Abstract: A differential plane mirror interferometer comprises a source (10) which emits a light beam containing two linear orthogonally polarized components; a beamsplitter/beam folder assembly (16, 16A) for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams to produce two separated parallel beams with the same polarization; means including a polarizing beamsplitter (44), for causing each of the separated parallel beams with the same polarization to be reflected twice by one of two plane mirrors (71, 70) to produce two parallel output beams with the same polarization; a half-wave retardation plate (29B, 29) located in one of the separated parallel output beams, with the beamsplitter/beam folder assembly (16, 16B) converting the two separated parallel orthogonally polarized output beams into a single output beam in which the phase difference between the two polarization components of the single output beam i

Abstract: A differential plane mirror interferometer comprises a source (10) which emits a light beam containing two orthogonally polarized components of different frequencies; a source of a stabilized electrical reference signal (11) of a frequency corresponding to a difference frequency between the two components of the light beam; a beamsplitter/beam folder assembly (16, 16A) for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams to produce two separated parallel beams with the same polarization; means including a polarizing beamsplitter (44), for causing each of the separated parallel beams with the same polarization to be reflected twice by one of two plane mirrors (71, 70) to produce two parallel output beams with the same polarization; a half-wave retardation plate (29B, 29) located in one of the separated parallel output beams, with the beamsplitter/beam folder assembly (16, 16B) converting the two s

Abstract: An interferometer system capable of measuring accurately the deviations from straightness of travel comprises a source (10) of a frequency stabilized input beam (12) with two linear orthogonally polarized components which may or may not be of the same frequency; a tilted parallel plate or shear plate (16) with regions of reflection, antireflection, and polarizing coatings, for converting the input beam into two separated, parallel, orthogonally polarized beams (30, 31); a half-wave retardation plate (24), located in one of the separated beams (31), for converting the two separated, orthogonally polarized beams 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 prism assembly (45), attached to the mechanical apparatus whose straightness of travel is to be measured, for refracting the parallel first and second beams (36, 37) i

Abstract: A differential plane mirror interferometer comprises a source (10) which emits a light beam containing two orthogonally polarized components of different frequencies; a source of a stabilized electrical reference signal (11) of a frequency corresponding to a difference frequency between the two components of the light beam; a tilted parallel plate (16) having regions of reflection, antireflection and polarization coatings for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams for converting the two separated, parallel, orthogonally polarized beams into two separated parallel beams with the same polarization; means including a polarizing beamsplitter (44), for causing each of the separated parallel beams with the same polarization to be reflected twice by one of two plane mirrors (71,70) to produce two parallel output beams with the same polarization; a half-wave retardation plate (29B, 29) located

Abstract: An angle measuring interferometer comprises a source (10) which emits a light beam containing two linear orthogonally polarized components; means, such as a tilted shear plate (16) or a beamsplitter/beam folder assembly (116, 116A) for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams for converting the two separated parallel orthogonally polarized beams into two separated parallel beams with the same polarization; means including a polarizing beamsplitter (44), for causing each of the separated parallel beams with the same polarization to be reflected once by each of two plane mirrors (71, 70) to produce two parallel output beams with the same polarization; a half-wave retardation plate (29B, 29) located in one of the separated parallel output beams, for converting the two separated parallel output beams of the same polarization into two separated parallel output beams with orthogonal polarizatio

Abstract: Apparatus capable of measuring either changes in the refractive index, or, if desired, the absolute refractive index, of a gas is provided which comprises a differential plane mirror interferometer to produce a pair of measurement beams and a pair of reference beams; and a gas-tight refractive index cell means (78) comprised, most preferably, of a window (70) affixed to the end of a cylindrical tube (73) closest to the interferometer and a mirror (75) affixed to the other end of the tube (73), the cell (78) being aligned to the interferometer so that the reference beams pass inside of the tube (73) in a sealed volume and the measurement beams pass outside of the tube (73), such as in ambient air, for the measurement of changes in the refractive index of the gas surrounding the gas-tight cell (78).

Abstract: An angle measuring interferometer comprises a source (10) which emits a light beam containing two orthogonally polarized components of different frequencies; a source of a stabilized electrical reference signal (11) of a frequency corresponding to a difference frequency between the two components of the light beam; means, such as a tilted shear plate (16) or a beamsplitter/beam folder assembly (116, 116A) for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams for converting the two separated parallel orthogonally polarized beams into two separated parallel beams with the same polarization and frequency difference; means including a polarizing beamsplitter (44), for causing each of the separated different frequency parallel beams with the same polarization to be reflected once by each of two plane mirrors (71, 70) to produce two parallel output beams with the same polarization; a half-wave retardati

Abstract: A differential plane mirror interferometric comprises a source (10) which emits a light beam containing two linear orthogonally polarized components; a tilted parallel plate (16) having regions of reflection, antireflection and polarization coatings for converting the input beam into two separated, parallel, orthogonally polarized beams; a half-wave retardation plate (29A, 29) located in one of the separated beams for converting said two separated, parallel, orthogonally polarized beams into two separated parallel beams with the same polarization; means including a polarizing beamsplitter (44), for causing each of the separated parallel beams with the same polarization to be reflected twice by one of two plane mirrors (71, 70) to produce two parallel output beams with the same polarization; a half-wave retardation plate (29B, 29) located in one of the separated parallel output beams, with the tilted parallel plate (16) having regions of reflection, antireflection and polarization coatings for converting the t

Abstract: A heterodyne interferometer system utilizes a single stabilized frequency linearly polarized laser input beam (18) from a light source (10) which is provided to an acousto-optic device (20) along with a frequency stabilized electrical reference signal (32) from an oscillator (30) for transforming the input beam (18) into a pair of orthogonally polarized beams (40,50) differing in frequency by the reference signal frequency prior to providing these beams (40,50) to a polarization type interferometer (70). A mixing polarizer (60) mixes the beams (46,56) after they traverse the interferometer (70) and provides the mixed beams (62,64) to a photoelectric detector (65) where they are utilized to produce an electrical measurement signal (66).

Abstract: An electro-optical apparatus transforms a single stabilized frequency, linearly polarized laser input beam (18) from a light source (10) into an output beam (28) having two collinear orthogonally polarized output beam components (24,26) differing in frequency from each other by the frequency of a frequency stabilized electrical signal (32) provided from an electronic oscillator (30). The input of the oscillator (30) is provided to a power amplifier (34) which is used to drive a piezoelectric transducer (40) affixed to an acousto-optical Bragg cell (44) through which the input beam (18) passes and is transformed into the output beam (28) composed of the two beam components (24,26). The electrical output (36) of the power amplifier (34) is adjusted so that each of the output beam components (24,26) have approximately the same intensity which is each approximately half of the input beam (18) to provide a nominal efficiency of about 100%.

Abstract: An optical apparatus capable of measuring the absolute refractive index of a gas is provided which comprises: (1) an evacuated cell (50) comprised, most preferably, of a bellows (52) with transparent plano windows (41, 61) which have diameters larger than the outside diameter of said bellows (52) attached to each end of said bellows (52); (2) means, most preferably, high reflectivity mirror coating spots (46, 47, 66, 67), for obtaining reflections from the surfaces on the vacuum sides of said windows (41, 61); (3) means for varying the distances between said high reflectivity mirror coatings from less than a few micrometers to approximately 100 millimeters; (4) means, most preferably a first differential plane mirror interferometer (23) with its measurement leg in the gas to be measured outside of the vacuum cell (50); means, most preferably a second differential plane mirror interferometer (33) with its measurement leg in the vacuum cell (50); (6) means, for measuring the first phase variation (73, 75, 77) i

Abstract: An electro-optical apparatus transforms a single stabilized frequency, linearly polarized laser input beam (18) from a light source (10) into an output beam (46) having two orthogonal polarization components of different frequency. The input beam (18) is provided to an acousto-optic Bragg cell (20) which is driven by the output of an electrical oscillator (30) which provides the Bragg cell (20) with a frequency stabilized electrical signal (32) comprised of two different frequencies. The Bragg cell (20) transforms the input beam (18) into two intermediate beams (40, 42) having the same linear polarization as the input beam (18) but whose directions of propagation and frequencies differ from the input beam (18) and which are at one-half the intensity of the input beam (18).

Abstract: Apparatus is disclosed for the measurement of the absolute distance between a plano test and a plano reference surface which are in close proximity to each other. The preferred way of accomplishing this is with a polarization phase modulated Fizeau interferometer in which the reference surface is a front surface polarizer. The modulated interference pattern is photosensed with an array camera, and the signals processed to provide the absolute distance between the plano test surface and the plano reference surface. A method is also disclosed, using the instant invention, for determining the flying height of a magnetic head assembly used in computer mass storage systems.

Abstract: Apparatus is disclosed for the phase measurement of an interference pattern produced by an unequal path interferometer. The invention comprises in one embodiment the use of a diode laser light source whose wavelength is varied so that the phase difference between the two wavefronts producing the interference pattern is modulated by a known amount. The modulated interference pattern is photosensed with an imaging device, and the signals processed to provide a phase map representing the optical path difference between the reference and measurement wavefronts of the interferometer.

Abstract: Method and apparatus for testing the deviation of the face of an object from a flat smooth surface using a laser beam having two plane-polarized components, one of a frequency greater than the other to produce a difference frequency with a phase to be used as a reference. The beam also is split into its two components which are directed onto spaced apart points on the face of the object. The object is rotated on an axis coincident with one component as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a difference frequency having a phase that is shifted in an amount that is proportional to the difference in path length as compared to the reference phase to produce an electrical output signal proportional to the deviation of the height of the surface along the circular track.

Abstract: A method and apparatus is disclosed for testing the deviation of the face of an object from a flat smooth surface using a beam of coherent light of two plane-polarized components, one of a frequency constantly greater than the other by a fixed amount to produce a difference frequency with a constant phase to be used as a reference. The beam also is split into its two components with the separate components directed onto spaced apart points onthe face of the object to be tested for smoothness. The object is rotated on an axis coincident with one component which is directed to the face of the object at the center which constitutes a virtual fixed point. This component also is used as a reference. The other component follows a circular track on the face of the object as the object is rotated.