We have developed an optical and near-infrared instrument HONIR (Hiroshima Optical and Near-InfraRed
camera) with imaging, spectroscopy, and polarimetry capabilities in two (one optical and one near-infrared)
bands simultaneously. Imaging capability with a field of view of 10 arcmin by 10 arcmin has been available
since 2011, as reported in the previous SPIE conference. In addition, spectroscopic and polarimetric optical
components (grisms, an Wollaston prism, a half-wave plate, and focal masks) were installed in the instrument,
which enabled us to perform spectroscopy and linear polarization measurement by imaging polarimetry and
spectro-polarimetry. Spectral resolution of R = λ/(triangle)λ ~ 440 - 800 is achieved in spectroscopy using a slit
mask with an 1".3 width. In polarimetry, instrumental polarization is less than ~0.05 % with stability of
better than ~0.05 %, which is sufficiently small to achieve an aimed accuracy of polarization measurement
of ~0.1 % at primal observing wavelengths.
We developed a new readout system for the near-infrared detector VIRGO-2K (2kx2k HgCdTe array) installed in the optical-infrared simultaneous camera, HONIR, for the 1.5 m Kanata telescope at Higashi-Hiroshima observatory. The main goal of this development is to read out one frame within ~ 1 second through 16 output readout mode of the detector, in order to reduce the overhead time per exposure. The system is based on a CCD controller, Kiso Array Controller (KAC). We redesigned the analog part of KAC to ﬁt VIRGO-2K. We employed a fully diﬀerential input circuit and a third order Bessel low-pass ﬁlter for noise reduction and a constant current system to improve the linearity of the detector. We set the cutoﬀ frequency of the Bessel low-pass ﬁlter at the readout clock rate (120 kHz). We also set the constant current at 200 μA according to the data sheet of VIRGO-2K. We tested the new readout system at room temperature and conﬁrmed that the low-pass ﬁlter works well as designed. The ﬂuctuation of the current level of the constant current system is less than 2% for the typical output voltage range of VIRGO-2K (3.2-4.4 V). We measured the readout noise caused by the new readout system (connected to cooled multiplexer) and found that it is 30-40 μV rms, being comparable to or slightly higher than the typical readout noise of VIRGO-2K, ∼ 37 μV rms.
We have developed an optical-infrared instrument HONIR (Hiroshima Optical and Near-InfraRed camera) to be attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Hiroshima University. HONIR is a three color (one optical and two near-infrared bands among 0.5–2.4 µm) simultaneous imager and spectrograph with a polarimetry function. The field of view of the imaging mode is 10 arcmin square with a spatial sampling of 0".29. Among the planned multipurpose functions, a two color (0.5–1.0 µm and 1.15–2.40 µm) simultaneous imaging function has been installed and operated so far. The remaining functions, spectroscopy and polarimetry, and the second near-infrared band arm, are under development and will be installed in the near future.
The Thirty Meter Telescope (TMT) is a next-generation optical/infrared telescope to be constructed on Mauna Kea,
Hawaii toward the end of this decade, as an international project. Its 30 m primary mirror consists of 492 off-axis
aspheric segmented mirrors. This paper describes the progress of the test fabrication of an outermost mirror segment for
the TMT as a joint R&D program between National Astronomical Observatory and Canon. A zero-expansion glass
CLEARCERAM™ blank was polished by a computer-controlled small-tool polishing machine (CSSP, Canon) and its
surface shape was measured by a touch-probe measuring machine(A-Ruler, Canon). Residuals of lower Zernike terms of
the surface shape were 11 nmRMS, clearing the original specifications based on the structure function. There remains,
however, a need to fulfill latest revised specifications. Possible solutions to improve and achieve the new specifications
and a plan for revising the process for mass production are also described.
We evaluated depth of subsurface damage on a ground surface of the ultra low expansion glass-ceramics
CLEARCERAMR®-Z HS (CC-Z HS) by Ohara Inc., which is one of the candidates for material for segmented
mirrors of the Thirty Meter Telescope. We made polishing spots of Magnetorheological Finishing on the
ground surface of CC-Z HS and measured exposed subsurface damage features on the spot surface. We also
studied on hydrofluoric acid etching of the CC-Z HS ground surface, which is expected to be an effective
method to remove a subsurface damage layer compared with time-consuming polishing. We etched small
ground surfaces of CC-Z HS and evaluated its uniformity.
We developed an aspheric convex 33-cm diameter secondary mirror of the Hiroshima University 1.5-m Ritchy-Chretien telescope using Zero-expansion Pore-free ceramics, which has physical properties (thermal expansion,
stiffness, thermal conductance, etc.) comparable with or better than existing zero-expansion glasses. After
high-precision grinding, polishing, and coating aluminum and silicon monoxide, we obtained the sufficient
optical reflecting surface with a figure error within λ/10 and a roughness of about 3 nm rms. The mirror has
been attached on the telescope and we confirmed its sufficient performance through a Hartmann test. To date
it has shown a good performance in our application and we suggest that this ceramic material has a potential
to be used for astronomical telescopes and related area.