基于~(87)Rb原子的大失谐光晶格的设计与操控

提出了一种基于~(87)Rb原子的大失谐光学晶格的设计方案,详细介绍了光晶格光束的校准、频率失谐的调整以及光强输出的控制方式.在磁光阱和偏振梯度冷却的基础上,研究了光学晶格的总光强和频率失谐等参数对原子装载的影响,实现了光晶格中冷原子的绝热装载与卸载.通过光强调制的方法,测量了光晶格的振动频率.光晶格的引入,使得温度降低为原有的1/3.涉及的系统设计和结论对其他碱金属原子光晶格的实验设计具有参考价值.

Design and control of large-detuned optical lattice based on 87Rb atoms

An innovative and practical scheme of building far-detuned optical lattice for ⁸⁷Rb atoms is proposed.The disposals of aligning the lattice beams,tuning the lattice frequency and controlling the tapered amplifier for output are described in detail.Alignment of optical lattices is quite difficult in principle,for several beams are required to hit the same atomic cloud.For the relatively near-detuned one-and two-dimensional lattices,the coarse alignment is accomplished by tuning the lattice laser onto resonance with the magnetic-optic trap(MOT) frequency,and then blowing away the MOT in real time.A more precision alignment is implemented at the end of the MOT loading,the atoms are first pumped into the lower hyperfine level by turning off the repumping for some time;then,the pulsed lattice beams are turned on for a short time at some reasonably large detuning.Finally,a fluorescent image of the MOT is taken without repumping,in order to detect only those atoms which are repumped by the lattice laser.For the purpose of controlling the detuning of the lattice easily and accurately,a home-made grating wavemeter with a resolution better than 1 GHz is used.This way allows the laser to be locked at any frequency by using a software PID and is experimentally simple to implement.The intensity of the lattice is controlled directly by pulsing the current through the tapered amplifier using a function generator and a laser diode driver.This technique has already been demonstrated before by Prof.M.Kasevich's group at Stanford. Our experiment starts with a MOT capturing approximately 4×10⁷ atoms in 200 ms.The lattice loading is overlap with the end of polarization gradient cooling(PGC),after that,the molasses laser beams are extinguished, and the adiabatic expansion is accomplished in the same time by a decrease in the lattice light intensity according to release function.On the basis of MOT and PGC,the dependences of atomic loading on such parameters as the intensity and frequency detuning of optical lattice are investigated experimentally.The vibration frequency is measured by intentionally modulating the trap intensity.Experimental results show that the lattice structure facilitates the cooling with the temperature of atoms cloud being reduced to 1/3 compared with free space polarization gradient cooling.The system design,experimental results and conclusions are of definite significance and can serve as a fine reference for other kinds of lattices designs or alkali atomic plans.