Opto-Mechanical Design of a Three Degree-of-Freedom Homodyne Interferometer for Freeform Optics Metrology

Michael Ricci, MS Candidate

Hopeman 224

The advancement of freeform optical manufacturing capabilities has enabled optical designers to utilize the more efficient and multi-functional geometries with increasing frequency. However, the available techniques for reliable metrology of the highly sloped and complex freeform shapes have lagged behind the advancements in manufacturing. High slope departures from spherical and lack of symmetry present challenges for manufacturers relying on conventional full aperture interferometry techniques as they are unable to resolve the interference fringes, and tactile metrology methods risk damaging the part. Some optical metrology techniques have been developed to assess the freeform geometries, but each struggle with either error buildup or complex alignment procedures which contribute to high manufacturing costs.

A novel non‑contact compact probe for freeform optical metrology will be presented. The probe featured in this work measures in three degrees-of-freedom with a polarization-based Twyman‑Green homodyne architecture for linear displacement sensitivity and a focusing lens and position sensitive detector for angular sensitivity. The opto-mechanical design, development, and qualification of a compact interferometry probe will be discussed and its viability as a metrology solution for freeform optics is assessed. Challenges in the design and fabrication of the probe are also highlighted, as well as future improvements to the mechanical and optical design for future development.