Noise Behaviour of a THz Superconducting Hot-Electron Bolometer Mixer

A quasi-optical superconducting NbN hot-electron bolometer （HEB） mixer is measured in the frequency range of 0.5-2.5 THz for understanding of the frequency dependence of noise temperature of THz coherent detectors. It has been found that noise temperature increasing with frequency is mainly due to the coupling loss between the quasioptical planar antenna and the superconducting HEB bridge when taking account of non-uniform distribution of high-frequency current. With the coupling loss corrected, the superconducting HEB mixer demonstrates a noise temperature nearly independent of frequency.     

Ultra-high efficiency multilayer blazed gratings through deposition kinetic control

Diffraction efficiency of multilayer-coated blazed gratings (MBG) strongly depends on the perfection of the sawtooth-shaped layers in the overall composite structure. Growth of multilayers on sawtooth substrates should be carefully optimized to reduce groove profile distortion and, at the same time, to avoid significant roughening of multilayer interfaces. In this work, we report on a way to optimize growth of sputter-deposited Mo/Si multilayers on sawtooth substrates through variation of the sputtering gas pressure. We believe a new record for diffraction efficiency of 44% was achieved for an optimized MBG with groove density of 5250 lines/mm at the wavelength of 13.1 nm.     

Luminescence spectra of Ho3+ in distorted parity-breaking HoF63− octahedra

Low temperature luminescence spectrum of holmium ions in monoclinic Rb₂KHoF₆ crystal was found to be well analyzable by the comparison with earlier studied cubic Cs₂NaHoF₆. The manifestation of the local symmetry influence on the strength of individual lines is found to be distinctive. In the absence of structural data, the local symmetry of holmium in Rb₂KHoF₆ is proved to be a non-centrosymmetric one. The concentration quenching of holmium luminescence in Rb₂KHoF₆ is found to be rather modest.     

Potassium and ammonium dihydrogen phosphates activated with thallium: Growth and luminescence and scintillation properties

The conditions for the growth of potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) crystals with concentrations of the thallium activator in the initial solution of 0.01, 0.1, and 1.0 wt % are investigated. It is shown that the character of incorporation and distribution of thallium in the KDP and ADP lattices is limited, apparently, by the difference in the ionic radii of K⁺, NH ₄ ⁺ , and Tl⁺ cations and the charge state of prismatic {100} and pyramidal {101} growth planes. Doping of KDP and ADP with thallium (to 0.1 and 1.0 wt %, respectively) does not deteriorate the structural quality of these crystals. The dependence of the lattice parameters a and c on the thallium impurity concentration is investigated. The absorption bands of thallium in the KDP:Tl⁺ and ADP:Tl⁺ crystals peak at 218 and 215 nm, respectively, while the photoluminescence band peaks at 280 nm for both types of crystals. The relative light yield upon excitation of scintillations by α particles (Pu²³⁹) and β particles (Bi²⁰⁷) is measured.     

A spectrum analyzer for the millimeter-wavelength range and the results of an investigation of ozone of the upper atmosphere

Radiophysics and Quantum Electronics -     

On the Poisson envelope of a Lie algebra. “Noncommutative” moment space

Moscow State University; e-mail: theodore@mech.math.msu.su, theodore@nw.math.msu.su. Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 29, No. 3, pp. 61–64, July–September, 1995.     

Experimental investigation of the behavior of the specific heat in finite systems in the vicinity of the critical mixing point

The specific heat of a 2,6-lutidine-water mixture is measured in the vicinity of the lower critical mixing point in the bulk and in porous media. The results of the measurements are interpreted by finite-size scaling. In particular, a universal function of the ratio t/t* [t is the dimensionless deviation of the temperature from the specific-heat maximum T _m (L), and t* is the characteristic dimensionless temperature, which depends on the pore size] describing the behavior of the specific heat in the vicinity of the critical point in porous media with different pore sizes is obtained. The results obtained are consistent with the predictions of finite-size scaling and with the data from a numerical calculation of the specific heat of the finite three-dimensional Ising model. Zh. éksp. Teor. Fiz. 113, 1071–1080 (March 1998)