MagAO 2018A Day 15: Fringe Science

Read Below to find out what this odd looking video is!

Hi All,

Yesterday we mounted the SAO’s Giant Magellan Telescope (GMT) dispersed fringe sensor prototype (Proto3 — Brian McLeod’s 3rd version — it keeps getting better). This is a complex set of infrared cameras and optics that mimic 3 of the GMT primary mirrors boundaries. It is basically a 2 slit experiment that interferes light (to make “fringes”) from the edge of each primary (where they almost touch) of the GMT. In this manner we hope to measure if one primary is slightly higher (out of phase in piston) with respect to the other primary — this will be a critical measurement to enable a diffraction-limited GMT in the future.

So that means we turned Magellan/MagAO into just 3 pairs of slits and look at the interference between the pairs. See photo below of the Magellan pupil with these 3 slits pairs superimposed over it.

The Proto 3 pupil — basically 3 double slits

The fringes produced by the 2 slits are then dispersed in the vertical direction — in this way it can capture/measure up to ~40 microns of piston between GMT segments.

In the photo below you can see the 1.1-1.3 micron (infrared) spectra of the fringes, here MagAO was locked on 300 modes.

Fringes from Proto3 ! The fringes are dispersed from red to blue (in the J band) from top to bottom — if there was piston between the slits the fringes would twist and look like a “barber-pole”.

Jan Kansky took this great photo of Proto3 (the box above Derek) mounted on the back of the NAS

Derek Kopon and Proto3

The main test of the system is to understand the “fringe behavior” when Proto 3 looks far away from the guide star that MagAO is correcting. Below we show a video of what the fringes look like when the fringes come from a star that is 6 arcminutes away from the guide star.

Movie of the fringes 6 arcminutes off axis from MagAO's guide star

Movie of the fringes 6 arcminutes off axis from MagAO’s guide star

So in keeping with tonight’s theme — here is a Fringe song about the TV show of the same name:

Here is a different version:

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