Abstract: Light of multiple wavelengths passes through, in order, a plane polarizer, a ½ wave plate, a means for attenuating polarized light in a selected plane, and a ¼ wave plate. The ¼ wave plate and the ½ wave plate are selected for green light. The ½ wave plate induces an error for nongreen light which is twice the error which the ¼ wave plate would induce for a particular light wavelength but of opposite sign. The errors are reduced by ½ by attenuation by passing all wavelengths of light through glass air interfaces defined by a plurality of glass plates, angled at between about 45 and 55 degrees with respect to the optical axis. Light which is plane polarized for green light, and precorrected for every other wavelength is passed through the ¼ wave plate and all wavelengths are converted to circularly polarized light.

Abstract: Light of multiple wavelengths passes through, in order, a plane polarizer, a ½ wave plate, a means for attenuating polarized light in a selected plane, and a ¼ wave plate. The ¼ wave plate and the ½ wave plate are selected for green light. The ½ wave plate induces an error for nongreen light which is twice the error which the ¼ wave plate would induce for a particular light wavelength but of opposite sign. The errors are reduced by ½ by attenuation by passing all wavelengths of light through glass air interfaces defined by a plurality of glass plates, angled at between about 45 and 55 degrees with respect to the optical axis. Light which is plane polarized for green light, and precorrected for every other wavelength is passed through the ¼ wave plate and all wavelengths are converted to circularly polarized light.

Abstract: An optical assembly divides a single image into a plurality of images which are simultaneously projected onto a single sensor array. The optical assembly is arranged so that each of the plurality of images can be made to pass through a filter of a different type. For example a polarizing filter of a different orientation, or a filter which passes a different spectral band. In this way a single digital camera having a single chip sensor array can simultaneously receive multiple substantially identical images which have been acted on by different filters. This allows data capture from a single frame of a single camera to be used to perform stress analysis, or spectral analysis. This is particularly useful when high speed image capture is desired which contains stress or spectral data, because each frame captured from the sensor array contains multiple images which can be processed to obtain stress or spectral data.

Abstract: Portions of an organism, object, engineering structure, sheet or moving web are selectively heated, and thereby marked with a thermal spot or spots, which are imaged by an infrared camera. The positions of the imaged markings are tracked over time, to thereby extract kinematic and other information about the marked object.

Abstract: A structural specimen coated with or constructed of photoelastic material, when illuminated with circularly polarized light will, when stressed; reflect or transmit elliptically polarized light, the direction of the axes of the ellipse and variation of the elliptically light from illuminating circular light will correspond to and indicate the direction and magnitude of the shear stresses for each illuminated point on the specimen. The principles of this invention allow for several embodiments of stress analyzing apparatus, ranging from those involving multiple rotating optical elements, to those which require no moving parts at all. A simple polariscope may be constructed having two polarizing filters with a single one-quarter waveplate placed between the polarizing filters. Light is projected through the first polarizing filter and the one-quarter waveplate and is reflected from a sub-fringe birefringent coating on a structure under load.

Abstract: A structural specimen coated with or constructed of photoelastic material, when illuminated with circularly polarized light will, when stressed; reflect or transmit elliptically polarized light, the direction of the axes of the ellipse and variation of the elliptically light from illuminating circular light will correspond to and indicate the direction and magnitude of the shear stresses for each illuminated point on the specimen. The principles of this invention allow for several embodiments of stress analyzing apparatus, ranging from those involving multiple rotating optical elements, to those which require no moving parts at all. A simple polariscope may be constructed having two polarizing filters with a single one-quarter waveplate placed between the polarizing filters. Light is projected through the first polarizing filter and the one-quarter waveplate and is reflected from a sub-fringe birefringent coating on a structure under load.

Abstract: Cracks in bridges or other structures are detected by applying a thermal gradient to the test structure in a selected region so heat flows from left to right. A first image of the thermal gradient with heat flowing from left to right is taken and stored for further processing. Next a thermal gradient is applied so heat flows from right to left through the selected region. A second thermal image is taken and stored of the heat flowing from right to left. An image taken before a thermal gradient is applied is subtracted from the first and second images to remove thermal reflection and non-induced gradients from the stored images. Each differentiated image is then normalized by dividing each pixel of the differentiated image by the total photon flux from the undifferentiated image. The second image is than subtracted from the first image producing a third image which highlights features which produce thermal gradients of opposite signs.

Abstract: An instrument employs a projector which projects a moving pattern of heat onto a test object. An exemplary pattern is formed of bars or lines of infrared radiation separated by unheated areas, or areas of shadow. An infrared camera which is not sensitive to the wavelength of the projected light is used to detect the heat emitted by the test object. The projected bands of thermal radiation heat the surface of the test object. Some of the energy in the form of heat sinks into the structure, while some of the heat energy flows laterally from the heated band to the unheated bands between the projected bands. The lateral flow of heat between bands is resisted by cracks in the surface. This resistance causes heat energy to build up on one side of each crack. The downward flow of heat energy is resisted by less conductive material such as a debonding between layers which traps the heat, causing it to build up laterally.

Abstract: An instrument employs a projector which projects a moving pattern of heat onto a test object. An exemplary pattern is formed of bars or lines of infrared radiation separated by unheated areas, or areas of shadow. An infrared camera which is not sensitive to the wave-length of the projected light is used to detect the heat emitted by the test object. The projected bands of thermal radiation heat the surface of the test object. Some of the energy in the form of heat sinks into the structure, while some of the heat energy flows laterally from the heated band to the unheated bands between the projected bands. The lateral flow of heat between bands is resisted by cracks in the surface. This resistance causes heat energy to build up on one side of each crack. The downward flow of heat energy is resisted by less conductive material such as a debonding between layers which traps the heat, causing it to build up laterally.

Abstract: The instrument has a focal plane array of infrared sensors of the integrating type such as a multiplexed device in which a charge is built up on a capacitor which is proportional to the total number of photons which that sensor is exposed to between read-out cycles.The infrared sensors of the array are manufactured as part of an overall array which is part of a micro-electronic device. The sensor achieves greater sensitivity by applying a local offset to the output of each sensor before it is converted into a digital word. The offset which is applied to each sensor will typically be the sensor's average value so that the digital signal which is periodically read from each sensor of the array corresponds to the portion of the signal which is varying in time. With proper synchronization between the cyclical loading of the test object and the frame rate of the infrared array the output of the A/D converted signal will correspond to the stress field induced temperature variations.