Multiple wavelength image plane interferometry

摘要

A system for interferometric inspection of an object includes a number of improvements to reduce spurious reflections and provide precision measurement of large objects. A neutral density filter of absorptive glass is used as an attenuator to reduce undesirable reflections which may otherwise result in detector saturation. A wedge-shaped beam splitter having at least one anti-reflective surface is also utilized to reduce unwanted reflections. The system uses multiple wavelength interferometry to provide range information for an object. Additional improvements in precision may be provided by using a wavelength calibration device such as an etalon, a wavemeter, or a reference cell having relatively narrow transmission peaks, to improve the accuracy in determining the laser wavelengths. The wavelength information may be used to more precisely determine range values for the object. The various improvements in precision and accuracy facilitate use of differing optical path lengths for the reference beam and object beam so that overall system size and complexity is reduced.