Showing papers on "Collimated light published in 2002"

MeV Ion Jets from Short-Pulse-Laser Interaction with Thin Foils

Abstract: Collimated jets of carbon and fluorine ions up to 5 MeV/nucleon ( approximately 100 MeV) are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2). The normally dominant proton acceleration could be surpressed by removing the hydrocarbon contaminants by resistive heating. This inhibits screening effects and permits effective energy transfer and acceleration of other ion species. The acceleration dynamics and the spatiotemporal distributions of the accelerating E fields at the rear surface of the target are inferred from the detailed spectra.

Direct aperture optimization: a turnkey solution for step-and-shoot IMRT.

Abstract: IMRT treatment plans for step-and-shoot delivery have traditionally been produced through the optimization of intensity distributions (or maps) for each beam angle. The optimization step is followed by the application of a leaf-sequencing algorithm that translates each intensity map into a set of deliverable aperture shapes. In this article, we introduce an automated planning system in which we bypass the traditional intensity optimization, and instead directly optimize the shapes and the weights of the apertures. We call this approach “direct aperture optimization.” This technique allows the user to specify the maximum number of apertures per beam direction, and hence provides significant control over the complexity of the treatment delivery. This is possible because the machine dependent delivery constraints imposed by the MLC are enforced within the aperture optimization algorithm rather than in a separate leaf-sequencing step. The leaf settings and the aperture intensities are optimized simultaneously using a simulated annealing algorithm. We have tested direct aperture optimization on a variety of patient cases using the EGS4/BEAM Monte Carlo package for our dose calculation engine. The results demonstrate that direct aperture optimization can produce highly conformal step-and-shoot treatment plans using only three to five apertures per beam direction. As compared with traditional optimization strategies, our studies demonstrate that direct aperture optimization can result in a significant reduction in both the number of beam segments and the number of monitor units. Direct aperture optimization therefore produces highly efficient treatment deliveries that maintain the full dosimetric benefits of IMRT.

Led light assembly

Abstract: An light source utilizes a parabolic reflector to collimate light emitted from at greater than a predetermined angle relative to the optical axis of an LED arranged at the focus of the reflector. An optional collimating lens is arranged to collimate light emitted at less than the predetermined angle. Both variations provide light in the form of a substantially collimated beam. The parabolic reflector is preferably extended along its focal point to form a linear parabolic section having a linear focal axis. A linear array of LEDs is arranged such that the linear focal axis passes through the area of light emission of each LED. The linear parabolic section may be provided with parabolic dish ends. Alternatively, the ends of the parabolic section may be left open for increased wide angle visibility.

Photonic crystal light deflection devices using the superprism effect

Abstract: The superprism effect allows wide-angle deflection of the light beam in a photonic crystal (PC) by a slight change of the wavelength or the incident angle. In this paper, we discuss such light deflection outside the PC, which is expected when the output end of the PC is tilted against the input end. The analysis of the dispersion surfaces indicates a deflection angle of /spl plusmn/50/spl deg/ in a two-dimensional PC composed of triangular lattice airholes by changing the incident angle by /spl plusmn/2/spl deg/ or the wavelength by /spl plusmn/2%. Light deflections inside and outside the PC are numerically demonstrated by the finite difference time-domain method. It displays not only the main output beam but also many diffracted waves, which satisfy the wavevector conservation condition. These waves are sufficiently suppressed and an almost collimated output beam is realized by a flat interface.

Method and instrument for detecting biomolecular interactions

Abstract: Method and apparatus for detecting biomolecular interactions. The use of labels is not required and the methods may be performed in a high-throughput manner. An instrument system for detecting a biochemical interaction on a biosensor. The system includes an array of detection locations comprises a light source for generating collimated white light. A beam splitter directs the collimated white light towards a surface of a sensor corresponding to the detector locations. A detection system includes an imaging spectrometer receiving the reflected light and generating an image of the reflected light.

Optical apparatus which uses a virtually imaged phased array to produce chromatic dispersion

Abstract: An optical apparatus for producing chromatic dispersion. The apparatus includes a virtually imaged phased array (VIPA) generator, a mirror and a lens. The VIPA generator receives an input light at a respective wavelength and produces a corresponding collimated output light traveling from the VIPA generator in a direction determined by the wavelength of the input light, the output light thereby being spatially distinguishable from an output light produced for an input light at a different wavelength. The mirror has a cone shape, or a modified cone shape. The lens focuses the output light traveling from the VIPA generator onto the mirror so that the mirror reflects the output light. The reflected light is directed by the lens back to the VIPA generator. In this manner, the apparatus provides chromatic dispersion to the input light. The modified cone shape of the mirror can be designed so that the apparatus provides a uniform chromatic dispersion to light in the same channel of a wavelength division multiplexed light.

Waveguide, edge-lit illumination arrangement and display comprising such

Abstract: A polarized light-emitting waveguide for use in an edge-lit lighting arrangement /77) has polarization-selective outcoupling means including at least a volume hologram (87) for selectively diffracting waveguided light towards the exit surface of the waveguide with high contrast and efficiency. The light emitted by the waveguide is selectively emitted to one side thereof , highly polarized, highly collimated and may be homogeneously distributed across the exit surface. Also, light emission may be normal or near-normal to the exit surface. If combined with light recycling means (89) the contrast, brightness and/or efficiency of the edge-lit illumination arrangement may be further increased.

Underdosage of the upper-airway mucosa for small fields as used in intensity-modulated radiation therapy: a comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations.

Abstract: Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons. especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis (lose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rin) situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLi plus linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A 10 x 2 cm(2) and a 10 K 1 cm(2) field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild-up was studied. Radiochromic film measurements were performed in an in-house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax-TMS (MDS Nordion, Kanata. Canada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas. CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild-up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of I rum, the maximum dose overestimation was 14% or 24%. (Less)

Attenuation of 1310- and 1550-nm laser light through sound dental enamel

Abstract: Inexpensive laser diodes and fiber-optic technology have revived optical transillumination as a promising diagnostic method for the early detection of dental caries. The principal factor limiting transillumination through dental hard tissue is light scattering in the normal enamel and dentin. Previous studies have shown that the scattering coefficient decreases with increasing wavelength. Therefore, the near-IR region is likely to be well suited for fiber optic transillumination. The objective of this study was to measure the optical attenuation of near-IR light through dental enamel at 1310-nm and 1550-nm. These laser wavelengths are readily available due to their suitability for application to fiber optic communication. In this study the collimated transmission of laser light through polished thin sections of dental enamel for various thickness from 0.1 to 2.5 mm was measured in cuvettes of index matching fluid with n= 1.63. Beer-Lambert plots show that the attenuation coefficients are 3.1+/- 0.17cm -1 and 3.8+/- 0.17cm -1 for 1310-nm and 1550-nm, respectively. This study indicates that near-IR laser wavelengths are well-suited for the transillumination of dental enamel for caries detection since the attenuation through normal tissue is an order of magnitude less than in the visible.

Optical module for high-speed bidirectional transceiver

Abstract: The optical module of the invention for high-speed bidirectional transceiver consists of a signal receiving unit, a signal transmitting unit, a common receiving-transmitting optical fiber, and a fiber coupling unit. The laser diode and the photodiode are arranged parallel to each other in closely located recesses of the module housing. Such an arrangement makes it possible to shorten distances for guiding lead wires from the terminals of the PC board to the respective terminals of the transmitting and receiving diodes. The laser diode emits a first transmitting laser beam that passes through a microobjective that collimates the beam and directs into onto a full-reflection mirror located inside the module housing. The full-reflection mirror reflects the first transmitting beam at an angle of 90° and transmits it to the end face of an optical fiber through an optical fiber collimator that centers the beam with the fiber core. The module is provided with a second mirror, which is fully transparent to the aforementioned first transmitting beam, but is fully reflective to a second transmitting beam that may propagate in a direction opposite to the first transmitting beam on a different wavelength. Alignment of the optical components is facilitated due to the fact that it is carried out with diffractionally limited and collimated beams.

Generation of MeV electrons and positrons with femtosecond pulses from a table-top laser system

Abstract: In experiments, the feasibility was demonstrated of generating multi-MeV electrons in a form of a collimated beam utilizing a table-top laser system delivering 200 fs pulses with P-L=1.2 TW and 10 Hz capability. The method uses the process of relativistic self-channeling in a high-density gas jet producing electron densities in the range of 3x10(19)-6x10(20) cm(-3). In a thorough investigation, angularly resolved and absolutely calibrated electron spectra were measured and their dependence on the plasma density, laser intensity, and gas medium was studied. For the optimum electron density of n(e)=2x10(20) cm(-3) the effective temperature of the electron energy distribution and the channel length exhibit a maximum of 5 MeV and 400 mum respectively. The laser-energy to-MeV-electron efficiency is estimated to be 5%. In a second step, utilizing the multi-MeV electron beam anti-particles, namely positrons, were successfully generated in a 2 mm Pb converter. The average intensity of this new source of positrons is estimated to be equivalent to a radioactivity of 2x10(8) Bq and it exhibits a very favorable scaling for higher laser intensities. (C) 2002 American Institute of Physics. (Less)

Dosimetric characteristics of Novalis shaped beam surgery unit

Abstract: The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6×6 mm to 100×100 mm. The effects of collimator size, micro-multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini-ion-chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6×6 mm.

Integrated wavefront-directed topography-controlled photoablation

Abstract: A system and method combining wavefront analysis with narrow-beam scanning photoablation where optimal corneal topography is first calculated then followed by real-time topographic feedback controlled photoablation Eye movement and beam position sensing to within a tolerance of 5 μm are provided by high speed digital computation in conjunction with specialized charge coupled devices Lasers of three different wavelengths—one low-powered pulsed ultraviolet, a second continuous visible band type, and a pulsed infrared type are combined together into narrow beams whereupon a scanning mechanism generates coaxial collimated beams for the functions of ablation, beam position sensing, and fundus spot imaging Transepithelial ablation is performed utilizing the same CCD used for wavefront analysis by switching between two dichroic mirrors The light source for the raster videokeratography topography means is the UV laser used for ablation

Effective pinhole-collimated ultrasmall-angle x-ray scattering instrument for measuring anisotropic microstructures

Abstract: Small-angle scattering is widely used for measuring materials microstructure in the 1–100 nm size range. Ultrasmall-angle x-ray scattering (USAXS), typically achieved through crystal collimation, extends this size range to include features over 1 μm in size. This article reports on USAXS on the UNICAT beam line 33-ID at the Advanced Photon Source. The instrument makes use of a six-reflection crystal pair as a collimator and another six-reflection crystal pair as an analyzer. First principle absolute calibration and a broad scattering vector range make this a very effective instrument, limited only by the fact that the measurement of anisotropic microstructures is excluded due to slit smearing from the crystal collimation. This limitation has recently been removed by adding a horizontally reflecting crystal before and another after the sample. This creates a USAXS instrument with collimation in two orthogonal directions. We call this configuration effective pinhole USAXS. Now, anisotropic materials are probed using 9–17 keV photons in the same physically-relevant (from 50 nm to over 1 μm) microstructural size range as that available for materials which scatter isotropically.

Laser beam delivery system with trepanning module

Abstract: A laser beam delivery system for supplying a laser beam to a computer generated hologram which shapes and divides the supplied laser beam into a plurality of pseudo flat top laser beams. The plurality of pseudo flat top laser beams are then passed through collimated optics which alter the beams so that the beams are conveyed along the optical axis in a parallel manner. The plurality of collimated laser beams then passes through a converging mechanism which facilitates converging of the plurality of separated collimated laser beams through a clear aperture of a mirror of a first repeat positioning device so that all of the light is received by the repeat positioning device and appropriately reflected thereby to a second mirror of a second repeat positioning device and then to a rear surface of an F-Theta lens. The F-Theta lens focuses the plurality of separated collimated laser beams at the object to be processed. The converging mechanism facilitates converging of all of the supplied light so that substantially all of the supplied light passes through the clear aperture(s) of the repeat positioning device(s).

Semiconductor laser device and solid state laser device using the same

Abstract: A semiconductor laser device increased in energy density at the focus; and a semiconductor laser excitation solid laser device using the same. A row of dotted-line-wise series-connected laser beams are disposed in front of stack array laser elements emitting a group of two-dimensional array-like parallel laser beams, each row of laser beams refracted substantially normal to the direction of the dotted lines and collimated are received, the direction of the laser beams from emitters or a group of emitters is turned through a right angle and the laser beams are emitted, whereby the laser beams are converted into a plurality of rows of laser beams paralleled substantially in a ladder form, which rows of laser beams are beam-compressed into a row of laser beams, the latter being converted into a series disposition, a row of parallel compressed laser beams are turned through a right angle and emitted, whereby all laser beams are converted into a group of laser beams paralleled in a single row, the group of laser beams being collimated and converged to a focus.

Pump–probe mode-mismatched thermal-lens Z scan

Abstract: We report on a pump–probe mode-mismatched thermal-lens Z-scan method for the measurement of small absorption coefficients. In this method the pump light beam is focused into the sample to induce a thermal lens, which is tested by a collimated probe-light beam. Comparison between mode-matched and mode-mismatched Z-scan schemes is performed by use of a Fresnel-diffraction approximation model. This method is used to measure the absorption of distilled water and optical glass in the near-infrared and visible regions of the spectrum.

Method and system to display a virtual input device

Abstract: A system to project the image of a virtual input device includes a substrate bearing a diffractive pattern, and a source of collimated light, such as a laser diode. The collimated light interacts with the substrate and the pattern to project a user-viewable image that preferably is the image of a virtual input device. Interaction between a user and the projected image of the virtual input device can then be sensed, and used to input information or otherwise control a companion device, for example a PDA or a cellular telephone.

Radiation imaging system and method of collimation

Abstract: A radiation imaging system comprises a movable radiation source adapted to be disposed in a plurality of respective radiation source positions; a radiation detector and a collimator assembly configured to displace a collimator in a plurality of respective collimator positions, each of the collimator positions being coordinated with at least one of the radiation source positions such that a radiation beam emanating from the radiation source is collimated to limit radiation incident on the detector to a predetermined exposure area. Another radiation imaging system comprises a movable radiation source; a radiation detector; and a collimator comprising an adjustable geometry aperture assembly configured such that an adjustment of the aperture geometry is synchronized with the movement of the radiation source and coordinated with the radiation source position so as to limit the incident radiation to a predetermined exposure area at the detector.

Diffraction grating-based wavelength selection unit having improved polarization dependent performance

Abstract: An optical wavelength selection device containing an optical beam source, a device for collimating the optical beam to produce a collimated optical beam, a diffraction grating assembly for diffracting the collimated optical beam to produce a collimated optical diffracted beam, a device for modifying the polarization state of the collimated optical beam, and a lens assembly for focusing the collimated optical diffracted beam. The device for modifying the polarization state of the collimated optical beam is located within the diffraction grating assembly in one embodiment and before the diffraction grating assembly in another embodiment.

High-intensity third-harmonic generation

Abstract: The azimuthal dependence of third-order and cascaded second-order nonlinear coupling are used to measure the relative contributions of each to direct third-harmonic generation in β-barium borate. This enabled the measurement of the values of χ10(3),χ11(3), and χ16(3) relative to the known χij(2). Finally, conversion efficiencies to 3ω of up to 6% from a single crystal were achieved with a femtosecond chirped-pulse-amplification laser with 200 GW/cm2 in collimated beams.

Configuration of and method for optical beam shaping of diode laser bars

Abstract: An optical beam shaping element is used to produce a beam of high brightness from a diode bar or a single emitter diode, allowing for efficient coupling of the beam into an optical fiber. An embodiment of the beam shaping element allows the construction of a quasi-monolithic or truly monolithic beam shaper incorporating both fast axis collimation as well as beam rotation. Additional slow axis collimation or collimation of the beam-rotated fast axes of the individual emitting elements of the diode bar is also possible in one quasi-monolithic or truly monolithic design. The beam rotation element comprises an array of beam-inverting planar grin lenses aligned with their axes of equal refractive index at an angle of ±45° with respect to the slow axes of the emitters. Alterative embodiments comprise beam rotation elements based on two planar grin lens arrays, arrays of uniaxial grin lenses, arrays of uniaxial focusing reflective optic or arrays of cylindrical Fresnel lenses. The beam shaping element can be used in conjunction with stacks of diode bars or alternatively optical beams of ultra-high power can be generated by combining multiple fiber coupled diode bars in a fiber bundle incorporating metallization and a heat sink.

Luminosity and variability of collimated gamma-ray bursts

Abstract: Within the framework of the internal shock model, we study the luminosity and variability in gamma-ray bursts from collimated fireballs. In particular, we pay attention to the role of the e(+/-) pa ...

Production of ultracollimated bunches of multi-MeV electrons by 35 fs laser pulses propagating in exploding-foil plasmas

Abstract: Very collimated bunches of high energy electrons have been produced by focusing super-intense femtosecond laser pulses in submillimeter under-dense plasmas. The density of the plasma, preformed with the laser exploding-foil technique, was mapped using Nomarski interferometry. The electron beam was fully characterized: up to 10^9 electrons per shot were accelerated, most of which in a beam of aperture below 10^−3 sterad, with energies up to 40 MeV. These measurements, which are well modeled by three-dimensional numerical simulations, validate a reliable method to generate ultrashort and ultracollimated electron bunches.

Wave optical analysis of light-emitting diode beam shaping using microlens arrays

Abstract: We investigate the use of optical systems consisting of either one or two refractive microlens arrays, a collimating and Fourier trans- forming lens for LED beam homogenization. Due to the small lenslet diameters, diffraction can lead to significant deviations from the desired homogene intensity distribution. Therefore, we analyze the two setups applying scalar diffraction theory and explain the occurring effects using numerical calculations. Our theoretical calculations are supported by ex-

Pool cue alignment and training apparatus

Abstract: An pool cue aiming apparatus for billiards games includes a cue provided with a source for a narrow collimated beam of light emerging from the playing tip along the longitudinal axis of the cue. An electrical communication system is located within the cue, having a pressure sensitive handle housing batteries, thereby transmitting electricity when the handle is depressed and closes an electrical circuit. Electricity generated from the batteries is transmitted to a light source in the tip portion of the cue and the light therefrom moves through a longitudinal bore along the length of the cue to emerge from an orifice located at the striking tip. The collimated light allows a user to learn proper striking technique in the game of billiards.

Generation of high-power, high brightness optical beams by optical cutting and beam-shaping of diode lasers

Abstract: An optical beam-shaping element is used to produce a high brightness laser beam from a diode bar or a single emitter diode, allowing for efficient coupling of the beam into an optical fiber. An embodiment of the beam-shaping element allows the construction of a quasi-monolithic beam shaper incorporating both fast axis collimation as well as beam rotation. Additional slow axis collimation of the individual emitting elements of the diode bar is also possible in one quasi-monolithic design. The beam rotation element may comprise an array of beam-inverting planar grin lenses aligned with their axes of equal refractive index at an angle of ±45° with respect to the slow axes of the emitters. Alternative embodiments comprise beam rotation elements based on Fresnel lens arrays or aspheric cylindrical lens arrays. The beam-shaping element can be used in conjunction with stacks of diode bars, where optical cutting of the diode bar beams in a parallelepiped coated with multiple reflective stripes can be further implemented to symmetrize the resulting optical beam. Alternatively optical beams of ultra-high power can be generated by combining multiple fiber coupled diode bars in a fiber bundle incorporating rectangular fiber cores, metallization and a heat sink.

Method and apparatus for the non-invasive measurement of blood glucose levels in humans

Abstract: An apparatus (10) for determining a diagnostic glucose level in a human subject includes a light source (30) that produces collimated light at a selected wavelength. The collimated light is arranged such that it passes through a portion of an eye (12) of the subject and reflects off an eye lens (16) at a selected angle (θB) as reflected light. A polarization analyzer (70) measures a polarization of the reflected light that exits the eye (12). A path length processor (68) determines an optical path length (Lλ) of the reflected light within an aqueous humor (22) of the eye (12). A glucose level processor (90) computes a glucose concentration based on the measured polarization and the determined optical path length (Lλ).

Method and apparatus for coupling radiation from a stack of diode-laser bars into a single-core optical fiber

Abstract: A method of coupling laser-radiation into an optical fiber includes providing a stack of diode-laser bars and first and second parallel mirrors, the second mirror is selectively reflective only for one polarization plane of the laser-radiation. Each of the diode-laser bars includes at least two spaced-apart diode-laser emitters each emitting a plane-polarized beam of laser-radiation having a fast axis and a slow axis. The laser-radiation beams are collimated in the fast axis by a cylindrical lens located in front of each bar. In one arrangement the polarization orientation of one collimated beam from each diode-laser is rotated by 90 degrees and transmitted through the selectively-reflective mirror. The other collimated beam from each diode-laser bar is reflected onto the selectively-reflective mirror by the first mirror and reflected from the selectively-reflective mirror such that the reflected beam combines with the transmitted beam to form a combined beam. As many combined beams are formed as there are diode-laser bars in the stack. These combined beams are focused into an entrance face of the optical fiber.