We systematically investigate the polarization gradient cooling （PGC） process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequency is stepped to the setting value while its intensity is ramped, is found to be the best for the PGC, compared with other modes studied. We verify that the heating effect of the cold atoms, which appears when the cooling laser intensity is lower than the saturation intensity, arises from insufficient polarization gradient cooling. Finally, an exponential decay function with a statistical explanation is introduced to explain the dependence of the cold atom temperature on the PGC interaction time.
We have employed recoil-induced resonance（RIR） with linewidth on the order of 10 k Hz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T = 84 ± 4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.
Ultracold polar RbCs molecules are produced via photoassociation in a laser-cooled mixture of ^85Rb and ^133Cs atoms. The a3∑＋ state molecules which decay from electronically excited （2）0- state RbCs molecules are detected by resonance- enhanced two-photon ionization. The new rovibrational levels （v = 189, 190） in the （2）0- state are also observed, which exist in theory and have not been observed in experiments yet. The corresponding rotational constants are measured by photoassociation spectroscopy, which are consistent with theoretical calculations using a nonrigid rotor model.
