Theory of absorption and amplification spectra of a weak electromagnetic field by two-level quantum systems

A theory is developed of the absorption and amplification spectra of a weak (probe) electromagnetic field (EMF) by open two-level quantum systems in a strong quasiresonant EMF, assuming separability of the triplet spectrum components. The theory describes the intensity and the form of the spectral lines for arbitrary intensities and detunings of the strong EMF, and also the dependence of the parameters of the adiabatic relaxation on the frequency of the weak EMF. The influence of nonlinear dynamic effects (NDE) due to the dependence of the relaxation on the EMF parameters on the shape of the spectral lines is investigated. It is shown, in particular, that under certain conditions the NDE can lead to a nonlinear dynamic transformation of the dispersion of the sideband dispersion lines into Lorentzian lines and to a considerable increase of the absorption in the central region of the spectrum. Particular attention is paid to an investigation of the NDE on the characteristics of the central component of the spectrum. Methods and results of an investigation of the spectra in a basis of unperturbed wave functions in in a basis of dressed states are compared.Radiophysics Division, Lebedev Physics Institute. Translated from Preprint No. 117 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1990.     

Investigation of preheating of laser thermonuclear targets

The preheating level of the thermonuclear fuel and of the gas-compressing shell is the main criterion of the target-compression efficiency in experiments on laserdriven thermonuclear fusion. This paper contains the result of investigations of electronic, radiative, and impact preheating in experiments on compression and heating of hlgh-aspect shell targets in the Del'fin-l laser-derived thermonuclear facility. A procedure, based on analysis of the epithermal emission of the plasma, is considered for measuring the target preheating by fast electrons. The radiative and impact preheating of compressing shells in DD gas are estimated. The results of the investigation demonstrate the high degree of adiabaticity of the compression of the thermonuclear fuel in experiments with the Del'fin-l facility.Nuclear Plasma Laboratory of the Lebedev Physics Institute. Translated from Preprint No. 3, Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1990.     

Photoemission study of the electronic structure of Mn in Ag

The electronic structure of the (001) surfaces of Ag and two Ag–Mn alloys (5 and 10 at.% Mn) was studied using angle-resolved photoelectron spectroscopy with unpolarised HeI, NeI and ArI radiations. Compared to pure Ag, the alloy spectra are found to be broadened and the main features slightly (0.1 eV) shifted to higher binding energy as a result of adding Mn into Ag. In addition, there is an increase in intensity between Fermi level and top of the Ag 4d-band and significant changes in thed-band region. However, a well-defined Mn spin-up feature clearly separated from the top of Ag 4d-band is not seen in the alloy photoemission spectra. It is suggested that this is due to the strong hybridisation between the Mnd-states and Agd- andsp-states. Our results do not support the virtual bound state model for Mn in Ag for concentration range5 at.% Mn.     

Electronic structure and Fermi surface of Bi2Sr2CaCu2O8

Applying angle-resolved photoemission spectroscopy of high angular and energy resolution we have measured the electronic structure of single crystals of Bi₂Sr₂CaCu₂O₈ near the Fermi energy. Along the high symmetry direction X a band is observed to disperse upwards and to cross the Fermi level, whose unoccupied part constitutes the hole-like carriers responsible for the superconductivity. From spectra along the M direction we find evidence for an electron pocket around the M point. The measured band widths appear to be drastically reduced compared with band structure calculations indicating strong electronic correlation effects. From the observation of Fermi-Dirac-like cut-offs in the spectra due to band crossings through the Fermi level we can confirm the existence and, in particular, the shape of the Fermi surface as calculated by band structure calculations.     

Dependence of “Reststrahlen” bands in far-infrared reflectivity on configuration of GaAs/AlAs multiple quantum well heterostructures

Far infrared reflectivity measurements are performed on a series of GaAs/AlAs multiple quantum well (MQW) heterostructures with systematically varied thicknesses of the constituent layers. In addition to the artificial anisotropy we observe two distinct bulk-like Reststrahlen regions. The widths of the GaAs-like and the AlAs-like Reststrahlen bands strongly depend on the relative thicknesses of the constituent layers of the MQW heterostructures, in excellent agreement with the predictions of the effective-medium theory.Prof. Aldo Cingolani passed away just before the publication of this article. We would like to dedicate this paper to his memory     

Laser evaporation as a source of small free radicals

It is shown that laser evaporation of a solid target followed by adiabatic expansion can be used to produce cold beams of neutral small open shell molecules. LIF is applied to detect CuH (X ¹), CH (X ²), SiH (X ²), CuO (X ²), and FeO (X ⁵). A production of 10^9±1 molecules/sr in a single pulse is obtained for SiH. For a copper target, the optical emission of the jet plume is discussed.     

Quantum field-theory models on fractal spacetime

Continuing the analysis of a previous paper, the present work applies rigorous renormalization group methods to the hierarchical models to establish the existence of field theories with non-Gaussian ultraviolet renormalization group fixed points in 4- dimensions.     

Analytic extrapolation inL ∞-norm: An alternative approach to “QCD Sum Rules”

In view of physical applications (especially to QCD Sum Rules), the following problem, pertaining to analytic extrapolation techniques, is studied. We are considering amplitudes, which are (real) analytic functions in the complex plane cut along=[s ₀, ). A modelF ₀(s) of the amplitude is given through the values ofF ₀(s) on some interval=[s ₂,s ₁] (withs ₁<s ₀) and the values of its discontinuity on. These values are approximate, and are supplemented by prescribed error channels, measured inL -norm (both on and). Investigating the compatibility between these data leads to an extremum problem which is solved up to a point where numerical methods can be implemented.Unité Associée au CNRS n^o040768