Laser induced dynamics of atomic sublevel coherences

Mao Huang, John G. Coffer, James C. Camparo

In ultraminiature atomic physics (UAP), where the goal is to perform low-power, 'chip-scale' precision spectroscopy, stochastic-field/atom interactions can play a primary role in defining the limits of sensitivity. Unfortunately, the transient responses of a quantum system to random changes in the amplitude, phase or polarization of a resonant field are not well understood, forming the basis of what has come to be known as the stochastic-field/atom interaction problem. As the first step in understanding the more complicated stochastic problem, the present work considers the response of a coherent-population-trapping (CPT) signal to a sudden, step-function change in laser polarization. We find that the transient behaviour depends on both the redistribution of atomic population among the atom's Zeeman sublevels and the regeneration of atomic coherence between these sublevels. Despite the complicated nature of the dynamics, we develop and experimentally validate a semi-empirical, reasonably intuitive model of the CPT transient and demonstrate that in the 'typical' CPT signal the polarization-induced transients are dominated by redistribution of atomic population among the Zeeman sublevels. Further, the amplitudes of the polarization-induced transients are relatively large and could potentially 'swamp' the CPT signals of interest for UAP.

Amitabh Joshi, Wenge Yang, Min Xiao

Dieter Suter, J. Mlynek

The dynamics of coherences between sublevels of an electronic ground state is investigated under conditions of modulated optical pumping. It is shown that the modulation corresponds to an effective reduction of the apparent sublevel splitting, thereby allowing the excitation of coherences between atomic sublevels whose energy splitting would require very high laser intensities for dc excitation. In addition, the frequency and phase of the modulation introduce additional degrees of freedom that can be utilized for the design of new experiments. The theoretical evaluations are compared with experiments on the ground state of atomic sodium.

Guo Qin Ge

Dieter Suter

After the discussion of ionic solids we shift our attention to atomic vapours. Here, we discuss the dynamics of microscopic order within the angular momentum substates under the influence of light and magnetic fields. For this purpose, we combine optical pumping as outlined in Chapter 5 to prepare the ordered states, and polarisation-selective detection introduced in Chapter 6 for its observation. In contrast to the introductory sections, we no longer discuss these dynamics as mathematical models, but for specific physical systems, using experimental data to illustrate the theoretical description. The systems we use for this illustration are vapours of alkali metal atoms, in particular sodium. These one-electron systems allow the most direct application of the theoretical models developed above. In addition, we concentrate on electronic ground states, whose long lifetimes permit long observation times and correspondingly precise observations. Experimental arrangement General considerations Laser-induced dynamics This chapter surveys the coherent evolution of coherences between angular momentum sublevels. Optical pumping excites this microscopic order, and it evolves under the influence of external magnetic fields and the laser radiation. The primary goal of this section is to show how the mathematical models developed in the preceding sections apply to real physical systems. We discuss how the observed signals arise and by which parameters the experimenter can control the dynamics of these systems.

Yifu Zhu