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We are currently developing transition edge sensors (TES) for the gamma-ray spectroscopy using a single gold bump post to connect the bulk metal absorber to the superconducting thin film. In order to develop a multi-pixel TES array for the gamma-ray spectroscopy, a stable and feasible method of mounting gamma-ray absorbers is indispensable. However, mounting gamma-ray absorbers on a single gold bump post is difficult from a structural stability and process development perspective. To overcome this problem, we have established a method to improve the structural stability in mounting gamma-ray absorbers by using 4 gold bump posts. We developed a TES array coupled with a Sn absorber which was mounted with our newly established method and used it to collect gamma-ray spectrum from an Am241 source. The rise time of the signal waveform was shorter than 200 μs and showed a favorable energy resolution considering the high transition temperature of the Ir/Au superconducting film. This new method to mount gamma-ray absorbers on TES will contribute to the development of multi-pixel TES arrays using bulk metal for gamma-ray absorbers.

We have measured the energy of each charged particle in carbon ion beam using a transition edge sensor (TES). The TES was irradiated by carbon ion beam of 100 MeV/u in Heavy Ion Medical Accelerator in Chiba. We have measured the energy of each charged particle in the carbon ion beam. This will contribute to the establishment of a new dosimetry method of carbon ion beam for radiotherapy.

Photon imaging technology is applied in various research fields such as quantum information communication and biological imaging. We have been developing photon-counting devices using optical transition edge sensors (TES). We demonstrated a single-photon spectroscopic imaging system comprising an optical TES and a scanning microscope. However, a great number of TES pixels are required to increase the field of view in the imaging system. To read out the TES array, output signals need to be multiplexed. Microwave SQUID multiplexer (MW-Mux) is a kind of frequency multiplexing method with a carrier wave having a frequency of several GHz, and it can be used to widen the frequency band. In this paper, we report the first demonstration on readout of an optical TES with MW-Mux.

An important figure of merit in microwave superconducting quantum interference device multiplexer (MW-MUX) is the quality factor of superconducting resonators. In advanced industrial science and technology (AIST), the intrinsic quality factor ${\boldsymbol{Q}_{{\mathbf i}}}$ of the resonators in the MW-MUX chips degraded significantly compared to those in the resonator-only chips owing to something during the fabrication process. In this study, we have investigated the damage process by conducting controlled experiments and an SEM-EDX analysis. As a result, we have confirmed that the metallic layers (Pd and Nb) were not removed completely and remained along the edge of the resonator, which resulted in the degradation of ${\boldsymbol{Q}_{{\mathbf i}}}$ . Further, we have invented a new process to overcome this imperfection during the removal of Pd layer using so called “caldera planarization”. The metal line that remained along the edge was not observed in the MW-MUX chips fabricated using this improved process. Finally, we have achieved ${\boldsymbol{Q}_{{\mathbf i}}}$ as high as that of resonator-only chips using the improved process.

We are developing an x-ray imaging spectrometer for Super DIOS satellite mission, a future x-ray observatory, planned by JAXA, to be launched in 2030’s. Super DIOS will reveal the nature of the missing baryon in the warm-hot intergalactic medium because of its fine energy and angular resolution, large effective area and large field of view. A main detector on-board Super DIOS consists of a transition-edge sensor (TES) microcalorimeter array of over 30,000 pixels working at a temperature below 100 mK and it poses a considerable technical difficulty to the readout. A microwave superconducting quantum interference device (SQUID) multiplexing is promising technique and expected to achieve a large scale readout of more than 30,000 pixels. We describe our development of a 40-channel microwave SQUID multiplexer with low-noise characteristics∗ and a demonstration of simultaneously reading out 40-pixel TESs. Finally, we discuss a future prospect and a feasibility of reading out an array of more than 30,000 pixels.

We present the development of a frequency-domain multiplexing readout of kinetic inductance detectors (KIDs) for pulse signals with a self-trigger system. The KIDs consist of an array of superconducting resonators that have different resonant frequencies individually, allowing us to read out multiple channels in the frequency domain with a single wire using a microwave-frequency comb. The energy deposited to the resonators break Cooper pairs, changing the kinetic inductance and, hence, the amplitude and the phase of the probing microwaves. For some applications such as X-ray detections, the deposited energy is detected as a pulse signal shaped by the time constants of the quasiparticle lifetime, the resonator quality factor, and the ballistic phonon lifetime in the substrate, ranging from microseconds to milliseconds. A readout system commonly used converts the frequency-domain data to the time-domain data. For the short pulse signals, the data rate may exceed the data transfer bandwidth, as the short time constant pulses require us to have a high sampling rate. In order to overcome this circumstance, we have developed a KID readout system that contains a self-trigger system to extract relevant signal data and reduces the total data rate with a commercial off-the-shelf FPGA board. We have demonstrated that the system can read out pulse signals of 15 resonators simultaneously with about 10 Hz event rate by irradiating \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha $$\end{document}α particles from \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{241}$$\end{document}241Am to the silicon substrate on whose surface aluminum KID resonators are formed.

The quality factors and noise performances of superconducting resonators play an important role in microwave SQUID multiplexer (MW-MUX). Since we develop microwave SQUID multiplexer for transition edge sensor arrays, the operation temperature is around 100 mK where the effects of two level system (TLS) can be significant. In this paper, we have investigated the electrode-material or wafer dependence of noise performance of MW-MUX by characterizing four types of resonators. Although the temperature dependence of resonance frequency and the power dependence of ${{\boldsymbol{Q}}_{\boldsymbol{u}}}$ show clear difference among the materials, frequency noises which contribute the readout noise of MW-MUX are similar. Theoretical model predicts that not TLS but other loss dominates ${{\boldsymbol{Q}}_{\boldsymbol{u}}}$ in the power region suitable for the low-noise operation of our MW-MUX. Further, the estimated flux noise calculated from the measured frequency noise and the conversion coefficient from frequency to flux were 1–5 $({{{\mathbf \mu }}{{{\mathbf \Phi }}_0}/\sqrt {{{\mathbf Hz}}} })$ @ 1 Hz, 0.2–0.8 $({{{\mathbf \mu }}{{{\mathbf \Phi }}_0}/\sqrt {{{\mathbf Hz}}} })$ @ 3 kHz. These results indicate the noise of our MW-MUX has small material dependence and the compatible low noise operation to typical dc SQUIDs would be possible. Therefore, the MW-MUX with our materials would not suffer from the low frequency noise due to TLS.

In order to read out current signals from large-scale arrays of transition edge sensors (TES), microwave SQUID multiplexers (MW-MUX) have been developed by several groups. Reduction of crosstalk induced in the multiplexer is important in order to maintain the energy resolution or the noise equivalent power of detector arrays. In the present study, crosstalk between channels in MW-MUX with five different designs is experimentally evaluated. The resonance frequency separation is ten times as large as the resonator bandwidth. Without flux-ramp modulation, crosstalk between two adjacent channels neighboring in position decreases to ≍1 × 10–3 with increasing resonance frequency separation to ≍100 MHz. Crosstalk between SQUID channels neighboring in resonance frequency also decreases to 4 × 10–3 with increasing the distance to 2.5 mm. We show that nonlinear error can occur due to the crosstalk with flux-ramp modulation. Flux readings from a well-designed multiplexer exhibit crosstalk of less than 1 mΦ0 peak-to-peak and nonlinear errors of less than 2 mΦ0 peak-to-peak, which is sufficient for the readout of the gamma-ray TES arrays being developed. These results can provide guidelines for suppressing both the crosstalk and the nonlinear error to less than the criterion of TES spectrometers with typical energy-resolving ability.

Digital-to-analog converter circuits utilizing NbTiN/Ti-TiN/NbTiN Josephson junctions were fabricated as quantum voltage standards, and were evaluated at around 10 K in a cryocooler. The first Shapiro step was generated at 2 V and had a height of more than 0.5 mA. Instead of a conventional microwave power divider that uses a quarter-wavelength resonator, a serial–parallel power divider was employed. This consisted of coplanar waveguides connected in parallel and coplanar strips connected in series. As a result, the chip area for the power divider was reduced by about 70%, and uniform frequency characteristics for the operating current margin were obtained.

Accepted: 2016-02-17, 資料番号: SA1150323000

We have succeeded in operating a transition-edge sensor (TES) spectrometer and evaluating its performance at the SPring-8 synchrotron x-ray light source. The TES spectrometer consists of a 240 pixel National Institute of Standards and Technology (NIST) TES system, and 220 pixels are operated simultaneously with an energy resolution of 4 eV at 6 keV at a rate of ∼1 c/s pixel-1. The tolerance for high count rates is evaluated in terms of energy resolution and live time fraction, leading to an empirical compromise of ∼2 × 103 c/s (all pixels) with an energy resolution of 5 eV at 6 keV. By utilizing the TES's wideband spectroscopic capability, simultaneous multi-element analysis is demonstrated for a standard sample. We conducted x-ray absorption near-edge structure (XANES) analysis in fluorescence mode using the TES spectrometer. The excellent energy resolution of the TES enabled us to detect weak fluorescence lines from dilute samples and trace elements that have previously been difficult to resolve due to the nearly overlapping emission lines of other dominant elements. The neighboring lines of As Kα and Pb Lα2 of the standard sample were clearly resolved, and the XANES of Pb Lα2 was obtained. Moreover, the x-ray spectrum from the small amount of Fe in aerosols was distinguished from the spectrum of a blank target, which helps us to understand the targets and the environment. These results are the first important step for the application of high resolution TES-based spectroscopy at hard x-ray synchrotron facilities.

We report very-low-noise, fast-response, middle-scale multiplexing in a microwave superconducting quantum interference device multiplexer (MW-Mux) as a transition-edge sensor (TES) readout. Our MW-Mux is able to read 40 channels with 500 kHz sampling and has a low readout noise of 0.9 μ Φ 0 / Hz (where Φ 0 is the magnetic flux quantum), equivalent to 9 pA / Hz. By contrast, a multiplexer of less than 10 pixels with 500 kHz sampling and ∼ 2 μ Φ 0 / Hz readout noise has so far been reported in the literature. Owing to the 500 kHz sampling, our MW-Mux exhibits a fast response to detect a TES pulse with a rise time around 12 μ s. We demonstrated simultaneous readout of 38 pixels from an array of x-ray TES microcalorimeters. The measured full-width values at half-maximum spectral resolution ranged from 2.79 to 4.56 eV, with a median value of 3.30 eV at 5.9 keV, including a ∼ 10 % contribution of readout noise, i.e., 0.9–1.7 eV.

Accepted: 2013-12-17, 資料番号: SA1004633000

Accepted: 2017-05-02, 資料番号: SA1170002000

We are developing a superconductor-insulator-superconductor (SIS) mixer receiver to realize a highly sensitive and easy-to-use terahertz (THz) spectrum analyser, which measures both the frequency and the power of a terahertz signal. Although commercially available cryocoolers can cool the SIS mixer to a cryogenic temperature without troublesome cooling operations, the mechanical and thermal vibrations of a cryocooler can impede the sensitive detection of terahertz signals. We have developed a reduced-vibration cryostat that produces less than 10-μm peak-to-peak mechanical vibration at the 4-K stage; the temperature fluctuations are as small as 6 mK, which have negligible effects on the measurements of our SIS mixer receiver.

We have demonstrated that a superconductor-insulator-superconductor (SIS) mixer is applicable for a power detector to evaluate the sideband noise radiated from a submillimeter-wave local oscillator (LO) under development. A simple analysis shows SIS mixers provide better resolution of LO noise than Schottky barrier diode mixers when the available LO power is less than ~ 0.4 mW. Systematic measurement of dependence of receiver noise temperature T RX on components and operational conditions of a photonic LO (Ph-LO) is carried out, which provides a guide to their optimization, e.g., source-laser power, photodiode drive current, use of an optical filter, and selection of an optical amplifier. Noise temperature of the Ph-LO estimated from experimental results ranges from ~ 1 times 103 K to ~ 5 times 104 K as a function of operational conditions and parameters.

Fast readout with low noise is essential to apply superconducting detectors to such experiments as time-of-flight mass spectrometry or X-ray spectroscopy, where high counting efficiency is required. We have developed a thin seamless superconducting coaxial cable employing NbTi alloy in both of the outer and inner electrical conductors. The outer diameter is 1.60 mm, and both conductors are separated by dielectric material of PTFE. The coaxial cable revealed to become superconductive below about 10 K. The thermal conductance was measured between 0.4 and 6 K and consistent with literature. Performance at high frequency was also measured at 4.2 K. The attenuation was very small and less than 1 dB up to about 7 GHz. The effect of mechanical treatment to thermal and electrical properties of NbTi alloy seems to be small in the present forming process of coaxial cable.

A SIS mixer with RF bandwidth of 1 octave is designed, fabricated, and characterized. The mixer chip consists of 8 Nb/AlOx/Nb junctions connected in parallel through Nb/SiO2/Nb microstrip lines (MSL), a twin-slot antenna, and a 3-stage MSL transformer. Experimentally, the 2.5 dB RF band is found to be 230-440 GHz, which agrees quantitatively with theoretical calculation. Receiver noise temperature Trx is measured as 260-680 K in the band. After correction for IF-amplifler noise and beam-splitter reflectivity, the noise is 170-320 K, i.e., 13-20 times of the quantum noise. The sensitivity flatness in the band can be improved to 1.9 dB by further optimization of the transformer.

The thermal stress of the voltage standard chip soldered on a copper or sapphire substrate was numerically analyzed by a finite element method. It was confirmed that the thermal stress in the chip soldered on the sapphire substrate is much smaller than that in the chip soldered on the copper substrate. Since the magnitude of the thermal stress applied to the chip depended on the thickness of the substrate, the thickness of the substrate should be properly chosen, e.g., the 0.5-mm thick sapphire minimized the thermal stress for the 0.4-mm thick silicon chip. It was also found that the copper substrate with a few slits did not decrease the risk of the damage due to the thermal stress.

We are developing low-power dc-SQUIDs to read out TES X-ray microcalorimeter arrays with frequency-division multiplexing (FDM) towards future X-ray satellite missions. In future space missions, large-format TES X-ray microcalorimeter arrays with hundreds to thousands of pixels are promising detectors achieving high energy resolution and high spatial resolution at the same time. To read out such a large-format array with a limited cooling power at the cryogenic stage, TES pixels are multiplexed in the frequency domain and read out using SQUIDs with small heat dissipations. We are developing low-powered dc-SQUIDs with an adequate gain and a low noise characteristic for TES FDM readouts. With these features, the SQUID can suffice to be the only amplifier in the cold electronics even though it can be placed at the cryogenic stage below 100 mK, enabling a simple single-staged cryogenic configuration. Using the low-power SQUID, we are developing multi-input SQUID chips with built-in bandpass filters used for the channel separation in FDM. Within the size of 2.5×2.5 mm, it carries the low-power SQUID, a TES shunt resistor, and LC bandpass filters for four channels. We are also developing a same-size extension chip that consists of the bandpass filters for four other channels, and it can be attached to the multi-input SQUID chip with only two bonding wires. With these chips, the cryogenic stage setup is drastically simplified. The designs and experimental results of the SQUIDs will be discussed.

A low-noise rf amplifier based on a dc SQUID (SQA) is developed and tested within frequency range 3.0-4.5 GHz. The 4-channel chips are designed using proven balanced output configuration; they employ special damping filters. Each channel is tested separately demonstrating the following parameters at 3.95 GHz central frequency: gain (9.5 /spl plusmn/ 1.0) dB, 3-dB bandwidth 300 MHz and noise temperature (1.0 /spl plusmn/ 0.5) K. The 1-dB gain compression estimate is 50 K*GHz for bias voltage 80 /spl mu/V and characteristic voltage 285 /spl mu/V.

For the optimum design of integrated receivers operating above the gap frequency of Nb, we have designed, fabricated and tested NbN-based quasi-optical superconductor/insulator/superconductor (SIS) mixers. The mixer chip incorporates a resonant half-wavelength epitaxial NbN/AlN/NbN junction, a twin-slot antenna and their coupling circuits. We adopted two kinds of coupling circuit between the antenna and the SIS junction: one is an in-phase feed with a length of 95 µm and the other is an anti-phase feed of 30 µm length. It was found that the anti-phase mixer reveals a 3 dB bandwidth of 43% of the centre frequency; the uncorrected double-sideband receiver noise temperature TRX = 691 K at 0.91 THz and TRX = 844 K at 0.80 THz, while 17% and TRX = 1250 K at 0.79 THz for the in-phase version. Possible reasons for this difference are discussed, which could be transmission loss and its robustness with respect to the variation of junction parameters. These experimental results suggest the NbN-based distributed mixer with the anti-phase feed is a better candidate for wide-band integrated receivers operating above 0.7 THz.

To develop an efficient local oscillator (LO) integrated with a SIS mixer operating above the gap frequency of Nb, we have investigated the radiation power P of NbN-based flux-flow-type Josephson oscillators (FFO's). The designed and fabricated chip incorporates FFO's, SIS power detectors (DET's), and their coupling circuits. Both FFO's and DET's consist of epitaxial NbN/AlN/NbN junctions with high critical current density J/sub C/ (15 200 nW, enough for the optimum pumping of a SIS mixer with rf-resistance of 50 /spl Omega/, is coupled to DET's for 0.5-0.9 THz. The coupling bandwidth is larger than 20% of its central frequency. In the band, the radiation frequency is tuned by the control current through the FFO of 10-100 mA. The maximum coupling frequency of the present experiment is quantitatively agreed with the theoretical one. The peak power of 1.3 /spl mu/W is detected at 0.76 THz. The dissipated power in a FFO is smaller than 500 /spl mu/W, which is 10/sup -4/ times less than that of semiconductor sources. These results indicate the feasibility of NbN-based FFO's for a practical on-chip LO.

A novel approach, frequency-domain cascading microwave multiplexers (MW-Mux), has been proposed and its basic operation has been demonstrated to increase the number of pixels multiplexed in a readout line U of MW-Mux for superconducting detector arrays. This method is an alternative to the challenging development of wideband, large power, and spurious-free room-temperature (300 K) electronics. The readout system for U pixels consists of four main parts: (1) multiplexer chips connected in series those contain U superconducting resonators in total. (2) A cryogenic high-electron-mobility transistor amplifier (HEMT). (3) A 300 K microwave frequency comb generator based on N(≡U/M) parallel units of digital-to-analog converters (DAC). (4) N parallel units of 300 K analog-to-digital converters (ADC). Here, M is the number of tones each DAC produces and each ADC handles. The output signal of U detectors multiplexed at the cryogenic stage is transmitted through a cable to the room temperature and divided into N processors where each handles M pixels. Due to the reduction factor of 1/N, U is not anymore dominated by the 300 K electronics but can be increased up to the potential value determined by either the bandwidth or the spurious-free power of the HEMT. Based on experimental results on the prototype system with N = 2 and M = 3, neither excess inter-pixel crosstalk nor excess noise has been observed in comparison with conventional MW-Mux. This indicates that the frequency-domain cascading MW-Mux provides the full (100%) usage of the HEMT band by assigning N 300 K bands on the frequency axis without inter-band gaps.

Height of current steps I S in current–voltage characteristics and radiation power P are studied experimentally of flux-flow Josephson oscillators (FFOs) with 1 J CF 2 , where J CF is the critical current density of FFOs. It has been found I S , which is proportional to the generated power in the FFO, is almost proportional to J CF . In addition, P coupled to a superconductor–insulator–superconductor detector vertically stacked on the FFO increases with J CF , i.e. from P =6 nW for J CF =1 kA/cm 2 up to P =360 nW for J CF =12 kA/cm 2 . These experimental results suggest the advantage of high- J CF FFOs.

Optical conductivity spectra σ(ω)=σ1(ω)+iσ2(ω) of NbN1−xCx thin films have been measured in the far-infrared region at temperatures above and below Tc, and have been analyzed based on the Mattis–Bardeen theory. The results suggest that NbN1−xCx is a typical dirty-limit BCS-type superconductor in the strong-coupling regime. The value of the superconducting energy gap and the London penetration depth were estimated from optical results, which agree well with values reported previously and obtained from the electrical measurements.

The performance of a LiNbO/sub 3/ optical modulator employing superconducting electrodes as a transmission line for a traveling-wave signal has been studied theoretically as well as experimentally. In the case of velocity matching between signal and optical waves using a shielding plane on top of a coplanar waveguide, numerical calculations of the attenuation constants of both superconducting and normal-conducting transmission lines indicate that the performance of the optical modulator can be far superior to that using normal-metals with respect to the figure of merit of bandwidth/driving-voltage. Microwave operation of a velocity-matched traveling-wave-type optical modulator with superconductor electrodes (NbN) has been successfully demonstrated. In the frequency range between dc and 26.5 [GHz] it is shown that the obtained modulation depth is in good agreement with the theoretically expected one.

Overdamped NbC x N 1− x Josephson junctions have been fabricated using either sputter-deposited TiN x layers or MgO/TiN x bilayers as barriers. NbC x N 1− x /TiN x /NbC x N 1− x junctions with different TiN x thicknesses and resistivities show no hysteresis and yield low I c R N values. To improve the I c R N values of NbC x N 1− x /TiN x /NbC x N 1− x junctions, we have replaced the TiN x layers with MgO/TiN x bilayers and fabricated NbC x N 1− x /MgO/TiN x /NbC x N 1− x SINS Josephson junctions. The I c R N values estimated from the current–voltage ( I – V ) characteristics of the SINS junctions vary between 30 and 375 μ V at 4.2 K. By adequately adjusting the thicknesses of the MgO and TiN x layers, we have obtained overdamped SINS junctions with I c R N values as high as 160 μ V, much higher than that of a typical as-fabricated SNS junction. Our experimental results show that the optimum thickness of the TiN x barrier should be about 50 nm to ensure the overdamped I – V characteristics.

This paper presents the preparation process and the characteristics of titanium nitride films and nonhysteretic NbCxN1-x,/TiNx/NbCxN1-x SNS junctions using TiNx as the barrier material. Structural studies show that TiNx films prepared by rf sputtering at room temperature have a preferential orientation of TiN(111) phase, while those grown at higher substrate temperatures are (200)-oriented. Resistivilies of the TiNx films range from 4SμΩ·cm to 1lOμΩ·cm, depending on the values of N2 partial pressure. Polycrystalline NbCxN

Vertically stacked NbCN/MgO/NbCN Josephson junctions with thin intermediate electrodes (2 nm-11 nm) have been fabricated on a wafer in a computer-controlled sputtering. The tunneling characteristics of fabricated junctions have been evaluated as functions of the number of stacks and thickness of intermediate electrodes d. As a result, it has been found that the energy gap for intermediate electrodes reduced with d linearly depending on 1/d. The junction quality parameter R/sub SG//R/sub N/ gradually decreased with d.

A novel coupling configuration between an SIS mixer, an antenna, and a local oscillator has been numerically characterized for an integrated receiver operated in the sub-THz region. The configuration consists of two vertically stacked superconducting striplines, where the thickness of their common electrode t/sub 2/ is of the order of its magnetic penetration depth /spl lambda//sub 2/. It has been found that the coupling efficiency between the antenna and the mixer decreases with decrease of t/sub 2///spl lambda//sub 2/, while that between the mixer and the local oscillator has a local maximum. It is also shown that the coupling efficiencies increase with decrease of Q/sub A/, the Q-factor due to the tunneling loss in the mixer. For Q/sub A/=5.0 and 16, 75-85% of the available signal power and sufficient power from the local oscillator can be absorbed in the tunnel conductance of the mixer at 1 THz. This coupling efficiency is equal to or larger than that of a conventional planar coupler.

All-NbCN flux-flow oscillators (FFO) with tapered slotline antenna (TSA) were fabricated on MgO substrates. A five-step microstrip transformer was used to couple an FFO, which has a low impedance, to a TSA having a high impedance, The microstrip transformer is designed to have a return loss more than 20 dB at the center frequency. We have measured submillimeter wave radiation from the oscillators using an off-chip silicon-composite bolometer. Radiation from a fabricated FFO was detected in a bias voltage range from 1.18 mV to 1.48 mV, which corresponds to a frequency range from 570 GHz to 710 GHz. >

Epitaxial NbN and NbC/sub x/N/sub 1-x/ (x

We measured gas content in smoke simultaneously with a continuous-wave sub-terahertz (THz) spectrometer and Fourier transform infrared spectrometer. The consistency of both measurements shows the validity of the THz spectroscopy for the analysis of gaseous substances in smoke.

A remote gas sensor based on a continuous-wave sub-terahertz spectrometer with an operation bandwidth between 200 and 500 GHz has been developed. The performance of the developed system was investigated in a full-scale fire. The measured transmission spectra of smoke show the existence of hydrogen cyanide (HCN) and water molecules, which were generated due to the combustion of a foam urethane block. The HCN content estimated from the absorption intensity agrees quite well with that obtained from the chemical analysis of gases sampled from the fire site. These results demonstrate the potential of the developed sensing system as a remote toxic gas sensor at disaster sites.

Flux-flow-type Josephson oscillators consisting of epitaxial NbCN/MgO/NbCN junctions were fabricated and their current-voltage (I-V) characteristics were measured in various magnetic fields to evaluate their oscillation characteristics. On the I-V curve for a fabricated oscillator, clear current steps were observed up to 3 mV, indicating that oscillation occurs up to 1.4 THz. Using a theoretical model, available output power for the oscillator was calculated to be in the range from 20 mu W to 40 mu W in the frequency range from 500 GHz to 1.2 THz. >

We developed a frequency difference stabilizer for an optically synchronized dual-channel terahertz-signal generator. The stabilizer reduces the amplitude fluctuation in spectrometer signal, enabling us to instantaneously observe the spectra, whose absorption characteristics change rapidly with time.

A compact Programmable Josephson Voltage Standard (PJVS) system based on a cryocooler is under development at the National Institute of Advanced Industrial Science and Technology (AIST). The system uses a 2V NbN/TiN/NbN PJVS chip operating at 12K. Since the PJVS chip requires cooling power of less than 100mW, it is possible to use a compact-size cryocooler, which may be mounted inside a standard 19-inch rack-mount chassis. By combining the 2V PJVS chip with a high-precision semiconductor voltage multiplier circuit, it is possible to generate arbitrary voltages up to 20V.

We propose a high-sweeping-speed optically synchronized dual-channel terahertz (THz) signal generator for an active gas-sensing system with a superconductor-insulator-superconductor (SIS) mixer. The generator can sweep a frequency range from 200 to 500 GHz at a speed of 375 GHz/s and a frequency resolution of 500 MHz. With the developed gas-sensing system, a gas-absorption-line measurement was successfully carried out with N(2)O gas in that frequency range.