Nobuyuki Kanda

LARGE-SCALE CRYOGENIC GRAVITATIONAL WAVE TELESCOPE

We present here the Large-scale Cryogenic Gravitational wave Telescope (LCGT) project which is aimed to improve the sensitivity of the existing gravitational wave projects by ten times. LCGT is the project constructing the km-scale gravitational wave detector in Japan succeeding the TAMA project, which adopts cryogenic mirrors with a higher power laser. We are planing to build it in an underground site in Kamioka mine. If its target sensitivity is attained, we will be able to catch a few events per month.

Japanese large-scale interferometers

The objective of the TAMA 300 interferometer was to develop advanced technologies for kilometre scale interferometers and to observe gravitational wave events in nearby galaxies. It was designed as a power-recycled Fabry–Perot–Michelson interferometer and was intended as a step towards a final interferometer in Japan. The present successful status of TAMA is presented. TAMA forms a basis for LCGT (large-scale cryogenic gravitational wave telescope), a 3 km scale cryogenic interferometer to be built in the Kamioka mine in Japan, implementing cryogenic mirror techniques. The plan of LCGT is schematically described along with its associated R&D.

Transfer function of a crossed wire pendulum isolation system

We measured the vibrational transfer function of a newly proposed crossed wire pendulum in the frequency range 0.03–3 Hz. We confirmed that it behaves as a much longer simple pendulum of the same period as far as one dimensional movement of its center of mass is concerned. We conclude that the pendulum shows promise as a component in an ultra‐low frequency anti‐vibration system.

A MEASUREMENT OF THE FREQUENCY DEPENDENCE OF THE SPRING CONSTANT

Abstract We measured the inelasticity of a tungsten fiber by using a torsion balance. We concluded that the spring constant increases along with the angular frequency. This measurement supports the statement that the inelasticity of a torsional fiber causes a systematic error in the measurement of the Newtonian gravitational constant using the time-of-swing method.

A low‐frequency vibration isolation table using multiple crossed‐wire suspensions

A practical low‐frequency one‐dimensional vibration isolation system has been developed exploiting a previously developed crossed wire suspension technique. A table is supported by two such suspensions so as to be stiff in 5° of freedom but with a very long period in one horizontal direction. The rotation of the suspended mass in the original system is eliminated and the transfer function at high frequencies is greatly improved. Periods of 10 s were achieved in experimental tests, giving isolation of 40 dB at 1 Hz and up to 60 dB at 10 Hz. The system is suitable for one‐dimensional optics experiments or as a base for further stages of vibration isolation.

Development of a light source with an injection-locked Nd:YAG laser and a ring-mode cleaner for the TAMA 300 gravitational-wave detector

We have developed a light source suitable for laser interferometric gravitational-wave detectors. The developed light source has high power, TEM00 mode, linear polarization, high frequency stability, and low intensity noise. The light source with the quality is essential for attaining the goal sensitivity in the TAMA 300 and was found to be available for a observation run of a gravitational-wave detector.

Measuring the anelasticity of CuBe film under tensile stress using the X-pendulum

Abstract We measured the anelasticity of Cuue5f8Be foil at very low frequencies by incorporating it in an X-pendulum. The imaginary part of the spring constant was constant from 0.03 Hz to 0.5 Hz under tensile stresses of 12–20 MPa. The X-pendulum technique proved convenient for low frequency use.

Two-dimensional X pendulum vibration isolation table

We have extended to two dimensions a previously developed vibration isolation table using crossed wire suspensions (X mechanisms). A load table is suspended using a combination of normal and upside-down X mechanisms so that it moves freely with a very long period in both horizontal directions but is moderately stiff in all other degrees of freedom. Periods of 5 s are easily achievable. The transfer function of the prototype reported here contains a number of elastic mode resonance peaks, but it is shown by analysis how to reduce or eliminate nearly all of these.

Force measurements of a superconducting-film actuator for a cryogenic interferometric gravitational-wave detector

We measured forces applied by an actuator with a YBCO film at near 77 K for the Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. An actuator consisting of both a YBCO film of 1.6 micrometers thickness and 0.81 square centimeters area and a solenoid coil exerted a force of up to 0.2 mN on a test mass. The presented actuator system can be used to displace the mirror of LCGT for fringe lock of the interferometer.Abstract We measured forces applied by an actuator with a YBa 2 Cu 3 O 7 (YBCO) film at near 77 K for the Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. An actuator consisting of both a YBCO film of 1.6 μm thickness and 0.81 cm 2 area and a solenoid coil exerted a force of up to 0.2 mN on a test mass. The presented actuator system can be used to displace the mirror of LCGT for fringe lock of the interferometer.