Chinese Physics B

Theoretical simulation of the photoassociation process for NaCs

Chang-Zhe Zhang, Bin Zheng, Jun Wang, Qingtian Meng

Published Feb 1, 2013• 6 citations

Abstract

We investigate the two-step association process of NaCs using the time-dependent wave packet method. Ground state atoms can be photoassociated to the low vibrational levels of the ground state for an NaCs molecule by the two-step association. The time-dependent Schrödinger equation of the association process is solved within a three-state model and the wave packet is propagated with the “split operator-Fourier transform" scheme and the rotating-wave approximation (RWA). The vibrational population distribution of the ground state can be obtained by projecting the wave packet to every vibrational level of the ground state. The results not only show that for NaCs achievement of photoassociation production is accompanied by the photodissociation of the higher vibrational molecules, but also show that the vibrational distribution in lower vibrational levels of the ground state changes with the laser parameters.

DOI: 10.1088/1674-1056/22/2/023401

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Chinese Physics B

Theoretical simulation of the photoassociation process for NaCs

Chang-Zhe Zhang, Bin Zheng, Jun Wang, Qingtian Meng

Published Feb 1, 2013• 6 citations

Publisher

Abstract

DOI: 10.1088/1674-1056/22/2/023401

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arXiv:1007.2400Physical Review AOct 29, 201030 citations

{\mathrm{Cs}}_{2}{1}_{g}{(6s+6p}_{3/2})

and ${a}^{3}{\ensuremath{\Sigma}}_{u}^{+}(6s+6s)$ channels by a cw laser slightly red detuned relative to the

{\mathrm{D}}_{2}

resonance line. The results show Rabi oscillations in the populations of the two channels during time intervals when the vibrational motion is stopped at the outer turning point. At intensities of $\ensuremath{\approx}250\mathrm{kW}{\mathrm{cm}}^{\ensuremath{-}2},$ a new characteristic time appears, a factor of 2 larger than the classical vibrational period, which corresponds to vibrational motion in the upper adiabatic potential created by the coupling. Such an effect modifies the scattering length for collisions in the lower state, and it clearly opens a possibility of control by tuning the laser intensity.

{v}{\kern 1pt} '

= 17–21, Cs2:

{v}{\kern 1pt} '

= 21–25, and RbCs:

{v}{\kern 1pt} '

= 18–22) to ground state. By using quantum wave-packet dynamic methods, the yields with time evaluation of the selected states are calculated interacting with a resonant laser pulse. Using gaussian pulse leads to the yield of Rb2 up to 82% at 860 fs. After a laser pulse, the positive chirp promotes the yield of vibrational states to increase, but the negative chirp inhibits it. That is to say, by changing the laser parameters and pulse shapes, it is much easier to control the photochemical process along desired direction. For photoassociation of alkali-metal dimers, homonuclear molecules have a better response to laser pulse than heteronuclear molecules. The efficiency of photochemical reaction of homonuclear molecules is much better and the photoassociative yield is much higher. Those conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical research.

We demonstrate that a photoassociation resonance detuned less than a wave number below the Cs

6 {}^{2}{P}_{3/2}

atomic line can be used to create a deeply bound molecular sample of ultracold polar NaCs. We assign $1 {}^{1}{\ensuremath{\Sigma}}^{+}$ (

v=4,5,6,11,19

) vibrational levels utilizing a pulsed depletion spectroscopic method (scanning

~700

cm${}^{\ensuremath{-}1}$ at a time) in which we observe the $1 {}^{1}{\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}2 {}^{1}{\ensuremath{\Sigma}}^{+}\ensuremath{-}1 {}^{3}\ensuremath{\Pi}$ vibrational progression. These data are compared with results from a hot-molecule collision-enhanced laser-induced fluorescence experiment and shown to be in good agreement. This technique is a powerful tool to experimentally determine the population distribution in any ultracold molecular system.