Photoassociation Of Cold And Ultracold Atoms And Rovibrational Cooling Of Photoassociated Molecules

The photoassociation of ultracold ⁸⁵ Rb atoms and the photoassociation of cold ⁸⁵Rb atoms at several millikelvins and the rovibrational cooling of photoassociated ⁸⁵Rb₂ molecules are investigated theoretically using the time-dependent quantum wavepacket method.The main research contents are summarized as follows:The photoassociation dynamics of ultracold ⁸⁵Rb atoms driven by the second-and third-order phase-modulated laser fields is investigated theoretically.The interplay between the second-order and third-order terms of the phase-modulated pulse has an obvious influence on photoassociation dynamics.The different combinations of the second-order and third-order phase coefficients lead to different pulse shapes.Most of the molecular population in the excited electronic state driven only by the third-order phase pulses can be distributed in a single vibrational level.The second-order term of the phase-modulated pulse can change the instantaneous frequency and therefore the final population is distributed on several resonant vibrational levels,instead of concentrating on a single level.Although the second-and third-order phase-modulated pulse covers more resonant vibrational levels,the total population on the resonant vibrational levels is much smaller than that controlled only by the third-order phase pulse.Especially,the third-order term of the phase-modulated pulse can weaken the"multiple interaction" in some degree.The photoassociation process of ⁸⁵Rb atoms driven by short laser pulse at several mil-likelvins is investigated theoretically.At this temperature,the actions of the rotational bar-rier,weights of initial scattering states and shape resonance emerge and have the influence on the thermally averaged photoassociation probability.The calculated thermal weighted population distribution of rotational states agrees well with photoassociation spectrum ex-periment.The thermally averaged photoassociation probability decreases with the increase of temperature.The rovibration cooling of the ⁸⁵Rb₂ molecule resulting from the photoassociation of ⁸⁵ Rb atoms at millikelv1n temperature is investigated theoretically.At several millikelvin temperature,the populations of the initial state and the photoassociated ⁸⁵Rb₂ molecule are distributed on hundreds of rovibrational levels.In the laser rovibration cooling process,the population of photoassociated molecule is firstly transferred to the deep vibrational state|?v"=39>,and then further to the rovibrational ground state |?v"=0,l=0)via the intermediate state |?_v'=42,le=1).After the cooling process is over,the population transferred from the intermediate state |?_v'=42,le=1)is fully distributed in vibrational ground state |v"=0).Of the population in the vibrational ground state,51.59%is concentrated in the rotational ground state |l?0),and the rest of population is distributed in the low rotational states|l?1-3>.