Millimeter-wave Radiation Research Articles

Four-photon polarization spectroscopy of water in a millimeter-wave radiation field

Resonance (frequency 1.4 cm(−1) changes induced in the four-photon optical spectrum of water by a millimeter-wave electromagnetic field are observed experimentally. Comparison with the spectrum of ice in the range 0‒2 cm(1 shows that the action of such a field is of a structure-forming character.

Millimeter-wave beams with phase singularities

Beams of millimeter-wave radiation carrying phase singularities have been generated using specially configured plane and blazed gratings. The blazed grating converts a plane wave into such a beam with very high efficiency. All of the properties of these beams that have been seen at optical wavelengths, such as the hollow profiles of the beams and the way a beam already carrying a singularity is subsequently diffracted, are shown to appear at millimeter wavelengths.

Topical Papers on Microchip Lasers and Applications. Generation of Narrow-Band Millimeter-Wave Radiation by Means of a Two-mode Microchip Laser.

The generation of narrow-band millimeter-wave radiation has been achieved by photomixing two longitudinal modes in a two-mode microchip laser. The two modes were frequency-converted to their second harmonics using an external cavity, then focused onto the photoconductive gap of an LTG-GaAs photomixer . A millimeter wave was generated from the photoconductive antenna and examined using a spectrum analyzer with a millimeter-wave mixer. The linewidth observed for the millimeter wave was 430 Hz at 101 GHz, which is only 1/230 the width of the individual laser modes. This narrow linewidth of the millimeter wave can be attributed to the cancellation of most of the frequency fluctuations embedded in the two modes due to their sharing the same volume in the same cavity.

High-Tc ramp-type Josephson junctions on MgO substrates for terahertz applications

The authors successfully fabricated high-Tc ramp-type junctions with PrBa/sub 2/Cu/sub 3-x/Ga/sub x/O/sub 7-/spl delta// (PBCGO: x=0.1, 0.4) barriers on MgO substrates. The junctions showed resistively shunted Josephson junction (RSJ)-like I-V curves with thermally and voltage activated conductivity. The I/sub c/R/sub n/ products for these junctions scaled very well with the Ga-doping. Maximum response of the junctions for 100-GHz millimeter-wave irradiation could be observed up to 12 mV corresponding to 6 THz. Using far infrared laser radiation, we confirmed a terahertz (THz) response of these junctions. These results show promise for THz-wave applications of ramp-type Josephson junctions.

Properties of Y1Ba2Cu3O7−δ and Ba1−XKXBiO3 step-edge grain boundary junctions

A technique for the fabrication of sharp and straight step-edges on LaAlO3 (LAO) substrates by Ar-ion milling is reported here. Diamond-like carbon (DLC) thin films, deposited by pulsed laser ablation, were used as masks. Clear Shapiro steps were observed in the current-voltage (IV) characteristics of Y1Ba2Cu3O7−δ (YBCO) step-edge junctions with millimeter-wave irradiation. Also, the transport properties of epitaxial Ba1−XKXBiO3 (BKBO) films deposited on LaAlO3 step-edge substrates were studied.

Millimeter-wave radiation in high-T/sub c/ Josephson junctions

We have investigated millimeter-wave radiation from single Josephson junctions and small phase-locked Josephson junction arrays. Josephson junctions were fabricated on sapphire bicrystal substrates. Emission could be measured up to 110 GHz. Resonances in ten-junction circuits yield linewidths narrower than 200 MHz. This type of array might be useful for applications in integrated receiver systems.

Josephson properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ bicrystal junctions grown by a sequential deposition technique using molecular beam epitaxy

We report Josephson and crystallographic properties of the Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ junctions fabricated on MgO(100) bicrystal substrates by a molecular-beam-epitaxy method incorporating co-evaporation and sequential deposition techniques. With the sequential deposition technique which has the advantage of promoting the surface diffusion of adatoms, we obtained the highly growth-controlled films without precipitation of any second impurity phases. During the film growth, the sharp reflection high-energy electron diffraction (RHEED) patterns were also observed. However, the RHEED patterns showed the a-b twin structures due to the lattice mismatch, which influenced the Josephson transport properties at the junction boundary. The normal resistance of the bicrystal junction was 1.5 /spl Omega/ and the I/sub c/R/sub n/ product was 0.75 mV at 4.2 K. The Shapiro steps under millimeter-wave irradiation were clearly observed up to 65 K. The Josephson microwave self-radiation spectra at receiving frequency f/sub REC/=22 GHz. The observed Josephson transport properties are discussed in relation to the microscopic crystallographic properties.

Reflectometry on ITER

Reflectometry will be used on ITER to measure the density profile in the main plasma and divertor regions, and to measure the plasma position and shape in order to provide a standby reference for the magnetic diagnostics in long pulse discharges. The high temperatures of the ITER core and the resultant significant relativistic downshift of the second-harmonic electron cyclotron absorption imply that both low-field side O-mode and high-field side lower cut-off (X−l mode) systems are required to access the full plasma profile. A low-field side upper cut-off (X−u mode) system will also be required for measurements of the scrape-off layer. For measurements of the plasma position and shape, an O-mode system is optimum due to the large range of magnetic field along the plasma periphery and the wide range of possible plasma configurations achievable on ITER. A robust real-time calibration technique of the whole transmission line is required. It is likely that an accurate estimate of the position of the plasma will require the simultaneous use of signals from the profile reflectometer. For the divertor, profiles with peak densities in the range 1019–1022/m3 are to be measured with a target resolution of 3 mm. The large density range will necessitate the use of more than one system. Installing these reflectometers on ITER incurs additional difficulties such as the routing of the millimetre wave radiation around the complicated first wall and divertor structures and design of antennas able to operate through the first wall and blanket.

First results of collective scattering on JET (invited)

The fast ion and α-particle diagnostic at JET is based on collective Thomson scattering of high power millimeter-wave radiation. The principal aim of the diagnostic will be the measurement of the spatially resolved velocity distribution of fast α particles when tritium is introduced in JET plasmas, although several other applications are foreseen. The diagnostic uses a 140 GHz, 500 kW, gyrotron as the source of probing radiation and a heterodyne detection system. The diagnostic came into operation during the last JET operational campaign. First measurements were made of the thermal and mildly suprathermal (induced by ion cyclotron resonance heating) ion feature. The results confirmed expectations, indicating that the diagnostic should give the predicted performance for observation of α-particle populations in the DT phase. The signal-to-noise ratio is limited by the noise on the background radiation (electron cyclotron emission), which has a minimum around 140 GHz only when JET is operated at B∼3.4 T. To further improve the S/N and to make the diagnostic suitable for operation at higher field, which is now being considered for some of the DT plasmas, a viewing dump will be installed before the DT phase.

Search for frequency-specific effects of millimeter-wave radiation on isolated nerve function.

Effects of a short-term exposure to millimeter waves (CW, 40-52 GHz, 0.24-3.0 mW/cm2) on the compound action potential (CAP) conduction were studied in an isolated frog sciatic nerve preparation. CAPs were evoked by either a low-rate or a high-rate electrical stimulation of the nerve (4 and 20 paired pulses/s, respectively). The low-rate stimulation did not alter the functional state of the nerve, and the amplitude, latency, and peak latency of CAPs could stay virtually stable for hours. Microwave irradiation for 10-60 min at 0.24-1.5 mW/cm2, either at various constant frequencies or with a stepwise frequency change (0.1 or 0.01 GHz/min), did not cause any detectable changes in CAP conduction or nerve refractoriness. The effect observed under irradiation at a higher field intensity of 2-3 mW/cm2 was a subtle and transient reduction of CAP latency and peak latency along with a rise of the test CAP amplitude. These changes could be evoked by any tested frequency of the radiation; they reversed shortly after cessation of exposure and were both qualitatively and quantitatively similar to the effect of conventional heating of 0.3-0.4 degree C. The high-rate electrical stimulation caused gradual and reversible decrease of the amplitude of conditioning and test CAPs and increased their latencies and peak latencies. These changes were essentially the same with and without irradiation (2.0-2.7 or 0.24-0.28 mW/cm2), except for attenuation of the decrease of the test CAP amplitude. This effect was observed at both field intensities, but was statistically significant only for certain frequencies of the radiation. Within the studied limits, this effect appeared to be dependent on the frequency rather than on the intensity of the radiation, but this observation requires additional experimental confirmation.

Generation of millimetre-wave radiation using adual-longitudinal-mode microchip laser

The generation of narrowband millimetre-wave radiation has been demonstrated by photomixing with two longitudinal modes of a Nd:YVO/sub 4/ microchip laser. The observed linewidth of 430 Hz at 101 GHz frequency indicates that the common-mode-rejection effect or the laser cavity efficiently suppresses frequency fluctuations between the oscillating modes, enabling stable millimetre-wave radiation to be generated.

Resonant magnetoabsorption of millimeter-wave radiation in the quasi-two-dimensional organic metals alpha -(BEDT-TTF)2MHg(SCN)4 (M=K,Tl).

The magnetoabsorption of millimeter-wave radiation by single crystals of the organic metals \ensuremath{\alpha}-(BEDT-TTF${)}_{2}$TlHg(SCN${)}_{4}$ and \ensuremath{\alpha}-(BEDT-TTF${)}_{2}$KHg(SCN${)}_{4}$ has been studied in the frequency range 30--120 GHz. The experiments reveal two dominant contributions to the magnetoabsorption spectra. The first is interpreted as the cyclotron resonance of two-dimensional carriers, and is characterized by broad lines (linewidth/magnetic field \ensuremath{\Delta}B/B\ensuremath{\sim}0.5--1). In addition to a resonance exhibiting a cyclotron mass ${\mathit{m}}_{\mathit{c}}$\ensuremath{\sim}2.8${\mathit{m}}_{0}$, there are two further lines corresponding to frequency-dependent cyclotron masses in the ranges ${\mathit{m}}_{\mathit{c}}$\ensuremath{\sim}(1--1.5)${\mathit{m}}_{0}$ and ${\mathit{m}}_{\mathit{c}}$\ensuremath{\sim}(0.5--0.8)${\mathit{m}}_{0}$. This frequency dependence is believed to result from many-body effects. The second contribution to the magnetoabsorption is formed by a series of narrow lines with \ensuremath{\Delta}B/B\ensuremath{\sim}0.03--0.1 and amplitudes 5--10 times smaller than the features interpreted as cyclotron resonances. These narrow lines are attributed to a superposition of modes due to antiferromagnetic resonance and conduction-electron-spin resonance (ESR). The feature characteristic of antiferromagnetic resonance is the presence of a mode with a frequency that decreases with increasing magnetic field. The magnetoabsorption structure attributed to ESR consists of a relatively broad maximum upon which a sharp dip is superimposed. This behavior is believed to be analogous to the resonant transparency observed in thin metallic films undergoing ESR. \textcopyright{} 1996 The American Physical Society.

Millimetre-wave radiation from arrays of high- Josephson junctions

We have used a novel high-frequency circuit incorporating a resonant parallel-bias scheme to demonstrate millimetre-wave radiation from arrays of high-temperature superconductor Josephson junctions. The power of a five-junction array was measured with a detector junction on chip, and the Josephson oscillations of a ten-junction array were detected directly with a radiometer from 73 GHz to 123 GHz.

Absorption Measurements of Ar–COb-Type Rotational Transitions with a Supersonic Jet Millimeter-Wave Spectrometer

Pure rotationalb-type transitions of Ar–CO were observed in the frequency range from 70 to 103 GHz using a combination of millimeter-wave absorption spectroscopy with supersonic jet expansion. The millimeter-wave radiation was generated by precision tunable synthesizers equipped with backward wave oscillators. Altogether 14 transitions belonging toQandRbranches withKa= 1 − 0 have been measured with an accuracy of about 50 kHz. Our results confirm the microwave–millimeter-wave double resonance experiments of Jäger and Gerry [J. Chem. Phys.102,3587–3592 (1995)] and demonstrate the sensitivity of the direct absorption technique for the detection of van der Waals clusters with a small dipole moment.

Continuous Millimeter-Wave Radiation Has No Effect on Lipid Peroxidation in Liposomes

The effect of millimeter waves on lipid peroxidation was studied in the presence and absence of melanin. Irradiation of liposomes with continuous millimeter electromagnetic waves at frequencies of 53.6, 61.2 and 78.2 GHz and incident power densities of 10, 1 and 500 mW/cm2, respectively, did not show an enhancement in the formation of lipid peroxides compared to unirradiated samples. Liposomes exposed to 254 nm UVC radiation at 0.32 mW/cm2 and 302 nm UVB radiation at 1.12 mW/cm2 served as positive controls. No increment in the formation of lipid peroxides was observed when irradiation of liposomes was carried out in the presence of ADP-Fe+3 and EDTA-Fe+3. Direct irradiation of melanin with millimeter waves did not exhibit an increased formation of superoxide or hydrogen peroxide. The present results indicate that millimeter waves of the above frequencies and intensities do not cause lipid peroxidation in liposomal membranes.

Advanced Ceramics Sintering Using High-Power Millimeter-Wave Radiation

AbstractThe results of ceramics sintering experiments using high-power millimeter-wave radiation are reported. Sintering of silicon nitride with 5%Al2O3 and 5%Y2O3 was performed in a multi-mode applicator using a 10-kW 28-GHz gyrotron in CW operation. It was found that the silicon nitride samples sintered with 28 GHz radiation at 1650'C for 30 min reached to as high as theoretical density (TD), while the conventionally sintered samples at 1700°C for 60 min resulted in the density as low as 90% TD. Focusing experiments of millimeter-wave radiation from the high-power pulsed 60-GHz gyrotron have been performed using a quasi-optical antenna system (two-dimensional ellipso-parabolic focusing antenna system) to demonstrate the feasibility of the power density of as high as 100 kW/cm2. Typical heating characteristics using the focused beam were made clear for this system. It was found that the densification of yttria-stabilized zirconia (ZrO2-8mol%Y2O3) samples to as high as 97% TD was obtained from the sintering with focused 60 GHz beam in pulse operation with a 10-ms pulse duration at a 0.5Hz repetition. The densification temperature for the zirconia could be lowered by 200°C than that expected conventionally.

A comparison of mm-wave Sintering and Fast Conventional Sintering of Nanocrystalline Al2O3

AbstractThe phase transformation and densification behavior under high power millimeter-wave (mm-wave) radiation of a 30 GHz gyrotron and during fast conventional sintering of nanocrystalline γ-A12O3 powder have been investigated and compared. The powder used for compacts was synthesized from aluminum metal by application of the exploding wire technique in an oxidizing atmosphere. The particle size distribution of this powder has a maximum at about 20 nm. Magnetic pulse technique was applied for the compression of samples up to 80% of the theoretical density (TD). Both mm-wave sintering and fast firing in a conventional electrical resistance furnace enable the densification and a complete phase transformation into α-A12O3 already at a temperature of approximately 1150 %C. The average grain size of the sintered ceramic is in the range of 50 to 100 nm. With mm-waves densification starts at about 50 °C lower temperatures compared to conventional techniques and higher final densities were obtained already at 150°C lower temperatures.

High T/sub c/ superconducting step-edge junctions and their properties in millimeter-wave band

Superconducting step-edge junctions were fabricated on step-edges in (100) LaAlO/sub 3/ substrates by sputter-deposited epitaxial YBaCuO and TlBaCaCuO thin films. The substrate steps were patterned by ion beam etching using metal film as a mask. The transport properties of the junctions were characterized by four-probe electrical measurements. The critical current-normal resistance product (I/sub c/R/sub N/) was larger than 0.2 mV (77 K) for most of the junctions. Clear Shapiro steps were observed in the current-voltage characteristics of the junctions with 36 GHz or 95 GHz millimeter-wave irradiation. The high frequency properties of these high T/sub c/ Josephson junctions showed that they were quite suitable for the Josephson harmonic mixer used in the digital phase locked millimeter and sub-millimeter wave sources.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reception of low-intensity millimeter-wave electromagnetic radiation by the electroreceptors in skates.

Low intensity millimeter-wave electromagnetic radiation of less than 10 mW cm-2 power intensity has a nonthermal effect on the body and it is widely used in medical practice for treatment of various diseases. Nevertheless, the effect of EMR on biological tissues is not understood. The skin and its sensory receptors are considered to be responsible for EMR reception, but this has yet to be confirmed. The present experiments were designed to study the effect of millimeter-wave electromagnetic radiation on the ampullae of Lorenzini in skates, which are very sensitive to weak electrical stimuli at low frequency. Reception of low-intensity millimeter-wave electromagnetic radiation at 37-55 GHz by the electroreceptors (ampullae of Lorenzini) in the skate has been shown. At a power intensity of 1-5 mW cm-2 irradiating the duct opening at 1-20 mm distance caused a transient increase in the firing rate of a single afferent unit. When the power intensity was increased inhibitory responses were also observed. Some receptors responded with a prolonged excitatory activity lasting up to 30 min to the irradiation of the duct opening. Direct irradiation of the sensory cells produced only an inhibition, probably due to a rise in temperature. It is proposed that millimeter-wave electromagnetic radiation generates a d.c. potential at the vicinity of duct opening which can be detected by the electroreceptors.

Ten-volt Josephson junction array

An array of 20144 Josephson junctions divided into four strip line branches has been developed and tested. The array generates quantized voltages up to about 14 V under millimeter-wave irradiation of 90 mW at 92.5 GHz, and will be used in a 10-V voltage standard. >