Since the last IODC meeting, the field of optical design with freeform surfaces has burst onto the scene. This talk will present a first of its kind, all reflective, unobscured, three-mirror 10° full field of view, F/1.9 operational freeform imaging telescope from design to full assembly.
Advances in diamond turning technology have offered optical designers new degrees of freedom in beam shaping optics.
While designers have these new manufacturing methods at their disposal, they may not be aware of special process
limitations and cost drivers. The purpose of this paper is to present some of these critical manufacturing issues. We will
discuss briefly special beam shaping optic types and applications. Then in more detail we will discuss the four key
diamond turning techniques and the types of optics they can produce. These four key manufacturing techniques are:
standard 2 axis diamond turning, slow tool servo, fast tool servo, micromilling. During the discussion we will present
surface shapes, process limitations, as well as cost drivers for each technique. In summary will we present this data in a
matrix that will aid the designer in selecting manufacturing techniques and optic types.
Monolithic lens arrays are used in applications such as hyper-spectral imaging, Shack-Hartmann wavefront sensors, and
lens replication molds, where lens-to-lens registration is critical. Traditionally, monolithic lens arrays are produced by
diamond turning one lens at a time on axis. This process requires the substrate to be shifted to a new position before the
next lens is machined. This intermediate step increases production time and makes it difficult to achieve lens-to-lens
registration accuracy. Freeform diamond machining allows lens arrays to be produced in a single setup. Since there are
no intermediate shifts of the substrate, the lens-to-lens registration is inherent to the program and machine accuracy. The
purpose of this paper is to compare different freeform manufacturing processes in the production of a three-element
germanium lens array. Freeform machining technologies including Slow Tool Servo (STS), Fast Tool Servo (FTS) and
Diamond Micro-Milling (DMM) will be used to produce this lens array. The results for process times, figure, and finish
characteristics will be compared across all three techniques.
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.