Showing papers in "International Journal of Infrared and Millimeter Waves in 1999"
TL;DR: In this article, an experimental investigation of the far-infrared properties of several nonlinear crystals using terahertz time-domain spectroscopy (THz-TDS) was reported.
Abstract: In this article we report an experimental investigation of the far-infrared properties of several nonlinear crystals, LiNbO3, LiTaO3, ZnTe and CdTe Using Terahertz Time-Domain Spectroscopy (THz-TDS) we have measured the complex frequency response, ie both index of refraction and absorption up to 3 THz (100 cm−1) for the electro-optic crystals at room temperature The single Lorentzian oscillator model is used to describe the aquired data Additional resonance features are observed, especially in the II-VI compounds
174 citations
TL;DR: In this article, a modern approach to studies of characteristics of intense helical electron beams (HEBs) for gyrotrons is presented, which consists in finding functions of electron distribution with respect to oscillatory velocities in the beam both by numerical simulation and experimentally.
Abstract: The paper presents a modern approach to studies of characteristics of intense helical electron beams (HEBs) for gyrotrons. The essence of the method consists in finding functions of electron distribution with respect to oscillatory velocities in the beam both by numerical simulation and experimentally. Experimental and calculated data for beams with different topologies were compared in different frequency ranges. Evolution of the electron oscillatory velocities distribution function as the beam current grows has been traced. Influence of the reflected electrons on beam parameters has been simulated numerically.
48 citations
TL;DR: In this article, the problem of reaching maximal sensitivity of microwave spectrometers is studied and a novel method based on the phase switching of radiation is presented. But the calculation carried out show that spectrometer realizing this method provides the best approach to the theoretical limit of sensitivity.
Abstract: We study the problem of reaching maximal sensitivity of microwave spectrometers. The comparative analysis of the spectroscopy methods is carried out. Novel method based on the phase switching of radiation is presented. The calculation carried out show that spectrometer realizing this method provides the best approach to the theoretical limit of sensitivity. Description of the phase switched and some experimental results have been given.
42 citations
TL;DR: In this paper, a complete frequency-field chart for all the AFMR modes predicted from the theory has been observed and a complete analysis of the properties of these modes is presented.
Abstract: Antiferromagnetic resonance (AFMR) measurements on a well characterized single crystal sample of MnF2 have been performed using various kinds of millimeter and submillimeter sources up to 570 GHz and a superconducting magnet up to 20 T. All the AFMR modes predicted from the theory have been observed. We report a complete frequency-field chart for these AFMR modes.
25 citations
TL;DR: In this article, experimental results on polarizers with nonrectangular grooves to be used in high power millimeter wave transmission lines for electron cyclotron heating (ECH) of fusion plasmas were presented.
Abstract: This paper presents experimental results on polarizers with nonrectangular grooves to be used in high power millimeter wave transmission lines for electron cyclotron heating (ECH) of fusion plasmas. A low-power test at a frequency of 106.4 GHz has been carried out for several polarizers with different groove depths. The polarization characteristics experimentally measured are in good agreement with numerical results in which the actual groove shape functions are taken into account. This confirms the design optimization for future polarizer. Favorable results have also been obtained in a 400 kW-level high-power test for the polarizer installed in an ECH transmission line of the Heliotron-E plasma device.
24 citations
TL;DR: In this article, the 2D periodic pattern of the electromagnetic crystal structure is implemented with circles etched in the ground plane of the microstrip line by means of a numerical milling machine.
Abstract: Recently, new promising two-dimensional (2-D) Photonic Bandgap Structures (PBG), or more properly Electromagnetic Crystal Structures, for microstrip lines have been proposed. In this paper, we analyze these structures in a manner like a Bragg reflector in optical wavelengths. Joining two of such Bragg like reflectors by means of a conventional microstrip transmission line allows one to design Bragg Resonators. The 2-D periodic pattern of the electromagnetic crystal structure is implemented with circles etched in the ground plane of the microstrip line by means of a numerical milling machine. Simulations have been performed by using HP
TM Momentum and MDS software, and in accordance with the measurements give, for the Electromagnetic Crystal Structures, new promising potential applications both in microwave and millimeter wave integrated circuits, and also in the experimentation of expensive short wavelength (including photonic) devices by using simpler and cheaper microwave down scaling.
23 citations
TL;DR: In this paper, the relationship between the phase shift, as measured by a microwave interferometer, and the plasma number density is not straightforward, as is the case in collisionless plasmas.
Abstract: Diagnosing atmospheric pressure discharges requires more sophisticated techniques than for low pressure plasmas. The plasma number density is a crucial parameter in several applications. Langmuir probe as a number density measuring technique is not applicable at high pressures because the electron mean free path is shorter than the Debye distance. Microwave interferometry appears to be an effective diagnostic technique in this case. However, because of the high collisionality of atmospheric pressure plasmas, the relationship between the phase shift, as measured by a microwave interferometer, and the plasma number density is not straightforward, as is the case in collisionless plasmas. For the special case of a uniform discharge, the plasma number density is found to depend on the square root of the phase shift.
20 citations
TL;DR: In this article, the relative observing efficiency of single sideband and double sideband (DSB) receiver systems in the presence of atmospheric and antenna losses was discussed. And the authors also developed some analytic expressions for SSB and DSB observing.
Abstract: This paper discusses the relative observing efficiency of single sideband (SSB) and double sideband (DSB) receiver systems in the presence of atmospheric and antenna losses. We use the antenna parameters currently specified for the NRAO Millimeter Array (MMA) antennas and atmospheric opacities appropriate to an excellent site such as Mauna Kea or the MMA site on the Llano de Chajnantor in northern Chile. We find that for spectroscopic observations in one sideband, SSB measurements are always more efficient. Below 400 GHz, the observing time advantage is 50-80%. Above 400 GHz, the advantage is over a factor of 2, indicating that SSB-mode observing is more efficient even if spectral lines of interest are present in both sidebands. We discuss the goals for the ultimate, practical receiver performance that one should aim for in the presence of atmospheric and telescope losses. Observing efficiencies are displayed as a function of frequency using atmospheric opacity models as input. We also develop some analytic expressions for SSB and DSB observing.
19 citations
TL;DR: Using a scattering matrix formalism, the relative TE/TM eigenmode contents of hybrid modes in oversized corrugated rectangular waveguides have been calculated in this article, where the influences of slot depth and corrugation period on the eigen mode mixture have been examined.
Abstract: Using a scattering matrix formalism the relative TE/TM eigenmode contents of hybrid modes in oversized corrugated rectangular waveguides has been calculated. The influences of slot depth and corrugation period on the eigenmode mixture have been examined.
18 citations
TL;DR: In this paper, a compact continuously tunable general purpose radiation source was developed for the sub-millimeterwave band (180 - 1500 GHz) by using Backward Wave Oscillator (BWO) of the range 180 - 260 GHz or 250 - 375 GHz fixed in a small permanent magnet.
Abstract: This paper is concerned with development of compact continuously tunable over all the submillimeterwave band (180 – 1500GHz) general purpose radiation source. The source consists of Backward Wave Oscillator (BWO) of the range 180 – 260 GHz or 250 – 375 GHz fixed in a small permanent magnet, followed by specially developed broadband frequency multiplier producing second, third, fourth, fifth and sixth harmonics of BWO fundamental frequency. The conversion losses for all the harmonics are measured. The estimations of output power of the source depending on frequency band are given. The examples of applications are presented in phase lock-in scanning BWO regime.
18 citations
TL;DR: In this paper, a large aperture free-standing metal wire grid was constructed for the lower end of the millimeter wave spectral region and the co-polarized and crosspolarised components of transmitted power were measured at 45° oblique incidence.
Abstract: Construction of large aperture free-standing metal wire grids is demonstrated for the lower end of the millimeter wave spectral region. For the constructed two grids the co-polarized and cross-polarized components of transmitted power were measured at 45° oblique incidence. The measurements were performed as a function of wire orientation angle and in more detail at selected angles. The results are in good agreement with the theoretical results presented in the literature. In order to save time and costs the construction apparatus was simplified from those reported previously by other authors. It was shown that for this frequency range the grid characteristics are not degraded when such an apparatus is applied. One of the constructed grids will be used in a calibration system of the Helsinki University of Technology (HUT) polarimetric radiometer.
TL;DR: In this article, a Fourier Transform Spectrometer (FTS) was designed and constructed for the study of sub-millimeter-wave mixers and optical components, which operates in the 100-3750 GHz frequency range with a resolution of up to 75 MHz (0.0025 cm^(−1)).
Abstract: We have designed and constructed a Fourier Transform Spectrometer (FTS) for the study of submillimeter-wave mixers and optical components. The FTS has a large aperture (up to 25.4 cm) and small focal ratio (as fast as f/2.5) to achieve a large throughput. It operates in the 100-3750 GHz (3.3-125 cm^(−1)) frequency range with a resolution of up to 75 MHz (0.0025 cm^(−1)). Here we discuss the design goals and provide a detailed description of the construction of the FTS. In addition, we highlight the variety of studies which have been conducted with this instrument, which include characterizing SIS mixers through both direct and heterodyne detection and measuring the properties of optical materials.
TL;DR: In this article, an automatic frequency control (AFC) for an optically pumped far infrared (FIR) ring laser applicable for high resolution THz sideband spectroscopy by mixing a fraction of the laser power and a harmonic of a phase-locked synthesizer on a planar Schottky diode was reported.
Abstract: We report an automatic frequency control (AFC) for an optically pumped far infrared (FIR) ring laser applicable for high resolution THz sideband spectroscopy by mixing a fraction of the laser power and a harmonic of a phase-locked synthesizer on a planar Schottky diode. We achieve a relative frequency accuracy of about 0.5 kHz rms at 803 GHz (15NH3) and about 1 kHz rms at 1626.6 GHz (CH 2F 2) over hours of lock time. The absolute frequency accuracy is estimated to be about 5 kHz at 1626.6 GHz.
TL;DR: In this paper, the frequency dependence of the reflectivity of a Gaussian beam from a high-power 110 GHz gyrotron was calculated and the cold test results were in good agreement with the theory.
Abstract: A novel distributed window for output radiation from a high power 110 GHz gyrotron is made of thin slats of sapphire interleaved and brazed to hollow metal vanes. We report the results of electromagnetic theory and cold test of this distributed window. We calculate the frequency dependence of the reflectivity of a Gaussian beam from the window. The theory indicates a significant frequency shift of the minimum reflectivity with temperature rise of the sapphire slab. This effect is of great importance for high power operation. In cold test, the distributed window reflectivity was measured while the window was heated. The cold test results are in good agreement with the theory.
TL;DR: In this article, the design and measurements of a Gaussian profiled horn antenna for the 11.7-12.2 GHz frequency band for the HISPASAT 1C satellite are presented.
Abstract: In this paper, the design and the measurements of a Gaussian profiled horn antenna for the 11.7-12.2 GHz frequency band for the HISPASAT 1C satellite are presented. The study shows the possibility of improving the electromagnetic and physical features of conventional horn antennas by using Gaussian techniques.
TL;DR: In this paper, the phase bunching of a gyrating electron beam under the second harmonic operation reduces the starting current for the fundamental operation and increases total output power as well as beam efficiency.
Abstract: At certain gyrotron operating conditions, mode cooperation instead of mode competition takes place between a fundamental and a second harmonic mode. This means the phase bunching of a gyrating electron beam under the second harmonic operation reduces the starting current for the fundamental operation and increases total output power as well as beam efficiency. Such mode cooperation is observed in experiments and confirmed by computer simulations for submillimeter wave Gyrotron FU II.
TL;DR: In this article, a method for determination of the mode content of a spurious microwave radiation of the gyrotron with a straight circular axisymmetrical output is discussed, and the experimental results on the determination of mode content at the output of the coaxial gyroron, operating on the mode TE ∼ 14.8 MHz, are in good agreement with the theoretical calculations.
Abstract: The method for determination of the mode content of a spurious microwave radiation of the gyrotron with a straight circular axisymmetrical output is discussed. As demonstrated, in the test task accuracy of this method is several percents. The experimental results on the determination of the mode content at the output of the coaxial gyrotron, operating on the mode TE
14.8
are in a good agreement with the theoretical calculations.
TL;DR: Schottky barrier diodes have been integrated into on-chip rectangular waveguides and a method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.C.F. output in a mixer circuit.
Abstract: Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized.
TL;DR: Reflection properties of square apertures metal mesh mirrors are studied theoretically with the Finite Difference Time Domain (FDTD) method associated to Floquet Boundary Conditions in this article, where the reflector is illuminated by a normally incident plane wave and is located at an interface between two semi infinite low loss dielectric materials.
Abstract: Reflection properties of square apertures metal mesh mirrors are studied theoretically with the Finite-Difference Time-Domain (FDTD) method associated to Floquet Boundary Conditions. The reflector is illuminated by a normally incident plane wave and is located at an interface between two semi infinite low loss dielectric materials. Reflectivity and phase of the reflection coefficient are given in the non diffraction region for a wide range of square apertures, and for the four situations corresponding to an interface between free space and fused quartz.
TL;DR: In this article, the dispersion relation for the ground subband of quantized holes in a quantum well of zink-blende-like semiconductors contains an extensive section with negative effective mass (NEM).
Abstract: The dispersion relation for the ground subband of quantized holes in a quantum well (QW) of zink-blende-like semiconductors contains an extensive section with negative effective mass (NEM). Under certain biases, stationary concentration distributions of the ballistic quantized holes in p+pp+-structures hold a self-organized region where holes with NEM predominate. The existence of such region causes a global instability of the entire stationary regime and the appearance of an oscillatory regime. We describe the dependence of the oscillatory regime on material and geometric parameters of the structure and consider factors that influence the oscillation frequency. The typical frequencies for 0.1 μm-structures are in the terahertz range (1-2 THz). The ballistic NEM-diodes have been classified as short, medium and long diodes depending on their oscillatory portrait. A new high-voltage region of oscillations that was not analytically predicted in early works is revealed in the so-called medium and long diodes. The region appears side by side with the stable stationary regime at high voltages. Switching between oscillatory and stationary regimes is studied.
TL;DR: A quasioptical system of 100/150 GHz band for dual channel receiver is developed for simultaneous observation for both bands in this article, where the frequency independent Gaussian beam matching is applied to design the quasi-optical systems for wide band operation.
Abstract: 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
TL;DR: In this article, the performance of a new fast photodetector based on a W-InSb metal-insulator-semiconductor point contact diode operating at room temperature and with no bias voltage was presented.
Abstract: We present preliminary data on the performance of a new fast photodetector based on a W–InSb metal-insulator-semiconductor point contact diode operating at room temperature and with no bias voltage The device can work either as a video detector or as harmonic mixer for radiation from far–infrared (FIR) to visible In the FIR region, for wavelengths from 200 to 400 μm, the W–InSb point contact diode showed a sensitivity comparable to that of Golay cells In the visible region the device showed a video and heterodyne detection responsivity much higher with respect to standard MIM point contact diodes Owing to its ruggedness, low cost and wide band of operation, the W–InSb point contact diode may be very attractive as a general purpose optical sensor
TL;DR: In this article, the Dammann Grating (DG) is used as a binary optical component and thus straightforward to manufacture. But the results in this paper confirm DGs to be particularly suitable multiplexers for sparse arrays of finite bandwidth.
Abstract: This paper is concerned with the analysis of phase gratings as passive quasi-optical multiplexing devices. One important application of such components is in the local oscillator injection chain of heterodyne array receivers. Gaussian beam mode analysis can be applied as a powerful tool when modelling the optical performance of phase gratings in a real submillimeter system of finite throughput and bandwidth. In our experimental investigations we have concentrated on the Dammann Grating (DG) which is a binary optical component and thus straightforward to manufacture. A number of quartz gratings were fabricated and carefully tested to evaluate the practical limitations of such quasi-optical components. Because of its convenient refractive index quartz can be used to produce gratings with very low reflection losses. The results presented confirm DGs to be particularly suitable multiplexers for sparse arrays of finite bandwidth.
TL;DR: In this article, the effect of the structural eccentricity on the output power of a coaxil-cavity gyrotron oscillator was investigated by making use of a gyrokinetic description.
Abstract: The effect of the structural eccentricity on the output power of a coaxil-cavity gyrotron oscillator is investigated by making use of a gyrokinetic description. It is found that the output power will be substantially weaken by the structural eccentricity of the inner-rod axis to the outer-cavity axis. The influences of the operating magnetic field and the electron-beam energy on the output power are analysed with the consideration of the structural eccentricity.
TL;DR: In this article, the fine structure constant of ruby has been measured using an ESR spectrometer with a pulse magnetic for high fields and a gyrotron as a radiation source in a millimeter to submillimeter wave range.
Abstract: Fine structure constant of ruby has been measured using an ESR spectrometer with a pulse magnetic for high fields and a gyrotron as a radiation source in a millimeter to submillimeter wave range. The measurement was carried out at room temperature. The Zeeman energy in this frequency range is large enough compared with the fine structure constant. The higher order term in the effective spin Hamiltonian can explain the dependence of fine structure constant on the frequency. The observed fine structure constants depend on the field intensity.
TL;DR: In this paper, the authors used Fabry-Perot resonator with quality factor ≃ 600 000 and fast precision (down to one Hertz) frequency control of coherent millimeterwave radiation source to obtain 20 Hz accuracy in measurements of the width of resonance curve.
Abstract: By the use of Fabry–Perot resonator with quality factor ≃ 600 000 and fast precision (down to one Hertz) frequency control of coherent millimeterwave radiation source the 20 Hz accuracy in measurements of the width of resonance curve is obtained. This accuracy corresponds to the detection of 1.8 × 10−3 dB/km absorption in the sample filling the resonator and exceeds the before known sensitivity more than by an order of magnitude. The example of precise measurement of 60 GHz oxygen absorption band in the real atmosphere is presented. The new possibilities of application of precision resonator microwave spectroscopy to the atmospheric problems as well as to the ultra-low absorptions measurements in dielectrics and metal surfaces up to Terahertz frequencies are discussed.
TL;DR: In this paper, a Cherenkov oscillator operating simultaneously at two different wave bands (3cm and 8mm) is described, and the measured output power is 10 MW at 3cm wave band, and 1MW at 8mm wave band.
Abstract: A Cherenkov oscillator operating simultaneously at two different wave bands (3cm and 8mm) is described in this paper. Experimental results from the oscillator are reported. The measured output power is 10 MW at 3cm wave band, and 1MW at 8mm wave band. The operating modes for BWO and R-orotion are E01 and E13, respectively.
TL;DR: A multilayer perceptron neural network (MLPNN) is used to model the gap discontinuities in stripline circuits, electromagnetically developed with a set of training data produced by the full-wave finite-difference time-domain (FDTD) method.
Abstract: Gap discontinuities appear in many stripline circuits, such as the multilayer microwave monolithic ICs and the interconnect systems in high-speed digital circuits. In this paper, a multilayer perceptron neural network (MLPNN) is used to model the gap discontinuities in stripline circuits. The MLPNN is electromagnetically developed with a set of training data that are produced by the full-wave finite-difference time-domain (FDTD) method. The full-factor design of experiments is used for determining the size of the training data.
TL;DR: In this article, the authors reported the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH3OD in the range 42.6 μm to 207.2 μm.
Abstract: This work reports the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH3OD in the range 42.6 μm to 207.2 μm. A highly efficient CO2 laser was used as the pump laser for an Optically-pumped Fabry-Perot FIR laser. The frequencies of most of the new lines were measured in the range 1.7 to 6.4 THz. Twenty-eight CO2 lines were used as pump lines; nineteen of these had frequencies lower than those previously used to pump CH3OD in a FIR laser. Sixteen of the new FIR lines had absorption transitions which belong to the OD bending vibrational mode.
TL;DR: A full–wave algorithm for the design and the optimization of quasi–optical frequency multipliers and its implementation in a specialized computer code, able to simulate as a whole the non–linear device, the planar antenna and the embedding layered structure is presented.
Abstract: This paper presents a full–wave algorithm for the design and the optimization of quasi–optical frequency multipliers and discusses its implementation in a specialized computer code, able to simulate as a whole the non–linear device, the planar antenna and the embedding layered structure. The electromagnetic analysis of the multiplier is performed under the simplifying approximation of an infinite array excited by a uniform plane wave incident from the broadside direction. The array parameters are deduced from a full–wave analysis, based on the Method of the Moments, while the solution of the non–linear circuit is found by the Harmonic Balance Method.