Beam Correction Research Articles

Lossy wavefront sensing and correction of distorted laser beams.

The art of rectifying a laser beam carrying amplitude and phase distortions has been demonstrated through several competing methods. Both wavefront sensor and wavefront sensor-less approaches show that the closed-loop correction of a laser beam can be accomplished by exploiting high-resolution sampling of the beam distortion in its spatial or time domain, respectively. Moreover, machine-learning-based wavefront sensing has emerged recently, and uses training data on an arbitrary sensing architecture to map observed data to reasonable wavefront reconstructions. This offers additional options for beam correction and optical signal decoding in atmospheric or underwater propagation. Ideally, wavefront sensing can be achieved through any resolution in spatial samples, provided that more frequent sampling in the time domain can be achieved for a reduced number of spatial samples. However, such trade-offs have not been comprehensively studied or demonstrated experimentally. We present a fundamental study of lossy wavefront sensing that reduces the number of effective spatial samples to the number of actuators in a deformable mirror for a balanced performance of dynamic wavefront corrections. As a result, we show that lossy wavefront sensing can both simplify the design of wavefront sensors and remain effective for beam correction. In application, this concept provides ultimate freedom of hardware choices from sensor to sensorless approaches in wavefront reconstruction, which is beneficial to the frontier of study in free-space optical communication, lidar, and directed energy.

Real-time phase measurement and correction of dynamic multimode beam using a single spatial light modulator

In this Letter, a novel system for adaptively correcting the phase of a dynamic multimode beam is proposed. While using merely one spatial light modulator, the phase measurement of the first-order diffraction pattern and the correction of the zeroth diffraction order are simultaneously realized. The real-time experimental result is obtained at a control rate of 10 Hz. The power-in-the-bucket value is improved from 38.5% to 61.8%, even with fundamental mode content that is consistently below 30%. To the best of our knowledge, this is the first implementation of real-time adaptive correction of the entire multimode beam.

A Two-Stage Approach for Beam Hardening Artifact Reduction in Low-Dose Dental CBCT

This article presents a two-stage method for beam hardening artifact correction of dental cone beam computerized tomography (CBCT). The proposed artifact reduction method is designed to improve the quality of maxillofacial imaging, where soft tissue details are not required. Compared to standard CT, the additional difficulty of dental CBCT comes from the problems caused by offset detector, FOV truncation, and low signal-to-noise ratio due to low X-ray irradiation. To address these problems, the proposed method primarily performs a sinogram adjustment in the direction of enhancing data consistency, considering the situation according to the FOV truncation and offset detector. This sinogram correction algorithm significantly reduces beam hardening artifacts caused by high-density materials such as teeth, bones, and metal implants, while tending to amplify special types of noise. To suppress such noise, a deep convolutional neural network is complementarily used, where CT images adjusted by the sinogram correction are used as the input of the neural network. Numerous experiments validate that the proposed method successfully reduces beam hardening artifacts and, in particular, has the advantage of improving the image quality of teeth, associated with maxillofacial CBCT imaging.

Multiband Optical Light Curves of Black-widow Pulsars

Abstract We collect new and archival optical observations of nine “black-widow” millisecond pulsar binaries. New measurements include direct imaging with the Keck, Gemini-S, MDM, and Las Cumbres Observatory 2 m telescopes. This is supplemented by synthesized colors from Keck long-slit spectra. Four black-widow optical companions are presented here for the first time. Together these data provide multicolor photometry covering a large fraction of the orbital phase. We fit these light curves with a direct (photon) heating model using a version of the ICARUS light-curve modeling code. The fits provide distance and fill-factor estimates, inclinations, and heating powers. We compare the heating powers with the observed GeV luminosities, noting that the ratio is sensitive to pulsar distance and to the gamma-ray beaming. We make a specific correction for “outer gap” model beams, but even then some sources are substantially discrepant, suggesting imperfect beaming corrections and/or errors in the fit distance. The fits prefer large metal abundance for half of the targets, a reasonable result for these wind-stripped secondaries. The companion radii indicate substantial Roche-lobe filling, f c ≈ 0.7−1 except for PSR J0952−0607, which with f c < 0.5 has a companion density ρ ≈ 10 g cm−3, suggesting unusual evolution. We note that the direct-heating fits imply large heating powers and rather small inclinations, and we speculate that unmodeled effects can introduce such bias.

Isolation Improvement and Beam Manipulation of Dual-Polarized RIS-Halved Lens Antennas for Compact Transceiver Systems

A pair of mirror-symmetrical half-lens antennas separated by two finite back-to-back reactive impedance surfaces (RISs) is proposed to improve the isolation between the transmitting and receiving high-gain dual-polarized antennas for a compact monostatic transceiver system. By introducing the desired surface wave and reducing the interference between the source and its image, the RIS is able to manipulate the deflected boresight beam and suppress the increased sidelobes for TM-polarized waves, while TE-polarized performance is maintained as in the case where a perfect electrical conductor (PEC) is used. The effects of RIS properties and feeder orientation on antenna isolation and far-field performance are discussed and compared with the PEC cases. To validate this method, two identical ${X}$ -band half plano-convex dielectric lenses with a diameter of 237 mm and a thickness of 154 mm integrated with two 32°-rotated feeders and RISs of $479\times258.3$ mm2 with a characteristic impedance of $\text{j}189~\Omega $ are designed as an example. The measured results show that the isolation of >51 and >36 dB over a 10dB return loss bandwidth of 2 GHz is achieved for TE and TM polarization, respectively. Compared to the PEC case, the boresight beam correction reaches 7.5° and the first sidelobe close to the adjacent antenna even vanishes in TM polarization when using the RIS. A boresight gain of 20 dBi/21 dBi at 10 GHz is realized for TE/TM polarization, respectively. Hence, the proposed method is a good option for radar systems requiring compact high-performance transceivers.

Determining the shading correction factor using a smartphone camera with a fisheye lens

Quasi-steady-state methods to calculate monthly heating and cooling energy needs require the quantification of solar heat gains through windows. The presence of external obstacles, such as natural topography, other buildings, overhangs, or side fins, may significantly decrease solar gains. Simplified methods to evaluate shading on windows throughout the year use the shading correction factor concept, i.e., the ratio between the surface solar irradiation in the presence of external obstacles and in their absence. This paper presents a photographic method using a low-cost fisheye lens attached to a smartphone to quantify the shading correction factor. It is based on image processing, solar geometry, and climate databases and does not require 3D building design or angle measurement of external obstacles. Both beam and diffuse correction factors are calculated monthly. The model correctly predicts the real Sun’s position in the photos and the expected monthly shading of a South window with an overhang. For the diffuse correction factor, errors up to 11% are obtained when compared to the analytical solution of a window with a large overhang. Standard tabulated values for windows with multiple obstructions are conservative when compared to those of the photographic method. The tabulated approach considers the effect of various obstacles shading even when overlapping occurs, which possibly explains the difference between methods.

Application and analysis of an electronic–mechanical dual stable platform for radars with a three‐axis stable turntable

This study proposes the concept of an electronic–mechanical dual stable platform for radars with a three-axis stable turntable. Based on an assumption, an electron stable equation of the first order is applied to the beam pointing correction of the radar with three-axis stable turntable based on the equivalence principle. Furthermore, through a comparative analysis of two kinds of algorithms, it is shown that when the instantaneous value of the tracking error in the platform servo-loop of the mechanical platform is smaller than a certain range, assuming the conditions are established, the error method of the electron stable equation of the first order can directly replace the electron stable equation of the second order that is applied to the spatial orientation correction of the radar beam to improve computational efficiency. At the same time, error analysis was performed on the data link of the dual stable platform.

Adaptive phase correction of dynamic multimode beam based on modal decomposition.

We propose and demonstrate a method for the adaptive phase correction of dynamic multimode fiber beams. The phase of incident beam is reconstructed in real-time based on the complete modal information, which obtained by using the modal decomposition of correlation filter method. For the proof of principle, both of the modal decomposition and the phase correction are implemented using the same computer-generated hologram, which was encoded into a phase-only spatial light modulator. We demonstrate the phase correction of dynamic multimode beam at a rate of 5 Hz and achieve a 1.73-fold improvement on the average power-in-the-bucket. The experimental results indicate the feasibility of the real-time phase correction for the large mode area fiber laser by adaptive optics.

Theoretical research on the novel adaptive optics configuration based on the tubular deformable mirror for the aberration correction of the annular laser beam.

The annular laser beam (ALB) has been widely used in many fields for its unique intensity distribution. Especially, in the materials processing, the power and the beam quality of the large-aperture thin-wall ALB are of vital. However, limited by the aperture, the actuators' spacing or the damage threshold, the existing deformable mirrors (DMs) are not suitable for the correction of the ALB. Considering the stretching effect of the oblique incidence, in this paper, by using the tubular DM (TDM), a novel adaptive optics (AO) configuration is promoted to increase the number of the effective actuators covered by the input ALB. The coordinate transformation equations and correction principle of the novel AO configuration are derived based on the ray tracing. A typical TDM prototype is designed based on the coordinate transformation equations. The influence function characteristics of the TDM is analyzed using the finite element method, and the correction ability of the novel AO configuration based on the TDM is verified. Simulation results show that the TDM could perfectly compensate the wavefront distortions described by the 2th to 15th order Zernike annular aberrations.

Improvements in Forecasting Intense Rainfall: Results from the FRANC (Forecasting Rainfall Exploiting New Data Assimilation Techniques and Novel Observations of Convection) Project

The FRANC project (Forecasting Rainfall exploiting new data Assimilation techniques and Novel observations of Convection) has researched improvements in numerical weather prediction of convective rainfall via the reduction of initial condition uncertainty. This article provides an overview of the project’s achievements. We highlight new radar techniques: correcting for attenuation of the radar return; correction for beams that are over 90% blocked by trees or towers close to the radar; and direct assimilation of radar reflectivity and refractivity. We discuss the treatment of uncertainty in data assimilation: new methods for estimation of observation uncertainties with novel applications to Doppler radar winds, Atmospheric Motion Vectors, and satellite radiances; a new algorithm for implementation of spatially-correlated observation error statistics in operational data assimilation; and innovative treatment of moist processes in the background error covariance model. We present results indicating a link between the spatial predictability of convection and convective regimes, with potential to allow improved forecast interpretation. The research was carried out as a partnership between University researchers and the Met Office (UK). We discuss the benefits of this approach and the impact of our research, which has helped to improve operational forecasts for convective rainfall events.

Development of an automated system for radiochromic film analysis

Radiochromic films (RCFs) are widely used to check the dose distribution for quality assurance in radiation therapy. A flatbed scanner is the most common tool for RCFs. Analyzing RCFs with a flatbed scanner requires many considerations, including the energy correction for various beams, scanning orientation, film handling, film uniformity in a sheet or in a batch, scanning temperature, scanning software, and optical density to dose conversion. For RCFs to be a good tool for measuring the two-dimensional dose distribution, medical physicists should carefully follow a confirmed procedure to obtain the best dose distribution results. We focused on the absolute dose measurement at a point instead of the two-dimensional dose distribution and reduced human loads. A one-stop processing system from film readings to the dose evaluation was developed using a spectrometer, a light emitting diode (LED), and a film changer. Our system is characterized by the flexibility of selective light sources for RCFs and the ability to analyze absorbance spectra. EBT3 film was selected for this study, and our system was constructed to fit RCFs. The performance of the system was tested, and the evaluated dose was compared with a scanner. The irradiated dose and evaluated dose showed good agreement, within 3.2% deviation.

Implementation and assessment of the black body bias correction in quantitative neutron imaging.

We describe in this paper the experimental procedure, the data treatment and the quantification of the black body correction: an experimental approach to compensate for scattering and systematic biases in quantitative neutron imaging based on experimental data. The correction algorithm is based on two steps; estimation of the scattering component and correction using an enhanced normalization formula. The method incorporates correction terms into the image normalization procedure, which usually only includes open beam and dark current images (open beam correction). Our aim is to show its efficiency and reproducibility: we detail the data treatment procedures and quantitatively investigate the effect of the correction. Its implementation is included within the open source CT reconstruction software MuhRec. The performance of the proposed algorithm is demonstrated using simulated and experimental CT datasets acquired at the ICON and NEUTRA beamlines at the Paul Scherrer Institut.

AKARI and IRAS: From beam corrections to SEDs

Abstract There is significant scientific value to be gained from combining AKARI fluxes with data at other far-infrared (IR) wavelengths from the Infrared Astronomical Satellite (IRAS) and Herschel missions. To be able to do this we must ensure that there are no systematic differences between the data sets that need to be corrected before the fluxes are compatible with each other. One such systematic effect identified in the Bright Source Catalog version 1 (BSCv1) data is the issue of beam corrections. We determine these for the BSC version 2 (BSCv2) data by correlating ratios of appropriate IRAS and AKARI bands with the difference in 2 Micron All Sky Survey (2MASS) J-band extended and point source magnitudes for sources cross-matched between the IRAS Faint Source Catalog (FSC), AKARI BSCv2 and 2MASS catalogs. We find significant correlations (p ≪ 10 −13) indicating that beam corrections are necessary in the 65 and 90 μm bands. We then use these corrected fluxes to supplement existing data in spectral energy distribution (SED) fits for ultraluminous infrared galaxies (ULIRGs) in the Herschel ULIRG Survey (HERUS). The addition of AKARI fluxes makes little difference to the results of simple (T, β) fits to the SEDs of these sources, though there is a general decrease in reduced χ2 values. The utility of the extra AKARI data, however, is in allowing physically more realistic SED models with more parameters to be fitted to the data. We also extend our analysis of beam correction issues in the AKARI data by examining the Herschel Reference Sample (HRS) galaxies, which have Herschel photometry from 100 to 500 μm and which are more spatially extended than the HERUS ULIRGs. 34 of the HRS sources have good Herschel SEDs and matching data from AKARI. This investigation finds that our simple 2MASS-based beam correction scheme is inadequate for these larger and more complex sources. There are also indications that additional beam corrections at 140 and 160 μm are needed for these sources, extended on scales >1′.

EasySLM-STED: Stimulated emission depletion microscopy with aberration correction, extended field of view and multiple beam scanning.

We demonstrate a simplified set-up for STED microscopy with a straightforward alignment procedure that uses a single spatial light modulator (SLM) with collinear incident excitation and depletion beams to provide phase modulation of the beam profiles and correction of optical aberrations. We show that this approach can be used to extend the field of view for STED microscopy by correcting chromatic aberration that otherwise leads to walk-off between the focused excitation and depletion beams. We further show how this arrangement can be adapted to increase the imaging speed through multibeam excitation and depletion. Fine adjustments to the alignment can be accomplished using the SLM only, conferring the potential for automation.

Gamma-Ray Burst Jet Breaks Revisited

Abstract Gamma-ray Burst (GRB) collimation has been inferred with the observations of achromatic steepening in GRB light curves, known as jet breaks. Identifying a jet break from a GRB afterglow light curve allows a measurement of the jet opening angle and true energetics of GRBs. In this paper, we re-investigate this problem using a large sample of GRBs that have an optical jet break that is consistent with being achromatic in the X-ray band. Our sample includes 99 GRBs from 1997 February to 2015 March that have optical and, for Swift GRBs, X-ray light curves that are consistent with the jet break interpretation. Out of the 99 GRBs we have studied, 55 GRBs are found to have temporal and spectral behaviors both before and after the break, consistent with the theoretical predictions of the jet break models, respectively. These include 53 long/soft (Type II) and 2 short/hard (Type I) GRBs. Only 1 GRB is classified as the candidate of a jet break with energy injection. Another 41 and 3 GRBs are classified as the candidates with the lower and upper limits of the jet break time, respectively. Most jet breaks occur at 90 ks, with a typical opening angle θ j = (2.5 ± 1.0)°. This gives a typical beaming correction factor f b − 1 ∼ 1000 for Type II GRBs, suggesting an even higher total GRB event rate density in the universe. Both isotropic and jet-corrected energies have a wide span in their distributions: log(E γ,iso/erg) = 53.11 with σ = 0.84; log(E K,iso/erg) = 54.82 with σ = 0.56; log(E γ /erg) = 49.54 with σ = 1.29; and log(E K/erg) = 51.33 with σ = 0.58. We also investigate several empirical correlations (Amati, Frail, Ghirlanda, and Liang–Zhang) previously discussed in the literature. We find that in general most of these relations are less tight than before. The existence of early jet breaks and hence small opening angle jets, which were detected in the Swfit era, is most likely the source of scatter. If one limits the sample to jet breaks later than 104 s, the Liang–Zhang relation remains tight and the Ghirlanda relation still exists. These relations are derived from Type II GRBs, and Type I GRBs usually deviate from them.

Electron diffraction data processing with DIALS.

Electron diffraction is a relatively novel alternative to X-ray crystallography for the structure determination of macromolecules from three-dimensional nanometre-sized crystals. The continuous-rotation method of data collection has been adapted for the electron microscope. However, there are important differences in geometry that must be considered for successful data integration. The wavelength of electrons in a TEM is typically around 40 times shorter than that of X-rays, implying a nearly flat Ewald sphere, and consequently low diffraction angles and a high effective sample-to-detector distance. Nevertheless, the DIALS software package can, with specific adaptations, successfully process continuous-rotation electron diffraction data. Pathologies encountered specifically in electron diffraction make data integration more challenging. Errors can arise from instrumentation, such as beam drift or distorted diffraction patterns from lens imperfections. The diffraction geometry brings additional challenges such as strong correlation between lattice parameters and detector distance. These issues are compounded if calibration is incomplete, leading to uncertainty in experimental geometry, such as the effective detector distance and the rotation rate or direction. Dynamic scattering, absorption, radiation damage and incomplete wedges of data are additional factors that complicate data processing. Here, recent features of DIALS as adapted to electron diffraction processing are shown, including diagnostics for problematic diffraction geometry refinement, refinement of a smoothly varying beam model and corrections for distorted diffraction images. These novel features, combined with the existing tools in DIALS, make data integration and refinement feasible for electron crystallography, even in difficult cases.

Detector-specific correction factors in radiosurgery beams and their impact on dose distribution calculations.

Silicon-diode-based detectors are commonly used for the dosimetry of small radiotherapy beams due to their relatively small volumes and high sensitivity to ionizing radiation. Nevertheless, silicon-diode-based detectors tend to over-respond in small fields because of their high density relative to water. For that reason, detector-specific beam correction factors () have been recommended not only to correct the total scatter factors but also to correct the tissue maximum and off-axis ratios. However, the application of to in-depth and off-axis locations has not been studied. The goal of this work is to address the impact of the correction factors on the calculated dose distribution in static non-conventional photon beams (specifically, in stereotactic radiosurgery with circular collimators). To achieve this goal, the total scatter factors, tissue maximum, and off-axis ratios were measured with a stereotactic field diode for 4.0-, 10.0-, and 20.0-mm circular collimators. The irradiation was performed with a Novalis® linear accelerator using a 6-MV photon beam. The detector-specific correction factors were calculated and applied to the experimental dosimetry data for in-depth and off-axis locations. The corrected and uncorrected dosimetry data were used to commission a treatment planning system for radiosurgery planning. Various plans were calculated with simulated lesions using the uncorrected and corrected dosimetry. The resulting dose calculations were compared using the gamma index test with several criteria. The results of this work presented important conclusions for the use of detector-specific beam correction factors ( in a treatment planning system. The use of for total scatter factors has an important impact on monitor unit calculation. On the contrary, the use of for tissue-maximum and off-axis ratios has not an important impact on the dose distribution calculation by the treatment planning system. This conclusion is only valid for the combination of treatment planning system, detector, and correction factors used in this work; however, this technique can be applied to other treatment planning systems, detectors, and correction factors.

Efficient correction of wavefront inhomogeneities in X-ray holographic nanotomography by random sample displacement

In X-ray tomography, ring-shaped artifacts present in the reconstructed slices are an inherent problem degrading the global image quality and hindering the extraction of quantitative information. To overcome this issue, we propose a strategy for suppression of ring artifacts originating from the coherent mixing of the incident wave and the object. We discuss the limits of validity of the empty beam correction in the framework of a simple formalism. We then deduce a correction method based on two-dimensional random sample displacement, with minimal cost in terms of spatial resolution, acquisition, and processing time. The method is demonstrated on bone tissue and on a hydrogen electrode of a ceramic-metallic solid oxide cell. Compared to the standard empty beam correction, we obtain high quality nanotomography images revealing detailed object features. The resulting absence of artifacts allows straightforward segmentation and posterior quantification of the data.

Active laser beam correction using continuous-surface deformable mirrors: algorithm and laboratory tests

We propose an optically efficient active beam-shaping system which consists of two continuous-surface deformable mirrors correcting for both phase and amplitude distortions to improve the beam quality of a laser. We present the results obtained with simulations and we validate next the technique using an experimental setup with two Boston micromachines MEMS deformable mirrors of 12 x 12 actuators each.

The main beam correction term in kinetic energy release from metastable peaks.

The correction term for the precursor ion signal width in determination of kinetic energy release is reviewed, and the correction term is formally derived. The derived correction term differs from the traditionally applied term. An experimental finding substantiates the inaccuracy in the latter. The application of the "T-value" to study kinetic energy release is found preferable to kinetic energy release distributions when the metastable peaks are slim and simple Gaussians. For electronically predissociated systems, a "borderline zero" kinetic energy release can be directly interpreted in reaction dynamics with strong curvature in the reaction coordinate.