THD Bench

Bench description

vendredi 10 juin 2016, par Pierre Baudoz

The source’s light is brought from the source unit to the bench by a fiber which exit in the first focal plane (FP1). The light is then reflected on the first off axis parabola (OAP-1) then sent of the tip-tilt mirror. This mirror is located 20 mm before the first pupil plane (PP1), where an 8.23 mm circular and unobstructed pupil is in place. After this pupil, the beam encounters the first deformable mirror (DM-1), then the second off axis parabola (OAP-2). The second deformable mirror (DM-2) is located in a diverging beam right after (FP2) which is empty for the moment. The light is reflected on OAP 3 then on the third deformable mirror (DM-3), located in a second pupil plane (PP2). We focalize the light, using OAP 3 again, on the coronagraphic mask in focal plane (FP3). Finally, the beam is collimated to go through the Lyot pupil in pupil plane (PP3). A last OAP and a couple of plan mirrors are used to focalized the beam on either one of the detectors.

A low-order wavefront sensor uses the light reflected by the Lyot stop to measure the tip-tilt of the beam. Compensation of the tip-tilt errors is done using the Tip-Tilt mirror at a frequency >100Hz.