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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.

GroundBIRD is a ground-based experiment for the precise observation of the polarization of the cosmic microwave background (CMB). To achieve high sensitivity at large angular scale, we adopt three features in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID) and cold optics. The rotation scanning strategy has the advantage to suppress $1/f$ noise. It also provides a large sky coverage of 40\%, which corresponds to the large angular scales of $l \sim 6$. This allows us to constrain the tensor-to-scalar ratio by using low $l$ B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 144 GHz and 23 are for 220 GHz. This array is currently under development and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment., 7 pages, 5 figures, LTD18 proceeding, Published in JLTP

Millimeter (MM) and Terahertz (THz) waves are transparent to many non-metallic materials and is expected to be applicable for non-destructive inspections. Especially, the radar 3D imaging technology using the semiconductor continuous wave (CW) MMW and THz sources is important because of its compactness, stability and high signal-to-noise ratio (SNR). In this presentation, we will introduce the development of a prototype of a 300 GHz walk-through body scanner for the security gates. For the actual system, we are developing the frequency-modulated continuous wave (FMCW) imaging method around 300 GHz. We have demonstrated the 3-dimentional real-time imaging of a material hidden underneath cloths. We will demonstrate the system configuration and the current status as well as some results of the actual imaging.

The capability for actual measurements—not just simulations—of the dynamical behavior of THz electromagnetic waves, including interactions with prevalent 3D objects, has become increasingly important not only for developments of various THz devices, but also for reliable evaluation of electromagnetic compatibility. We have obtained real-time visualizations of the spatial evolution of THz electromagnetic waves interacting with a single metal micro-helix. After the micro-helix is stimulated by a broadband pico-second pulse of THz electromagnetic waves, two types of anisotropic re-emissions can occur following overall inductive current oscillations in the micro-helix. They propagate in orthogonally crossed directions with different THz frequency spectra. This unique radiative feature can be very useful for the development of a smart antenna with broadband multiplexing/demultiplexing ability and directional adaptivity. In this way, we have demonstrated that our advanced measurement techniques can lead to the development of novel functional THz devices., 微小金属らせんとテラヘルツ光との相互作用を可視化 --次世代超高速移動通信などにおける高性能アンテナへ応用--. 京都大学プレスリリース. 2021-02-09.

The influence of the terahertz (THz) radiation for deep tissues has been neglected due to its strong absorption by water molecules on the surface of the skin. In this report, we found for the first time the demolishing effect of the THz pulsed radiation on actin filaments located in aqueous solution with a few millimeters in depth. This result demonstrates that the THz photon energy propagates in water with several millimeters in depth, possibly as shockwave, and affected actin filaments. Thus, it is implicated that THz waves have the potential to manipulate functions of proteins and cells in deep tissues.

With the dramatic development of source and detector components, terahertz (THz) spectroscopy technology has recently shown a renaissance in various fields such as medical, material, biosensing and pharmaceutical industry. As a rapid and noninvasive technology, it has been extensively exploited to evaluate food quality and ensure food safety. In this review, the principles and processes of THz spectroscopy are first discussed. The current state-of-the-art applications of THz and imaging technologies focused on foodstuffs are then discussed. The advantages and challenges are also covered. This review offers detailed information for recent efforts dedicated to THz for monitoring the quality and safety of various food commodities and the feasibility of its widespread application. THz technology, as an emerging and unique method, is potentially applied for detecting food processing and maintaining quality and safety.

Arbitrary control of high-power THz polarization and frequency is studied by the numerical calculation based on the coupled wave approach. THz wave generation using organic crystals via optical rectification provides high conversion efficiency. To overcome the limitation of the generated THz field direction which comes from their optical anisotropy, we propose the synthesis of THz wave generated from two crystals whose optical axis are orthogonal each other. By the calculation, the linearly and circularly polarized THz wave generation by changing the time delay of two pump pulses is demonstrated.

Micro helical antennas whose resonance correspond to THz frequency region can be fabricated from biological algae spirulina via electroless metal coating. Radiation characteristics of the micro helical antenna are investigated by using THz near-field microscope. Both normal and end-fire mode radiations with different frequency characteristics can be successfully observed in real time.

We present a depth super-resolved 3D imaging method for inspection of defects in walls using terahertz swept-source optical coherence tomography. A depth profile analysis based on an annihilating filter method with noise reduction was applied for signal processing, and the results were compared with those of conventional inverse fast Fourier transform (IFFT) analysis. To evaluate the depth resolution, we measured a plastic step sample with 1 mm thickness, and its front and back surfaces were discriminated. This is corresponding to about 1/3 of the theoretical depth resolution of the conventional IFFT analysis. Moreover, we demonstrated 3D imaging of the void with a 10 mm width behind a ceramic tile and succeeded in reconstructing a significantly sharper cross-sectional void image than in the conventional analysis.

A microwave kinetic inductance detector (MKID) is a cutting-edge superconducting detector, and its principle is based on a superconducting resonator circuit. The superconducting transition temperature (Tc) of the MKID is an important parameter because various MKID characterization parameters depend on it. In this paper, we propose a method to measure the Tc of the MKID by changing the applied power of the readout microwaves. A small fraction of the readout power is deposited in the MKID, and the number of quasiparticles in the MKID increases with this power. Furthermore, the quasiparticle lifetime decreases with the number of quasiparticles. Therefore, we can measure the relation between the quasiparticle lifetime and the detector response by rapidly varying the readout power. From this relation, we estimate the intrinsic quasiparticle lifetime. This lifetime is theoretically modeled by Tc, the physical temperature of the MKID device, and other known parameters. We obtain Tc by comparing the measured lifetime with that acquired using the theoretical model. Using an MKID fabricated with aluminum, we demonstrate this method at a 0.3 K operation. The results are consistent with those obtained by Tc measured by monitoring the transmittance of the readout microwaves with the variation in the device temperature. The method proposed in this paper is applicable to other types, such as a hybrid-type MKID., Comment: 4 pages, 5 figures

We proposed a highly sensitive transillumination imaging method with THz CW sources based on the heterodyne detection. The method was applied to tomosynthesis imaging of a 5-mm-thick wooden board to reproduce the depth information.

Superconducting detectors are a modern technology applied in various fields. The microwave kinetic inductance detector (MKID) is one of cutting-edge superconducting detector. It is based on the principle of a superconducting resonator circuit. A radiation entering the MKID breaks the Cooper pairs in the superconducting resonator, and the intensity of the radiation is detected as a variation of the resonant condition. Therefore, calibration of the detector responsivity, i.e., the variation of the resonant phase with respect to the number of Cooper-pair breaks (quasiparticles), is important. We propose a method for responsivity calibration. Microwaves used for the detector readout locally raise the temperature in each resonator, which increases the number of quasiparticles. Since the magnitude of the temperature rise depends on the power of readout microwaves, the number of quasiparticles also depends on the power of microwaves. By changing the power of the readout microwaves, we simultaneously measure the phase difference and lifetime of quasiparticles. We calculate the number of quasiparticles from the measured lifetime and by using a theoretical formula. This measurement yields a relation between the phase response as a function of the number of quasiparticles. We demonstrate this responsivity calibration using the MKID maintained at 285mK. We also confirm consistency between the results obtained using this method and conventional calibration methods in terms of the accuracy., Comment: 4 pages, 4 figures

We construct a terahertz swept source optical coherence tomography system using a continuous-wave diode multiplier source in the 600-GHz band for defect inspection in multilayer objects and evaluate its performance. Using this system, we image a multilayer plastic sample to demonstrate the effectiveness of nondestructive three-dimensional imaging. To enhance the depth resolution, we apply an annihilating filter to the analysis and confirm that two surfaces of a 1-mm-thick plastic plate can be resolved. In addition, the repeatability of measured thicknesses is 0.22 mm. These values are approximately one-half and one-tenth of the resolution achievable by conventional Fourier analysis, respectively.

We constructed two types of compact terahertz three-dimensional (3D) imaging systems for practical imaging applications such as the inspection of defects In building walls and infrastructures: a swept source optical coherence tomography (SS-OCT) system, and a phase-shifting interferometry (PSI) system. Experiments using physical phantoms showed the depth resolutions of SS-OCT and PSI were 6 mm and $\mathbf{5} \ \boldsymbol\mu \mathbf{m}$ , respectively. We also imaged a 3D plastic sample using the SS-OCT system to demonstrate the effectiveness of non-invasive 3D imaging.

High-power terahertz pulse generation and its polarization and frequency control by optical rectification with nonlinear organic crystals were studied. Terahertz pulses up to 730 nJ/pulse was generated from a DAST crystal pumped by 250 $\mu \mathbf{J}$ femotosecond laser pulses with a central wavelength of 1500 nm. The terahertz peak electric field is estimated as 860 kV/cm if we focus the terahertz beam to $\phi = 300\mu \mathrm{m}$ spot, which is expected to nonlinear material control application. We proposed the high-power terahertz polarization pulse shaping using the double stacked nonlinear organic crystals excited with tailored pump pulses. Through the terahertz modulation of pump pulses, the waveform shaping of the high-power terahertz pulses are expected, which leads to selective excitation of molecules or spin waves.

The cosmic microwave background (CMB) radiation is an afterglow of the Big Bang. It contains the crucial keys to understand the beginning of the universe. In particular, the odd-parity patterns of CMB polarization, B-modes, at more than degree-scale, are the best probe to detect primordial gravitational waves at the cosmic inflation. The GroundBIRD experiment aims to detect this large angular scale patterns from the ground. The experiment employs novel techniques; a high-speed rotational scanning system (20 revolution-per-minutes) with cold optics below 4K, and microwave kinetic inductance detectors (MKIDs) as the focal plane detectors. The fast scanning modulation is a crucial characteristic in our observation strategy to mitigate effects of the atmospheric fluctuation. The telescope rotates and scans the sky along the azimuth at the elevation angle of 60 degrees at Teide observatory in the Canary Islands. It allows us to measure CMB polarization patterns at a wide multipole range, 6 < \ell < 300, i.e. aiming to catch the reionization bump. We have developed a telescope mount with 3-axis rotation mechanism (azimuth, elevation, and boresight). We are evaluating the vibration at the focal plane position with rotating the telescope mount. The focal plane consists of seven hexagonal corrugated horn coupled MKIDs array: six hexagon units are for 145 GHz band (55 pixels/unit), and one unit is for 220 GHz band (112 pixels). Each pixel consists of a corrugated horn, a planner OMT, millimeter wave circuits for transmission of dual-polarization signals with the suppression of crosstalk modes, and two MKIDs for each polarization. Magnetic shields are also mounted so as to suppress the external magnetic fields. Trapped magnetic fields inside of the superconducting materials decrease the performance of the MKID. The geomagnetism is the static and large magnetic fields. The telescope motion makes modulation of the geomagnetism as well as the modulation of CMB signals. Therefore, we need careful evaluation associating with the telescope rotation. By using a small evaluation system with modulated magnetic fields, we understand impacts the magnetic shield as well as responses of the MKID for the modulated magnetic field. We design the shield based on them. In this presentation, we will report an evaluation of detector responses on the high-speed rotating system along the azimuth. We will also show demonstrations of our own readout electronics which is well matching with the rapid scan modulation strategy.

A stilbazolium material comprising 4-dimethylamino-N′-methyl-4′-stilbazolium tosylate (DAST), which has a large nonlinear optical susceptibility, was studied for application in terahertz (THz)-wave generation. The temperature-dependent structure of the DAST crystal was measured by using powder X-ray diffraction from −100 to 200 °C, indicating a volume expansion of 4.6 %. The lattice constants show anisotropic thermal expansion. Also, the temperature dependence of THz absorption spectra was measured by terahertz time-domain spectroscopy (THz-TDS) in the temperature range varying from −80 to 88.1 °C. A strong absorption peak was found at around 1 THz, shifting slightly toward a lower frequency with increasing temperature. The temperature dependence of the THz spectra was compared with that of X-ray diffraction. The shifting of THz-vibrational frequencies of the DAST crystal suggests that the change in its lattice structure is temperature dependent.

The relatively low energy of the terahertz light (THz, 1 THz = 4.14 meV) promises the non-invasive optical imaging of the biomedical objects. However, the THz light inherently suffers the optical diffraction limit and the subwavelength microstructures cannot be resolved. We propose the planar hybrid-lens comprising the multiple slits and the two-dimensional rod array for the subwavelength focusing of the THz light beyond the diffraction limit. The hybrid-lens is investigated by the finite difference time domain simulation (FDTD). The spectra of the rod array obtained by FDTD are compared with the spectra calculated by the analytical model. The subwavelength focal spot about 20 µm (λ/7.5) at the frequency 2 THz is demonstrated by FDTD. The array of the subwavelength focal spots on the opposite side of the multiple slits are generated by the interferences of the Floquet-Bloch waves which can be guided through the rod array. The hybrid-lens can function as the subwavelength focusing and the substrate simultaneously which may serve as the new tool in the high-speed imaging and sensing of the subwavelength biomedical objects by using the THz light.

Microwave kinetic inductance detectors (MKIDs) are promising for THz direct detector arrays of large size, particularly with simple frequency-division multiplexing. Purple Mountain Observatory is developing a terahertz superconducting imaging array (TeSIA) for the DATE5 telescope to be constructed at Dome A, Antarctica. Here we report on the development of a prototype array for the TeSIA, namely an $$8\times 8$$ CPW MKID array at 0.35 THz. The resonance frequencies of the MKIDs span the 4–5.575 GHz band with an interval of 25 MHz. Each detector is integrated with a twin-slot antenna centered at 0.5 THz and with a relative bandwidth of 10 %, while the whole MKID array with a micro-lens array. Detailed design and measurement results will be presented.

We investigated the relationship between loaded quality factor (QL) and responsivity of microwave kinetic inductance detectors (MKIDs) using a dual-function spiral strip (DFSS). Three types of DFSSs with different QL values were designed, and the S 21 properties were simulated when kinetic inductance of a superconductor was changed by using a 2.5-dimentional simulator. The simulated results showed that a very high Q L value was not necessarily required. The resonator frequencies of the 25-MKID array using a better type of DFSS (Q L ~ 3500) were adjusted to be separated by 5 MHz around 2.0 GHz. The 25-MKID array were fabricated using 20-nm thick niobium nitride films deposited on r-plane sapphire substrates. We clearly observed 25 half-wavelength resonances around 2.0 GHz at 2.245 K. The optical responses were also confirmed using hot and cold radiation. The dependence of the responsivity on the Q L indicated that the Q L value of approximately 2000 could obtain higher responsivity.

We propose a novel computed tomography (CT) imaging method based on phase-contrast using a continuous wave (CW) THz source with a frequency of 0.54 THz. The system acquires phase-shift by phase modulation technique using Mach-Zehnder interferometer at each data point, and collects projections of the phase-shift from multiple directions over 360 degrees to finally reconstruct a spatial distribution of refractive index. We construct a preliminary system for proof of the concept, and perform an imaging experiment using a polystyrene foam phantom. It was shown that the THz-CT produces an artifact-free and quantitative reconstruction at a spatial resolution of a few mm.

著者人数: 152名（所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 長谷部, 孝; 堂谷, 忠靖; 羽澄, 昌史; 今田, 大皓; 満田, 和久; 坂井, 真一郎; 関本, 裕太郎; Tomida, T.; 辻本, 匡弘; Yamamoto, R.; 山崎, 典子), Accepted: 2018-04-07, 資料番号: SA1180209000

The applicability of a blackbody source to sensitivity measurements and calibration of an uncooled Terahertz (THz) focal plane array (FPA) is discussed, but the combination of a blackbody source and a band-pass filter may not be suitable for these purposes. Two ways to measure the minimum detectable power (MDP) of uncooled THz-FPAs are described and compared when used with strong THz sources such as a quantum cascade laser (QCL). The MDP is defined as the radiant power that produces a signal-to-noise ratio of unity in the output of a THz imager that uses a THz-FPA operating at a TV frame rate. One method (method 1) is based on the hypothesis that the beam pattern of the THz source is close to a Gaussian pattern. In another method (method 2), the signal level of the background in an image that does not contain a THz source is subtracted from the signal of the image. While method 2 is more flexible, how large the signals coming from THz source should be, as compared with the noise level, remains to be defined. Finally, based on issues with the current non-uniformity correction (NUC) technique, specifications are proposed for THz source power and wobbling technique to obtain uniform illumination for an ideal NUC technique.

We have designed and fabricated a hard X-ray and gamma-ray TES spectrometer for nuclear materials analysis. A superconducting tin (Sn) absorber is coupled to the TES film by using a gold (Au) bump post to improve the thermal contact between the absorber and the TES. To obtain a sufficient detection efficiency at the high energy photons near 100 keV, an 8-pixel array of TES microcalorimeters were developed. In this new device, the epoxy glue which is used to connect the absorber and the gold bump post was well controlled and hence the slow component of the decay time constant was improved from 7.82 ms to 4.46 ms compared to our old device. The energy resolution was 131 eV FWHM at 59.5 keV gamma rays, which is better than the limit of HPGe detectors (400 eV FWHM at 60 keV).

We present a review of a pioneering database on terahertz spectroscopy established by the National Institute of Information and Communication Technology and RIKEN. The database is universally available on the World Wide Web via the Internet since 2008 and was recently restructured on the basis of contemporary HTML5 technology. Flexibility and convenience to browse spectroscopic data are much improved. In the database, no less than 1500 spectroscopic data have been consolidated and provided for various materials under different conditions. Furthermore, a data upload system from general users has been prepared to enrich the database further.

Superconducting transition edge sensors (TES) are used for high-resolution X-ray spectroscopy. In our group, we developed an Ir-TES and reported an energy resolution of 6.9 eV FWHM at 5.9 keV ( Kunieda et al., 2004 ). In this study, we have designed a new TES detector using a superconducting tin (Sn) absorber to detect high energy photons over 100 keV. The Sn absorber is coupled to an Ir/Au superconducting film which is deposited on an ultra-thin SiN membrane (500 nm thick) with a small amount of epoxy post (Stycast 2850FT) by handling with a flip-chip bonding machine. The measured energy resolution is 485 eV FWHM at 60 keV and is better than that of HPGe detector.

Hot carrier dynamics in single-layered doped graphene after the photo-excitation has been studied by ultra-broadband optical-pump/THz-probe spectroscopy (OPTP). We successfully determined the frequency-dependent carrier scattering rate Γ(ω) and Drude weight D(o) of photo-excited graphene from 1 to 8 THz. The Γ(ω) shows a strong frequency dependence and the reduction of the averaged D(o) cannot be explained by the simple carrier temperature model previously reported [1], indicating the many body effects should be taken into account for the hot carrier dynamics in single-layered graphene.

In this presentation, we succeed in altering polymer morphology using terahertz (THz) wave irradiation. Pulsed THz waves generated by a free electron laser (FEL) were irradiated to a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization. Morphological observation shows the formation of micrometer-sized crystals via the THz wave irradiation. Further, a 10–20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra.

Polarized patterns in the cosmic microwave background (CMB) radiation contains rich knowledge for early stage of the universe. In particular their odd-parity patterns at large angular scale (> 1°), primordial B-modes, are smoking-gun evidence for the cosmic inflation. The GroundBIRD experiment aims to detect these B-modes with a ground-based apparatus that includes several novel devices: a high-speed rotational scan system, cold optics, and microwave kinetic inductance detectors (MKIDs). We plan to start observations in the Canary Islands in 2017. In this paper, we present the status of the development of our instruments. We established an environment that allows operation of our MKIDs in an optical configuration, in which the MKIDs observe radiations from the outside of the telescope aperture. We have also constructed MKID prototypes, and we are testing them in the optical configuration.

We present quasi-analytical solutions (QANS) of hybrid platform (HP) comprising metallic grating (MG) and stacked dielectric layers for terahertz (THz) radiation. The QANS are validated by finite difference time domain simulation. It is found that the Wood’s anomalies induce the high-order spoof surface plasmon resonances in the HP. The QANS are applied to optimize a new perfect absorber for THz sensing of large-area thin film with an ultrahigh figure of merit reaching a fifth order of magnitude for the film thickness 0.0001p (p:MG period). The first-order Wood’s anomaly of the insulator layer and the Fabry–Perot resonance in the slit’s cavity account for the resonance of the perfect absorber. The QANS and the new perfect absorber may lead to a highly sensitive and practical nano-film refractive index sensor for THz radiation.

The satellite LiteBIRD (Light satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection) is being designed to detect the B-mode polarization of the cosmic microwave background radiation. LiteBIRD will carry about 2,000 detectors for measurements in five bands (60, 80, 100, 150, and 220 GHz). Microwave kinetic inductance detectors (MKIDs) that can be multiplexed in a single readout line are suitable for the large focal plane detector array. We develop an MKID readout system for LiteBIRD to monitor the amplitude, phase, and resonant frequency of each MKID resonator simultaneously and follow movements of the resonant frequency caused by changes in the input radiation intensity. This mechanism enables us to have a larger dynamic range for the MKIDs, compared with a system that monitors the amplitude and phase on the resonant frequency. We also propose an MKID having a half-wavelength resonator. This MKID transmits the resonant microwave signal from one feedline to another. It can offer clear microwaves passing through the resonators, even if the coupling and internal quality factors are mismatched. With this MKID, our readout system can track resonance frequency changes much more easily. We present the status of the readout system development and demonstrate the performance with the half-wavelength MKID.

Spirulina-templated metal μ coils (STMμC) are interesting materials for a wide range of terahertz (THz) applications due to their distinctive interactions with THz-light. We measured inclusive Mueller matrices of randomly distributed and one-dimensional (1D) STMμC-embedded paraffin sheets using Stokes polarimetry at 1.6 THz, where strong optical activity has already been reported. We demonstrated that the one-dimensional STMμC paraffin sheet can simultaneously express five polarization effects including linear-birefringence, linear-dichroism, circular-birefringence, circular-dichroism, and depolarization. Hence, STMμC can potentially be utilized for the control of various polarization phenomena of THz-light.

We have investigated the characteristics of a terahertz (THz) beam steering method based on a combination of difference-frequency generation (DFG) with the principle of the phased array antenna. In the DFG of THz radiation from a nonlinear optical crystal pumped by optical beams, the phase front of the THz radiation is indirectly tilted by adjusting the relative incidence angle between the pump beams to the crystal. A magnification of the steering angle with a factor of 193 is demonstrated as the most important effect provided by the method. The effect allows the use of a high-speed optical deflector for adjusting the incidence angle, accelerating the steering more than a hundred times compared with mechanical methods. The phase mismatching between the THz radiation and the pump beams as well as the refraction at the crystal surface limit the steering angle of the THz radiation to 56°, full width at half maximum.

X-rays were measured using quantum superconducting series-junction detectors that consist of an Si substrate and four arrays of superconducting tunnel junctions on the substrate. The detectors are not calorimeters but quantum detectors even though they are making use of phonons; therefore, the detectors can be larger and faster than micro-calorimeters. Superconducting tunnel junctions with thinner tunnel barriers and a new arrangement contributed in obtaining higher energy resolutions than before. The full rise-time of signal outputs from charge-sensitive preamplifiers, i.e., charge collection time of the detector, was approximately 5 μs. A peak-to-background ratio of 8000 and an energy resolution of 70 eV were obtained for 5.9 keV X-rays. The energy resolution is about two times better than those of semiconductor detectors. These results suggest that the superconducting series-junction detectors can be practical high resolution detectors for X-rays.

Carbon dioxide ( CO 2 ) induced pressure broadening coefficients of water vapor ( H 2 O ) lines have been determined using a terahertz time-domain spectrometer (TDS). Thirty-two rotational transitions of H 2 O were observed in the spectral range of 18– 102 cm - 1 (550–3050 GHz) for the first time. Using TDS allows one to measure absorption spectra with one order of magnitude better precision than Fourier transform spectrometer in this frequency region. The precision of our broadening coefficient measurements was 2.4% in average. The measured CO 2 induced pressure broadening coefficients are compared to those calculated by the complex Robert–Bonamy formalism. The difference between the measurement and the theoretical estimation was in the range of - 10.7 % to + 19.0 % confirming the credibility of the theoretical approach. The impact on retrieval of water vapor abundance was examined by performing inversion analysis on H 2 O spectra of Venus atmosphere obtained with the Submillimeter Wave Astronomy Satellite. In this example case, the retrieved water vapor mixing ratio reduces by half at the altitude region of 70–85 km when applying the newly measured broadening coefficient compared to the air-broadening coefficient, and changes by 5% compared to that estimated by the complex Robert–Bonamy formalism.

We have proposed and developed a novel technique for a non-contact inspection of defective interconnections in an LSI chip using a laser terahertz emission microscope (LTEM). The LTEM measures the THz emission images of an LSI chip by scanning it with fs laser pulses. When a fs laser pulse irradiates a p–n junction in an LSI chip, transient photocurrent flows into interconnections resulting in the emission of the THz pulse into free space. We investigated the characteristics of the THz emissions from simple test element group samples which consist of p–n junctions connected to metal lines. It was found that the metallic lines connected to photo-excited p–n junctions worked as THz emission antennae which enhance the emission efficiency of THz pulses near their resonant frequencies corresponding to the line lengths. This result indicates that THz emission signals from p–n junctions in circuits strongly depend on the structure of the interconnections. We show the successful results on the inspection of defective interconnections in MOSFET devices and C7552 ISCAS’85 benchmark circuits using LTEM. By comparing the THz emission images between a normal circuit and a defective one, it is possible to identify the p–n junctions connected to the defective interconnections without electrical contacts.

We propose a new structure of a TES and a series connection of radiation absorber, which can stabilize the absorber temperature through a negative feedback process in the absorber. We consider that this structure of the self-heating absorber might allow TES to improve detection efficiency with large effective area and high count rate by the cooling power inside the absorber. The 150 mum times 150 mum gold film absorber and the 25 mum times 25 mum heat sensor made by Iridium/Gold bi-layer superconductor which has a Tc of 110 mK are biased in series. In this device the gold film absorber generates the self Joule heating to a certain extent to maintain the temperature of the TES pixel. By the photon incidence to the gold film absorber, thermalization of the heat sensor induces the large current reduction, then the current through the gold film absorber also reduces, therefore the gold film absorber is expected to be cooled rapidly by the reduction of joule heating power. This TES pixel achieves the energy resolution of 34 eV (FWHM) @ 5.9 keV and the time decay constant of 150 mus. Furthermore, we tried to perform the experiment of X-ray fluorescence analysis in the SPring-8 synchrotron facility. This TES pixel succeeded to resolve into the energy peaks derived from the material elements which contained in a stainless steel sample.

The pressure broadening parameters g N2 and g O2 of pure rotational transitions of water vapor with nitrogen and oxygen as foreign gases, respectively, were measured with a terahertz time-domain spectrometer (THz-TDS) in the frequency region from 0.5 to 3.5 THz. A White-type multi-pass cell was introduced in the THz-TDS system to precisely measure the absorption spectra of water vapor. The parameters of 36 lines were determined for both N2 and O2, of which 25 parameters for gN2 and 28 parameters for gO2 were the first laboratory experimental data. The quantum number dependence of the parameters was experimentally observed for the first time due to the good signal-to-noise ratio of this system compared with the conventional Fourier transform infrared spectrometer (FT-IR) experiments. r 2008 Elsevier Ltd. All rights reserved.

Accepted: 2007-10-05, 資料番号: SA1000685000

A gas sensing technique on a fire site was developed. An output of is-TPG in a necessary low frequency for gas sensing controlled was obtained by optimizing the seeder so far. A reflection spectrum of an architectural material that used N2O gas that was the model gas of CO gas generated at a fire was successfully obtained, and a realizability of remote spectrum sensing in the THz range was showed experimentally. An attenuation rate of the THz-wave when the long distance was propagated under the atmospheric pressure was measured experimentally, and an error margin with the calculation was within 10 %. A calculation result was able to endure practical use in the THz range to which the accuracy of the calculation was doubted.

The air induced broadening coefficients of the pure rotational transitions of H 2 O at 556.936 GHz ( 1 10 ← 1 01 ) , and 752.033 GHz ( 2 11 ← 2 02 ) were measured by terahertz time-domain spectroscopy. The air broadening coefficient was determined to be 4.012 ( 30 ) MHz Torr - 1 for the 556.936 GHz line and 3.964 ( 40 ) MHz Torr - 1 for the 752.033 GHz line, respectively. The present broadening coefficients for the 556.936 GHz water line are significantly smaller than those of Markov and Krupnov [Measurements of the pressure shift of the 1(10)–1(01) water line at 556.936 GHz produced by mixtures of gases. J Mol Spect 1995:172;211–4] but relatively close to the values of the HITRAN database. The measured data may improve the accuracy of the abundance of water vapor retrieved from spectra obtained by the Odin/SMR satellite instrument. The effect on the satellite retrieval processing is discussed.

A series of experiments in the field of THz-wave spectroscopy is described. The measurement of absorption spectra of solid samples, powders, and liquids is demonstrated using various optical setups. One of the sources we used is a widely tunable coherent THz-wave generator relying on an optical parametric process: nanosecond Q-switched Nd : YAG laser light scattering from the polariton mode of a MgO-doped LiNbO3 crystal. For the measurement of the absorption of THz waves in liquids, a train of waves is allowed to oscillate inside a silicon prism. A liquid placed on a total internal reflection surface lowers the quality factor of the resonator, which allows determining the complex refraction index of the sample by frequency scanning. We have also developed a technique for THz chemical imaging, by introducing the component spatial pattern analysis. The spatial distribution of the chemicals, such as illicit drugs concealed in an envelope, is obtained from terahertz multispectral transillumination images and absorption spectra. To compensate for the low imaging speed, a prescreening step is proposed, by first detecting the presence of powders in the envelopes, which is achieved by measuring in real time the amount of scattering produced by the envelopes. Details and examples are provided.

We present a method of detecting production faults in flexible plastic packages using terahertz (THz) radiation. A focused THz beam is scanned along the sealed area of a package, and the transmitted signal is collected. Defect detection is effected through the large difference between the absorption coefficients of plastic and water for water-filled channel defects, and on the refraction index difference between plastic and air for air-filled channel defects owing to reduction of the incident signals into the detector. Compared to previous methods, such as visual and ultrasound inspection, our technique can be applied to optically opaque packages and does not require immersion in a matching liquid. The method was tested on fabricated 10∼100-μm diameter water-filled and air-filled channel defects imbedded in polyethylene films. The detection limit (the minimum size of a detectable defect), which depends on the conveying speed, was determined and analyzed. The results show that our system has potential for application in actual-production, real-time, inspection.

We have been developing terahertz (THz) wave detectors using superconducting tunnel junctions (STJs). The STJs consist of the Nb/Al/AlOx/Al/Nb structure. We fabricated THz-wave detectors on LiNbO3 substrates that have a high absorption coefficient for the frequency range of 1012 Hz. Two kinds of signals were detected when the THz-wave was irradiated from the substrate side. One was an indirect signal related to the generation of phonons. The other was a signal that corresponds to directly generated quasi-particles in the Nb electrode of the STJ. The pulse height of the indirect signal was larger than that of the latter signal. To enlarge the detector area, we designed a STJ that has different areas of the base electrode and top electrode. In this paper, the characteristics of the THz-wave detector area will be discussed.2007 Elsevier B.V. All rights reserved.