The addition of a high resolution encoder to the spindle of a standard diamond turning lathe has allowed for precision
control of angular rotation. With three precision controlled axes, (rotational C, linear X and linear Z), tool path programs
can be defined in cylindrical coordinates, which enables the production of freeform geometries. Optical designers are
now exploring complex shapes that were previously unachievable. These shapes range from long radius toroids to
freeform wavefront corrector plates. From a manufacturing point of view, interfacing between optical design programs,
fabrication equipment, and metrology equipment often proves to be the most difficult part of the production process.
The optical design must be translated into a tool path for the diamond turning lathe, and in some cases the design must be
imported into the metrology software for surface comparison. The purpose of this report is to inform the reader about
some of these manufacturing challenges using one specific example: a freeform phase plate that suppresses diffraction
in an astronomical image and enhances searches for extrasolar planets around nearby stars. Designed by Johnan Codona
and Roger Angel from the University of Arizona, this ZnSe lens has many ridges and valleys that have been optimized to
reduce the 4 micron wavelength light observed from a nearby star to a level that makes planet detection possible. The
phase plate had an aperture of 4.44mm and was placed on a 12.7mm diameter 4mm thick substrate. Surface feature size
was approximately 2.5 micron peak-to-valley. In on-sky testing, the optic attenuated diffracted light from the star
approximately 100 fold.