Selective reflection spectrum in a quasi-lambda four-level atomic system

At low vapour densities the conventional theory of absorption and dispersion of light in an atomic vapour near a resonance line is inadequate. This is manifest in the sub-Doppler structure appearing in selective reflection spectra. A modified theory is summarized which explains these spectra by taking into account collisions of atoms with the solid wall of the cell containing the vapour.

The effect of the van der Waals interaction of cesium atoms with the sapphire windows of a nanocell was experimentally investigated using the selective reflection process. The distance L between the windows varied in the range of 50–2000 nm and the nanocell was filled with the vapors of cesium atoms. For the Cs atoms (the transition 6S1/2 → 6P1/2), the C3 coefficient of the van der Waals interaction with the sapphire windows of the nanocell is measured. It is shown that it is possible to determine the magnetic fields with the spatial resolution of 70 nm using the selective reflection spectrum and, consequently, both the homogeneous and highly gradient magnetic fields can be measured.

We theoretically and experimentally investigate hyperfine dipole-dipole broadening in the selective reflection (SR) spectroscopy at the gas-solid interface with the atomic density of 1014–1015 cm−3. The two-level SR theory considering pump beam and dipole-dipole interaction between excited-state atom and ground-state atom is presented. The numerical simulation of the SR spectrum is in agreement with experimental results. The reduction of spectral width is observed by introducing a pump beam which is an effective technique to improve the resolution of spectroscopy. We analyze the dependence of dipole-dipole broadening on atomic density and pump beam power. This study is helpful for the description of the SR spectroscopy at the gas-solid interface where the Doppler broadening is comparable with dipole-dipole broadening.

This paper studies the narrow spectral feature appearing in a four-level system coupled by two strong coherent fields and probed by a weak laser field. The linewidth is examined as a function of the Rabi frequencies of coupling fields, and the result is explained by using the dressed-state formalism.

In this paper we study the coherent transient property of a &Lambda;-three-level system (&Omega;_<i>d</i> = 0) and a quasi- &Lambda; -four-level system (&Omega;_<i>d</i>&gt;0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In &Lambda; -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9_&Gamma;0 (_&Gamma;0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2_&Gamma;0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5_&Gamma;0 and 6.1_&Gamma;0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

A theory of selective reflection (SR) of a light beam from the interface of a dielectric medium and a dense atomic vapor is presented. Following another earlier work on this subject [J. Guo et al., Opt. Commun. 110, 732 (1994)], we calculate the atomic density matrix and the transmitted field in the vapor self-consistently. We extend our previous theory to include an attractive atom-dielectric wall interaction and multiple atomic transitions. We examine the limits at which the conventional SR theories, which are based on the assumption of a plane-wave field in the vapor, start to fail. It is shown that at or above vapor densities of order ${10}^{17}$/${\mathrm{cm}}^{3}$, the frequency shifts of the SR line shape due to the local-field correction (Lorentz-Lorenz shift), the atom-wall interaction, and the nonexponential attenuation of the field in the vapor can have comparable orders of magnitude, and the proper determination of all these effects is essential for calculating the correct SR signals. A comparison of the theoretical SR spectra with an experimental result for a Rb vapor with a density of order ${10}^{17}$/${\mathrm{cm}}^{3}$ is also presented. \textcopyright{} 1996 The American Physical Society.

Dual-frequency-addressable photochromic cholesteric mixture with photo- and electro-switchable optical properties

Selective reflection spectra have been studied for cholesteric matrices doped with certain steroids of vitamin D group, and substantial effect of the dopants upon the helical pitch was noted. Under UV irradiation, shifts of selective reflection peaks were observed. It is argued that the effect studied can be used for monitoring of vitamin D formation reactions induced by UV irradiation, thus being a base of bioequivalent UV dosimetry.

On an example of the D2-line of the Rb atoms the work of the frequency reference of atomic transitions is demonstrated, based on the application of the spectrum of a selective reflectance (SR) from the boundary of atom vapors with the use of nano-cell (NC) with the thickness L ~ λ/2, where λ is the laser wavelength equal to 780 nm. When changing the thickness of the nano-cell near the thickness L ~ λ/2, we observe the inversion of sign of the SR slope profile which is positive when L λ/2. In the case when the incidence angle of the laser beam on the surface of the nano-cell is close to the normal, in real-time it is possible to form the derivative of the SR which represents a resonance peak with ~35 MHz spectral linewidth and located at the atomic transition. The phenomenon of oscillation of the sign of slope while changing the nano-cell thickness from L ~ λ/2 up to L ~ 3/2λ is demonstrated. The practical application of the SR is noted.

Preparation, structure and optical properties of thermochromic liquid crystal compounds containing (−)-menthyl with selective reflection

Fluorescence spectra of atomic vapours may contain sub-Doppler structure due to the transient behaviour of the light-induced polarization of atoms which have just collided at the wall of the cell containing the vapour. This structure arises in spectra measured in reflection and in emission produced by atoms within a wavelength distance from the entrance window of the cell. Excitation spectra of transmitted light and laterally scattered light are not affected by the atom–wall collisions. Absorption and dispersion of light in an atomic vapour is conventionally described by a complex-valued and frequency-dependent index of refraction. In the presence of atom–wall collisions this theoretical description fails. This report gives an account of how the theory may be modified to include atom–wall collisions; it is assumed that the induced polarization of an atom is lost in such collisions. The modified theory qualitatively describes the experimental results. We review the conventional theory, the modified theory and the experiments featuring sub-Doppler structure related to the transient polarization behaviour.

A set of measures and means to control the electromagnetic situation of the environment in the territories of urban development, in buildings and individual premises has been substantiated and developed. The simulation tools show the ability to rationalize the parameters of overhead lines with voltages of 220 kV and below, which will reduce the electromagnetic load in the territories. Modeling the propagation of fields from underground high-voltage lines has established that the values of magnetic fields compared to overhead lines are lower up to 30 times. Models of propagation of electromagnetic fields of very high and ultrahigh frequency were built. Sources of electromagnetic fields of non-production origin in industrial buildings have been investigated. Uncompensated currents in power networks with nonlinear electric consumers generate magnetic fields by induction of 0.35−1.20 μT, which exceeds the maximum permissible levels of operation of computer equipment. Leakage currents on grounded metal structures generate magnetic fields with 1.52−6.75 μT. Simulation of the propagation of electric and magnetic fields of components of personal computers of controlled ranges according to the MPRII standard was carried out. Models of propagation of the magnetic field of industrial frequency around electric motors and generators with their cross sections were built. On the basis of such models, design schemes for placing equipment in production areas are selected or places of safe stay and movement of personnel are selected. The expediency of using shielding to reduce field levels to safe values due to coating surfaces with liquid protective mixtures was shown. Metal-containing composition based on water-dispersion paint makes it possible to reduce the level of magnetic field of industrial frequency by 2.5−2.6 times, electric field by 1.6−1.7 times, electromagnetic field of industrial frequency – by 1.2−1.3 times.

Frequency Selective Surface (FSS) is a specialized structure used in the field of electromagnetic waves and radio frequency (RF) engineering. It is designed to exhibit selective transmission or reflection properties based on the frequency of the incident electromagnetic waves. This article describes the design, construction, and analysis of a textile-based band-stop frequency selective surface for use in the highly EM-polluted GSM, Wi-Fi, LTE, and WiMAX bands. A full-wave EM solver called CST Microwave Studio was used to develop and simulate the unit cell of the proposed FSS at the relevant frequency. In this study, embroidered and screen-printed textile based FSSs were designed. According to the results of this study, it was demonstrated that both embroidery and screen printing FSSs exhibit resonance at a frequency of 3.5 GHz. The screen printing method yielded the best results in terms of resonance frequency sensitivity, while the embroidery method showed a resonance frequency shift. It was observed that the stitch directions and density are important parameters in the embroidery method. Gaps between the embroidery paths in the production of embroidered FSSs resulted in differences from simulations due to the disruption of the structural integrity of the unit cell. Consequently, textile-based FSSs offer advantages over traditional FSSs. This study highlights the potential of textile FSSs as an effective means of reducing electromagnetic pollution, and suggests that further improvements in the design and production processes of textile FSSs can be made.

We investigate the dipole—dipole broadened selective reflection spectrum with the Cs atomic density of 1014−1015 cm−3. The dipole—dipole broadening is reduced and the hyperfine splitting is well resolved when the ground state atoms are excited by a detuned pump beam. The dependences of dipole—dipole broadening of Cs atoms in the 6S1/2(F = 3) → 6P3/2(F′ = 4) hyperfine transition line on atomic density and the excitation factor are studied. It is found that the reduction of the dipole—dipole broadening is dependent on the pump beam power and is independent of the atomic density in this density range. These results are useful for understanding of the dynamical process in this range of atomic density.

A selective reflecting film with a temperature-dependent pitch length