Jones matrix formalism for quasioptical EPR

The Jones matrix formalism that has been used to analyze quasioptical millimeter-wave circuits is extended for specific application to high-frequency electron paramagnetic resonance (EPR). A survey of general expressions for Jones matrices of elements commonly used in quasioptical EPR spectrometers is given. The Jones matrix representations of quasioptical transmission and reflection cavities are derived, and their relationship to the equivalent circuit and transmission line representations used for conventional EPR cavities is demonstrated. The formalism is applied to selected quasioptical EPR spectrometer designs and experimental tests of the formalism are presented for two configurations of a quasioptical spectrometer operating at 220 GHz.     

High-field/high-frequency EPR spectrometer operating in pulsed and continuous-wave mode at 180 GHz

A novel electron paramagnetic resonance (EPR) spectrometer is reported, which has been developed to allow pulsed EPR experiments with high sensitivity and time resolution at a microwave (MW) frequency of 180 GHz (G-band) and wavelengths of approximately 1.6 mm. This corresponds to a magnetic field of about 6.4 T forg ≈ 2 signals. The “hybrid” system architecture combines components of quasioptical as well as conventional MW techniques, making it possible to achieve excellent spectrometer performance with respect to sensitivity and time resolution. Quasioptical MW components have been used to design an MW circulator allowing high sensitivity and low bias operation in the reflection mode. A miniaturized, closed-type cylindrical cavity provides a high sample filling factor and an adequate MW field strength (B₁) enhancement and thus permits reasonably short MW pulses (60 ns for a π/2 pulse) even with a moderate MW input power (15 mW at the cavity). Commercial quartz capillaries (up to 0.5 mm internal diameter) can be used as sample holders for a broad range of applications.     

A Quasioptical System of the Dual Channel SIS Receiver for Trao Telescope

A quasioptical system of 100/150GHz band for dual channel receiver is developed for the simultaneous observation for both bands. The frequency independent Gaussian beam matching is applied to design the quasioptical system for wide band operation. A beam measurement system is constructed to measure the quasioptical system and to align its components. The beam from Cassegrain focus is divided into two polarizations by the beam splitter and then fed to corrugated feed horns of their bands through their quasioptical system. The intensity distributions near the Cassegrain focus and the variations of the beam widths along the propagation are measured in the laboratory. The performances of the developed quasioptical system are evaluated by comparing the measured results with theoretical calculations. The dual channel receiver with this quasioptical system is installed in the 14m telescope. The relative pointing offset between two bands is 3. We have successfully observed the various sources with both bands using this receiver since October 1998.     

Angular variation of electron paramagnetic resonance spectrum: simulation of a polycrystalline EPR spectrum

A procedure based on homotopy, involving a quick calculation of EPR line positions for various orientations of the external magnetic field by the method of least-squares fitting and Taylor-series expansion, using a known line position at an infinitesimally close orientation of the external magnetic field as the initial value, by using the eigenvectors and eigenvalues of the spin-Hamiltonian matrix in single crystals, has been exploited to simulate a polycrystalline EPR spectrum. This requires rigorous calculations of intensities of resonant lines, along with their positions. Specifically, details are given of the numerical techniques involving time-efficient matrix diagonalization to obtain the eigenvalues and eigenvectors required to calculate positions and intensities of EPR lines by the method of least-squares fitting. Finally, the procedure of how to simulate a polycrystalline EPR spectrum is outlined, the required steps are listed, and illustrative examples are given.     

Ohmic effects in quasioptical resonators

Several properties of the Fabry-Perot-type open resonator used in the quasioptical gyrotron (QOG) and the quasioptical induced resonance electron cyclotron (IREC) maser are derived. The electric fields of the normal modes are given for the general case of the resonator axis tilted with respect to the direction perpendicular to the electron beam axis. The ohmic quality factor and the power dissipated in the mirrors are derived, as is the energy stored in the resonator. The time dependence of the mirror heating, relevant for pulsed experiments, is also derived. The formulae are applied to an example of current relevance, the quasioptical IREC maser resonator.     

On the quasioptical approximation in dissipative media with spatial dispersion

A new form of the quasioptical equation is proposed to describe the propagation of an electromagnetic wave beam in a stationary smoothly inhomogeneous medium with spatial dispersion and dissipation. The proposed approach guarantees the positive definiteness of the absorbed power in the locally dissipative medium, which is a nontrivial property for inhomogeneous media with spatial dispersion. An efficient numerical scheme is constructed to solve the derived quasioptical equation.     

镱掺杂钼酸铅的光谱和EPR谱的理论研究

该文表达了一个研究Yb³⁺掺杂PbMoO₄晶体的光谱和电子顺磁共振谱(EPR)的理论方法. 采用晶体场理论,推导了有关光谱和电子顺磁共振谱的公式. 基于这些理论公式,构建了4f¹³电子组态在D_2d晶体对称下包括Zeeman磁相互作用的14阶能量矩阵. 通过对角化这一能量矩阵,研究了Yb³⁺掺杂PbMoO₄晶体的光谱和电子顺磁共振谱. 所得的理论结果与实验值很好符合. 而且,相关的晶体场参量也在研究中确定.     

Whisker-contacted diode-multipliers as quasioptical SMMW-arrays

Starting from a SMMW-multiplier design with quasioptical output two different multiplier compounds are presented. These new multipliers consist of a quasioptical antenna array in the output circuit which acts as a tunable power combiner. The multipliers work as quadruplers with an output frequency of 600 GHz. In all constructions the pump energy is fed into the diodes by a screened waveguide network. Optimum configurations for all arrays concerning quasioptical power combining are calculated and a theoretical comparison between the different multiplying conceptions is made. Finally some characteristic measurements of the quasioptical quadruplers are illustrated.This work was proposed by Prof. Dr.-Ing. H. Brand under DFG research project Br 522/12. The author gratefully acknowledges the help of H. Froitzheim and U. Wohlrab who worked within their diploma thesis on the realization of the different multiplier arrays. Special thanks to G. Bauer, L. Höpfel, J. Popp and H. Froitzheim for machining and contacting the presented multiplier setups.     

Quasioptical ferrite switches used in radiometric systems

A quasioptical ferrite switch is proposed as an essential building block in millimeter wave systems. In this communication the configuration of the quasioptical ferrite switch is described. The performance of the switch is calculated, and its application in radiometric system is pointed out. The isolation of such device is greater than 30 dB and insertion loss less than 1.0dB over whole W band.     

Impregnation of polymers with 2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl (TEMPONE) paramagnetic probe in sub- and supercritical CO<Subscript>2</Subscript>

The spin probe method is used to study the impregnation of polycarbonate (PC) based on bisphenol A, polyethylene oxide (PEO), and crosslinked acrylamide–acrylic acid copolymer (PAA) with organic molecules in sub- and supercritical CO₂ media. Electron spin resonance (EPR) data show that, at 196 bar and 307 K, 2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl (TEMPONE) paramagnetic spin probe molecules penetrate into the PC and PEO matrices, which are, respectively, in the glassy and elastic states under normal conditions. The degree of impregnation of PAA under these conditions is negligibly small. Estimates of the local concentration of probe molecules show that, in the PEO matrix, TEMPONE is distributed much more uniformly than in the PC matrix. Analysis of the effect of temperature on the shape of the EPR spectra of the radical in the polymer matrix shows that, under the same conditions, the mobility of TEMPONE molecules in the PEO matrix is much higher than in the PC matrix. The results suggest that the spin probe method is promising for studying the characteristics of macro- and micro-processes in polymer–supercritical fluid solvent–organic molecule ternary systems.     

Range and azimuth measurements of a mm-wave coherent point source by spatial interferometry

Spatial interferometry is a technique which can be used to determine the range and bearing of objects by measuring the phasefront radiated by the object. The basic method of performing such measurements has been described previously [1]. In this paper we describe how a 3-port quasioptical circuit has been used to locate a single coherent source.     

New methodologies for computer simulation of paramagnetic resonance spectra

A new software package, SOPHE, for computer simulation of randomly oriented EPR spectra is described. A central feature of SOPHE is that all interactions associated with the electronic spins and major nuclear spins are treated equally through full matrix diagonalisation. In order to make this approach “workable”, several new methodologies have been developed, which include a novel partition scheme for partitioning the unit sphere, an interpolation scheme involving a combination of cubic spline and linear interpolations, and a segmentation method for handling multiple resonances between a given pair of energy levels. As a result, these new developments have led to a significant reduction in computational times. The SOPHE package can be used to simulate a variety of EPR spectra arising from isotropic organic radicals to complex coupled spin systems. It also incorporates the major linewidth models developed previously for the simulation of randomly oriented EPR spectra from magnetically isolated spin systems.     

Kinetic theory of high-relativistic electron cyclotron maser with anovel quasioptical cavity

Using the Laplace transformation, the kinetic theory of the high-relativistic electron cyclotron maser having a novel open-resonator-the axisymmetrical quasioptical cavity of oblique rotation at arbitrary angle, is carried out within the framework of the linearized Vlasov-Maxwell equations. The beam-wave interaction power, starting current and frequency shift have been derived and numerically calculated. The influence of rotation angle on the beam-wave interaction is also studied. A series of important conclusions obtained reveal the characteristics of this novel quasioptical electron cyclotron maser     

A New Millimeter Wave Geometric Phase Demonstration

In this paper we compare two ways of achieving geometrical phase changes in millimeter-wave systems. The first involves the conversion between linear and circular polarizations in a waveguide; the second the conversion between Hermite-Gaussian and Laguerre-Gaussian modes in a quasioptical arrangement. The two ways are demonstrated using a minimum number of specialized waveguide and quasioptical components.     

Quasioptical design for an EPR spectrometer based on a horizontal-bore superconducting solenoid

We describe a novel high-frequency electron paramagnetic resonance (HF-EPR) spectrometer design based on a horizontal-bore superconducting solenoid. Designs for components of a quasioptical HF-EPR spectrometer operating with a horizontal-bore 7.85 T solenoid are discussed. A rigid concentric tube construction permits precise placement and control of the optical elements in the magnet bore. A mechanically coupled, sliding optical table bearing the quasioptical bridge is another essential feature of the design. The horizontal configuration greatly improves optical alignment as well as physical access to the sample area compared to existing vertical-bore instruments. As a result, the minimum spin concentration that is detectable with an inexpensive room-temperature diode is comparable to the lowest values reported for aqueous samples in vertical-bore magnets using high-sensitivity detectors.     

Low frequency characteristics of a quasioptical Schottky diode detector part II: Experimental results

A detailed experimental study of the low frequency (video) response of a quasioptical Schottky diode detector over the microwave and FIR wavelength range is presented. An optimization of the responsivity versus the bias current is proposed and a generalized curve of the saturation power versus the FIR wavelength is given. This curve defines for any antenna point-contact Schottky diode detector, suitable for FIR detection, the power range for a linear detector response. A simple method is also described to calculate the coupling efficiency of the laser radiation into the antenna reception pattern.     

Influence of perturbations in a magnetoplasma on the propagation of quasioptical wave beams

We analyzed features of the influence of perturbations in an anisotropic medium on the propagation of quasioptical wave beams. The solutions of the quasioptical equation in the nonaberrational approximation are found, which describe the evolution of the wave-beam width. It is shown that the influence of perturbations in an anisotropic medium differs qualitatively from the influence of the perturbations in an isotropic medium. Examples are presented of numerical calculations of the wave beam profiles in model media corresponding to the cases of density and magnetic field perturbations in the magnetoplasma confined in toroidal devices (tokamaks and stellarators).     

Broadband IF matching for quasioptical mixers

Everyone recognizes the need to drive symmetric quasioptical antennas in a symmetric way to maintain clean antenna patterns; in this note we report on the advantages of bringing out the IF in a symmetric (balanced) way as well. The main difference in IF circuits between waveguide and open structure mixers is that the quasioptical mixers are usually also open at IF wavelengths, so IF currents can flow on the outside of the mixer mounting structures. We measured these surface currents and their associated resonances on a scale model of our mixer block for a 690 GHz SIS mixer. Bringing the IF off the mixer with a balanced circuit solves the surface current problems, yielding a broad bandwidth with predictable impedances. We successfully tested an octave bandwidth IF matching circuit for open structure mixers that incorporates a commercial 180° hybrid at cryogenic temperatures. We also found that surface currents are not significant for corner cube mixers because they generate their own balancing currents.     

Investigations of the optical and EPR spectra for (NiX6) (X=Cl, Br, I) clusters

In this paper, the formulae of optical spectral levels and electron paramagnetic resonance (EPR) spectra in trigonal symmetry of 3d⁸ ions are established on the basis of strong field mechanism and a two spin-coupling (SO) parameters model. Unlike the classical crystal-field approach which has only taken the SO coupling of the central metal ions into account, the contribution of the SO coupling of the ligand ions to the optical and EPR spectra has been included in these formulae. When the optical and EPR spectra of the strong covalent crystals are calculated, the reasonable results can be obtained if the two SO parameters model has been put into action. As an application, the optical and EPR spectra of the (NiX₆)⁴⁻ clusters in CsMgX₃:Ni²⁺ (X=Cl, Br, I) crystals have been studied by the complete diagonalization (of energy matrix) method (CDM). The calculated results agree well with experimental findings. From the investigations, a more valid method to calculate the optical and EPR spectra for 3d⁸ ions clusters is provided.     

Biochemical EPR imaging of skin

EPR Imaging (EPRI) of spin labels is a powerful method for investigating skin and can give information about biochemical processes which are involved in numerous skin diseases. Furthermore it enables the non invasive investigation of the liberation, penetration and distribution of spin labelled drugs. The basis of these measurements is spectral spatial EPR imaging employing modulated field gradients and simultaneous field scans (MOSS). A skin region (?=6 mm) was treated with a 10 μl spin label solution (1 mM). EPR spectra of 128 points were recorded in 128 spatial planes resulting in a 128×128 image matrix. A spatial resolution of better than 10 μm can be obtained for a spectral line width of 0.1 mT and a gradient of 4 Tm^?1.In vivo imaging on mammalian skin can be performed by employing surface coils at S-band frequencies, 3 GHz.