A Multibeam SIS Mixer Module for a Focal Plane Array Receiver

The integration of many receiver units into a receiver array is a common method of improvement of imaging systems. This approach, well known in the mm band for Schottky mixer arrays, has not so far been developed for Superconductor - Insulator - Superconductor (SIS) junction mixers, which give the best sensitivity in the short mm wave range and in the submm range.We demonstrate for the first time a practical low noise multibeam receiver module using SIS mixer technology. The basis for the integration of several SIS mixers with a common local oscillator source is given by the saturation of the SIS receiver noise dependence upon local oscillator power. The module comprises three identical SIS mixers integrated with a common local oscillator, coupled through a three branch waveguide directional coupler. The multibeam module has been developed for a focal plane array receiver of the 30 meter radio telescope of the Institut de Radioastronomie Millimétrique (IRAM).     

A Low Noise NbTiN-Based 850 GHz SIS Receiver for the Caltech Submillimeter Observatory

We have developed a niobium titanium nitride (NbTiN) based superconductor-insulator-superconductor (SIS) receiver to cover the 350 micron atmospheric window. This frequency band lies entirely above the energy gap of niobium (700 GHz), a commonly used SIS superconductor. The instrument uses an open structure twin-slot SIS mixer that consists of two Nb/AlN/NbTiN tunnel junctions, NbTiN thin-film microstrip tuning elements, and a NbTiN ground plane. The optical configuration is very similar to the 850 GHz waveguide receiver that was installed at the Caltech Submillimeter Observatory (CSO) in 1997. To minimize front-end loss, we employed reflecting optics and a cooled beamsplitter at 4 K. The instrument has an uncorrected receiver noise temperature of 205K DSB at 800 GHz and 410K DSB at 900 GHz. The degradation in receiver sensitivity with frequency is primarily due to an increase in the mixer conversion loss, which is attributed to the mismatch between the SIS junction and the twin-slot antenna impedance. The overall system performance has been confirmed through its use at the telescope to detect a wealth of new spectroscopic lines.     

A Tuning Circuit with Two Half-Wave Distributed Junctions for All-NbN SIS Mixers

A novel broadband tuning circuit composed of two low-current-density half-wave NbN/MgO/NbN tunnel junctions connected by a half-wave NbN/MgO/NbN microstrip line has been successfully tested in a quasi-optical mixer at frequencies above 700 GHz. The circuit had a designed center frequency of 870 GHz, was integrated in a center-fed twin-slot antenna, and was fed via a quarter-wave impedance transformer. Heterodyne measurments showed double-side-band receiver noise temperatures equivalent to 6-9 quanta from 675 to 810 GHz for a mixer with a current density of 6.7 kA/cm². The RF bandwidth was broader than that of a conventional mixer using a full-wave junction with the same current density.     

Design and Implementation of a Millimeter Wave Monolithic Integrated Mixer

This paper discusses design and implementation of a millimeterwave monolithic integrated balanced mixer, the measured performance compared with the predicted one is also reported. By designing this MMIC mixer, various mathematical methods are used, in which the Method of Conversion Matrix has been extended by the author to meet the requirement of inter-modulation analysis. The mixer is realized in a 2×3mm ² GaAs chip, working in Ka band with bandwidth of 5GHz with a noise figure less than 10 dB.     

Magnetooptical properties and FMR in granular nanocomposites (Co84Nb14Ta2) x (SiO2)100? x

For nanodimensional magnetically inhomogeneous amorphous granular films of the system (Co₈₄Nb₁₄Ta₂) _x (SiO₂)_100−x , 30≤x≤60 at.% the concentration dependences of the magnetooptical Kerr effect (MOKE) spectra and FMR have been investigated. The observed changes in the MOKE and FMR spectra are associated with transformations of microstructure and topology of the nanocomposites. For the compositions within the percolation region the transversal Kerr effect increases by an order of magnitude.     

Electrical conductivity studies of mixed phthalocyanine thin films

Thin films of mixed of Copper Phthalocyanine (CuPc) and Nickel Phthalocyanine (NiPc) are deposited onto a pure glass substrate by a simultaneous thermal evaporation technique at room temperature. The material D.C. electrical conductivity of films at room temperature and also films annealed at 523 K has been investigated. The optical absorption and band gaps of the films are also measured. The results show that the electrical resistance is lower for the mixed films compared with the pure samples and also the optical band gap decreases for the mixed samples compared to the pure samples.     

基于λ/4相移分布反馈半导体激光器四波混频的THz波长转换特性研究

利用耦合模方程，分析了基于λ/4相移分布反馈半导体激光器四波混频的波长转换特性.数值模拟表明：增大偏置电流、减小失谐量有利于扩展转换效率及消光比的动态范围，同时恶化了频率啁啾的动态范围; 受激射效应影响，消光比及频率啁啾在弛豫振荡频率处达到极大值.通过合理选择系统参量，可以获得较理想的波长转换效果.该方案无需抽运光输入，可实现高速、宽带波长转换，在光通信系统中有一定的应用前景. 关键词： λ/4相移分布反馈半导体激光器')" href="#">λ/4相移分布反馈半导体激光器 四波混频 波长转换     

Phosphorescence of thin benzophenone films

Institute of Physics, National Academy of Sciences of Ukraine, 46, Prospekt Nauki, Kiev 252650 Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 117–121, May–June, 1995.     

Development of a Resonator with Automatic Tuning and Coupling Capability to Minimize Sample Motion Noise for in Vivo EPR Spectroscopy

EPR spectroscopy has been applied to measure free radicals in vivo; however, respiratory, cardiac, and other movements of living animals are a major source of noise and spectral distortion. Sample motions result in changes in resonator frequency, Q, and coupling. These instabilities limit the applications that can be performed and the quality of data that can be obtained. Therefore, it is of great importance to develop resonators with automatic tuning and automatic coupling capability. We report the development of automatic tuning and automatic coupling provisions for a 750-MHz transversely oriented electric field reentrant resonator using two electronically tunable high Q hyperabrupt varactor diodes and feedback loops. In both moving phantoms and living mice, these automatic coupling control and automatic tuning control provisions resulted in an 8- to 10-fold increase in signal-to-noise ratio.     

Magnetic field and currents in HTSC films

Magnetic field measurements above type-II superconductor films in a remanent magnetization state have been used to determine two dimensional surface current distributions. Using the Biot-Savart law for the surface current density, integral equations (of 2-D convolution type) for two components of current have been obtained. These equations have been solved by employing Tikhonov's method of generalized discrepancy, and the surface current pattern in superconductors as well as the magnetic field distribution on the film surface have been obtained. Current peculiarities related to various kinds of inhomogeneities, specific character of the film form, and a laser pulse effect have been observed. In particular, it was discovered that a laser pulse can signficantly redistribute the film currents without changing the total number of current vortices in the film.     

Traresonator formation of submicron periodic structures

To whom correspondence should be addressd.     

A simple scheme to generate χ-type four-charge entangled states in circuit QED

We propose a simple scheme to generate χ-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator (TLR). The coupling between the superconducting qubit and the TLR can be effectively controlled by properly adjusting the control parameters of the charge qubit. The experimental feasibility of our scheme is also shown.