Evolution of dark state of an open atomic system in constant intensity laser field

Abstract

We studied experimentally and theoretically the evolution of open atomic systems in the constant intensity laser field. The study is performed by analyzing the line shapes of Hanle electromagnetically induced transparency (EIT) obtained in different segments of a laser beam cross section of constant intensity, i.e., a -shaped laser beam. Such Hanle EIT resonances were measured using a small movable aperture placed just in front of the photodetector, i.e., after the entire laser beam had passed through the vacuum Rb cell. The laser was locked to the open transition F g = 2 → F e = 1 at the D 1 line of 87 Rb with laser intensities between 0.5 and 4 mW/cm 2 . This study shows that the profile of the laser beam determines the processes governing the development of atomic states during the interaction. The resonances obtained near the beam center are narrower than those obtained near the beam edge, but the significant changes of the linewidths occur only near the beam edge, i.e., right after the atom enters the beam. The Hanle EIT resonances obtained near the beam center exhibit two pronounced minima next to the central maximum. The theoretical model reveals that the occurrence of these transmission minima is a joint effect of the preparation of atoms into the dark state and the optical pumping into the uncoupled ground level F g = 1. The appearance of the transmission minima, although similar to that observed in the wings of a Gaussian beam [A. J. Krmpot et al., Opt. Express 17, 22491 (2009)], is of an entirely different nature for the -shaped laser beam.

Influence of a laser beam radial intensity distribution on Zeeman electromagnetically induced transparency line-shapes in the vacuum Rb cell

“…In the wings of the Gaussian laser beam, a Ramsey-like effect can reshape EIT resonances with respect to those near the laser beam centre, as shown in [16,17]. For the profile, optical pumping to the uncoupled ground level dominantly influences the line-shape [18]. The theory demonstrates that the atomic dark state is more sensitive to magnetic field when the atoms are traversing the Gaussian laser beam than when passing through a constant intensity field of the laser beam.…”

“…The importance of the laser beam profile on the EIT was indeed demonstrated theoretically for the vacuum [26] and the buffer gas cells [23][24][25]. Our previous studies have shown that the evolution of the states of the atoms passing through laser beams of different profiles is governed by distinct physical processes [17,18]. Consequently, line-shapes of EIT resonances obtained from various segments of the laser beam cross-section reflect these differences.…”

“…Thus, the results of figures 7 and 8 show that the outer parts of the laser beam cross-section are primarily responsible for the observed differences between EIT line-widths obtained with the two laser beam profiles. Physical mechanisms leading to such differences are explained in detail in [17,18].…”

“…Rb atoms traverse the laser beam at different trajectories with different velocities. Maxwell-Boltzmann velocity distribution, diversity of atomic trajectories, the custom cylindrical symmetric radial profile of the laser electric field, effects of the laser propagation along the cell and induced atomic polarization of the Rb vapour are treated similarly as in [18,26]. The cell temperature was set to room temperature as in the experiment.…”

Electromagnetically induced coherent effects in laser excited Raman resonances in rubidium vapor

“…Therefore, it is important to take into account the real laser beam profile for proper modeling and analysis of coherent effects in alkali-metal vapors. Subsequent sections will present the details of the work published in [53,54,55].…”