Coherent flash of light emitted by a cold atomic cloud

Abstract

When a resonant laser sent on an optically thick cold atomic cloud is abruptly switched off, a coherent flash of light is emitted in the forward direction. This transient phenomenon is observed due to the highly resonant character of the atomic scatterers. We analyze quantitatively its spatio-temporal properties and show very good agreement with theoretical predictions. Based on complementary experiments, the phase of the coherent field is reconstructed without interferometric tools.Comment: Submitted to Phys. Rev. Let

Coherent forward broadening in cold atom clouds

“…The predictions described above should be realizable for any azimuthally symmetric cloud of atoms with densities similar to those shown here when the inhomogeneous broadening is negligible. Manipulating cold atomic clouds is common in experiments [8,[32][33][34][35], which makes testing the predictions of this letter feasible. For example using a magneto-optical trap (MOT), one could create a cold atomic cloud with a Gaussian density distribution equivalent to that in Eq.…”

Large optical depth frequency modulation spectroscopy

“…Thus, the relevant parameter to compare the two temperature cases is indeed 6πρL/k 2 ; the OD at T = 0. We note that for finite temperature, we get b 0 = 6πρLg(kv/Γ)/k 2 where g(x) = π/8 exp 1/8x 2 erfc 1/ √ 8x /x [42]. For large x, g(x) π/8/x, leading to a substantial reduction of the OD (of a factor kv/Γ) for the finite temperature medium compared to the T = 0 case.…”

Cooperative Emission of a Pulse Train in an Optically Thick Scattering Medium

“…In particular, the intensity of the forward scattering is bounded by 4 times the incident intensity ("superflash effect") [27]. The temporal evolution of the transmitted field, after the abrupt switch off of the incident field, is not a simple function having only one characteristic decay rate [26]. However, we get a clear physical insight by considering only the initial decay time (at t = 0 + ), which takes a simple analytical expression (see Supplemental Material [35]):…”

“…In a FID experiment where the incident field is abruptly switched off at t = 0, the intensity of the transmitted field at t = 0 + is a direct measurement of the forward scattered intensity in the stationary regime. Its properties are studied in detail in [26,27]. In particular, the intensity of the forward scattering is bounded by 4 times the incident intensity ("superflash effect") [27].…”