Atomic coherence

About: Atomic coherence is a research topic. Over the lifetime, 877 publications have been published within this topic receiving 29395 citations.

Electromagnetically induced absorption with sub-kHz spectral width in a paraffin-coated Rb vapor cell.

Abstract: We report on electromagnetically induced absorption (EIA) with sub-kHz spectral width in a paraffin-coated Rb vapor cell in the Hanle configuration of the 5S1/2(F=2)-5P3/2(F’=3) transition of 87Rb atoms. Using a linearly polarized laser, the spectral width of the Hanle EIA spectrum was measured to be 0.55 mG (390 Hz). The narrow spectral width was due to the maintaining of atomic coherence between ground states while atoms collided with the anti-relaxation coated wall of the Rb vapor cell. Under a weak transverse residual magnetic field, the angle between the transverse residual magnetic field and the direction of linear polarization affected the magnitude of the narrow Hanle EIA spectrum. This is because of the change of atomic magnetic momentum due to the weak transverse residual magnetic field around the zero value of the longitudinal magnetic field.

Control of light in an M-type five-level atomic system

Abstract: An M-type five-level atomic model is proposed to achieve a large index of refraction with vanishing absorption. We present a novel model, to our knowledge, in theoretical analysis, in which an incoherent pumping rate is adopted to simplify the M-type five-level system to be an equivalent four-level system. The theoretical and experimental results show that, by adjustment of the intensity of the incoherent pump, lower group velocity (than that obtained in a conventional Lambda-type three-level electromagnetically induced transparency system) is obtained in cesium atomic vapor. Moreover, a saturation limit for the group velocity is also presented. The experimental results show good agreement with the theoretical analysis.

Propagation dynamics in an autoionization medium

Abstract: The study of the propagation of electromagnetic pulses in multi-level media has lead to the discovery of a number of interesting phenomena. These include the simultaneous propagation of two pulses having different fundamental frequencies ~‘‘simultons’’ !@ 1,2#, electromagnetically induced transparency under matched pulse conditions @3‐7# and the creation and propagation of ‘‘adiabatons,’’ a general class of pulses which show solitonic behavior in adiabatically evolving atomic systems @8‐11#. Pulse propagation effects have also been investigated within other contexts. Examples include the study of lasing without population inversion @12#, the influence of the quantized nature of laser fields @13,14#, ‘‘dragging and cloning’’ of laser pulses @15#, the effects of initial superpositions of the atomic states @16,17#, and the effects of Doppler broadening @18#. Furthermore, systems where a spatial excitation can be controlled @19# or even imaged in the temporal profile of laser pulses@20# have been discussed. In these studies, systems involving bound states were considered. The introduction of dissipative processes are detrimental to, and can even destroy, the coherence required for the manifestation of the above mentioned phenomena. However, recently it has been shown that, using the laser-induced continuum structure ~LICS! scheme @21,22#, atomic coherence can be preserved even in systems in which dissipative processes ~e.g., ionization! are present. These latter studies utilize two lasers in a probe-coupling configuration. Interfering processes arising from the coherent laser-matter interaction involving both of these lasers are necessary for transparency or solitonlike propagation in the medium. In this paper, we investigate the propagation dynamics of a short laser pulse interacting with an autoionizing medium. We show that Fano interference @23# can lead to transparency in the medium, thereby allowing the laser pulse to propagate without absorption. This phenomenon is closely related to the transparency predicted in a four-level medium via spontaneous-emission interference @24#. The essential feature of the present system is the presence of a continuum of atomic states, so that dissipation is intrinsic to the system. However, the decay processes can interfere and this can give rise to transparency in the medium, as will be discussed below. In contrast to the LICS scheme @21,22#, here only a single laser, the probe laser that couples the ground state to both the autoionizing state and the continuum, is involved. The configuration interaction which couples the autoionizing state to the continuum is responsible for the necessary interference in this case, rather than a second laser field. Since Fano’s original work, a number of studies have considered the total absorption of a laser field in the autoionizing medium in the weak-field limit @25#. Numerical studies of the Maxwell-Bloch equations for the pulse propagation have also been carried out @26#. In this article, we re-examine short laser pulse propagation in an autoionizing medium. We place emphasis on establishing the connection between adiabatic population trapping in short, pulsed laser fields @27,28# and transparency in the propagation of the laser pulse in the medium. Furthermore, we calculate both analytically and numerically corrections to the adiabatic behavior and show that in the first approximation the laser pulse retains its shape and only its group velocity is modified. In the following section we derive the Maxwell‘ ‘

Enhancement of six-wave mixing by atomic coherence in a four-level inverted Y system

Abstract: The authors have considered the coexisting dressed four-wave mixing (FWM) and six-wave mixing (SWM) in an open four-level inverted Y configuration. The authors also report an experimental observation of optical pumping-assisted FWM and electromagnetically induced transparency (EIT)-assisted SWM. The efficient SWM can be selected by EIT window and controlled by the coupling as well as dressed field detuning and power. Due to EIT and optical pumping assistance, the enhanced SWM signal is more than ten times lager than the coexisting FWM signal.

Phase-dependent properties for absorption and dispersion by spontaneously generated coherence in a four-level atomic system

Abstract: A four-level atomic system with two closely lying upper levels driven by two coherent fields is considered. We show that, in the presence of a weak incoherent pump, steady-state gain can be achieved as a result of quantum interference from spontaneous emission. The gain depends on the relative phase between the two fields, so it can be modulated by control of the relative phase. Also, by controlling the relative phase, one can always obtain a large index of refraction with zero absorption.