Abstract: A method for determining information about an object including a curved portion and a planar portion, the curved portion having a first curved surface having an apex and defining an axis of the object, includes: directing measurement light to the object; detecting measurement light reflected from the first curved surface of the curved portion; detecting measurement light reflected from at least one other surface of the object; and determining, based on the detected light, information about the apex of the first curved surface of the curved portion.

Abstract: Systems and methods for generating 3D representations of shape and color texture of a test surface are described. In one aspect, surface topography interferometers are equipped with a multi-element detector and an illumination system to produce a true-color image of the measured object surface. Color information can be presented as a true-color two-dimensional image or combined with topography information to form a three-dimensional representation of the shape and color texture of the object, effectively creating for a human observer the impression of looking at the actual part.

Abstract: Methods and systems for measuring asymmetric surface topology are described. In one aspect, a method includes directing a test beam including a spherical wave front along an optical axis to reflect from a test surface; combining the test beam reflected from the test surface with a reference beam to form an interferogram on a detector, where the test and reference beams are derived from a common source; and recording the interferogram for each of multiple lateral displacements of the test surface relative to the optical axis. For each recorded interferogram, the curvature of the spherical wave front at the test surface substantially matches a local curvature of the test surface along a first axis orthogonal to the optical axis, and the multiple lateral displacements of the test surface each include a component along a second axis orthogonal to each of the first axis and the optical axis.

Abstract: A photo-mask for use in extreme ultraviolet (EUV) lithography, in which the photo-mask has low coefficient of thermal expansion and high specific stiffness.

Abstract: An interferometry system includes: a light source, defining a coherence length, an interferometer configured to combine measurement and reference beams to form an output beam, where the interferometer includes a dispersion imbalance between measurement and reference paths large enough to produce a coherence envelope for the system having a width more than twice the coherence length; a phase modulation device configured to introduce a variable phase between the measurement and reference beams; a detector; imaging optics to direct the output beam to the detector and produce an image of the measurement surface; and an electronic processor electronically coupled to the phase modulation device and the detector and configured to record multiple interference signals corresponding to different locations on the measurement surface, in which the interference signals are based on the intensity of the output beam as a function of the variable phase for the different locations of the measurement surface.

Abstract: In-situ calibration of an interferometer includes making a sequence of phase measurements of a test object using the interferometer, each of the measurements having a same carrier fringe frequency, where at least some of the measurements are made at three or more different orientations of carrier fringes, and determining information about the test object based on at least some of the phase measurements, in which determining the information includes reducing errors in the measurements arising from imperfections in the interferometer based on the measurements made at the three or more different orientations.

Abstract: An encoder system includes an encoder scale and an encoder head, in which the encoder head is configured to combine each twice-diffracted measurement beam of multiple twice-diffracted measurement beams with a corresponding reference beam to form multiple output beams, where the encoder head includes a monolithic optical component having multiple facets, the multiple facets being arranged to: receive multiple once-diffracted measurement beams from a surface of the encoder scale; and redirect the multiple once-diffracted measurement beams back towards the surface of the encoder scale, the encoder scale being positioned in a path of the once-diffracted measurement beams to produce the twice-diffracted measurement beams.

Abstract: Disclosed is an apparatus including a mechanical reference frame and a rigid object mechanically coupled to the reference frame by two or more constraints. The stiffnesses of at least two of the constraints are different from one another, and the relative locations and stiffnesses of the constraints cause a designated point on the rigid object to remain stationary with respect to the reference frame during thermal expansion of the rigid object over a range of temperatures.

Abstract: An optical element includes a monolithic body portion, the monolithic body portion having an inner body portion, an outer body portion extending at least partially around the inner body portion, and exactly three flexural hinges connecting the inner body portion to the outer body portion. One of the inner body portion and the outer body portion defines an optical active portion configured to reflect, refract, or diffract light, and the other of the inner body portion and outer body portion defines a mount portion.

Abstract: A method includes obtaining, from a detector of an interferometry system, an interference signal based on a combination of a first beam and a reference beam, subsequent to the first beam being diffracted by an encoder scale, obtaining, through an electronic processor, an error compensation signal based on a non-harmonic cyclic error that modifies the interference signal, and outputting information about a change in a position of the encoder scale relative to an optical assembly of the interferometry system based on the interference signal and the error compensation signal.

Abstract: An encoder interferometry system includes a beam splitting element positioned to receive an input beam from a light source, in which the beam splitting element is configured to direct a first portion of the input beam along a measurement path to define a measurement beam and a second portion of the input beam along a reference path to define a reference beam, an encoder scale positioned to diffract the measurement beam at least once, one or more optical components configured and arranged to alter a direction of a first diffracted portion of the measurement beam and a direction of a second diffracted portion of the measurement beam such that beam paths of the first diffracted portion and the second diffracted portion are non-parallel subsequent to the first diffracted portion and the second diffracted portion passing through the beam splitting element, and a detector positioned to receive the first diffracted portion.

Abstract: An interferometry system for monitoring changes in the position of an object, the system includes a spectrally broadband light source, a sensor module having an interferometer that direct portions of the light received from the source along separate paths. The system includes an intensity monitor having a detector configured to measure the intensity of additional light derived from the source and to produce a monitor output signal. The system includes an electronic processing module to process a sensor output signal based on the monitor output signal to account for intensity fluctuations in light output by the source, and determine information about the changes in the position of the object. The intensity monitor is configured to characterize the intensity fluctuations as a function of wavelength or intensity fluctuations that are spectrally correlated.

Abstract: In-situ calibration of an interferometer includes making a sequence of phase measurements of a test object using the interferometer, each of the measurements having a same carrier fringe frequency, where at least some of the measurements are made at three or more different orientations of carrier fringes, and determining information about the test object based on at least some of the phase measurements, in which determining the information includes reducing errors in the measurements arising from imperfections in the interferometer based on the measurements made at the three or more different orientations.

Abstract: A method is disclosed which includes: using a scanning interferometry system, generating a sequence of phase-shifted interferometry images at different scan positions of an object comprising a buried surface, identifying a scan position corresponding to a position of best focus for the buried surface based on the sequence of phase-shifted interferometry images of the object, and generating a final image based on the phase-shifted interferometry images and the scan position, where the interferometric fringes in the final image are reduced relative to the interferometric fringes in the phase-shifted interferometry images.

Abstract: An encoder head includes one or more components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to the encoder scale; ii) receive a first return beam from the encoder scale at a first return angle, the first return angle being different from the first incident angle; iii) redirect the first return beam to the encoder scale as a second incident beam at a second incident angle; and iv) receive a second return beam back from the encoder scale at a second return angle, the second return angle being different from the second incident angle, in which a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle.

Abstract: A method for determining information about changes along a degree of freedom of an encoder scale includes directing a first beam and a second beam along different paths and combining the first and second beams to form an output beam, where the first and second beams are derived from a common source, the first and second beams have different frequencies, where the first beam contacts the encoder scale at a non-Littrow angle and the first beam diffracts from the encoder scale at least once; detecting an interference signal based on the output beam, the interference signal including a heterodyne phase related to an optical path difference between the first beam and the second beam; and determining information about a degree of freedom of the encoder scale based on the heterodyne phase.

Abstract: An encoder head includes one or more components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to the encoder scale; ii) receive a first return beam from the encoder scale at a first return angle, the first return angle being different from the first incident angle; iii) redirect the first return beam to the encoder scale as a second incident beam at a second incident angle; and iv) receive a second return beam back from the encoder scale at a second return angle, the second return angle being different from the second incident angle, in which a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle.

Abstract: A system includes an interference microscope having one or more optical elements arranged to image a test object to an image plane by combining test light from the test object with reference light from a reference object to form an interference pattern at the image plane, wherein the test and reference light are derived from a common broadband light source.

Abstract: An encoder interferometry system includes an interferometer positioned to receive first and second beams having different frequencies, in which the interferometer has at least one polarizing beam splitting element for directing the first beam along a measurement path to define a measurement beam and the second beam along a reference path to define a reference beam. The encoder interferometry system further includes a encoder scale positioned to diffract the measurement beam at least once, a detector positioned to receive the measurement and reference beams after the measurement beam diffracts from the encoder scale, and an output component positioned to receive the measurement and reference beams before they reach the detector and deflect spurious portions of the first and second beam away from the detector.

Abstract: A method for determining information about a test object includes combining two or more scanning interference signals to form a synthetic interference signal; analyzing the synthetic interference signal to determine information about the test object; and outputting the information about the test object. Each of the two or more scanning interference signals correspond to interference between test light and reference light as an optical path length difference between the test and reference light is scanned, wherein the test and reference light are derived from a common source. The test light scatters from the test object over a range of angles and each of the two or more scanning interferometry signals corresponds to a different scattering angle or polarization state of the test light.