A method for measuring a spatial distortion of a target surface (110) of a workpiece (110A). Light is transmitted twice through a reference pattern-generator (104) and impinged upon a workpiece pattern-generator (108). Then, with an optical detector (116), first and second beams formed by the light as a result of interaction with two pattern- generators (104) (106) is acquired to produce a signal characterizing geometry of interference fringes formed at the detector (116) by the first and second beams. Indicia representing at least one of a type and a value of spatial distortion of the target surface (110) is generated and recorded. A system embodying the implementation of the method.

A position measurement system configured to measure a position of an object. The system includes an optical system to obtain a first measurement wave and a second measurement wave from a radiation source, and to allow the first and second measurement wave to at least partially interfere with each other after interaction of at least one of the first and second measurement wave with the object to form a first detection beam. The system further includes a first detector to receive the first detection beam. The system also has a processing unit configured to receive an output from the first detector and to determine a signal representative for the position of the object from the output, wherein the optical system includes a phase modulator configured to modulate a phase difference between the first measurement wave and the second measurement wave.

A method is presented for determining a phase of an input beam (110, E.sub.in) without a reference ray. In the method, an input beam (110, E.sub.in) having a plurality of input rays is split into a main beam (112, E1) and a reference beam (114, E2) in such a way that each input ray is split into a main ray of the main beam (112, E1) and a comparative ray of the reference beam (114, E2). The main beam (112, E1) is propagated along a first interferometer arm, and the reference beam (114, E2) is propagated along the second interferometer arm. The propagated main beam (112, E1) and the propagated reference beam (114, E2) are superposed to form an interference beam having a plurality of interference rays. The propagation along the first and second interferometer arms is carried out such that at least one interference ray of the interference beam is a superposition of a main ray of the propagated main beam (112, E1) assigned to a first input ray of the input beam (110, E.sub.in), and of a comparative ray of the propagated reference beam (114, E2) assigned to a second input ray of the input beam (110, E.sub.in) different from the first input ray.

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.

In an alignment sensor of a lithographic apparatus, position sensing radiation is delivered to a target (P1). After reflection or diffraction from the target, position sensing radiation is processed to determine a position of the target. Reference radiation interferes with the position sensing radiation) while a relative phase modulation is applied between the reference radiation and the position sensing radiation. The interfering radiation includes a time-varying component defined by the applied phase modulation. The interfering radiation is delivered to two photodetectors in such a way that each photodetector receives said time-varying component in anti-phase to that received at the other photodetector. A difference signal (i(t)) from said photodetectors contains an amplified, low noise version of said time-varying component. This is used in determining the position of the target. Mode matching enhances interference. Surface scattered radiation is rejected.

The problem of measuring height properties (for instance, for aspheric optical components) is addressed by systems and methods that employ heterodyne optical interferometry to detect a plurality of interference patterns corresponding to a plurality of orientations of the surface and that determine a height property (such as a mid-spatial frequency spectrum or topography) of the surface from the plurality of interference patterns.

The invention relates to a three-dimensional interferometer (100) for measuring a light field generated by an object (110), in particular the determination of an electric field (E1.sub.ij, E2.sub.ij), especially of the phase (1.sub.ij, 2.sub.ij) or of the phase (1.sub.ij, 2.sub.ij) and of the intensity or the absolute value of the electric field (E1.sub.ij, E2.sub.ij), having a first interferometer arm (150), which can be so configured or adjusted, especially configured, that a first light beam runs through it, a second interferometer arm (152) so configurable or adjustable, especially configured, that a second light beam runs through it, a beam splitter (101)that is configuredlocated between an object point (112) of the object (110) on the one hand and the first interferometer arm (150) and the second interferometer arm (152) on the other hand, to split a light beam emanating from the object point (112) at the beam splitter (101) into the first light beam and the second light beam, a detection plane (131) or detection surface, which is located after the first interferometer arm (150) and the second interferometer arm (152) and which is configured so that on it the first light beam and the second light beam are brought into inference in an interference area (132), and an overlap device (106) located between the detection plane (131) on the one hand and between the first interferometer arm (150) and the second interferometer arm (152) on the other hand, wherein the beam splitter (101), the first interferometer arm (150), the second interferometer arm (152), the overlap device (106) and the detection plane (131) can be configured or adjusted, especially configured so that there is an object point (112) of the object (110) exactly a central ray (114) emanating from the object point (112) which is split at the beam splitter (101) into a first central ray (120) and a second central ray (121), wherein the central ray (114) is a part of the light beam, the first central ray (120) is part of the first light beam and runs through the first interferometer arm (150) and the second central ray (121) is part of the second beam and runs through the second interferometer arm (152), and wherein the first central ray (120) and the second central ray (121) overlap in a central image point (133) on the detection plane (131) in the interference a

A position measurement system configured to measure a position of an object. The system includes an optical system to obtain a first measurement wave and a second measurement wave from a radiation source, and to allow the first and second measurement wave to at least partially interfere with each other after interaction of at least one of the first and second measurement wave with the object to form a first detection beam. The system further includes a first detector to receive the first detection beam. The system also has a processing unit configured to receive an output from the first detector and to determine a signal representative for the position of the object from the output, wherein the optical system includes a phase modulator configured to modulate a phase difference between the first measurement wave and the second measurement wave.

The present invention is related with the two-channel point-diffraction interferometer for testing the optical systems or optical elements. The two-channel point-diffraction interferometer comprising a laser source inducing a linearly polarized laser beam which is divided by a beam splitter to a working channel and to a reference channel whereas the one half of light as working channel is directed from the first collimator to the working collimator by a first single-mode optical fiber to keep polarization of light unchanged, and another half of light as reference channel is directed from the second collimator to the reference collimator by a second single-mode optical fiber to keep polarization of light unchanged.

A semiconductor measurement apparatus may include an illumination unit configured to irradiate light to the sample, an image sensor configured to receive light reflected from the sample and output multiple interference images representing interference patterns of polarization components of light, an optical unit in a path through which the image sensor receives light and including an objective lens above the sample, and a control unit configured to obtain, by processing the multi-interference image, measurement parameters determined from the polarization components at each of a plurality of azimuth angles defined on a plane perpendicular to a path of light incident to the image sensor. The control unit may be configured to determine a selected critical dimension to be measured from a structure in the sample based on measurement parameters. The illumination unit and/or the optical unit may include a polarizer and a compensator having a ? wave plate.