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Optically pumped threshold fluences are a widely reported metric to benchmark the performance of thin‐film gain media and lasers. Estimating the threshold fluence for nonhomogeneous beams, such as a circular Gaussian excitation, is not trivial since the average fluence depends on the estimated spot diameter. Using an exemplary lead halide perovskite film, the inversion volume at different pump energies is mapped. It is shown that the peak fluence of an arbitrary spatial beam profile is more relevant at the threshold, as it provides an upper bound to the threshold fluence. Also, simple conversion factors to estimate the peak fluence using Gaussian excitation beams are provided and the methodology to arbitrary profiles is extrapolated. Furthermore, it is advocated for using flat‐top or uniform stripe excitations to unambiguously extract the threshold fluence, since these excitations display minor discrepancies between the average and peak fluence, and keep the inversion volume relatively constant during the measurement. [ABSTRACT FROM AUTHOR]

Optically pumped threshold fluences are a widely reported metric to benchmark the performance of thin‐film gain media and lasers. Estimating the threshold fluence for nonhomogeneous beams, such as a circular Gaussian excitation, is not trivial since the average fluence depends on the estimated spot diameter. Using an exemplary lead halide perovskite film, the inversion volume at different pump energies is mapped. It is shown that the peak fluence of an arbitrary spatial beam profile is more relevant at the threshold, as it provides an upper bound to the threshold fluence. Also, simple conversion factors to estimate the peak fluence using Gaussian excitation beams are provided and the methodology to arbitrary profiles is extrapolated. Furthermore, it is advocated for using flat‐top or uniform stripe excitations to unambiguously extract the threshold fluence, since these excitations display minor discrepancies between the average and peak fluence, and keep the inversion volume relatively constant during the measurement.

The maximum energy of photons from high-harmonic generation (HHG) increases with the wavelength of the driving laser. A free electron laser (FEL) is a continuously tunable light source in the mid-IR wavelength range and it is useful for investigating the extension of the accessible photon energy in HHG. Recently, the undulator magnets of the IR FEL at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, have been replaced, and then the output power of the FEL has increased. Here, we evaluate the pulse duration and focal beam size of the FEL and show that the LEBRA FEL with 2 and 3 μ m laser wavelengths under a 44 MHz bunch repetition mode can drive HHG. [ABSTRACT FROM AUTHOR]

The recognition, decoding and tracking of vortex patterns is of increasing importance in many fields, ranging from the astronomical observations of distant galaxies to turbulence phenomena in liquids or gases. Currently, coherent light beams with orbital angular momentum (OAM) are of particular interest for optical communication, metrology, micro-machining or particle manipulation. One common task is to identify characteristic spiral patterns in pixelated intensity maps at real-world signal-to-noise ratios. A recently introduced combination of polar mapping and Fast Fourier Transform (FFT) was extended to novel sampling configurations and applied to the quantitative analysis of the spiral interference patterns of OAM beams. It is demonstrated that specific information on topological parameters in non-uniform arrays of OAM beams can be obtained from significantly distorted and noisy intensity maps by extracting one- or two-dimensional angular frequency spectra from single or concatenated circular cuts in either spatially fixed or scanning mode. The method also enables the evaluation of the quality of beam shaping and optical transmission. Results of proof-of-principle experiments are presented, resolution limits are discussed, and the potential for applications is addressed. [ABSTRACT FROM AUTHOR]

We used a single-shot ptychographic microscope to image the complex-valued (intensity and phase) spatial profiles of multiple ultrashort pulses. Specifically, we present a characterization of a burst of three ultrashort pulses with three nanoseconds delays between pulses using data recorded by a single camera exposure with millisecond integration time. This scheme is promising for various applications, including characterizing spatiotemporal mode-locked or Q-switched lasers, potentially shedding light on their buildup dynamics.

The influence of thermal blooming on characterizations of focused general astigmatism Gaussian beams (GAGBs) propagating through the atmosphere is studied analytically and numerically. The analytical formula of distortion number of focused GAGBs is derived. It is found that a GAGB with smaller value of the rotation parameter has greater resistance to the thermal blooming effect, and a GAGB has greater resistance to the thermal blooming effect than a simple astigmatism Gaussian beam (SAGB), which may be useful in practice. On the other hand, there exists a maximum of the distortion number as the astigmatism parameter varies, i.e., the GAGB is most affected by thermal blooming when a certain value of the astigmatism parameter arrives, which should be avoided in practice. In addition, it is shown that the orbital angular momentum and the gradient force of GAGBs decrease because of thermal blooming effect in the atmosphere. [ABSTRACT FROM AUTHOR]

Mode decomposition is a powerful tool for analyzing the modal content of optical multimode radiation. There are several basic principles on which this tool can be implemented, including near-field intensity analysis, machine learning, and spatial correlation filtering (SCF). The latter is meant to be applied to a spatial light modulator and allows one to obtain information on the mode amplitudes and phases of temporally stable beams by only analyzing experimental data. As a matter of fact, techniques based on SCF have already been successfully used in several studies, e.g., for investigating the Kerr beam self-cleaning effect and determining the modal content of Raman fiber lasers. Still, such techniques have a major drawback, i.e., they require acquisition times as long as several minutes, thus being unfit for the investigation of fast mode distribution dynamics. In this paper, we numerically study three types of digital holograms, which permits us to determine, at the same time, the parameters of a set of modes of multimode beams. Because all modes are simultaneously characterized, the processing speed of these real-time mode decomposition methods in experimental realizations will be limited only by the acquisition rate of imaging devices, e.g., state-of-the-art CCD camera performance may provide decomposing rates above 1 kHz. Here, we compare the accuracy of conjugate symmetric extension (CSE), double-phase holograms (DPH), and phase correlation filtering (PCF) methods in retrieving the mode amplitudes of optical beams composed of either three, six, or ten modes. In order to provide a statistical analysis of the outcomes of these three methods, we propose a novel algorithm for the effective enumeration of mode parameters, which covers all possible beam modal compositions. Our results show that the best accuracy is achieved when the amplitude-phase mode distribution associated with multiple frequency PCF techniques is encoded by Jacobi–Anger expansion. [ABSTRACT FROM AUTHOR]

Foreground mitigation is critical to all next-generation radio interferometers that target cosmology using the redshifted neutral hydrogen 21 cm emission line. Attempts to remove this foreground emission have led to new analysis techniques as well as new developments in hardware specifically dedicated to instrument beam and gain calibration, including stabilized signal injection into the interferometric array and drone-based platforms for beam mapping. The radio calibration sources currently used in the literature are broad-band incoherent sources that can only be detected as excess power and with no direct sensitivity to phase information. In this paper, we describe a digital radio source which uses Global Positioning Satellite (GPS) derived time stamps to form a deterministic signal that can be broadcast from an aerial platform. A copy of this source can be deployed locally at the instrument correlator such that the received signal from the aerial platform can be correlated with the local copy, and the resulting correlation can be measured in both amplitude and phase for each interferometric element. We define the requirements for such a source, describe an initial implementation and verification of this source using commercial Software Defined Radio boards, and present beam map slices from antenna range measurements using the commercial boards. We found that the commercial board did not meet all requirements, so we also suggest future directions using a more sophisticated chipset. [ABSTRACT FROM AUTHOR]

Purpose: The recently released Ethos therapy system (Varian Medical Systems) allows for online CBCT‐guided adaptive radiation therapy (RT). The clinical introduction of multiple systems requires machine characterization and machine variation quantification to allow patient interchangeability between systems. Despite several clinical introductions, limited vendor‐independent information on machine performance is available. Our aim was to determine the relevant dosimetric and mechanical characteristics of individual machines and to quantify machine variations. Methods: Six Ethos treatment machines, equipped with a 6‐MV FFF beam including dual‐layer MLC and kV‐CBCT system, were recently introduced clinically after extensive machine characterization and pre‐configured beam model verification. Point doses and profiles were measured and compared to vendor‐provided reference data and dose calculations. Also, dose calculations were verified based on point measurements for non‐standard fields and dose distributions for optimized treatment plans. Agreements between dose profiles (dose distributions) were quantified using 1D (3D) γ‐analysis. Additionally, we quantified leaf transmission, dosimetric leaf gap (DLG) and couch attenuation, determined isocenter accuracy and kV‐MV isocenter coincidence and verified the kV‐CBCT system. Machine variations were quantified for all dosimetric and mechanical characteristics. Results: For all machines, distinct agreements were found between measurements and vendor‐provided reference data as well as measurements and dose calculations. Mean γ1%/1mm values for all profiles were below 0.30. All profiles, point measurements and dose distributions matched well among the six machines. Minimal machine variations were found in terms of DLG (0.05 mm), leaf transmission (0.001%), isocenter accuracy (0.08 mm), kV‐MV isocenter coincidence (0.15 mm), couch attenuation (0.69%), and CBCT imaging dose (0.29 mGy). Conclusions: This study demonstrates excellent agreement between individual Ethos therapy systems and vendor‐provided reference data as well as a pre‐configured beam model. Furthermore, our results show good consistency among all machines and provide valuable insights on relevant machine characteristics. The systematically obtained results provide benchmark data for future clinical introduction of Ethos therapy systems. [ABSTRACT FROM AUTHOR]

Mode decomposition is a powerful tool for analyzing the modal content of optical multimode radiation. There are several basic principles on which this tool can be implemented, including near-field intensity analysis, machine learning, and spatial correlation filtering (SCF). The latter is meant to be applied to a spatial light modulator and allows one to obtain information on the mode amplitudes and phases of temporally stable beams by only analyzing experimental data. As a matter of fact, techniques based on SCF have already been successfully used in several studies, e.g., for investigating the Kerr beam self-cleaning effect and determining the modal content of Raman fiber lasers. Still, such techniques have a major drawback, i.e., they require acquisition times as long as several minutes, thus being unfit for the investigation of fast mode distribution dynamics. In this paper, we numerically study three types of digital holograms, which permits us to determine, at the same time, the parameters of a set of modes of multimode beams. Because all modes are simultaneously characterized, the processing speed of these real-time mode decomposition methods in experimental realizations will be limited only by the acquisition rate of imaging devices, e.g., state-of-the-art CCD camera performance may provide decomposing rates above 1 kHz. Here, we compare the accuracy of conjugate symmetric extension (CSE), double-phase holograms (DPH), and phase correlation filtering (PCF) methods in retrieving the mode amplitudes of optical beams composed of either three, six, or ten modes. In order to provide a statistical analysis of the outcomes of these three methods, we propose a novel algorithm for the effective enumeration of mode parameters, which covers all possible beam modal compositions. Our results show that the best accuracy is achieved when the amplitude-phase mode distribution associated with multiple frequency PCF techniques is encoded by Jacobi–Anger expansion.

Concentrated Solar Power (CSP) utilizing solar tower power plants exhibits significant potential for dispatchable sustainable power generation and fuel production, by concentrating up to hundred thousand focal spots of individual mirrors onto one surface. The irradiance on the receiver is a critical parameter for power plant operators, not only to prevent component-damaging temperature peaks and gradients but also to optimize the distribution of heliostat's focal spots. Therefore, recent approaches aim to exploit images of isolated focal spots on a Lambertian target, taken on a day-to-day basis in most commercial power plants, to achieve more accurate flux predictions. State-of-the-art methods for flux measurements require additional equipment and are mostly time-intensive. This study introduces a novel methodology to derive single heliostat irradiance profiles using simple digital camera images, employing an image-to-image neural network. The model we propose is capable of generating accurate, high-resolution flux distributions from single images. It uniquely accounts for the target surface's irregularities and reflectivity as well as background irradiation, factors critical for precise measurements of individual focal spots. By incorporating these factors, our methodology offers a new scaling approach for the measured flux density based on a calculated total flux, obviating the need for additional equipment such as flux gauges or moving bars. This enables effortless integration into the daily calibration routine in-situ using the camera-target method. This seamless integration not only supports existing flux prediction methodologies but also paves the way for future enhancements by potentially improving the accuracy of overall flux prediction. • Introduces a UNet-based approach for enhanced flux calculation in camera-target method in CSP plants using digital camera images. • Addresses traditional camera-target method limitations by accounting for background irradiation and surface irregularities. • Seamlessly integrates UNet architecture into existing heliostat calibration workflows in CSP plants. • Method enables calculation of absolute flux values without the need of flux gauges. [ABSTRACT FROM AUTHOR]

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar+ ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– $20\times10$ −5 Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– $3.75\times10$ −9 AV−3/2. The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode. [ABSTRACT FROM AUTHOR]

Purpose: Unique characteristics of MRI-linac systems and mutual interactions between their components pose specific challenges for their commissioning and quality assurance. The Australian MRI-linac is a prototype system which explores the inline orientation, with radiation beam parallel to the main magnetic field. The aim of this work was to commission the radiation-related aspects of this system for its application in clinical treatments.Methods: Physical alignment of the radiation beam to the magnetic field was fine-tuned and magnetic shielding of the radiation head was designed to achieve optimal beam characteristics. These steps were guided by investigative measurements of the beam properties. Subsequently, machine performance was benchmarked against the requirements of the IEC60976/77 standards. Finally, the geometric and dosimetric data was acquired, following the AAPM Task Group 106 recommendations, to characterize the beam for modeling in the treatment planning system and with Monte Carlo simulations. The magnetic field effects on the dose deposition and on the detector response have been taken into account and issues specific to the inline design have been highlighted.Results: Alignment of the radiation beam axis and the imaging isocentre within 2 mm tolerance was obtained. The system was commissioned at two source-to-isocentre distances (SIDs): 2.4 and 1.8 m. Reproducibility and proportionality of the dose monitoring system met IEC criteria at the larger SID but slightly exceeded it at the shorter SID. Profile symmetry remained under 103% for the fields up to ~34 × 34 and 21 × 21 cm2 at the larger and shorter SID, respectively. No penumbra asymmetry, characteristic for transverse systems, was observed. The electron focusing effect, which results in high entrance doses on central axis, was quantified and methods to minimize it have been investigated.Conclusion: Methods were developed and employed to investigate and quantify the dosimetric properties of an inline MRI-Linac system. The Australian MRI-linac system has been fine-tuned in terms of beam properties and commissioned, constituting a key step toward the application of inline MRI-linacs for patient treatments.

Purpose: Unique characteristics of MRI-linac systems and mutual interactions between their components pose specific challenges for their commissioning and quality assurance. The Australian MRI-linac is a prototype system which explores the inline orientation, with radiation beam parallel to the main magnetic field. The aim of this work was to commission the radiation-related aspects of this system for its application in clinical treatments. Methods: Physical alignment of the radiation beam to the magnetic field was fine-tuned and magnetic shielding of the radiation head was designed to achieve optimal beam characteristics. These steps were guided by investigative measurements of the beam properties. Subsequently, machine performance was benchmarked against the requirements of the IEC60976/77 standards. Finally, the geometric and dosimetric data was acquired, following the AAPM Task Group 106 recommendations, to characterize the beam for modeling in the treatment planning system and with Monte Carlo simulations. The magnetic field effects on the dose deposition and on the detector response have been taken into account and issues specific to the inline design have been highlighted. Results: Alignment of the radiation beam axis and the imaging isocentre within 2 mm tolerance was obtained. The system was commissioned at two source-to-isocentre distances (SIDs): 2.4 and 1.8 m. Reproducibility and proportionality of the dose monitoring system met IEC criteria at the larger SID but slightly exceeded it at the shorter SID. Profile symmetry remained under 103% for the fields up to ~34 × 34 and 21 × 21 cm2 at the larger and shorter SID, respectively. No penumbra asymmetry, characteristic for transverse systems, was observed. The electron focusing effect, which results in high entrance doses on central axis, was quantified and methods to minimize it have been investigated. Conclusion: Methods were developed and employed to investigate and quantify the dosimetric properties of an inline MRI-Linac system. The Australian MRI-linac system has been fine-tuned in terms of beam properties and commissioned, constituting a key step toward the application of inline MRI-linacs for patient treatments. [ABSTRACT FROM AUTHOR]

The Neutron Radiography Reactor at Idaho National Laboratory (INL) has two beamlines extending radially outward from the east and north faces of the reactor core. The control rod withdrawal procedure has recently been altered, potentially changing power distribution of the reactor and thus the properties of the neutron beams, calling for characterization of the neutron beams. The characterization of the East Radiography Station involved experiments used to measure the following characteristics: Neutron flux, neutron beam uniformity, cadmium ratio, image quality, and the neutron energy spectrum. The ERS is a Category-I neutron radiography facility signifying it has the highest possible rank a radiography station can achieve. The thermal equivalent neutron flux was measured using gold foil activation and determined to be 9.61 × 106 ± 2.47 × 105 n/cm2-s with a relatively uniform profile across the image plane. The cadmium ratio measurement was performed using bare and cadmium-covered gold foils and measured to be 2.05 ± 2.9%, indicating large epithermal and fast neutron content in the beam. The neutron energy spectrum was measured using foil activation coupled with unfolding algorithms provided by the software package Unfolding with MAXED and GRAVEL (UMG). The Monte-Carlo N-Particle (MCNP6) transport code was used to assist with the unfolding process. UMG, MCNP6, and measured foil activities were used to determine a neutron energy spectrum which was implemented into the MCNP6 model of the east neutron beam to contribute to future studies.

The neutron radiography reactor (NRAD) is a 250 kW Mark-II Training, Research, Isotopes, General Atomics (TRIGA) reactor at Idaho National Laboratory, Idaho Falls, ID, USA. The East Radiography Station (ERS) is one of two neutron beams at the NRAD used for neutron radiography, which sits beneath a large hot cell and is primarily used for neutron radiography of highly radioactive objects. Additional fuel elements were added to the NRAD core in 2013 to increase the excess reactivity of the reactor, and may have changed some characteristics of the neutron beamline. This report discusses characterization of the neutron beamline following the addition of fuel to the NRAD. This work includes determination of the facility category according to the American Society for Testing and Materials (ASTM) standards, and also uses an array of gold foils to determine the neutron beam flux and evaluate the neutron beam profile. The NRAD ERS neutron beam is a Category I neutron radiography facility, the highest possible quality level according to the ASTM. Gold foil activation experiments show that the average neutron flux with length-to-diameter ratio (L/D) = 125 is 5.96 × 106 n/cm2/s with a 2σ standard error of 2.90 × 105 n/cm2/s. The neutron beam profile can be considered flat for qualitative neutron radiographic evaluation purposes. However, the neutron beam profile should be taken into account for quantitative evaluation.

Unambiguous determination of the electric field of arbitrary ultrashort pulses is the key for time and frequency standards, attosecond science, and precision spectroscopy. However, a single-step technique that can simultaneously and directly characterize the spectrum, spectral phase, and the carrier-envelope phase (CEP) information of an arbitrary ultrashort pulse remains elusive. This technological roadblock hinders the current field from studying non-repeating single-shot events, since ultrashort laser pulses are often unstable. Here, we introduce a single-step reference-free technique through polarization interfering electric field with phase inverted electric field (PIE-PIE) to directly measure arbitrary ultrashort pulses in single-shot operation without using any retrieval algorithm. PIE-PIE utilizes highly efficient spectral phase conjugation based on four-wave-mixing. The ability to fully determine the spectrum, spectral phase, and CEP of relatively low intensity single-shot pulses will revolutionize ultrafast sciences and enable studies of arbitrary non-repeating ultrafast events.

Highlights • Partially coherent vortex beam with periodical coherence properties is introduced theoretically and generated experimentally. • Intensity lattices with controllable beamlet can be formed through varying initial coherence width. • Partially coherent vortex beam with periodical coherence properties is useful for particle trapping and information transfer. Abstract We introduce a new kind of partially coherent vortex beam with periodical coherence properties, named optical coherence vortex lattices (OCVLs). With the help of the generalized Collins formula, we explore the propagation properties of the intensity and the complex degree of coherence of OCVLs focused by a thin lens. Compared to conventional partially coherent vortex beam, OCVLs display extraordinary propagation properties, i.e., a Gaussian beam spot evolves into multiple beam spots (i.e., intensity lattices) in the focal plane (i.e., in the far field). The intensity lattices with solid or hollow beamlets can be formed through manipulating the coherence width in the source plane. We also find that the topological charge of the OCVLs can be determined from the distribution of its complex degree of coherence in the focal plane. Furthermore, we report experimental generation of OCVLs. The OCVLs will be useful for particle trapping and information transfer. [ABSTRACT FROM AUTHOR]

As proton therapy is becoming an established treatment methodology for cancer patients, the number of proton centres is gradually growing worldwide. The economical effort for building these facilities is motivated by the clinical aspects, but might be also supported by the potential relevance for the research community. Experiments with high-energy protons are needed not only for medical physics applications, but represent also an essential part of activities dedicated to detector development, space research, radiation hardness tests, as well as of fundamental research in nuclear and particle physics. Here we present the characterization of the beam line installed in the experimental room of the Trento Proton Therapy Centre (Italy). Measurements of beam spot size and envelope, range verification and proton flux were performed in the energy range between 70 and 228 MeV. Methods for reducing the proton flux from typical treatments values of 10 6 –10 9 particles/s down to 10 1 –10 5 particles/s were also investigated. These data confirm that a proton beam produced in a clinical centre build by a commercial company can be exploited for a broad spectrum of experimental activities. The results presented here will be used as a reference for future experiments. [ABSTRACT FROM AUTHOR]

We demonstrate the influence on mode features with introducing typical intracavity perturbation and results of aberrated wavefront compensation in a folded-type unstable resonator used in high energy lasers. The mode properties and aberration coefficient with intracavity misalignment are achieved by iterative calculation and Zernike polynomial fitting. Experimental results for the relation of intracavity maladjustment and mode characteristics are further obtained in terms of S-H detection and model wavefront reconstruction. It indicates that intracavity phase perturbation has significant influence on out coupling beam properties, and the uniform and symmetry of the mode is rapidly disrupted even by a slight misalignment of the resonator mirrors. Meanwhile, the far-field beam patterns will obviously degrade with increasing the distance between the convex mirror and the phase perturbation position even if the equivalent disturbation is inputted into such the resonator. The closed-loop device for compensating intracavity low order aberration is successfully fabricated. Moreover, Zernike defocus aberration is also effectively controlled by precisely adjusting resonator length, and the beam quality is noticeably improved. [ABSTRACT FROM AUTHOR]

We demonstrate the influence on output coupling mode with introducing typical intracavity disturbation and results of aberrated mode compensation in a folded-type optical resonator used in high-energy lasers. The eigenmode profiles and relevant Zernike aberration with intracavity reflector misalignment are achieved by numerical calculation. Experimental result about the function of the reflector maladjustment and the mode features are described in terms of model reconstruction combined with Zernike annular polynomials. Results show that phase disturbation has significant influence on out-coupling beam property, and the uniform and symmetry of the mode are rapidly disrupted by a slight misalignment of the resonator reflectors. The influence on PSF profile in the far-field will be obviously different even if equivalent disturbation is inputted into the same cavity. The device of real-time controlling of the cavity reflector for compensating intracavity phase distortion is successfully constructed. In addition, Zernike defocus aberration is effectively controlled by precisely adjusting the resonator length. A high beam quality in the output coupling mode is realized, which is in good agreement with the analytical predictions. [ABSTRACT FROM AUTHOR]

A feasibility study of an experimental setup for the irradiation of biological samples at the cyclotron facility installed at the National Centre of Accelerators (Seville, Spain) is presented. This cyclotron, which counts on an external beam line for interdisciplinary research purposes, produces an 18 MeV proton beam, which is suitable for the irradiation of mono-layer cultures for the measurement of proton cell damages and Relative Biological Effectiveness (RBE) at energies below the beam nominal value. Measurements of this kind are of interest for proton therapy, since the variation of proton RBE at the distal edge of the Bragg curve may have implications in clinical proton therapy treatments. In the following, the characteristics of the beam line and the solutions implemented for the irradiation of biological samples are described. When dealing with the irradiation of cell cultures, low beam intensities and broad homogeneous irradiation fields are required, in order to assure that all the cells receive the same dose with a suitable dose rate. At the cyclotron, these constraints have been achieved by completely defocusing the beam, intercepting the beam path with tungsten scattering foils and varying the exit-window-to-sample distance. The properties of the proton beam thus obtained have been analysed and compared with Monte Carlo simulations. The results of this comparison, as well as the experimental measurement of the lateral dose profiles expected at the position of samples are presented. Meaningful dose rates of about 2⁻3 Gy/min have been obtained. Homogeneous lateral dose profiles, with maximum deviations of 5%, have been measured at a distance of approximately 50 cm in air from the exit window, placing a tungsten scattering foil of 200 μm in the beam path.

This work presents four methods based on phase-space tomography for the characterization of the spatial structure of optical beams - the results of my PhD thesis. Each technique is optimal for characterizing beams with a particular symmetry. All methods are experimentally exercised to prove their feasibility in real world applications. [ABSTRACT FROM AUTHOR]

Eigenmode of resonators with asymmetric circular mirrors based on misalignment passive positive-branch unstable resonator is investigated in the paper. To do so, we use iterative algorithm to simulate the effect of intracavity phase perturbation on eigenmode structure properties of the passive confocal unstable resonator. On this basis, further experiment of output beam properties on a misaligned passive unstable laser resonator has been performed by adopting Hartmann–Shack (H–S) method and Zernike modal wavefront reconstruction. Wavefront distribution and the first 35-order Zernike coefficient included in the wavefront are obtained. The results show that intracavity tilt perturbation notablely affects outcoupled beam intensity distribution, and will also increase some high-order aberrations of beam phase properties. However, low-order Zernike tilt aberration is the main component with phase-tilted perturbation is introduced into resonator cavity. Defocus, low-order astigmatism and coma aberration will all be brought with the augument of phase tilt aberration, which will obviously degrade output beam quality. When intracavity compensating elements are adopted for optical aberration correction, the correction of tilt aberration should be considered first. [ABSTRACT FROM AUTHOR]

Some representative factors of intracavity perturbation will obviously degrade output power and beam mode properties for crystal passive Q -modulated solid-state lasers. In this paper, eigenmode of resonators using general asymmetric circular mirrors in solid-state lasers is briefly discussed, moreover, experiment analysis of the output beam quality on a passive Q -switched zig-zag slab Nd:YAG laser has been presented by adopting Hartmann–Shack (H–S) method and Zernike mode reconstruction theory. In this way, the PV and RMS errors of the wavefront aberration, each order Zernike aberrations can be acquired accurately, distribution of circle energy in far-field and other beam evaluation factors can also be obtained by further calculation, so beam mode properties and quality can be analyzed comprehensively. Experimental results illuminate that wavefront aberration of the laser is concentrated in the frontal 10 ranks of Zernike aberration, mainly including the defocus Z 3 , the low-order astigmatism Z 5 , the coma aberration Z 6 and the spherical aberration Z 10 because of the crystal thermal effect and the intracavity phase perturbation. [ABSTRACT FROM AUTHOR]

The eigenmode of resonators with symmetric circular mirrors used in solid-state lasers is investigated. Further experiments on output beam quality on a passive Q-switched zigzag slab Nd:YAG laser have been performed by adopting Hartmann-Shack and Zernike-mode reconstruction methods. By the means of peakvalley and root mean square errors of the wavefront distribution, each order of Zernike aberrations are achieved accurately. Moreover, the distribution of circle energy in the far-field and corresponding beam evaluation factors can also be obtained by further calculation. Experimental results indicate that the wavefront aberration is mainly concentrated in the first 10 Zernike aberrations, which mainly includes the defocus Z3, the low-order astigmatism Z5, the coma aberration Z6, and the spherical aberration Z10, because of the crystal thermal effect and the intracavity phase perturbation. The method can be used to further analyze the compensation of intracavity aberration and optimal design for such lasers. [ABSTRACT FROM AUTHOR]

We report a method for characterizing the focussing laser beam exiting the objective in a laser scanning microscope. This method provides the size of the optical focus, the divergence of the beam, the ellipticity and the astigmatism. We use a microscopic-scale knife edge in the form of a simple transmission electron microscopy grid attached to a glass microscope slide, and a light-collecting optical fibre and photodiode underneath the specimen. By scanning the laser spot from a reflective to a transmitting part of the grid, a beam profile in the form of an error function can be obtained and by repeating this with the knife edge at different axial positions relative to the beam waist, the divergence and astigmatism of the postobjective laser beam can be obtained. The measured divergence can be used to quantify how much of the full numerical aperture of the lens is used in practice. We present data of the beam radius, beam divergence, ellipticity and astigmatism obtained with low (0.15, 0.7) and high (1.3) numerical aperture lenses and lasers commonly used in confocal and multiphoton laser scanning microscopy. Our knife-edge method has several advantages over alternative knife-edge methods used in microscopy including that the knife edge is easy to prepare, that the beam can be characterized also directly under a cover slip, as necessary to reduce spherical aberrations for objectives designed to be used with a cover slip, and it is suitable for use with commercial laser scanning microscopes where access to the laser beam can be limited. [ABSTRACT FROM AUTHOR]

The 'brightness' of coherent beams such as lasers is known as 'radiance' in radiometric terms. It is a concept which is rarely taken into account in laser material processing, laser system design, and for the characterization of laser beams. The typical beam parameters such as: laser power; spot size; intensity; wavelength; beam divergence and the beam propagation factor - M, combined together are factors which determine the 'radiance' of lasers or energy beams in general. The concept of 'brightness' ('radiance' in particular), and how the laser beam parameters contribute to affect 'radiance', has not so far been reported in previous literature. Thus, we have investigated the theoretical 'radiance' for each parameter in relation to one another. In addition, a rather suitable empirical equation to determine the 'radiance' was also introduced herein, since, the existing equation for calculating 'brightness' do not employ the total power intensity of the beam. Based on this, we consider 'power density' rather than the 'output power' for determining radiance of a selected 1.064 μm wavelength Nd:YAG laser for a set laser processing parameter window. The analytical investigation firstly concluded that the inclusion of 'power density' into the equation takes in account of 'spot size' and 'laser power' to cover all laser beam parameters. Secondly, the results have shown wavelength to be the most contributory parameter to influence the radiance value followed by power density, M, laser power and lastly the spot size of the laser beam. This was for a set-condition applied, but is generically applicable to different conditions and parameters, whereby, the same tendency would occur. This novel concept of brightness (radiance), of light sources such as a laser beam is not just useful for process control during laser material processing, but could prove to be a very effective concept for laser beam characterization, and in laser system design for enhancing the 'brightness' or 'radiance' of lasers. Also not just lasers but, the concept could be applicable for other energy beams in general. [ABSTRACT FROM AUTHOR]

The International Organization for Standardization (ISO), in collaboration with the academic community, has developed and published a comprehensive system of standards for the characterization of optical components and laser beams. Our study offers a pedagogical introduction to the theory and application of laser beam characterization in accordance with ISO 13694:2018 and ISO 11145:2018. The characterizing parameters of each ISO standard are presented, defined mathematically, and explained in detail through the use of a minimum working example. A laser beam applied to an actual industrial process [laser-assisted bonding (LAB) process in the semiconductor packaging industry] is thoroughly analyzed to help the reader understand and interpret the characterizing results. Background noise correction and unit conversion methods are also discussed. We target researchers new to the field of laser beam analysis who want the acquire background knowledge, as well as more experienced researchers who want to implement their own laser beam analysis software and propose new definitions for their specific application. Although our study deals with only two ISO standards, the methods covered in our study can be easily applied to other norms that fit the reader's application. Our study should not be treated as a full review of the LAB process nor of the beam profiling instruments and measurement principles. These are only mentioned to enhance the reader's learning experience. [ABSTRACT FROM AUTHOR]

The minimum size of objects or geometrical features that can be distinguished within a laser scanning point cloud is called the resolution capability (RC). Herein, we develop a simple analytical expression for predicting the RC in angular direction for phase-based laser scanners. We start from a numerical approximation of the mixed-pixel bias which occurs when the laser beam simultaneously hits surfaces at grossly different distances. In correspondence with previous literature, we view the RC as the minimum angular distance between points on the foreground and points on the background which are not (severely) affected by a mixed-pixel bias. We use an elliptical Gaussian beam for quantifying the effect. We show that the surface reflectivities and the distance step between foreground and background have generally little impact. Subsequently, we derive an approximation of the RC and extend it to include the selected scanning resolution, that is, angular increment. We verify our model by comparison to the resolution capabilities empirically determined by others. Our model requires parameters that can be taken from the data sheet of the scanner or approximated using a simple experiment. We describe this experiment herein and provide the required software on GitHub. Our approach is thus easily accessible, enables the prediction of the resolution capability with little effort and supports assessing the suitability of a specific scanner or of specific scanning parameters for a given application. [ABSTRACT FROM AUTHOR]