Coherent diffusion pertains to the motion of atomic dipoles experiencing frequent collisions in vapor while maintaining their coherence. Recent theoretical and experimental studies on the effect of coherent diffusion on key Raman processes, namely, Raman spectroscopy, slow polariton propagation, and stored light, are reviewed in this Colloquium.

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Colloquium: Coherent diffusion of polaritons in atomic media

We investigate experimentally the lifetime of the photons in a cavity containing a medium exhibiting strong positive dispersion. This intracavity positive dispersion is provided by a metastable helium gas at room temperature in the electromagnetically induced transparency regime, in which light propagates at a group velocity of the order of 104 m·s−1. The results definitely prove that the lifetime of the cavity photons is governed by the group velocity of light in the cavity and not its phase velocity.

Photon lifetime in a cavity containing a slow-light medium.

We investigate experimentally the lifetime of the photons in a cavity containing a medium exhibiting strong positive dispersion. This intracavity positive dispersion is provided by a metastable helium gas at room temperature in the electromagnetically induced transparency (EIT) regime, in which light propagates at a group velocity of the order of 10000 m/s. The results definitely prove that the lifetime of the cavity photons is governed by the group velocity of light in the cavity, and not its phase velocity.

Photon lifetime in a cavity containing a slow-light medium

We theoretically study the propagation and storage of a classical field in a Λ-type atomic medium using coherent population oscillations (CPOs). We show that the propagation eigenmodes strongly relate to the different CPO modes of the system. Light storage in such modes is discussed by introducing a "populariton" quantity, a mixture of populations and field, by analogy to the dark state polariton used in the context of electromagnetically induced transparency light storage protocol. As experimentally shown, this memory relies on populations and is then-by contrast with usual Raman coherence optical storage protocols-robust to dephasing effects.

Coherent Population Oscillation-Based Light Storage.

Electromagnetically-induced transparency, slow light, and negative group velocities in a room temperature vapor of 4He∗

Electromagnetically induced transparency (EIT) is observed in gaseous 4He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. The measurement of slow light opens up possible ways to applications.

https://iopscience.iop.org/article/10.1209/0295-5075/82/54002/pdf

Observation of ultra-narrow electromagnetically induced transparency and slow light using purely electronic spins in a hot atomic vapor

Electromagnetically induced transparency (EIT) is observed in gaseous 4He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. Measurement of slow light opens up possible ways to applications.

Observation of Ultra-narrow Electromagnetically Induced Transparency and Slow Light using Purely Electronic Spins in a Hot Atomic Vapor

EIT and light velocities as low as 7000 m.s-1 were observed at 1.083 µm using a4He* cell at room temperature. The 1 GHz Doppler broadening opens the door to broadband radar applications.

M. David

Papers

Observation of ultra-narrow electromagnetically induced transparency and slow light using purely electronic spins in a hot atomic vapor

Observation of Ultra-narrow Electromagnetically Induced Transparency and Slow Light using Purely Electronic Spins in a Hot Atomic Vapor

Electromagnetically Induced Transparency (EIT) and Slow Light in a 4He* Hot Atomic Vapor