Development of a magneto optical trap for Rubidium 87

[摘要] ENGLISH ABSTRACT: A Magneto Optical Trap (MOT) is a configuration formed by three orthogonal pairs of counterpropagatingcircularly polarized laser beams and a magnetic field gradient. A MOT is used tocool, capture and trap large numbers of atoms in vacuum at very low temperature inK range.In this thesis the development of an experimental setup for realising a MOT of 87Rb atomsis presented. The atomic structure of Rb and the theoretical background of laser cooling andmagneto optical trapping was reviewed. The influence of rubidium background pressure in thevacuum system, the laser beam size and the power and frequency on the number of the trappedatoms were studied in literature. The trapping and repumping lasers were characterised experimentally.Six circularly polarised trapping beams with equal power were formed and properlyaligned to intersect at the center of the trapping cell. Two optical setups were designed and exploitedto investigate and optimise the trapping beam polarisation. The repumping laser beamwas successfully aligned and colinearly combined into all the trapping beams. Three differentexperimental setups for saturated absorption spectroscopy were developed. Saturated absorptionspectra showing the hyperfine structure of both 85Rb and 87Rb isotopes were measuredand are discussed. Using two saturated absorption spectroscopy setups, the frequencies of bothlasers were successfully locked to the trapping and repumping transitions of 87Rb respectively.A rectangular trapping cell was designed and attached to the vacuum system. A pressure ofabout 10­¯7 mbar was achieved. The magnetic field coils were characterised and affixed on bothsides of the cell in an anti-Helmholtz configuration. Setups for imaging and quantification of the87Rb atoms in the MOT were designed. Finally, the procedures for demonstrating a MOT are presented. In conclusion, the current status of the project is reported, with recommendationsfor the future work.

[发布机构] Stellenbosch University