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Low-coherence surface metrology using a multiple-beam optical probe

Despite increasing demand for freeform optical elements, at present there are no commercial systems to measure such components. In previously published research we demonstrated that a scanning low-coherence dual-wavelength interferometer can accurately measure the transmitted wavefront of hemispheric dome optics by mapping the optical thickness of the dome as a function of probe probe position. To address the issue of more generalized freeform surfaces, we have developed a new probe for the interferometer. This probe incorporates a reference surface and simultaneously projects four beams. This allows the instrument to measure both the position and orientation of the surface with respect to the probe as the probe is scanned over the object. Both the interior and exterior surfaces can be measured simultaneously. Furthermore, by overlapping the measurement regions, the redundant data can be used to minimize some forms of measurement error.