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Laser Physics

Photoassociation dynamics controlled by a spectral π-jump laser pulse

Zeyu Zhao, Wei Zhang, Yin Hui Huang, Shu‐Lin Cong

Published Jan 23, 2013• 4 citations
Publisher

Abstract

The formation of ultracold Cs 2 molecules via photoassociation (PA) with a spectral π-jump laser pulse is theoretically investigated by solving the time-dependent Schrödinger equation using the mapped Fourier grid method. Numerical calculations show that the population distributions of associated molecules mainly result from the off-resonant excitation of the π-jump laser pulse. Compared with the transform-limited pulse, an efficient population accumulation in the PA process is achieved with the π-jump pulse. An oscillation pattern appears in the population on the vibrational levels of the state owing to the action of the post-half-pulse in the π-jump pulse. The PA efficiency is related to the Rabi angle of the laser pulse. A π-jump pulse can be used to enhance more effectively the PA efficiency than a transform-limited pulse with the same Rabi angle.

DOI
10.1088/1054-660x/23/3/035502

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The formation of ultracold Cs 2 molecules via photoassociation (PA) with a spectral π-jump laser pulse is theoretically investigated by solving the time-dependent Schrödinger equation using the mapped Fourier grid method. Numerical calculations show that the population distributions of associated molecules mainly result from the off-resonant excitation of the π-jump laser pulse. Compared with the transform-limited pulse, an efficient population accumulation in the PA process is achieved with the π-jump pulse. An oscillation pattern appears in the population on the vibrational levels of the state owing to the action of the post-half-pulse in the π-jump pulse. The PA efficiency is related to the Rabi angle of the laser pulse. A π-jump pulse can be used to enhance more effectively the PA efficiency than a transform-limited pulse with the same Rabi angle.
The photoassociation (PA) dynamics of ultracold cesium atoms steered by the picosecond laser pulse with cubic-phase modulation has been investigated theoretically by solving numerically the time-dependent Schr\"odinger equation using the mapped Fourier grid method. The temporal duration of the pulse is prolonged, and the pulse area is enlarged by modulating the cubic phase. The PA efficiency is related to the pulse area. When the pulse area is larger than a certain value, the cubic-phase pulses noticeably enhance the PA efficiency, although they have lower energies.
We investigate theoretically the formation of ultracold Cs2 molecules via photoassociation (PA) with three kinds of pulses (the Gaussian pulse, the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time). For the three kinds of pulses, the final population on vibrational levels from v′ = 120 to 175 of the excited state displays a regular oscillation change with pulse width and interaction strength, and a high PA efficiency can be achieved with optimised parameters. The PA efficiency in the excited state steered by the SL1-pulse (SL2-pulse) train with optimised parameters which is composed of four SL1 (SL2) pulses is 1.74 times as much as that by the single SL1 (SL2) pulse due to the population accumulation effect. Moreover, a dump laser is employed to transfer the excited molecules from the excited state to the vibrational level v″ = 12 of the ground state to obtain stable molecules.
Photoassociation (PA) dynamics of ultracold cesium atoms steered by a modulated two-color laser field $\phantom{\rule{4pt}{0ex}}E(t)={E}_{0}f(t)\mathrm{cos}(\frac{2\ensuremath{\pi}}{{T}_{p}}\ensuremath{-}\ensuremath{\varphi})\mathrm{cos}({\ensuremath{\omega}}_{L}t)$ is investigated theoretically by numerically solving the time-dependent Schr\"odinger equation. The PA dynamics is sensitive to the phase of envelope (POE) $\ensuremath{\varphi}$ and the period of the envelope Tp{T}_{p}Tp​, which indicates that it can be controlled by varying POE $\ensuremath{\varphi}$ and period Tp{T}_{p}Tp​. Moreover, we introduce the time- and frequency-resolved spectrum to illustrate how the POE $\ensuremath{\varphi}$ and the period Tp{T}_{p}Tp​ influence the intensity distribution of the modulated laser pulse and hence change the time-dependent population distribution of photoassociated molecules. When the Gaussian envelope contains a few oscillations, the PA efficiency is also dependent on POE $\ensuremath{\varphi}$. The modulated two-color laser field is available in the current experiment based on laser mode-lock technology.
We investigate theoretically the preparation of ultracold photoassociated Cs 2 molecules in the lowest vibrational level of the ground electronic state via the stimulated Raman adiabatic passage (STIRAP) by solving the time-dependent Schrödinger equation using the mapped Fourier grid method. A negative chirped laser pulse is used to produce the unstable photoassociated molecules in the excited electronic state. A dump pulse is utilized to transfer a partial population of the unstable photoassociated molecules to the vibrational v″ = 18 level of the ground electronic state. This part of population is then transferred to the v″ = 0 level of the ground electronic state by the pump and Stokes laser pulses via an intermediate state which is taken to be the v′ = 7 level of the excited electronic state, forming the stable photoassociated molecules. The population transfer efficiency from v″ = 18 to v″ = 0 in the ground electronic state reaches 96.2% via the STIRAP.
The photoassociation dynamics of ultracold lithium atoms controlled by a cut-off pulse has been investigated theoretically by solving numerically the time-dependent Schrodinger equation using the mapped Fourier grid method. The frequency components of the laser pulse close to the atomic resonance are partly cut off. Compared with the typical Gauss-type pulses, the cut-off pulse is helpful to suppress efficiently the weakly bound states and prepare the associated molecules in the lower vibrational states. Especially, the dependence of photoassociation probability on the cut-off position of the laser pulse is explored.
The formation of the NaH molecule from unaligned ultracold atoms via photoassociation (PA) is theoretically investigated by numerically solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom. The PA processes via one- and two-photon excitations are described. The calculated results show that the associated molecule can be prepared to a desired rovibrational state of the ground electronic state for NaH. Compared with the one-photon association probability, the two-photon association probability is obviously enhanced.