Showing papers on "Collimated light published in 2022"

Performance of the time-resolved ultra-small-angle X-ray scattering beamline with the Extremely Brilliant Source

Abstract: The new technical features and enhanced performance of the ID02 beamline with the Extremely Brilliant Source (EBS) at the ESRF are described. The beamline enables static and kinetic investigations of a broad range of systems from ångström to micrometre size scales and down to the sub-millisecond time range by combining different small-angle X-ray scattering techniques in a single instrument. In addition, a nearly coherent beam obtained in the high-resolution mode allows multispeckle X-ray photon correlation spectroscopy measurements down to the microsecond range over the ultra-small- and small-angle regions. While the scattering vector (of magnitude q) range covered is the same as before, 0.001 ≤ q ≤ 50 nm-1 for an X-ray wavelength of 1 Å, the EBS permits relaxation of the collimation conditions, thereby obtaining a higher flux throughput and lower background. In particular, a coherent photon flux in excess of 1012 photons s-1 can be routinely obtained, allowing dynamic studies of relatively dilute samples. The enhanced beam properties are complemented by advanced pixel-array detectors and high-throughput data reduction pipelines. All these developments together open new opportunities for structural, dynamic and kinetic investigations of out-of-equilibrium soft matter and biophysical systems.

The very small angle neutron scattering instrument at the National Institute of Standards and Technology

Abstract: A description and the performance of the very small angle neutron scattering diffractometer at the National Institute of Standards and Technology are presented. The measurement range of the instrument extends over three decades of momentum transfer q from 2 × 10-4 to 0.7 Å-1. The entire scattering angle range from 8 × 10-5 to π/6 rad (30°) can be measured simultaneously using three separate detector carriages on rails holding nine 2D detector arrays. Versatile choices of collimation options and neutron wavelength selection allow the q resolution and beam intensity to be optimized for the needs of the experiment. High q resolution is achieved using multiple converging-beam collimation with circular pinholes combined with refractive lenses and prisms. Relaxed vertical resolution with much higher beam intensity can be achieved with narrow slit collimation and a broad wavelength range chosen by truncating the moderator source distribution below 4 Å with a Be crystalline filter and above 8 Å with a supermirror deflector. Polarized beam measurements with full polarization analysis are also provided by a high-performance supermirror polarizer and spin flipper, capable of producing flipping ratios of over 100, along with a high-efficiency 3He polarization analyzer.

Comparison of radiation shielding ability of Bi2O3 micro and nanoparticles for radiation shields

Abstract: We reported the radiation attenuation ability of Bi2O3 powder in different sizes. We measured the linear attenuation coefficient for the two investigated Bi2O3 samples using a narrow collimated beam method. A HPGe detector was used to report the number of photons that can penetrate the samples and the energies of the photons was selected in the energy range of 0.0595 up to 1.408 MeV. The LAC for the Bi2O3 in micro size is relatively higher than that for the sample with nano- Bi2O3 if the two samples have the same volume, and the difference between the LAC for the two samples is 33.4% at 0.059 MeV, while it is 29.8% at 0.081 MeV. The mass and thickness ((M1/2 and H1/2) needed to shield the intensity of the initial photon to its half value were also reported. The results demonstrated that if we have two different sizes of Bi2O3 with the same masses, we need lighter sample of Bi2O3 nanoparticles to reduce 50% of the incoming photons in comparison with the micro Bi2O3

Expanding Nuclear Physics Horizons with the Gamma Factory

Abstract: The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to ≈400 MeV and photon fluxes (up to ≈1017 photons s−1) exceeding those of the currently available gamma sources by orders of magnitude. The high-energy (secondary) photons are produced via resonant scattering of the primary laser photons by highly relativistic partially-stripped ions circulating in the accelerator. The secondary photons are emitted in a narrow cone and the energy of the beam can be monochromatized, down to 10−3–10−6 level, via collimation, at the expense of the photon flux. This paper surveys the new opportunities that may be afforded by the GF in nuclear physics and related fields.

Holographic Plasma Lenses.

Abstract: A hologram fully encodes a three-dimensional light field by imprinting the interference between the field and a reference beam in a recording medium. Here we show that two collinear pump lasers with different foci overlapped in a gas jet produce a holographic plasma lens capable of focusing or collimating a probe laser at intensities several orders-of-magnitude higher than the limits of a nonionized optic. We outline the theory of these diffractive plasma lenses and present simulations for two plasma mechanisms that allow their construction: spatially varying ionization and ponderomotively driven ion-density fluctuations. Damage-resistant plasma optics are necessary for manipulating high-intensity light, and divergence control of high-intensity pulses-provided by holographic plasma lenses-will be a critical component of high-power plasma-based lasers.

Micrometer-Resolution X-ray Imaging Enabled by a Flexible Perovskite Screen.

Abstract: Spatial resolution improvement has been keenly sought recently in the perovskite-based scintillation community. Here, micrometer resolution (∼2.0 μm) was achieved by using an X-ray imaging screen of self-assembled perovskite nanosheets. The assembly behavior of nanosheets was applicable to many substrates, including glass, metal, and polymer surfaces. The use of a polymer substrate not only eliminated the parasite absorption of X-ray but also enabled a flexible screen with robust bending stability. The assembly behavior, on the other hand, provided vicinity for an efficient energy transfer between nanosheets of varied thicknesses, as evidenced by both transient absorption and photoluminescence lifetime measurements. Importantly, the ensuing large Stokes shift (∼316 meV) significantly mitigated the reabsorption issue, leading to a comparable light yield to LYSO/Ce crystals. With the aid of the synchrotron-based collimated X-ray beam, the fine structure of two-dimensional objects, such as microchips, was clearly visualized with the flexible scintillation screen. Furthermore, those challenging biological samples were also scanned by phase-contrast imaging, whereby a three-dimensional reconstruction was obtained successfully. Despite the labile nature of the perovskite screen, this work represents the state-of-the-art spatial resolution for perovskite scintillation.

Beam commissioning of the first clinical biology‐guided radiotherapy system

Abstract: Abstract This study reports the beam commissioning results for the first clinical RefleXion Linac. Methods: The X1 produces a 6 MV photon beam and the maximum clinical field size is 40 × 2 cm2 at source‐to‐axis distance of 85 cm. Treatment fields are collimated by a binary multileaf collimator (MLC) system with 64 leaves with width of 0.625 cm and y‐jaw pairs to provide either a 1 or 2 cm opening. The mechanical alignment of the radiation source, the y‐jaw, and MLC were checked with film and ion chambers. The beam parameters were characterized using a diode detector in a compact water tank. In‐air lateral profiles and in‐water percentage depth dose (PDD) were measured for beam modeling of the treatment planning system (TPS). The lateral profiles, PDDs, and output factors were acquired for field sizes from 1.25 × 1 to 40 × 2 cm2 field to verify the beam modeling. The rotational output variation and synchronicity were tested to check the gantry angle, couch motion, and gantry rotation. Results: The source misalignments were 0.049 mm in y‐direction, 0.66% out‐of‐focus in x‐direction. The divergence of the beam axis was 0.36 mm with a y‐jaw twist of 0.03°. Clinical off‐axis treatment fields shared a common center in y‐direction were within 0.03 mm. The MLC misalignment and twist were 0.57 mm and 0.15°. For all measured fields ranging from the size from 1.25 × 1 to 40 × 2 cm2, the mean difference between measured and TPS modeled PDD at 10 cm depth was −0.3%. The mean transverse profile difference in the field core was −0.3% ± 1.1%. The full‐width half maximum (FWHM) modeling was within 0.5 mm. The measured output factors agreed with TPS within 0.8%. Conclusions: This study summarizes our specific experience commissioning the first novel RefleXion linac, which may assist future users of this technology when implementing it into their own clinics.

Micrometer-sized droplets from liquid helium jets at low stagnation pressures

Abstract: Droplets and droplet beams produced from the breakup of micrometer-sized liquid helium jets in vacuum were studied in this work, advancing into previously unexplored regimes of low stagnation pressures. Using a 5 μm orifice, the droplet beam shows surprisingly diverse characteristics at increasing nozzle pressures from 0.6 to 100 bar: a well-collimated beam at low stagnation pressures, a spray at some intermediate values, and a less-collimated beam at high pressures. Focusing on a nozzle stagnation of 0.6 bar and 2.7 K, we highlight the spectrum of jet disturbances, resulting in different droplet beam behaviors. On some occasions, we observed uniformly sized and equidistant droplets with diameters ranging from 11 up to more than 25 μm and separations from 15 to 100 μm. From simple estimates using the ratio between the droplet separations and diameters, we determined the disturbance frequencies benchmarking the production of repeatable targets for future experiments with superfluid helium droplets. Further analysis of the droplet beam behavior at farther distances from the nozzle revealed that the droplet diameter grew downstream up to 22 μm from an initial value of 13 μm, while their aspect ratio decreased from 1.33 to 1.16. These results indicate that droplet coagulation and superfluidity both influence the droplet beam up to several hundreds of millimeters after the nozzle exit.

Design of a high-sensitivity differential Helmholtz photoacoustic cell and its application in methane detection.

Abstract: A high-sensitivity differential Helmholtz photoacoustic cell based on multiple reflection was reported, and its performance parameters and gas replacement time were optimized by finite element simulation. To realize the long absorption path of the measured gas, the collimated excitation light was reflected multiple times on the gold-plated wall of the absorption cavity, and the wavelength modulation technology was used to reduce the multiple reflection noise. Additionally, the differential could suppress external co-phase noise and double the photoacoustic signal. When a laser with a central wavelength of 1653 nm was employed as the excitation light source, the minimum detection limit of 177 ppb (signal-to-noise ratio, SNR = 1) for methane was achieved within a detection time of 1 s, and the corresponding normalized noise equivalent absorption coefficient was 4.1×10-10 cm-1WHZ-1/2.

Towards bright gamma-ray flash generation from tailored target irradiated by multi-petawatt laser

Abstract: One of the remarkable phenomena in the laser-matter interaction is the extremely efficient energy transfer to [Formula: see text]-photons, that appears as a collimated [Formula: see text]-ray beam. For interactions of realistic laser pulses with matter, existence of an amplified spontaneous emission pedestal plays a crucial role, since it hits the target prior to the main pulse arrival, leading to a cloud of preplasma and drilling a narrow channel inside the target. These effects significantly alter the process of [Formula: see text]-photon generation. Here, we study this process by importing the outcome of magnetohydrodynamic simulations of the pedestal-target interaction into particle-in-cell simulations for describing the [Formula: see text]-photon generation. It is seen that target tailoring prior the laser-target interaction plays an important positive role, enhancing the efficiency of laser pulse coupling with the target, and generating high energy electron-positron pairs. It is expected that such a [Formula: see text]-photon source will be actively used in various applications in nuclear photonics, material science and astrophysical processes modelling.

Performance Analysis of a Perovskite-Based Thing-to-Thing Optical Wireless Power Transfer System

Abstract: This paper presents an analysis on the performance of an optical wireless power transfer system in which optical transceivers made from a perovskite are used. Experiments are performed under different settings, whose resulted data reveal interesting findings. First, system performance is only matched with the existing theory when no collimating lens is employed. Hence, a data-driven mathematical model is proposed and verified when a collimating lens is used. Second, a collimating lens helps increase the amount of wirelessly transferred power and the transfer distance if perfect alignment between optical transceivers is guaranteed, but substantially limits the sliding distance between them otherwise.

Cylindrical-lens-embedded photonic crystal based on self-collimation

Abstract: Photonic crystals can be engineered so that the flow of optical power and the phase of the field are independently controlled. The concept is demonstrated by creating a self-collimating lattice with an embedded cylindrical lens. The device is fabricated in a photopolymer by multi-photon lithography with the lattice spacing chosen for operation around the telecom wavelength of 1550 nm. The lattice is based on a low-symmetry rod-in-wall unit cell that strongly self-collimates light. The walls are varied in thickness to modulate the effective refractive index so light acquires a spatially quadratic phase profile as it propagates through the device. Although the phase of the field is altered, the light does not focus within the device because self-collimation forces power to flow parallel to the principal axes of the lattice. Upon exiting the device, ordinary propagation resumes in free space and the curved phase profile causes the light to focus. An analysis of the experimentally observed optical behavior shows that the device behaves like a thin lens, even though the device is considerably thick.

Radially Periodic Metasurface Lenses for Magnetic Field Collimation in Resonant Wireless Power Transfer Applications

Abstract: In this paper, a new procedure and topology of magnetic metasurface lens are proposed for improving the performance of Resonant Wireless Power Transfer systems. Firstly, three subwave-length unit cells are optimized in order to get negative magnetic permeability in the same frequency, each one with a different refractive index, and they are experimentally characterized. Then, the Transformation Optics technique is applied in order to find the unit cell arrangements which lead to the magnetic field focusing in a given direction. For this purpose, two coordinate transformations are proposed, and the effective electric permittivity and permeability that generate these profiles are calculated. It is shown from simulations and measurements that the refractive index gradient produced by the radial disposition of the unit cells can lead to a magnetic field manipulation similar to the optical converging and diverging lenses. Both metamaterials lenses are built, and the calculation of the magnetic flux density as a function of the measured induced voltage in a probe coil verifies their effects on the magnetic field. Finally, their performance in a resonant wireless power transfer system is tested, and improvements in terms of efficiency and range are presented. The proposed design method and the lenses that were developed demonstrate that metasurface lenses can improve efficiency without reducing the range, once these lenses are positioned close to the transmitter coil. Besides that, this method can reduce the losses due to misalignment between coils once the field can be collimated in a specific direction.

Development of a quasi-collimated UV LED backlight for producing uniform and smooth 3D printing objects.

Abstract: 3D printing techniques have great potential in the direct fabrication of microfluidic and many kinds of molds, such as dental and jewelry models. However, the resolution, surface roughness, and critical dimension uniformity of 3D printing objects are still a challenge for improvement. In this article, we proposed a 405nm light emitting diode (LED) backlight module based on stacks of structured films, and the full width half maximum (FWHM) of the angular distribution of this module is reduced to less than ± 15°. Compared with the commercial lens array optical module, the ten points intensity uniformity of an 8.9" build area is improved from 56% to 80%. Moreover, we found that the surface roughness and the sharpness of the edge of the printing objects are also obviously improved by our novel quasi-collimated LED backlight module. These features give us a promising way for the application of microfluidics and micro-optics components in the future.

Absolute multilateration-based coordinate measurement system using retroreflecting glass spheres

Abstract: We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n=2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 µm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 µm.

Characterizing magnetically focused contamination electrons by off‐axis irradiation on an inline MRI‐Linac

Abstract: Abstract Purpose The aim of this study is to investigate off‐axis irradiation on the Australian MRI‐Linac using experiments and Monte Carlo simulations. Simulations are used to verify experimental measurements and to determine the minimum offset distance required to separate electron contamination from the photon field. Methods Dosimetric measurements were performed using a microDiamond detector, Gafchromic® EBT3 film, and MOSkin TM. Three field sizes were investigated including 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm2. Each field was offset a maximum distance, approximately 10 cm, from the central magnetic axis (isocenter). Percentage depth doses (PDDs) were collected at a source‐to‐surface distance (SSD) of 1.8 m for fields collimated centrally and off‐axis. PDD measurements were also acquired at isocenter for each off‐axis field to measure electron contamination. Monte Carlo simulations were used to verify experimental measurements, determine the minimum field offset distance, and demonstrate the use of a spoiler to absorb electron contamination. Results Off‐axis irradiation separates the majority of electron contamination from an x‐ray beam and was found to significantly reduce in‐field surface dose. For the 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm2 field, surface dose was reduced from 120.9% to 24.9%, 229.7% to 39.2%, and 355.3% to 47.3%, respectively. Monte Carlo simulations generally were within experimental error to MOSkin TM and microDiamond, and used to determine the minimum offset distance, 2.1 cm, from the field edge to isocenter. A water spoiler 2 cm thick was shown to reduce electron contamination dose to near zero. Conclusions Experimental and simulation data were acquired for a range of field sizes to investigate off‐axis irradiation on an inline MRI‐Linac. The skin sparing effect was observed with off‐axis irradiation, a feature that cannot be achieved to the same extent with other methods, such as bolusing, for beams at isocenter.

Absolute multilateration-based coordinate measurement system using retroreflecting glass spheres

Abstract: We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n = 2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 μm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 μm.

Image-mode performance characterization of a positron emission tomography subsystem designed for Biology-guided radiotherapy (BgRT).

Abstract: OBJECTIVES In this study, we characterize the imaging-mode performance of the positron emission tomography (PET) subsystem of the RefleXion X1 machine using the NEMA NU-2 2018 standard. METHODS The X1 machine consists of two symmetrically opposing 900 arcs of PET detectors incorporated into the architecture of a ring-gantry linear accelerator rotating up to 60 RPM. PET emissions from a tumor are detected by the PET detectors and used to guide the delivery of radiation beam. Imaging performance of the PET subsystem on X1 machine was evaluated based on1 sensitivity of the PET detectors,2 spatial resolution,3 count-loss performance,4 Image quality, and daily system performance check. RESULTS PET subsystem sensitivity was measured as 0.183 and 0.161 cps/kBq at the center and off-center positions, respectively. Spatial resolution: average FWHM values of 4.3, 5.1, and 6.7 mm for the point sources at 1, 10, and 20 cm off center, respectively were recorded. For count loss, max NECR: 2.63 kcps, max true coincidence rate: 5.56 kcps, and scatter fraction: 39.8%. The 10 mm sphere was not visible. Image-quality contrast values were: 29.6%, 64.9%, 66.5%, 81.8%, 81.2%, and background variability: 14.8%, 12.4%, 10.3%, 8.8%, 8.3%, for the 13, 17, 22, 28, 37 mm sphere sizes, respectively. CONCLUSIONS When operating in an imaging mode, the spatial resolution and image contrast of the X1 PET subsystem were comparable to those of typical diagnostic imaging systems for large spheres, while the sensitivity and count rate were lower due to the significantly smaller PET detector area in the X1 system. Clinical efficacy when used in BgRT remains to be validated. ADVANCES IN KNOWLEDGE This is the first performance evaluation of the PET subsystem on the novel BgRT machine. The dual arcs rotating PET subsystem on RefleXion X1 machine performance is comparable to those of the typical diagnostic PET system based on the spatial resolution and image contrast for larger spheres.

Feasibility of dual-energy cone-beam CT of bone marrow edema using dual-layer flat panel detectors

Abstract: Purpose: We investigated the feasibility of detection and quantification of bone marrow edema (BME) using dual-energy (DE) Cone-Beam CT (CBCT) with a dual-layer flat panel detector (FPD) and three-material decomposition. Methods: A realistic CBCT system simulator was applied to study the impact of detector quantization, scatter, and spectral calibration errors on the accuracy of fat-water-bone decompositions of dual-layer projections. The CBCT system featured 975 mm source-axis distance, 1,362 mm source-detector distance and a 430 × 430 mm2 dual-layer FPD (top layer: 0.20 mm CsI:Tl, bottom layer: 0.55 mm CsI:Tl; a 1 mm Cu filter between the layers to improve spectral separation). Tube settings were 120 kV (+2 mm Al, +0.2 mm Cu) and 10 mAs per exposure. The digital phantom consisted of a 160 mm water cylinder with inserts containing mixtures of water (volume fraction ranging 0.18 to 0.46) - fat (0.5 to 0.7) - Ca (0.04 to 0.12); decreasing fractions of fat indicated increasing degrees of BME. A two-stage three-material DE decomposition was applied to DE CBCT projections: first, projection-domain decomposition (PDD) into fat-aluminum basis, followed by CBCT reconstruction of intermediate base images, followed by image-domain change of basis into fat, water and bone. Sensitivity to scatter was evaluated by i) adjusting source collimation (12 to 400 mm width) and ii) subtracting various fractions of the true scatter from the projections at 400 mm collimation. The impact of spectral calibration was studied by shifting the effective beam energy (± 2 keV) when creating the PDD lookup table. We further simulated a realistic BME imaging framework, where the scatter was estimated using a fast Monte Carlo (MC) simulation from a preliminary decomposition of the object; the object was a realistic wrist phantom with an 0.85 mL BME stimulus in the radius. Results: The decomposition is sensitive to scatter: approx. <20 mm collimation width or <10% error of scatter correction in a full field-of-view setting is needed to resolve BME. A mismatch in PDD decomposition calibration of ± 1 keV results in ~25% error in fat fraction estimates. In the wrist phantom study with MC scatter corrections, we were able to achieve ~0.79 mL true positive and ~0.06 mL false positive BME detection (compared to 0.85 mL true BME volume). Conclusions: Detection of BME using DE CBCT with dual-layer FPD is feasible, but requires scatter mitigation, accurate scatter estimation, and robust spectral calibration.

Design and performance evaluation of a 4<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e519" altimg="si7.svg"><mml:mi>π</mml:mi></mml:math>-view gamma camera with mosaic-patterned 3D position-sensitive scintillators

Abstract: Gamma hotspots imaging is of dramatic demand in nuclear-related industrial and homeland security activities such as nuclear facilities monitoring, nuclear emergency response and border inspection. Gamma cameras with mechanical collimation (i.e., coded-aperture) have reduced sensitivity, limited FOV and are typically heavy-weighted. Compton cameras with electrical collimation can achieve higher sensitivity as well as being capable of performing portable 4π-view imaging. However, imageable isotopes of Compton cameras are limited to middle- or high-energy ones. We have previously proposed the concept to image gamma hotspots with a 3-D position-sensitive scintillation detector. This approach achieves high sensitivity, 4π-view FOV and is effective in a wide energy range. In this work, we present a novel gamma camera design aiming for high-resolution gamma imaging. The proposed detector consists of interspaced GAGG(Ce) scintillators that form a mosaic pattern, which is coupled to SiPM arrays on both ends. 3-D photon interaction position information is measured with a dual-end-readout technique. The measured interaction positions for detected photon events are rebinned into the projection data, and the gamma image is reconstructed using a maximum likelihood expectation maximization (MLEM) algorithm. We perform Monte Carlo simulations and experiments to evaluate the performance of the proposed gamma camera design for imaging 99mTc and 137Cs sources. Results show that the proposed gamma camera achieves a positioning accuracy of less than 1° for a 99mTc source and 3° for a 137Cs source. It can clearly resolve two 99mTc sources with 10° separation and two 137Cs point sources with 23° separation, as well as a 2 × 6 99mTc point-source-array with 20° separation clearly. We conclude that the proposed gamma camera design is profitable in portability, FOV, sensitivity, image resolution and energy range. It has promising application potential in fast and accurate radiation monitoring tasks in nuclear security applications.

Optical Drills by Dynamic High-Order Bessel Beam Mixing

Abstract: One of the key trends in laser material processing is the usage of structured laser beams. Collimated and focused Gaussian beams are the most common tools; however, more exotic beams can be beneficial too. For instance, Bessel beams with elongated focal area and self-healing properties, or vortex beams with helical wave fronts and a dark area along the optical axis are being increasingly used. Here, we propose and experimentally demonstrate dynamical ``optical drill'' beams presenting nonstationary intensity distributions that resemble a spinning mechanical drill. Optical drills appear as the spatiotemporal interference of two Bessel-vortex beams of different topological charges and different carrier frequencies. By mixing a pair of high-order Bessel beams, synthesized using a liquid crystal spatial light modulator, optical drills of tuned helicities are experimentally observed, and the simplest cases of matter processing (fluorescence) with such beams are demonstrated. Optical drill beams are expected to be useful in material processing by light or in cell and particle manipulation in biomedical applications.

Developing an optical module for large-scale UV-LED water disinfection reactors by numerical modeling

Abstract: The emergence of alternative UV radiation sources, such as ultraviolet light emitting diodes (UV-LEDs), has created an opportunity to develop novel water disinfection reactors. Radiation management is a major parameter affecting the performance of these reactors, and it is essential to develop highly efficient optical modules to pave the way toward commercially viable systems. An effective way to improve optical efficiency is by creating collimated beams. Here, an optical module design for the collimation of UV-LED radiation is proposed that employs multi-parabolic aluminum reflectors. To design and optimize the optical module, a ray optics computational model was initially developed to study the radiation profiles of multi-UV-LEDs and optical manipulators with complex geometries. This model was applied to the virtual prototyping and optimization of the reflector’s geometry. Once the optimized design was determined, a physical prototype was fabricated and characterized. The developed module was characterized using several scenarios that confirmed the formation of collimated beams. The simulation results were further evaluated against experimental measurements, quantitatively and qualitatively, indicating good agreement. It was found that the reflectors significantly increased the uniformity of the fluence rate and its magnitude at longer distances from the radiation source (e.g., 30 times higher at 22 cm). The optical module was then installed on a water disinfection reactor, and the radiation profile was measured in the reactor filled with water. The optimally designed reflectors resulted in significantly better distribution and preservation of the irradiance along a water disinfection reactor, ultimately increasing the fluence rate and the delivered UV dose.

Probing highly collimated photon-jets with deep learning

Abstract: Many extensions of the standard model (SM) predict the existence of axion-like particles and/or dark Higgs in the sub-GeV scale. Two new sub-GeV particles, a scalar and a pseudoscalar, produced through the Higgs boson exotic decays, are investigated. The decay signatures of these two new particles with highly collimated photons in the final states are discriminated from the ones of SM backgrounds using the Convolutional Neural Networks and Boosted Decision Trees techniques. The sensitivities of searching for such new physics signatures at the Large Hadron Collider are obtained.

Ultra-Wideband Frequency Modulated Continuous Wave Photonic Radar System for Three-Dimensional Terahertz Synthetic Aperture Radar Imaging

Abstract: Three-dimensional (3D) imaging remains an expensive and challenging task in the THz band. In this study, a frequency-modulated continuous-wave photonic radar system was presented in the 300-GHz band, instead of using electronic-based devices. The proposed system can obtain a 6-dB bandwidth of 120 GHz to achieve a range resolution of ∼1.1 mm. The frequency sweep linearity of a laser source was calibrated with respect to the imaging distance and range resolution, through which a maximum detectable distance of ∼800 mm was achieved with the collimated beam. To obtain the desired 3D information, the synthetic aperture radar (SAR) technique was introduced to the proposed system to achieve 3D imaging, which was not bounded by the fixed focal distance of a focus lens. It can provide a spatial resolution of ∼1.5 mm within a 3D imaging range up to ∼300 mm. The potential and limitations of SAR imaging schemes are discussed based on the theoretical and experimental results.

Feed corrective lenslets for enhanced beamscan in flat lens antenna systems.

Abstract: A method for improving beamscan performance of flat lens antenna systems is proposed, wherein small gradient index (GRIN) lenses are included in the feed apertures to correct spillover losses and improve scan collimation. Given a lens system with a flat feed surface, these feed-corrective-lenslets (FCLs) sit in the apertures of offset feed elements and squint the feed pattern toward the center of the lens, reducing spillover radiation and increasing gain at scan. Furthermore, the FCLs shift the effective phase center of the feed to be closer to the Petzval surface, improving scanned collimation and enhancing beam angle. A GRIN lens and FCLs for three offset positions are designed, fabricated and demonstrated in the Ku-band. The FCLs improve the gain of the scanned beam by up to 2 dB out to 50°, reducing the scan loss exponent from 5.0 to 2.5 at 18 GHz.