Tatsuya Zama

Titanium-based transition-edge photon number resolving detector with 98% detection efficiency with index-matched small-gap fiber coupling

We have realized a high-detection-efficiency photon number resolving detector at an operating wavelength of about 850 nm. The detector consists of a titanium superconducting transition edge sensor in an optical cavity, which is directly coupled to an optical fiber using an approximately 300-nm gap. The gap reduces the sensitive area and heat capacity of the device, leading to high photon number resolution of 0.42 eV without sacrificing detection efficiency or signal response speed. Wavelength dependent efficiency in fiber-coupled devices, which is due to optical interference between the fiber and the device, is also decreased to less than 1% in this configuration. The overall system detection efficiency is 98%±1% at wavelengths of around 850 nm, which is the highest value ever reported in this wavelength range.

Photon number resolving detection with high speed and high quantum efficiency

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.

Titanium Superconducting Photon-Number-Resolving Detector

High-efficiency photon-number-resolving detectors have been developed using titanium-based transition-edge sensors. Device performances have been evaluated with respect to the response photon distribution, dark count, and timing jitter. In the analysis of the photon statistics, the observed detection probabilities were consistent with Poisson distributions. From a comparison of the measured distribution with theory, 98% detection efficiency was deduced at 850 nm. The dark count probability of the device is less than 10-6, corresponding to a dark count rate of 0.6 Hz. The timing jitter is 25 ns, the best value ever reported (to our knowledge) in transition-edge sensors used for optical photon measurements.

UV DETECTOR CALIBRATION BASED ON ESR USING UNDULATOR RADIATION

Abstract Undulator radiation was used for detector calibration based on a room-temperature-operated electrical substitution radiometer (ESR) in the wavelength range from 200 to 400 nm. The intense radiation from an undulator was shown to be very suitable for use with a thermal detector such as an ESR which has low responsivity.

Improvement of the beamline for calibration of the transfer standard in the UV and VUV regions

The electron storage ring TERAS was used to calibrate the spectral radiance of transfer standard light sources in the ultraviolet (UV) and vacuum ultraviolet (VUV) regions. This calibration system, constructed at the beamline, is an improvement on a prototype system we constructed previously. The new system is simpler and does not require breaking the vacuum of the calibration system. Also, the signal from the transfer standard light source is strong, the conditions of the light sources (synchrotron radiation and transfer standard light source) can be observed directly (it is possible to evaluate the profiles or some parameters of light sources without breaking the vacuum), the polarimeter is improved and the uncertainty due to the polarization effect is expected to be improved. In addition to describing these improvements, we re-examine some uncertainties.

Spatially resolved study of superconducting tunnel junctions X-ray detectors by low temperature scanning synchrotron microscopy

A low temperature scanning synchrotron microscope (LTSSM) has been developed for spatial analysis of superconducting tunnel junction X-ray detectors. One and two-dimensional images of the detector response to X-rays were measured by scanning the junctions kept at a working temperature of about 0.4 K with a highly collimated synchrotron radiation beam. The collimation was performed by inserting a pinhole mounted on a scanning unit into the synchrotron radiation in the range of 3-6 keV. The spatial resolution of the LTSSM is between 5 and 10 micrometer. The present results indicate a large discrepancy between the experimental spatial response and a quasiparticle diffusion and edge-loss model. The LTSSM plays an important role in the development of cryogenic X-ray detectors.

IMPROVEMENT OF THE AGING CHARACTERISTICS OF DEUTERIUM LAMP

Abstract For an improvement of the aging characteristic of deuterium lamp, it was tried to exchange its regular window glass material(Type III silica glass) for other glass material(fluorine-doped silica glass). By using fluorine-doped silica glass as a new window material. The spectral irradiance of deuterium lamp was improved maximum 20% in comparison to those with TypeIII silica glass window after 402hours operation. This phenomenon is explained by difference of window material degradation. A cause of degradation is photoabsorption produced by defects which were made by photochemical reaction in the glass.

Realization of total spectral radiant flux scale at NMIJ with a goniophotometer/spectroradiometer

In response to the strong demand for a total spectral radiant flux (TSRF) standard from domestic lighting manufacturers, such a scale has been realized in the visible range by means of a relative gonio-spectroradiometric method at the National Metrology Institute of Japan (NMIJ). Our gonio-spectroradiometric method employs spectral irradiance as well as a luminous intensity standard as reference standards. We have investigated several models of quartz-halogen lamps from domestic manufacturers with respect to their stability and decided a set of reference standard lamps for TSRF. Our carefully selected quartz-halogen lamps have sufficient stability as the standard lamp for TSRF after a 100 h seasoning process. The relative expanded uncertainty (k = 2) for realization of the TSRF scale is between 3.1% (visible regions) and 4.1% (near ultraviolet region). We evaluated uncertainties related to the characteristics of the array spectroradiometer using experimental results and found some of those, such as effect of bandpass function, noticeably contributed to the total uncertainty.

Titanium TES based photon number resolving detectors with 1 MHz counting rate and 65% quantum efficiency

A transition edge sensor (TES) is one of superconducting photon detectors, which has a photon number resolving ability in light pulses. The TES device is a kind of calorimeters operated at an extremely low temperature, and the energy of the photons is measured as a resistance change in a superconducting transition region of the TES. The advantages of the TESs are an excellent energy resolution and a high quantum efficiency. However a response speed is limited due to slow thermal recovery time. To overcome this, we fabricated new TES devices which are based on a titanium superconductor. The critical temperature of our titanium films is around 410 mK, which greatly improves the thermal recovery time. The observed decay time constant of response signals to the light pulses is around several hundreds of ns, that make it possible to operate the devices at a counting rate over 1 MHz. The photon number resolving power is 0.35 eV(FWHM) for a 5 μm size device even at the high operating temperature. The system quantum efficiency is 65 % by embedding the TES films in an optical structure with a high reflection dielectric mirror and an anti-reflection coatings fabricated by an ion beam assisted sputtering method. These features are very promising for high speed photon number resolving applications in the quantum information field.

Beamline for calibration of transfer standard light sources in the UV and VUV regions

A beamline which serves for calibrating transfer standard light sources (deuterium lamps, excimer lamps, Xe lamps etc.) in the UV and VUV regions is being constructed. The synchrotron radiation from the electron storage ring TERAS (750 MeV) is used as a primary standard of spectral radiant intensity. In order to use synchrotron radiation as a primary standard, the electron beam and synchrotron radiation beam parameters need to be evaluated. Uncertainties of synchrotron radiation flux evaluated by measurements of the magnetic flux density, the position of the electron orbital plane, the electron beam size and the distance from the synchrotron radiation tangent point to the detector system are expected to be about 0.003, 0.01, 0.05 and 0.1%, respectively.