Zygo Corporation

James F Biegen

Peter J De Groot

Leslie Ludwig Deck

Xavier Colonna De Lega

Jan Liesener

Chris Koliopoulos

Robert Smythe

David A Grigg

An optical assembly for use in an interferometer is provided. The optical assembly includes first and second partially reflective surfaces positioned along an optical axis and oriented at different non-normal angles to the optical axis. The second partially reflective surface is configured to receive light transmitted through the first partially reflective surface along the optical path, transmit a portion of the received light to a test object to define measurement light for the interferometer and reflect another portion of the received light back towards the first partially reflective surface to define reference light for the interferometer. The reference light makes at least one round trip path between the second and first partially reflective surfaces.

Equal-path interferometer

An apparatus including: an interferometric objective comprising a beam splitter surface configured to separate input light into test light and reference light, and a reference surface configured to receive the reference light and direct it back to the beam splitter surface, which is configured to recombine the reference light with test light reflected from a test surface, the interferometric objective further comprising one or more optical elements positioned in the path of the input light and having positive or negative optical power, wherein the reference surface is curved and defines a window to pass the input light towards the beam splitter surface.

Interference objective for annular test surfaces

The invention features a method for determining a geometric property of a test object, the method including: interferometrically profiling a first surface of the test object in a first coordinate system; interferometrically profiling a second surface of the test object in a second coordinate system different from the first coordinate system; providing a relationship between the first and second coordinate system; and calculating the geometric property based on the interferometrically profiled surfaces and the relationship between the first and second coordinate system. In some embodiments, the relationship may be determined by using calibrated gage blocks or by using a displacement measuring interferometer. Corresponding system are also described.

Optical systems for measuring form and geometric dimensions of precision engineered parts

Apparatus and means for calibrating optical gap-measuring instruments, including a preferred calibration standard (100) comprised of a substantially flat, transparent element (10) held in contact with the convex spherical surface (25) of a substantially opaque element (20) to provide an obvious and unambiguous region over which the gap is zero. The optical gap measuring tool that is to be calibrated is oriented so as to illuminate the interface. The calibration standard (100) is translated in position with respect the gap measuring tool in such a way as to vary the measured gap, while at the same time data storage means record the gap measurement as a function of relative position. This data is then compared to the predicted variation from the geometry of the calibration standard (100). Provided that the elements (10, 20) are of high optical quality, deviations of the measured data from an ideal parabolic curve are indicative of calibration errors.

Calibration standard for optical gap measuring tools

A non-contact method for measuring the composition-dependent phase change on reflection that occurs using profile measuring interferometry. A profile measuring interference microscope utilizing an extended, narrow bandwidth illumination source is used to generate a two-beam interference intensity pattern at a given field position on a detector array. A reference surface of known surface characteristics and an unknown test surface being profiled are axially translated relative to each other while the interference intensity pattern impinging on the detector array is sampled, digitized, stored and then utilized to produce a digitized two-beam interference intensity pattern, the shape of which is characteristic of the particular interferometer configuration. The axial position of maximum interference contrast and the phase of the digitized two-beam interference intensity pattern at this position of maximum interference contrast are determined by mathematical analysis of the intensity data. The phase at the maximum interference contrast position is divided by an analytically-derived constant to determine the phase change on reflection from the test surface, without regard to the compositional characteristics of the test surface material. The ability to measure and quantify the phase change on reflection for materials with complex indices of refraction notably improves the accuracy of heretofore-known profile measuring interferometric techniques when profiling test surfaces formed of two or more dissimilar materials with at least one having a complex index of refraction.

Interferometric method and apparatus to measure surface topography

An interferometric profiler for measuring the topography of a spherical test surface (48), comprises a linearly polarized light source (10), a rotating diffuser disc (18, 20); an optical system (26, 30, 31) for collecting and directing light from the extended light source; a first quarter-wave phase retardation plate (38); a lens (34) for focusing the resultant circularly polarized light beam onto a spherical test surface (48and a spherical reference surface (45), the surface (45) having a reflective coating (46) and an anti-reflection coating; a piezoelectric transducer (80) for varying the relative distance between the spherical test surface (48) and the spherical reference surface (45); means for recombining the test and reference wavefronts (53T,53R) to produce an interference pattern (74); a lens (65) for imaging the spherical test surface (48) and the spherical reference surface (45) onto the photosensitive elements (58) of an imaging device (56); means for optically isolating the imaged spherical test surface (48) and the spherical reference surface (45) and the interference pattern (74); means (38) for converting the test wavefront (53T) and reference wavefront (53R) into a third linearly polarized light beam which has its polarization vector rotated 90 degrees relative to the first linearly polarized light beam; the polarizing beamsplitter (30, 31) directing the third linearly polarized light beam to the imaging device (56); the imaging device (56) sensing the interference pattern (74), a CCTV monitor (72) for viewing the imaged spherical test surface (48) and the spherical reference surface (45) and the interference pattern (74); and means (76) for processing the output of the imaging device (56) to profile the topography of the test surface (48).

Interferometric surface profiler for spherical surfaces

In accordance with several embodiments of the instant invention, an interferometric profiler is provided which is capable of measuring accurately the topography of a test surface comprising a light source with high spatial and temporal coherence, a rotating diffuser disc, onto which light from said source impinges to form a second extended light source having greatly reduced spatial coherence while retaining high temporal coherence; a first lens and beamsplitter assembly, most preferably a polarizing beamsplitter and quarter-wave phase retardation plate, to collect a direct, preferably without significant light loss, a light beam produced from the light from said extended second light source; a second lens for focusing said light beam onto test and reference surfaces; a two-beam interferometer which divides said light beam into test wavefronts and reference wavefronts and directs said test wavefronts and reference wavefronts onto said test and reference surfaces; and a piezoelectric transducer, for varying the relative distance between said test and reference surfaces; said two-beam interferometer, recombining said test wavefronts and reference wavefronts after they have interacted separately with said test and reference surfaces to produce an interference pattern; said second lens, imaging said test and reference surfaces onto the photosensitive elements of an imaging device. In accordance with another embodiment of the instant invention, the interferometric profiler can have a light source which can be either spatially coherent or incoherent of either temporally coherent or incoherent electromagnetic radiation.

Interferometric surface profiler

An improved system for testing a full reflectivity range of optical surfaces employs an improved Fizeau spherical or plano wavefront interferometer comprising a laser source (2) and an optical element (18) located in the wavefront (16) having a reference surface (20) everywhere normal to the wavefront (16) which has a partially reflective, partially absorbtive, and partially transmissive beamsplitting coating (19) applied to the plano or spherical reference surface (20) and having a transmittance such that there will be only two beam interference and the contrast of the two beam interference fringes between the reflected reference wavefront (25R) and the reflected test wavefront (25T) will be substantially equalized at the two extremes of the test surface (28) reflectivity.

Coating and method for testing plano and spherical wavefront producing

An interferometric profiler capable of accurately measuring the topography of a surface under test (48) employs a laser source (10), with the surface under test (48) ultimately being imaged onto the photosensitive elements (58) of a solid state array camera (56) by an objective lens (34). In accomplishing this, the input beam (12) is transformed by a lens (14) into a spherically converging wavefront (16) which is focused onto a rotating diffuser disk (18) to significantly reduce the spatial coherence of the resultant spherically diverging wavefront (22) which is transformed by a lens (26) into a spherically converging wavefront (28) which is totally reflected by a polarizing beamsplitter (30) to produce a diverging wavefront (32). This wavefront (32) is transformed into a collimated wavefront (36) by the lens (34) and enters a quarter-wave phase retardation plate (38) which has an antireflection coating on this surface (40) with the other surface (42) being a flat reference surface. Objective lens (34) transforms the resulting wavefronts (52R) and (52M) into spherical wavefronts (53R) and (52M) which are transmitted as wavefronts (54R) and (54M) by beamsplitter (30) and fall onto the elements (58) of the imaging device (56).

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Middletown, CT, United States of America

James F Biegen