BLINC

BLINC is a liquid nitrogen-cooled set of fore-optics for the MIRAC system.

The entrance window provides the reflection surface for the visible light to be sent to the AO wavefront sensor. The Cassegrain focus is reimaged by an off-axis ellipse within BLINC which is capable of being rotated to send the light to either the nulling interferometer or the imaging channel. The imaging channel forms an image of the secondary on a reflective cold stop which baffles out warm radiation from the telescope. The mirror at the cold stop is mounted on a rotating voice coil actuator. This allows chopping at 1-10 Hz within the cryostat.

The nulling interferometer splits the entrance pupil in half and overlaps these two beams on a 50% transmissive beamsplitter. Manual alignment of the beams can be achieved with feedthrough actuators. Pathlength changes are introduced by translating the beamsplitter mount using a stepper motor with 42 microns of motion per revolution. Small pathlength changes can be introduced by a PZT-mounted mirror in the right arm of the interferometer. Both outputs of the interferometer are sent to a NICMOS3 detector within BLINC to allow sensing of phase variations in the interferometer. One of the outputs has a short pass dichroic which sends 8-13 micron light to MIRAC.