An Infrared Camera for the Chicago Adaptive Optics System

The performance of an adaptive optics system improves as you observe at longer wavelengths. The Chicago Adaptive Optics System (ChAOS) is designed to optimally operate in the near infrared from 0.8 microns to 2.4 microns. We have set out to construct a high quality science instrument to operate at these wavelengths with ChAOS. The development of this instrument is detailed below, and here we present the first astronomical images from our recent observing run in late September, 1996.


Tip-Tilt Correction
Enhanced to show structure.

Tip-Tilt Correction
Plotted with comparable levels
as closed loop image.

Closed Loop with
Full Correction
of 87 Actuator mirror.

The first astronomical images with ChAOS CAM. The first observing run with the infrared camera was very cloudy, but in small holes in the clouds, we managed to take these preliminary images of the bright star Capella at 1.6 microns (H band). Unfortunately, we did not have the 10 minutes of clear sky required to properly focus the camera, and so the final closed loop image is probably significantly out of focus. The displayed field of view of each image is only 2.7 arcseconds on the sky. The left image was taken with the tip-tilt mirror operating at a fairly low gain setting. The full width half maximum (fwhm) of this image is about 1 arcsecond, typical for normal ground based images. The middle image is the same as the left image but it is plotted with a comparable stretch as the closed loop image on the right for a direct comparison of the images. The right image shows the star with the full adaptive correction of the 87 actuator mirror. The fwhm of this image is less than 0.2 arcseconds (at least five times sharper than with only tip-tilt correction) and the peak height is at least 8 times higher. Since we know the camera was slightly out of focus and based on recent images obtained with an optical camera, we expect to achieve results closer to a fwhm of 0.1 arcseconds in the main core and improvements closer to 50 in peak height at 1.6 microns.

The infrared camera's primary dewar. The upper most portion of the dewar (gold cylinder) contains liquid nitrogen to cool the infrared detector and the optics which are located in the lower cylinder. The detector is a 256 pixel square NICMOS 3 infrared array manufactured by the Rockwell Science Center. The HgCdTl array is sensitive from 0.8 to 2.5 microns. The interface electronics is contained in the silver box mounted to the dewar. It contains preamp and clocking cards manufactured by Wallace Instruments ((607) 347-4836). The camera is controlled by a DSP2101 microprocessor which also drives the stepper motors and a high speed fiber optic link with a Macintosh Computer which serves as the data acquistion computer. The Macintosh software and all of the control electronics were developed within the ChAOS group. The main cylinder and optical bench were also designed within the ChAOS group and the dewar was machined at Yerkes Observatory.

The electronics for the camera were ready for initial tests in September 1996, and it was decided to prepare a test dewar to bring to the telescope in time for the next scheduled observing run (Sept. 21, 1996). A small dewar manufactured by IR Labs was borrowed from Yerkes Observatory, and the detector and an H band (1.6 micron) filter were placed within. This photo shows the primary camera designer James Larkin removing the instrument from ChAOS after the September run. ChAOS is the large black box at the bottom of the image. The test dewar is the small bronze colored cylinder in between two electronics boxes. The left box contains the electronics and detector for the tip-tilt system. In between ChAOS and the dewar is an open optical bench including a wide field imaging system.

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Maintained by James Larkin