Agilent Technologies, Inc.

Hewlett-packard Company

John J. Bockman

John J Bockman

Greg C Felix

Miao Zhu

Alan B Ray

Lawrence Lee

Eric Stephen Johnstone

Kerry D Bagwell

Kenneth J Wayne

Douglas P Woolverton

W Clay Schluchter

R Todd Belt

Kevin R Fine

Ron P Bevis

Terry E Riener

Ludmila M Golyanskaya

Kerry Bagw Ell

A beam distribution apparatus includes a stack of parallelogram prisms and beam-splitting coatings each located between opposing parallel faces of adjacent parallelogram prisms. The stack is mounted on an entrance face of a triangular prism. The triangular prism includes the entrance face, a reflective face, and an exit face. The reflective face has optical surfaces for shaping output beams from the stack and reflecting the output beams through the exit face.

High efficiency beam distribution with independent wavefront correction

An interferometer system includes a rhomboid assembly having a first optical stack and a second optical stack mounted on the first stack. The first stack includes a first prism having an angled face mounted to an angled face of a second prism. The interface between these angled faces includes a first polarizing beam-splitter. The second stack includes a third prism having an angled face mounted to an angled face of the fourth prism. The interface between these angled faces includes a second polarizing beam-splitter. First, second, third, and fourth wave plate elements are located in beam paths between the rhomboid assembly and at least one of a measurement optic and a reference optic. A redirecting optic is located at least adjacent to the vertical faces of the first and the third prisms.

Differential interferometers creating desired beam patterns

An interferometer system includes a plane mirror interferometer, a turning mirror, a retardation plate assembly having a retardation plate that can be adjusted and then fixed, and a retroreflector. A light beam travels in a path comprising the plane mirror interferometer, the turning mirror, the retardation plate assembly, and the retroreflector. The retardation plate assembly may include a plurality of bearings, a ring riding on the bearings, the retardation plate mounted to the ring, and a plunger pushing the ring against the bearings. The retardation plate may be fixed by adhesive after determining an orientation that produces little polarization leakage in the system.

Differential interferometer with improved cyclic nonlinearity

Measurement systems that separate polarization components can use retroreflectors to preserve or transform polarization and avoid unwanted mixing of the polarization components. A suitable retroreflector can include a coated cube corner reflector with retardation plates having a slow axis set at a non-zero angle away from 45&#xb0; with the directions of linearly polarized component beam. The non-zero angle can be set in situ to minimize polarization mixing in a measurement system. Alternatively, a cube corner reflector with one or more polarization manipulating elements controls the polarization of a reflected beam to preserve or transform the polarization of an incident beam.

Systems using polarization-manipulating retroreflectors

A phase-compensating cube comer retroreflector includes three rear reflecting surfaces. All three rear reflecting surfaces can be coated with a phase-compensating film stack that induces 2n&#x3c0; phase difference when handling polarized light. So coated, the phase-compensating cube comer preserves the polarization orientation and ellipticity of the incident light. Such a phase-compensating cube comer can be used to improve the accuracy of distance-measuring interferometers. The cube corner directs light to and from other optical elements, including a polarizing beam-splitters, mirrors, and quarter-wave plates.

Phase-compensated cube corner in laser interferometry

A phase-compensating cube corner retroreflector includes three rear reflecting surfaces. The first and the third rear reflecting surfaces can be coated with a phase-compensating film stack that induces 2n&#x3c0; phase difference upon reflection, where n is an integer including 0. Alternatively, all three rear reflecting surfaces can be coated with a phase-compensating film stack that induces n&#x3c0; phase difference when handling linearly polarized light, or 2n&#x3c0; phase difference when handling linearly or circularly polarized light. So coated, the phase-compensating cube corner preserves the polarization orientation and ellipticity of the incident light. Such a phase-compensating cube corner can be used to improve the accuracy of distance-measuring interferometers. The cube corner directs light to and from other optical elements, including a polarizing beam-splitters, mirrors, and quarter-wave plates.

An interferometer returns parallel beams that are subject to walk-off caused by reflector misalignment for an additional pass through the interferometer optics and thereby eliminates beam walk-off. A return reflector can be a plane mirror that directs returning beams to retrace paths through the interferometer optics to combine and exit along the axis of the input beam. Separation optics can separate the combined beam from the input beam. Alternatively, a return reflector such as an isosceles prism or a trapezoidal prism reflects and offsets returning beams so that the combined beam is offset from the input beam. The return reflector more generally responds to a shift in incident beam position with a matching shift of the reflected beam in contrast to a retroreflector, which shifts a reflected beam in a direction opposite to the shift in the incident beam.

Interferometer using beam re-tracing to eliminate beam walk-off

A multi-axis interferometer uses a combined beam for a first pass through the interferometer optics. Measurement and reference components of the combined beam that exit the interferometer optics are subject to walk-off that measurement or reference reflector misalignment can cause. A return reflector and non-polarizing beam splitter system split the combined beam into separated input beams for the various axes of the interferometer and return the separated beams for respective second passes through the interferometer optics. Walk-off for the separated beams in the interferometer optics cancels the walk-off for the combined beam to eliminate beam walk-off in separated output beams. Sharing a combined beam for a first pass through the interferometer optics reduces the sizes required for the interferometer optics and reference and measurement mirrors. The multi-axis interferometer may have a single return reflector.

Compact beam re-tracing optics to eliminate beam walk-off in an interferometer

A cube corner reflector is oriented so that incident and reflected beams either entirely miss the edges at the intersections of reflective surfaces or so that the beams have only peripheral portions incident on the edges. A symmetry plane of the cube corner reflector is midway between the incident and reflected beams of the cube corner reflector and contains the central axis of the cube corner reflector and one of the edges between the reflective surfaces. For a minimum size reflector that permits the tight beam spacing, trimmed surfaces perpendicular to the symmetry plane are at different distances from the central axis. The edges, variations in the orthogonality of the reflective surfaces, and beam walk off cause less wavefront distortion that could affect measurements in systems such as interferometers.

Cube-corner reflector permitting tight beam spacing and minimal wavefront distortion in a multi-axis interferometer

A manufacturing method for rhomboid assemblies cuts stacks of glass plates that are glued together with coatings between the glass plates. The cuts are at an angle such as 45&deg; and surfaces resulting from the cuts are finished to optical tolerances. These optical surfaces permit attachment of rhomboid assemblies directly to optical elements such as a polarizing beam-splitter (PBS) in a multi-axis interferometer. Further, elements such as quarter-wave plates, cube corner reflectors, and rhomboid elements that extend the separation of measurement beams can be attached to the PBS to provide integrated beam optics that are compact and thermally stable. Placing a reflective coating or other reference reflector on a quarter-wave plate for the reference beam can keep the entire beam path for the reference beam within the integrated structure. When rhomboid elements extend the separation between measurement beams, an extension to the PBS can match the optical path lengths of reference and measurement beams.

Multi-axis interferometer with integrated optical structure and method for manufacturing rhomboid assemblies

In the claimed invention for an improved AC type interferometric metrology apparatus, a change in position of an item disposed in a rotating reference frame is measured. The rotating reference frame accumulates a rotation angle over a time period with respect to a fixed reference frame. A quarter wave plate and an interferometer comprising a polarizing beam splitter, a reference path reflector, and a measurement path reflector are all mounted in the rotating reference frame. The measurement path reflector is mounted to item so that changes in its radial position along an axis orthogonal to the axis of rotation of the rotating reference system are measurable. In one preferred embodiment, the components in the fixed reference frame are a two-frequency laser light source, a stationary quarter wave plate, a receiver, for producing a measure signal containing information representing the change in optical path length between the measurement and reference paths of the rotating interferometer, the difference in the two frequencies of the beams from the laser source, and the rotation angle, and a signal processor. The signal processor receives the measure signal, a reference signal representing the difference frequency of the laser light source, and a signal from a rotary encoder containing information proportional to the rotation angle. The signal processor produces a signal representing the measurement of the change in position. In another embodiment, the rotary encoder is replaced by added optical components which automatically produce optical signals that contain information about the rotation angle and the difference in the two frequencies of the beams from the laser source.

Method and interferometric apparatus for measuring changes in

A linear-and-angular measuring plane mirror interferometer measures two degrees of freedom, both linear translation and rotation angle, using a single interferometer optical assembly. In alternate orientations it can be used to measure either the pitch, roll or yaw angle. The linear-and-angular measuring interferometer splits the measurement beam at the interferometer optic, using a single integrated optical assembly to make measurements at two locations on a measuring mirror on a stage. In a first embodiment, the input beam is split, and two separate measurements, X and X', are made at two locations separated by a distance d. A second embodiment optically produces a direct measurement of X--X' at a detector. The input beam makes one interferometer measurement for X, then the polarization of part of the resulting output beam is rotated and the rotated part of the beam is returned for a second pass to make an interferometer measurement at a location offset by a distance d from the first pass measurement.

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Santa Clara, CA, United States of America

John J Bockman