Superradiant Rayleigh Scattering and Collective Atomic Recoil Lasing in a Ring Cavity

S. Slama, S. Bux, G. Krenz, C. Zimmermann, and Ph. W. Courteille

Phys. Rev. Lett. 98, 053603 – Published 1 February 2007

Abstract

Collective interaction of light with an atomic gas can give rise to superradiant instabilities. We experimentally study the sudden buildup of a reverse light field in a laser-driven high-finesse ring cavity filled with ultracold thermal or Bose-Einstein condensed atoms. While superradiant Rayleigh scattering from atomic clouds is normally observed only at very low temperatures (i.e., well below $1 μ K$ ), the presence of the ring cavity enhances cooperativity and allows for superradiance with thermal clouds as hot as several $10 μ K$ . A characterization of the superradiance at various temperatures and cooperativity parameters allows us to link it to the collective atomic recoil laser.

Received 25 October 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.053603

Authors & Affiliations

S. Slama, S. Bux, G. Krenz, C. Zimmermann, and Ph. W. Courteille

Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany

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Vol. 98, Iss. 5 — 2 February 2007

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Images

Figure 1
(a) Schematic view of the experimental setup. A two-dimensional MOT (2D MOT) feeds a MOT in the main chamber. From here the cloud is transferred adiabatically in several intermediate steps into a Ioffe-Pritchard (IP) type magnetic trap overlapping with the ring cavity mode volume. A Ti:sapphire laser resonantly pumps the cavity mode $P_{+}$ . Both cavity modes $P_{\pm}$ are observed via the light fields leaking out through one of the cavity mirrors. The atomic cloud can be visualized by absorption imaging. Typical images of a condensate cloud at $T = 0.5 T_{c}$ having and not having interacted with the cavity are shown in (c) and (b), respectively. The images are recorded after 10 ms of free expansion. Curve (d) shows the vertically integrated optical density (OD) of image (c).Reuse & Permissions
Figure 2
(a) Measured time evolution of the reverse power $P_{-}$ . The pump laser power is $P_{+} = 4 W$ . The cavity is operated at high finesse. The atom number is $N = 1.5 \times 10^{6}$ and the laser wavelength is $λ = 797.3 nm$ . Curve (b) marks the time evolution of the recorded pump laser power scaled down by 1000. Curve (c) shows (offset by 7 mW) a numerical simulation of the reverse power using the above parameters (see text). To account for the finite switch-on time of the pump laser power, its experimentally recorded time evolution is plugged into the simulations, where we assume that the pump laser frequency is fixed and resonant to a cavity mode. (d) Measured and calculated (solid line) height $P_{-, 1}$ of the first peak as a function of pump power $P_{+}$ . Here $N = 2.4 \times 10^{6}$ and $λ = 796.1 nm$ .Reuse & Permissions
Figure 3
(a) Measured height of the first peak as a function of atom number $N$ . The cavity is operated at high-finesse (good-cavity limit), the pump laser is set to $P_{+} = 0.5 W$ and $λ = 796.1 nm$ . The solid line shows a simulation. To emphasize the $N$ dependence we also plot curves going like $N^{2}$ (dotted line) and $N^{4 / 3}$ (dashed line). Those dependences are expected in the superradiant and in the good-cavity limit, respectively. (b) Same as (a) but the cavity is now operated at low finesse (superradiant limit), the pump laser is set to $P_{+} = 70 mW$ . To compensate for the loss in cooperativity the laser is tuned closer to resonance at $λ = 795.3 nm$ . The amount of light in the reverse mode due to mirror backscattering in steady state without atoms is $P_{-, s} = 1.8 \times 10^{- 4} P_{+}$ .Reuse & Permissions
Figure 4
(a) Measured time-evolutions of the reverse mode at various temperatures. The cavity is operated at high finesse. For clarity the curves are vertically shifted from one another by 0.35 mW. The atom number is the same for all data points, $N = 10^{6}$ . The pump power is $P_{+} = 1 W$ . The reverse power observed at high temperatures is there even without atoms and is caused by mirror backscattering. (b) Measured SRyS peak height as a function of temperature.Reuse & Permissions

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