Dynamic diffraction coupling is examined in superfluorescence with use of a semiclassical model in which diffraction and transverse density variations are rigorously included. The Cs data are correctly simulated for the first time.PACS numbers: 42.65.Gv, 32.50.+d Superfluorescence 1 (SF) is the process by which coherent emission occurs from an ensemble of two-level atoms all intially in the upper state. An important question in SF experiments is why the output pulse is sometimes smooth, but at other times exhibits multiple structure or ringing. Strong ringing or pulsing has been observed by several groups, including the initial HF-gas studies. 2 Recent Cs experiments, 3 however, never show ringing at low densities, whereas at higher densities, highly fluctuating multiple pulsing is usually observed, and is believed to arise from transverse-mode competition. Strong BurnhamChiao ringing 4 is predicted by plane-wave models, 5 which neglect variations transverse to the propagation direction. We find that inclusion of transverse effects, both spatial averaging and Laplacian diffraction, substantially alters the one-dimensional Cs predictions, 313 leading to greater conformity with the Cs data.The initial SF state is prepared by rapidly inverting a sample of three-level atoms by transferring population from the ground state to the upper state with a short light pulse, creating a cylindrical region of excited atoms. 2 SF pulse emission subsequently occurs between this excited state and the intermediate state. There is no optical cavity and stray feedback is negligible.This study employs the semiclassical approach to explore the influence of transverse effects, using the average value 6 of the initial tipping angle. 4 ' 5a Both longitudinal fluctuations 6 and transverse flucutations, as influenced by diffraction, will be discussed elsewhere.Transverse effects are expected to influence the pulse shapes in at least two ways, one of which is spatial averaging. In SF experiments the initial inversion density n 0 (r) is radially dependent since the pump light pulse typically has a Gaussian-like profile. 7 In the absence of diffraction this cylinder can be thought of as a set of concentric cylindrical shells, each with its own density, tipping angle, and delay time. 8 The radiation will be a sum of plane-wave intensities; when the entire output signal is viewed the ringing averages out, resulting in an asymmetric pulse with a long tail. 9 A second transverse effect, diffraction, causes light emitted by one shell to affect the emission from adjacent shells. This coupling mechanism, which causes transverse energy flow, is more important for samples with small Fresnel numbers F.SF is inherently a transverse-effect problem even for large-JP samples since the off-axis modes are not discriminated against. This work is the first to correctly include this crucial element.Our analysis adopts the coupled Maxwell-Schrodinger equations, which fully take into account propagation and transverse effects. Previous approaches examined transver...
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