James R. Stilburn

Performance of the Canada-France-Hawaii Telescope Adaptive Optics Bonnette

ABSTRACT Extensive results from the commissioning phase of PUEO, the adaptive optics instrument adaptor for the Canada‐France‐Hawaii Telescope (CFHT), are presented and discussed. Analyses of more than 750 images recorded with a CCD and a near‐IR camera on 16 nights in wavelengths from B to H are used to derive the properties of the compensated wavefront and images in a variety of conditions. The performance characteristics of the system are analyzed and presented in several ways, in terms of delivered Strehl ratios, full width half‐maxima (FWHM), and quantities describing the improvements of both. A qualitative description is given of how the properties of the corrected images result from the structure function of the compensated phase. Under median seeing conditions, PUEO delivers essentially diffraction‐limited images at H and K and images with FWHM ∼ 0 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepac...

GMOS: the GEMINI Multiple Object Spectrographs

The two Gemini multiple object spectrographs (GMOS) are being designed and built for use with the Gemini telescopes on Mauna Kea and Cerro Pachon starting in 1999 and 2000 respectively. They have four operating modes: imaging, long slit spectroscopy, aperture plate multiple object spectroscopy and area (or integral field) spectroscopy. The spectrograph uses refracting optics for both the collimator and camera and uses grating dispersion. The image quality delivered to the spectrograph is anticipated to be excellent and the design is driven by the need to retain this acuity over a large wavelength range and the full 5.5 arcminute field of view. The spectrograph optics are required to perform from 0.36 to 1.8 microns although it is likely that the northern and southern versions of GMOS will use coatings optimized for the red and blue respectively. A stringent flexure specification is imposed by the scientific requirement to measure velocities to high precision (1 - 2 km/s). Here we present an overview of the design concentrating on the optical and mechanical aspects.

CFHT adaptive optics: first results at the telescope

The adaptive optics instrument adaptor for the 3.6 m Canada- France-Hawaii telescope (CFHT) is currently in the commissioning phase. The heart of the system is a 19 electrode bimorph mirror (1:6:12), used with a 19 sub-aperture, curvature wave-front sensor and a separate tip-tilt re-imaging mirror. The performance evaluated in the laboratory and on the sky are presented: the adaptive optics control system provides a 100 Hz servo bandwidth with modal control capabilities. We report astronomical images with median Strehl ratio of 20 (at 1.25 micrometer) to 60% (at 2.2 micrometer), with a FWHM of 0.1 arcsec and a sensitivity allowing image quality improvement with guide stars as faint as mR equals 17.

High-efficiency sol-gel antireflection coatings for astronomical optics

The antireflective properties of silica sol-gel coatings have been known for some time, and such coatings have bene used to reduce losses in the optical elements of high- powered lasers used in fusion experiments. Research at DAO has developed the technology to the pont where optical elements in three 4-meter class telescopes at CFHT, KPNO, and CTIO have benefitted from coatings made form high- efficiency sol-gel films. The process is attractive because it is simple to apply, is inexpensive, and is as effective as multi-layer vacuum-deposited coatings which it can replace. A description is given of the basic chemistry involved and the techniques used to apply the coatings. Techniques used to improve the durability of the films by hardening and waterproofing are described, as well as a two- layer coating in combination with magnesium fluoride.

Fabrication of narrow-slit masks for the Gemini Multiobject Spectrograph

The fabrication requirements of the Gemini multi-object spectrograph (GMOS) slit mask is discussed particularly in terms of the slit-to-slit position, slit geometry and the telescope operation. The demand for precision slit masks with high quality slits of width of less than quarter arcsecond and an allowable fabrication time of two hours required examination of innovative fabrication processes and mask materials. Different fabrication processes including high precision cutting processes, water-jet and laser machining systems are evaluated according to cost, speed and efficiency, and the findings are documented. Different candidate mask materials including low thermal expansion metals and novel materials such as graphite paper and carbon-fiber composite sheet, are evaluated according to their relevant mechanical and physical properties, and the findings are also documented. In addition to identifying that the most suitable mask material is unidirectional carbon fiber sheet and the corresponding fabrication process is a Nd:YAG laser machining system, the mask handling system for GMOS is described and methodology to minimize systematic fabrication errors is also proposed.

The Gemini Multi-Object Spectrographs

Each GEMINI telescope will be equipped with a versatile optical/near-IR spectrographs which will fully exploit its large aperture and excellent image quality. The basic parameters of the GEMINI Multi-object Spectrographs (GMOS) are summarised in the table below.

A HIGH-SENSITIVITY QUADRANT DETECTOR FOR IMAGE-STABILIZATION APPLICATIONS

A description is given of the design and performance of a quadrant detector offering improvements in sensitivity and ease of construction over earlier devices. The optics are compact, and low-noise high-sensitivity operation is achieved with the use of avalanche photodiode detectors. The device is installed on the SIS spectrograph on the CFH 3.6-m telescope and allows image stabilization to be achieved by a tip-tilt mirror system using guide stars as faint as magnitude 18.5.

Integration and alignment of components for curvature wavefront sensors

The components used in curvature wavefront sensors are described with respect to mounting and adjustment requirements. In particular, the techniques used in the construction of the wavefront sensor employed in the adaptive optics bonnette at the Canada-France-Hawaii telescope are described in detail. Descriptions include methods of mounting components, design and adjustment of optics and of fiber-optic feeds for avalanche photo-diodes, and ways of monitoring wavefront sensor alignment and performance during operation.