A reference surface is used to develop an empirical plot between a parameter of interest, such as roughness or modulation, and the position of the reference mirror in an interferometer by repeating measurements of the reference surface at different positions of the reference mirror so as to identify the in-focus position of the reference mirror. Serial quality-control measurements of samples of interest are carried out with the reference mirror in such in-focus position until a predetermined quality-control event triggers an automated system re-calibration by re-measuring the reference surface and, if the result does not correspond to the in-focus position of the reference mirror according to the plot, by finding a new in-focus position for the reference mirror using the same plot or, alternatively, a new similarly produced plot. Sample measurements are then resumed with the mirror placed at that new position.

A grazing incidence interferometer is configured to measure a profile of a target surface using a measurement beam radiated on the target surface in a direction oblique to a normal line of the target surface and reflected on the target surface to cause an interference with a reference beam. The grazing incidence interferometer includes: a light source to emit light; a first polarization beam splitter that splits the light from the light source into the reference beam and the measurement beam; a ratio changer that changes a light amount ratio between the reference beam and the measurement beam; a second polarization beam splitter that synthesizes the measurement beam reflected on the target surface and the reference beam; and an image capturing camera that receives the synthesized beam of the reference beam and the measurement beam.

A compact and portable apparatus for measuring properties of objects utilizing a fiber optic Sagnac interferometer is enabled. The fiber optic Sagnac interferometer may be a double differential Sagnac interferometer. The interferometer core may be implemented with fiber optic components including polarization maintaining optical fiber, and by utilizing an auto-balanced avalanche photodetector. An optical switch may be incorporated to maintain relatively low average probe signal power while allowing optimal peak probe signal power. The compact and portable apparatus may be configured to measure ultrasonic vibrations, a displacement of an object surface in response to ultrasonic vibrations, and/or a vibration speed of the object surface. A wideband light source may be amplified and stabilized. A sensor head of the interferometer may incorporate a collimator adjustable to block a central portion of the projected probe beam thereby at least in part enabling in-plane and out-of-plane measurements.

Methods, systems and devices for estimating a parameter of interest in a borehole. The method may include generating information from an optical displacement device relating to relative motion between two or more reflective surfaces thereof that is indicative of the parameter of interest; and preventing changes in the information resulting from changes at the optical displacement device in at least one of i) temperature, or ii) pressure, by compensating for the changes. Compensating may include adjusting at least one light source generating an electromagnetic beam at least partly received by the optical displacement device responsive to information relating to a control optical displacement device at the optical displacement device. Compensating may include using an optical displacement device and configuring the optical displacement device such that a difference between a first variable gap and a second variable gap is substantially zero while the apparatus is subject to nominal conditions.

A polarization-sensitive OCT apparatus includes an interference unit configured to split light emitted from a light source into measurement light and reference light and to generate interfered light by causing returning light of the measurement light that has irradiated a subject to interfere with the reference light that has traveled through a reference arm, a splitting unit configured to split the interfered light into different polarization components, a generation unit configured to detect the polarization components split by the splitting unit and to generate a signal, detection units configured to detect respective polarization states of the measurement light in a sample arm, the returning light of the measurement light that has passed through the interference unit, and the reference light that has passed through the interference unit, and polarization control units configured to control the respective polarization states on the basis of the respective polarization states that have been detected.

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.

Provided are a detection system, compensation method and computer-readable recording medium applicable to semiconductor surface morphology to provide feature information corresponding to spectral signals to a neural network model and provide feature information corresponding to spectral signals, a detected height, and an actual height actually measured to another neural network model. The combinational neural network models thus trained and built can generate a compensation value for a to-correct height corresponding to a to-correct spectral signal having variability. The compensation value provides required compensation for height information to not only enhance the precision of the detection of semiconductor surface morphology but also enhance the reliability of the detection system.

An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.

A system and method include a microscope with an interferometer. Another aspect of an optical microscope with interferometry includes tilting a reference mirror and/or a sample offset from a centerline of an adjacent objective or telescope lens. A further aspect provides a microscope system and method which are configured to simultaneously detect a fringe pattern with a phase-shift using light polarization in a single-shot.

A measurement apparatus for measuring a thickness of a semiconductor wafer includes: an optical system configured to perpendicularly irradiate a sample wafer and a reference wafer with light, and receive interference signals of the light reflected on front and back surfaces of the respective wafers; a signal processor configured to perform frequency analysis of the interference signals received by the optical system to obtain peak positions of a point spread function of the respective wafers; and a calculator configured to calculate a thickness tsample of the sample wafer based on the peak position x of the sample wafer and the peak position y of the reference wafer obtained by the signal processor, and a thickness treference of the reference wafer.