I propose a symmetric geometry for grazing-incidence interferometry of flat surfaces using diffraction gratings for beam splitting and recombination. The geometry employs a reference mirror to correct for relative inversion of the measurement and reference wave fronts. Preliminary testing with a 4-μm equivalent-wavelength system shows a 3ς repeatability of 20 nm for both smooth and rough surfaces, including a variety of precision-engineered metal, ceramic, and glass objects. The system has a comfortable working distance and large field of view, suitable for production testing.
© 2000 Optical Society of America
(050.1950) Diffraction and gratings : Diffraction gratings
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(150.3040) Machine vision : Industrial inspection
(220.4840) Optical design and fabrication : Testing
Peter de Groot, "Diffractive Grazing-Incidence Interferometer," Appl. Opt. 39, 1527-1530 (2000)