Beam Intensity Research Articles

Enhancement of cascaded frequency upconversion by ultrafast temporal correlation of twin beams.

We experimentally and numerically study the effect of ultrafast temporal correlations in two-stage frequency upconversion pumping by using intense twin beams. Enhancement in the upconversion efficiency of each stage due to ultrafast temporal correlation is evaluated by varying the time delay between pumping beams. It is found that the temporal correlation of the twin beams is transferred to the first upconverted beam, thereby also enhancing the efficiency of the second sum-frequency generation (SFG). This result suggests that temporal correlations play an important role in enhancing the efficiency of light sources that incorporate a parametric downconversion process.

Incoherent tune measurement of an ion storage ring using single ions

The measurement of betatron tunes is important in the studies of beam dynamics in circular accelerators. Here, we report a new method to extract the fractional tune values using revolution times of single ions stored for a few hundred turns in a heavy-ion storage ring utilizing a single time-of-flight detector. The experiment was done at the experimental Cooler Storage Ring (CSRe) in Lanzhou. The unbunched cocktail secondary beam was injected into the ring and allowed to coast without further excitation. Since the average number of simultaneously stored ions inside the 128.8 m-circumference ring was merely ∼20, the obtained tune values are considered to be incoherent. Given that the revolution time of an individual ion is related to its momentum, the chromaticity of the ring could be addressed. Moreover, the data indicate a possible beam mismatch in vertical direction y^ at the injection into CSRe. The new method is developed for ultralow beam intensities and is thus a sensitive approach to tune measurements. Thanks to its simplicity, the method can straightforwardly be employed at other circular accelerators by applying the same detection approach. Published by the American Physical Society 2024

Tight focusing of hybridly polarized optical vortex

In this work, using the Richards-Wolf formalism, we consider the sharp focusing of optical vortices with hybrid polarization, which combines the properties of azimuthal and circular polarizations. It is shown that these beams have a number of interesting properties: the intensity in such beams rotates with distance from the focal spot, and the longitudinal component of the spin angular momentum has an asymmetric appearance.

Development of a non-intercepting weak beam current measurement electronics for Heavy Ion Accelerator Facility in Lanzhou.

Non-destructive measurements of low-intensity charged particle beams are particularly challenging for beam diagnostics. At the Heavy Ion Accelerator Facility in Lanzhou (HIRFL), beams with weak currents below 1 µA are often provided for experiments. The detection of such low beam current is below the threshold of typical standard beam current transformers. Therefore, a low-intensity monitoring system is developed by using a sensitive capacitive pick-up (PU) and low-noise electronics. This device measures beam currents by digitally analyzing the amplitude of the PU signals using a homodyne detection scheme. During lab tests, the amplitude nonlinearity is <0.5% in the operational range of 1 nA-45 µA and the amplitude resolution is 0.94 nA. At present, four measurement systems for low beam currents are installed at HIRFL for the monitoring of standard operating conditions with low beam currents below 1 µA. After an absolute calibration with a Faraday cup, it can be used for accurate beam intensity measurement with a current resolution of about 1 nA.

Comparison of wavefront sensing and ablation imprinting for FEL focus diagnostics at FLASH2

Extreme ultraviolet (EUV) photon beam characterization techniques, Hartmann wavefront sensing and single shot ablation imprinting, were compared along the caustic of a tightly focused free-electron laser (FEL) beam at beamline FL24 of FLASH2, the Free-electron LASer in Hamburg at DESY. The transverse coherence of the EUV FEL was determined by a Young’s double pinhole experiment and used in a back-propagation algorithm which includes partial coherence to calculate the beam intensity profiles along the caustic from the wavefront measurements. A very good agreement of the profile structure and size is observed for different wavelengths between the back-propagated profiles, an indirect technique, and ablation imprints. As a result, the Hartmann wavefront sensor including its software MrBeam is a very useful, single shot pulse resolved and fast tool for non-invasive determination of focal spot size and shape and also for beam profiles along the caustic.

Self‐Excited Free‐Standing VO2 Film for Infrared Optical Limiter

AbstractEffective optical limiters (OLs) are necessary devices for the protection of various sensitive photo‐detectors, cameras, infrared sensors, or even the human eyes once encountering unexpected high‐intensity illumination or laser blinding attacks. Vanadium dioxide (VO2) shows pronounced infrared switching behavior across the phase transition, which is considered as an idea optical limiter for broad‐band infrared laser protection. However, the self‐adapting optical limiter function based on VO2 is quite difficult to realize since the open‐state absorptance of the VO2 layer is always very low, which makes the laser irradiation cannot trigger the phase transition quickly. In the current study, a self‐excited VO2 infrared optical limiter is proposed, which is integrated by a transferred VO2 layer, InGaAs micro/nano wires, and a local heater. Based on the“optical response–electric heating” strategy, the phase transition of VO2 layer can be quickly triggered once the incident laser beam intensity exceeds the pre‐set threshold value. In addition, this integrated device has an excellent switching ratio, flexible controllability, and stability. This work achieves a practical VO2 optical limiter device and provides a promising strategy for developing VO2‐based integrated multifunctional devices in the future.

New accelerator designs: NIMMS

Abstract Purpose This article summarises the presentation given at the “Hadrontherapy: status and perspectives” event. Methods Structure, methodology, and objectives of the Next Ion Medical Machine Study collaboration are introduced. Its four Work Packages are: small synchrotrons for particle therapy, curved superconducting magnets for synchrotrons and gantries, superconducting gantry design, and high-frequency ion linacs. Synchrotrons under study include a superconducting design for carbon ion therapy, and a normal-conducting design for ions up to helium. Superconducting magnet R&amp;D is carried out in two European projects. Within the scope of these projects, five magnet demonstrators with different technologies are in different phases of design and production. Beam optics and mechanical design of a superconducting gantry for carbon ions is being developed. A high-frequency linac design has been completed, and tests are starting on a prototype high-frequency injector. Results The designs of two facilities based on NIMMS technological developments are presented. A carbon ion research and therapy facility was designed for the SEEIIST project, based on a conventional synchrotron with high beam intensity. A smaller facility aimed at cancer therapy and research with light ions, in particular helium beams has also been designed. Both facilities can produce FLASH-type beams. Conclusions The traditional design of carbon ion therapy facilities can be improved by adding new features as higher beam intensity and new beam extraction schemes. A cost-effective alternative to the traditional design is a compact facility for light ions, exploiting the potential for treatment with helium ions and allowing an experimental programme with different ion species.

Theoretical realization of tunable hollow beams using a periodical ring structure with a complex phase

Hollow beam is a peculiar structure beam, which has been widely used in various areas. Here, we propose a novel diffraction optical element to generate tunable hollow beams. This element is composed of periodic concentric rings. The phase of each ring is periodically distributed between −π and π and satisfies a complex variable function. By tuning the parameters of the structure, we can flexibly manipulate the size and length of the hollow beam. The length of the beam can be increased from 98 λ to 248 λ, and the full width at half maximum varies from 0.43 λ to 0.61 λ. Moreover, the light intensity and side lobe of the hollow beam can also be regulated using the designed diffraction optical element. The potential applications of this highly tunable hollow beam include optical nanomanipulation, microscopic imaging, and nanolithography.

Longitudinal ion-clearing mechanism in space-charge neutralization of low energy beams

In electron guns, generating high-intensity beams comes with the cost of increasing the number of secondary ions produced by the residual gas ionization which can be a limiting factor in the cathode lifetime. However, it is often overlooked that the longitudinal potential generated by the beam can be the main factor influencing secondary ions to drift back toward the source and limit the maximum beam intensity. Using 3D simulations, this paper shows how the flux of trapped ions depends on the beam parameters. The results provide a practical framework that can be used as a guide in the design of the electron gun focal point to mitigate the ion back bombardment. Published by the American Physical Society 2024

Symmetric and asymmetric Tricomi-Gaussian beams in a gradient-index medium

In this paper, the propagation dynamics of the Tricomi-Gaussian Beam (TGB) in a gradient-index medium is studied. Influences of various beam parameters, the gradient-refractive index coefficient, and vortices on the propagation of TGB are investigated thoroughly. The research is mainly on the transmission characteristics of TGB with different modes, including symmetric and asymmetric patterns. Notably, the manipulations of beam modes, propagation trajectory, and intensity distribution of TGB by varying beam parameters α and β are explored. In addition, the autofocusing properties of TGB under off-axis conditions are investigated, which could find potential applications in optical trapping, laser energy focusing, and photonic waveguiding.

Study of curtaining effect reduction methods in Inconel 718 using a plasma focused ion beam.

The curtaining effect is a common challenge in focused ion beam (FIB) surface preparation. This study investigates methods to reduce this effect during plasma FIB milling of Inconel 718 (nickel-based superalloy). Platinum deposition, silicon mask and XeF2 gas injection were explored as potential solutions. These methods were evaluated for two ion beam current conditions; a high ion beam intensity condition (30kV-1µA) and a medium one (30kV-100nA) and their impact on curtaining reduction and resulting cross-section quality was assessed quantitatively thanks to topographic measurements done by atomic force microscopy (AFM). XeF2 assistance notably improved cross-section quality at medium current level. Pt deposition and Si mask individually mitigated the curtaining effect, with greater efficacy at 100nA. Both methods also contributed to reducing cross-section curvature, with the Si mask outperforming Pt deposition. However, combining Pt deposition and Si mask with XeF2 injection led to deterioration of these protective layers and the reappearance of the curtaining effect after a quite short exposure time.

Degraded image restoration of vortex beam array based on deep learning

The phase aberration and intensity fluctuation of the vortex beam array caused by atmospheric turbulence decrease the decoding accuracy of the optical communication system. This paper proposes an end-to-end turbulence-degraded image restoration method based on deep learning to solve the problem. The K-means clustering algorithm is employed to obtain the coordinate information of each beam in the array, and the distorted vortex beam array is segmented. The neural network constructed is used to restore the degraded image of a single vortex beam obtained by segmentation. Then the restored intensity image of the vortex beam array is obtained by combining the existing coordinate information. The simulation results show that the intensity correlation coefficients of the 3 × 3 rectangular distribution Laguerre–Gaussian beam arrays are increased to more than 0.99 after restoring from 1000 meters of transmission in both varied and unknown turbulence intensities, alongside differing CCD signal-to-noise ratios. This method does not require wavefront reconstruction, which further improves the restoration speed and saves computational resources, and has good generalization ability and robustness in quickly restoring the distorted light intensity of vortex beams. The results provide a theoretical basis for studying atmospheric turbulence influence mitigation techniques for vortex optical communication.

Structural intensity in thin plates and beams under transient and stationary forces using time-resolved, full-field optical slope measurements

Structural intensity, or structure-borne intensity or power flow, was introduced in the 1970s and implemented at that time using contact sensors like accelerometers. Point and contactless measurement methods removed added mass and sensor size constraints. Time-resolved and full-field vibration measurement techniques now open new perspectives for the estimation of structural intensity, but these prospects also come with many challenges. In this work, we study the applicability of optical deflectometry measurements to calculate the structural intensity in thin plates or beams under transient and stationary loadings. Since deflectometry directly provides slope fields, a slope formulation of structural intensity is proposed and evaluated. The effect of various parameters like frame rate (sampling frequency) and spatial resolution is studied from a numerical point of view on a simply-supported plate. Experimental results are then presented on a simply-supported plate and on a cantilever beam. Numerical and experimental results allow identifying the main challenges related to the implementation of structure intensity estimation using full-field and time-resolved data.

Nasopharyngeal carcinoma in a young adolescent with unilatral palatal palsy and neck mass – A rare case report

Less than 1% of all head and neck neoplasms are juvenile nasopharyngeal angiofibromas, a cancer almost exclusively found in adolescent males. Here we present a case report of 14 year old male presented with neck swelling, nasal discharge mixed with blood, right sided proptosis and right sided palatal palsy where we performed CECT scan of the patient which showed homogenous opacity over nasopharynx extending to soft palate and posteriorly to C1 vertebra and DNE was performed. Later patient was planned for DNE along with biopsy which came out to be undifferentiated non-keratinized squamous cell carcinoma grade III. Further patient received external beam intensity modulated radiation therapy with complete response to treatment.

Dual-mode rectangular microwave cavity for precision spectroscopy of hyperfine structure in muonium

Precision microwave spectroscopy of the ground-state hyperfine structure in muonium provides a stringent test of the Standard Model in particle physics. The MuSEUM collaboration is preparing for such a measurement, aiming for precision down to ≈1ppb, utilizing the world’s most intense pulsed muon beam at J-PARC. The measurement of the Zeeman-split structure with an external magnetic field of 1.7T also precisely determines the muon’s magnetic moment (≈10ppb). In the future, improved precision of the magnetic moment can be potentially obtained by measurements with different magnetic field strengths, however, it entails upgrading current cylindrical microwave cavities to rectangular ones. As the first step for the upgrade, we have developed a dual-mode rectangular cavity for the measurement with 2.9T field. The electromagnetic design and production have been established, and frequency sweeping with two desired modes has been successfully demonstrated. Moreover, the overall performance of the measurement at 2.9T field was evaluated with Monte Carlo simulations. These studies pave the way for a further extension of the MuSEUM experiment at various strengths of the magnetic fields.

Highly focused beam generated with a height tuned micro-optical structure for high contrast microscopic imaging

Light sheet illumination technology improves the signal-to-noise ratio, resolution, and reduces scattered backgrounds for biological microscopic detection system. Here, we developed a novel micro-optical structure to produce a focused and uniform beam for the enhancement of imaging contrast. The beam intensity and working distance can be modified by adjusting the height and period of the structure. Our experiments successfully recorded structured light illumination, demonstrating the ability of the structure to capture high-contrast imaging data. We compared the light fields generated with and without the structure to assess the imaging quality, revealing a maximum 4.78-fold improvement in the signal-to-noise ratio. This work provides a potential method for high-resolution and high-contrast light sheet fluorescence microscopic detection.

Neutralized, intense-ion beams for fusion

A charge- and current-neutralized, intense-ion beam (IIB) will propagate undeflected in a magnetized plasma by the E×B , or diamagnetic, drift for a distance large compared to the beam-ion gyro-radius. This propagation occurs because of collective plasma effects when the beam-energy density is sufficient to sustain the polarization-electric field, or diamagnetic-screening currents. Our principal interest is the E×B drift, with β=Ebeam/Efield<1 . IIBs are characterized by parameters in the range: 0.1–2 MeV ion energy, 1–100 MA m−2 ion-current density, and 17–350 kW average power produced on repetitively-pulsed systems. Multi-MW average-beam power is possible with appropriate modifications to the power supply and ion-source/accelerator. IIBs can be focused geometrically, and/or magnetically, to spot sizes of the order of a few cm’s and their angular divergence is typically, ∼15 mRadians, suitable for long-range propagation in a vacuum beam-line. IIBs lose energy and momentum in the same manner as particles injected by a neutral-beam injector (NBIs), hence could be useful for fusion applications, including: heating, current drive, fueling, profile modifications, etc and such applications have yet to be thoroughly studied. Summarized here are the physical principles accounting for IIB propagation; ion-source designs used to produce the IIB; and pulsed-power methods for energizing the IIB accelerator. This technology base informs scalable metrics for the ion-source/accelerator (excluding the HV power supply and interconnects) used in a conceptual injector that provides the same ion energy and injected power (1 MeV, 17 MW) as NBIs used on ITER. A comparison indicates that the IIB injector would be much smaller in size, lower cost, and have much greater efficiency, while also providing for real-time modulation of the beam energy and intensity and the use of small-diameter injection ports that could minimize fuel contamination and magnetic-field leakage between the IIB injector and tokamak.

Twisted splitting and propagation factor of superimposed twisted Hermite-Gaussian Schell-model beams in turbulent atmosphere

We believe this to be a new superposition twisted Hermite-Gaussian Schell-model (STHGSM) beam hat is proposed. Analytic formulas for the intensity distribution and propagation factor of the STHGSM beam in non-Kolmogorov turbulence are derived by utilizing the generalized Huygens-Fresnel principle (HFP) and the Wigner function. The evolution characteristics of STHGSM beams propagating are numerically calculated and analyzed. Our findings indicate that the light intensity of the STHGSM beam gradually undergoes splitting and rotation around the axis during propagation through non-Kolmogorov turbulence, eventually evolving into a diagonal lobe shape at a certain distance of transmission. The anti-turbulence capability of the beam strengthens with higher beam order or twist factor values.

Analyzing the time-fractional (3 + 1)-dimensional nonlinear Schrödinger equation: a new Kudryashov approach and optical solutions

The paper focuses on investigating the time-fractional (3 + 1)-dimensional cubic and quantic nonlinear Schrödinger equation. We adopt the novel Kudryashov method to generate a distinct class of optical solutions for the current conformable fractional derivative problem. Our method explores various solution forms, including dark, wave, mixed dark-bright, and singular solutions. The soliton solutions we construct are visually represented to illustrate the influence of the fractional order derivative. Further, we elucidate the influence of solution parameters on the wave envelope, providing clear interpretations through 2D graphics presentations. The results underscore the efficacy of our approach in discovering exact solutions for nonlinear partial differential equations, especially in cases where alternative methods prove ineffective. The significance of the present paper lies in its contribution to advancing the understanding of the behavior of optical solutions in nonlinear systems, providing valuable insights for both theoretical and practical applications. In the field of nonlinear optics, this equation can describe the propagation of optical pulses in nonlinear media. It helps in understanding the behavior of intense laser beams as they propagate through materials exhibiting nonlinear optical effects such as self-focusing, self-phase modulation, and optical solitons.

Photonic hook propagation from eccentric microcylinder

The Photonic hook (PH) is an intricately curved photonic nanojet (PNJ) or a highly intense electromagnetic beam featuring a subwavelength waist, whose principal hallmark lies in its capacity to bend light at the nanoscale. According to existing literature, the origin of PH can be attributed to symmetry breaking, whereas symmetrical microstructures predominantly contribute to PNJ formation. This study presents the novel revelation of PH emergence from an isolated eccentric core–shell dielectric microcylinder, achieved through the illumination of a paraxial Gaussian beam (PGB). The eccentrically structured core–shell microscale geometry introduces an additional degree of freedom, influencing PH formation and directly shaping its characteristic parameters. Much like PNJ, the propagation of PH depends on different parameters such as core and shell refractive indices of the micro-structures, microstructure geometry, incident light type, and direction of propagation. A fascinating outcome from our numerical simulations is the switchable occurrence of PNJ and PH from an eccentric core–shell microcylinder by a simple adjustment of eccentricity, either parallel or perpendicular to the PGB’s propagation direction. This computational investigation emphasizes the impact of eccentricity and the incident wave’s beam waist, maintaining a consistent refractive index contrast between the core and shell. The outcomes are interpreted in terms of key parameters governing PH generation characteristics, encompassing FWHM, maximum electric field enhancement, and focal plane. Notably, we have observed the coexistence of whispering gallery modes (WGM) and PH within this system and these modes exhibit high sensitivity to the excitation wavelength. The potential applications of PH are believed to be far-reaching, including areas like optical trapping, sensing, and functioning as a versatile focusing element. This study contributes to the fundamental understanding of PH and illuminates its potential as a robust tool across diverse optical applications.