An optical system configured as part of optical metrology unit used to assess the operational status of a workpiece and, in a specific case, configured as an encoder head of a lithographic exposure tool. The optical system is devoid of a stand-alone optical corner-cubes and includes, instead, a single, imperfect or frustrated cuboid of optically-isotropic material that, in operation with the diffraction grating of the workpiece, simultaneously forms four interferometric signals for measuring x-, y, and z-positions of the workpiece grating relative to the optical system. Proposed system and method solve problems of (i) structural complexity of a conventional metrology unit for use in an exposure tool, (ii) burdensome alignment of the multitude of optical prisms in the process of forming such metrology unit, and (iii) cyclic non-linear errors associated with measurements involving conventional corner-cubes-based metrology units.

A stage system includes a movable stage, and an encoder for measuring a position of the stage, wherein the encoder includes an emitter for emitting an encoder beam, a grating for interacting with the encoder beam, and a detector for detecting the encoder beam having interacted with the grating, the encoder beam in use propagating along an optical path; a purging cap at least partly enclosing the optical path; and a purging medium supply device for supplying a purging medium into the purging cap.

A stage system includes a movable stage, and an encoder for measuring a position of the stage, wherein the encoder includes an emitter for emitting an encoder beam, a grating for interacting with the encoder beam, and a detector for detecting the encoder beam having interacted with the grating, the encoder beam in use propagating along an optical path; a purging cap at least partly enclosing the optical path; and a purging medium supply device for supplying a purging medium into the purging cap.

An encoder head includes one or more components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to the encoder scale; ii) receive a first return beam from the encoder scale at a first return angle, the first return angle being different from the first incident angle; iii) redirect the first return beam to the encoder scale as a second incident beam at a second incident angle; and iv) receive a second return beam back from the encoder scale at a second return angle, the second return angle being different from the second incident angle, in which a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle.

An encoder head includes one or more components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to the encoder scale; ii) receive a first return beam from the encoder scale at a first return angle, the first return angle being different from the first incident angle; iii) redirect the first return beam to the encoder scale as a second incident beam at a second incident angle; and iv) receive a second return beam back from the encoder scale at a second return angle, the second return angle being different from the second incident angle, in which a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle.

An optical position-measuring device for detecting the position of two objects movable relative to each other includes a measuring standard that is joined to one of the two objects and has a measuring graduation having a periodic arrangement of graduation regions along at least a first graduation direction. The position-measuring device also includes a scanning unit having a plurality of optical elements, which is disposed in a manner allowing movement relative to the measuring standard. Via the arrangement and formation of the optical elements of the scanning unit, a scanning beam path results in which partial beams of rays reaching interference propagate in mirror symmetry in relation to a plane of symmetry and either fall in V-shaped fashion on the measuring standard and/or are reflected back in a V-shape by the measuring standard. The plane of symmetry is tilted by a defined tilt angle about an axis of rotation that is oriented parallel to the surface of the measuring standard and extends in a direction perpendicular to the first graduation direction.

An optical position-measuring device for detecting the position of two objects movable relative to each other includes a measuring standard that is joined to one of the two objects and has a measuring graduation having a periodic arrangement of graduation regions along at least a first graduation direction. The position-measuring device also includes a scanning unit having a plurality of optical elements, which is disposed in a manner allowing movement relative to the measuring standard. Via the arrangement and formation of the optical elements of the scanning unit, a scanning beam path results in which partial beams of rays reaching interference propagate in mirror symmetry in relation to a plane of symmetry and either fall in V-shaped fashion on the measuring standard and/or are reflected back in a V-shape by the measuring standard. The plane of symmetry is tilted by a defined tilt angle about an axis of rotation that is oriented parallel to the surface of the measuring standard and extends in a direction perpendicular to the first graduation direction.

The invention relates to a system and a method for active grating position tracking in X-ray differential phase contrast imaging and dark-field imaging. The alignment of at least one grating positioned in an X-ray imaging device is measured by illuminating a reflection area located on the grating with a light beam, and detecting a reflection pattern of the light beam reflected by the reflection area. The reflection pattern is compared with a reference pattern corresponding to an alignment optimized for X-ray differential phase contrast imaging, and the X-ray imaging device is controlled upon the comparison of the reflection pattern and the reference pattern.

A distance measuring device includes a deflecting mirror configured to reflect transmission waves, and a swing motor configured to swing the deflecting mirror round a swing shaft so that scanning with the transmission waves is performed within a predetermined scanning region. The swing motor is configured to swing the deflecting mirror within a range of a predetermined rotation angle from a reference position, which is a rotational position of the deflecting mirror that reflects the transmission waves in a direction to a substantial center of the scanning region. The deflecting mirror is configured to return to the reference position when a distance measuring process, in which scanning with the transmission waves is repeated, ends.

An optical position measuring instrument including a scale and a scanning unit, wherein the scanning unit and the scale are movable with respect to one another. The scanning unit includes a detector unit, and a reflector unit that has a first and second wave front correctors and a beam direction inverter. The reflector unit is disposed so that beams first pass through the scale and the first wave front corrector, then a back-reflection of partial beams is effected in a direction of the scale, and the partial beams then pass through the scale and the second wave front corrector before the partial beams then arrive at the detector unit, wherein it is ensured that wave front deformations of the partial beams are converted into wave front deformations that compensate for resultant wave front deformations of the partial beams upon a second diffraction at the scale.