Thursday, July 2, 2009

The M5 mystery

Despite significantly enlarging the holes in the pinhole stages, we still couldn't get the M5 wavefront test to work without apparently vignetting the outer 25 mm of the mirror... Most bizarre, since the Zemax & CAD models are fine, the M5 test hardware was appropriately manufactured & the measured physical size of the mirror is correct.

So what's going on?? & why do we now (after attacking the pinhole stage assembly with the plasma cutter) see a weird halo/"chromosphere" around the edge of out-of-focus images of the mirror?

Extraordinary levels of ingenuity went into investigating this frustrating puzzle, including every possible way of viewing the system: with eyeballs, webcams, projections, photographs, the wavefront camera, the alignment telescope...

Still no helpful clues - although we did get a rather nifty "globular cluster" image when we peered through the alignment telescope at what was probably the dust on the mirror being illuminated by the pinhole!

At times the clean room took on a sinister look as various forms of lighting were employed.

When the going really got tough, some of us retreated to the relative safety of the optical bench where we unwrapped the N2 null lens & played around with getting fringes off its flat back surface. We need to establish how accurately the interferometer will allow us to align the null lens in tip & tilt for the M2 test that will happen at a later stage.

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