High-aperture low-coherence interferometer with a diffraction reference wave.

A high-aperture low-coherence interferometer with a diffraction reference wave based on a tipped single-mode optical fiber was proposed and investigated. Due to the usage of the central least-aberrated region of the diffracted wavefront, the interferometer comprise record working aperture among known PDIs. The interferometer makes it possible to study samples with a reflectance that varies over a wide range. A demonstration of the use of this interferometer for high-precision measurements of a spherical mirror is presented. Sub-nanometer reproducibility of measurements in terms of the peak to valley (PV) parameter and sub-angstrom reproducibility in terms of the rms are demonstrated.