Abstract: An optically sensing device is made up of the sensor materials that cause the value of birefringence to vary itself in accordance with external physical volume; a polarizer and an element provided with two total reflection surfaces causing the beam path to invert its direction by an angle of 180.degree.. The optically sensing device has the capability of setting the phase bias by applying the two total reflection surfaces causing the beam path to invert its direction by an angle of 180.degree.. Since each element has different functions, one functioning as a mirror and the other as a quarterwave plate, the optically sensing device is of extremely simple structure and is compact. In addition, since the optically sensing device provides a constant phase bias unlike the unstable performances of conventional quarterwave plates, it guarantees high-precision performance. Also, the use of inexpensive elements ensures reduced cost.

Abstract: An optical frequency domain distributed strain sensor for determining the strain distribution along an optical fiber includes an optical source that provides a polarization controlled optical interrogation signal having a frequency that varies in a recurring linear manner. The interrogation signal is injected into a sensor fiber embedded within a composite structure that places the fiber under strain. A portion of the interrogation signal is backscattered from the sensing fiber as a consequence of the strain experienced by the fiber and is mixed with a reference signal to produce beat frequency signals. The frequency of the beat signals is directly related the to position of backscatter in the sensing fiber while the amplitude of each beat frequency signal is directly related to the integrated strain-induced birefringence up to the backscatter point.

Abstract: Mechanical stress applied to a crystal (10) by a procedure for forming a bond (13) between an electrical connector (12) and a metallized surface (11) of the crystal (10) is measured to obtain a quantitative indication of the quality of the bond (13). A beam of optical radiation generated by an illuminator (21) is divided by a first beamsplitter (22) into a first component and a second component. The power of the first component is measured by a first detector (23). The second component is circularly polarized by a circular polarizer (24), collimated by an imaging lens (25), and directed as an incident beam along an optical path through the crystal (10) to the metallized surface (11) in the vicinity of the bond (13). The metallized surface (11) reflects the incident beam back along the same optical path as a return beam.

Abstract: A method for obtaining quantitative data which relates the sound pressure distribution in a body to an ultrasound pulse waveform which propagates through the body, based on photoelastic measurement and analysis. The method involves producing a first image of the body, into which the ultrasound pulse was launched, by recording the image of linearly polarized straboscopic light which is directed into the body. Thereafter, a second image is taken of the stroboscopic light with the principal axis of the linear polarizer offset by 45.degree. relative to the first image. The first and second images are combined to produce a synthesized image and the above-mentioned quantitative data is derived from the synthesized image.

Abstract: Relative retardation resulting from passage of polarized white light through a stressed transparent material is measured automatically, by dividing the emerging polychromatic light into plurality of component beams, each containing one wavelength (or color) only, transforming the light intensity carried by each component beam into an electrical signal, and using these electrical signals to measure the relative retardation, proportional to the stress in the transparent material.Means are provided to compare the spectral distribution of the light intensity measured at several wavelengths to the calculated distribution using an assumed value of retardation. Iterative (repetitious) calculations are performed until the measured distribution and calculated, using assumed retardation, agree. The retardation yielding agreement with the measured distribution is the measured retardation reflecting the stress in the material.

Abstract: Certain materials (e.g. polymers, glasses) exhibit the photo-elastic effect, whereby when they are subject to stress become birefringent, which influences a light beam passing through the glass. This beam, e.g. from a laser is collimated and circularly polarized as it approaches the glass and is again polarized as it leaves the glass. This stress is applied, according to this invention, by magnetostrictive strips on the glass which are influenced, by the magnetic field to be measured or the AC bias field. A miniaturized arrangement using this principle is described.

Abstract: A photoelastic transducer is constructed with a photoelastic element receiving a 45.degree. polarized light beam with a wave plate providing a 90.degree. phase displacement in its orthogonal components. The element has reflective surface coatings to produce multiple internal reflections so as to lengthen the optical path, and increase the sensitivity of the unit. Analysis of the orthogonal outputs can be according to the difference divided by the sum with one of the outputs being multiplied by the ratio of the D.C. component of the other output to its D.C. component, for the purpose of compensating for changes in tramsmission of the two signals.

Abstract: An instrument for measuring stress is arranged to be insensitive to stresses caused by conditions other than that of the phenomenon to be measured. The instrument employs two equal lengths of optical fibers of the kind exhibiting birefringence when stressed. Polarized light is directed into one of the optical fibers along its longitudinal axis. The two optical fibers are arranged in series with respect to the longitudinal transmission of the polarized light through those fibers. A polarization rotator is situated in the light path between the two optical fibers. The polarized light transmitted through the polarization rotator is rotated by an amount causing stresses imposed equally on the two optical fibers to have equal and opposite effects of the transmitted polarized light.

Abstract: In a detecting system adapted to detect foreign matters as faults of a glass bottle, between a projection path of a diffused light towards the object to be inspected and said object, a plane polarizing plate of a circular polarizer which includes the plane polarizing plate combined with a 1/4 wave plate is disposed at the side of a diffused light side, while, in a light path which causes light transmitted through the object to form an image on the photoelectric detector 6 through the lens, a detecting side circular polarizer which includes a 1/4 wave plate and a plane polarizing plate is placed. An output electric signal of the photoelectric detector is subjected to analog operation processing.

Abstract: A signal processor is arranged to process polarized light signals obtained from a stress sensor of the type having a photoelastic element that responds to stress by causing a phase difference between components of the polarized light propagating through that element. The stress sensor provides two output beams, each of which has a different polarized component of the transmitted light. The signal processor employs a pair of photodetectors which respond to the intensities of the two polarized light beams by converting the polarized light into electrical signals. Those two electrical signals provide the inputs to a difference differentiator that provides an output proportional to the difference between the derivatives of the inputs. The two electrical output signals of the photodetectors are also applied as inputs to a multiplier whose output is related to the product of its inputs.

Abstract: A photoelastic sensing device comprising a photoelastic member of transparent material, first means for supplying polarized light fluxes to the member for transmission therethrough along a plurality of respective paths, and second means for receiving and detecting the transmitted light fluxes. A third means applies stresses to the member in response to the application thereto of force which is variable and has a magnitude and direction represented by its components along a plurality of vector coordinates which define a space of at least two dimensions. The light fluxes which are transmitted respectively along the plurality of paths of the member are each responsive to the stresses in the member along its path, and the second means provides an output signal which is responsive to the force and to each of the components of the force applied to the third means.

Abstract: In a strain sensing system in which a strained grating is illuminated with a pair of beams chosen from three possible beams to sense strain in two dimensions, an arrangement is disclosed of two beam splitters, as least one plane mirror, and three tilted mirrors, all fixed to a support plate and which can supply the three required illuminating beams.

Abstract: Photoelastic sensing means, and more particularly photoelastic sensing means capable of providing high sensitivity for measuring pressure, force, displacement, acceleration or inertial force, proximity, temperature and other measurands. The photoelastic sensing means comprises a thin photoelastic member of transparent material having closely spaced top and bottom outer surfaces with peripheral edges and an edge surface extending between the peripheral edges of the other surfaces. Light flux is provided to the edge surface of the member at a first region for transmission by the member along a path to a second region at the edge surface where it is received and detected. The spacing between the top and bottom outer surfaces of the member is relatively small compared to the length of the path of the light flux in the member. The member is supported to produce bending stresses in the member in a direction transverse to the path of the light flux in the member with the application of force to the member.

Abstract: A sensor is provided for sensing or detecting the presence of an environmental field condition such as acceleration, temperature change, magnetic or acoustic fields. The field is sensed by interference between two mutually orthogonal polarized eigenmodes in a single monomode optical fiber which may be disposed either linearly or wound on a mandrel made of compliant material for sensing an acoustic field, or made of magnetostrictive material for sensing a magnetic field. Polarized light propagated through the optical fiber is detected at its outlet independent of environmentally induced low frequency variations whereby the sensor may be maintained at quadrature and maximum sensitivity.

Abstract: A system for sensing pressure features an electrically passive sensing head connected to electrically active components by a fiber optic cable. A preferred embodiment combines a polariscope bracketing a quarter wave plate and a photoelastic medium. The dependence of the intensities of two polarization components of light emerging from the photoelastic medium on the pressure applied to the medium permits the measurement of that pressure in a manner that has quadratic error dependence on optical misalignment.

Abstract: Disclosed is an apparatus for measuring surface stress of glass coating and transparent plastic product, which comprises means for projecting the coherent light on the surface of the object to be measured, an output prism having a refractive index greater than that of said surface, mounted proximal to the light incident point on said surface in such a manner that one face thereof is in optically close contact with said surface, a telescope to measure the critical angle at the interface of said surface and said output prism in respect of the projected light from said output prism, and a polarizer located on the optical path of said projected light. The apparatus facilitates easily a direct and non-destructive measurement of the surface stress without any complex calculation.

Abstract: A pulsed laser beam intensity monitor measures the peak power within a selectable cross section of a test laser beam and measures integrated energy of the beam during the pulse period of a test laser. A continuous wave laser and a pulsed ruby laser are coaxially arranged for simultaneously transmitting optical output energy through a crystal flat during the time a test laser pulse is transmitted through the flat. Due to stress birefringence in the crystal, the ruby laser pulse transmitted through the flat is recorded and analyzed to provide peak power information about the test laser output pulse, and the continuous wave laser output reflected from the crystal flat provides a measurement of energy during the test laser pulse.

Abstract: An apparatus for pressure measurement employs fiber optics to transport a broadband beam light to and from a remote electrically passive sensing head. In the sensing head, a linearly polarized beam is phase shifted in a birefringent plate, then passed through a photoelastic pressure sensor and a polarization analyzer. The wavelength for which the output light has an intensity minimum is a measure of the applied pressure.

Abstract: A reflected light method of paleocurrent determination uses laser light source for investigation of paleocurrent direction for oriented sandstone samples from surface and from drill cores. The technique determines the average optic axis orientation by the variations in the intensity of a beam of reflected light from a polished surface of the sample as the sample is rotated.

Abstract: An optical fiber having at least two cores positioned in a common cladding can be fabricated to be responsive to strain or hydrostatic pressure but not to temperature through the selection of materials, spacing and shape of the cores and cladding in the fiber. Accordingly, the cross-talk between adjacent cores in the optical waveguide can be optimized to respond to a change in hydrostatic pressure or in unidirectional strain along the length of the fiber. The strain or pressure change, can be determined by measuring the relative intensity of light emerging from the different cores of the fiber. A larger unambiguous range for strain or hydrostatic pressure changes can be provided by a multi-core optical fiber embodiment.

Abstract: The filter comprises a multiplicity of light polarizing elements which polarize light in a plurality of planes, and a multiplicity of filtering means associated with the light polarizing elements. In a polariscope, light is directed from a source through such a filter to the specimen to be analyzed. Light passed through the specimen once or twice is coupled through another such filter termed an analyzer. In certain embodiments, the polarizer and the analyzer are combined. Patterns representing the stress in the specimen are produced. The pattern includes isochromatics and a number of isoclinics.

Abstract: An accelerometer utilizing a laser source and a resonant cavity formed by a pair of spaced mirrors. A birefringent isotropic material is disposed in the resonant cavity. Light generated by the laser is reflected back and forth between the mirrors and through the birefringent material to generate a pair of orthogonally polarized beams. The optical path of one beam is changed in response to acceleration forces acting on a proof mass carried on the birefringent material. The pair of beams produced have different phases. The phase difference will be by an amount proportional to the difference in refractive indexes along and perpendicular to the optic axis of the birefringent material.

Abstract: Method comprises (1) introducing a polarized light beam into the convex surface of an optically-transparent body whereby the beam propagates in the body in a guided manner near the surface, (2) extracting at least a portion of the beam from the body through the surface at a distance from where the beam was introduced, (3) sensing the change in polarization state of the extracted portion of the beam occurring during its propagation in the body, and (4) calculating the value of stress from the sensed change in polarization state.

Abstract: At least four beams of linearly polarized light are produced separately at one and the same point of measurement in a single direction of observation at right angles to a unitary sheet of a specimen of photoelastic material in order to determine the state of mechanical stress in the plane of the sheet.

Abstract: This invention relates to a dynamic photoelasticimeter with a rotating birefringent element. It comprises a laser, a birefringent plate rotatable at a constant speed, a model to be studied, a circular analyzer and a photodetector supplying signals at its output having frequency components of 2.omega. and 4.omega.. The ratio of the amplitudes of these signals supplies an indication of the phase shift .phi. (t) contributed by the model, and the phase of the signal of the frequency 4.omega. contributes information as to the orientation .theta. of the axes of the model at the point in question.The present invention provides a particularly simple and accurate dynamic photoelasticimeter.

Abstract: An ellipsometer for measuring the polarization parameters .alpha. and .lambda. of an elliptically polarized light wave. The light wave passes successively through an orientable quarter-wave plate, a birefringent plate rotatable at a constant speed .omega. and a polarizer and then impinges upon a photodetector. Reference signals having angular frequencies of 2.omega. and 4.omega. are generated, one of these signals being employed to synchronously detect the signal at the output of the photodetector by adjusting the quarter-wave plate until the synchronously detected signal component is zero, the orientation of the quarter-wave plate then corresponding to the polarization parameter .alpha.. The parameter .lambda. is obtained by measuring the phase of the component at the output of the photodetector having an angular frequency of 4.omega..The invention applies in particular to photoelasticimetry.

Abstract: A strain sensor providing an optical read-out that is suitable for use in electrically noisy environment or one subject to mechanical vibration consists of one or a set of single mode optical fibres wound round an expanding strain member. The principle of operation relies upon the fact that transverse straining of a single mode fibre destroys mode degeneracy thereby producing birefringence effects that can be rendered obversable using polarized light and a polarization analyzer.

Abstract: An automatic two wavelength photoelasticimeter comprising, in succession, a light source for emitting light having at least two wavelengths, .lambda..sub.1 and .lambda..sub.2 ; a polarizer rotating at constant speed, an orientable quarter-wave plate of orientation .beta. with respect to a reference axis; a model to be analyzed exhibiting double-refraction and having a fast axis which forms an angle .theta. with respect to the reference axis and which provides a phase shift .phi. (which parameters .theta. and .phi. are to be measured) and three photodetectors 5, 6, and 7 preceded by analyzers 10, 11 and 12 respectively. The photodetectors 6 and 7 are preceded by filters 8 and 9 of wavelengths .lambda..sub.1 and .lambda..sub.2 respectively. The difference between the phases of the signals of the frequency 2.omega.

Abstract: A biasing element for use in a force-measuring system employing a circularly polarized ring laser. The biasing element is a pre-stressed photoelastic element placed in the path of the laser beam to generate a steadystate frequency difference at the output of the beat detector. In a preferred form, the biasing element is pre-stressed by bonding to a second photoelastic element and a second ring laser is positioned to detect the torque in the second element to allow monitoring of any changes in the bias level.

Abstract: A device for indicating the force applied by a tool comprises a bar arranged so as to be deflected in accordance with the force applied, a pair of spaced stops carried by the bar, a frame enclosing both stops with one end of the frame engaging one side of one stop and the opposite end of the frame extending past the other stop to define a space therebetween, and a load sensing member disposed in the latter space, whereby the deflection of the bar is converted by the two stops and the frame to a compressive force on the load-sensing member. The described load-sensing member is a photoelastic member and the described device in which it is used is a surgical spreader hand tool wherein the photoelastic member indicates to the surgeon the force applied.

Abstract: A device to test for the presence of chemically hardened glass wherein a collimated light source and a windowed container are filled with a fluid of refractive index substantially equalling that of the glass. The glass is immersed in the container with the container placed between crossed polarizers. When the glass is chemically hardened, light traversing therethrough is refractively bent thereby to produce a component of the light vector in the optical axis of one of the polarizers and an observable light pattern emanating therefrom.

Abstract: An improved device for detection of stones in the sidewalls of glass containers. Stones in the sidewalls of glass containers cause stress patterns to be formed. These patterns are visible if the glass container is viewed through crossed polarizing filters due to the refraction of polarized light. A television camera and electronic analysis circuit may be substituted for the human eye. The detection capability and reliability of the system is improved if the glass container is illuminated with primarily infra-red radiation. Then, polarizing filters which polarize infra-red radiation and remove visible light are used. A filter before the television camera lens removes far infra-red radiation and allows only near infra-red radiation to be measured. This makes the device insensitive to glass color, flutes or stippling and improves the signal to noise ratio.

Abstract: The photoelastic strain gauge coating comprises a sheet of photoelastic material of predetermined shape having a multiplicity of minute discontinuities or sets of discontinuities arranged in a predetermined grid. The predetermined shape and grid, together with boundary devices, provide a standard format to enable use of supporting computer programs. In practicing the method, the coating is bonded to the workpiece surface to be analyzed, and then illuminated by polarized light and photographed. The photograph is then magnified greatly to enable examination seriatim of the patterns at and about each discontinuity or set of discontinuities. The data thus obtained is processed, using the supporting computer programs to obtain a strain field of the portion of the workpiece covered by the coating.

Abstract: An optical examining apparatus, particularly an isochromatic multiplier, with two optical elements, particularly partly light-transmitting mirrors arranged at a distance and at a definite angle to one another which enclose an object-receiving space, whereby the object is to be inserted between the two mirrors at a definite distance and/or in a defined angular position; an object carrier is thereby mounted at the edge or enclosure of at least one of the optical elements, which is provided with receiving and holding surfaces and fastening means for the object and which is adjustable in the angular position of the receiving and holding surfaces with respect to the plane of one and/or the other optical element; the object carrier thereby projects with its receiving surfaces and fastening means between the two optical elements.

Abstract: A glass ophthalmic lens which has been strengthened by thermal tempering or ion exchange treatment has increased impact resistance and durability, but such strengthening does not alter the appearance of the lens sufficiently to render the presence or absence of strengthening visually ascertainable even by one of high skill. It being necessary to inspect for the presence or absence of strengthening prior to dispensing lenses to the public, the present invention contemplates immersion of the lenses in a transparent liquid of approximately the same refractive index as the material of the lenses and projection of linearly polarized light through the fluid and lens. Viewing of the thus illuminated lens through a light polarizing analyzer reveals readily observable stress patterns in strengthened lenses and a lack of such patterns in non-strengthened lenses.

Abstract: A device for detecting a strain and foreign matters in a glass container is designed to amplify the electrical output obtained by bringing vertical scanning lines into intersection with the image of horizontally rotating strain polarized light. A polarizer and an analyzer are disposed in such a manner that their optical axes cross each other at right angles, and polarized light from the polarizer is projected upon a rotating glass container under inspection and is allowed to pass through the analyzer only when strain and/or foreign matter is found in the glass container. The resulting strain polarized light is projected upon a non-storage camera tube through a lens so as to vertically scan with a line through the center of an image of the glass container on the photoelectric surface of the tube at a speed proportional to the moving speed of the glass container to thereby bring the vertical scanning lines into intersection with the image of the horizontally rotating strain polarized light.

Abstract: A piezo-optic measuring transducer is disclosed herein and an accelerometer, a pressure gauge, a dynamometer, and a thermometer based thereon.The piezo-optic measuring transducer comprises two polarization-optical channels. Each of these channels includes the following components arranged in series downstream the luminous flux produced by a light source: a polarizer, an elastic element which is common to both channels and sensitive to stress variations therein caused by a variation in the measurand, an analyzer, and a photocell. Both channels are provided with a means for varying the intensity of the luminous flux incident upon one of the photocells which intensity variation is opposite in polarity to that in the luminous flux incident upon the other photocell. Both photocells are arranged in a differential relationship with the difference in the electrical signals produced thereby being representative of the measurand.

Abstract: An instructional polariscope which is easily disassembled, reassembled, cbrated and operated in the classroom by individual students for the purposes of teaching and demonstrating the interoperation of components of a polariscope and the principles of photoelasticity. This polariscope can be assembled for use as either a plane or a circular polariscope and employs a reflector which allows use of an external light source.