Progress with the XCALIBIR interferometer at NIST

In response to the increasing need for the characterization of precision optics, the National Institute of Standards and Technology has initiated a program for the development of SI traceable surface and wavefront metrology. A key instrument in this program is the “eXtremely accurate CALIBration InterferometeR” (XCALIBIR). XCALIBIR is a multi-configuration phase-measuring precision interferometer for the measurement of flat, spherical, and aspheric surfaces. We describe the interferometer and the calibration of the 300 mm aperture Fizeau configuration and the spherical Fizeau configuration. An uncertainty of 0.2 nm rms was achieved in a 3-flat calibration of three 300 mm diameter optical flats. Additional recent measurement results will be presented that illustrate the capabilities of the XCALIBIR interferometer.