State Preparation in a Cold Atom Clock by Optical Pumping

We implement optical pumping to prepare cold atoms in our prototype of the ^87Rb space cold atom clock, which operates in the one-way mode. Several modifications are made on our previous physical and optical system. The effective atomic signal in the top detection zone is increased to 2.5 times with 87% pumping efficiency. The temperature of the cold atom cloud is increased by 1.4 \muK. We study the dependences of the effective signal gain and pumping efficiency on the pumping laser intensity and detuning. The effects of \sigma transition are discussed. This technique may be used in the future space cold atom clocks.