Abstract: Disclosed is a method and corresponding apparatus for determining an absolute optical distance between two reflecting surfaces that make up an interferometric cavity, the method comprising: moving an illumination spot in a back focal plane of an interferometer along a trajectory that has a nonzero radial component relative to an optical axis to cause different radial positions for the illumination spot along the trajectory while synchronously acquiring images of interferograms of the interferometric cavity; and using one or more electronic processors to analyze the images to determine a functional dependence of an optical path difference (OPD) for the interferometric cavity versus radial position for the illumination spot and extract the absolute optical distance between the two reflecting surfaces based on the determined functional dependence.

Abstract: Disclosed is a method and corresponding apparatus for determining an absolute optical distance between two reflecting surfaces that make up an interferometric cavity, the method comprising: moving an illumination spot in a back focal plane of an interferometer along a trajectory that has a nonzero radial component relative to an optical axis to cause different radial positions for the illumination spot along the trajectory while synchronously acquiring images of interferograms of the interferometric cavity; and using one or more electronic processors to analyze the images to determine a functional dependence of an optical path difference (OPD) for the interferometric cavity versus radial position for the illumination spot and extract the absolute optical distance between the two reflecting surfaces based on the determined functional dependence.

Abstract: Disclosed is an illumination system for an interferometer including: a source of system light; a steering-mirror assembly to receive and reflect the system-light in at least two orthogonal directions; a tracking mechanism to track an angular orientation of the steering-mirror assembly in the two orthogonal directions and provide electronic signals representative of the angular orientation; a focus lens assembly to focus the system light reflected off the steering mirror assembly onto a focused spot on a 2-dimensional plane corresponding to a source plane of the interferometer; and an electronic controller operatively coupled to the steering-mirror assembly and configured to cause the focused spot on the source plane to follow a predetermined motion trajectory.

Abstract: A method for measuring a bond gap includes receiving a light beam at a first interferometer cavity and a reference interferometer cavity, in which the first interferometer cavity is defined by a first surface and a contact interface, and the contact interface is defined by a contact gap less than 1 ?m. The method includes determining a first interference amplitude of the first interferometer cavity and a second interference amplitude of the reference interferometer cavity by applying wavelength tuning and spectral analysis to measured intensities of light from the first interferometer cavity and the reference interferometer cavity. The contact gap is determined based on a ratio of the first interference amplitude and the second interference amplitude and information about a mapping between various interference amplitude ratios and expected contact gap values.

Abstract: A method for measuring a property of a test object with an interferometer includes: a) providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer; b) determining the position of the test object relative to the reference surface; and c) using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object.

Abstract: A method for measuring a property of a test object with an interferometer includes: a) providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer; b) determining the position of the test object relative to the reference surface; and c) using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object.

Abstract: Method and apparatus for determining the wavelength of a light beam are provided. An input light beam is received, and light from the input light beam is distributed to multiple channels. At a first pair of interferometer cavities that has a first free spectral range, two of the multiple channels of light are received. The intensity of light reflected from the first pair of cavities is measured, and a first estimate of the wavelength or optical frequency of the input light beam is determined based on measurements of interference signals from the first pair of cavities and an initial estimate of the wavelength or optical frequency. At a second pair of cavities that has a second free spectral range smaller than the first free spectral range, another two of the multiple channels of light are received.

Abstract: Techniques for removing interferometry signal phase variations caused by distortion and other effects in a multi-layer stack include: providing an electronic processor sample interferometry data acquired for the stack using a low coherence imaging interferometry system; transforming, by the electronic processor, the sample interferometry data to a frequency domain; identifying a non-linear phase variation from the sample interferometry data in the frequency domain, in which the non-linear phase variation is a result of dispersion introduced into a measurement beam by the test sample; and removing the non-linear phase variation from the sample interferometry data thereby producing compensated interferometry data.

Abstract: Method and apparatus for determining the wavelength of a light beam are provided. An input light beam is received, and light from the input light beam is distributed to multiple channels. At a first pair of interferometer cavities that has a first free spectral range, two of the multiple channels of light are received. The intensity of light reflected from the first pair of cavities is measured, and a first estimate of the wavelength or optical frequency of the input light beam is determined based on measurements of interference signals from the first pair of cavities and an initial estimate of the wavelength or optical frequency. At a second pair of cavities that has a second free spectral range smaller than the first free spectral range, another two of the multiple channels of light are received.

Abstract: A method for measuring a property of a test object with an interferometer includes: a) providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer; b) determining the position of the test object relative to the reference surface; and c) using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object.

Abstract: An optical method for determining an orientation of surface texture of a mechanical part includes: i) acquiring data for a first areal surface topography image using a surface topography measurement instrument, wherein the first image corresponds to a first field of view of the mechanical part for the surface topography measurement instrument; ii) rotating the mechanical part with respect to a rotation axis provided by a rotatable mount used to secure the mechanical part to provide a second field of view of the mechanical part for the surface topography measurement instrument, wherein the first and second fields of view overlap to provide image information about a common region of the mechanical part; iii) acquiring data for a second areal surface topography image using the surface topography measurement instrument, wherein the second image corresponds to the second field of view; and iv) processing the data from the images.

Abstract: Techniques for removing interferometry signal phase variations caused by distortion and other effects in a multi-layer stack include: providing an electronic processor sample interferometry data acquired for the stack using a low coherence imaging interferometry system; transforming, by the electronic processor, the sample interferometry data to a frequency domain; identifying a non-linear phase variation from the sample interferometry data in the frequency domain, in which the non-linear phase variation is a result of dispersion introduced into a measurement beam by the test sample; and removing the non-linear phase variation from the sample interferometry data thereby producing compensated interferometry data.

Abstract: Method include using an apparatus to measure a first surface field, at a first surface of the apparatus, of an artifact having one or more surface features with known topography. The method includes determining a first focus metric at the first surface based on at least a portion of a first surface profile containing the one or more surface features. Methods include digitally transforming, the first surface field into a second surface field at a second surface of the apparatus, deriving, a second surface profile from the second surface field and computing a second focus metric for the second surface profile, and determining, based on two or more focus metric values, an optimum surface for evaluating the instrument transfer function. Method include determining the instrument transfer function of the apparatus based on at least a portion of the surface profile derived from the surface field of the optimum surface.

Abstract: A method for determining characteristics of a test cavity, the method includes for each of a plurality of optical frequencies within a bandwidth of a tunable laser, measuring interference signals from the test cavity and a reference cavity having a known characteristic. The method includes determining values for the plurality of optical frequencies from the measured interference signals from the reference cavity and the known characteristic of the reference cavity, and determining the characteristic of the test cavity using the determined values of the plurality of optical frequencies.

Abstract: An optical method for determining an orientation of surface texture of a mechanical part includes: i) acquiring data for a first areal surface topography image using a surface topography measurement instrument, wherein the first image corresponds to a first field of view of the mechanical part for the surface topography measurement instrument; ii) rotating the mechanical part with respect to a rotation axis provided by a rotatable mount used to secure the mechanical part to provide a second field of view of the mechanical part for the surface topography measurement instrument, wherein the first and second fields of view overlap to provide image information about a common region of the mechanical part; iii) acquiring data for a second areal surface topography image using the surface topography measurement instrument, wherein the second image corresponds to the second field of view; and iv) processing the data from the images.

Abstract: A method for measuring a property of a test object with an interferometer includes: a) providing calibration information relating a focus setting for the interferometer to a position of the test object relative to a reference surface of the interferometer; b) determining the position of the test object relative to the reference surface; and c) using the interferometer to collect interferometric images of the test object for use in measuring the property of the test object.

Abstract: Determining information about a degree of freedom of rigid body motion of an encoder scale includes: directing a first beam toward an encoder scale, in which the first beam diffracts from an encoder scale; combining a diffracted component of the first beam with a second beam to form an interfering output beam; monitoring changes in the output beam as a function of a wavelength of the first and second beams; and determining the information about a degree of freedom of rigid body motion of the encoder scale based on changes in the output beam as a function of the wavelength.

Abstract: A method for determining characteristics of a test cavity, the method includes for each of a plurality of optical frequencies within a bandwidth of a tunable laser, measuring interference signals from the test cavity and a reference cavity having a known characteristic. The method includes determining values for the plurality of optical frequencies from the measured interference signals from the reference cavity and the known characteristic of the reference cavity, and determining the characteristic of the test cavity using the determined values of the plurality of optical frequencies.

Abstract: Method include using an apparatus to measure a first surface field, at a first surface of the apparatus, of an artifact having one or more surface features with known topography. The method includes determining a first focus metric at the first surface based on at least a portion of a first surface profile containing the one or more surface features. Methods include digitally transforming, the first surface field into a second surface field at a second surface of the apparatus, deriving, a second surface profile from the second surface field and computing a second focus metric for the second surface profile, and determining, based on two or more focus metric values, an optimum surface for evaluating the instrument transfer function. Method include determining the instrument transfer function of the apparatus based on at least a portion of the surface profile derived from the surface field of the optimum surface.

Abstract: Determining information about a degree of freedom of rigid body motion of an encoder scale includes: directing a first beam toward an encoder scale, in which the first beam diffracts from an encoder scale; combining a diffracted component of the first beam with a second beam to form an interfering output beam; monitoring changes in the output beam as a function of a wavelength of the first and second beams; and determining the information about a degree of freedom of rigid body motion of the encoder scale based on changes in the output beam as a function of the wavelength.