Light exotic atoms in excited states: scattering and atomic cascade

Hongmei Ma, L. Q. Chen, Chun-Hua Yuan

A new Raman process can be used to realize efficient Raman frequency conversion by coherent feedback at low light intensity [Chen B, Zhang K, Bian C L, Qiu C, Yuan C H, Chen L Q, Ou Z Y, and Zhang W P 2013 Opt. Express 21 , 10490]. We present a theoretical model to describe this enhanced Raman process, termed as cascade correlation-enhanced Raman scattering, which is a Raman process injected by a seeded light field. It is correlated with the initially prepared atomic spin excitation and driven by the quasi-standing-wave pump fields, and the processes are repeated until the Stokes intensities are saturated. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics, and optical metrology due to its simplicity.

Wilhelm Raith

P. Kochan, H. J. Carmichael

Under usual laboratory conditions the absorption of a beam of light by a dilute two-level medium depends on the intensity and spectrum of the incident light. If the incident photon flux is small compared to the decay rate of the absorber’s excited state, saturation effects can be neglected and only the spectrum of the light is important; thus, weak-field absorption depends only on the firstorder correlation function of the incident light. This result relies, however, on a requirement that the incident beam cross-section be much larger than the absorption cross-section of an atom. Then individual atoms act as low efficiency scatterers and the statistics of the scattering process is governed by the law of large numbers applied to many scattering sites. In contrast, if it is arranged that just one atom significantly absorbs (scatters) a beam of photons, correlation functions of the incident light beyond the first-order must be considered. For a beam that is focused within an absorption cross-section, we might naively predict that every photon will be scattered and none transmitted. In fact, even for a very weak beam there is a finite probability for two photons to arrive at the atom within the excited state lifetime, and in this event at least one of them will be transmitted (statistical saturation). In this paper we calculate the transmitted photon flux for a weak beam of photons focussed strongly onto a single, resonant two-state atom. We study the dependence of the transmitted flux on the statistics of the incident photons. Photon beams derived from sources of coherent, chaotic, squeezed, coherent-antibunched, and broadband-antibunched light are considered. our calculations are based on a recently developed theory of cascaded open systems,1,2 and serve to illustrate the usefulness of this theory.

Daniel Kleppner

Julia F. M. Werra, Paolo Longo, Kurt Busch

We present a theoretical analysis of the spectral features of coherent light pulses traveling in a one-dimensional waveguide with an embedded two-level quantum system. In particular, we clarify and explain the relevant physical mechanisms that lead to a rich variety of distinct features in the spectrum of the scattered light. This includes the phenomenon of discrete steps in the transmitted intensity as a function of the excitation amplitude, frequency mixing as a consequence of cascaded nonlinear processes, and the role of atom-photon bound states.

A. P. Kazantsev, Gregory I. Surdutovich, Valery P. Yakovlev