Zygo Corporation

University of California

The United States of America as Represented by the United States

Other

Gary E Sommargren

Peter S Young

Eugene W Campbell

Peter A Krulevitch

Abraham Phillip Lee

Charles F McConaghy

Earl W Ebert

Moshe Schaham

H Joseph Weaver

To measure a convex mirror, a reference beam and a measurement beam are both provided through a single optical fiber. A positive auxiliary lens is placed in the system to give a converging wavefront onto the convex mirror under test. A measurement is taken that includes the aberrations of the convex mirror as well as the errors due to two transmissions through the positive auxiliary lens. A second measurement provides the information to eliminate this error. A negative lens can also be measured in a similar way. Again, there are two measurement set-ups. A reference beam is provided from a first optical fiber and a measurement beam is provided from a second optical fiber. A positive auxiliary lens is placed in the system to provide a converging wavefront from the reference beam onto the negative lens under test. The measurement beam is combined with the reference wavefront and is analyzed by standard methods. This measurement includes the aberrations of the negative lens, as well as the errors due to a single transmission through the positive auxiliary lens. A second measurement provides the information to eliminate this error.

Application of the phase shifting diffraction interferometer for measuring convex mirrors and negative lenses

The invention uses the phase shifting diffraction interferometer (PSDI) to provide a true point-by-point measurement of absolute flatness over the surface of optical flats. Beams exiting the fiber optics in a PSDI have perfect spherical wavefronts. The measurement beam is reflected from the optical flat and passed through an auxiliary optic to then be combined with the reference beam on a CCD. The combined beams include phase errors due to both the optic under test and the auxiliary optic. Standard phase extraction algorithms are used to calculate this combined phase error. The optical flat is then removed from the system and the measurement fiber is moved to recombine the two beams. The newly combined beams include only the phase errors due to the auxiliary optic. When the second phase measurement is subtracted from the first phase measurement, the absolute phase error of the optical flat is obtained.

Absolute calibration of optical flats

To measure a convex mirror, a reference beam and a measurement beam are both provided through a single optical fiber. A positive auxiliary lens is placed in the system to give a converging wavefront onto the convex mirror under test. A measurement is taken that includes the aberrations of the convex mirror as well as the errors due to two transmissions through the positive auxiliary lens. A second, measurement provides the information to eliminate this error. A negative lens can also be measured in a similar way. Again, there are two measurement set-ups. A reference beam is provided from a first optical fiber and a measurement beam is provided from a second optical fiber. A positive auxiliary lens is placed in the system to provide a converging wavefront from the reference beam onto the negative lens under test. The measurement beam is combined with the reference wavefront and is analyzed by standard methods. This measurement includes the aberrations of the negative lens, as well as the errors due to a single transmission through the positive auxiliary lens. A second measurement provides the information to eliminate this error.

A visible light method for detecting sub-100 nm size defects on mask blanks used for lithography. By using optical heterodyne techniques, detection of the scattered light can be significantly enhanced as compared to standard intensity detection methods. The invention is useful in the inspection of super-polished surfaces for isolated surface defects or particulate contamination and in the inspection of lithographic mask or reticle blanks for surface defects or bulk defects or for surface particulate contamination.

Inspection of lithographic mask blanks for defects

Embedded fiducials are provided in optical surfaces and a method for embedding the fiducials. Fiducials, or marks on a surface, are important for optical fabrication and alignment, particularly when individual optical elements are aspheres. Fiducials are used during the course of the polishing process to connect interferometric data, and the equation describing the asphere, to physical points on the optic. By embedding fiducials below the surface of the optic and slightly outside the clear aperture of the optic, the fiducials are not removed by polishing, do not interfere with the polishing process, and do not affect the performance of the finished optic.

Embedded fiducials in optical surfaces

A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

Micromachined electrostatic vertical actuator

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. Whereas current interferometers illuminate the optic to be tested with an aberrated wavefront which also limits the accuracy of the measurement, this interferometer uses an essentially perfect spherical measurement wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Phase shifting interferometer

The present invention is a laser with a high reflector mirror and an output coupler mirror defining a laser resonator having an optical axis and optical path length. A gain medium, with a first refractive index and a first Verdet constant, is positioned in the resonator. The laser also includes an apparatus to excite and cause a population inversion in the gain medium to produce an output laser beam. An optically transparent medium is positioned in the laser resonator. The optically transparent medium has a second refractive index and a second Verdet constant. The second Verdet constant is typically larger than the first Verdet constant. One or more permanent and electromagnets are positioned at least partially around the exterior of the laser resonator. The magnets apply an axial magnetic field to at least a portion of the gain medium and the optically transparent medium producing a Zeeman split in the gain medium and also producing an optical path length difference between left and right circular polarizations in the laser resonator in both the gain medium and the optically transparent medium. The output laser beam is split into left and right circularly polarized output laser beams with a finite difference frequency that can be tuned and stabilized to a predetermined value which is higher than current Zeeman split lasers. The optically transparent medium can be a solid, liquid or gas, and the laser can be, by way of illustration and without limitation, a He--Ne, ion, or semiconductor laser. In embodiments, where the gain medium is a solid or liquid, the functions of the optically transparent medium are included in the gain medium.

Apparatus for increasing the frequency difference and stability of

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Phase shifting diffraction interferometer

Apparatus is disclosed for the measurement of the distance between a test surface (55) and a plano reference surface (58) which are in close proximity to each other. The preferred way of accomplishing this is with a polarization phase modulated interferometer. The modulated interference pattern is photosensed with an array camera (52), and the signals are processed by a computer (80), which also controls the rotation speed of the rotating glass disk (54) which contains the plano reference surface (58), to provide not only the distance between the test surface (55) and the plano reference surface (58) but also the topography of the test surface (55) independent of the phase changes on reflection from the test surface (55). A method is also disclosed, using the instant invention, for determining the flying height (h) of a slider assembly used in magnetic storage systems. In this method, the computer (80) synchronizes the frame rate of the camera (52) such that the camera (52) integrates the intensity at each photosensitive element over one revolution of the disk (54) and collects four frames of such integrated intensity in order to determine the flying height (h). To eliminate the phase shift on reflection, a second set of data is taken with the glass disk (54) rotating at a different rotation rate.

Flying height and topography measuring interferometer

A high accuracy linear displacement interferometer capable of measuring changes in displacement of two plane mirror surfaces (60, 61) comprises a source (10) of an input beam (12) with two linear orthogonally polarized components which may or may not be of the same optical frequency, a birefringent optical element (40) and a quarter-wave phase retardation plate (42) for converting the input beam (12) into two separated, parallel, oppositely handed circularly polarized beams (16, 17); a first plane mirror (60) comprising one of the two (60, 61) plane mirror surfaces; a second plane mirror (61) nominally parallel to and rigidly connected to the first plane mirror (60) surface comprising the other of the two plane mirror surfaces; the birefringent optical element (40), the quarter-wave phase retardation plate (42), a right angle prism (48) with reflective, orthogonal faces, and a pair of retroreflectors (44, 45) causing each of the separated, parallel, oppositely handed circularly polarized output beams (32, 33); the quarter-wave phase retardation plate (42) and the birefringent optical element (44) converting the two separated, parallel, oppositely handed circularly polarized output beams (32, 33) into a single output beam (52) in which the phase difference between the two orthogonally polarized components of the single output beam (52) is directly proportional to the linear displacement of the two plane mirrors (60, 61); a polarizer (70) for mixing the orthogonal components of the single output beam (52); a photoelectric detector (83), for producing an electrical measurement signal; means to extract the phase difference from the electrical measurement signal (85), the extracted phase difference being proportional to the optical path length changes between the two plane mirrors (60, 61); and a probe (62) mounted symmetrically in the right angle prism (48).

High accuracy linear displacement interferometer with probe

An angular displacement interferometer system capable of measuring accurately changes in angular displacement comprises a source (10) of a frequency stabilized input beam with two linear orthogonally polarized components; a tilted parallel plate or shear place (16) with regions of reflection, antireflection, and polarizing coatings for converting the input beam (12) into two separated, parallel, orthogonally polarized beams (30, 31); a half-wave retardation plate (29) located in one of the separated beams (31) for converting the two separated, parallel, orthogonally polarized beams (30, 31); into first and second beams which are spatially separated parallel, and have the same polarization (30, 33); a polarizing beamsplitter (40) and quarter-wave retardation plate (44) for transmitting the first and second beams (34, 35) to a fixed plano mirror (70) nominally perpendicular to the first and second beams for reflecting the first and second beams back into the quarter-wave retardation plate (44), polarizing beamsplitter (40), and retroreflector (48) for producing third and fourth beams (56, 67); a rotatable angle prism (72, 93) attached to the mechanical apparatus whose angular displacement is to be measured, located such that the third and fourth beams enter adjacent polygon faces of prism (72) or legs of prism (93) and are refracted to produce fifth and sixth beams which are reflected from the fixed plano mirror (70) back through the angle prism (72, 93) back through the quarter-wave retardation plate (44), beamsplitter (40), retardation plate (29) and shear plate (16) where the fifth and sixth beams are recombined into a single output beam (80) having two orthogonally polarized components in which the phase difference between the two components of the output beam (80) is related to the angular displacement; a polarizer (81) for mixing the orthogonal components of the output beam (80); a photoelectric detector (83) for producing an electrical measurement signal (85); and a phase meter/accumulator (90) for indicating the measured phase (92), the measured phase being related to the angular displacement.

Angular displacement measuring interferometer

The invention provides a method and apparatus for focusing and imaging x-rays. An opaque sphere is used as a diffractive imaging element to diffract x-rays from an object so that the divergent x-ray wavefronts are transformed into convergent wavefronts and are brought to focus to form an image of the object with a large depth of field.

An image focusing means by using an opaque object to diffract x-rays

A system for generating a spatially stable, small diameter light beam (18) which serves as a straight reference line over long distances may use the direction of propagation of light and one fixed point (11, 12) or may be between two fixed points (12, 21). In either instance, a light source (1) emits a beam (2) which is expanded, collimated and spatially filtered (3, 4). In the first instance, the collimated light wave (11) produced is diffracted by a sphere (12) to produce the small diameter light beam (18) which is constituted by a continuum of spots (16) which, in turn, produces a Poisson's spot (16) on a detector (21) which spatially samples the intensity of the spot (16). The resultant voltage (22) from each active detection are sent to a center locating electronics/computer (24) which processes the voltages (22) to give the position of the detector (21) relative to the straight reference line (18). In the second instance, the collimated light wave (11) is produced by reflecting the beam (5) passing through the pinhole (4) from a steering mirror (6) which can be tilted about two axes by applying error signal voltages (27, 28) to tilt adjusters (7, 8) which are related to the displacement of spot (16) from the center of detector (21) in the X and Y directions. The tilting of the mirror (6) changes the angle of incidence of the light wave (11) on the sphere (12) so that the spot (16) is centered on the detector (21).

Method and apparatus for generating a straight reference line

A differential plane mirror interferometer system comprises a laser source (10) which emits an input beam (12) having two linear orthogonally polarized components, which may or may not be of the same optical frequency. A birefringent optical element (64) converts the input beam components (20,21) into two separated, parallel, orthogonally polarized beams (22,23). The birefringent element (64) together with a first quarter-wave phase retardation plate (66), a second quarter-wave phase retardation plate (62) with a pair of holes, and a retroreflector (60) with a pair of holes aligned with the holes in the second quarter-wave phase retardation plate (62), causes each of the separated, parallel, orthogonally polarized beams to be reflected twice by one of two plane mirrors (68,70), namely a first plane mirror (68) or a second plane mirror (70), respectively, to produce two separated, parallel, orthogonally polarized output beams (54, 55). The birefringent optical element (64) converts the two separated, parallel, orthogonally polarized outbeams (54, 55) into a single output beam (80) in which the phase difference between the two polarization components of the single output beam (80) is directly proportional to the optical path length between the two plane mirrors (b 68, 70). This phase difference is measured by passing the output beam (80) through a polarizer (81) which mixes the two orthogonally polarized components in beam (80) with the interference between these two components being detected by a photodector (83) which produces an electrical signal (85). An electronic module (80) extracts the phase variation from this signal (85).

Growing community of inventors

Santa Cruz, CA, United States of America

Gary E Sommargren