Masato Naruse

Developments of wide field submillimeter optics and lens antenna-coupled MKID cameras

Wide field cryogenic optics and millimeter-wave Microwave Kinetic Inductance Detector (MKID) cameras with Si lens array have been developed. MKID is a Cooper-pair breaking photon detector and consists of supercon- ducting resonators which enable microwave (~GHz) frequency multiplexing. Antenna-coupled Aluminum CPW resonators are put in a line on a Si substrate to be read by a pair of coaxial cables. A 220 GHz - 600 pixels MKID camera with anti-reflection (AR) coated Si lens has been demonstrated in an 0.1 K cryostat. A compact cryogenic system with high refractive index materials has been developed for the MKID camera.

Design of SIS imaging array for terahertz astronomy

In this paper, the optical design of astronomical detector array with SIS for 600–700 GHz is proposed. A unit has 127 pixel, and SIS junctions are coupled to double slot antennas and extended hemisphere lens made from Silicon or Alumina ceramics. A lens with multi-pixel system is compared to 1 lens with 1 antenna system (fly-eye)from the view point of antenna spacing, aberration, and beam efficiency.

Superconducting THz Camera with GaAs‐JFET Cryogenic Readout Electronics

We describe the development of large format array of superconducting tunnel junction detectors that is readout by SONY GaAs‐JFET cryogenic integrated circuits. High quality SIS photon detectors have high dynamic impedance that can be readout by low gate leakage GaAs‐JFET circuits. Our imaging array design, with niobium SIS photon detectors and GaAs‐JFET cryogenics electronics, uses integrating amplifiers, multiplexers and shift‐registers to readout large number of pixels that is similar to CMOS digital cameras. We have designed and fabricated GaAs‐JFET cryogenic integrated circuits, such as AC‐coupled capacitive trans‐impedance amplifier, multiplexers with sample‐and‐holds and shift‐registers, for 32‐channel readout module. The Advanced Technology Center of National Astronomical Observatory of Japan have started extensive development program for large format array of SIS photon detectors.

Effect of Quasiparticles in the Intragap States on the Superconducting Surface Resistance

The Mattis-Bardeen theory is extended by introducing the complex number of the superconducting gap energy, by which BCS density of states is broadened and the small density of quasiparticle states that appears in the energy gap is well predicted. Using the extended Mattis-Bardeen theory, the surface resistance of superconductors and quality factors of superconducting resonators are calculated. It is shown that simulated temperature dependence of quality factors of superconducting resonators agree very well with the measured ones. It is also demonstrated that the calculated residual quasiparticle number of a superconducting resonator using the density of states consisting of the gap-broadened and localized quasiparticle states agrees quantitatively with the measured one.