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Focus: The Laser Glow of an Atom Cloud

Michael Schirber

Published May 4, 2009• 0 citations
OpenAlex

Abstract

Calculations reveal that a dense cloud of cold atoms pumped with lasers can glow with its own laser light. Such ‘random lasers’ have previously been made only from solid and liquid materials.

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The Laser Glow of an Atom Cloud

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Calculations reveal that a dense cloud of cold atoms pumped with lasers can glow with its own laser light. Such ‘random lasers’ have previously been made only from solid and liquid materials.

Focus•May 1, 2009•0 citations

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Threshold of a Random Laser with Cold Atoms

Luis S. Froufe‐Pérez, William Guerin, Rémi Carminati +1 more

We address the problem of achieving an optical random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. The lasing threshold can be defined using the on-resonance optical thickness b0 as a single critical parameter. We predict the threshold quantitatively, as well as power and frequency of the emitted light, using two different light transport models and the atomic polarizability of a strongly pumped two-level atom. We find a critical b0 on the order of 300, which is within reach of state-of-the-art cold-atom experiments. Interestingly, we find that random lasing can already occur in a regime of relatively low scattering.

arXiv:0812.0266•Physical Review Letters•May 1, 2009•49 citations
We demonstrate experimentally that a dense cloud of cold atoms with a size comparable to the wavelength of light can induce large group delays on a laser pulse when the laser is tightly focused on it and is close to an atomic resonance. Delays as large as $\ensuremath{-}10\phantom{\rule{0.28em}{0ex}}\mathrm{ns}$ are observed, corresponding to ``superluminal'' propagation with negative group velocities as low as $\ensuremath{-}300\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$. Strikingly, this large delay is associated with a moderate extinction owing to the very small size of the dense cloud. It implies that a large phase shift is imprinted on the continuous laser beam. Our system may thus be useful for applications to quantum technologies, such as variable delay line for individual photons or phase imprint between two beams at the single-photon level.
We implement optical pumping to prepare cold atoms in our prototype of the 87 Rb space cold atom clock, which operates in the one-way mode. Several modifications are made on our previous physical and optical system. The effective atomic signal in the top detection zone is increased to 2.5 times with 87% pumping efficiency. The temperature of the cold atom cloud is increased by 1.4 μK. We study the dependences of the effective signal gain and pumping efficiency on the pumping laser intensity and detuning. The effects of σ transition are discussed. This technique may be used in the future space cold atom clocks.
We address the problem of achieving an optical random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. The lasing threshold can be defined using the on-resonance optical thickness b0 as a single critical parameter. We predict the threshold quantitatively, as well as power and frequency of the emitted light, using two different light transport models and the atomic polarizability of a strongly pumped two-level atom. We find a critical b0 on the order of 300, which is within reach of state-of-the-art cold-atom experiments. Interestingly, we find that random lasing can already occur in a regime of relatively low scattering.