Showing papers on "Collimated light published in 2018"

The high-intensity reflectometer of the Jülich Centre for Neutron Science: MARIA

Abstract: MARIA (magnetism reflectometer with high incident angle) is a world class vertical sample reflectometer dedicated to the investigation of thin films in the fields of magnetism, soft matter and biology. The elliptical vertically focusing guide allows one to measure small samples with a typical size of 1 × 1 cm very efficiently. The double-bounce polarizer and the in situ pumped 3He SEOP (spin-exchange optical pumping) neutron spin filter cell for analysing the polarization of the reflected neutron beam can be moved into the beam in seconds. The polarized flux of MARIA amounts to 5 × 107 n (s cm2)−1 at the sample position with a horizontally collimated beam of 3 mrad, a wavelength of λ = 4.5 A and a wavelength resolution of Δλ/λ = 10%. In the non-polarized mode a flux of 1.2 × 108 n (s cm2)−1 is achieved in this configuration. MARIA is also capable of grazing-incidence small-angle neutron scattering measurements, using a pinhole collimation with two four-segment slits and an absorber that prevents the focusing of the elliptical guide in the vertical direction.

Laser projection device and safety control method thereof

Abstract: The invention provides a laser projection device which comprises a light source used for emitting light beams; a collimating lens used for converging the light beams emitted by the light source and projecting parallel light beams; a diffractive optical element (DOE ) used for receiving and splitting the parallel light beams, and projecting the patterned light beams; a transparent conducting thin film which is attached to the surface(s) of the collimating lens and/or the diffractive optical element and has a resistance attribute; a monitoring and controlling unit which is electrically connectedwith the transparent conducting thin film and is used for monitoring voltage/current/resistance signals between the transparent conducting thin films in real time, indirectly judging the integrity ofthe collimating lens and/or the DOE and carrying out the corresponding safety control. The invention further provides a safety control method of the laser projection device. According to the laser projection device and the safety control method thereof, the laser safety performance of the laser projection device in the using process can be improved.

Two-dimensional beam-steering device using a doubly periodic Si photonic-crystal waveguide.

Abstract: We demonstrate a nonmechanical, on-chip optical beam-steering device using a photonic-crystal waveguide with a doubly periodic structure that repeats the increase and decrease of the hole diameter. We fabricated the device using a complementary metal–oxide–semiconductor process. We obtained a beam-deflection angle of 24° in the longitudinal direction, while maintaining a divergence angle of 0.3°. Four such waveguides were integrated, and one was selected by a Mach–Zehnder optical switch. We obtained lateral beam steering by placing a cylindrical lens above these waveguides. By combining the lateral and longitudinal beam steering, we were able to scan the collimated beam in two dimensions, with 80 × 4 resolution points.

Laser projection module, depth camera and electronic device

Abstract: A laser projection module, a depth camera and an electronic device are provided. The laser projection module includes a laser emitter, a collimation element, a diffraction element and a detection component. The laser emitter is configured to emit laser. The collimation element is configured to collimate the laser. The diffraction element is configured to diffract the laser collimated by the collimation element to define a laser pattern. The detection component is disposed to at least one of the collimation element and the diffraction element, and configured to output an electrical signal. The processor is coupled to the detection component, and configured to receive the electrical signal and detect whether the at least one of the collimation element and the diffraction element are abnormal according to the electrical signal.

A study of lateral fall-off (penumbra) optimisation for pencil beam scanning (PBS) proton therapy.

Abstract: The lateral fall-off is crucial for sparing organs at risk in proton therapy. It is therefore of high importance to minimize the penumbra for pencil beam scanning (PBS). Three optimisation approaches are investigated: edge-collimated uniformly weighted spots (collimation), pencil beam optimisation of uncollimated pencil beams (edge-enhancement) and the optimisation of edge collimated pencil beams (collimated edge-enhancement). To deliver energies below 70 MeV, these strategies are evaluated in combination with the following pre-absorber methods: field specific fixed thickness pre-absorption (fixed), range specific, fixed thickness pre-absorption (automatic) and range specific, variable thickness pre-absorption (variable). All techniques are evaluated by Monte Carlo simulated square fields in a water tank. For a typical air gap of 10 cm, without pre-absorber collimation reduces the penumbra only for water equivalent ranges between 4-11 cm by up to 2.2 mm. The sharpest lateral fall-off is achieved through collimated edge-enhancement, which lowers the penumbra down to 2.8 mm. When using a pre-absorber, the sharpest fall-offs are obtained when combining collimated edge-enhancement with a variable pre-absorber. For edge-enhancement and large air gaps, it is crucial to minimize the amount of material in the beam. For small air gaps however, the superior phase space of higher energetic beams can be employed when more material is used. In conclusion, collimated edge-enhancement combined with the variable pre-absorber is the recommended setting to minimize the lateral penumbra for PBS. Without collimator, it would be favourable to use a variable pre-absorber for large air gaps and an automatic pre-absorber for small air gaps.

Application of self-collimated beams in realizing all-optical photonic crystal-based half-adder

Abstract: In this paper an all-optical half-adder was proposed by using self-collimation effect in two-dimensional photonic crystals Self-collimation effect was obtained in XM direction for wavelength 1500 nm by using square lattice rod-type photonic crystal structure Plane wave expansion and finite-difference time-domain methods were used to obtain the band structure diagram and simulate the optical behavior of the proposed structure, respectively The maximum delay time and required input intensity are 1 ps and 54 mW/μm2, respectively The normalized power-level margins for logics 0 and 1 were obtained to be about 20 and 70%, respectively The total footprint of the structure is about 75 μm2, which is suitable for all optical integrated circuits

Giant collimated gamma-ray flashes

Abstract: Bright sources of high-energy electromagnetic radiation are widely employed in fundamental research, industry and medicine1,2. This motivated the construction of Compton-based facilities planned to yield bright gamma-ray pulses with energies up to 3 20 MeV. Here, we demonstrate a novel mechanism based on the strongly amplified synchrotron emission that occurs when a sufficiently dense ultra-relativistic electron beam interacts with a millimetre-thickness conductor. For electron beam densities exceeding approximately 3 × 1019 cm−3, electromagnetic instabilities occur, and the ultra-relativistic electrons travel through self-generated electromagnetic fields as large as 107–108 gauss. This results in the production of a collimated gamma-ray pulse with peak brilliance above 1025 photons s−1 mrad−2 mm−2 per 0.1% bandwidth, photon energies ranging from 200 keV to gigaelectronvolts and up to 60% electron-to-photon energy conversion efficiency. These findings pave the way to compact, high-repetition-rate (kilohertz) sources of short (≲30 fs), collimated (milliradian) and high-flux (>1012 photons s−1) gamma-ray pulses. The generation of gamma-ray flashes by dense ultra-relativistic electron beams travelling across a millimetre-thickness solid conductor is theoretically investigated. Peak brilliance above 1025 photons s−1 mrad−2 mm−2 per 0.1% bandwidth is expected.

Designing double freeform surfaces for collimated beam shaping with optimal mass transportation and linear assignment problems.

Abstract: We propose a method for designing refractive optical elements for collimated beam shaping in the geometrical optics approximation. In this method, the problem of finding a ray mapping is formulated as a linear assignment problem, which is a discrete version of the corresponding mass transportation problem. A method for reconstructing optical surfaces from a computed discrete ray mapping is proposed. The method is suitable for designing continuous piecewise-smooth optical surfaces. The design of refractive optical elements transforming beams with circular cross-section to variously shaped (rectangular, triangular, and cross-shaped) beams with plane wavefront is discussed. The presented numerical simulation results confirm high efficiency of the designed optical elements.

Low cost, compact 4-DOF measurement system with active compensation of beam angular drift error.

Abstract: In this paper, a compact four-degree-of-freedom (4-DOF) measurement system is presented. With a special optical configuration, the pitch error, yaw error, and two straightness errors of the moving target are able to be detected by only a single laser beam from a collimated laser diode. A 2D hybrid mirror angle steering mount is designed to perform the large angle turning for the axis alignment and very fine angle tuning by PZT actuators for real-time beam drift compensation. A series of calibration and comparison experiments have been carried out to verify the performance of the proposed system. The developed active compensation system could effectively suppress the beam’s angular drift to within ± 0.01 arc-sec in both of yaw and pitch directions. The developed 4-DOF measuring system is compact, low cost, and suitable for long distance geometric error measurement of linear stages.

Metal-Dielectric Parabolic Antenna for Directing Single Photons.

Abstract: Quantum emitters radiate light omni-directionally, making it hard to collect and use the generated photons. Here, we propose a three-dimensional metal–dielectric parabolic antenna surrounding an individual quantum dot as a source of collimated single photons, which can then be easily extracted and manipulated. Our fabrication method relies on a single optically induced polymerization step once the selected emitter has been localized by confocal microscopy. Compared to conventional nanoantennas, our geometry does not require near-field coupling, and it is, therefore, very robust against misalignment issues and minimally affected by absorption in the metal. The parabolic antenna provides one of the largest reported experimental directivities (D = 106) and the lowest beam divergences (Θ1/2 = 13.5°) and a broadband operation over all of the visible and near-infrared range together with extraction efficiency of more than 96%, offering a practical advantage for quantum technological applications.

Low Etendue Yellow-Green Solid-State Light Generation by Laser-Pumped LuAG:Ce Ceramic

Abstract: A low Etendue (6.1 mm2) yellow-green solid-state light source with optical conversion efficiency up to 101.3 lumen/Watt is demonstrated by through high-power laser diode pumping of a static LuAG:Ce transparent ceramic plate. A 443-nm blue laser diode array with a full-width-half-maximum (FWHM) of <1.5 nm and a maximum output power of 15.2 W is used to attain a high spectral absorption efficiency. The output from the high-power laser diode array is collimated, shaped, despeckled, and focused to display a Gaussian-like profile with a 1.5-mm beam waist (1/e2 radius) to stimulate a 1.2-mm thick LuAG:Ce transparent ceramic plate with an emission FWHM spectra at 505–585 nm. No thermal quenching, pump absorption saturation, and obvious luminous flux decrease is found during test.

Beam shaping with a plano-freeform lens pair.

Abstract: It has been shown in [ J. A. Hoffnagle C. M. Jefferson , Opt. Eng.42, 3090, (2003)] that a pair of plano-aspheric lenses can be used to transform a radially symmetric, Gaussian beam to a radially symmetric flat-top beam. In this paper it is shown that a pair of plano-freeform lenses can be used to transform a collimated light beam of arbitrary (including, non-radially symmetric) intensity profile to a collimated output beam of constant phase and a priori specified intensity pattern over a given flat region. The curved surfaces of both lenses can be chosen strictly convex which should facilitate fabrication. The required pair of plano-freeform lenses is designed using the supporting quadric method (SQM) [ V. I. Oliker in Trends in Nonlinear Analysis, (Springer-Verlag, 2003)] combined with ideas from optimal mass transport [ V. I. Oliker , Arch. Rational Mechanics and Analysis201, 1013 (2011)]. Such approach provides a rigorous methodology for designing freeform optics for irradiance redistribution. In this paper, this approach is applied to design of a laser beam shaping system with two lenses.

Ultrahigh-charge electron beams from laser-irradiated solid surface.

Abstract: Compact acceleration of a tightly collimated relativistic electron beam with high charge from a laser–plasma interaction has many unique applications. However, currently the well-known schemes, including laser wakefield acceleration from gases and vacuum laser acceleration from solids, often produce electron beams either with low charge or with large divergence angles. In this work, we report the generation of highly collimated electron beams with a divergence angle of a few degrees, nonthermal spectra peaked at the megaelectronvolt level, and extremely high charge (∼100 nC) via a powerful subpicosecond laser pulse interacting with a solid target in grazing incidence. Particle-in-cell simulations illustrate a direct laser acceleration scenario, in which the self-filamentation is triggered in a large-scale near–critical-density plasma and electron bunches are accelerated periodically and collimated by the ultraintense electromagnetic field. The energy density of such electron beams in high-Z materials reaches to ∼ 1 0 12 J / m 3 , making it a promising tool to drive warm or even hot dense matter states.

Simulations of bremsstrahlung emission in ultra-intense laser interactions with foil targets

Abstract: Bremsstrahlung emission from interactions of short ultra-intense laser pulses with solid foils is studied using particle-in-cell (PIC) simulations. A module for simulating bremsstrahlung has been implemented in the PIC loop to self-consistently account for the dynamics of the laser–plasma interaction, plasma expansion, and the emission of gamma ray photons. This module made it possible to study emission from thin targets, where refluxing of hot electrons plays an important role. It is shown that the angular distribution of the emitted photons exhibits a four-directional structure with the angle of emission decreasing with the increase of the width of the target. Additionally, a collimated forward flash consisting of high energy photons has been identified in thin targets. The conversion efficiency of the energy of the laser pulse to the energy of the gamma rays rises with both the driving pulse intensity, and the thickness of the target. The amount of gamma rays also increases with the atomic number of the target material, despite a lower absorption of the driving laser pulse. The angular spectrum of the emitted gamma rays is directly related to the increase of hot electron divergence during their refluxing and its measurement can be used in experiments to study this process.

Digitally designed holographic optical element for light field displays.

Abstract: Concave micro-mirror arrays fabricated as holographic optical elements are used in projector-based light field displays due to their see-through characteristics. The optical axes of each micro-mirror in the array are usually made parallel to each other, which simplifies the fabrication, integral image rendering, and calibration process. However, this demands that the beam from the projector be collimated and made parallel to the optical axis of each elemental micro-mirror. This requires additional collimation optics, which puts serious limitations on the size of the display. In this Letter, we propose a solution to the above issue by introducing a new method to fabricate holographic concave micro-mirror array sheets and explain how they work in detail. 3D light field reconstructions of the size 20 cm×10 cm and 6 cm in depth are achieved using a conventional projector without any collimation optics.

A Miniature Fiber Collimator for Highly Sensitive Bend Measurements

Abstract: A Fabry–Perot interferometer (FPI) composed of a miniature fiber collimator is proposed and demonstrated for high-sensitivity bend measurements. The device consists of a quarter-pitch graded index fiber (GIF) spliced with a section of silica tube, which is interposed between single-mode fibers. The divergence angle of the included miniature fiber collimator was 0.058 rad, which was found to enhance the sensitivity of the proposed FPI to –3.353 dB/degree over the applied angle range. In comparison, the divergence angle without the collimator was 0.130 rad and FPI sensitivity was –0.618 dB/degree over the applied angle range. The fiber bend sensors demonstrated in this paper are compact, robust, and highly sensitive, and hence, are promising in various biomedical applications.

An edge-readout, multilayer detector for positron emission tomography.

Abstract: Purpose We present a novel gamma-ray-detector design based on total internal reflection (TIR) of scintillation photons within a crystal that addresses many limitations of traditional PET detectors. Our approach has appealing features, including submillimeter lateral resolution, DOI positioning from layer thickness, and excellent energy resolution. The design places light sensors on the edges of a stack of scintillator slabs separated by small air gaps and exploits the phenomenon that more than 80% of scintillation light emitted during a gamma-ray event reaches the edges of a thin crystal with polished faces due to TIR. Gamma-ray stopping power is achieved by stacking multiple layers, and DOI is determined by which layer the gamma ray interacts in. Method The concept of edge readouts of a thin slab was verified by Monte Carlo simulation of scintillation light transport. An LYSO crystal of dimensions 50.8 mm × 50.8 mm × 3.0 mm was modeled with five rectangular SiPMs placed along each edge face. The mean-detector-response functions (MDRFs) were calculated by simulating signals from 511 keV gamma-ray interactions in a grid of locations. Simulations were carried out to study the influence of choice of scintillator material and dimensions, gamma-ray photon energies, introduction of laser or mechanically induced optical barriers (LIOBs, MIOBs), and refractive indices of optical-coupling media and SiPM windows. We also analyzed timing performance including influence of gamma-ray interaction position and presence of optical barriers. We also modeled and built a prototype detector, a 27.4 mm × 27.4 mm × 3.0 mm CsI(Tl) crystal with 4 SiPMs per edge to experimentally validate the results predicted by the simulations. The prototype detector used CsI(Tl) crystals from Proteus outfitted with 16 Hamamatsu model S13360-6050PE MPPCs read out by an AiT-16-channel readout. The MDRFs were measured by scanning the detector with a collimated beam of 662-keV photons from a 137 Cs source. The spatial resolution was experimentally determined by imaging a tungsten slit that created a beam of 0.44 mm (FWHM) width normal to the detector surface. The energy resolution was evaluated by analyzing list-mode data from flood illumination by the 137 Cs source. Result We find that in a block-detector-sized LYSO layer read out by five SiPMs per edge, illuminated by 511-keV photons, the average resolution is 1.49 mm (FWHM). With the introduction of optical barriers, average spatial resolution improves to 0.56 mm (FWHM). The DOI resolution is the layer thickness of 3.0 mm. We also find that optical-coupling media and SiPM-window materials have an impact on spatial resolution. The timing simulation with LYSO crystal yields a coincidence resolving time (CRT) of 200-400 ps, which is slightly position dependent. And the introduction of optical barriers has minimum influence. The prototype CsI(Tl) detector, with a smaller area and fewer SiPMs, was measured to have central-area spatial resolutions of 0.70 and 0.39 mm without and with optical barriers, respectively. These results match well with our simulations. An energy resolution of 6.4% was achieved at 662 keV. Conclusion A detector design based on a stack of monolithic scintillator layers that uses edge readouts offers several advantages over current block detectors for PET. For example, there is no tradeoff between spatial resolution and detection sensitivity since no reflector material displaces scintillator crystal, and submillimeter resolution can be achieved. DOI information is readily available, and excellent timing and energy resolutions are possible.

The generation of collimated γ-ray pulse from the interaction between 10 PW laser and a narrow tube target

Abstract: A scheme to radiate a highly collimated γ-ray pulse is proposed through the interaction between an ultra-intense laser pulse and a narrow tube target. The γ-ray pulse, with high conversion efficiency, can be generated as a result of electron acceleration in a longitudinal electric field. In a Particle-in-Cell simulation with a 10-PW laser, 18% of the laser energy is transferred into the forward γ-rays in a divergence angle less than 3 ° . It is also found that such a highly collimated γ-ray pulse can be produced with a large range of tube diameters and laser intensities. This scheme could be realized in experiment with the coming 10-PW class lasers in the near future.

Calibration of a neutron time-of-flight detector with a rapid instrument response function for measurements of bulk fluid motion on OMEGA

Abstract: A newly developed neutron time-of-flight (nTOF) diagnostic with a fast instrument response function has been fielded on the OMEGA laser in a highly collimated line of sight. By using a small plastic scintillator volume, the detector provides a narrow instrument response of 1.7 ns full width at half maximum while maintaining a large signal-to-noise ratio for neutron yields between 1010 and 1014. The OMEGA hardware timing system is used along with an optical fiducial to provide an absolute nTOF measurement to an accuracy of ∼56 ps. The fast instrument response enables the accurate measurement of the primary deuterium-tritium neutron peak shape, while the optical fiducial allows for an absolute neutron energy measurement. The new detector measures the neutron mean energy with an uncertainty of ∼7 keV, corresponding to a hot-spot velocity projection uncertainty of ∼12 km/s. Evidence of bulk fluid motion in cryogenic targets is presented with measurements of the neutron energy spectrum.A newly developed neutron time-of-flight (nTOF) diagnostic with a fast instrument response function has been fielded on the OMEGA laser in a highly collimated line of sight. By using a small plastic scintillator volume, the detector provides a narrow instrument response of 1.7 ns full width at half maximum while maintaining a large signal-to-noise ratio for neutron yields between 1010 and 1014. The OMEGA hardware timing system is used along with an optical fiducial to provide an absolute nTOF measurement to an accuracy of ∼56 ps. The fast instrument response enables the accurate measurement of the primary deuterium-tritium neutron peak shape, while the optical fiducial allows for an absolute neutron energy measurement. The new detector measures the neutron mean energy with an uncertainty of ∼7 keV, corresponding to a hot-spot velocity projection uncertainty of ∼12 km/s. Evidence of bulk fluid motion in ...

Design of a Smartphone Platform Compact Optical System Operational Both in Visible and Near Infrared Spectral Regime

Abstract: We report here the design of a low-cost and field portable smartphone-based compact optical system, which is suitable for applications in the visible (VIS)-near infrared (NIR) spectroscopic region. Using the universal serial bus-on the go protocol, the battery of the smartphone is used to power an external light-emitting diode, and its ambient light sensor (ALS) is used as a photo-detector. Using simple optical arrangements, a collimated light beam of a specific wavelength is allowed to pass through the sample solution, and the transmitted modulated light signal from the sample is received by the ALS of the smartphone. A custom built application “PhotoSense” has been developed, which configures the smartphone to measure intensity variation of the modulated signal into a readable form from the ALS sensor. Further using the same application, the field sensing data can be saved as a text file in the phone memory, and by using the communication facility, it can be shared anywhere in the world. The performance of the designed optical device has been evaluated for the VIS-NIR wavelength region of the incident light by measuring iron(II) and phosphate concentrations in water medium. The sensitivity of the device in measuring iron(II) and phosphate concentrations is found to be in terms of absorbance unit (AU) as 0.189 and 0.274 AU/(mg.L−1), respectively. The limit of detection of the proposed device is found to be 0.053 and 0.069 mg.L−1 for both the analytes.

Response function and linearity for high energy γ-rays in large volume LaBr3:Ce detectors

Abstract: The response function to high energy γ γ -rays of two large volume LaBr 3 :Ce crystals (3.5”x8”) and the linearity of the coupled PMT’s were investigated at the NewSUBARU facility, where γ γ -rays in the energy range 6 –38 MeV were produced and sent into the detectors. Monte Carlo simulations were performed to reproduce the experimental spectra. The photopeak and interaction efficiencies were also evaluated both in case of a collimated beam or an isotropic source.

Characterization of Compton-scatter imaging with an analytical simulation method

Abstract: By collimating the photons scattered when a megavoltage therapy beam interacts with the patient, a Compton-scatter image may be formed without the delivery of an extra dose. To characterize and assess the potential of the technique, an analytical model for simulating scatter images was developed and validated against Monte Carlo (MC). For three phantoms, the scatter images collected during irradiation with a 6 MV flattening-filter-free therapy beam were simulated. Images, profiles, and spectra were compared for different phantoms and different irradiation angles. The proposed analytical method simulates accurate scatter images up to 1000 times faster than MC. Minor differences between MC and analytical simulated images are attributed to limitations in the isotropic superposition/convolution algorithm used to analytically model multiple-order scattering. For a detector placed at 90° relative to the treatment beam, the simulated scattered photon energy spectrum peaks at 140–220 keV, and 40–50% of the photons are the result of multiple scattering. The high energy photons originate at the beam entrance. Increasing the angle between source and detector increases the average energy of the collected photons and decreases the relative contribution of multiple scattered photons. Multiple scattered photons cause blurring in the image. For an ideal 5 mm diameter pinhole collimator placed 18.5 cm from the isocenter, 10 cGy of deposited dose (2 Hz imaging rate for 1200 MU min−1 treatment delivery) is expected to generate an average 1000 photons per mm2 at the detector. For the considered lung tumor CT phantom, the contrast is high enough to clearly identify the lung tumor in the scatter image. Increasing the treatment beam size perpendicular to the detector plane decreases the contrast, although the scatter subject contrast is expected to be greater than the megavoltage transmission image contrast. With the analytical method, real-time tumor tracking may be possible through comparison of simulated and acquired patient images.

Light beam shaping for collimated emission from white organic light-emitting diodes using customized lenticular microlens arrays structure

Abstract: We present a design approach to realizing a desired collimated planar incoherent light source (CPILS) by incorporating lenticular microlens arrays (LMLAs) onto the substrates of discrete white organic light-emitting diode (WOLED) light sources and demonstrate the effectiveness of this method in collimated light beam shaping and luminance enhancement simultaneously. The obtained collimated WOLED light source shows enhanced luminance by a factor of 2.7 compared with that of the flat conventional device at the normal polar angle and, more importantly, exhibits a narrowed angular emission with a full-width at half-maximum (FWHM) of ∼33.6°. We anticipate that the presented strategy could provide an alternative way for achieving the desired large scale CPILS, thereby opening the door to many potential applications, including LCD backlights, three-dimensional displays, car headlights, and so forth.

An Orthogonal Type Two-Axis Lloyd’s Mirror for Holographic Fabrication of Two-Dimensional Planar Scale Gratings with Large Area

Abstract: In this paper, an orthogonal type two-axis Lloyd’s mirror interference lithography technique was employed to fabricate two-dimensional planar scale gratings for surface encoder application. The two-axis Lloyd’s mirror interferometer is composed of a substrate and two reflective mirrors (X- and Y-mirrors), which are placed edge by edge perpendicularly. An expanded and collimated beam was divided into three beams by this interferometer, a direct beam and two reflected beams, projected onto the substrate, X- and Y-mirrors, respectively. The unexpected beam sections having twice reflected off the mirrors were blocked by a filter. The remaining two reflected beams interfered with the direct beam on the substrate, generating perpendicularly cross patterns thus forming two-dimensional scale gratings. However, the two reflected beams undesirably interfere with each other and generate a grating pattern along 45-degree direction against the two orthogonal direction, which influence the pattern uniformity. Though an undesired grating pattern can be eliminated by polarization modulation with introduction of waveplates, spatial configuration of waveplates inevitably downsized the eventual grating, which is a key parameter for grating interferometry application. For solving this problem, theoretical and experimental study was carefully carried out to evaluate the fabrication quality with and without polarization modulation. Two-dimensional scale gratings with a 1 μm period in X- and Y-directions were achieved by using the constructed experiment system with a 442 nm He-Cd laser source. Atomic force microscopy (AFM) images and the result of diffraction performances demonstrated that the orthogonal type two-axis Lloyd’s mirror interferometer can stand a small order undesired interference, that is, a degree of orthogonality between two reflected beams, denoted by γ, no larger than a nominal value of 0.1.

Dynamic collimator trajectory algorithm for multiple metastases dynamic conformal arc treatment planning.

Abstract: Purpose To develop an algorithm for dynamic collimator positioning to optimize beam's-eye-view (BEV) fitting of targets in dynamic conformal arc (DCA) based radiotherapy procedures, of particular use in multiple metastases stereotactic radiosurgery procedures. Methods A trajectory algorithm was developed to dynamically modify the angle of the collimator as a function of arc-based control point to provide optimized collimation of target volume(s). Central to this algorithm is a concept denoted herein as “whitespace” defined as any non-target area in the BEV that is not covered by any collimation system and is open to exposure from the radiation beam. Calculating whitespace at all collimator angles and every control point, a two-dimensional topographical map depicting the tightness-of-fit of the MLC was generated. A bi-directional gradient trajectory algorithm identified a number of candidate trajectories of continuous collimator motion. Minimization of integrated whitespace was used to identify an optimal solution for the navigation of the parameter space. Plans with dynamic collimator trajectories were designed for multiple metastases targets and were compared with fixed collimator angle dynamic conformal arc (DCA) plans and standard VMAT plans. Results Algorithm validation was performed on simple test cases with known solutions. The whitespace metric showed a strong correlation (R2 = 0.90) with mean dose to proximal normal tissue. Seventeen cases were studied by using our algorithm to generate dynamic conformal arc (DCA) plans with optimized collimator trajectories for three and four target SRS patients and comparing them to DCA plans generated with optimized fixed collimator angles per arc and standard VMAT plans generated via template. Optimized collimator trajectories were found to produce a reduction in monitor units of up to 49.7 ± 5.1% when compared to VMAT across seventeen patients, and all organ-at-risk and normal brain metrics were found to be superior or comparable. Conclusion Dynamic collimator trajectories have the potential to improve DCA deliveries through increased efficiency, especially in treatment of multiple cranial metastases. Implementation of this technology should not be hindered by mechanical safety considerations as collimator motions do not modify or introduce any new risks of collisions with patients. This article is protected by copyright. All rights reserved.

Characterization of a Novel Revolving Radiation Collimator.

Abstract: Introduction The ZAP-X is a novel self-contained and first-of-its-kind self-shielded therapeutic radiation device dedicated to brain and head and neck radiosurgery By utilizing a 27-MV linear accelerator and incorporating a design in which a beam stop and major mechanical elements serve a radiation shielding function, the Zap-X does not typically require a radiation bunker The unique collimator design of the Zap-X is especially critical to the performance of the overall system The collimator consists of a shielded tungsten wheel oriented with its rotational axis perpendicular to the beam's central axis; the goal of this design is to minimize radiation leakage Beam selection is accomplished by rotating the wheel within its tungsten-shielded housing We investigated radiation leakage from the Zap-X collimator to determine its compliance with internationally accepted standards using direct radiation measurements Materials and methods To measure collimator leakage in the plane of the patient, equidistant measurement stations were defined in a plane perpendicular to the central beam axis (cax) 1 m from this axis (1 m from the radiation focal spot) To measure leakage alongside and adjacent to the accelerator, equidistant measurement stations were located 1 m from the cax along a line parallel to the cax in the plane of the collimator wheel and along a line parallel to the cax 90 degrees offset from the first line of stations Results Radiation leakage emanating from the collimating head of the linear accelerator in the patient plane ranged between 40 and 104 mR Radiation along the linear accelerator (1000 R delivered in the primary beam) varied between 17 and 68 mR and constituted between 000017% to 000068% of the primary beam The former radiation originated from X-ray target leakage, while the latter is produced directly by the linear accelerator and both contributed to the overall leakage radiation that would reach a patient Discussion Due to the large diameter of the Zap-X tungsten collimator wheel and the massive Zap-X tungsten cylindrical collimator shield, the overall patient leakage is 000104% of the primary beam at a 1-m distance from the beam central axis in the patient plane Leakage radiation in the patient plane is limited by the International Electrotechnical Commission (IEC) to 01% of the total primary radiation Radiation leakage along the linear accelerator and the collimator housing was determined to be 000068% of primary radiation intensity This leakage value is lower than the 01% leakage limit stipulated by IEC by more than a factor of 100 Conclusions Typically, an MV radiation therapy system minimizes exposure by utilizing a combination of device and structural shielding However, the Zap-X has been uniquely designed to minimize the need for structural shielding Our results indicate radiation leakage from the collimator meets internationally accepted standards as defined by the IEC