Alkali-metal atoms in laser fields: optical pumping, coherent population trapping, and laser cooling

Alkali metals have played an important role in optical and atomic physics from the very beginning. This thesis deals with three aspects and applications of alkali-metal atoms, in particular rubidium (Rb). Optical pumping changes both the amplitudes and the center positions of the absorption profiles in the Doppler-broadened D-line spectra of the alkali-metal atoms. This effect has been studied by reducing the multilevel system to an effective three-level system and by treating the finite interaction time and collisions with the vapor-cell walls in two different ways: as ground-state relaxation and by averaging the time-dependent absorption over the distribution of interaction times. The former is a computationally efficient way to compare theoretical spectra to experimental results, and the latter reveals lineshape details that are due to the coupling between the Doppler shift and the interaction times through the longitudinal velocity of the atoms. Using coherent population trapping (CPT) in 85Rb, an all-optical atomic clock has been realized. The good noise properties of the diode laser, an optimized buffer gas, and a very low light intensity allow detection of ultranarrow CPT resonances <20 Hz, apparently the narrowest optically induced hyperfine CPT resonance ever measured. The Q value of this resonance, 1.5 × 108, is comparable to Q values in cesium clocks and the stability of the CPT clock is sufficient for many high-precision applications. Trapping of Rb atoms in microscopic magneto-optical traps (MOTs) a few hundred micrometers from the surface of an optically transparent ferrite-garnet permanent-magnet atom chip has been demonstrated. The required magnetic fields are created by magnetic patterns magneto-optically written into the ferrite-garnet film and the transparency of the chip allows using a conventional MOT geometry. The magnetic patterns can be erased and re-written in situ, even during the experiments. Magnetic traps with a trap depth up to 1 mK could be realized using this type of atom chip.