Incident Beam Research Articles

Effective working regions of the grating chip for planar-integrated magneto-optics trap

Abstract We experimentally investigate the effective working regions of a planar-integrated magneto-optical trap (MOT). By scanning a blocking point in the incident laser beam, we identify four effective working regions of the laser beam contributing to MOT: a central region corresponding to the downward incident beam and three regions associated with the upward diffracted beams. The latter three regions are the effective regions of the grating chip. It is demonstrated that only three 3.5 mm radius grating regions can produce a MOT that is capable of trapping 105 atoms with a temperature below 150 μK, retaining over 60% of atoms compared to a complete grating chip. This finding suggests that more than 60% of the grating chip area can be saved for other on-chip components, such as metasurfaces and nanophotonic devices, without significantly compromising MOT performance, paving the way for more compact and versatile atom-photon interfaces.

Imaging the Progression of Radiolytic Damage in Molecular Crystals with Scanning Nanobeam Electron Diffraction

Almost every electron microscopy experiment is fundamentally limited by radiation damage. Nevertheless, little is known about the onset and progression of radiolysis in beam-sensitive materials. Here we apply ambient-temperature scanning nanobeam electron diffraction to record simultaneous dual-space movies of organic and organometallic nanocrystals at sequential stages of beam-induced radiolytic decay. We show that the underlying mosaic of coherently diffracting domains undergoes internal rearrangement as a function of accumulating electron fluence, causing the intensities of some associated Bragg reflections to fade nonmonotonically. Furthermore, we demonstrate that repeated irradiation at a single probe position leads to the isotropic propagation of delocalized radiolytic damage well beyond the direct footprint of the incident beam. We refer to these expanding tides of amorphization as “impact craters.” Published by the American Physical Society 2025

Long distance propagation of light in random media with partially coherent sources

Optical beam propagation in random media is characterized by familiar speckle patterns generated by intricate interference effects. Such patterns may be modified and possibly attenuated for partially coherent incident beam profiles. In the weak-coupling regime of the Itô-Schrödinger paraxial model of wave propagation, we show how the spatio-temporal statistics of the partially coherent beams interact with the statistics of the random medium to enhance or suppress scintillation effects.

Laser system for remote 3D registration and measurement of vibration and translational movements of objects

Abstract The article presents a physic-technical solution in which a laser interference-wedge-based system is implemented for remote optical registration and measurement from a distance of metres or tens of metres of mechanical vibrations and translations of objects in three perpendicular directions: horizontally along the X-axis, vertically along the Y-axis, and in the direction of the incident laser beam, along the Z-axis. This enables purely 3D measurement of the object, which can be separately measured in each of these directions. The measured vibrations and translations amplitude range from units of mm up to 10-15 cm on concrete structures, bridges, subways, buildings, and rocks.

Manipulation of annular electron beams in plasmas

The annular electron beam has significant practical potential in high-energy physics and condensed matter physics, which can be used for edge-enhancement electron imaging, collimation of antiprotons in conventional linear accelerators, acceleration of positively particles like positrons, structured x-ray generation, and manipulation of nanomaterials. The quality of an annular electron beam depends on its energy, flux, and topology. In this article, we study the transport characteristics of the annular electron beam in a plasma medium and propose a scheme to modify it. According to our theory and full three-dimensional LAPINS simulations, we have found that the self-generated magnetic field focuses the incident annular electron beam, enabling the adjustment of its annular width (AW). In addition, the annular electron beam, endowed with angular momentum (AM), exhibits contrasting transport characteristics compared to an annular electron beam without AM. The former requires an external magnetic field to ensure stable transportation in the plasma. Under the influence of this magnetic field, the radius of the annular electron beam can oscillate periodically, with the direction of change whether increasing or decreasing dependent on the field's strength. In this case, the radius of the annular electron beam will be affected by the external magnetic field and allows for the simultaneous adjustment of its radius and AW, significantly broadening its application range.

A novel approach for detecting negative charge accumulation induced by electron beam irradiation using power MOSFET devices.

Micro-discharging and electrostatic discharges, caused by secondary electron emission and other factors, can severely impact spacecraft and vacuum equipment. Therefore, electrostatic protection is essential for their safe and reliable operation. This paper presents a quantitative method for detecting surface charge accumulation from electron beam irradiation using power MOSFETs, enabling the controlled release of accumulated charges for electrostatic protection. First, a response model was developed for the drain-to-source voltage of MOSFETs based on gate charge accumulation from electron beam irradiation. The study investigated the charge response of four device types: N-channel depletion/enhancement and P-channel depletion/enhancement MOSFETs. Based on this, a dual-model test system for charge accumulation detection and electrostatic discharge protection was designed, with an external capacitor to adjust the charge accumulation-discharge threshold, offering flexibility for various applications. Quantitative measurement of charge accumulation under 30keV electron beam irradiation was conducted in the scanning electron microscope chamber, with a charge-discharge pulse precision of 3.27 nC. The measurement system can be calibrated using the actual incident beam current measurement results, with the charge accumulation rate measurement error being less than 0.15 nC/s. This research contributes to a measurement system based on a novel approach for electrostatic detection and controllable discharging, which can accurately detect weak charging and dynamically monitor the charge accumulation rate. It provides an innovative concept for electrostatic protection design.

Acoustic demonstration of virtual impedance matching by transiently echoless complex frequency waves.

The ability of a wave to pass through a material boundary can be improved by adding a tuned middle layer, known as an impedance-matching layer. However, in many situations, it is unfeasible to modify the physical system itself. This paper demonstrates that virtual impedance matching without added tuned layers is possible by allowing the frequencies of incident waves to take on complex values. The resulting tailored waveforms directly excite the zeros of the reflection coefficient and lead to complex generalizations of Fabry-Pérot resonances and quarter-wavelength matching. This is demonstrated experimentally whereby the reflection coefficient for an ultrasound beam incident on a bi-layer plate immersed in water is reduced by more than an order of magnitude. While the technique is naturally limited in temporal duration due to the quasi-steady state nature of the signals, it provides an alternative approach to traditional impedance matching by eliminating the need for extra tuned layers and may prove useful in applications where reduction of reflections is desired without modifying the system itself.

Multi-user frequency selective beam steering by reconfigurable intelligent surfaces in the Ka-band

Reconfigurable intelligent surfaces (RIS) have been proposed to extend the coverage of wireless communication signals at mm-wave frequencies. Here, we designed and fabricated a reconfigurable intelligent surface (RIS) for multi-user frequency selective beam steering (MU-FSBS) that achieves higher channel capacity than traditional time division multiple access (TDMA) techniques in multi-user communication scenarios. MU-FSBS is enabled by a varactor diode-tuned RIS that allows to steer several beams in the Ka-band independently at the same time. For such targeted multi-frequency beam steering, we implemented a customized neural network-based machine learning architecture specifically designed to optimize the bias voltage patterns of the RIS. As an experimental demonstration, we first accomplished independent beam steering of normally incident beams at 27 GHz and 31 GHz to deflection angles between 10 and 45 in a defined plane. Secondly, we compared the achievable channel capacities of the proposed MU-FSBS approach with those of TDMA, finding an average increase of approximately 50% in channel capacity at a fixed SNR of 20 dB. At an SNR of 60 dB, MU-FSBS even demonstrated a remarkable 84% increase in channel capacity compared to TDMA.

Tight focusing of mixed-polarization beams and its impact on focal plane electric field distributions

Abstract Mixed-polarization beam has multiple and arbitrary polarization states in different regions of the beam, leading to complex interactions between the polarization states of the input and the electric fields after tight focusing. This complexity holds vast potential for applications in optical physics, optical imaging, optical manipulation, and so on. However, there is currently a lack of research analyzing the variation patterns of the electric field distribution after tight focusing. In this paper we proposed an integration approach to accurately calculate the tight focusing electric fields of a mixed-polarization beam. Using this approach, we designed various mixed-polarization beams incident to a tight focusing system and obtained the output electric fields of the system. The distributions of the mixed polarization states in the incident beams were found to drastically affect the electric-field distributions on the focal plane of the tight focusing system. Hence, the output electric fields of a tight focusing system can be tailored and analyzed with the designated distribution of the polarization states of an incident beam.

The generation of ultra-long pure longitudinal magnetization needle and magnetization chain with multi-belt filter

In this paper, we optimized a multi-belt filter with ternary phase amplitude. Single and dual channel longitudinal magnetization needles were obtained by tight focusing azimuthally polarized sinh-Gaussian beam using by the multi-belt filter and spiral phase plate in single-lens system. And longitudinal magnetization chains were obtained using by the same incident beam and multi-belt filter in 4π focusing system. The depth of focus and transverse size was 64λ and 0.36λ in the obtained magnetization needles, respectively. For magnetization chains, the DOF was 60λ when the normalized intensity was within 0.8, and there were 43 magnetization spots in the range. The depth of focus and transverse size were 0.566λ and 0.36λ in each magnetization spots, respectively. In addition, the longitudinal magnetization chains can move along z-axis linearly by changing phase difference of the two counter-propagating incident beams.

ITO Meta-Absorber-Loaded Conformal UHF Monopole Antenna with Wide-Angel RCS Reduction.

In this paper, a conformal UHF antenna with a wide-angle radar cross section (RCS) reduction capability is proposed. The radiator of the design is a planar monopole antenna. Since the large physical size of the antenna in UHF band can generate a scatter beam with a large RCS in the high operating frequency of radars and other sensing applications, i.e., the X band, two types of ITO (Indium Tin Oxide) meta-absorber are proposed and loaded onto the monopole antenna to suppress the scatter. For the incident beam around the direction orthogonal to the radiator plane, the periodical meta-absorber can realize around a 20 dB RCS reduction in the X band. The incident wave around the parallel direction of the radiator is absorbed by the taper meta-absorber, which can greatly suppress the surface and then reduce the RCS in the horizontal plane. The combined effect means the antenna can achieve a wide-angle RCS reduction. It should be noted that the antenna can still produce a high-efficiency omnidirectional beam after the lossy meta-absorber is loaded. In our opinion, the advantages of the proposed antenna design, including good radiation performance in UHF band and high RCS reduction in X band, make it a suitable candidate for airborne and drone applications.

Hybrid Monte Carlo model for efficient tissue Cherenkov emission estimation to assess changes from beam size, energy and incidence.

Hybrid Monte Carlo model for efficient tissue Cherenkov emission estimation to assess changes from beam size, energy and incidence.

High spatial resolution dosimetry for radiation oncology with "MagicPlates," a new 976-pixel monolithic silicon detector.

We introduce the next generation of "MagicPlate" 2D monolithic pixelated semiconductor detectors - MagicPlate-976 (MP976). It features a larger array area, higher spatial resolution, and does not require external triggering. We perform a comprehensive characterization for small-field steep-dose-gradient dosimetry applications in radiation therapy focusing on x-ray beams used in stereotactic treatments. The MP976, developed by the Centre for Medical Radiation Physics, consists of 976 ion-implanted diodes on a thin n-type epitaxial silicon substrate with a total array area of 58×58mm2. The central region has "small" diodes with an area of 0.2×0.2mm2 and 1mm pitch and the peripheral region has "large" diodes with an area of 0.6×0.6mm2 and 2mm pitch. The detector was primed with 10kGy (Co-60) and tested using a Varian TrueBeam linear accelerator for sensitivity change and dose linearity, and variations in response due to dose-per-pulse and beam incidence angle. Output factors, depth dose, and beam profiles were measured and compared with reference data. After the 10kGy, the sensitivity declined by (74±5)% for "large" diodes and by (78±7)% for the "small" ones, the dose-per-pulse (DPP) dependence was in the range of commercially available diodes, however, a difference in the DPP dependence between the "large" and "small" diodes of (8.4±0.2)% was found in the studied DPP range from 0.131-1.111mGy/pulse. The minimum angular response was at 90° for 6MV and 100° for 10MV flattened beams (76% and 82%, respectively). The output factors and depth dose response showed agreement with the reference within 3.1% and 1%, respectively. Deviation in small field 80%/20% penumbra measurements was within 0.5mm for 6MVFF and 0.3mm for 10MV FFF. Full width at half maximum (FWHM) for the beam profiles agreed within 0.5mm for both beam qualities. The new MagicPlate-976 detector system is shown to be suitable for dosimetry in small fields and steep dose gradients. It provides 1mm spatial resolution in the central region and 2mm on the periphery and has no dependence on the field size. The system's high spatial and temporal resolution opens new opportunities for trigger-less, film-less, and time-resolved verification and error identification for complex stereotactic treatment plans.

Retinal reconstruction from peripheral biometry

This study presents a method for retinal reconstruction using peripheral biometry. The incident beam is presumed to be directed toward the center of curvature of the anterior cornea, reaching the retina with minimal deviation. A significant advancement is demonstrated by extending previous approaches to three dimensions and effectively capturing the complexity of astigmatic corneal surfaces. The method was evaluated in Zemax using Navarro’s eye model featuring a retina of 12 mm radius, across various levels of accommodation ranging from 0 to 8 D, and a visual field angle between 25 and 25°. The method's reliability diminishes for field angles ≥ 35°. Validation was carried out using 500 synthetically generated eyes, and the method's performance was also assessed with an ellipsoidal retina. The findings revealed that spherical equivalent differences were consistently under 0.25 D at 25° for both types of retinas. Overall, these results demonstrate the method’s effectiveness, offering a promising new tool for retinal reconstruction.

Ion beam etching of barium titanate for integrated photonics

The perovskite material barium titanate (BTO) has shown great promise in the next generation electro-optical modulators integrated on Si photonic platforms. In this work, the dry etching of BTO using an argon (Ar) ion beam etching system and the underlying mechanisms are investigated. The results indicate that reducing the pressure and increasing ion beam current, ion energy, and incidence angle all contribute to an increased etch rate. The increase in ion energy and beam current leads to higher surface roughness, whereas a negative incidence angle effectively reduces surface roughness. Through the optimization of various process parameters, an etching recipe showing an etch rate of 16.1 nm/min and a postetching surface roughness of 0.486 nm is realized.

Manipulation of Surface Plasmon Polariton Patterns by Adjusting the Polarization State of Incident Beam

Manipulation of Surface Plasmon Polariton Patterns by Adjusting the Polarization State of Incident Beam

Modeling snow optical properties from single wavelength airborne lidar in steep forested terrain

Airborne lidar is a powerful tool used by water resource managers to map snow depth and aid in producing spatially distributed snow water equivalent (SWE) when combined with modeled density. However, limited research so far has focused on retrieving optical snow properties from lidar. Optical snow surface properties directly impact albedo, which has a major control on snowmelt timing, which is especially useful for water management applications. Airborne lidar instruments typically emit energy at a wavelength of 1,064 nm, which can be informative in mapping optical snow surface properties since grain size modulates reflectance at this wavelength. In this paper we present and validate an approach using airborne lidar for estimating snow reflectance and optical grain size at high spatial resolution. We utilize three lidar flights over the Boise National Forest, United States, during a winter season from December 2022 to March 2023. We discuss sensitivities to beam incidence angles, compare results to in situ measurements snow grain size, and perform spatial analyses to ensure reflectance and optical grain size varies across space and time as anticipated. Modeled optical grain size from lidar performed well (Root mean squared difference = 49 μm; percent mean absolute difference = 31%; n = 28), suggesting that aerial lidar surveys can be useful in mapping snow reflectance and optical grain size for dry snow, and may support development of other remote sensing technologies and aid water resources management.

Incident beam optics optimization for the single crystal neutron diffractometer Pioneer with a polarized beam option

Pioneer, a next-generation single-crystal neutron diffractometer, is under development for Oak Ridge National Laboratory’s Second Target Station. Designed to address a wide range of scientific questions, Pioneer will deliver homogeneous neutron beams with customizable size and divergence and provide a polarized beam option. This article introduces its incident beam optics, highlighting the optimization methodology and the simulated performance. Pioneer will utilize a modified elliptical-straight guide for neutron transport and deploy slit packages and insertable apertures to control beam size and divergence. The optimized guide geometry matches the optimal-and-full-sample-illumination condition, and the beam control system effectively filters out unwanted neutrons while preserving the desired ones. In addition, we have found that polygon-approximated guides provide satisfactory transport efficiency and beam homogeneity, eliminating the need for truly curved guides. To enhance neutronics performance and reduce cost, the coatings of supermirror elements are individually optimized to the lowest half-integer m-values that are sufficient to deliver the desired neutrons. After evaluating polarizing V-cavities and 3He spin filters over the default polarized wavelength band of 1.2–5.5 Å, we selected a translatable multichannel polarizing V-cavity as the incident beam polarizer. Strategically placed at a location where the beam divergence is low and a large in-guide gap has negligible impact on transport efficiency, the optimized V-cavity achieves an average P2T of ∼35%.

Cover Picture: Contrib. Plasma Phys. 03/2025

Diagram of beam distribution of the magnetic trap at 50 ns with different beam incidence velocities. Green points represent protons, red points represent electrons and blue lines represent magnetic induction lines. Part of Fig. 6 of the paper by Fang‐Ping Wang et al. https://doi.org/10.1002/ctpp.202400040 image

Superoscillation focusing of high-order cylindrical-vector beams

Traditional superoscillation focusing (SOF) typically requires complex optimization of the incident light field. These complexities may limit the practical application of superoscillation. High-order radially polarized Laguerre-Gaussian beams inherently support SOF due to their multi-ring amplitude distribution and 0-π phase alternation, which align with the necessary destructive interference mechanisms. In this study, we demonstrate that by adjusting the beam’s mode order together with the incident beam size, we can easily control the full width at half maximum, field of view, and energy distribution of SOF. Moreover, high-order azimuthally polarized vortex-phase Laguerre-Gaussian beams can also achieve SOF, offering even better super-resolution effects. The distinct focusing behaviors of their circular components present unique opportunities for applications involving circular dichroism materials.