Selective reflection from high-pressure mercury vapor

Selective regular reflection in the neighborhood of the 253.7 nm mercury resonance line was investigated in the pressure range extending up to 700 bar by applying a new technology, an internally heated autoclave with a window of synthetic sapphire. The measurements yield the maximum of spectral reflectance, which was shown to be constant up to a density of about 10¹⁸ cm⁻³, first to arise and then to fall off with increasing pressure. In this density range the impact theory of resonance broadening and the classical equations of anomalous dispersion are no longer valid and a statistical theory of multilateral dipole-dipole interactions should be developed to describe the reflection profiles.     

Selective reflection by atomic vapor: experiments and self-consistent theory

Selective reflection of laser radiation from the interface between atomic vapor and a dielectric is studied for a wide range of vapor density. A self-consistent model is developed, some analytical results are obtained, as well as a number of curves are computed that are in good agreement with experimental spectra measured in cesium and rubidium vapor cells.     

Selective reflection of a laser beam from a dilute rubidium vapor

We study the selective reflection of the laser beam from rubidium atomic vapor at the D₂ line (wavelength λ = 780 nm) at different atomic densities. We use a tunable free-running diode laser. We observed a measurable signal at a low atomic density N when the mean distance between resonance atoms reached two wavelengths. In our experiment, the dimensionless parameter N ^1/3 λ varied from 0.5 to 2.8. The reflectivity increased with density monotonically. It is interesting to perform experiments when the parameter N ^1/3 λ ≪ 1.     

Selective reflection of laser radiation from submicron layers of Rb and Cs atomic vapors: Applications in atomic spectroscopy

We studied selective reflection (SR) of laser radiation from a window of a nanocell with thickness L ~ λ_1,2/2 filled with Rb and Cs atoms, where λ₁ = 780 nm and λ₂ = 852 nm are the wavelengths resonant with the D₂ laser lines for Rb and Cs, respectively. It is demonstrated that the negative derivative of the SR signal profile for L > λ/2 changes to the positive one for L < λ/2. It is shown that the real-time formation of the SR signal profile derivative (SRD) with the spectral width 30–40 MHz and located at the atomic transition is, in particular, a convenient frequency marker of D₂ transitions in Rb and Cs. The amplitudes of SRD signals are proportional to the atomic transition probabilities. A comparison with the known saturated absorption (SA) method demonstrated a number of advantages, such as the absence of cross-over resonances in the SRD spectrum, the simplicity of realization, a low required power, etc. An SRD frequency marker also operates in the presence of the Ne buffer gas at a pressure of 6 Torr, which allowed us to determine the Ne–Rb collisional broadening, whereas the SA method is already inapplicable at buffer gas pressures above 0.1 Torr. The realization simplicity makes the SRD method a convenient tool for atomic spectroscopy. Our theoretical model well describes the SRD signal.     

Topological solitons in active optical cavities: Fundamental properties and possible applications

Fundamental properties of topological spatial solitons existing in active cavities with high (above 100) Fresnel numbers, laser and/or parametric amplification, and saturated absorber were numerically and experimentally studied. Writing and erasing of bi- and tristable laser solitons (fundamental solitons [1, 2] and vortex solitons [3]) using an external control light pulse were considered in various regions of the laser cross section. The existence of optical domain walls (separated phase domains which are in antiphase) in the form of expanding spiral waves and the localized domain soliton rotating about the Neel defect (in this connection, we called it the “Neel soliton”) in active cavities with mixed laser and parametric amplification was shown in a numerical experiment for the first time. We proposed potential possibilities of using topological solitons in optical data processing, storage, and transmission.     

Double radiooptical resonance in <Superscript>87</Superscript>Rb atomic vapor in cells with antirelaxation wall coating

The object of investigation is double radiooptic resonance in ⁸⁷Rb atomic vapor contained in a cell covered by an antirelaxation coating. The Dicke narrowing is studied in terms of the quantum-kinetic approach. It is found that optical pumping using a laser with a “wide” radiation spectrum makes it possible to improve the short-term stability of the frequency standard by an order of magnitude compared with a narrow-spectrum laser.     

Features of vapor transfer in the evaporation of liquids from capillaries in an inhomogeneous temperature field

The process of vapor transfer in conditions of linear change in temperature along the channel is considered. The excess pressure of the vapor-gas mixture above the liquid meniscus is calculated as a function of the capillary radius and temperature. Expressions are found for the vapor flux and time of evaporation. It is shown that these expressions are in good agreement with experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 65–70, May, 1984.     

传输线中脉冲信号反射波的测量和应用

将高频单脉冲信号输入同轴电缆，借助数字存储示波器记录输入、输出端的波形和相对延时，可以测量传输线的电缆长度和衰减系数，同时观察脉冲波形因色散引起的畸变．     

Quantum de Sitter algebra and some possible applications in cosmology

I summarize results recently obtained in collaboration with Amelino-Camelia, Bruno and Mandanici (preprint University of Rome “La Sapienza”, August, 2005) that concern an analysis of the path of a massless particle in a q-de Sitter space-time and an approximation scheme suitable for the corresponding analysis in a quantum FRW Universe. On the basis of some arguments in the quantum-gravity literature, the q deformation parameter is assumed to depend on both the Planck scale and the curvature, leading to results that are significantly different from those of other studies of Planck-scale effects in cosmology, where the possibility of an interplay between curvature and Planck scale was ignored. Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005.     

Difference-frequency conversion of λ =1.06 μm Nd: YAG laser radiation in two-photon dye-laser resonantly pumped Rb vapor

Conversion of ir Nd: YAG laser radiation to the visible range 420 nm has been obtained as a result of resonant four-photon difference-frequency mixing with a λ = 604 nm dye-laser radiation in the Rb vapor. Resonant enhancement of third-order nonlinearity has been achieved by two-photon resonant pumping of high-lying Rb 15d and 16d levels and also due to converted radiation frequency being close to the frequency of the allowed 5s-6p transition.     

Interference wedge properties relevant to laser applications: transmission and reflection of restricted light beams

The optical properties of the interference wedge are analysed for the case of restricted laser beam illumination. By further development of Brossel's method, equations describing this case are derived and used to calculate the reflected and transmitted beam profiles for typical intracavity laser beam diameters (0.2–0.6 mm) for Gaussian and uniform intensity distributions. In particular, the experimentally observed formation of bright fringes outside the beam impact area at resonant wavelengths is explained. some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.     

Mass synchronization: occurrence and its control with possible applications to brain dynamics

Occurrence of strong or mass synchronization of a large number of neuronal populations in the brain characterizes its pathological states. In order to establish an understanding of the mechanism underlying such pathological synchronization, we present a model of coupled populations of phase oscillators representing the interacting neuronal populations. Through numerical analysis, we discuss the occurrence of mass synchronization in the model, where a source population which gets strongly synchronized drives the target populations onto mass synchronization. We hypothesize and identify a possible cause for the occurrence of such a synchronization, which is so far unknown: Pathological synchronization is caused not just because of the increase in the strength of coupling between the populations but also because of the strength of the strong synchronization of the drive population. We propose a demand controlled method to control this pathological synchronization by providing a delayed feedback where the strength and frequency of the synchronization determine the strength and the time delay of the feedback. We provide an analytical explanation for the occurrence of pathological synchronization and its control in the thermodynamic limit.     

Selective refocusing pulses in magic-angle spinning NMR: characterization and applications to multi-dimensional protein spectroscopy

Band-selective pulses are frequently used in multi-dimensional NMR in solution, but have been used relatively less often in solid-state NMR applications because of the complications imposed by magic-angle spinning. In this work, we examine the frequency profiles and the refocusing efficiency of several commonly employed selective general rotation pi pulses through experiments and numerical simulations. We demonstrate that highly efficient refocusing of transverse magnetization can be achieved, with experiments that agree well with numerical simulations. We also show that the rotational echo is shifted by a half rotor period if a selective pulse is applied over an integer number of rotor periods. Appropriately synchronizing indirect evolution periods with selective pulses ensures proper phasing of cross peaks in 2D spectra. The improved performance of selective pulses in multi-dimensional protein spectroscopy is demonstrated on the 56-residue beta1 immunoglobulin binding domain of protein G (GB1).     

Synchrotron-based multiple-beam FTIR chemical imaging of a multi-layered polymer in transmission and reflection: towards cultural heritage applications

IRENI (infrared environmental imaging) is a recently commissioned Fourier transform infrared (FTIR) chemical imaging beamline at the Synchrotron Radiation Center in Madison, WI, USA. This novel beamline extracts 320 mrad of radiation, horizontally, from one bending magnet. The optical transport separates and recombines the beam into 12 parallel collimated beams to illuminate a commercial FTIR microspectrometer (Bruker Hyperion 3000) equipped with a focal plane array detector where single pixels in the detector image a projected sample area of either 0.54×0.54 μm² or 2×2 μm², depending in the measurement geometry. The 12 beams are partially overlapped and defocused, similar to wide-field microscopy, homogeneously illuminating a relatively large sample area compared to single-beam arrangements. Both transmission and reflection geometries are used to examine a model cross section from a layered polymer material. The compromises for sample preparation and measurement strategies are discussed, and the chemical composition and spatial definition of the layers are distinguished in chemical images generated from data sets. Deconvolution methods that may allow more detailed data analysis are also discussed.