Abstract

A Mirau-type interferometer has been developed for microscope objectives with an unobscuring reference surface. Using polarization optics and a specially designed coating, the central obscuration inherent in the Mirau interferometer has been eliminated. The absence of a central obscuration improves the mid-range spatial frequency, response of the objective lens transfer function, thereby improving image contrast. The unobscuring reference surface extends the Mirau interferometer technique to low magnification objective lenses. (i.e., 1–5×). The Mirau interferometer technique used at low magnification allows increased working distances, compared with the Michelson- type interferometer technique for microscopic objectives. The Mirau interferometer technique can be extended to high-power high-N.A. (i.e., 100×/N.A. = 1.4) oil immersion objectives so that the highest possible lateral resolution is achievable.

© 1988 Optical Society of America