BLINC / MIRAC
MIRAC5 (Unavailable): is a mid-infrared camera (3-13 microns) in development and testing with the new MAPS adaptive optics system. It uses a GeoSnap detector – a long-wave Mercury-Cadmium-Telluride array produced by Teledyne, with high quantum efficiency, large well-depth, and low noise. It has a 19″ field of view with a pixel scale of 0.019″/pix.
| Basics | More information | |
| Detector | 1024 x 1024 | further info |
| Filters | 24 filters in two filter wheels | further info |
The Mid-Infrared Array Camera (MIRAC) is a set of cameras that began as a collaboration between UA, SAO and NRL in the late 1980s. You can read about the long history of the instrument. MIRAC3 and the Bracewell Infrared Nulling Cryostat (MIRAC-BLINC) was an instrument developed for use with the adaptive optics system on the 6.5m MMT. It had two main modes of operation: imaging at 8-25 microns, and nulling interferometry at 8-13 microns. The fourth version of MIRAC (MIRAC4) saw first light in late October 2006. The camera featured a 256×256 array with high quantum efficiency and low dark current. It was cooled using a pulse tube mechanical cooler which eliminated the need for liquid helium cooling. BLINC was a liquid nitrogen-cooled set of fore-optics for the MIRAC system.
The entrance window provided the reflection surface for the visible light to be sent to the AO wavefront sensor. The Cassegrain focus was reimaged by an off-axis ellipse within BLINC which was capable of being rotated to send the light to either the nulling interferometer or the imaging channel. The imaging channel formed an image of the secondary on a reflective cold stop which baffles out warm radiation from the telescope. The mirror at the cold stop was mounted on a rotating voice coil actuator. This allowed chopping at 1-10 Hz within the cryostat.
The nulling interferometer split the entrance pupil in half and overlapped these two beams on a 50% transmissive beamsplitter. Manual alignment of the beams was achieved with feedthrough actuators. Path-length changes were introduced by translating the beamsplitter mount using a stepper motor with 42 microns of motion per revolution. Small path-length changes were introduced by a PZT-mounted mirror in the right arm of the interferometer. Both outputs of the interferometer were sent to a NICMOS3 detector within BLINC to allow sensing of phase variations in the interferometer. One of the outputs had a short pass dichroic which sends 8-13 micron light to MIRAC.
There is some additional information about the upgrades and science plans for MIRAC5.