Hisanori Suzuki

Hyper Suprime-Cam

Hyper Suprime-Cam (HSC) is an 870 Mega pixel prime focus camera for the 8.2 m Subaru telescope. The wide field corrector delivers sharp image of 0.25 arc-sec FWHM in r-band over the entire 1.5 degree (in diameter) field of view. The collimation of the camera with respect to the optical axis of the primary mirror is realized by hexapod actuators whose mechanical accuracy is few microns. As a result, we expect to have seeing limited image most of the time. Expected median seeing is 0.67 arc-sec FWHM in i-band. The sensor is a p-ch fully depleted CCD of 200 micron thickness (2048 x 4096 15 μm square pixel) and we employ 116 of them to pave the 50 cm focal plane. Minimum interval between exposures is roughly 30 seconds including reading out arrays, transferring data to the control computer and saving them to the hard drive. HSC uniquely features the combination of large primary mirror, wide field of view, sharp image and high sensitivity especially in red. This enables accurate shape measurement of faint galaxies which is critical for planned weak lensing survey to probe the nature of dark energy. The system is being assembled now and will see the first light in August 2012.

Characterization of the Advanced Satellite for Cosmology and Astrophysics x-ray telescope: preflight calibration and ray tracing

The x-ray properties of multinested thin-foil mirror x-ray telescopes (XRTs) on board ASCA, the Advanced Satellite for Cosmology and Astrophysics, were fully evaluated with an x-ray pencil beam.Scanning over the telescope aperture of 35 cm in diameter with an x-ray pencil beam, we found the effective area of a set of XRTs to be 325, 200, and 113 cm(2) at energies of 1.5, 4.5, and 8.0 keV, respectively. We derive the point-spread functions (PSFs) of the XRTs by measuring the image profile at the focal plane with an x-ray CCD. The PSF is found to exhibit a sharp core concentrated within 30 arcsec and a broad wing extended to 3 arcmin in half-power diameter. We also evaluate the contribution of stray light, which is caused by the single reflection of x rays by primary or secondary mirrors and by the backside reflection of the mirrors. To obtain the characteristics of the XRT in the energy region of 0.5-10.0 keV, incorporated with the measurements at discrete energies, we develop a ray-tracing method with the telescope design parameter, the PSF, and optical constants. In particular, we obtain the optical constants around the gold-atom M shell (Au-M) absorption-edge energies by measuring the reflectivity of our mirror sample, with monochromatized x-rays in the energy range of 2.0-3.5 keV from synchrotron radiation. Taking into account the PSFs and optical constants, we find that our ray-tracing program can reproduce all these XRT performances.

Feasibility Study of Single-Photon Counting Using a Fine-mesh Phototube for an Aerogel Readout

The fine-mesh phototube is one type of photodetector which can be used under a strong magnetic field. For an aerogel readout, the single-photon detection efficiency should be close to 100% in order to identify particle species. We carried out a feasibility study of single-photon counting using fine-mesh phototubes, and obtained a possible solution.The fine-mesh phototube is one type of photodetector which can be used under a strong magnetic field. For an aerogel readout, the single-photon detection efficiency should be close to 100% in order to identify particle species. We carried out a feasibility study of single-photon counting using fine-mesh phototubes, and obtained a possible solution.

STUDY ON FINE-MESH PMTS FOR DETECTION OF AEROGEL CHERENKOV LIGHT

Abstract Most recent fine-mesh photomultipliers (FM-PMTs), with 19 dynode stages, have been tested for application to a threshold aerogel Cherenkov counter. Two properties, the gain and the pulse height resolution, have been particularly studied in a magnetic field of up to 1.5 T. The obtained results show that a FM-PMT is a suitable device for detection of aerogel Cherenkov light.

Recent results of the fully-depleted back-illuminated CCD developed by Hamamatsu

We have been developing fully-depleted CCDs fabricated on N-type silicon wafer in collaboration with HAMAMATSU Photonics K.K.We have made several wafer runs to optimize the basic characteristics of the devices such as the charge transfer efficiency (CTE), the full-well capacity and the amplifier gain, followed by the optimization of the backside treatment to improve quantum efficiency (QE) in blue wavelengths. The optimization process is successfully completed, and Hamamatsu recently started to deliver the 2k × 4k (15 μm pixel) four-side buttable devices for acceptance evaluation at the National Astronomical Observatory of Japan. Based on the measured QE in the X-ray, the depletion depth reaches 200 μm with CTE as good as >0.999995 for serial and parallel directions and with readout noise of < 5 e- for 130 kHz readout. The size of charge diffusion is estimated to be < 7.5 μm (one sigma) for pinhole image at wavelength of 450 nm. The device flatness is < 15-20 μm, and the dark current is a few e-/hour/pixel at -100°C and ~ 20 e-/hour/pixel at -80°C.

CONTINUUM X-RAY SOURCE AS A CALIBRATION SYSTEM FOR CHARGE COUPLED DEVICES

We present x-ray spectra obtained by a charge coupled device (CCD) from an electron impacting x-ray source using several kinds of electron targets: Au, Al–bronze, Al, and pure Al. The x rays from the source are dispersed by a grating and the dispersed x rays are focused on the CCD. Owing to the fine spatial and moderate energy resolutions of the CCD, fine spectra with 2 eV energy resolution up to 2.2 keV are obtained. X rays from the pure Al target (99.999% purity) provide good continuum x rays except for Al K x rays. This continuum source is useful as a calibration source for low energy x-ray detectors.

Development of thick back-illuminated CCD to improve quantum efficiency in optical longer wavelength using high-resistivity n-type silicon

Quantum Efficiency (QE) of CCDs decreases at λ >~ 0.7 μm since photons penetrate a depletion layer of CCD. If one makes the layer thicker, the QE will be largely improved. In collaboration with HAMAMATSU Photonics, we have been developing the thicker CCDs which are implemented on the high resistivity n-type silicon wafers. We have made several wafer runs to optimize the basic characteristics of the devices such as charge transfer efficiency (CTE), full-well and node sensitivities of the amplifiers. The results obtained so far mostly satisfied the specifications imposed by astronomical observations. We also attempted to build back-side illuminated devices to realize high QE in wider wavelength. The test devices shows that the QE exceeds 60% at 1 μm, which is roughly 5 ~ 6 times improvement over ordinary CCDs. We will present the current status of the projects.

CCD DEVELOPED FOR SCIENTIFIC APPLICATION BY HAMAMATSU

Abstract We have developed CCDs for scientific applications that feature a low readout noise of less than 5xa0e-rms and low dark current of 10–25xa0pA/cm 2 at room temperature. CCDs with these characteristics will prove extremely useful in applications such as spectroscopic measurement and dental radiography. In addition, a large-area CCD of 2k×4k pixels and 15xa0μm square pixel size has recently been completed for optical use in astronomical observations. Applications to X-ray astronomy require the most challenging device performance in terms of deep depletion, high CTE, and focal plane size, among others. An abuttable X-ray CCD, having 1024×1024 pixels and 24xa0μm square pixel size, is to be installed in an international space station (ISS). We are now striving to achieve the lowest usable cooling temperature by means of a built-in TEC with limited power consumption. Details on the development status are described in this report. We would also like to present our future plans for a large active area and deep depletion CCD that delivers high performance at reasonable cost.

Thirty-meter X-ray pencil beam line at the Institute of Space and Astronautical Science

A 30-m-long X-ray beam line has been built at the Institute of Space and Astronautical Science (ISAS) to evaluate the performance of X-ray optical instruments for space programs, in particular for the X-ray telescope onboard the Astro-D (Asca) satellite. This beam line consists of an X-ray generator, a 30-m-long vacuum duct, and measuring chambers. Strong and stable X-ray pencil beams from Al, Ti, Cu, Mo and W targets are available with the parallelism of several arcs [full width at half maximum (FWHM)]. Three kinds of detectors are prepared: a conventional gas proportional counter equipped with a thin plastic window, a one-dimensional position-sensitive proportional counter with a Be window, and a charge-coupled device (CCD) modified for X-ray measurements. At the present compact beam line, instead of giant systems of hundreds of meters, the combination of a strong X-ray (0.2-10 keV) pencil beam and translation stages enables us to examine the entire aperture of large X-ray optical instruments of up to 40 cm and 1 m in length.

Characterization and performance of hyper Suprime-Cam CCD

Hyper Suprime-Cam (HSC) is a second-generation wide field imaging camera for Subaru telescope with 10 times wider field of view (FOV) compared with Suprime-Cam (SC) currently being used. HSC makes the survey speed considerably faster than SC, while maintaining the high image quality of SC. The 1.5 degrees in diameter FOV is covered with 116 of 2K × 4K fully depleted back-illuminated CCDs with 15 μm pixels developed by HAMAMATSU Photonics K. K. and National Astronomical Observatory of Japan (NAOJ). The CCDs for HSC are designed to have higher quantum efficiency than those for SC in a wider range in the visible wavelengths, especially in the blue region. We at NAOJ have started acceptance inspection of the CCDs being delivered from HAMAMATSU. We used the X-ray source of 55Fe and the LED to measure charge transfer efficiency, readout noise, linearity, and full-well capacity of 33 CCDs. In addition, we measured the quantum efficiency of 7 CCDs. We confirmed all the CCDs have good performances and quality. In this paper, we report the results from the acceptance inspection and characterization of these CCDs.