Abstract: The invention features a method for determining non-linear cyclic errors in a metrology system that positions a measurement object under servo-control based on an interferometrically derived position signal. The method includes: translating the measurement object under servo-control at a fixed speed; identifying frequencies of any oscillations in the position of measurement object as it is translated at the fixed speed; and determining amplitude and phase coefficients for sinusoidal components at the identified frequencies which when combined with the position signal suppress the oscillations. The invention also features a method for positioning a measurement object under servo-control based on an interferometrically derived position signal indicative of a position for the measurement object.

Abstract: An interferometer that includes a first beam-splitting surface positioned to separate an input beam into a first beam and a second beam. A first set of optics is positioned to receive the first beam, direct it to contact a first reflector multiple times and produce a first intermediate beam. The first intermediate beam follows a nominal output path when the first reflector has a first alignment normal to the first beam prior to reflection by the first reflector. The first set of optics includes a second beam-splitting surface, a third beam-splitting surface, and a first fold optic that are positioned to reduce displacement of the first intermediate beam from the nominal output path when the first reflector has an alignment different from the first alignment.

Abstract: In certain aspects, the invention features an interferometry system that utilizes coupled cavities (e.g., at least one remote cavity and a main cavity) and an extended light source. The remote cavity and the main cavity can have similar optical properties (e.g., similar numerical apertures (NA's)), allowing them to introduce offsetting, and therefore compensating, non-zero optical path differences (OPD's) between the measurement and reference beams without degrading interference fringe contrast due to source spatial coherence. In other words, for each non-zero OPD in the main cavity there exists a configuration of the remote cavity such that the total OPD between test and reference chief rays, and between test and reference marginal rays is substantially zero.

Abstract: Methods and apparatus for reducing the effects of non-isotropic gas distributions on interferometry measurements are disclosed.

Abstract: An apparatus including: an interferometer comprising a series of three partially reflective reference surfaces, wherein the interferometer is configured to direct electromagnetic radiation to a test surface along a path through the series of three partially reflective reference surfaces, and direct the electromagnetic radiation reflected from each of the surfaces to form an optical interference pattern on a detector, wherein the interferometer comprises a first reference optic supporting the first reference surface and a second reference optic supporting the second and third reference surfaces, and wherein the second reference optic is configured to adjustably rotate to exchange an order of the second and third reference surfaces along the path relative to the first reference surface.

Abstract: In some aspects, the invention relates to methods and systems for creating apodized periodic structures, such as apodized gratings in fibers. To create the periodic structures, a photosensitive medium is exposed to a spatially-varying radiation pattern. During the exposure, the position of the radiation pattern can oscillate with the respect to the photosensitive medium, thereby changing the average local refractive index of the medium. These methods and systems may be used to create regular structures in any appropriate medium, such as doped glasses and photosensitive polymers.

Abstract: Methods and apparatus for characterizing and compensating non-cyclic errors in fiber optic pickups in interferometry systems are disclosed.

Abstract: An interferometry method including: i) forming an optical interference image by combining different portions of an optical wave front reflected from a pair of surfaces; ii) recording an interference signal at different locations of the optical interference image in response to varying the relative position of the two surfaces over a range of positions; iii) transforming the interference signal for at least one of the locations to produce a spectrum having a peak at a spectral coordinate corresponding to the variation in the relative position of the two surfaces over a range of positions; iv) identifying the spectral coordinate of the peak; and v) for each location, extracting the spectral phase of the interference signal at the coordinate of the peak. For example, the method may further include, for each of the different locations, determining a surface profile of one of the surfaces based on the spectral phase of the interference signal at each of the multiple locations.

Abstract: An interferometer for receiving a measurement beam from a target location on a stage of a semiconductor lithography machine and a reference beam from a reference location separated from the target location by a separation distance. The interferometer has a reference path to be traversed by the reference beam within the interferometer and a measurement path to be traversed by the measurement beam within the interferometer. Both the measurement path and the reference path are at least as long as the separation distance between the reference location and the target location.

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

Abstract: Interferometer systems are described that comprise optical assemblies to measure multiple degrees of freedom of a stage mirror and the topography of a reflecting surface of a stage mirror represented by datum lines and datum lines with corresponding local rotations of the reflecting surface of the stage mirror about the datum lines with high lateral spatial resolution. The interferometer systems measure slopes of datum lines and local rotations of the reflecting surface about the datum lines using single pass interferometric measurements of angular changes of directions of beams reflected by the reflecting surfaces. Two or more datum lines on a reflecting surface with concomitant measures of local rotations may be used to characterize topographic features, and these may be measured in situ in a lithography tool or measured off line either before installation or after removal from a lithography tool.

Abstract: In certain aspects, the invention features scanning interferometry systems and methods that can scan an optical measurement surface over distances greater than a depth of focus of imaging optics in the interferometry system, while keeping an optical measurement surface in focus (i.e., maintaining an image of the optical measurement surface coincident with the detector). The optical measurement surface refers to a theoretical test surface in the path of test light in the interferometer that would reflect the test light to produce an optical path length difference (OPD) between it and reference light that is equal to a constant across a detector.

Abstract: A corner cube retroreflector having a coating including one or more layers at each reflecting surface. The coating causes the retroreflector to have polarization eigenstates that are substantially linear and to have the properties of a half-wave plate. The coated retroreflector can be used in interferometry and microlithography system.

Abstract: Methods for determining an appropriate tuning rate for interferometry systems employing phase-shifting interferometry are disclosed.

Abstract: A method including: providing a coherence profile and a phase profile derived from interferometry data for a test surface; calculating a phase gap map, wherein the phase gap map is related to a difference between the coherence profile and the phase profile; fitting an expression including a term based on the coherence profile to the phase gap map; and determining a height profile for the test surface using information derived from the fit.

Abstract: Interferometers can be configured to maintain a measurement beam substantially orthogonal to a plane measurement mirror and to minimize the lateral beam shear between the measurement and reference beam components of the output beam to a detector. These interferometers use a dynamic beam steering element to redirect the input beam in response to changes in the orientation of the measurement plane mirror. These interferometers may be further configured to measure displacement and change in orientation of the plane mirror or configured in a combination of single pass interferometers fed by the input beam for measuring displacement and change in orientation of the plane mirror.

Abstract: Interferometric apparatus and methods for assembling and measuring highly precise optical assemblies such as triple corner cubes, and the like. The apparatus and methods use one or more interferometers that can simultaneously measure the shape, orientation, and distance to one or more surfaces.

Abstract: A method and apparatus used to reduce glitches in measurements made by an accumulation of phase changes over a range greater than 2?. Embodiments of the invention feature the use of a glitch filter that receives a phase input indicating a position value. The glitch filter reduces glitches by using a feedback term that has been reduced modulo 2?. The method includes measuring a plurality of values of a measurement signal, determining a current position value based on each of the plurality of measured values, wherein determining includes determining a delta value based on a current measured value and a previous position value, wherein the delta value is reduced modulo 2? to a range of ±?, and determining the current position value based on the determined delta value, and outputting at least one of the determined current position value and a velocity value.

Abstract: The invention features an apparatus including a first portion defining an optical axis and configured to connect to an optical fiber, a second portion having a reference surface configured to connect with a terminal, and a third portion between the first and second portions. The third portion bends more easily than either the first or second portion to permit adjustable alignment of the optical axis relative to the reference surface.