Abstract: Methods and systems for interferometrically characterizing diffractive elements are disclosed.

Abstract: Conical surfaces (and other complex surface shapes) can be interferometrically characterized using a locally spherical measurement wavefront (e.g., spherical and aspherical wavefronts). In particular, complex surface shapes are measured relative to a measurement point datum. This is achieved by varying the radius of curvature of a virtual surface corresponding to a theoretical test surface that would reflect a measurement wavefront to produce a constant optical path length difference (e.g., zero OPD) between the measurement and reference wavefronts.

Abstract: The invention features a surface profiling method including: collecting interferometric data related to a surface profile of a measurement object; and calculating the surface profile based on the collected interferometric data and at least one value indicative of dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object. The invention also features a surface profiling system including: an interferometry system which during operation provides interferometric data related to a surface profile of a measurement object; and an electronic processor coupled the interferometry system, wherein during operation the electronic processor calculates the surface profile based on the interferometric data and at least one parameter indicative of dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object.

Abstract: The invention features a method for determining a geometric property of a test object, the method including: interferometrically profiling a first surface of the test object in a first coordinate system; interferometrically profiling a second surface of the test object in a second coordinate system different from the first coordinate system; providing a relationship between the first and second coordinate system; and calculating the geometric property based on the interferometrically profiled surfaces and the relationship between the first and second coordinate system. In some embodiments, the relationship may be determined by using calibrated gage blocks or by using a displacement measuring interferometer. Corresponding system are also described.

Abstract: A full-field, geometrically-desensitized interferometer (GDI) instrument incorporates a combination of reflecting and refracting optics to perform beam splitting and recombining operations for surface profilometry. Symmetrically-positioned inbound and outbound optical subassemblies typically are arranged to direct inbound collimated beams from a light generator to the profiled surface of a test object and to direct outbound reflected beams to an imaging device as a single recombined outbound interference beam. Every point on the detector has a corresponding point on the object from which reflected illumination originated from both reflected beams. The optical path difference between the two inbound beams or between the two reflected outbound beams can be substantially independent of field position.

Abstract: The invention features an interferometry system for a measuring a surface profile or thickness of a measurement object.

Abstract: The optical assembly of a GDI instrument is configured to deviate or steer stray beams away from the pupil of the instrument's imaging device and/or to suppress stray beams. Stray beam deviation is optimized by selecting particular wedge and/or tilt configurations that achieve the desired stray beam deviation while avoiding or at least minimizing phase offset at the optimum metrology plane. Stray beam suppression can be achieved by providing the diffractive groove profile of the instrument's optical assembly with smooth edges. The resultant profile facilitates effective diffraction order management as well as a reduction in back reflection. The invention is particularly well-suited for use with a GDI instrument in which the optical assembly comprises first and second diffraction gratings.