Beam Profile Research Articles

Improved SPGD algorithm for optical phased array chip phase error correction in Lidar applications

Random phase errors in silicon-photonic-based OPA (optical phased array) chips can significantly affect their output beam quality, making efficient phase error correction an important requirement for Lidar systems utilizing OPA chip technology. We report an improved ASPGD algorithm for performing OPA random phase error correction with high efficiency and accuracy, especially for large channel count designs. We successfully demonstrated the ASPGD algorithm phase error calibration capability using a fabricated 16-channel chip, and we also showed that the ASPGD algorithm has significantly faster convergence and higher cosine similarity values for the corrected output beam profile compared with traditional SPGD and genetic algorithms, especially for higher channel count OPA chip designs. We believe our work can make an important contribution to the field deployment of OPA technology for chip scale long-range Lidar applications.

Amplitude and Phase Imaging of CW-THz Waves Using a Photomixing System with Coherent Detection

Continuous-Wave Terahertz (CW-THz) phase and amplitude imaging provides valuable insights into the interaction between THz waves and matter, particularly in low-absorption materials. This information is also essential for enhancing CW-THz beam profiling, a critical aspect in the design of free-space THz devices. Hereby, we introduce a single-pixel THz amplitude and phase imaging technique based on frequency scanning and fringe analysis, incorporated into a straightforward experimental setup. We validate the usefulness of the proposed approach by demonstrating two representative case studies. The first is a 3-D measurement of the amplitude and phase profile of a THz wave that is transmitted through a 3-D printed metalens. The second is beam profiling of a THz beam emitted from a photomixer antenna. In both cases, our results are in excellent agreement with previous predictions and validate the usefulness of this imaging technique. As such, we believe that the demonstrated approach will provide an important tool in the quest for establishing THz as an important method for a myriad of applications, including imaging, range finding and metrology.

Influence of the laser-plume interaction on the beam profile during deep-penetration welding with coherent beam shaping.

A high-power laser beam profiling system was set up to investigate the influence of the interaction between the laser beam and the process emissions during welding with a shaped beam profile. A positional instability of the beam on the workpiece in the order of magnitude of tens of µm and noticeable distortions of the beam shape were observed when no cross jet was used. Both perturbations were reduced when a cross jet was applied to remove the process emissions from the beam path and minimized when the cross jet was positioned closest to the workpiece.

Atomic fluorescence collection into planar photonic devices

Fluorescence collection from individual emitters plays a key role in state detection and remote entanglement generation, fundamental functionalities in many quantum platforms. Planar photonics have been demonstrated for robust and scalable addressing of trapped-ion systems, motivating consideration of similar elements for the complementary challenge of photon collection. Here, using an argument from the reciprocity principle, we show that far-field photon collection efficiency can be simply expressed in terms of the fields associated with the collection optic at the emitter position alone. We calculate collection efficiencies into ideal paraxial and fully vectorial focused Gaussian modes parameterized in terms of focal waist, and further quantify the modest enhancements possible with more general beam profiles, establishing design requirements for efficient collection. Toward practical implementation, we design, fabricate, and characterize two diffractive collection elements operating at λ = 397 nm; a forward emitting design is predicted to offer 0.25% collection efficiency into a single waveguide mode, while a more efficient reverse-emitting design offers 1.14% collection efficiency, albeit with more demanding fabrication requirements. Close agreement between simulated and measured emission for both designs indicates practicality of these collection efficiencies, and we indicate avenues to improved devices approaching the limits predicted for ideal beams. We point out a particularly simple integrated waveguide configuration for polarization-based remote entanglement generation enabled by integrated collection.

Quality Control And Dosimetric Accuracy Assessment Of Cobalt-60 Teletherapy Unit At Ssdl, Bangladesh

External beam radiotherapy, often known as teletherapy, is one of the most efficient ways to treat cancer since it targets harmful cells with radiation. Dosimetric accuracy of a recently installed Cobalt-60 teletherapy unit (Theratron Equinox100#2149, Initial Activity: 12000 Ci) at the Bangladesh Atomic Energy Commission's Secondary Standard Dosimetry Laboratory (SSDL), Savar, Dhaka, has been the main focus of this work. Several measurements are made that are necessary to ensure the accuracy of the Cobalt-60 teletherapy unit in terms of dosimetric level, specifically the accuracy of absolute and relative dosimetry. These measurements include the following dosimetric parameters: absorbed dose to water, percentage depth dose (PDD), beam profile, inter-chamber comparison (to ensure the highest level of dosimetry accuracy), and comparison of absorbed doses using two protocols named IAEA TRS-277 and IAEA TRS-398. The absorbed dose rate at reference field size (10 × 10 cm2) was found to be 1.548 Gy/min with an uncertainty of ±0.020. In the case of the inter-chamber comparison, the maximum deviation among values of absorbed dose to water for four Farmer chambers was 0.27% for Dw(Zref) and 0.26% for Dw(Zmax). The resultant output of this study may contribute to developing the treatment planning system in the realm of cancer treatment. Bangladesh Journal of Physics, 28(1), 1-10, June 2021

Real-time detection and auto-focusing of beam profiles from silicon photonics gratings using theYOLO model.

When observing chip-to-free-space light beams from silicon photonics (SiPh) to free space, manual adjustment of camera lens is often required to obtain a focused image of the light beams. In this Letter, we demonstrated an auto-focusing system based on the you-only-look-once (YOLO) model. The trained YOLO model exhibits high classification accuracy of 99.7% and high confidence level of >0.95 when detecting light beams from SiPh gratings. A video demonstration of real-time light beam detection, real-time computation of beam widths, and auto-focusing of light beams is also included.

Efficient and accurate commissioning and quality assurance of radiosurgery beam via prior-embedded implicit neural representation learning.

Dosimetric commissioning and quality assurance (QA) for linear accelerators (LINACs) present a significant challenge for clinical physicists due to the high measurement workload and stringent precision standards. This challenge is exacerbated for radiosurgery LINACs because of increased measurement uncertainty and more demanding setup accuracy for small-field beams. Optimizing physicists' effort during beam measurements while ensuring the quality of the measured data is crucial for clinical efficiency and patient safety. To develop a radiosurgery LINAC beam model that embeds prior knowledge of beam data through implicit neural representation (NeRP) learning and to evaluate the model's effectiveness in guiding beam data sampling, predicting complete beam dataset from sparse samples, and verifying detector choice and setup during commissioning and QA. Beam data including lateral profile and tissue-phantom-ratio (TPR), collected from CyberKnife LINACs, were investigated. Multi-layer perceptron (MLP) neural networks were optimized to parameterize a continuous function of the beam data, implicitly defined by the mapping from measurement coordinates to measured dose values. Beam priors were embedded into network weights by first training the network to learn the NeRP of a vendor-provided reference dataset. The prior-embedded network was further fine-tuned with sparse clinical measurements and used to predict unacquired beam data. Prospective and retrospective evaluations of different beam data samples in finetuning the model were performed using the reference beam dataset and clinical testing datasets, respectively. Model prediction accuracy was evaluated over 10 clinical datasets collected from various LINACs with different manufacturing modes and collimation systems. Model sensitivity in detecting beam data acquisition errors including inaccurate detector positioning and inappropriate detector choice was evaluated using two additional datasets with intentionally introduced erroneous samples. Prospective and retrospective evaluations identified consistent beam data samples that are most effective in fine-tuning the model for complete beam data prediction. Despite of discrepancies between clinical beam and the reference beam, fine-tuning the model with sparse beam profile measured at a single depth or with beam TPR measured at a single collimator size predicted beam data that closely match ground truth water tank measurements. Across the 10 clinical beam datasets, the averaged mean absolute error (MAE) in percentage dose was lower than 0.5% and the averaged 1D Gamma passing rate (1%/0.5mm for profile and 1%/1mm for TPR) was higher than 99%. In contrast, the MAE and Gamma passing rates were above 1% and below 95% between the reference beam dataset and clinical beam datasets. Model sensitivity to beam data acquisition errors was demonstrated by significant model prediction changes when fine-tuned with erroneous versus correct beam data samples, as quantified by a Gamma passing rate as low as 18.16% between model predictions. A model for small-field radiosurgery beam was proposed that embeds prior knowledge of beam properties and predicts the entire beam data from sparse measurements. The model can serve as a valuable tool for clinical physicists to verify the accuracy of beam data acquisition and promises to improve commissioning and QA reliability and efficiency with substantially reduced number of beam measurements.

Modeling Femtosecond Beam Propagation in Dielectric Hollow-Core Waveguides

The propagation of femtosecond pulses in guided structures is a matter of both fundamental and practical interest in nonlinear optics. In particular, hollow-core waveguides (HCWs) filled with a gas medium are fabricated and used as devices for the generation of attosecond pulses from high-order harmonics. In this process, the configuration of the laser field (intensity and phase) inside the waveguide is of crucial importance for enhancing the (well-known, low) efficiency of high-order harmonic generation (HHG). Here, we present numerical calculations which demonstrate the main features of the propagation process in fabricated HCWs. We consider a variety of experimental parameters like gas pressure, waveguide size, laser wavelength, and pulse energy and duration. In particular, the beam profile at the fiber input is found to be a sensitive parameter which influences the whole evolution of the laser field along the propagation. Our model is based on a split-step method modified to account for propagation in ionized media and is validated against experimental and theoretical data from the literature. Our results contribute to the description of the main features of beam propagation in HCWs and provide guiding directions for designing efficient configurations for HHG.

Second harmonic Bessel-Gauss beam shaping with elliptic axicon aberrations

The second harmonic (SH) of an axicon generated Bessel-Gauss beam is created through the nonlinear interaction of photons with a crystal, resulting in the energy doubling of the output photons. In this work, we show experimentally that in addition to frequency doubling, the SH of Bessel-Gauss beams under asymmetric aberrations from an elliptic axicon exhibit intriguing beam formation. Particularly, the central region of the SH beam profile is composed of two central spots of various geometries surrounded by nested ellipses; one of which is the configuration of two central gamma dots with similar radius knotted by nested ellipses for a zeroth-order Bessel-Gauss pump. These SH beams consistently maintain their spatial profile throughout propagation, reminiscing the behavior of screw dislocations in wave patterns. Our numerical simulations produce beam dynamics consistent with that of experiments and further implicate the remarkable interweaving of bright spots with dark vortices. This is especially noticeable when the beams dynamically oscillate along the optical axis, resulting in the genesis of spatially polarized beams with a knotted framework. The insights gained from our study establish a novel paradigm for exploring interactions of Bessel-like beams with vortex dynamics. This, in turn, has the potential to spark innovations in optical applications, fostering new methodologies to harness and manipulate complex light structures. Our experimental findings could spur new methods of generating logical states of light and new opportunities for material processing control. Published by the American Physical Society 2025

Fluorescent nanodiamond scintillators for beam diagnostics of EUV and soft X-ray in photolithographic applications.

Extreme ultraviolet (EUV) lithography is a cutting-edge technology in contemporary semiconductor chip manufacturing. Monitoring the EUV beam profiles is critical to ensuring consistent quality and precision in the manufacturing process. This study uncovers the practical use of fluorescent nanodiamonds (FNDs) coated on optical image sensors for profiling EUV and soft X-ray (SXR) radiation beams. We employed a positive electrospray ion source to deposit 100 nm FNDs onto indium tin oxide (ITO)-coated substrates, forming 1 μm thick films. The scintillation films exhibited approximately 50% transparency in the visible region and could emit red fluorescence from neutral nitrogen-vacancy (NV0) centers in the FNDs when exposed to EUV/SXR radiation. We evaluated the performance of a device featuring an FND coating on a fiber optic plate (FOP) attached to the sensor of a complementary metal-oxide semiconductor (CMOS) camera using synchrotron radiation across the 80-1400 eV energy range. At 91.8 eV (or a wavelength of 13.5 nm), the fiber-coupled device exhibited a noise-equivalent power density of 0.25 μW cm-2 Hz-1/2, approximately eight times lower than that of an f/1.0 lens-coupled system. This enhanced sensitivity makes the FND/FOP-based detection system useful for beam profiling of various EUV/SXR radiation sources. Our results highlight the promising potential of electrosprayed FND scintillators as a cost-effective and versatile diagnostic tool for advancing next-generation photolithography.

Modelling and Classification of Optical Beam Profiles Using Vision Transformer

Modelling and Classification of Optical Beam Profiles Using Vision Transformer

Tailoring beam profile and OAM spectrum in domain-engineered nonlinear photonic crystals

Nonlinear frequency conversion provides a powerful tool to generate and manipulate structured light at new wavelengths. In this work, to meet the demands of applications such as high-capacity optical communications and high-dimensional entanglement generation, we use ferroelectric domain engineering to generate frequency-doubled light beams carrying orbital angular momentum (OAM) superposition states and with adjustable radial intensity distribution. Angular and radial phase modulations were introduced into the modulation function of the second-order nonlinear coefficient distribution of lithium tantalate nonlinear photonic crystals, achieving simultaneous tailoring of the OAM spectrum and the radial intensity profile of the second harmonic (SH) waves. As a representative example, we demonstrate the generation of a SH wave that carries a comb-like OAM spectrum, with the radial intensity distribution concentrating on a ring with a specific radius. In addition, the nonlinear photonic devices developed in this work feature polarization insensitivity and broadband characteristics.

Development of a transportable neutron imager for localization of radioactive sources

Locating radioactive hot spots presents a significant challenge for the nuclear industry and security applications, such as waste management, decommissioning, radiation protection, and the management of nuclear accidents. The detection of fast-neutron emissions offers an alternative technique to gamma imaging for verifying the location of radioactive materials, particularly in cases where gamma imagers face challenges in detection. In this study, we present the performance of a prototype gamma-neutron imaging system based on a custom-fabricated plastic scintillator, designed to effectively discriminate between signals from gamma radiation, fast neutrons, and thermal neutrons.We conducted Geant4 simulations to investigate neutron interactions within the plastic scintillator and compared the simulation results with experimental data. Additionally, we performed experiments on the prototype using a proton beam at the CYRCé facility at IPHC, utilizing a CMOS Monolithic Active Pixel Sensor (MAPS) called MIMOSIS to analyze the beam profile. Through these efforts, we examined neutron interactions with our scintillator, validated the prototype's imaging capabilities under proton beam exposure, and conducted a calibration study of its energy response.

Silicon-via (Si-via) hole metrology and inspection by grayfield edge diffractometry

Silicon-via (Si-via) hole metrology and inspection by grayfield edge diffractometry

Laboratory demonstration of single-camera PPPP wavefront sensing using neural networks

Laser guide stars in astronomical adaptive optics systems have the focus anisoplanatism problem, especially for telescopes larger than 4 m in diameter. The Projected Pupil Plane Pattern (PPPP) offers an alternative solution by projecting a collimated laser beam across the telescope’s entire pupil. One significant challenge is dealing with gain-related issues, necessitating the use of two beam profiles obtained simultaneously from two different distances from the telescope pupil. In this work, we explore the integration of a convolutional neural network (CNN) with experimental data emulating PPPP. We investigate how CNNs can significantly simplify the PPPP design by enabling operation with a single beam profile. These results permit the development of the PPPP concept to use a single beam profile without distance-gain degeneracy. In this work, it is shown that a 10% residual error can be achieved for test data randomly chosen over the SNR range of 4 to 12.

Helical Surface Relief Formation by Two-Photon Polymerization Reaction Using a Femtosecond Optical Vortex Beam.

Optical vortices possess a helical phase wavefront with central phase dislocation and orbital angular momentum. We demonstrated three-dimensional microstructure formation using a femtosecond optical vortex beam. Two-photon polymerization of photocurable resin was induced by long-term exposure, resulting in the fabrication of cylindrical structures. The ring shape represents the intensity profile of optical vortex beam, and the diameter and height of the structures are related to the laser power. Periodic helical surface relief was observed on the inner surface. Significantly, the helical direction of the surface relief is consistent with the direction in which the orbital angular momentum acts and changes depending on the sign of the topological charge. Our proposed method can form three-dimensional microstructures with helical periodic surface relief, and the pitch is smaller than the diffraction limit without laser scanning. This method paves the way for further applications in optical devices such as three-dimensional chiral metamaterials.

Transfer matrix model of beam propagation and optimization method for bulk multi-pass cell

Abstract Bulk multi-pass cell (MPC) is an effective technique used for spectral broadening and temporal compression in the fields of ultrafast optics. In an actual experiment, due to mode-mismatching, the beam profile changes at each pass transmitting through the medium, which will damage the optical elements and has a negative impact on the nonlinear effects. In this paper, based on the symmetry configuration of MPC and ABCD transfer matrix, we propose the ABCD transfer matrix model for beam propagation and adjusted optimization method for input beam. To verify the model, the result is compared with the theoretical value of the resonator. The beam propagation and B-integral before and after mode-matching are calculated. The results demonstrate that the mode-matching adjustment method significantly improves beam quality and nonlinear effects during transmission. This technique provides a potential tool for the design, experiment and evaluation in the generation of ultrashort pulse.

Comprehensive evaluation of lens and planar circular ultrasonic transducer combinations to enhance C-scan imaging: a phantom study at 10 and 15 MHz

Abstract Objective. To evaluate the imaging capabilities of four polydimethylsiloxane-based acoustic lenses with subsonic refractive indices, focusing on a spherical lens and three designed aspherical lenses with varying focus. Approach. We investigated a spherical lens with a radius curvature of 8 mm (SL-R8), two aspherical lenses with focal lengths of 15 mm and 10 mm (AL15 and AL10), and an aspherical folding lens with a focal length of 10 mm (AFL10). The equation cross-section profile of an aspherical lens is calculated using the assumption that all trajectories passing through the lens have the same flight duration when they reach the focal point. Furthermore, we observed that we can fold this aspherical lens without greatly diminishing its focusing capability. Utilizing circular planar ultrasonic transducers at frequencies of 10 MHz and 15 MHz, we examined the reflected waveforms via pulse-echo tests and measured focal points and beam widths using a needle hydrophone in the acoustic intensity measurement system. The target resolution was assessed using a C-Scan imaging system. Main results. Analysis of the axial and lateral beam profiles revealed that AFL10 and AL10 lenses exhibited narrower beam widths at the focal point. We evaluate the AFL10 and AL10 lenses combined with a 15 MHz transducer for preclinical testing using standard medical phantoms containing microparticles in gelatin- and agar-based matrices. In conclusion, using these twocombinations, C-Scan imaging successfully formed a 25 µm backscatter inside the phantom image. Significance. Due to their high-resolution capabilities, applying cross-sectional profile equations in the lateral plane of the lens surface in linear ultrasonic array probes offers promises for early-stage medical diagnostics.

Ultrafast Airy Beam Generation with a Mode-Locked Fiber Laser

We generate an ultrafast Airy beam with a mode-locked fiber laser. A diffractive optical element is placed inside the laser cavity and applies phase modulation on the pulses propagating in the cavity. The pulsed Airy beam is then obtained by Fourier transform of the first order diffracted beam of the diffractive optical element. The experimental results show that the beam profile and propagation characteristics of the laser pulses are consistent with the theoretical analysis. The pulsed Airy beam fiber laser we constructed has the advantages of compactness, easy integration, low cost, and high stability and robustness, which are of great significance for applications in industrial and other tough environments.

Spatially Fractionated Radiotherapy with Very High Energy Electron Pencil Beam Scanning.


To evaluate spatially fractionated radiation therapy (SFRT) for very-high-energy electrons (VHEEs) delivered with pencil beam scanning. Radiochromic film was irradiated at the CERN Linear Electron Accelerator for Research (CLEAR) using 194 MeV electrons with a step-and-shoot technique, moving films within a water tank. Peak-to-valley dose ratios (PVDRs), depths of convergence (PVDR≤1.1), peak doses, and valley doses assessed SFRT dose distribution quality. A Monte Carlo (MI) model of the pencil beams was developed using TOPAS and applied to a five-beam VHEE SFRT treatment for a canine glioma patient, compared to a clinical 6 MV VMAT plan. The plans were evaluated based on dose-volume histograms, mean dose, and maximum dose to the planning target volume (PTV) and organs at risk (OARs).
Main Results:
Experimental PVDR values were maximized at 15.5 ± 0.1 at 12 mm depth for 5 mm spot spacing. A depth of convergence of 76.5 mm, 70.7 mm, and 56.6 mm was found for 5 mm, 4 mm, and 3 mm beamlet spacings, respectively. MC simulations and experiments showed good agreement, with maximum relative dose differences of 2% in percentage depth dose curves and less than 3% in beam profiles. Simulated PVDR values reached 180 ± 4, potentially achievable with reduced leakage dose. VHEE SFRT plans for the canine glioma patient showed a decrease in mean dose (>16%) to OARs while increasing the PTV mean dose by up to 15%. Lowering beam energy enhanced PTV dose homogeneity and reduced OAR maximum doses. The presented work demonstrates that pencil beam scanning SFRT with VHEEs could treat deep-seated tumors such as head and neck cancer or lung lesions, though small beam size and leakage dose may limit the achievable PVDR.&#xD.