Ya. A. Fofanov

Transformation of intensity fluctuations in nonlinear reflection of light

The transformation of intensity fluctuations accompanying the nonlinear resonance reflection of light from a glass-resonant gas interface is discussed. The illumination of the interface at angles close to the critical angle for total internal reflection is found to have certain advantages over orthogonal incidence. At the maximum of the strongest resonance, the reflected light intensity amounts to more than 50% of the incident light. In these conditions, a squeezing of the amplitude (photon) fluctuations is observed in the radiation generated by a semiconductor laser-nonlinear selective reflector system. A simple semiclassical theory adequately describes some important characteristics of this system: the shape of the reflection resonances, the strength of the saturation fields, and so on.

Laser polarization-optical detection of the magnetization process of a magnetically ordered crystal

This paper demonstrates the use of laser radiation with deep polarization modulation as a method of investigating a magnetically ordered substance. Using a model sample—single-crystal iron borate—as an example, it is shown that this technique can be used to study magnetization processes. A qualitative picture is given of the formation of the polarization-optical response in the sample being magnetized, and the corresponding experimental characteristics are obtained. Sudden changes of the response are recorded that are associated with abrupt reconstruction of the domain structure. The approach thus developed can be useful in studies of the domain structure and of other features of the structure of materials for optoelectronics, nonlinear and magnetooptics, laser engineering, etc.

The influence of collective effects on the propagation of electromagnetic radiation in dense ultracold atomic ensembles

Based on the already-developed general theory (I.M. Sokolov, D.V. Kupriyanov, and M.D. Havey, JETP 112 (2), 246 (2011)), we have studied the spatial distribution of excited atoms and of the atomic polarization that a weak monochromatic field creates in a dense ultracold atomic medium. We show that, in the case of a homogeneous random spatial distribution of atoms, the amplitude of atomic polarization averaged over spatial configurations decreases outside boundary regions according to an exponential law, while its phase linearly increases. Based on this, we have numerically determined the extinction coefficient and the light wavelength in the medium, as well as its dielectric permittivity. The dispersion of the permittivity at different concentrations has been studied. We show that, for dense clouds, the real part of the dielectric permittivity acquires negative values in a certain frequency range. Based on the calculation of the spatial distribution of excited atoms, we have analyzed the character of the transfer and trapping of quasi-resonant radiation in atomic clouds of differing density.

Controlling the intensity and fluctuations of light upon its selective reflection

Selective reflection of a semiconductor laser beam by a resonant gas is studied. The experiments were performed under conditions where the laser frequency is determined by the laser cavity mode structure. In this case, characteristic steps—intensity quasi-levels—arise on the reflectivity resonances. It is shown that the height of the quasi-levels depends on the degree of saturation of the resonance reflection by the laser field. Low-noise reflectivity regimes with different sensitivities to external signals are found on these quasi-levels.

Single-mode amplitude squeezing in a semiconductor laser at 780 nm

The problem of the creation of a sub-Poissonian radiation source on the basis of a semiconductor laser with an external cavity is considered, which operates, from the viewpoint of quantum optics, in the single-mode regime. The conditions of the generation of sub-Poissonian radiation, under which the whole set of sub-threshold modes, including the nearest modes of the external (long) cavity, is completely suppressed at room temperature, were experimentally revealed and theoretically studied. Single-frequency low-noise lasing is of interest not only for the creation of nonclassical light sources, but also for sensitive spectroscopic applications in the classical domain.

Investigation of polarization magnetooptic responses of a low-concentration ferrofluid

A highly sensitive laser polarization-optical technique was developed and applied to investigations of a ferrofluid, which was placed in a magnetic field. A colloid solution of magnetite in kerosene was used as a sample. It was shown that the magnetooptic response of this substance is reliably registered at a volume solid-phase content of down to ~10–5. It was revealed that within a very wide range of changes in the solution concentration, a quadratic dependence of the observed birefringence value on the low-intensity field (up to several tens of oersted) is retained.

Phonon echo in high-temperature superconductors as a nonlinear magnetoacoustic phenomenon

The nonlinear behavior of a phonon echo signal in high-temperature superconductors is studied experimentally. It is demonstrated that conventional consideration of anharmonic effects is insufficient for comprehensive explanation of the echo signal behavior. It is shown that the nonlinear properties of the phonon echo should be taken into account when the phonon echo is used as a means for studying superconductor parameters. An increase in the elastic nonlinearity in iron-doped yttrium ceramics is found.

Phonon echo probing of high-temperature superconductors containing magnetic ions

Polycrystalline high-temperature superconductors (HTSCs) containing iron and gadolinium ions have been studied using the phonon echo technique, whereby a powdered sample is probed by a special sequence of RF pulses and the response having an acoustic nature is measured. It is shown that the behavior of this signal in the iron-containing HTSC materials exhibits some distinctive features in comparison to the response of a conventional yttrium-based ceramic. The superconducting gap estimated for the samples with magnetic ions does not differ significantly from the value for a usual HTSC. This fact is related to a spatial separation of the magnetic and superconducting phases in the materials studied.

Strong resonance reflection of polarized light from an alkali vapor

Resonance reflection of light from the interface between a dielectric and an alkali vapor is studied. Two cases are considered in which a laser light beam is polarized either parallel or perpendicular to the plane of incidence. Upon scanning of the frequency of the incident laser radiation, in the first case, the reflection conditions vary from approximately the conditions of Brewster reflection to the conditions characteristics of total internal reflection. In the second case, the Brewster reflection conditions are not realized, and the variations in the intensity of the reflected light observed upon frequency scanning are smaller. The rotation of the plane of polarization and the laser frequency tuning make it possible to rapidly switch between these reflection conditions.