Re: ATM Using a CCD imager to create a topographical map oftelescope mirror

[Anthony Stillman <atmer@flash.net>]

David,

Clearly you are an insightful thinker.  It appears that, on your own, you
have invented the common path lateral shearing interferometer.  Sincerely,
I'm impressed.

I would like to add that, with a collimated wavefront (star test), an
alternate form of common path lateral shearing interferometer is rather
easier to both implement and its results analyze.  This being a Ronchi
grating.  As in your arrangement shearing occurs in one direction, here
perpendicular to the grating's rulings, and hence deviation of the
wavefront is detectable in only one direction.  Crossed Ronchi gratings,
otherwise known as a Hartmann mask, provide for shearing and hence defect
detection in two directions.  Both of these tests allow simultaneous
observation of the complete aperture.  Further, when used with a star they
create, in effect, a contour map of the system wavefront.  Determining the
sign of the distortion can still be an issue.  That is, is that a hole or a
hill?

Again, let me say the reasoning you show in your presentation is inspired.
I encourage you to read up on interferometry.  If you like I'de be glad to
point you in the direction of a number of good books and articles.  Bright
people, like yourself, may as well stand on the shoulders of others.

Anthony