Beam Spot Size Research Articles

Influence of astigmatic aberration on partially coherent Gaussian-Schell vortex beam focused by lensacon

Based on the mathematical framework of the partially coherent Gaussian Schell model vortex (PCGSMV) beam and the Huygens-Fresnel integral, we conducted a study to analyze the intensity distribution and depth of focus (DOF) of the PCGSMV beam as it propagates through a classical axicon. Our numerical results indicate the influence of factors such as the beam width, spatial degree of coherence, topological charge, and axicon base angle on the intensity distribution and DOF. In addition, we investigated the relationship between the beam spot size and propagation distance, as well as the effects of the spatial degree of coherence and propagation distance on the intensity profile. Our findings highlight the importance of the intensity values along the DOF for various applications, including the optical trapping and manipulation of micro particles.

Circular photocurrents in centrosymmetric semiconductors with hidden spin polarization

Centrosymmetric materials with site inversion asymmetries possess hidden spin polarization, which remains challenging to be converted into spin currents because the global inversion symmetry is still conserved. This study demonstrates the spin-polarized circular photocurrents in centrosymmetric transition metal dichalcogenide semiconductors at normal incidence without applying electric bias. The global inversion symmetry is broken by using a spatially-varying circularly polarized light beam, which could generate spin gradient owing to the hidden spin polarization. The dependence of the circular photocurrents on electrode configuration, illumination position, and beam spot size indicates an emergence of circulating electric current under spatially inhomogeneous light, which is associated with the deflection of spin-polarized current through the inverse spin Hall effect. The circular photocurrents is subsequently utilized to probe the spin polarization and the inverse spin Hall effect under different excitation wavelengths and temperatures. The results of this study demonstrate the feasibility of using centrosymmetric materials with hidden spin polarization and non-vanishing Berry curvature for spintronic device applications.

Morphological Characterization and Tribological Properties of TiCoNi Alloy Coatings on Ti–6Al–4V Alloy via Laser Deposition

The goal of this work is to improve the Ti–6Al–4V alloy's hardness and tribological behavior. Coaxial laser surface cladding was used to develop intermetallic layers of nickel (Ni), cobalt (Co), and titanium (Ti). Laser power of 900 W, beam spot size of 3 mm, powder feed rate of 1.0 g/min, and gas flow rate of 1.2 L/min are the optimized parameters used for laser depositions. The laser scan speeds were adjusted between 0.6 and 1.2 m/min. Investigations were conducted into the effects of powder admixture and laser parameters on the fabricated coatings' microstructure, tribological behavior and hardness. X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) with Scanning electron microscopy (SEM) was employed for the characterization of the microstructural evolution and phase identification, respectively. Additionally, the tribological experiment was conducted via UMT-2 –CETR reciprocating tribometer, and the coatings’ micro-hardness characteristics were examined using EmcoTEST DURASCAN. The micrographs exhibit no signs of porousness, cracks, or stress introduction, according to the results. For every manufactured sample, good metallurgical adhesion was obtained. By comparing the hardness of the ternary coating (Co–Ni–10Ti deposited at a scan speed of 1.2 m/min, with a hardness of 980 HV) to the substrate (Ti–6Al–4V, with a hardness of 330 HV), a hardness increase of approximately 2.96 times was observed. Furthermore, the Co–Ni–10Ti coating, deposited at a scan speed of 1.2 m/min, demonstrated a 51.1% reduction in the coefficient of friction (COF) compared to the base alloy, indicating superior anti-wear performance. The enhanced properties are attributed to the formation of hard intermetallic compounds such as Ti–Co, Co2Ti, Al5Co2, and Ni3Ti, along with their uniform distribution and finely tuned grain sizes.

REVIEW OF SILVER NANOPARTICLE SYNTHESIS USING LASER ABLATION; ITS CHARACTERIZATION, ANTIOXIDANT AND ANTIBACTERIAL FOR SKIN WOUNDS

This comprehensive review paper thoroughly investigates the synthesis of silver nanoparticles (AgNPs) through laser ablation and biosynthesis methods, exploring their potential applications in nanotechnology. The paper highlights the distinctive properties of AgNPs, including their notable antibacterial and anticancer attributes, wound healing capabilities, and therapeutic potential. The focus is specifically on the synthesis of small, spherical particles ranging from 2 to 5 nm. This investigation centers on key parameters crucial to the synthesis process, such as laser beam spot size, strength, ablation duration, and green synthesis factors like time, temperature, and concentration. In the realm of laser ablation optimization, the study scrutinizes the impact of various spot sizes on particle size distribution, variations in laser strength, and the intricate relationship between ablation duration and particle size. These analyses are strategically aligned to achieve the desired properties for the efficient production of AgNPs. Simultaneously, green synthesis techniques are employed to ensure an environmentally friendly approach, with careful consideration for factors like time, temperature, and concentration to attain targeted characteristics. The paper employs sophisticated characterization techniques, including dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV-Vis spectral analysis, for a comprehensive analysis of the synthesized AgNPs. DLS offers insights into size distribution and stability, SEM facilitates morphology visualization, and UV-Vis spectral analysis definitively confirms the presence of silver nanoparticles through characteristic absorption peaks.

Impact of molecular convection in time-resolved thermal lensing: a computational exploration

In this study, we comprehensively investigate thermal lens (TL) spectroscopy, known for its ultra-sensitivity in probing molecular properties through nonlinear heating responses to femtosecond lasers. Using time-resolved TL spectroscopy and numerical simulations, we focus on the influence of convection on heat generation and the resulting phase shift in the probe beam. We examined single-beam, dual-beam same wavelength, and dual-beam different wavelength scenarios, systematically investigating power dependence, pump beam spot size, and sample length limitations. Our findings reveal a direct relationship between the TL effect and pump power, resulting in decreased probe beam transmittance with increasing convection. Additionally, the TL strength grows within the Rayleigh regime as the sample length increases. Utilizing the same wavelength for the probe beam enhances the TL effect in dual-beam setups. Notably, tight focusing of the pump beam substantially reduces the lag between convection and conduction. Our empirical results closely match the experimental data, providing a thorough explanation of the TL process and its underlying principles. These insights can be applied to design and optimize TL-based optical devices and systems for higher sensitivity, highlighting the potential of TL spectroscopy in advanced molecular property probing.

CPOpt: A modular framework for genetic algorithm optimization and post-optimization analysis in complex charged particle optical design

This article reports on the development of an optimization framework for charged particle optics design (CPOpt). The optimization part of CPOpt involves a custom-developed Python multi-objective genetic algorithm (MOGA), which incorporates NSGA-II to optimize for multiple objectives, such as particle transmission and beam spot size. The simultaneous tuning of different types of parameters, such as electrode voltages and geometrical parameters, is facilitated by creating isolated groups of parameters. Modeling of parameter configurations is done with the charged particle optics simulation tool SIMION and a ZeroMQ-based communication interface enables a fully automated interaction with the MOGA. The post-optimization analysis part of CPOpt provides standardized and broadly applicable methods to identify suitable solutions, based on the outcome of the optimization part. Global sensitivity analysis, based on the Delta Moment-Independent-Measure in combination with dedicated Latin hypercube sampling, allows higher-level information about parameter sensitivity and robustness to be extracted, as well as effective randomized local optimization. Demonstrated on a two-lens system with intermediate aperture, the CPOpt framework effectively optimized the two conflicting objectives of reduced beam spot size and increased transmission at the detector plane for 12 parameters, covering both electrode voltages and geometrical parameters. The optimization process was performed within less than 11h on a workstation, while all the simulations required for the post-optimization analysis took another 7h. The additional computational effort for the post-optimization analysis can contribute to deliver solutions with high performance and stability.

Characterization of the LEBT based neutron source

Neutron generation by implantation and subsequent beam interaction of 40 keV deuterons at Soreq Applied Research Accelerator Facility (SARAF) low energy beam transport (LEBT) section was measured and characterized. The generation of 2.45 MeV neutrons by a deuteron beam of several mA was verified by a neutron spectrometer. Relative neutron yields were studied as a function of beam energy and beam spot size using two types of available implantation surfaces. The buildup of neutron yield was studied at long and short time scales. Absolute neutron yield was measured via activation at several conditions. The maximum neutron yield that could be obtained at the SARAF LEBT is of the order of 107 n/s, which presents a convenient source for testing neutron instrumentation in DC or pulsed mode.

Influences of Different Selective Laser Melting Machines on the Microstructures and Mechanical Properties of Co–Cr–Mo Alloys

Dental prostheses have been fabricated using various selective laser melting (SLM) machines; however, the impact of the type of machine on the microstructure and mechanical properties of Co–Cr–Mo alloys remains unclear. In this study, we prepared samples using two SLM machines (the small M100 and mid-sized M290) with different beam spot sizes (40 and 100 µm, respectively). The microstructures and tensile properties of the heated (1150 °C for 60 min) and as-built samples were evaluated. The grain sizes of the M100 samples were smaller than those of the M290 samples due to the small beam spot size of the M100 machine. Both heated samples exhibited recrystallized equiaxed grains; however, the amount of non-recrystallized grains remaining in the M290 sample exceeded that in the M100 sample. This suggests that the M100 samples recrystallized faster than the M290 samples after heating. The elongation of the M100 samples was higher than that of the M290 samples in the as-built and heated states, owing to the smaller grain size of the M100 samples. A comparison of the M100 and M290 SLM machines indicated that the M100 was suitable for producing dental prostheses owing to its good elongation and rapid recrystallization features, which shorten its post-heat-treatment duration.

Design and performance of a low-emittance electron gun for electron beam probe

An Electron Beam Probe (EBP) is preferable to provide a non-interceptive measurement of the transverse distribution of a dense bunched ion beam. During EBP operation, it was observed that the electron beam spot subjects to expansion when scanned across the ion beam due to the strong space charge field of the ion bunch, leading to significant degradation of spatial resolution. To mitigate this effect, a small electron beam spot is beneficial as demonstrated in previous research. This paper presents design details of a low-emittance, small-spot, and long-work-distance electron gun. Geometry optimization of the gun and focus lens is conducted using a multiobjective genetic algorithm (MOGA) interfaced with space charge simulation codes to maintain normalized thermal emittance within an acceptable increase and achieve a small spot at a long work distance. The emittance is measured using a slit-screen technique, resulting in a norm. rms emittance of 0.046(+-0.005) um*rad under low beam current conditions (50 nA). In high-resolution mode, a beam spot size of 0.6 mm (rms) is achieved at a work distance of 1.2 m with the combination of Einzel lens and solenoid. The gun has been successfully operated as part of EBP experiments for accurate and high-resolution measurement of ion beam width, demonstrating excellent agreement with wire scanner measurements with relative deviation not exceeding 1%.

Influence of orbital angular momentum of light on random spin-split modes in disordered anisotropic optical media

Spin–orbit interaction of light in a disordered anisotropic medium is known to yield spin split modes in the momentum domain because of the random spatial gradient of the geometric phase of light. Here, we have studied the statistics of such spin-split modes for beams carrying intrinsic orbital angular momentum through the quantification of momentum domain entropy and investigated its dependence on various beam parameters. The influence of the spatial structure of the beam and the phase vortex on the statistics of the spin split modes were separately investigated using input Laguerre–Gaussian and Perfect Vortex beams passing through a disordered anisotropic medium with controlled input disorder parameter, which was realized by modulating the pixels of a liquid crystal-based spatial light modulator. The results of systematic investigations on the impact of beam waist, spot size and topological charge of the vortex beam show that the influence of the spot size on the emergence of the random spin split modes is much more significant as compared to the other beam parameters.

Impact of Gaussian Beam Spot Size on Trapping Forces: Continuous versus Pulsed Beams

Impact of Gaussian Beam Spot Size on Trapping Forces: Continuous versus Pulsed Beams

Proton beam spot size and position measurements using a multi-strip ionization chamber

PurposeTo develop and characterize a large-area multi-strip ionization chamber (MSIC) for efficient measurement of proton beam spot size and position at a synchrotron-based proton therapy facility. Methods and MaterialsA 420 mm x 320 mm MSIC was designed with 240 vertical strips and 180 horizontal strips at 1.75 mm pitch. The MSIC was characterized by irradiating a grid of proton spots across 17 energies from 73.5 MeV to 235 MeV and comparing to simultaneous measurements made with a reference Gafchromic EBT3 film. Beam profiles, spot sizes, and positions were analyzed. Short term measurement stability and sensitivity were evaluated. ResultsExcellent agreement was demonstrated between the MSIC and EBT3 film for both spot size and position measurements. Spot sizes agreed within ± 0.18 mm for all energies tested. Measured beam spot positions agreed within ± 0.17 mm. The detector showed good short term measurement stability and low noise performance. ConclusionThe large-area MSIC enables efficient and accurate proton beam spot characterization across the clinical energy range. The results indicate the MSIC is suitable for pencil beam scanning proton therapy commissioning and quality assurance applications requiring fast spot size and position quantification.

An integrated system for measuring 3D dose distributions of carbon-ion pencil beams in regular QA practice

The accurate measurement of three-dimensional (3D) dose distribution of carbon-ion pencil beams in water is crucial for regular quality assurance (QA) practice. Although ionization chambers scanned in a water tank is conventionally used for this purpose, these measuring methods are time-consuming and labor-intensive. In addition, the beam of Heavy Ion Medical Machine (HIMM) changes continuously in each extracted duration, these methods cannot obtain the accurate 3D dose distribution. To solve these problems, an integrated system (PBDOSE) is conceived and established, which employs multi-strip ionization chambers (MSICs) to measure 2D lateral profile dose distributions. The lateral profile dose distribution in the context of various depths is measured by a mobile MSIC and normalized by the measurement of a reference MSIC to reduce the effect of beam instability. On this basis, a 3D dose distribution is created by stacking those profiles in depth direction. By conducting a single depth scan within 3 min at HIMM, information such as the 3D dose distribution, lateral contour images, the Bragg curve, beam spot size, beam position, incident direction, and energy of the beam can be obtained. The Bragg curve acquired from PBDOSE with statistical uncertainties of 1.5% was almost identical to those measured by a commercial water phantom. Besides that, the lateral profiles revealed a remarkable agreement with Gafchromic EBT3 film measurements within differences less than 0.1 mm. PBDOSE shows great prospects in the accurate and efficient measurement of 3D dose distribution for carbon-ion therapy, and the clinical application of this system will improve the efficiency of regular QA procedures to a great extent.

Effect of SiC addition on laser-based CoNi binary alloy coatings on Ti-6Al-4V alloy

This research explores the impact of variations in laser scanning speed and the incorporation levels of SiC-Ni-Co powders on Ti-6Al-4V alloy using laser surface cladding technique. Key parameters, including a consistent laser power of 700 W, a 4 mm beam spot size, a powder feed rate of 1.0 g/min, and a gas flow rate of 3 L/min, along with fixed powder compositions, were maintained. The laser scanning speeds were adjusted to 0.4 m/min, 0.8 m/min, and 1.2 m/min. Microstructural analyses were carried out using scanning electron microscopy (SEM) while Vickers microhardness was employed to assess coating hardness, and corrosion properties were evaluated using a linear potentiodynamic polarization technique. Following the corrosion attack, the protective oxides formed were identified through SEM and X-ray diffractometer (XRD). The results revealed a strong metallurgical relationship between the clad layer and the substrate, demonstrating the effectiveness of the laser-clad technique. Particularly, the highest laser scan speed exhibited the most significant improvements in hardness and corrosion resistance. The coatings displayed an average hardness value of 1269.20 HV0.1, a notable fourfold increase compared to the substrate's value of 334 HV0.1. Concerning corrosion, a clear correlation emerged between scan speed and polarization resistance, confirming that higher scan speeds could lead to enhanced polarization resistance.

Intensity distribution of the partially coherent Gaussian Schell vortex beam diffracted by classical axicon

Based on the mathematical framework of the partially coherent Gaussian Schell model vortex (PCGSMV) beam and the Huygens-Fresnel integral, we conducted a study to analyze the intensity distribution and depth of focus (DOF) of the PCGSMV beam as it propagates through a classical axicon. Our numerical results indicate the influence of factors such as the beam width, spatial degree of coherence, topological charge, and axicon base angle on the intensity distribution and DOF. In addition, we investigated the relationship between the beam spot size and propagation distance, as well as the effects of the spatial degree of coherence and propagation distance on the intensity profile. Our findings highlight the importance of the intensity values along the DOF for various applications, including the optical trapping and manipulation of micro-particles.

An artificial neural network based approach for predicting the proton beam spot dosimetric characteristics of a pencil beam scanning technique

Utilising Machine Learning (ML) models to predict dosimetric parameters in pencil beam scanning proton therapy presents a promising and practical approach. The study developed Artificial Neural Network (ANN) models to predict proton beam spot size and relative positional errors using 9000 proton spot data. The irradiation log files as input variables and corresponding scintillation detector measurements as the label values. The ANN models were developed to predict six variables: spot size in the x-axis, y-axis, major axis, minor axis, and relative positional errors in the x-axis and y-axis. All ANN models used a Multi-layer perception (MLP) network using one input layer, three hidden layers, and one output layer. Model performance was validated using various statistical tools. The log file recorded spot size and relative positional errors, which were compared with scintillator-measured data. The Root Mean Squared Error (RMSE) values for the x-spot and y-spot sizes were 0.356 mm and 0.362 mm, respectively. Additionally, the maximum variation for the x-spot relative positional error was 0.910 mm, while for the y-spot, it was 1.610 mm. The ANN models exhibit lower prediction errors. Specifically, the RMSE values for spot size prediction in the x, y, major, and minor axes are 0.053 mm, 0.049 mm, 0.053 mm, and 0.052 mm, respectively. Additionally, the relative spot positional error prediction model for the x and y axes yielded maximum errors of 0.160 mm and 0.170 mm, respectively. The normality of models was validated using the residual histogram and Q-Q plot. The data over fit, and bias were tested using K (k = 5) fold cross-validation, and the maximum RMSE value of the K fold cross-validation among all the six ML models was less than 0.150 mm (R-Square 0.960). All the models showed excellent prediction accuracy. Accurately predicting beam spot size and positional errors enhances efficiency in routine dosimetric checks.

Fiber optic photoacoustic gas sensor enhanced by multi-pass cell with overlapping phantom spots

A neotype fiber optic photoacoustic gas sensor with overlapping phantom spots based multi-pass is proposed, which greatly improves the reflection times and the length of gas absorption path. Moreover, the detection accuracy of photoacoustic spectroscopy (PAS) system is independent of the optical interference effect caused by overlapping spots, which is different from tunable diode laser absorption spectroscopy (TDLAS) technology. A mathematical model including light beam motion space, spot size and overlap discrimination of multi-pass structure based on overlapping phantom spots is established. The incident light is reflected up to dozens of times in the resonator with a diameter of only 8 mm. The emergent light does not need to converge on a photodetector, which reduces the difficulty of adjusting the optical path and promotes the realization of overlapping phantom spots. The experimental results show that the amplitude of photoacoustic signal is improved by about 40 times compared with the single spot structure. Appling high-sensitivity optical fiber cantilever to detect the sound pressure signal. The detection limit of C2H2 gas reaches 8.2 ppt. The normalized noise equivalent absorption (NNEA) coefficient of the gas sensor is achieved to be 9.3×10−11 cm−1WHz−1/2.

Influence of Grid Aperture Ratio on Electron Transmittance and Electron Beam Spot Size in Field Emission Processes of Carbon Nanotubes

Field emission is an important work mode for electron sources, and carbon nanotubes (CNTs) have been extensively studied for their good emission properties. It is well known that the parameters of the grid deeply influence the field emission performance of CNTs, a relationship that requires further elucidation. Therefore, in this study, the relationship between the grid aperture ratio and electron transmittance was studied through simulations and experiments. This study’s results indicate that the electron transmittance improved as the grid aperture ratio increased. Meanwhile, electron beam spot simulations and imaging experiments indicate that an increased grid aperture ratio will expand the cathode electron divergence, leading to a larger electron beam spot size. These results demonstrate that there is a trade-off in maintaining the grid aperture ratio between high electron transmittance and relatively small electron beam spot size, and the optimum grid aperture ratio is between 75% and 85%. These results will provide a reference for the design and optimization of X-ray tubes and other electron sources.

Depth of focus and intensity distribution of a lensacon illuminated by a partially coherent Gaussian Schell vortex beam

Using the extended Huygens–Fresnel principle, a cross-spectral density formula was developed for a Gaussian Schell model vortex (PCGSMV) beam diffracted through a lensacon (lens with an axicon). The intensity and depth of focus (DOF) shaped by the lensacon were calculated. Our numerical results show the relationship between the intensity distribution and depth of focus with the beam waist width as well as the spatial correlation of the coherence length. Furthermore, the relationship between the beam spot size and propagation distance was investigated. In the case of the lensacon tandem, the maximum intensity was greater than that attained by the axicon alone for the same beam parameters, and the DOF was smaller than that of the axicon alone. The vortex structure canceled out the low value of the spatial degree of coherence length. Our numerical model exhibited high-intensity values and high-quality Bessel rings along the DOF, which are critical for various applications.

Development of porous structure for broadening Bragg-peak in scanning carbon-ion radiotherapy: Monte Carlo simulation and experimental validation

PurposeThe present study aimed to develop a porous structure with plug-ins (PSP) to broaden the Bragg peak width (BPW, defined as the distance in water between the proximal and distal 80% dose) of the carbon ion beam while maintaining a sharp distal falloff width (DFW, defined as the distance along the beam axis where the dose in water reduces from 80% to 20%). MethodsThe binary voxel models of porous structure (PS) and PSP were established in the Monte Carlo code FLUKA and the corresponding physical models were manufactured by 3D printing. Both experiment and simulation were performed for evaluating the modulation capacity of PS and PSP. BPWs and DFWs derived from each integral depth dose curves were compared. Fluence homogeneity of 430 MeV/u carbon-ion beam passing through the PSP was recorded by analyzing radiochromic films at six different locations downstream the PSP in the experiment. Additionally, by changing the beam spot size and incident position on the PSP, totally 48 different carbon-ion beams were simulated and corresponding deviations of beam metrics were evaluated to test the modulating stability of PSP. ResultsAccording to the measurement data, the use of PSP resulted in an average increase of 0.63 mm in BPW and a decrease of 0.74 mm in DFW compared to PS. The 2D radiation field inhomogeneities were lower than 3 % when the beam passing through a ≥ 10 cm PMMA medium. Furthermore, employing a spot size of ≥ 6 mm ensures that beam metric deviations, including BPW, DFW, and range, remain within a deviation of 0.1 mm across various incident positions. ConclusionThe developed PSP demonstrated its capability to effectively broaden the BPW of carbon ion beams while maintaining a sharp DFW comparing to PS. The superior performance of PSP, indicates its potential for clinical use in the future.