Time-frequency analysis in laser-atom interactions

Zhonghua Ji, Jinpeng Yuan, Yanting Zhao +4 more

We systematically investigate the dependence of the temperature of cold cesium atoms of polarization gradient cooling (PGC) in optical molasses on experimental parameters, which contain changing modes of cooling laser, PGC interaction time, cooling laser frequency and its intensity. The SR mode of cooling laser, that means the cooling laser frequency is changed with step mode and cooling laser intensity is changed with ramp mode, is found to be the best for PGC comparing with other SS, RS, and RR modes. We introduce a statistical explanation and an exponential decay function to explain the variation of cold atomic temperature on time. The heating effect is observed when the cooling laser intensity is lower than the saturation intensity of cold atoms. After optimization, the lowest temperature of cold cesium atoms is observed to be about 4uK with the number of 2x10^9, a density of 1x10^11/cm^3 and the phase space density of 4.4x10^(-5). The optimization process and analysis of controllable experimental parameters are also meaningful for other cold atomic systems.

C. J. Joachain

TONG Xiao-Min, TOSHIMA Nobuyuki

Joseph W. Haus, Maciej Lewenstein, Kazimierz Rza̧żewski

Using an exactly soluble model for the radiative coupling of bound and autoionizing states, we explore the modification in the shape of the photoemission spectra and the total number of scattered photons (photon yield) resulting from finite interaction times. The photon yield studied as a function of the laser-field amplitude (Rabi frequency) or laser–atom detuning has a maximum. This maximum narrows and in certain circumstances shifts as the interaction time is. increased. Near the confluence of coherences the finite time spectra exhibit a rich structure; the heights and widths of the peaks, as well as their positions, are sensitively dependent on the interaction time. Moreover, the narrow central peak is accompanied by strong periodic wiggles, whose period is inversely proportional to the interaction time. The effects of laser broadening on the spectra are fully accounted for. Furthermore, the algebraic expressions for the ground-state occupation probability and the photon yield are considerably simplified from those of our previous analysis of the problem.

Jean Dalibard, Claude N. Cohen-Tannoudji

V. I. Romanenko, Леонід Петрович Яценко

A theoretical analysis is presented of the change in the momentum of a three-level atom due to its interaction with counterpropagating laser pulses that overlap in time. The two lower energy states of the atom are metastable; i.e., a lambda-type configuration of atomic levels is considered. The cases of two and four counterpropagating pulses having different carrier frequencies are considered. In the case of adiabatic atom-field interaction, it is shown that the atom’s momentum can change by an integer multiple of the photon momentum and the corresponding standard deviation is small as compared to the photon momentum squared.