Jeff Ward

CFHT-WIRCam: Interlaced science and guiding readout with the Hawaii-2RG IR sensor

CFHTs experience with interlacing science and guide pixel readout using the Hawaii-2RG infrared sensors on WIRCam has been problematic due to timing limitations inherent to this approach as well as unexpected behaviour in the sensors themselves. These problems have been overcome by implementing high-speed readout (1.4 s per read) for WIRCams array of four Hawaii-2RG sensors, obviating the need for interlaced readout. The effect of the reset anomaly on the science and guide frames has been minimized by introducing suitable delays and a clocking scheme that does not significantly impact the minimum exposure time of the camera.

CFHTIR: 1k x 1k NIR Spectro-Imaging Camera for the CFHT

The CFHTIR is a large format near IR camera based on the Rockwell HAWAII Array. CFHTIR is designed for both direct imaging at the f/8 Cassegrain focus, as well as spectroscopy on the OSIS multiobject spectrograph. The camera provides 0.21 inch/pixel sampling in both applications with a single set cold transfer optics and pupil mask. The camera includes two eight-position filterwheels driven by cryogenic stepper motors with position control using a novel Hall effect sensor technique. CFHTIR also uses a novel dewar wiring technique employing flexible circuit vacuum feedthrus. CFHTIR is the second large format IR camera based on the Hawaii array constructed at CFHT, the first being the KIR camera for the CFHT Adaptive Optics Bonnette which was commissioned in 1997. This paper describes the system architecture of the CFHTIR highlighting key design concepts and detailing the physical elements.

FlyEyes: integrating CCID-35 into PUEO AO system at CFHT

A project to upgrade PUEO, the CFHT AO system, was first proposed in 2002. As part of the upgrade effort, a technology project was conceived to evaluate and characterize the backside-illuminated CCID-35 detector as suitable a replacement for the array of avalanche photo diode modules (APDs) in the curvature wavefront sensor. The CCID-35 was envisioned to replace an array of expensive APDs thus providing a cost-effective means of upgrading PUEO to a higher-order system. Work on the project, dubbed FlyEyes, occurred sporadically until Oct 2005 but substantial progress has been made since. This paper was intended to report on the performance of FlyEyes in PUEO but unfortunately the instrument was not ready for tests at the time of this writing. This paper summarizes the progress made on the project thus far and touches upon some of the difficulties encountered.

The on-chip guiding system of the wide-field infrared camera at CFHT

The Canada-France-Hawaii Telescope (CFHT) is commissioning a new Wide field Infrared Camera (WIRCam) that uses a mosaic of 4 HAWAII-2RG near-infrared detectors manufactured by Rockwell. At the heart of the instrument is an On-Chip Guiding System (OCGS) that exploits the unique parallel science/guide frame readout capability of the HAWAII-2RG detectors. A small subsample of each array is continuously read at a rate of 50 Hz while the integration of the science image is ongoing with the full arrays. Each of these guiding windows is centered on a star to provide an error signal for the telescope guiding. An Image Stabilizer Unit (ISU) (i.e. a tip-tilt silica plate), provides the corrections. A Proportional Integral Differential (PID) closed loop controls the ISU such that telescope tracking is corrected at a rate of 5 Hz. The guide window size and readout rate are adjustable but typical numbers are 8×8-16×16 boxes read at 50 or 1.5 Hz. This paper presents the technical architecture of the guiding system and performance measurements on the sky with WIRCam.

Converting a Liquid Nitrogen Cooled Camera to Closed Cycle Cooling

The detector for the ESPaDOnS spectrograph at the Canada-France-Hawaii Telescope (CFHT) is a CCD42-90 4.5kx2k CCD from e2v Industries in a liquid nitrogen cooled GL Scientific cryostat. This paper describes the conversion of this camera to closed-cycle cooling using a Polycold® cryogenic refrigeration system. Topics covered include vibration analysis, positional stability of the image plane, cool-down characteristics, PLC integration, and annual operational overheads for both systems.

Infrared guiding with faint stars with the wide-field infrared camera at CFHT

The Canada-France-Hawaii Telescope (CFHT) is commissioning a new Wide field Infrared Camera (WIRCam) that uses a mosaic of 4 HAWAII-2RG near- infrared detectors manufactured by Rockwell. At the heart of the instrument is an On-Chip Guiding System (OCGS) that exploits the unique parallel science/guide frame readout capability of the HAWAII-2RG detectors. A small sub sample of each array is continuously read at a rate of up to 50 Hz while the integration of the science image is ongoing with the full arrays (read at a maximal rate of 1.4 s per full frame). Each of these guiding windows is centered on a star to provide an error signal for the telescope guiding. An Image Stabilizer Unit (ISU) (i.e. a tip-tilt silica plate), provides the corrections. A Proportional Integral Differential (PID) closed loop controls the ISU such that telescope tracking is corrected at a rate of 5 Hz. This paper presents the technical architecture of the guiding system and performance measurements on the sky in engineering runs with WIRCam with faint stars up to magnitude 14.

FlyEyes: A CCD-based Wavefront Sensor for PUEO, the CFHT Curvature AO System

Abstract : Adaptive optics wavefront sensing imposes stringent requirements on detectors due to the simultaneous need for extremely low read noise and high frame rates. Curvature wavefront sensing measurements are based on the normalized intensity of the signal in a given subaperture and Avalanche Photo Diodes (APDs) have traditionally been used as detectors in curvature systems such as the Canada France Hawaii Telescope (CFHT) Adaptive Optics (AO) Bonnette, called PUEO after the endemic Hawaiian owl. Passively quenched APDs are robust but have low QE (approximately 40%), while actively quenched APDs can have much higher QE, but have been known to fail. Furthermore, curvature systems with large numbers of subapertures are now in operation and the cost of individual APDs may become prohibitive for such systems. Thus a CCD-based alternative appears very attractive, and development of a specific chip was initiated at ESO ten years ago. In this paper, we report on the performance of the FlyEyes camera, a project which was conceived to compare the performance of the backside-illuminated custom-designed CCD detector with an array of APDs, used in an operational and well-characterized curvature wavefront AO system. The on-sky performance is demonstrated to be unaffected on bright guide stars (i.e. negligible latency) and although the faint end suffers from the 2.5 e- read noise, the performance can be regained by lowering the frame rate on the wavefront sensor. In this paper, we report on results that show that the CCD can be used to replace an array of expensive APDs. This would enable to cost-effectively upgrade PUEO to a higher order system, as has been proposed at various occasions.

Making a better shutter

This paper will describe the development of better shutters for astronomy instrumentation at the CFHT observatory. Over a six year period several exposure control shutters and shutter like devices have been built by modifying existing products or custom machining in house. With each new shutter project, experience from the previous shutter design enhances development. This has resulted in the latest shutter, a magnetic latching, springless, low power, sensed exposure shutter to be used for CFHTIR, an IR camera.

Novel telescope-mounted spectral calibration source for the CFHT

At the Canada-France-Hawaii Telescope (CFHT) recent gains in Spectrographic capability has pointed out the need for a telescope-mounted Spectral Calibration Source that has three features: (1) A precise simulated pupil image, (2) Emission lines from .36 microns to 2.5 microns, (3) High throughput in the infrared. This paper describes the CFHT f/8 focus and then describes the Spectrographs and the Spectral Calibration Source (SCS) that use this focus.