Diamond Machining of Two-in-one Optical Element Including Slice Mirror Array for Near-infrared Integral-field Spectrograph

A two-in-one optical element consisting of a planar pick-off mirror (16 x14 mm(2)) and a slice mirror array (twenty-six 0.52 mm-wide and 18 mm-long mirror facets) was developed as a component for a near-infrared integral field unit: SWIMS-IFU for a near-infrared imager and spectrograph SWIMS for TAO 6.5 m telescope. The two optical entities were formed on a single bulk of aluminum alloy using a 5-axis ultraprecision machine and a specialized pair of diamond cutting tools. The relative position and orientation of the two optical entities were controlled to satisfy the tight optical tolerance, by precise measurement of tool tip positions with respect to the axes of the machine tool. Regarding measurement, an X-ray CT scanner was introduced as a solution to a major problem in the evaluation of complex monolithic optics, where some facets cannot be measured due to geometric constraints. The diamond-machining and measurement methods proposed in this study will be useful also for more complex monolithic optics to be developed in the future.

Automated summary

A two-in-one optical element consisting of a planar pick-off mirror and a slice mirror array was developed and controlled using advanced machining and measurement techniques. The study demonstrates the practical value of these methods for developing complex monolithic optics in the future.