A spatial accuracy correction apparatus performs a spatial accuracy correction of a positioner displacing a displacer to a predetermined set of spatial coordinates using a measurable length value measured by an interferometer and a measurable value of the set of spatial coordinates of the displacement body that is measured by the positioner. The measured length value and the measured value for each measurement point are acquired by displacing the displacement body to a plurality of measurement points in order, one or more repeated measurements are conducted for at least one of the plurality of measurement points being measured after conducting measurement of the measured length value and the measured value for each of the plurality of measurement points, and the plurality of points are measured again when a repeat error of the measured length value is equal to or greater than a threshold value.

The invention discloses a method for measuring a complex degree of coherence of a random optical field by using a mutual intensity-intensity correlation, including the steps of: building a test optical path; rotating a quarter-wave plate to enable the fast axis of the quarter-wave plate to be consistent with a polarization direction of reference light, to obtain light intensity distribution information of a first combined light; rotating the quarter-wave plate to enable the slow axis of the quarter-wave plate to be consistent with the polarization direction of the reference light, to obtain light intensity distribution information of a second combined light; blocking the reference light to obtain light intensity distribution information of to-be-tested light; blocking the to-be-tested light to obtain light intensity distribution information of the reference light; and calculating the amplitude and phase of a complex degree of coherence of the to-be-tested light.

A method for calibrating a measuring device (10) for interferometrically determining a shape of an optical surface (12) of an object under test (14). The measuring device includes a module plane (32) for arranging a diffractive optical test module (30) which is configured to generate a test wave (34) that is directed at the optical surface and that has a wavefront at least approximately adapted to a target shape (60) of the optical surface. The method includes: arranging a diffractive optical calibration module (44) in the module plane for generating a calibration wave (80), acquiring a calibration interferogram (88) generated using the calibration wave in a detector plane (43) of the measuring device, and determining a position assignment distribution (46) of points (52) in the module plane to corresponding points (54) in the detector plane from the acquired calibration interferogram.

A laser interference device includes a measurement laser that outputs a laser beam, a beam splitter that divides the laser beam into a measurement laser beam and a frequency monitor laser beam, a reference laser that outputs a reference laser beam, a frequency detector that detects a beat frequency resulting from interference between the reference laser beam and the frequency monitor laser beam, a wavelength calculator that calculates a wavelength of the frequency monitor laser beam (a wavelength measurement value) on the basis of the beat frequency, a light detector that detects an interference light of the measurement light and the reference light of the measurement laser beam and outputs a light detection signal, and a displacement calculator that calculates a displacement of the measurement mirror by performing an arithmetic process based on the wavelength measurement value and the light detection signal.

An optical coherence tomography (OCT) system comprises: an imaging catheter; a calibration phantom removably arranged at least partially surrounding the distal end of the catheter; and a processor configured to control the catheter to acquire OCT images. The phantom has known dimensions and specific optical properties which provide non-changing calibration fiducials that span the imaging range of the system. The phantom is imaged by the catheter upon first connection to the system. The processor calculates a thickness of the phantom in the OCT image, and preforms z-offset calibration by setting the position of a phantom surface in the OCT image to a known nominal value. The known nominal value is related to one or more of the known thickness of the phantom or a diameter of the catheter sheath or a nominal angle of the light beam or the imaging range of the system.

The present description relates to a stabilized interferometric system comprising: a light source (210) for emitting an initial beam of coherent light; a spatial light modulator (220) configured to receive at least a first part of said initial beam and input data (203) and configured to emit a spatially modulated beam resulting from a spatial modulation of a parameter of said first part of said initial beam based on said input data; a scattering medium (230) configured to receive said spatially modulated beam; a detection unit (240) configured to acquire an interference pattern (IN.sub.0) resulting from the interferences between randomly scattered optical paths taken by the spatially modulated beam through the scattering material; a control unit (250) configured to vary the frequency of the laser source in order to at least partially compensate a change in said interference pattern resulting from a change in at least one environmental parameter.

A measurement system for use in measuring parameters of a patterned sample, the system including a broadband light source, an optical system configured as an interferometric system, a detection unit, and a control unit, where the interferometric system defines illumination and detection channels having a sample arm and a reference arm having a reference reflector, and is configured for inducing an optical path difference between the sample and reference arms, the detection unit for detecting a combined light beam formed by a light beam reflected from the reflector and a light beam propagating from a sample's support, and generating measured data indicative of spectral interference pattern formed by spectral interference signatures, and the control unit for receiving the measured data and applying a model-based processing to the spectral interference pattern for determining one or more parameters of the pattern in the sample.

An OCT imaging method of some exemplary aspects includes acquiring a first three dimensional data set by applying an OCT scan targeting a first three dimensional region of a sample, creating a first two dimensional map based on representative intensity values respectively of a plurality of pieces of A-scan data included in the first three dimensional data set, designating a second three dimensional region of the sample based on the first two dimensional map, acquiring a second three dimensional data set by applying an OCT scan targeting the second three dimensional region, and generating image data from at least part of the second three dimensional data set.

We describe apparatus for measurement of thickness and topography of slabs of materials employing probes with filters using polarization maintaining fibers.

The disclosure discloses a phase delay extraction and compensation method in a PGC phase demodulation technology. The sinusoidal phase modulation interference signal is converted into a digital interference signal by an analog-to-digital converter after amplification and filtering, and the digital interference signal is subjected to orthogonal downmixing of first-order, second-order, and fourth-order harmonics simultaneously to obtain three pairs of orthogonal harmonic amplitude signals. The three pairs of orthogonal harmonic amplitude signals are used to extract phase delay, and the result is used to calculate the corresponding phase delay correction coefficients, and the phase delay correction coefficient are multiplied by the corresponding absolute harmonic amplitude signal equal to the sum of the absolute value of the orthogonal harmonic amplitude signals to obtain a new harmonic amplitude signal that is not affected by the phase delay, then the phase to be measured is obtained through the arc tangent operation.