability is better than 1.56×10^-14.The 698 nm laser source is locked on a midplane vertical cavity with a length of 10 cm.The linewidth is better than 1 Hz and the second stability is 1.3×10^-15.（2）The system development of transportable strontium optical clock mainly includes the development of vacuum system and optical system as well as the preparation of cold atom samples.The compact design reduces the volume of the vacuum system to 90 cm×20 cm×42 cm,and all the optical subsystems are integrated on individual optical panels to achieve integration and modularization.The optical system is connected with vacuum system by optical fiber.In addition to electronic equipment,the size of the whole transportable strontium optical clock unit is less than0.65 m³.In the experiment,the atoms are loaded in one dimensional optical lattice.The lifetime of atoms was measured to be about 628 ms and the temperature was3.3μK.When the 698 nm clock laser pulse time is 230 ms,the line width of spin polarization spectrum is 4.8 Hz,which is close to the Fourier limit.（3）In the evaluation of the instability and uncertainty of the transportable optical clock,the frequency instability of the system was evaluated by using the time interleaved self-comparison method.As the result,the time interleaved self-comparison frequency instability is determined to be 3.6×10^-15 at 1 s and6.3×10^-17 at an averaging time of 2000 s.In the evaluation of the systematic uncertainty,four main frequency shifts are measured,including blackbody-radiation（BBR）shift,collision shift,lattice Alternating Current（AC）Stark shift and second-order Zeeman shift.The systematic shift is 58.8×10^-15 and the total uncertainty is 2.3×10^-16.（4）Pre-research of strontium optical clock for space station is as follows.For strontium optical clock in space environment,compact and less power consumption of the vacuum system is designed to be 55 cm×40 cm×28 cm.The first and the second cooling optical systems are designed and built on two boards with the sizes of57 cm×40 cm.In addition,loading atoms in the one-dimensional optical lattice is realized and transition spectra are detected by using a transportable 698 nm ultra-stable laser.As the result,the bandwidth of the degenerate spectum is 6.1 Hz.