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Optics and Spectroscopy

Formation of inversion filaments in laser media due to interatomic interactions via the superradiation field

Vladimir I Emel'yanov, Vyacheslav I. Yukalov

Published Mar 1, 1986• 1 citation
OpenAlex

Abstract

It was theoretically shown that on taking into account interaction between atoms via the superradiation field, an inverted medium of two-level atoms becomes unstable, which leads to constriction of the inversion density into filaments randomly arranged with respect to the beam cross section. The estimates obtained are in good agreement with experiment.

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Journal of Modern Optics•Aug 1, 1990•13 citations
It was theoretically shown that on taking into account interaction between atoms via the superradiation field, an inverted medium of two-level atoms becomes unstable, which leads to constriction of the inversion density into filaments randomly arranged with respect to the beam cross section. The estimates obtained are in good agreement with experiment.
The theory of superradiance by an ensemble of two-level atoms embedded in a dielectric host is developed. It is shown that the near dipole-dipole interaction of a dense collection of two-level atoms is enhanced by the presence of the host material, decreasing the pulse temporal width and increasing the peak pulse intensity of superradiative emission. The influence of the inversion-dependent detuning effect on the parameters of the emitted pulses is investigated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
This study presents examples of observed optical pattern formation in which a single laser beam propagating through atomic sodium vapor without feedback develops a stable, regular transverse structure. In particular, a three-filament near-field pattern leading to a honeycomb far-field pattern occurs at intensities near the saturation intensity and at powers larger than (but of the order of magnitude of) the critical power for self-focusing. The three-filament pattern has a uniform phase profile and strongly correlated power fluctuations, which suggest that it is perhaps a quantum image. These observations are also found to be in good agreement with numerical simulations of filamentation in a two-level atomic medium.
Properties of the inverse lifetime $\frac{1}{\ensuremath{\tau}}$ of quasiparticles in an infinite system of nucleons ("nuclear matter") interacting via the exchange of a neutral scalar boson are studied in the dielectric formulation of the many-body problem. It is shown that the polarization of the nuclear medium plays an essential role in determining $\frac{1}{\ensuremath{\tau}}$. The presence of the medium mediates the interaction between two nucleons in it through the introduction of an effective "dielectric constant" for nuclear matter. The interaction becomes "dressed" in a fashion analogous to, but different in its details from, the screening of the Coulomb interaction between electrons in metals. Calculations of $\frac{1}{\ensuremath{\tau}}$ are made for nuclear matter both in second-order perturbation theory, and using the fully dressed interaction calculated in the random-phase approximation (RPA). The RPA estimate is lower by about a factor of 3 over a wide range of momenta and is in good agreement with empirical optical-model estimates of $\frac{1}{\ensuremath{\tau}}$. The second-order perturbation estimate is by contrast entirely inadequate, emphasizing the importance of taking the polarization effects into account for scattering processes at actual nuclear densities. The use of a dielectric constant for the medium also introduces another feature into the properties of $\frac{1}{\ensuremath{\tau}}$. The behavior of $\frac{1}{\ensuremath{\tau}}$ near the Fermi surface now becomes sensitive to whether or not the interacting ground state is unstable with respect to a permanent density fluctuation. If it is, then $\frac{1}{\ensuremath{\tau}}$ behaves like ($p\ensuremath{-}{p}_{F}$) instead of ${(p\ensuremath{-}{p}_{F})}^{2}$ near the Fermi surface (pF{p}_{F}pF​ is the Fermi momentum). This is not a new physical result, but rather a reflection of the inadequacy of the RPA if the system becomes unstable. It is shown that as the momentum increases the effect of such an instability, if present, decreases, and becomes entirely negligible when $p\ensuremath{\gtrsim}\sqrt{2}{p}_{F}$.