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Physical Review A

Ground-state grating echoes from Rb vapor at room temperature

Anantharaman Kumarakrishnan, Unyob Shim, S. B. Cahn, Tycho Sleator

Published Nov 1, 1998• 13 citations
Publisher

Abstract

We have used two sets of opposite circularly polarized traveling wave pulses separated in time to establish, and subsequently rephase, a spatially modulated coherence between the magnetic sublevels of the $F=3$ ground state in Doppler broadened ${}^{85}\mathrm{Rb}$ vapor. The rephasing results in a magnetic grating echo whose duration is an accurate measure of the velocity distribution. We demonstrate that the time scale of the experiment is determined solely by the transit time of atoms across the laser beam. The shortening of the lifetime due to a perturber (Ar) allows us to infer the Rb-Ar velocity changing collision cross section.

DOI
10.1103/physreva.58.3868

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Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)•Jan 1, 1997•2 citations

Collisional revival of magnetic grating free-induction decay

Unyob Shim, Anantharaman Kumarakrishnan, S. B. Cahn +1 more

Summary form only given. A ground-state coherence grating involving the magnetic sublevels of the F=3 ground state in /sup 85/Rb is created in Doppler-broadened vapor using an excitation pulse that consists of two traveling waves with orthogonally polarized wave vectors. The decay of the grating that is due to thermal motion is probed by a traveling-wave readout pulse. This results in a scattered signal magnetic grating free-induction decay (MGFID) that is detected using a heterodyne technique. In our experiment, collisional revival can be expected when the mean free path is less than the grating spacing.

Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)•Jan 1, 1997•0 citations
We have used two sets of opposite circularly polarized traveling wave pulses separated in time to establish, and subsequently rephase, a spatially modulated coherence between the magnetic sublevels of the F=3F=3F=3 ground state in Doppler broadened 85Rb{}^{85}\mathrm{Rb}85Rb vapor. The rephasing results in a magnetic grating echo whose duration is an accurate measure of the velocity distribution. We demonstrate that the time scale of the experiment is determined solely by the transit time of atoms across the laser beam. The shortening of the lifetime due to a perturber (Ar) allows us to infer the Rb-Ar velocity changing collision cross section.
We have initiated a new class of coherent transient experiments with Doppler-broadened atoms confined in a vapor cell. A spatially modulated coherence is created between magnetic sublevels of the F=3 ground state of /sup 85/Rb by a standing pulse. This pulse consists of two opposite circularly polarized traveling waves with wave vectors K/sub 1/ and K/sub 2/ at a small angle /spl theta/. The coherence grating is probed by the application of a readout pulse along K/sub 2/. The resulting coherent emission along K/sub 1/ is detected by a heterodyne technique.
We have used two sets of orthogonally polarized traveling-wave pulses separated in time to establish and, subsequently, rephase a spatially periodic coherence grating between the magnetic sublevels of the F=3F=3F=3 ground state in a cloud of laser-cooled 85Rb{}^{85}\mathrm{Rb}85Rb atoms. The rephasing results in a magnetic grating echo (MGE). We have used the shape of the signals to determine both transverse and longitudinal velocity distributions and to study the effects of magnetic fields. The amplitude of the MGE with counterpropagating pulses is modulated at the atomic recoil frequency, a consequence of matter wave interference.
We have developed a theoretical description of the evolution of ground state coherences between magnetic sublevels in Rb vapor in the presence of a magnetic field along an arbitrary direction. This formalism uses a rotation matrix approach to describe the evolution of coherences created by two traveling wave laser pulses with orthogonal polarizations. The effect of a magnetic field can be described as a time-dependent rotation of the atomic system about the quantization axis. Predictions based on this theoretical formalism for the functional form of Larmor oscillations in a magnetic field are studied using a coherent transient effect known as magnetic grating free induction decay (MGFID) using room temperature vapor and laser cooled atoms. We find the theoretical predictions to be in excellent agreement with data. The velocity distribution of the cold sample measured from the dephasing time of the MGFID in the absence of magnetic fields is in agreement with the sample temperature obtained by imaging the ballistic expansion of the trapped cloud. By using rate equations to model atomic coherences, it is also possible to predict the evolution of magnetic grating echoes (MGE) in a magnetic field. We compare these predictions with experiments from cold atoms and discuss applications of the MGFID and MGE that relate to a precision measurement of the atomic ggg factor ratio using 85Rb^{85}\mathrm{Rb}85Rb and 87Rb^{87}\mathrm{Rb}87Rb isotopes.
Summary form only given. A ground-state coherence grating involving the magnetic sublevels of the F=3 ground state in /sup 85/Rb is created in Doppler-broadened vapor using an excitation pulse that consists of two traveling waves with orthogonally polarized wave vectors. The decay of the grating that is due to thermal motion is probed by a traveling-wave readout pulse. This results in a scattered signal magnetic grating free-induction decay (MGFID) that is detected using a heterodyne technique. In our experiment, collisional revival can be expected when the mean free path is less than the grating spacing.
Summary form only given. A ground-state coherence grating involving the magnetic sublevels of the F=3 ground state in /sup 85/Rb is created in Doppler-broadened vapor using an excitation pulse that consists of two traveling waves with orthogonally polarized wave vectors. The decay of the grating that is due to thermal motion is probed by a traveling-wave readout pulse. This results in a scattered signal magnetic grating free-induction decay (MGFID) that is detected using a heterodyne technique. In our experiment, collisional revival can be expected when the mean free path is less than the grating spacing.
Summary form only given. A ground-state coherence grating involving the magnetic sublevels of the F=3 ground state in /sup 85/Rb is created in Doppler-broadened vapor using an excitation pulse that consists of two traveling waves with orthogonally polarized wave vectors. The decay of the grating that is due to thermal motion is probed by a traveling-wave readout pulse. This results in a scattered signal magnetic grating free-induction decay (MGFID) that is detected using a heterodyne technique. In our experiment, collisional revival can be expected when the mean free path is less than the grating spacing.