J. W. R. Tabosa

Collapses and revivals of stored orbital angular momentum of light in a cold-atom ensemble

We report on the storage of orbital angular momentum of light in a cold ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The stored information can be manipulated by an applied magnetic field and we were able to observe collapses and revivals due to the rotation of the stored atomic Zeeman coherence for times longer than 15

Spectroscopic observation of the rotational doppler effect

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Transient Bragg diffraction by a transferred population grating: application for cold atoms velocimetry

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Dynamics of a stored Zeeman coherence grating in an external magnetic field

We report on the first spectroscopic observation of the rotational Doppler shift associated with light beams carrying orbital angular momentum. The effect is evidenced as the broadening of a Hanle electromagnetically induced transparency coherence resonance on Rb vapor when the two incident Laguerre-Gaussian laser beams have opposite topological charges. The observations closely agree with theoretical predictions.

Single-photon superradiance in cold atoms

We report the observation of transient Bragg diffraction by an optical-pumping-transferred ground-state population grating in cold cesium atoms confined in a magneto-optical trap. The measurement of the grating decay time gives direct access to the temperature of the cold sample. In principle, the method can be employed to provide directional information on the trap velocity distribution. For strong excitation the transferred grating becomes anharmonic and higher-order diffraction is observed.

Degenerate multiwave mixing in SF6

We investigate the evolution of a Zeeman coherence grating induced in a cold atomic cesium sample in the presence of an external magnetic field. The gratings are created in a three-beam light storage configuration using two quasi-collinear writing and reading laser pulses with a counterpropagating pulse after a variable time delay. The phase-conjugated pulse arising from the atomic sample is monitored. Collapses and revivals of the retrieved pulse are observed for different polarizations of laser beams and for different directions of the applied magnetic field. While magnetic field inhomogeneities are responsible for the decay of the coherent atomic response, a five-fold increase in the coherence decay time, with respect to no applied magnetic field, is obtained for an appropriate choice of the direction of the applied magnetic field. A simplified theoretical model illustrates the role of the magnetic field mean and its inhomogeneity on the collective atomic response.

Methyl alcohol saturation spectroscopy using a CO 2 sequence band laser

The interaction of an ensemble of atoms with common vacuum modes may lead to an enhanced emission into these modes. This phenomenon, known as superradiance, highlights the coherent nature of spontaneous emission, resulting in macroscopic entangled states in mundane situations. The complexity of the typical observations of superradiance, however, masks its quantum nature, allowing alternative classical interpretations. Here we stress how this picture changed with the implementation ten years ago of a new process for single-photon generation from atomic ensembles. We present then the last piece of evidence for the superradiant nature of such process, reporting the observation of an accelerated emission of the photon with a rate that may be tuned by controllably changing the number of atoms in the ensemble. Such investigation paves the way to a new, bottom-up approach to the study of superradiance.

Polarization dependence of four-wave mixing in a degenerate two-level system

Abstract High-order diffraction of CW CO 2 laser radiation was observed in SF 6 in the Doppler broadening limit. The nonlinear susceptibilities, up to χ (9) , were separately monitored in Doppler free resonance lineshapes, using a near-collinear phase matched multiwave mixing configuration.

Angular dependence of phase conjugation in SF 6

Doppler-free saturated absorption spectra of CH(3)OH at 300 and 600 K have been observed with a cw CO(2) sequence-band laser tunable over 60 lines in the 9.4- and 10.6-microm bands. Sixteen inverted Lamb dips were observed.

Delayed four- and six-wave mixing in a coherently prepared atomic ensemble.

Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate two-level atomic transition is theoretically and experimentally examined. Using the model presented by A. Lezama et al [Phys. Rev. A 61, 013801 (2000)] the NDFWM spectra corresponding to different pump and probe polarization cases are calculated and discussed. The calculated spectra are compared to the observation of NDFWM within the