Showing papers on "Collimated light published in 1991"

An interferometer for atoms.

Abstract: We have demonstrated an interferometer for atoms. A three-grating geometry is used, in which the interfering beams are distinctly separated in both position and momentum. We used a highly collimated beam of sodium atoms with a de Broglie wavelength of 16 pm and high-quality 0.4-\ensuremath{\mu}m-period free-standing gratings which we fabricated using a novel method. The interference signal is 70 counts/s, which allows us to determine the phase to 0.1 rad in 1 min. Applications of atom interferometers are briefly discussed.

Non-uniform attenuation correction using simultaneous transmission and emission converging tomography

Abstract: Photon attenuation in cardiac single photon emission computed tomography (SPECT) is a major factor contributing to the quantitative inaccuracy and the decrease in specificity of lesion detection A measured map of the attenuation distribution was used in combination with iterative reconstruction algorithms to accurately compensate for the variable attenuation in the chest The transmission and emission data were acquired simultaneously using a multidetector, fan-beam collimated SPECT system with a transmission line source (Tc-99m) precisely aligned at the focal line opposite one of the detectors and of a different energy than the emission source (Tl-201) The contamination of transmission data by the high-energy photopeaks of Tl-201 was removed based on measurements from emission-only acquisition detectors An algorithm was derived to eliminate scatter of Tc-99m transmission photons into the lower-energy Tl-201 window of all three detectors Results are given for both phantom and patient studies >

Efficient optical elements to generate intensity weighted spot arrays: design and fabrication

Abstract: We report on the design and fabrication of fully 2-D surface relief diffraction elements that can split a single collimated beam into many beams in an arbitrary intensity distribution. These splitters were designed by computer using simulated annealing, and made into phase gratings by electron-beam lithography followed by plasma etching into quartz glass. Both two and four phase level gratings have been fabricated, allowing a wide range of uniform and weighted spot patterns to be generated. These grating elements have a measured diffraction efficiency of over 74%, with the beam intensity ratios accurate to within 1% of their target values.

Machine vision three dimensional profiling system

Abstract: A three dimensional imaging system having a diode laser and collimator along with a video camera and digital circuitry wherein when the light from the laser is collimated and hits the surface of an object with the reflected light images picked up by the video camera and the centroid location of each intersection is interpolated translating two dimensional pixels into three dimension coordinates.

Dark field imaging defect inspection system for repetitive pattern integrated circuits

Abstract: An optical inspection system for patterned semiconductor wafers generates a dark field image of the wafer by applying a collimated beam of monochrome light at an incident angle with respect to the surface of the wafer of between 8° and a maximum angle defined by the numerical aperture of the imaging system and collecting the light which is scattered at angles approximately normal to the surface of the wafer and within the numerical aperture of the imaging system. In addition, the incident light is at an angle of 45° in the surface plane of the wafer with respect to the rectangular lines which predominate in the pattern. Before forming the dark field image, the collected light is passed through a Fourier transform filter which substantially attenuates spatial frequency components corresponding to the pattern. In the resultant dark field image, defects in the pattern and contaminating particles are accentuated relative to the pattern features.

Scatter fringes of equal thickness

Abstract: IT is possible to test an optical system by means of white-light interference between two or more wave-fronts which have been scattered by equivalent obstacles out of the same collimated beam.

Contraband detection system using direct imaging pulsed fast neutrons.

Abstract: A system and method for detecting contraband generates a highly collimated beam (13) of pulsed fast neutrons, having a pulse width on the order of a nanosecond, and an energy of 5 to 9 MeV. An object (14) under investigation is scanned with the collimated pulsed beam. The neutrons in the beam cause (n, η) reactions in a limited object volume or voxel, defined by the intersection of the collimated beam and the scanned object. The highly penetrating fast neutrons produce nuclear reactions with the atomic elements present within the object, causing gamma rays to be emitted. The gamma rays are detected in a gamma ray detector (20). The approximate time of flight of the neutron pulse is measured, allowing a determination to be made as to the particular voxel from which the gamma ray originated. The energy of the detected gamma rays identifies the particular elements from which the gamma rays originated. Thus, e.g., the carbon, nitrogen, oxygen, and chlorine content, which elements are commonly found in contraband, of a particular voxel can be determined directly and precisely. The voxel content information may be combined from a substantial sample of the voxels that make up the object to provide a direct indication of the elemental content of the object, and hence whether contraband is present or absent within the object.

Light fixture including a partially collimated beam of light and reflective prisms having peaks lying on a curved surface

Abstract: A light fixture has a source of partially collimated light for emitting light having an axis of collimation. A structured surface has a plurality of prisms that are rendered reflective for reflecting light from the light source out of the cavity. The peaks of the prisms define a surface at least a portion of which makes an acute angle with the axis of collimation.

Optical grid alignment system for portable radiography and portable radiography apparatus incorporating same

Abstract: An optical alignment system for aligning a film cassette carrying grid cassette with an x-ray source of a portable x-ray apparatus. To facilitate accurate alignment of the central x-ray beam of the x-ray source of a portable x-ray apparatus with a focused grid in a clinical setting, the present invention uses a light projector and a reflector device. The light projector is substantially fixed relative to the x-ray source and projects a spot or line of light on the surface of the grid cassette. The reflector device, which can be temporarily or permanently fixed to the grid cassette, includes a reflector surface and an image surface. Images of the incident light spot or line and of the reflected light spot or line are formed on the image surface, and the distance between the images indicates the magnitude of angulation alignment error between the grid cassette and the x-ray source. When beam alignment is accurate, the incident light spot or line and reflected light spot or line will be substantially superimposed, producing a single image on the reflector element. In addition, an opaque line on the transparent front surface of the collimator housing of the x-ray apparatus appears as a dark shadow within the field projected by the collimation light. Coincidence between the incident light spot or line and the shadow produced by the opaque line on the collimator serves as a distance indicator facilitating the placement of the grid cassette at the proper focal distance from the x-ray source. Further aspects of the invention include radiopaque markers which are located on front and rear surfaces of the grid cassette, and which produce images on an x-ray film when exposed. The relative positions between the images of the markers on the exposed radiographs are indicative of the amount of angulation alignment error between the grid cassette and the x-ray source. Yet another aspect of the present invention is the capability of the grid cassette to accommodate a standard x-ray film cassette in either a horizontal or vertical orientation, without reorienting the grid cassette itself.

Hand held laser apparatus

Abstract: A hand held laser apparatus containing a semiconductor laser diode switchably connected to a power supply. The output of the laser diode is focused and collimated by a pair of lens. Circuitry is provided to allow for either continuous wave or pulsed modes of operation as well as the capability of varying the pulsewidth of the laser. A guide laser or a light emitting diode is provided to guide the operator. The power level of the guide laser is limited so that it transfers minimal power to the workpiece but provides a visible line of laser light along which the output of the semiconductor laser diode will travel. A photodetector may be positioned between the laser diode and the lenses. Additionally, the amount of current delivered to the laser in continuous wave mode of operation or the pulse width and duty cycle of a pulse may be measured and displayed. Embodiments are provided incorporating a plurality of laser diodes to allow continued operation upon failure of a diode, increased power with the simultaneous use of the multiple diodes, or either alternate wavelength selection or wavelength mixing. Alternative embodiments operate at a predetermined voltage level. These embodiments may utilize a set of batteries such that the entire batteries and control circuitry may be contained either within a portable package or the hand held laser apparatus itself. Such alternative embodiments may be made so as to be disposable upon the discharge of their batteries or the exhaustion of the laser.

High power light source

Abstract: An optical system for producing a high power light source comprises a number of laser diodes, or similar sources, which emit light from an emission stripe 8 having a long dimension a (x-axis) and a short dimension b (y-axis) and which have a higher numerical aperture in the y-axis than in the x-axis. The laser beams 9 are collimated by a lens 10 and focused onto an optical fibre by a further lens 20. Prior to the focusing, the collimating beams 11 are anamorphically expanded/reduced by beam shaping means 12, so that the width of each beam 11 in the x-axis is increased in relation to the width in the y-axis. The images 21 produced on the fibre end are thus anamorphically magnified so that the anamorphic ratio between the magnification of the stripe 8 in the y-axis and in the x-axis is greater than one. By the brightness theorem, this anamorphic magnification results in a correspondingly relative decrease in the y-axis numerical aperture to enable a corresponding increase in the number of beams 11, which can fit into the solid angle of the target.

Photo-acoustic leak detection system and method

Abstract: An apparatus and method for the rapid detection and location of a gas leak. A collimated beam of light (16) is scanned (12) across the component (13) under test which has been pressurized with a tracer gas (17) that strongly absorbs the light. When the light passes through the gas (15) emerging from the source of the leak, the light energy absorbed by the gas produces an acoustic emission (19) which is detected by a microphone (22). The resulting signal may be processed (20) either as an alarm (21) to notify the operator that a leak is present, or, it may be processed in coordination with the light beam scanning mechanism to indicate (26) exactly where the leak is located on the component under test.

Interference methods and interference microscopes for measuring energy path length differences, path length between two locaitons or for determiing refractive index

Abstract: Interference methods and interference microscopes for measuring energy path length differences, path length between two locations or for determining refractive index are disclosed. According to one embodiment a confocal interference microscope (100) may be employed to build up an interferogram of surface (123) of object (124) as follows. A portion of the light beam from coherent laser diode (101) is coherently guided to exit (115) and focussed into a diffraction limited spot (125) intersecting surface (123) by high quality lens (122). A portion of the scattered signal light resulting from spot (125) is collected by lens (122) and confocally injected back into exit (115) to be guided back to coupler (108). A second portion of the light beam from diode (101) is coherently guided to end (121) from whence it emerges collimated. This collimated beam termed the reference beam is partially reflected by mirror (126) through end (121) and is guided back to coupler (102) where it interferes with the signal beam. The result of the interference is detected by detector (127) and fed to a computer (128). A portion of the signal light injected into fibre exit (115) is guided to detector (145) which detects the intensity level. This intensity level is fed to a computer (128) and used to control scanner (130) so as to maintain the focus of spot (125) on surface (123). A portion of the reference beam reflected by mirror (126) is injected into single mode fibre (135) and guided coherently to coupler (138) where it interferes with illuminating light guided coherently from laser diode (101) and thence detected by detector (142). The resulting signal is fed to a computer (128). While scanner (130) is moving the exits the computer (128) keeps track of their position by monitoring the interference signal from detector (142).

Apparatus and method for interferometrically measuring the thickness of thin films using full aperture irradiation

Abstract: A measurement instrument which detects the thickness of the outer layer of a wafer 24, includes a filtered white light source forming an aperture image. The white light source includes a halogen lamp 10, a condensing lens 12, a circular aperture 14, a collimator lens 16, a narrow band filter wheel 18, and a second collimator lens 20. A monochromatic beam generated by this filtered white light source illuminates the entire surface of the wafer 24 with collimated light that has passed through a third collimator lens 22. The light reflected off the wafer 24 returns through the third collimator lens 22 and forms an aperture image upon an optical device which redirects this image to a charge coupled device (CCD) camera 30. The image is converted to a map of measured reflectance data by a digitizing circuit 34 and a computer 36. This map of measured reflectance data is then compared to reference reflectance data to generate a map of the outer layer thickness profile of the wafer 24.

Semiconductor laser weapon trainer and target designator for live fire

Abstract: Disclosed is a capability for training and other uses wherein a firearm cane aligned with its target by use of a laser beam, or the target can be designated to others by illuminating it with the laser beam. A laser diode that provides visible light is used in conjunction with the boresight of a gun to paint a visible spot on an intended target at the location the bullet will impact if the weapon were fired. The beam emitted by the diode is collimated by a miniature gradient refractive index lens co-located with the diode on a heat sink that is included to convey heat away from the heat sensitive components. A circuit having a photodiode and a differencing amplifier is included to provide stability in the output of the laser, in order to overcome the effects of thermal excursions, and to protect the reflective surfaces of the laser from power surges. The on-off switch is a pressure sensitive material removably attached to the gun in a convenient location for it to be operated by the user's gun hand.

Media edge sensor utilizing a laser beam scanner

Abstract: A system is described for providing positional information regarding a media sheet in an image forming apparatus. The system includes a laser for providing a beam of collimated light and a mechanism for moving a media sheet along an imprinting path. Beam sensors are placed in the imprinting path, and positioned so as to be partially shaded by a media sheet when it is moved along the imprinting path. A scanning system moves the light beam across the media sheet and past its edges to cause the beam to fall on the beam sensors, when the media sheet is partially shadowing the beam sensors. A processor is responsive to outputs from the beam sensors to determine positional information regarding the media sheet. Positional information is derived by determining the time during which the scanned beam is incident on a sensor.

Electro-optical methods and apparatus for high speed, multivariate measurement of individual entities in fiber or other samples

Abstract: Single entities such as fibers (12) are delivered one at a time to a fluid stream, and a nozzle orients the entities so that each entity along its length (major dimension) is generally parallel with the direction of fluid flow. The entity then enters a sample region (36) and a sensor senses entity data such as the speed of the entity as it passes through the sample region. A preferred embodiment includes a collimated beam of light (34) and two side-by-side photo detectors (46a, 46b) positioned to measure light extinction caused by fibers passing through the sample region. Another sensor (52) may be provided to detect light scattered forward at an angle of about forty degrees (40°). The sensor signals are used to generate data that corresponds to such parameters as length, fiber ribbon width, fineness, cross-sectional area, maturity, cross-sectional circularity, shape, surface roughness, etc. Optical filtering provides information about composition (natural or man-made) and appearance (color and polarization).

A simple intrinsic optical fibre refractometer

Abstract: A refractometer using low-cost components is described. A multimode optical fibre is illuminated by a collimated beam at a variable oblique incidence angle. The value of the refractive index of a liquid is deduced from the measurement of an angle and does not depend on fluctuations of the light intensity. The use of an optical fibre allows remote sensing to be performed. As predicted by a simple theoretical analysis based on geometrical optics, the accuracy of the refractometer is about 1 × 10−4 in refractive index units. Owing to its good sensitivity, this set-up can be used as a chemical sensor.

Paper roughness or glass sensor using polarized light reflection

Abstract: To detect roughness on a travelling surface of a web such as paper a beam of polarized light is directed at an angle onto the web and focused by a focal lens to illuminate a spot on the surface and a specularly reflected component of the light is collected through a second lens focused on the spot. A detector is aligned to receive a portion of the specularly reflected collimated light from the spot passing through a selecting aperture and generates a signal depending on the intensity of the specular light passing through the aperture and received by the detector thereby to provide an indication of the roughness (or smoothness) of the surface.

Method and apparatus for homogenizing a collimated light beam

Abstract: A method and apparatus for smoothing and homogenising the cross-sectional intensity distribution of the output from an excimer laser for improved application of excimer lasers to optical laser surgery to the cornea. The laser beam is focused by means of a cylindrical lens or mirror and then filtered using a narrow gap spatial filter to smooth the intensity distribution by removing high spatial frequencies. The resulting output beam may be collimated by means of a second cylindrical lens or mirror for application to further optical processes.

Scattering type liquid crystal device

Abstract: A liquid crystal device for controlling scattering of light beams made incident upon a plurality of portions of a liquid crystal layer (4) thereof so as to modulate the light beams, the liquid crystal device including: a first lens array (2a) having lenses disposed to correspond to the portions of the liquid crystal layer, the lenses causing the light beams transmitted from the corresponding portions of the liquid crystal layer to travel toward a focal plane; a mask (6) for shielding scattered light transmitted from the first lens array and as well as allowing non-scattered light to pass through, the mask having a plurality of aperture portions which are formed along the focal plane to correspond to the lenses of the first lens array so as to allow non-scattered light transmitted from corresponding lenses to pass through; and a second lens array (3a) having lenses arranged to correspond to the aperture portions of the mask, the lenses substantially collimating the non-scattered light transmitted from corresponding aperture portions of the mask.

Highly accurate in-situ determination of the refractivity of an ambient atmosphere

Abstract: A highly accurate in-situ determination of the refractivity of an ambient atmosphere is disclosed, which determination is utilizable to enhance the accuracy of a quantity measurement. The system includes use of a refractometer exposed to an ambient atmosphere and having light directed thereto to form an optical interference fringe pattern having a dependence upon the refractivity of the ambient atmosphere. The fringe pattern is measured as a function of angle either by sequentially scanning a collimated input beam in angle while collecting and detecting the transmitted light, or by imaging (onto a multi-element detector) the angular exit space of the interferometer illuminated with a diverging input beam. The electrical output of the detector is processed to provide an output indicative of the index of refraction of the ambient atmosphere. The determined index of refraction is utilizable to enhance the accuracy of a quantity measurement, such as, for example, the distance measurement provided by a Fabry-Perot or displacement-measuring Michelson interferometer.

Surveying instrument including low power light plane generator

Abstract: A surveying instrument is provided which includes an optical sighting scope having a sighting barrel and orthogonal reticular lines visible to an observer viewing through the barrel, in combination with a miniature light plane generator that is oriented to produce a plane of light that is coincident with one of the reticular lines in the direction viewed by an observer viewing through the barrel of the optical sighting scope. The miniature light plane generator includes a laser diode that generates a beam of light, a collimating lens positioned within the beam of light generated by the laser diode in order to produce a beam of collimated light, and a fan lens positioned within the beam of collimated light in order to divert the beam of light into a plane. The miniature generator additionally includes a power supply that supplyies power at a low duty cycle. Because of the resulting reduction in electrical power required by the generator, the components making up the generator, including a battery for supplying energy to the power supply, may be combined within the housing of the optical sighting scope in order to provide a compact instrument.

Interferometer spectrometer having tiltable reflector assembly and reflector assembly therefor

Abstract: A twin-arm interferometer spectrometer having a tiltable reflector assembly, which includes a pair of mutually facing parallel reflective elements, varies the path length of both interferometer arms simultaneously to achieve high resolution in a small, low maintenance design. Collimated electromagnetic radiation is split by a beamsplitter into first and second arm beams. Both arm beams impinge on the tiltable reflector assembly, to retroreflectors, and back to the beamsplitter wherein they recombine to form an exit beam. The exit beam is directed to a sample and then to a suitable detector. Modulation of the exit beam is produced by tilting the reflector assembly about an axis parallel to the reflective elements in the reflector assembly. This tilting causes a simultaneous variation in the path length of both interferometer arms, and thereby yields a large total path difference with a relatively small movement. Symmetry between the paths of the reference beam and test beam results in greater stability and greater immunity to thermal expansion.

Pre-aligned diode laser for external cavity operation

Abstract: An interchangeable insertable diode laser and lens frame is described in which a pair of lenses is disposed in the frame with a diode laser disposed between the lenses. The laser light from one of the facets is collimated by one of the lenses, such that when the frame is inserted into a housing and coupled to an external cavity in which a diffraction grating is disposed, the grating disperses the light and dispersed light is focused on the facet causing the diode laser to generate single frequency radiation.

Diffractive optical element for collimating and redistributing Gaussian input beam

Abstract: An optical element for producing a collimated output beam having a uniform intensity profile from a highly divergent input beam having a Gaussian intensity profile, the optical element consisting of a single convex-plano lens having a diffractive element etched into the plano side of the single lens in accordance with binary optics technology, the diffraction element being configured to complete collimation of the input beam directed at the convex side of the single lens while at the same time redistributing the input beam to produce a uniform intensity output beam.

Method and apparatus for imaging porous media and method for fabricating novel optical materials

Abstract: A method and apparatus is described for determining petrophysical properties of porous media by the use of light transmission through the media. Specifically, by using a highly collimated light source, preferably a laser, the permeability, grain size, wettability, porosity and clay swelling behavior of a sample can be determined on the scale of millimeters. A calibration curve or function is first established to correlate light transmission through a slab of sandstone on the order of 5 to 10 mm under known conditions. This curved is then used to determine unknown conditions by measuring light transmission and comparing the values to those on the curve. Other applications for the phenomenon of light transmission through porous media are disclosed whereby conditions in a flowing stream of liquid can be monitored by use of light transmission. Specifically, changes in the refractive index and immiscible contamination can be detected. Finally, the phenomenon described can be used to model subterranean hydrocarbon bearing reservoirs, particularly fluid flow at different points in the reservoir, using light rather than hydraulic flows to simulate fluid flow patterns.

Method and apparatus for measuring ion beam collimation, shaping the ion beam and controlling scanning thereof

Abstract: A method of measuring collimation of an ion beam used for electrostatically-controlled collimated scanning includes the steps of electrically detecting the ion beam to determine the time-dependent change in the scanning position of the ion beam both at an upstream location and at a downstream location of the ion beam, determining upstream and downstream positions of the ion beam at mutually corresponding times based on the time-dependent change determination, and determining the degree of collimation of the ion beam based on the relationship between the upstream and downstream positions.

Optical fiber circumferentially symmetric fusion splicing and progressive fibre polishing

Abstract: Two optical fiber segments are spliced in an end-to-end fashion by first axially aligning the optical fiber segments, and then fusing the optical fiber segments with a converging conical light beam convergently focused to an apex region along the optical fiber. The converging conical beam heats the optical fiber segments and the splice in a circumferentially uniform manner. The apex region at which the converging conical beam is focused can be moved progressively along the length of the optical fiber to effect the fusion, and also to directionally fire polish and stress relieve the optical fiber to minimize the presence of flaws in the optical fiber after fusion is complete. The converging conical light beam is achieved by creating a diverging conical beam using movable mirrors to deflect a collimated beam into a diverging conical beam. The diverging conical beam is reflected from a parabolic mirror to form the converging conical beam that is focused toward the optical fiber. Longitudinal movement of the apex region along the optical fiber is achieved by altering the amplitude of the movement of the mirrors to change the apex angle of the diverging conical light beam.