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Optical transition-edge sensors (TESs) have shown an energy resolution for resolving the number of incident photons at the telecommunication wavelength. However, a higher energy resolution is required for biological imaging and microscopic spectroscopy. In this study, we tested an Au/Ti (10/20 nm) bilayer TES that showed a high energy resolution. The high energy resolution was achieved by lowering the critical temperature T c to 115 mK, and the resultant energy resolution was 67 meV full width at half maximum (FWHM) at 0.8 eV. When T c was reduced to 115 mK, the theoretical resolution would scale up to 30 meV FWHM, considering that the typical energy resolution of optical TESs was 150 meV and T c was 300 mK. To investigate the difference between the theoretical expectation (30 meV) and the measured value (67 meV), we measured the complex impedance and current noise of the TES. We found excess Johnson noise in the TES; the excess Johnson noise term M was 1.5 at a bias point where the resistance was 10% of the normal resistance. For reference, the above mentioned TES was compared with a TES showing typical energy resolution (156 meV FWHM). We also discussed factors that improved or inhibited the energy resolution.

In the field of continuous-variable quantum information processing, non-Gaussian states with negative values of the Wigner function are crucial for the development of a fault-tolerant universal quantum computer. While several non-Gaussian states have been generated experimentally, none have been created using ultrashort optical wave packets, which are necessary for high-speed quantum computation, in the telecommunication wavelength band where mature optical communication technology is available. In this paper, we present the generation of non-Gaussian states on wave packets with a short 8-ps duration in the 1545.32 nm telecommunication wavelength band using photon subtraction up to three photons. We used a low-loss, quasi-single spatial mode waveguide optical parametric amplifier, a superconducting transition edge sensor, and a phase-locked pulsed homodyne measurement system to observe negative values of the Wigner function without loss correction up to three-photon subtraction. These results can be extended to the generation of more complicated non-Gaussian states and are a key technology in the pursuit of high-speed optical quantum computation., 14 pages, 5 figures

In this work, we remove the timing jitter of the photon-number-resolving detector which limited non-Gaussian state preparation using a continuous-wave light source, and generate a Schrödinger cat state with Wigner negativity.

A superconducting transition edge sensor (TES) is an energy-dispersive single-photon detector that distinguishes the wavelength of each incident photon from visible to near-infrared (NIR) without using spectral dispersive elements. Here, we introduce an application of the TES technique for confocal laser scanning microscopy (CLSM) as proof of our concept of ultra-sensitive and wide-band wavelength range color imaging for biological samples. As a reference sample for wide-band observation, a fixed fluorescence-labeled cell sample stained with three different color dyes was observed using our TES-based CLSM method. The three different dyes were simultaneously excited by irradiating 405 and 488 nm lasers, which were coupled using an optical fiber combiner. Even when irradiated at low powers of 80 and 120 nW with the 405 and 488 nm lasers respectively, emission signals were spectrally detected by the TES and categorized into four wavelength bands: up to 500 nm (blue), from 500 to 600 nm (green), from 600 to 800 nm (red), and from 800 to 1,200 nm (NIR). Using a single scan, an RGB color image and an NIR image of the fluorescent cell sample were successfully captured with tens of photon signals in a 40 ms exposure time for each pixel. This result demonstrates that TES is a useful wide-band spectral photon detector in the field of life sciences.

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.

We developed a Ti/Au bilayer optical superconducting transition edge sensor (TES) laying on an optical fiber self-aligned structure. The bilayer approach enables us to control the superconducting transition temperature T C , which results in 8-μm-square-sized TES with T C as high as 314.0 mK. Moreover, the TES device is micro-machined so that it can be easily assembled with an optical fiber via a self-aligned method. Our TES device achieved a system photon detection efficiency (PDE) of 83.6% at 940 nm with an energy resolution of 0.21 eV. Electrical and effective time constants (rise time and decay time) were as short as 74 and 75 ns, respectively. We also theoretically analyzed the imperfect system PDE. According to this analysis, the imperfection originated mainly from misalignment between the TES and the optical fiber, and the system PDE will be increased up to >95% by use of an optical fiber with a smaller mode field diameter.

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.

Optical transition-edge sensors (TESs) that can resolve the energy of a single photon have been proven useful in quantum information and biology. TESs can provide spectra ranging from near-infrared to visible regions and have the potential to reveal new phenomena in biology. In this paper, we have investigated the responses of TESs to photons at near-infrared and visible wavelengths, from 450 to 1000 nm in 10-nm increments using a supercontinuum laser and a tunable bandpass filter, which converted the multichromatic light source into monochromatic light. The system detection efficiency of an optical TES optimized for photon detection at 950 nm was nearly 100% at some wavelengths and was more than 10% for the overall bandwidth. We found that the detector responses strongly depended on the wavelengths. A spectrum of the filtered light at shorter wavelengths was more likely to show a second peak with energy lower than that of the primary peak.

Fluorescence color imaging at an extremely low excitation intensity was performed using an optical transition edge sensor (TES) embedded in a confocal microscope for the first time. Optical TES has the ability to resolve incident single photon energy; therefore, the wavelength of each photon can be measured without spectroscopic elements such as diffraction gratings. As target objects, animal cells labeled with two fluorescent dyes were irradiated with an excitation laser at an intensity below $$1\,\upmu \hbox {W}$$ . In our confocal system, an optical fiber-coupled TES device is used to detect photons instead of the pinhole and photomultiplier tube used in typical confocal microscopes. Photons emitted from the dyes were collected by the objective lens, and sent to the optical TES via the fiber. The TES measures the wavelength of each photon arriving in an exposure time of 70 ms, and a fluorescent photon spectrum is constructed. This measurement is repeated by scanning the target sample, and finally a two-dimensional RGB-color image is obtained. The obtained image showed that the photons emitted from the dyes of mitochondria and cytoskeletons were clearly resolved at a detection intensity level of tens of photons. TES exhibits ideal performance as a photon detector with a low dark count rate ( $$

Optical transition edge sensors (TESs) are characterized by a very fast response, of the order of $$\upmu $$ s, which is $$10^3$$ times faster than TESs for X-ray and gamma-ray. To extract important parameters associated with the optical TES, complex impedances at high frequencies (> 1 MHz) need to be measured, where the parasitic impedance in the circuit and reflections of electrical signals due to discontinuities in the characteristic impedance of the readout circuits become significant. This prevents the measurements of the current sensitivity $$\beta $$ , which can be extracted from the complex impedance. In usual setups, it is hard to build a circuit model taking into account the parasitic impedances and reflections. In this study, we present an alternative method to estimate a transfer function without investigating the details of the entire circuit. Based on this method, the complex impedance up to 30 MHz was measured. The parameters were extracted from the impedance and were compared with other measurements. Using these parameters, we calculated the theoretical limit on an energy resolution and compared it with the measured energy resolution. In this paper, the reasons for the deviation of the measured value from theoretically predicted values will be discussed.

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.

Quantum walks (QWs) simulate particle behaviors in the quantum mechanical regime, which exhibit time evolutions completely different from the classical (probabilistic) random works [1]. QWs offer quantum physical simulations and the novel approach to build quantum computers. Currently on-chip photonic devices implementing QWs have been intensively developed. QW photonic chips were realized using photonic circuits based on silica (SiO 2 ) waveguide platforms [1,2]. Here, we demonstrate a QW chip based on the other waveguide platform, namely the long-range surface plasmon polariton (LR-SPP) waveguide [3]. The LR-SPP waveguide allows a single-polarization mode, and has relatively low optical losses. Moreover, the LR-SPP waveguide platform will realize two-dimensional waveguide lattice structures with a high reliability. Thus, the LR-SPP waveguide is the potential platform to construct large-scale and high-dimension QW simulators.

We experimentally studied a continuous time evolution of a “plasmonic” walker in a 1-dimensional lattice structure based on long-range surface plasmon polariton waveguides. The plasmonic walker exhibited a typical time evolution of a 1-dimensional quantum walk, which indicates that the plasmonic system is a potential platform to construct quantum walk simulators. By comparing experimental results to numerical simulations, the fidelity of the plasmonic quantum walk simulator is estimated to be > 0.96, which demonstrates that the plasmonic system can be a feasible platform for large-scale and high dimensional quantum walk simulators.

Optical transition edge sensors (TESs) which can resolve an energy of a single photon have proven desirable in quantum information and biology. TESs can provide spectra ranging from near-infrared to visible regions, and have the potential to reveal new phenomena in biology. To obtain reliable spectra, wavelength dependence of the system detection efficiency should be calibrated. The dependence is due to a cavity structure of the detector, consisting of an anti-reflection coating and a mirror. We will present a calibration using a supercontinuum laser and acousto-optic tunable filters (AOTF).

Highly oriented crystalline Ga 2 O 3 thin films were fabricated at room temperature (RT) by excimer laser annealing. Amorphous Ga 2 O 3 thin films were grown on α -Al 2 O 3 (0001) substrates at RT by the pulsed laser deposition method using a focused KrF excimer laser and a sintered β -Ga 2 O 3 target. Amorphous precursor films were irradiated by a non-focused KrF excimer laser (100–250 mJ/cm 2 ) at RT. The results of x-ray and reflection high-energy electron diffraction measurements indicated that highly (101)-oriented crystalline β -Ga 2 O 3 thin films were obtained after RT laser annealing. The optical bandgaps of the crystalline thin films were approximately 4.7–4.9 eV, as determined from the UV/Vis transmittance. The film surfaces after laser annealing revealed slight planar grain growth, indicating a high degree of crystallinity and showed the root mean square roughnesses of 0.28–0.48 nm.

Broadband low reflectance materials have various applications in the field of optical energy management; however, materials with ultra-low reflectance (below 0.1%) have been considered as mechanically delicate. We have developed a novel hard-surface optical absorber with microstructured, diamond-like carbon coated ion tracks on CR-39 plastic substrate. The spectral reflectance of the first prototype was below 2% for wavelengths ranging from 400 nm to 1400 nm; moreover, the optical absorber had mechanically hard surface and exhibited temporal durability. Choosing the appropriate design of the surface structure and coating layer is likely to reduce the reflectance to the order of 0.1%. This technique yields easy-to-handle broadband ultra-low reflectance absorbers.

The chromatic group velocity dispersion tolerance of a fiber-optic two-photon interferometer is characterized for telecom-band photon pairs that are frequency entangled. Two indium–gallium–arsenide single-photon detectors are used to record the coincidence counts. A single-wavelength laser diode continuously pumps a periodically poled lithium niobate waveguide of 1-mm length. For near-degenerate spontaneous parametric downconversion, it generates wideband entangled collinear photon pairs. The spectral width of 115.8 nm is centered at 1550 nm. It is restricted by the performance of the single-photon detectors whose efficiency is poor beyond 1610 nm. Using a Michelson interferometer, two-photon interference signals are recorded with and without frequency entanglement. The frequency-entangled photon pairs are found to exhibit dispersion-tolerant two-photon interference, even though the two paths through the interferometer have different group velocity dispersion. The observed two-photon interference signal has a correlation time of 42.7 fs, in good agreement with calculations for a 115.8-nm spectral width. For comparison, results are also presented for photon pairs lacking frequency entanglement.

High-order dispersion of long-range surface-plasmon-polariton waveguides (LR-SPP-WGs) have been investigated using a two-photon interferometer. Since linear and even-ordered dispersions in two-photon interferometry are cancelled out by a nonlocal quantum correlation, odd-ordered dispersions of millimeter-long LR-SPP-WGs are revealed. Even under the highly dispersive condition, the indistinguishability between two photons emerged from LR-SPP-WGs was well preserved. In addition, we demonstrated a strong polarization-selection by the LR-SPP-WGs that leads to the polarization-stable and high-fidelity quantum interference.

Optical transition edge sensor (TES) detectors that can resolve the energy of a single optical photon have proven to be desirable in multicolor fluorescence microscopy. Here, detectors with a higher energy resolution can distinguish dyes having similar or closer emission wavelengths, thus enabling the observation of multiple kinds of dyes simultaneously. To improve energy resolution, it is necessary to know how different the measured energy resolution is from the limit determined by the temperature sensitivity αI and current sensitivity βI, as extracted from the complex impedance. Due to the very fast response of an optical TES (the time constant is shorter than 1 µs), the complex impedance must be measured up to frequencies larger than 10 MHz. However, at high frequencies, the parasitic impedance in the circuit and reflections of electrical signals caused by discontinuities in the characteristic impedance of the readout circuits become significant. To reduce these effects, twisted pair cables are replaced with coaxial ones in this work; thus, a cleaner transfer function of the readout at high frequencies is obtained. The measured impedance of the studied TES is consistent with that given by the single-block model.

We demonstrate a telecom-band fiber-optic two-photon Michelson interferometer using near-degenerate and collinear photon pairs with frequency entanglement. For spontaneous parametric down-conversion (SPDC), a continuous-wave laser diode pumps a periodically poled lithium niobate waveguide. Two threshold single-photon detectors record coincidence counts to observe two-photon interference and evaluate the correlation function. Multi-pair emission events are inevitable in SPDC and photon pairs without frequency entanglement are unintentionally registered as coincidence counts. In the demonstrated experiment, a mixture of photon pairs with and without frequency entanglement is present. The effects of such a mixed state on the correlation function are experimentally investigated. Two-photon interference of photon pairs without frequency entanglement is also measured for comparison.

Classical correlation can be locked via quantum means--quantum data locking. With a short secret key, one can lock an exponentially large amount of information, in order to make it inaccessible to unauthorized users without the key. Quantum data locking presents a resource-efficient alternative to one-time pad encryption which requires a key no shorter than the message. We report experimental demonstrations of quantum data locking scheme originally proposed by DiVincenzo et al. [Phys. Rev. Lett. 92, 067902 (2004)] and a loss-tolerant scheme developed by Fawzi, Hayde, and Sen [J. ACM. 60, 44 (2013)]. We observe that the unlocked amount of information is larger than the key size in both experiments, exhibiting strong violation of the incremental proportionality property of classical information theory. As an application example, we show the successful transmission of a photo over a lossy channel with quantum data (un)locking and error correction.

Quantum state tomography (QST) is widely used to evaluate entanglement generated by spontaneous parametric down-conversion. Two-fold coincidence counts for 16 different configurations have been measured using single-photon detectors to estimate the fidelity (i.e., the probability overlap between ideal and real states) from the reconstructed density matrix. However, multi-pair emission events degrade the fidelity. Here, we numerically analyze pulse-pumped polarization-entangled photon pairs for single-photon detectors that can or cannot count the number of incident photons to estimate the fidelity given by QST. Threshold single-photon detectors are desirable for QST from a practical point of view. Our analysis suggests that using four threshold single-photon detectors for two-fold coincidence measurements offers almost the same fidelity as that given by four photon-number-resolving single-photon detectors. The fidelity estimated by QST becomes poor and loss independent when two threshold single-photon detectors are used.

Spontaneous parametric downconversion (SPDC) is widely used to generate entangled photon pairs; however, multi-pair emissions degrade the quality of the entanglement. We numerically evaluate polarization-entangled photon pairs created by SPDC. The effects of multi-pair emission events on the visibility of two-photon interference and on the fidelity (the probability overlap for ideal and real states) are analyzed using single-photon detectors that can count the number of incoming photons and discard multiphoton events. Compared with conventional threshold single-photon detectors, photon-number resolving single-photon detectors have higher fidelity for the same or lower visibility.

A thin-gold-film-covered titanium transition edge sensor is newly developed for highly reliable optical photon detection. The aim of the gold film is to prevent a formation of a surface oxidation layer (typically 2.8 nm) on titanium that causes severe degradation of the titanium superconductivity. Optical properties for the gold-covered titanium TES embedded in an optical cavity are calculated, and we find that the maximum absorptance and absorption bandwidth will be reduced with increasing a thickness of the gold film. However, more than 99% absorptance can be possible for the gold (10 nm in thickness) and titanium (30 nm) if 11 dielectric layers are used in an anti-reflection coating. A depth profile of a chemical state for the fabricated device was analysed by an X-ray photoelectron spectroscopy. The profile shows no evidence of TiO2 existence in photoelectron spectrum. Superconducting critical temperature covered with the 10 nm gold were in the range of 200 mK to 320 mK depending on the titanium thickness of 18 nm to 26 nm.

This study discusses wavelength dependence of non-linearity of optical fibre power meters (OFPMs). The non-linearity for several kinds of OFPMs was measured at various wavelengths used in optical communication to determine its wavelength dependence. The response of OFPMs was intrinsically linear and the linearity seemed to be wavelength independent for a certain wavelength range that probably meets the conditions that almost all electron-hole pairs generated by incident light reach the space-charge region of a photodiode and contribute to photocurrent. This suggests that linearity calibration at a single or a few wavelength(s) would be sufficient to derive the linearity at arbitrary wavelength around the calibration point(s). The non-linearity of OFPMs appeared when carrier recombination is not negligible during carrier diffusion into the space-charge region, and it was probably wavelength dependent, as it can be described theoretically. It was also found that using a modulated test light source revealed whether the non-linearity measured for a continuous wave (CW) source is an intrinsic one (because of supraresponsivity, photodiode saturation) or range discontinuity.

We have implemented non-Gaussian operation in pulsed squeezed vacuum at a telecommunications wavelength. A one- or two-photon-subtracted squeezed state was generated using a titanium superconducting transition-edge sensor to resolve the incident photon number. We observed dips in the reconstructed Wigner functions of the generated quantum states, which provides clear evidence that non-Gaussian operation has been realized.

Photon number resolving detectors based on titanium-transition edge sensors with high speed and high quantum efficiency have been developed for quantum sensors in the fields of quantum information and quantum radiometry. The two devices optimized at wavelengths of interest showed 81% and 64% system detection efficiencies at 850 nm and 1550 nm, respectively. The response speed of the device optimized for a high counting operation is 190 ns, which corresponds to a counting rate over 1 MHz.

We have developed new photon number resolving detectors with titanium transition edge sensors (Ti-TESs) for a high counting rate operation in quantum information. The titanium superconducting films were fabricated by ultra-high vacuum electron beam evaporation, and showed a sharp superconducting transition at 359 mK. The device was coupled to a single mode optical fiber, and cooled down to 100 mK. Some of optical responses of the devices were measured by illuminating heavily attenuated laser pulses at wavelengths of 405 and 1550 nm. As a result, the device showed a fast decay time constant of 300 ns, which enables the operation at the counting rate of 400 kcps. The energy resolution was 0.76 eV at 405 nm and 0.68 eV at 1.5 µm, that make it possible to clearly resolve the number of photons of incident laser pulses. These features of the high counting rate operation and the reasonable energy resolution are very promising for quantum information field.

We have developed a TES optical photon detector with a titanium superconducting film showing a very fast response with rise time and fall times of 30 ns and 313 ns, respectively. The fast response is promising for many quantum measurement applications. Increasing the quantum efficiency of this device from the current value of ∼20% makes the detector even more suitable for these applications. Here we report on simulation and experimental results of a cavity designed to improve optical photon absorption of titanium.

A model describing spectral supralinearity for a silicon photodiode in the near-infrared region is presented. This theoretical model is based on the internal quantum efficiency model of the photodiode using Shockley-Read-Hall recombination, which depends on the inner structure parameters of the photodiodes. Comparing the experimental results with the theoretical calculation results, the model enables us to quantitatively predict the starting power level, shape, and wavelength dependence of the supralinearity for a silicon photodiode. This model contributes to high-accuracy measurements over wide optical power ranges and various incident wavelengths.

The calibration of a quantum channel, i.e. the determination of the transmission losses affecting it, is definitely one of the principal objectives in both the quantum communication and quantum metrology frameworks. Another task of the utmost relevance is the identification, e.g. by extracting its photon number distribution, of the noise potentially present in the channel. Here we present a protocol, based on the response of a photon-number-resolving detector at different quantum efficiencies, able to accomplish both of these tasks at once, providing with a single measurement an estimate of the transmission losses as well as the photon statistics of the noise present in the exploited quantum channel. We show and discuss the experimental results obtained in the practical implementation of such protocol, with different kinds and levels of noise., 6 pages, 4 figures

Transition edge sensor microcalorimeters can be used in many optical quantum measurements because of its low dark counts, high quantum efficiency, and high resolving power of a photon number in weak light pulses. In order to increase count rates up to a few MHz, we have developed a titanium transition edge sensor for the optical measurements, and its performances were analysed. Titanium is one of the ideal superconductor because of its higher transition temperature and lower optical reflectance at 1.5 wavelength. Our titanium film was fabricated with electron-beam evaporation, and showed high residual resistance ratio of 3.5. The sharp superconducting transition also was found at 359 mK, which is close to the critical temperature in bulk. The fabricated device showed a fast response to pulsed laser illumination of 1.5 wavelength with the fall time constant of 300 ns. These features are very promising for high-speed single photon detection in many quantum optical measurements.

We are developing a cryogenic radiometer (CR) with a superconducting thermometer for the optical laser power calibration. This device consists of a niobium transition edge sensor and an electrical substitution heater on a silicon substrate. The device temperature is locked at the niobium transition temperature with a superconducting quantum interference device amplifier and a proportional-integral-derivative controller. The device successfully determines the absolute optical power in the range from 20 nW to 600 muW, with a fast response of 3 s. The equivalence measurement shows that the response difference between the substitution power and the simulated optical power is less than 0.0034%. These properties are very attractive for next generation of a high-accuracy CR

We are developing high energy resolution X-ray microcalorimeters based on iridium and gold (Ir/Au) phase transition thermometers. Here we analyze the signal behavior of a 200×200 µm2 Ir/Au transition edge sensor (TES) with iridium and gold having the thicknesses of 100 and 25 nm, respectively. The energy resolution of this device was 15.4 eV full width at half maximum (FWHM) at 5.9 keV X-ray energy. For operation at bias resistances lower than 140 mΩ, we observed two distinct decay components, a slow component followed by a very fast component, which is thought to be due to the variation of current distribution inside the TES. However, taking into consideration the nonlinearity associated with the slow component, a very fast signal response makes the operation of this device promising at low-resistance bias points.

We have developed a new cryogenic radiometer for determining absolute power. This instrument is composed of a superconducting transition edge sensor as a thermometer, a silicon substrate as a heat absorber, and a SQUID amplifier as a readout. The input power is measured with electrical substitution of a heater on the device. By using very sharp transition of the thermometer, the device temperature is locked within its transition temperature. This device demonstrated very wide dynamic range of more than 105, very low noise equivalent power of 1.5 nW. These properties are very attractive to be used as highly precise power measurement instruments in metrological fields.

In recent years, cryogenic microcalorimeters using their superconducting transition edge have been under development for possible applications in the research for astronomical X-ray observations. To improve the energy resolution of superconducting transition edge sensors (TES), several correction methods have been developed. Among them, a clustering method has been recently proposed in terms of a digital signal processing. In this paper, we applied the clustering method to Ir/Au bilayer TES. This method resulted in almost 10% improvement in the energy resolution. On the other hand, from the point of view of imaging X-ray spectroscopy, we applied the clustering method to pixellated Ir/Au-TES devices. We will show the clustering method which sorts signals by their shapes is also useful for a position resolution.

A multi-pixel TES array is one of the attractive methods to read-out the incident x-ray position, which simplifies a read-out circuit for imaging applications. We fabricated a ten-pixel Ir/Au TES microcalorimeter with asymmetrical slits parallel to the electric current, and analyzed its noise and signal characteristics. The device was successfully operated in a strong electro-thermal feedback (ETF) mode. However, very large excess noise is observed, which cannot be explained by the noise theory for a single pixel TES. We have modeled the multi-pixel TES array as separated thermal group components, and analyzed noise performance theoretically. As a result, the current noise in our theory is well agreed with the measured noise at a low frequency below 3 kHz. From the x-ray irradiation measurements, ten divided signal groups are observed, which will be associated with the incident x-ray position pixel. The best energy resolution was 18 eV (FWHM) for 5.9 keV x-rays at 0.5 /spl mu/V bias voltage.

Conventional MicroStrip Gas Chambers (MSGCs) have encountered many difficulties such as limited gas gain, spark-induced damage, etc. We have proposed a new multi-grid-type MSGC (M-MSGC) to overcome some of these difficulties. Additional grid strips are inserted between the anode and the cathode in this new design. Gaps between these strips are chosen to be as small as 10 μm where one can expect an efficient removal of the surface charge. However, additional electrodes also screen all the electric field of the upper part of the substrate and we cannot observe induced signals from the backside of the substrate. To overcome the difficulty, floating pads are placed close to the cathode strip on the surface of the M-MSGC, and the induced charges are read out through these pads. If the area of pads is sufficiently large and the positive charges are moving toward the pads, the backside electrodes can sense the induced charge. Although the induced charge is spread out over several rear strips, position sensing along the anode strips has been achieved. Another approach is considered to use only the front electrodes. A test plate has shown a position resolution of 1.3 mm for the axis along the anode strip.

The superconducting-transition-edge temperature sensors (TES) for calorimeters operate in an intermediate state within normal-superconducting transition. The spatial profiles of a response to an x-ray microbeam exhibit that normal-superconducting phase separation occurs in an iridium TES with electrothermal feedback, as has been observed in many current-carrying conductors with self-heating. The resistive domain (normal region) in the 500 /spl mu/m-square TES grows as applied bias voltage increases. This observation agrees reasonably well with a one-dimensional model of the self-heating. On the other hand, two-dimensional features are explained by nonuniform supercurrent distribution in the superconducting domain. These findings are important for developing detectors with a large detection area for energy dispersive x-ray spectroscopy.

We are developing a new x-ray microcalorimeter based on superconducting transition edge sensors (TES) as an imaging sensor. This device has ten pixelated transition edge sensors with Iridium superconductive films. When a constant bias voltage is applied to all pixels, each pixel is operated at slightly different equilibrium temperature. This arises from the different thermal responses between pixels, so that response signal shapes would vary according to the position of the incident x-ray. We have fabricated a prototype of the pixelated array and examined its performance. The position dependency measurements by scanning the collimated x-ray over the device have successfully shown that the device is able to resolve its pixel position. The energy resolution of a test device was 13.1 eV (FWHM) for 3 keV x-rays.

We are developing an X-ray microcalorimeter with high energy resolution and position sensitivity by using an Iridium transition edge sensor. The Ir-TES with a new pixel-type geometry has ten small pixel TES array. Each pixel size is 80 μm ×200 μm . This device has shown a good energy resolution of 26 eV (FWHM) at 5.9 keV . Furthermore, the Ir-TES film was scanned along each pixel by a collimated X-ray microbeam and signal pulses were measured at each incident position. The pulse height and rise time map has shown ten different regions where pulses are concentrated which correspond to each pixel. This might be useful for an imaging TES array.

CdZnTe (CZT) detectors are promising detectors, which have many good characteristics such as room temperature operation, reasonable energy resolution, high-detection efficiency to gamma rays, etc. However, energy resolution of CZT is governed by poor mobilities of charge carriers. Many researchers have tried to solve this problem. Among them, a clustering method has been recently proposed which is based on a digital signal processing of preamplifier output waveforms. In this method, we can classify signals according to their shapes and independently treat different shapes. In this paper, we report a new clustering algorithm with adaptive shaping time. The obtained energy resolution for /sup 137/Cs was improved to 5.4-keV full width at half maximum (FWHM) by applying this method.

A new multi-grid-type MSGC (M-MSGC) has been designed and fabricated. This new MSGC has very narrow gaps between neighboring electrodes which can considerably reduce a surface charge effect. Several types of test detectors have been fabricated and the maximum gas gain was found to be beyond 10 4 for a 10 μm gap M-MSGC. The observed amplitude of the cathode signal was almost the same as the anode signal. This MSGC can be a promizing detector for the field, where both the high gain and the stable operation are required.

The response non-uniformities of laser beam profiling cameras were investigated experimentally at near-infrared laser wavelengths. A uniform-irradiance light source with near-infrared laser wavelengths, and also a visible wavelength as comparison, was constructed for testing several different commercially available beam profiling cameras. The response signals of all charge-coupled device (CCD)-type sensors showed a strong dependence on the irradiant wavelength. The pixel-to-pixel non-uniformity of CCDs at 1064 nm increased rapidly with the reduction of exposure time, whereas that of CMOS sensors was maintained independently of these parameters. The characteristics of CCDs were discussed in terms of charge leakage effect, which is a likely source of these phenomena.