用于可搬运锶光钟二级冷却光源的研制

Development and Application of Light Source for the Second Stage Cooling in the Transportable^(87)Sr Optical Clock

光钟在时间保持、精密测量、暗物质探测等方面有广泛的应用。可搬运光钟研制是光钟的重要方向,它是不同类型光钟比对以及引力红移测量的重要设备。研制用于冷原子制备的可搬运冷却光源是实现可搬运光钟研制的关键。本文主要介绍了可搬运锶光钟二级冷却光源的研制。首先,通过Pound-Drever-Hall稳频技术将半导体激光器锁定在超稳腔上,实现了用于锶光钟二级冷却的689 nm窄线宽稳频光源,其线宽优于263 Hz,频率秒稳定度优于1.56×10^(-14)。另外,利用注入锁定技术制备了两台同等性能的光源,分别用作二级冷却阶段的俘获光和匀化光。整个光学系统集成在一个0.56 m^(2)的光学面包板,通过光纤与真空系统耦合,整体可搬运。利用该稳频光源,实验上制备了数目为2×10^(6),温度为5.3μK的二级冷却原子团,这为下一步进行光晶格原子装载和钟跃迁谱探测奠定了基础。

The transportable optical clock can be widely used in clock comparison,timekeeping,precision measurement,dark matter detection,and so on.The development of transportable optical clocks is a significant direction of optical clocks.It is an important piece of equipment for the comparison of different types of optical clocks and the measurement of gravitational redshift.It is the crucial step to develop a transportable cooling light source for the preparation of cold atoms.This letter mainly introduces the development and application of the transportable light source for the second-stage cooling.Firstly,we simulated and analyzed a transportable cubic ultra-stable cavity with a length of 25 mm and the fineness is measured to be 1.94×10^(5).Then we locked a 689 nm semiconductor laser on the cubic ultra-stable cavity through the Pound-Drever-Hall frequency stabilization technology to obtain a narrow linewidth frequency stabilized laser source at the wavelength of 689 nm.After beating with a reference laser,the linewidth of the frequency stabilized laser is measured to be less thean 263 Hz,and the frequency stability is better than1.56×10^(-14) at one second,showing the laser source can be used for the second-stage cooling in a strontium optical clock.In addition,to verify the application of the laser source,two slave lasers with the same performance were prepared by injection locking technique,which was used as cooling and strring light respectively in the second-stage cooling.All optical parts are integrated on a 0.56 m^(2)optical breadboard to achieve transportability and fiber-coupled on the vacum system so as to be easily moved.At last,we applied the transportable system to the preparation of a cold strontium cloud.As a result,2×10^(6)atoms with a temperature of 5.3μK are prepared in the second-stage cooling experimentally,which laid the foundation for optical lattice loading and clock transition spectrum detection of cold atoms in the transportable strontium optical clock.