Showing papers on "Collimated light published in 1998"

Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy.

Abstract: The use of a multileaf collimator in the dynamic mode to perform intensity modulated radiotherapy became a reality at our institution in 1995. Unlike treatment with static fields using a multileaf collimator, there are significant dosimetric issues which must be assessed before dynamic therapy can be implemented. We have performed a series of calculations and measurements to quantify head scatter for small fields, collimator transmission, and the transmission through rounded leaf ends. If not accounted for, these factors affect the delivered dose to the prostate by 5%-20% for a typical plan. Data obtained with ion chambers and radiographic film are presented for both 6 and 15 MV x-ray beams. The impact on the delivered dose of the mechanical accuracy of the multileaf collimator, achieved during leaf position calibration and maintained during dose delivery, is also discussed.

Liquid-crystal adaptive lenses with modal control.

Abstract: We report on a novel approach to the realization of nematic liquid-crystal (LC) phase correctors to form spherical and cylindrical wave fronts. A LC cell with a distributed reactive electrical impedance was driven by an ac voltage applied to the cell boundary to yield the desired spatial distribution of the refractive index. The two-dimensional function of the phase delay introduced into the light beam depends on the frequency of the ac control voltage, the geometry of the boundary electrode surrounding the LC cell, and the electrical parameters of the cell. We realized a cylindrical adaptive lens with a clear aperture of 15 mm x 4mm and a spherical adaptive lens with circular aperture of 6.5 mm. Both devices are capable of focusing collimated light in the range infinity...0.5 m.

Adjustable optical attenuator

Abstract: An optical attenuator for attenuating a collimated beam of light propagating along an optical path while preserving the composition of polarization of the collimated beam of light is disclosed. The optical attenuator comprises a beam attenuator for attenuating a portion of the collimated beam of light when a portion of the beam attenuator is disposed within the optical path. The beam attenuator has a cross section along a plane perpendicular to the direction of propagation of the collimated beam of light of the portion of the attenuator in the shape of a wedge. The attenuation is varied using a controller for moving the beam attenuator in order to vary a size of the portion of the wedge within the optical path.

Signal and resolution enhancements in dual beam optical coherence tomography of the human eye.

Abstract: In the past 10 years, a dual beam version of partial coherence interferometry has been developed for measuring intraocular distances in vivo with a precision on the order of 0.3 to 3 mm. Two improvements of this technology are described. A special diffractive optical element allows matching of the wavefronts of the divergent beam reflected at the cornea and the parallel beam reflected at the retina and collimated by the optic system of the eye. In this way, the power of the light oscillations of the interfering beams incident on the photodetector is increased and the signal-to-noise ratio of in vivo measurements to the human retina is improved by 20 to 25 dB. By using a synthesized light source consisting of two spectrally displaced superluminescent diodes with an effective bandwidth of 50 nm, and by compensating for the dispersive effects of the ocular media, it was possible to record the first optical coherence tomogram of the retina of a human eye in vivo with an axial resolution of ; 6t o 7 m m. This is a twofold improvement over the current technology. © 1998 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(98)01601-3]

Multi-spectral two-dimensional imaging spectrometer

Abstract: A multi-spectral two-dimensional imaging spectrometer (10) includes a combination of achromatic, well-corrected lenses (14) for imaging a two-dimensional scene on an internal field stop (20). The light emanating from this intermediate image is collimated with another well-corrected lens (24). A spectral separation subassembly (22) that divides the incident light into multiple, identical, and independent arms is placed in the collimated space following the collimating lens (24). The light in each arm is spectrally filtered based on the properties of an interference filter (30) in each arm. An imaging subassembly (32) composed of a well-corrected lens (34) forms contiguous images onto a single two-dimensional detector array (36). The images are identical copies of the original object with each copy having a different spectral component and can be viewed on a standard monitor or alternatively on a computer employing an analog-to-digital conversion device.

Integrated bi-directional axial gradient refractive index/diffraction grating wavelength division multiplexer

Abstract: A wavelength division multiplexer that integrates an axial gradient refractive index element with a diffraction grating to provide coupling from a plurality of input optical sources (each delivering a single wavelength) which are multiplexed to a single polychromatic beam for output to a single output optical receiver. The device comprises means for accepting optical input from at least one optical source, the means including a planar surface (20a); a coupler element (20) comprising an axial gradient refractive index collimating lens (26) having a planar entrance surface onto which the optical input is incident and a homogeneous index boot lens (24, 28) affixed to the axial gradient refractive index collimating lens and having a planar but tilted exit surface (20b); a diffraction grating (22) on the tilted surface of the homogeneous index boot lens which combines a plurality of spatially separated wavelengths from the optical light; and means to output at least one multiplexed, polychromatic output beam, the means including a planar surface (20a). The device may be operated in the forward or reverse direction as a multiplexer or demultiplexer.

Theory of grating-confined broad-area lasers

Abstract: Angled-distributed-feedback semiconductor lasers have demonstrated 1-W diffraction-limited collimated output from a broad-area aperture. We present the first theoretical analysis of the modes of these devices, explaining their principle of operation and the reasons for their high spatial mode quality. A transfer matrix analysis is presented that can describe the general class of grating-guided waveguides with either finite and/or infinite grating boundaries. Lateral grating-confined broad-area waveguides are shown to have extremely high spatial mode selectivity. The theory is applied to describe the new angled-grating distributed feedback laser (/spl alpha/-DFB), predicting a broad near-Gaussian near field and a collimated diffraction-limited far field, in good agreement with experiment.

Laser diode array assemblies with optimized brightness conservation

Abstract: The invention relates to laser diode arrays having high beam quality and high beam brightness In one approach, a laser diode array package includes a mount and first and second laser diode arrays disposed on the mount Each of the laser diode arrays defines an optical axis and has an emitting surface lying in an emitting surface plane The emitting surface plane of the first laser diode array is displaced relative to the emitting surface plane of the second laser diode array in a direction parallel to one of the optical axes The optical axes of the first and second laser diode arrays are offset from each other in a direction perpendicular to one of the optical axes First and second lenses are disposed relative to respective emitting surfaces to reduce divergence of light output from the emitting surfaces In another approach, laser diode array bars are stacked and the individual output beam from each bar is collimated using a short focal length, low aberration lens The resulting collimated beams are treated with reflectors to reduce, or remove, the dead spaces between adjacent collimated beams, thus permitting the use of low aberration lenses, which results in an improved divergence-size product for each beam produced by a bar Additionally, the total beam output by the array of laser bars is condensed in size

Nanometric range depth-resolved analysis of coated-steels using laser-induced breakdown spectrometry with a 308 nm collimated beam

Abstract: The spatial profile from an XeCl excimer laser was modified using a simple two-lenses telescope to generate a flat energy-profile beam that impinged a layered sample (a Zn-coated steel) without beam conditioning. The irradiance obtained (about 107 W cm–2) was high enough to vaporize the target, to cause plasma formation and to allow atomic emission spectrometry with acceptable signal-to-noise ratio. Modification in beam energy distribution resulted in flat ablated profiles and improved depth-resolution up to the few nm pulse–1 range was attained. The net intensity areas were transformed into normalized values leading to plots in excellent agreement with those provided by commercial depth-resolved analysis instruments.

Massively parallel inspection and imaging system

Abstract: A massively parallel inspection and imaging system is provided which employs multiple focused beams to illuminate a specimen. Laser light energy passes through a relatively low resolution diffraction grating or digital optical element, which is either one or two dimensional, and concentrates the transmitted energy into multiple discrete directions or orders. The beams split by the diffraction grating pass through a beam expander or telescope and are recombined onto an optical element and diverted toward the specimen. On reflection toward the specimen, the beams diverge again toward a focusing objective. The resultant light thus comprises multiple focused beams, and a relatively large area of the specimen is illuminated simultaneously by these beams. Upon reflection of the light from the sample, light passes back through the focusing objective in multiple beams, and the beams converge toward the optical element and diverge outward in collimated beams. The collimated beams pass through a focusing lens, which brings all beams onto foci on a detector array. Scanning of patterned wafers by the system may occur using coordinated motion of both the scanning beam and the wafer. To achieve proper orientation and observation, the stage speed in the cross direction is set at the ratio of the distance between the first and last lines divided by the period of the scanner.

Device for distance measurement

Abstract: A device for measuring distance with a visible measuring beam (11) generated by a semiconductor laser (10), has a collimator object lens (12) to collimate the measuring beam towards the optical axis (13) of the collimator object lens (12), an arrangement to modulate the measuring radiation, a reception object lens (15) to receive and image the measuring beam reflected from a distant object (16) on a receiver, a switchable beam deflection device (28) to generate an internal reference path between the semiconductor laser (10) and the receiver and an electronic evaluation device (25) to find and display the distance measured from the object. According to the invention, the receiver contains a light guide (17') with a downstream opto-electronic transducer (24), in which the light guide inlet surface (17) is arranged in the imaging plane of the reception object lens (15) for long distances from the object and can be controllably moved (18') from this position (18) transversely to the optical axis (14). In an alternative embodiment, the light inlet surface (17) is fixed and there are optical means (36) outside the optical axis (14) of the reception object lens (15) which, for short object distances, deflect the imaging position of the measuring beam to the optical axis (14) of the reception object lens (15). The measuring radiation is pulse modulated with excitation pulses with a pulse width of less than two nanoseconds.

Architectural lighting distributed from contained radially collimated light and compact efficient luminaires

Abstract: From a quasi point source, light distribution means produce a selected one or ones of broadly distributed ambient light, non-shadowing task illumination, multi-beam display lighting, projective lineal lighting and projective surface washing illumination lineally or radially distributed. Collimation optics shape light from a quasi point source into a disc of selected axial thickness. Containment optics contain divergence of and direct light from the collimation optics to distribution optics. The distribution optics modulates and redirects the radiant energy into a shape or shapes useful in illuminating architectural space. The distribution optics may reflect or refract light to direct and shape it for a particular architectural illumination requirement. The efficient combination of the optics provides for a system of minimized thickness, permitting maximum flexibility in integration with or within shelves, soffits and other structural members. Collimating means may surround the light source and one or more light direction changing means provided to redirect the light into desired directions and patterns. There can be two reflector, and the light source can be movable with respect to one of the reflectors whereby the amount of upward and downward lighting can be continuously varied. Options are available for having the light directed all in one direction and for using refractors in lieu of reflectors in selected arrangements.

Optical fiber wavelength multiplexer and demultiplexer

Abstract: The present invention relates to an optical fiber wavelength multiplexing or demultiplexing device comprising: An optical fiber wavelength multiplexing device comprising: an array of input single-mode fibers (101 to 105) designed for carrying light beams at different wavelengths (λ1, λ2, λ2, . . . ,λn), an output single-mode fiber (161) designed for carrying the whole set of such light beams, a dispersing system (107) receiving light beams from the input fibers (101 to 105) in an end plane and generating superimposed light beams designed for the output fiber (161) in an output plane, an array of converging microlenses (171 to 175) being located in the input plane, whereas a microlens corresponds to each input fiber, wherein the microlens array has the same pitch as the input fiber anlay and produces diverging beams whose respective central axes are parallel and which are directed to a collimating lens (108) which produces parallel collimated beams whose respective central axes are converging on the dispersing system. The demultiplexer comprises the same elements, whereas the roles of the input/output fibers and planes are reversed.

Multi-beam light source unit

Abstract: A multi-beam light source unit includes a light source section having a plurality of semiconductor lasers, a plurality of collimating lenses for collimating light beams emitted from the semiconductor lasers, and a supporting member for supporting the plurality of semiconductor lasers and the plurality of collimating lenses arranged in a main scanning direction. There is a relation expressed by D/d≠1 relating to a distance D between adjacent ones of the semiconductor lasers and a distance d of adjacent ones of the collimating lenses, and the light source section is supported so that it can be angularly adjusted so as to change a rotational position of the light source section including the semiconductor lasers and the collimating lenses.

Synchrotron energy-dispersive X-ray diffraction tomography

Abstract: Energy-dispersive diffraction tomography using white-beam synchrotron X-rays with energies up to 140 keV yields images of the interior features of solid objects up to 50 mm thick. The volume sampled is determined by the geometry of the diffracting lozenge defined by the incident beam, the detector system collimation and the Bragg angle. Using conventional beam slits to form a highly collimated 50 μm × 50 μm incident beam and a 40 μm collimator aperture, we demonstrate on a PEEK phantom that a lateral resolution (transverse to the beam direction) of a few microns can be achieved. The resolution in the direction of the incident beam is necessarily poorer than this since the diffracting lozenge is elongated in this direction, with length increasing rapidly at small angles. There is no evidence of significant contamination of the diffracted intensity by the effects of multiple scattering from outside the primary lozenge.

A reduction in the AAPM TG-36 reported peripheral dose distributions with tertiary multileaf collimation

Abstract: Purpose: The American Association of Physicists in Medicine Task Group 36 (AAPM TG-36) data can be used to estimate peripheral dose (PD) distributions outside the primary radiation field. However, the report data apply to linear accelerators not equipped with tertiary multileaf collimators (MLCs). Peripheral dose distributions consist of internal scatter, collimation scatter, transmission through collimation, head leakage, and room scatter. Tertiary MLCs may significantly reduce the PD due to a reduction in collimation scatter, transmission through collimation, and head leakage. Measurements were performed on a multimodality linear accelerator, equipped with a tertiary MLC, to determine PD distributions as a function of energy, field size, distance from the primary radiation field edge, MLC position, and collimator orientation. Methods and Materials: Measurements were made using an ionization chamber embedded in a 20 × 40 × 120-cm 3 water-equivalent plastic phantom with the secondary collimator and MLC settings of 10 × 10, 15 × 15, 20 × 20, 25 × 25 cm 2 , and with the MLC fully retracted. Data were taken along the longitudinal axis of the machine for 6 and 18 MV photons. Peripheral dose distributions were evaluated with the collimator set to 180 and 90 degrees. Rotation of the collimator allowed measurements parallel and orthogonal to the direction of motion of the MLC. Results: For both photon energies, peripheral doses measured on a MLC machine were lower than the TG-36 data. When the collimator is rotated by 90 degrees, placing the lower jaws and the MLC leaves along the plane of interest, PD was reduced by as much as a factor of three compared with PDs measured with the MLC fully retracted and the collimator rotated to 180 degrees. PDs measured with the MLC fully retracted and collimator rotated to 180 degrees were comparable to the TG-36 data. Measured PDs were lower when the MLC was used to shape the field than when the MLC was fully retracted. Conclusion: A strategic orientation of the collimator with a tertiary MLC can reduce PD distributions by more than a factor of two. This decrease significantly lessens or eliminates the need for external lead shielding to reduce the critical organ dose. This method can be used even when Lipowitz metal blocking (such as for mantle fields) is used, with the MLC leaves oriented along the longitudinal plane.

Backlight assembly for a display

Abstract: Systems and methods for providing an LGD with a collimated backlight and a non-Lambertian diffuser are described. An LCD system includes: an illumination source for producing light; a collimating waveguide optically connected to the illumination source, the collimating waveguide including a top surface, an incident end and a plurality of substantially parallel optical elements for redirecting light from the incident end to, and through, the top surface by total internal reflection (TR), each of the plurality of substantially parallel optical elements including a first facet that is nonparallel to the top surface and a mirrored second facet that is nonparallel to the top surface; a reflector optically connected to the light source and optically connected to the collimating waveguide, the reflector (1) at least partially surrounding the illumination source, and (2) reflecting light from said illumination source to said incident end by direct reflection; a liquid crystal display optically connected to the collimating waveguide; and a non-Lambertian diffuser optically connected to the liquid crystal display for directing light from said liquid crystal display. The light from the reflector is directly incident upon the incident end. The systems and methods provide advantages in that the light from the LCD is bright and homogenous.

Phase mask with spatially variable diffraction efficiency

Abstract: A phase mask (15) for modulating a collimated light beam passing therethrough, the light beam being diffracted to photoinduce a refractive index profile in a photosensitive optical medium, the phase mask (15) comprises a substrate (17) having an outer surface provided with a plurality of parallel grating corrugations (19). The grating corrugations (19) have a non-uniform relief depth across the outer surface for photoinducing a non-uniform refractive index profile in the photosensitive optical medium. The non-uniform relief depth is defined by a variable thin film layer (21) of variable thickness overlaying the substrate (17). The grating corrugations (19) can either be etched into the variable thin film layer (21) itself or be etched into the substrate (17), with the variable thin film layer (21) being deposited on it after etching. Methods to make such phase masks are also provided.

Strictly non-blocking scalable matrix optical switch

Abstract: A scalable, non-blocking fiber optic matrix switch has two arrays of light beam collimators arranged to face one another in free space, and a number of optical fibers coupled to each of the arrays. Each collimator has a tubular body with a fiber receiving part at one end, and a lens mounting part at an opposite end of the body. A lens fixed in the mounting part produces a collimated light beam from light emitted from an end of an optical fiber inserted in the fiber receiving part. First and second motor assemblies with corresponding positioning elements displace the collimator body so that its light beam is steered to a desired position along "X" and "Y" axes in response to operation of the motor assemblies. A signal carried on a fiber entering a first collimator in one array can be switched into a fiber of a second collimator in the opposite array, by displacing the collimators so as to direct the beam of the first collimator to align with a lens axis of the second. For an N×N matrix switch, N collimators are used at each array, and up to N optical signals can be cross-connected without blocking.

Optical apparatus for measuring profiles of a wafer

Abstract: A pair of optical profile measuring systems 10, 20 are provided at positions faced to both sides of a wafer 1 vertically supported at its edge. Each system 10, 20 includes a light emitter 11, 21 for discharging a measuring light beam 12, 22, a collimator lens 14, 24 for rectifying the light beam 12, 22 into a collimated beam, an optical flat 15, 25 for transmitting the collimated light beam 12, 22, a light detector 16, 26 receiving the light beams 12, 22 reflected on a surface of the wafer 1 and on a referential plane of the optical flat 15, 25 through the collimator lens 14, 24 and a computer 17, 27 for processing interference fringes which occur between the surface of the wafer 1 and the referential plane of the optical flat 15, 25. Profiles of main and back surfaces of the wafer as well as its thickness variation are easily measured utilizing light interference fringes corresponding to both sides of a wafer.

Plane‐grating monochromator at BESSY II using collimated light

Abstract: At the German synchrotron radiation facility BESSY II, the VUV photon energy range between 15 and 600 eV is covered by the first, third and fifth harmonics of the U125 undulator. The beamline connected to this source is a plane-grating monochromator (PGM) with a variable deviation angle. The plane grating is illuminated by collimated radiation, allowing very flexible use of the monochromator. Depending on users' demands, it can be operated at high spectral resolution, high-order suppression or in high-flux mode, simply by software control.

Liquid crystal projector

Abstract: A liquid crystal projector in which light is effectively used and an excellent picture can be obtained is provided. In the liquid crystal projector, dichroic mirrors arranged at different angles are used to separate white light into beams of light of three primary colors of R, G, and B, and the respective beams of the light are incident on microlenses at different angles. The respective beams of light of the three primary colors are distributed by the microlenses to optical components corresponding to pixels, and highly collimated light beams can be obtained by the optical components. Since the highly collimated light beams are made incident on the pixels of the liquid crystal panel, the beams can be certainly made incident on desired pixels.

Development of a 3D position sensitive scintillation detector using neural networks

Abstract: This work presents a novel method of exploiting light division in a scintillating crystal to localise in three-dimensions the point of interaction of an impinging photon. For this, light output of a detector block is mapped for known irradiation positions of a collimated photon beam and used to train a set of three independent multilayer neural networks. Spatial resolutions obtained with a Monte Carlo simulation of a cubic 2/spl times/2/spl times/2 cm/sup 3/ CsI(Tl) crystal fully covered with 24 Si PIN photodiodes are better than 2 mm fwhm in the three directions over the entire volume of the detector block. For comparison, the spatial resolution reconstructed in two dimensions from a simple Anger logic based on the photodetectors coupled to the rear side of the crystal is about 3.5 mm fwhm for the same experimental setup.

Optical head and optical disk apparatus

Abstract: A small-sized optical head and optical disk apparatus capable of high-density recording at a high data transfer rate. A collimated light beam is incident on a first surface of a transparent condensing medium. The light beam incident on the first surface is reflected by a reflective structure, such as a metallic film or a hologram, formed on the outside of a second surface of the transparent condensing medium. The reflected light forms a beam spot on a third surface of the transparent condensing medium. Light condensed at the beam spot is emitted as near field light, and propagates to a recording medium for optical recording or reproduction.

Optical waveguide device and manufacturing method thereof

Abstract: In an optical waveguide device, a laser beam is collected to an end face of a channel waveguide, and introduced into a PLZT thin film optical waveguide The incident laser beam, when emitted from the channel waveguide, diverges in the PLZT waveguide, permeates a thin film lens and is collimated into 04 Mm size When a high frequency voltage is not applied to a comb Al electrode, the laser beam is collected after penetrating through the second thin film and emitted from the end face through the channel waveguide to form an emission beam When the high frequency voltage is applied to the comb Al electrode, a diffraction grating is formed by an acousto-optic effect, and the laser beam is deflected The deflected laser beam, when penetrating through the second thin film lens, is collected and emitted from the end face through the channel waveguide in adjacent with the above-described channel waveguide to form a deflected emission beam

Apparatus and method for delivery of light to skin

Abstract: Improvements to a system for the process of hair removal which employs a collimated laser beam delivered to a target. These improvements include a reflector for reflecting back light scattered from the surface and improving light coupling into the tissue, use of an array of micro lenses for focusing the incident beam, and an annular ring to thin the epidermis and upper dermis to reduce blood volume in the illuminated area, and increase flux density at significant depths.

Integrated beam shaper and use thereof

Abstract: A substrate having an optical element on an input surface thereof receives a light beam not having a desired beam shape and shapes the light beam into a predetermined intensity distribution. The substrate may further include a second optical element for providing a predetermined phase pattern to the light beam provided by the first optical element. The first optical element may, for example, circularize an elliptical light beam using a soft aperture for differential power attenuation or by altering the divergence of the light beam along the different axes of the light beam. When the divergence angles are altered and the collimating optical element is provided on the output surface, the thickness of the transparent substrate is determined in accordance with a resultant difference in the divergence and/or with the initial difference in beam size along each axis and with a required circularity. A light source is mounted close to the first optical element in order to minimize the amount of differing divergence present along the different axes of the light beam. The optical elements may be diffractive, refractive, or hybrids thereof and are preferably prepared photolithographically on the substrate itself. The light source may be mounted using fiducial marks and the photolithographic processes for forming the optical elements may also use fiducial marks. All elements of the integrated beam shaper may be formed on a planar, wafer level.

On the effect of narrow-band filters on the diffraction limited resolution of astronomical telescopes

Abstract: Sometimes Fabry-Perot and other narrow-band filters are used for astronomical imaging in the so-called telecentric mode. In it the pupil is collimated through the filter, resulting in different incidence angles on the filter for rays coming from different parts of the objective. This results in variations of the central transmission wavelength, which broaden the effective filter bandpath. In addition each wavelength within this filter bandpath sees a different illumination of the pupil when viewed from behind the filter. This causes the diffraction limited point-spread-function to vary with wavelength. With the advent of diffraction limited imaging using adaptive optics, this can cause complications. In this note I examine the magnitude of this effect.