Susumu Kuwamura

Wavelength scanning profilometry for real-time surface shape measurement

Wavelength scanning profilometry suitable for real-time surface shape measurement is proposed. A phase slope of the interference signal generated by a wavelength scan is measured at an individual image pixel on-line. The parallel outputs of these on-line measurements show a map of surface height in real time. Experiments where a tunable dye laser was used were conducted to simulate the real-time measurements of step objects with specular and diffuse surfaces. The results have shown that a height map is available at any moment during the wavelength scan, and the measurement accuracy of height increases as the scanning proceeds. For a scanning width of 25 nm, the accuracy was as high as 1 mum. Analyses of the measurement accuracy are given.

Speckle decorrelation in surface profilometry by wavelength scanning interferometry

The accuracy and the measurement range of surface profilometry by wavelength scanning interferometry applied to diffusely reflecting surfaces are investigated. The influences of surface roughness and the imaging system in the interferometer are theoretically analyzed by derivation of the autocorrelation function of interferograms arising from wavelength scanning. By using a dye laser with a tuning range of 4.2 nm to a yield resolution of 39.1 mum, we have observed interferograms and their Fourier transforms and autocorrelations to study effects of defocusing and the size ratio of speckle to the CCD pixel for a plane diffuse object positioned normal to the incident beam.

Stellar spectra reconstruction from speckle spectroscopic data

In the previous paper [AJ, 105, 665 (1993)], we described speckle spectroscopic instrumentation and presented some observational results with data acquired by our speckle spectrometer. The shift-and-add method was used for the data reduction in the previous paper. We have revised the speckle spectrometer to augment the performance. The cross-correlation method is newly introduced for data reduction. The spectra of single stars γ Cas and α Per are reconstructed in nearly diffraction-limited angular resolution with the resolved Hα emission and absorption lines, respectively. It is shown that the cross-correlation method is superior to the shift-and-add method in the narrow bandwidth region. The results of α Per are compared with the photometric measurement of Procyons spectrum which has the similar spectral type as α Per and they are shown to be fairly consistent

Performance of Software-Based Solar Adaptive Optics System

This paper reports the performance of our modified adaptive optics system for solar observations. This system operates at a frame rate of about 400 Hz and has the closed-loop cutoff frequency at 105 Hz. The results of the laboratory experiments show that this system compensates for a temporal wavefront-variation of less than 99 Hz and improves the Strehl ratio by a factor of five.

Image Restoration of Io by Shift-and-Add Method and Deconvolution

Atmospheric turbulence degrades the image resolution of a ground-based telescope, and a speckle imaging technique can restore the image with high resolution up to the diffraction limit. We have obtained the speckle data of Io (a Jupiters satellite) using the 2 m telescope in Nishi-Harima Astronomical Observatory. The speckle data are reduced by the shift-and-add method followed by a background-subtraction procedure. The reduced image is then deconvolved by the similarly reduced image of the unresolved binary star HR6168. The comparison with the close-up image taken by the Voyager 2 spacecraft reveals that the restored image shows well-resolved structural features on the surface of Io.

Solar adaptive optics system at the Hida Observatory

A solar adaptive optics system is developed for the 60 cm domeless solar telescope of the Hida Observatory in Japan. It is designed for compensating low order turbulence in G-band using a 52-electromagnetic-actuator deformable mirror, a 6x6 Shack-Hartmann wavefront sensor and standard personal computers. The details of the system, particularly features of the deformable mirror are described. Laboratory experiments show that the use of adaptive optics raises the Strehl ratio by a factor of five for turbulence of under 99Hz. In solar observations, the improvement of resolution in long-exposure images with the adaptive optics system is demonstrated.

Toward high-resolution imaging with a simple adaptive-optics system.

High-resolution imaging with reference to a widely separated star is examined. Peak tracking of the specklegram in the reference channel results in a high-resolution image in the observational channel. A binary star with angular separation of 30.5 arcsec is examined in white light, and the resultant image of the primary star obtained with reference to the secondary star is shown to have better resolution than the centroid tracking image by a factor of 3.

Advances in solar adaptive optics system at the domeless solar telescope of the Hida Observatory

A solar adaptive optics system for the 60 cm domeless solar telescope of the Hida Observatory in Japan is developed. A high-speed deformable mirror with 52 electromagnetic actuators is newly used in an experimental adaptive optics system. The use of the mirror resulted in the improvement of Strehl ratios in laboratory experiments. In solar observations, the system worked well when solar granulation was used as a target for wavefront sensing. An adaptive optics system being developed for a vertical spectrograph of the domeless solar telescope is described.

Deconvolution of partially compensated solar images from additional wavefront sensing

A technique for restoring solar images partially compensated with adaptive optics is developed. An additional wavefront sensor is installed in an adaptive optics system to acquire residual wavefront information simultaneously to a solar image. A point spread function is derived from the wavefront information and used to deconvolve the solar image. Successful image restorations are demonstrated when the estimated point spread functions have relatively high Strehl ratios.

Development of a new solar adaptive optics system at the Hida Observatory

We are developing a new adaptive optics (AO) system for the 60cm domeless solar telescope of the Hida Observatory, Japan. The system has a deformable mirror with 97 piezo-actuators, a Shack-Hartmann wavefront sensor with a 10×10-microlens array and standard personal computers. We conducted solar observations in September, 2013, and confirmed that our AO system cancelled image-shifts so that the deviations were within the resolution of the telescope. We report the detailed performances of our new AO system.