Submillimeter Wavelength Range Research Articles

Higher Harmonic Operations of Submillimeter Wave Gyrotrons (Gyrotron FU Series)

Higher harmonic operation of gyrotrons is necessary to obtain high frequencies. Some gyrotrons included in the Gyrotron FU series developed at Fukui University have achieved operation at the third and even fourth harmonics of the electron cyclotron frequency. The output lies in the millimeter to submillimeter wavelength range and the output powers are several watts to several tens of watts. In this paper, the gyrotrons and the conditions under which they operate are described in detail.

Microstrip stabilized semiconductor asymmetrical quantum well structure generator for millimeter and submillimeter wavelength range

Microwave oscillations have been observed from spacer-cladded GaAs/AlAs multiple-quantum-well resonant tunneling structures, stabilized by a microstrip resonator system. Being compatible with MBE technology, the system is shown to provide proper circuit conditions at high frequencies and can be effectively used in millimeter and submillimeter wavelength range nanoelectronics.

Plasma scattering measurement using a submillimeter wave gyrotron (gyrotron FU-II) as a power source

Electromagnetic waves of medium power ( P = 110 W) in the submillimeter wavelength range ( f= 354 GHz) are generated in long pulses (τ = 0.6 s) by the GYROTRON FU-II and they have been applied to plasma scattering measurements in compact helical system plasma. Use of a gyrotron as a power source improves the S/N ratio of the measurement. The results of low frequency density fluctuations correspond to those of reflectometry. A new transmission line is designed for conversion of gyrotron outputs into a high quality beam. Analysis using Huygen's equation supports the view that this system can produce a high quality beam. The final goal is to improve the performance of the scattering measurement by applying an optimal probe beam.

Frequency measurement of a submillimeter wave gyrotron output

Measurement of frequency spectra of the output of a gyrotron in the millimeter to submillimeter wavelength range using a Michelson interferometer have been made. The results are compared with frequency measurements using a Fabry-Perot interferometer. A correction for mesh transmittance is used to give the true frequency spectrum. The method is used to search for the presence of higher cyclotron harmonics (n=f /f c=3,4,…) which may be generated along with the more intense fundamentals (n=1) or second harmonics (n=2), and to study mode competition between the fundamental and the second harmonic modes.

Design of polarizing interferometer in sub-millimeter wavelength range

Based upon the quasi-optical technique consideration, the dependence of polarizing interferometer properties on Gaussion beam parameters were analyzed. The formulas for PI construction design and the errors of mechanical alignment of polarizing interferometer based on Gaussian beam parameters are given.

Determination of the spectral response of sis-junctions by a direct detection measurement

We present a simple method to determine the spectral response of an SIS detector in the millimeter and submillimeter wavelength range from its current response to a chopped cold-load. This direct detection response is also a good indicator of quantum efficiency and mixer noise temperature when using the SIS junction in heterodyne mode. A simple experimental setup without local oscillator, cryogenic IF-amplifier or any quasioptical interferometer allows a quick diagnosis of integrated planar impedance matching structures.

Development of a medium power, submillimeter wave gyrotron using a 17 T superconducting magnet

GYROTRON FU IV, a frequency tunable gyrotron for spectroscopy in the submillimeter wavelength range using a 17 T superconducting magnet, has been designed and constructed. Simulations predict that the gyrotron will emit radiation at high frequencies up to 394 GHz (TE041 cavity mode) at the fundamental of the electron cyclotron frequency, up to 858 GHz (TE091 mode) at the second harmonic and up to 1301 GHz (TE8 11 1 mode) at the third harmonic. Preliminary experimental results have demonstrated operation from 158 to 443 GHz at the fundamental and from 336 to 838 GHz at the second harmonic. Output powers are several hundred watts and efficiencies several percent.

Submillimeter spectroscopy from space — Missions planned between 1995 and 2005

The submillimeter wavelength range (100 μm≤ λ ≤ 1mm) is exceptionally rich in atomic and molecular transitions that provide direct measures of the chemical composition, temperature, density, and cooling of the interstellar medium. In part, this is due to the fact that the most abundant oxygen- and carbon-bearing species as well as the most common hydrides have their lowest lying transitions within this wavelength region. However, because of the great abundance of many of these same species in our own atmosphere (e.g., H2O and O2), terrestrial absorption at submillimeter wavelengths is strong, rendering much of the sky inaccessible to ground- and even airborne observing platforms. In recognition of the scientific importance of the submillimeter range to astronomy and the limitations placed on its pursuit by the atmosphere, both NASA and ESA have embarked on ambitious programs to explore these wavelengths from space.

Dynamic conductivity and the coherence peak in the submillimeter spectra of superconducting NbN films

A new technique is developed for measurement of electrodynamic parameters of superconducting films in the submillimeter wavelength range. In the frequency range 5–39 cm −1 at temperatures 5–300 K, the first detailed measurements of the temperature and frequency dependences of dynamic conductivity and dielectric permittivity of superconducting NbN films are performed. A coherence peak is discovered in the temperature dependence of dynamic conductivity of NbN films.

A novel small-period wiggler and simulations of its free-electron laser

A small-period wiggler constructed of edgy-wound bifilar-helical conducting sheets with ferromagnetic cores, which is intended for free-electron lasers, is presented. The performance characteristics of the wiggler fields with a 100 mm period are measured. A field as high as 1500 G has been obtained. Free-electron lasers with this small-period wiggler have been investigated numerically with a three-dimensional nonlinear theory. Simulation results estimated that a radiation power of 20.2 MW and a frequency of 170 GHz with an efficiency of 5.1% can be obtained. It is feasible to make Raman free-electron lasers with this type of wiggler operating in the millimeter and submillimeter wavelength range with a relatively low electron energy ( >

Design of conical corrugated feed horns for wide-band high-frequency applications

This paper presents a new analytical procedure for the design of the conical corrugated feed horns used in the millimeter and submillimeter wavelength range, which could achieve wide-band single-mode operation and wide-band, low return-loss impedance matching simultaneously. A test model of the feed horn designed using this procedure displayed excellent performance, and agreed well with the theoretical predictions. >

Helical microundulators of P.N. Lebedev Physical Institute

Abstract Helical undulators have been constructed with periods of 5,8 and 10 mm. The undulator with an 8-mm period operated with a transverse field of 3 kG on the axis. The undulator with a 10-mm period was wound with copper tubing and is water cooled, allowing a pulse repetition rate of about 10 Hz for a transverse field of about 2 T ( K = 2 ). The pulse duration is 30–40 μs. An axial magnetic field of 6–30 kG was used for transporting an electron beam of 0.5–1 MeV energy and 0.1–3 kA current for FEL experiments in the millimeter and submillimeter wavelength range. Various ways of forming adiabatic entry of the undulator and minimizing free and cyclotron motion arising from nonideal adiabatic entry and stray magnetic fields are discussed. The dependence on axial magnetic field of the ratio of cyclotron velocity to orbital velocity in the undulator is presented.

Cyclotron resonance of the quasi-two-dimensional electron gas at Hg1-xCdxTe grain boundaries

The magnetotransmission of a p-type Hg0.766Cd0.234Te bicrystal containing a single grain boundary with an inversion layer has been investigated in the submillimetre wavelength range. For the first time the cyclotron resonance lines belonging to the various electric subbands of a quasi-two-dimensional carrier system at a grain boundary could be detected. The measured cyclotron masses and the subband densities determined from Shubnikov-de Haas experiments are compared with theoretical predictions and it is found that the data can be explained very well within the framework of a triangular well approximation model which allows for non-parabolic effects.

The Cosmic Infrared Background

AbstractCosmic infrared background radiation, expected to carry the radiative record of luminous objects since they first formed, has yet to be detected. The Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE) satellite is designed to search for this primeval background over the spectral range from 1 to 300 μm. Initial examination of data from this experiment show that foreground radiations from the solar system and Galaxy dominate the diffuse infrared sky brightness, with relative minima near 3.5 μm and in the submillimeter wavelength range. DIRBE measurements do not confirm some previous data from rockets and IRAS. Preliminary upper limits on the cosmic infrared background are generally above theoretical expectations for pregalactic and protogalactic sources, and substantially above estimated lower limits based upon observations of external galaxies. Careful foreground modeling is required to reduce these limits or identify an isotropic residual.

Processes of electron-phonon interaction in thin YBaCuO films

The ultrafast voltage response of YBaCuO films to laser radiation is studied and compared with previously investigated quasiparicles response to radiation of submillimeter wavelength range. Voltage shift under the visible light radiation has two components. Picosecond response realized as suppression superconductivity by nonequilibrium excess quasiparticles, response time is determined by quasiparticles recombination rate. Nanosecond response is probably due to bolometric effect.

Mechanism of picosecond response of granular YBaCuO films to electromagnetic radiation

Ultrafast mechanisms of radiation detection in granular YBaCuO films are studied in the wide wavelength range from millimeter waves to near infrared. With an increase in radiation frequency, the Josephson detection at the grain-boundary weak links is replaced by electron heating into the grains. This change occurs in the submillimeter wavelength range. The electron-phonon relaxation time tau /sub eph/ is determined from direct measurements, quasi-stationary electron heating measurements, and the frequency dependence of the current at which maximum voltage shift is observed. The temperature dependence of tau /sub eph/ at T<or=40 K was found to be tau /sub eph/ approximately T/sup -1/. The results show that detectors with a response time of a few picoseconds at nitrogen temperature are attainable.

Mechanism of picosecond response of granular YBaCuO films to electromagnetic radiation

The ultrafast mechanisms of radiation detection in granular YBaCuO films are studied in the wide wavelength range from millimeter to near infrared. With the rise of radiation frequency the Josephson detection at the grain boundary weak links is replaced by electron heating into the grains. This change occurs in the submillimeter wavelength range. Electron-phonon relaxation time τeph is determined by direct measurements and analyses quasistationary electron heating. Temperature dependence of τeph at T ≤ 40 K was found to be τeph ∼ T−1. The results show that detectors with the response time of few picoseconds at nitrogen temperature are attainable.

Six-port and four-port reflectometers for complex permittivity measurements at submillimeter wavelengths

The frequency range of six-port reflectometry is extended into the submillimeter wavelength range. The complex permittivity of low-loss microwave materials is determined using novel six-port and four-port reflectometers. These either consist of quasi-optical components or utilize oversized waveguide techniques. Permittivity measurements of materials possessing a wide range of values of epsilon ' (2 to 7) and of the loss tangent (0.0003 to 0.03) were carried out at frequencies of about 380 GHz to 390 GHz. Good agreement with published permittivity data is shown. Moreover, the equivalance of the simple waveguide four-port reflectometer (which is preferred because of its easy handling and high stability against temperature fluctuations) to the quasi-optical reflectometers is shown. >

Effective Scattering Times of Inversion Electrons in InSb Grain Boundaries Deduced from Cyclotron Resonance Measurements

AbstractThe effective scattering times of inversion electrons in InSb grain boundaries are investigated by means of cyclotron resonance measurements in the submillimeter wavelength range between λ = 118.8 and 513 μm. It is found that the inversion electrons in the InSb grain boundary have essentially higher scattering times than estimated from the onsets of Shubnikov‐de Haas oscillation periods. Furthermore, it is shown that the scattering times decrease with increasing magnetic field in qualitativ agreement with the theoretical result for the limit of a short‐ranged scattering potential. The scattering behaviour is discussed in the framework of this model.

Magneto‐Optical Investigations on p‐InSb Bicrystals in the Submillimeter Wavelength Range

AbstractThe magneto‐optical properties of p‐type InSb bicrystals are investigated in the submillimeter wavelength range from λ = 57 to 251 μm at temperatures T ≦ 4.2 K and magnetic fields up to B = 6.5 T. At wavelengths λ = 118.8 and 251 μm the cyclotron resonance of the conduction electrons in the n‐inversion layer adjacent to the grain boundary can be detected. At all other wavelengths strong magnetic field dependent absorption effects in the p‐type bulk mask the relatively small absorption effects in the inversion layer. The acceptor excitation spectrum of the bulk is discussed. From the periodicity of quantum oscillations three occupied electric subbands are identified. The experimental cyclotron resonance spectra are modeled as the superposition of three cyclotron resonance lines belonging to the three occupied electric subbands. Cyclotron masses are obtained with a three‐level model in the triangular‐well approximation and compared to the experimental data.