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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

For high-energy particle detection at temperatures above 1 K, we investigated two superconducting films: niobium (Nb) and a high-temperature superconductor, namely $${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$$ (YBCO). Lumped element kinetic inductance detectors (LeKID) were fabricated using both the superconducting films. The alpha line (5.49 MeV emitted by Am-241) was irradiated from the top side of the devices. We observed only a very rapid signal from the YBCO-based LeKID, which cannot be attributed to a quasiparticle response because it is much faster than the resonator ring time ($$\sim 1\,{\upmu }$$s). Although the quality factor and noise level of the YBCO-based device were comparable to those of the Nb-base LeKID, the signal was suppressed because of the large gap energy and short quasiparticle lifetime. The performance of the Nb-based LeKID was consistent with expectations: The energy resolution was 17, and the decay time was approximately 1 $${\upmu }$$s. We distinguished between direct absorption events and phonon-mediated events.

We treat prospects for multimessenger astronomy with giant flares (GFs), a rare transient event featured by magnetars that can be as luminous as a hundred of the brightest supernovae ever observed. The beamed photons could correlate with an axion counterpart via resonant conversion in the magnetosphere. In a realistic parameter space, we find that the sensitivity limit to galactic GFs for currently viable experiments is $\mathrm{g}_{\phi \gamma}\!\gtrsim\!\mathrm{several}\!\times\!10^{-13}$ GeV$^{-1}$ \& $\mathrm{g}_{\phi e}\!\gtrsim\!\mathrm{few}\!\times\!10^{-12}$. We rule out the compatibility of axion flares with the recent XENON1T excess only due to the time persistence of the signal., Comment: 7 pages, 3 figures

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.

We have prepared superconducting resonators using high-quality Nb thin films with $RRR = 48$ and studied their resonance characteristics in detail. It was observed that the measured internal quality factor $Q_i$ reached as high as $4\times 10^7$ , which might be the highest value obtained among the Nb thin film superconducting resonators ever reported. It is demonstrated that the temperature dependence of the internal quality factors can be well explained by considering the temperature dependence of the residual resistance due to phonon scattering, electron–electron scattering, and the Kondo effect of the residual quasiparticle in addition to the extended Mattis–Bardeen theory. It is also found that the change of the resonance frequency of the Nb thin film resonator with respect to temperature can be well explained by considering the temperature dependence of both the Kondo effect and the kinetic inductance of the residual quasiparticles. These results strongly indicate that a finite number of quasiparticles are present in the superconducting gap of the high-quality Nb film even at a sufficiently low temperature of $T/T_c and form a Fermi liquid state.

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.

We compute the expected sensitivity on measurements of optical depth to reionization for a ground-based experiment at Teide Observatory. We simulate polarized partial sky maps for the GroundBIRD experiment at the frequencies 145 and 220 GHz. We perform fits for the simulated maps with our pixel-based likelihood to extract the optical depth to reionization. The noise levels of polarization maps are estimated as 110 $\mu\mathrm{K~arcmin}$ and 780 $ \mu\mathrm{K~arcmin}$ for 145 and 220 GHz, respectively, by assuming a three-year observing campaign and sky coverages of 0.537 for 145 GHz and 0.462 for 220 GHz. Our sensitivities for the optical depth to reionization are found to be $\sigma_\tau$=0.030 with the simulated GroundBIRD maps, and $\sigma_\tau$=0.012 by combining with the simulated QUIJOTE maps at 11, 13, 17, 19, 30, and 40 GHz., Comment: 14 pages, 6 figures, 4 tables, submitted to ApJ

In this article we treat the non-adiabatic photon-to-axion resonant conversion of curvature radiation, synchrotron emission and inverse Compton scattering dominating the spectral density function of pulsars. First, we introduce emission models and benchmark observational data.vWe adopt a state-of-the-art density profile that relieves tension with the quantum electrodynamics vacuum polarization effect in highly magnetic stars, leading to efficient mixing. Then, we estimate the dark matter flux induced by photon-axion oscillation across the light cylinder of the neutron star. We find that pulsars might produce axion overdensities many orders of magnitude over the occupation number of dark matter in the Galactic halo within a broad parameter space. We point out possible new methods for axion detection derived from these results and other future lines of work., Comment: 15pp., 4 figs; as accepted for publication in JCAP

GroundBIRD is a millimeter-wave telescope to observe the polarization patterns of the cosmic microwave background (CMB). The target science topics are primordial gravitational waves from cosmic inflation and reionization optical depth. Therefore, this telescope is designed to achieve the highest sensitivity at large angular scales, e = 6 - 300. For wide sky observations (~40% full-sky), scanning at a high rotation speed (120°/s) is important to remove atmospheric fluctuations. Microwave kinetic inductance detector (MKID) is utilized with the fast GroundBIRD rotation since its good time response. We have started the commissioning run at the Teide Observatory in the Canary Islands. We report the performance of the telescope, receiver, and data acquisition system, including cooling achievements, observations of astronomical objects, and observations taken during several days ahead of our main survey observations.

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.

Heavy ion cancer therapy allows the tumors to destroy while sparing surrounding, healthy tissues. By controlling the incident energy of heavy ions, the penetration depth can be adjusted precisely to the tumor area. The ionizing chambers are usually used for the determination of absorbed dose in the heavy ion irradiation fields; however, uncertainty in measurement of these detectors is expected to remain by more than 5%, and this has a negative influence on the therapeutic effect. Now we began to develop the precision heavy ion beam detector applying the superconducting transition-edge sensor (TES). Using the Ir/Au-TES coupled to a tin absorber, we have succeeded to detect the helium ions which were injected from Heavy Ion Medical Accelerator in Chiba. Although pulses are fully saturated because the temperature change is beyond the transition region, the signal length reflects the incident energy of each injected heavy ion. These results indicate the possibility of the precision heavy ion energy detection applying the TES detector.

Poly (ethylene-vinylalcohol) copolymer (EVOH) films under different humidity conditions were studied by THz absorption spectroscopy to obtain information about the bound water. An intermolecular stretching mode of bound water was observed at around 6 THz, similar to that in liquid water; and the very weak libration mode indicates that this water is frozen. By generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation 2D moving window (PCMW2D) correlation spectroscopy, the bound water was categorized into three types: frozen with amorphous structure (I), liquid-like with librational motion (II), and nearest neighboring water with weaker hydrogen bonding network (III). The strongly inhomogeneous intermolecular stretching band of water I shows that the frozen bound water is amorphous. The frequency shift of this band in water III indicates a weaker hydrogen bonding network around the ethylene group. Changes in the films' oxygen permeability are discussed and correlated with the dynamics of bound water.

The spectra change of sausage hog and sheep casings before and after casing modification in the terahertz range were obtained using a terahertz time-domain spectroscopy (THz-TDS) system. Casings were modified by a surfactant solution (composed of soy lecithin and soy oil) and lactic acid, and the water content, swelling ratio and thickness of original and modified casings were determined. THz absorbance spectra of casings were acquired by THz-TDS in the range of 0.5–3.5 THz in attenuated total reflectance (ATR) mode. The absorbances of terahertz spectra for modified hog and sheep casings were greatly higher than that without modification. The THz spectra changes of casings were monitored by THz-TDS using the shift time between low and high frequencies in the ATR system. The drying time under nitrogen gas at 20 L/min flow rate was 31.62 min for natural hog casing. The results demonstrate the potential of THz-TDS to determine aforementioned parameters of original and modified casings as well as other foodstuffs during drying process.

Terahertz (THz) spectroscopy was used to observe adsorbed water structure and dynamics within polymer films, ultimately providing a strong rationale for the observed rates of water desorption. The THz absorption spectra of nylon-6 films undergoes drastic changes during the hydration and drying process. Additionally, the structural change from g to a crystals, induced by the hydration, was observed by the characteristic band of a-nylon-6 at 6.5 THz. Importantly, the THz spectra of adsorbed water, as well as deuterated water, within in the nylon films were observed by the continuous measurement of a-nylon during dehydration. The differential spectra clearly show three absorption bands of water molecules named Peak I, II and III, which behaved differently between the H2O and D2O materials. The spectra were assigned using a combination of ab initio molecular dynamics simulations and solid-state density functional theory calculations, and were compared to previous spectral assignments of bulk water. The results show that the inclusion of H2O and D2O into polymer films results in a distinct set of spectral features that, while similar in frequencies to the dynamics of bulk water, represent significantly different motions owing to the unique chemical environment within the material. These results highlight the significant utility of using THz spectroscopy to study the hydration dynamics and spectral signature of bound water in this important class of materials.

Ultra-broadband THz conductivities of doped monolayer graphene on PET substrate after photo-excitation at various optical pump fluence are investigated. THz conductivity corresponds to the intra-band transition of hot carriers decreases and deviates from the Drude-type frequency dependence as the pump fluence increases, indicating the broader carrier-energy distribution and energy dependent scattering. However, we found that the semi-classical Boltzmann transport theory with dominant carrier scattering mechanisms such as charged impurity and intrinsic optical phonon scattering with e-ph coupling strength from Density functional theory within GGA approximation failed to explain the hot carrier temperature dependence of THz conductivity spectra. This result suggests that the underestimation of e-ph coupling by DFT calculation and the importance of e-e interaction on the e-ph coupling.

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.

Terahertz (THz) absorption spectra of the cross-linked polyurethane films are observed at the temperature between 30–180 °C. The obtained spectra show characteristic absorption band at 3 THz assigned as hydrogen bonded urethane group. Another band at 7 THz was assigned as intermolecular vibration of cross-linked structures between polymer chains. The temperature dependent spectra were analyzed by the perturbation correlation moving window two-dimensional spectroscopy (PCMW2D) to clarify the slight spectral change. The thermal behavior of the absorption intensities shows the dynamics of hydrogen bonds and cross-linked structures in the polyurethane films.

Calorimetric and terahertz-far-infrared (THz-FIR) spectroscopic and infrared (IR) spectroscopic measurements were conducted for [Li+@C60](PF6-) at temperatures between 1.8 and 395 K. [Li+@C60](PF6-) underwent a structural phase transition at around 360 K accompanied by the orientational order-disorder transition of Li+@C60 and PF6-. The transition occurred in a step-wise manner. The total transition entropy (ΔtrsS) of 40.1 ± 0.4 J K-1 mol-1 was smaller than that of the orientational order-disorder transition in a pristine C60 crystal (ΔtrsS = 45.4 ± 0.5 J K-1 mol-1). Thus, the orientational disorder of Li+@C60 in the high-temperature phase of [Li+@C60](PF6-) was much less excited than that of the pristine C60 owing to the Coulombic interactions, which stabilized the ionic crystal lattice of [Li+@C60](PF6-). At T100 K, upon cooling, Li+ ions were trapped in two pockets on the inner surface of C60, and no phase transition was observed. Finally, the Li+ ions achieved a complete order at 24 K through antiferroelectric transition. The ΔtrsS value of 4.6 ± 0.4 J K-1 mol-1 was slightly smaller than R ln 2 = 5.76 J K-1 mol-1 expected for the two-site order-disorder transition. The extent of the Li+ motion in the C60 cage was related to the selection rule in the THz-FIR and IR spectroscopy of the C60 internal vibrations, because a C60 cage should be polarized by the Li+ ion. It is shown that the local symmetry of the caged molecule can be modified by the rotational or hopping motion of the encaged ions.

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 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.

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.

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): 羽澄, 昌史; 堂谷, 忠靖; 長谷部, 孝; 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: 2019-01-18, 資料番号: SA1180402000

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.