Intensity Distribution Of Beam Research Articles

Intensity correlation scan (IC-scan) technique to characterize the optical nonlinearities of scattering media

Light scattering, whether caused by desired or spurious elements, is considered one of the main phenomena that present great challenges for the nonlinear (NL) optical characterization of turbid media. The most relevant disturbing factor is the random deformation suffered by the spatial intensity distribution of the laser beam due to multiple scattering. In this work, we report the intensity correlation scan (IC-scan) technique as a new tool to characterize the NL optical response of scattering media, by taking advantage of light scattering to generate speckle patterns sensitive to wavefront changes induced by the self-focusing and self-defocusing effects. Peak-to-valley transmittance curves, with a higher signal-to-noise ratio, are obtained by analyzing the spatial intensity correlation functions of the different speckle patterns, even in very turbid media where conventional NL spectroscopy techniques fail. To demonstrate the potential of the IC-scan technique, the NL characterization of colloids that contain a high concentration of silica nanospheres as scatterers, as well as gold nanorods, which act as NL particles and light scatterers, was performed. The results show that the IC-scan technique is more accurate, precise and robust to measure NL refractive indices in turbid media, overcoming limitations imposed by well-established Z-scan and D4σ techniques.

Properties of circular cosh-gaussian beams focused by a thin lens system under a turbulent atmosphere

The propagation of a Circular cosh-Gaussian beam (CiChGB) through a paraxial ABCD optical system in a turbulent atmosphere is investigated based on the extended Collins formula and Rytov theory. In particular, the analytical expression for the on-axis average intensity of a CiChGB focused by a thin lens in a turbulent atmosphere is derived in detail. From the obtained formula, the on-axis intensity distribution of the output beam is discussed numerically with a comparison to direct propagation in free space. The influences of the turbulence strength and initial beam parameters on the on-axis intensity are examined. It is found that the on-axis intensity near the focus region is less affected by atmospheric turbulence compared to the free space.

Single-pass cutting of frosted glass via change of laser incident medium.

We report a water medium-assisted composite laser cutting (WMACLC) technology for what is believed to be the first time to achieve single-pass separation of frosted glass (FG). The water medium was used to flatten the surface of FG to reduce the diffuse reflection and random refraction of the incident laser. The simulation results of picosecond pulsed laser Bessel beam (PPLBB) intensity distribution in FG showed that the peak intensity in the presence of water can reach about 24 times and 2.3 times that in the absence of water when the PPLBB is 0.08 mm and 0.3 mm below the upper surface of FG, respectively. A PPLBB with higher intensity can be formed along the thickness direction to realize the material modification. A coaxial CW laser provides the thermal tensile stress required for separation. Finally, high-quality separation of FG was achieved using the WMACLC technology with a speed of 50 mm/s. No deviation in the separation track and no edge collapse occurred. The roughness Sa of the separated sidewall is less than 0.3 µm.

Optical design and stray RF investigation of ITER EC H&CD equatorial launcher using mockup

The aim of this study is to assess power transmission characteristics of ITER EC H&CD equatorial launcher (EL) which will deliver 20 MW of millimeter wave power to the ITER tokamak. A precise optical mockup of the launcher is fabricated in order to experimentally verify the characteristics of 170 GHz beam transmission. To observe the intensity distribution of output beams, a mobile high-sensitivity power detection system is used for millimeter wave monitoring, which is in good agreement with quasi-optical calculations. Internal stray RF generation presents an additional concern regarding heat load inside the launcher especially in case of deteriorated input mode purity. Therefore, firstly, the stray RF power is quantified by observation after the beam duct (i.e., launcher exit) of the mockup. The results show that a significant portion of stray RF (>20%) is emitted and does not contribute to the heat load. For another approach to estimate the heat load, geometric optics is performed with various degrees of scattering. This approach indicates that nearly half of the stray RF power is emitted from the launcher exit. Thus, the internal heat load due to stray RF is calculated 44 kW/m2, which is an important result in relaxing the design conditions of the EL.

Propagation of vortex optical beams through artificial convective turbulence

The propagation of vortex optical beams through artificial convective turbulence is studied experimentally. It is found that as the refractive turbulence intensifies, instantaneous intensity distributions of vortex beams become speckled, and the initial ring structure of a beam distorts and disappears. In the averaged intensity distributions, the ring structure is gradually blurring with strengthening the refractive turbulence and becomes close to the Gaussian one with the intensity maximum at the center of the beam. The random wandering of vortex beams, whose initial transverse size increases with an increase of the topological charge, and beams, whose initial transverse size remains unchanged with a change of the topological charge, is compared. It is shown that the amplitude of random displacements of a vortex beam energy centroid is independent of the topological charge.

Periodic oscillation behavior of chirped cosh-Gaussian beam in parabolic potential

In this paper, based on the normalized linear Schrödinger equation, we analytically and numerically investigate the propagation dynamics of cosh-Gaussian beams in a medium with parabolic potential. The obtained results show that cosh-Gaussian beams perform a periodic oscillation behavior and the parabolic potential determines the focusing ability, including the focal distance as well as peak intensity at the focus. Especially, the intensity distributions of cosh-Gaussian beam are related to the initial parameter. We also demonstrate the effect of chirp factors on the beam and find the periodic oscillating behavior caused by linear chirp can be used to manipulate the propagation trajectory. The influence of quadratic chirp on the evolution of beam is also discussed and we find that it plays a significant role in the modulation of the energy localization.

Long-term repeatability improvement using beam intensity distribution for laser-induced breakdown spectroscopy

The relatively low measurement repeatability has long been considered as a major obstacle to the widespread use and commercialization of laser-induced breakdown spectroscopy (LIBS). Although many efforts have been made to improve the signal repeatability in the short term, how to improve the long-term signal repeatability is critical in practical applications and has rarely been studied. Moreover, the mechanisms behind the degradation of long-term repeatability are not fully revealed. This study proposes a new method to improve the long-term repeatability of LIBS measurement, which modifies the spectral intensity based on laser beam intensity distribution. It first pre-processes the beam intensity distribution profiles and spectral intensity. Then the relationship between the relative deviations of beam and spectral intensities is modelled using Partial Least Squares Regression (PLSR). The proposed method was tested on copper and silicon samples, and the spectra and laser beam intensity distribution were recorded for more than thirty days. Day-to-day variations in beam intensity distribution were observed. Such variations can lead to changes in spectral intensity, resulting in degraded signal repeatability. By modifying the spectral intensity, the long-term signal repeatability was improved. Specifically, in terms of day-mean spectral intensity, the valid correction rates were above 70% for both of copper silicon sample in most cases. Long-term RSD decreased from ∼13.5% to ∼4% for copper and decreased from ∼10.7% to 6.5% for silicon sample. These results indicate that the proposed method provides a viable method for improving the long-term repeatability of LIBS measurement.

Sensitivity Analysis of a 6 MeV Photon Beam Monte Carlo Model.

This study aimed to optimize efficiency in Monte Carlo (MC) simulation using sensitivity analysis of a beam model. The BEAMnrc-based model of 6 MV beam of a Siemens Primus linac was developed. For sensitivity analysis, the effect of the electron source, treatment head, and virtual phantom specifications on calculated percent depth dose (PDD) and lateral dose profiles was evaluated. The optimum mean energy (E) and the full width at half maximum (FWHM) of the intensity distribution of the electron beam were calculated as 6.7 MeV and 3 mm, respectively. Increasing E from 6.1 to 6.7 MeV, increased the PDD in the fall-off region by 4.70% and decreased the lateral profile by 8.76%. Changing the FWHM had a significant effect on the buildup region of PDD and the horns and out-of-field regions of the lateral profile. Increasing the collimators opening by 0.5 mm, PDD increased by 2.13% and the central and penumbra regions of profiles decreased by 1.98% and 11.40% respectively. Collimator properties such as thickness and density were effective in changing the penumbra (11.32% for 0.25 cm increment) and the out-of-field (22.82% for 3 g/cm3) regions of the lateral profiles. Analysis of a 6 MV model showed that PDD profiles were more sensitive to changes in energy than to FWHM of the electron source. The lateral profiles were sensitive to E, FWHM, and collimator opening. The density of the collimator affected only the out-of-field region of lateral profiles. The findings of this study may be used to make benchmarking of an MC beam model more efficient.

Design of an optical system for generating annular-focused beams using a conical mirror and a parabolic cylindrical mirror

A reflective optical system is designed for generating annular-focused beams using a conical mirror and a parabolic cylindrical mirror. The parameters of the mirrors are obtained in accordance with the design requirements of the annular beam. The rotation equation of the parabolic cylindrical mirror is derived with the same annular beam diameter, while the apex angle of the conical mirror changes. The uniformity of the annular beam intensity is improved by changing the parabolic cylindrical mirror into a concave–convex parabolic cylindrical integrating mirror, which is designed on the basis of the principles of surface division and beam superposition. The mirrors are processed by single-point diamond turning. An experimental facility is built to analyze the size and uniformity of the beam intensity distribution. The annular beam-width error is less than 3%, and the uniformity is 89%. The surface of the concave–convex parabolic cylindrical integrating mirror is smooth and continuous. The experimental data correspond to the theoretical design.

Influence of Curvature Feature on Laser Heating during Tape Placement Process for Carbon Fiber Reinforced Polyether Ether Ketone Composite

The curvature feature makes the irradiance and absorptivity change, resulting in an uneven power density distribution, which affects the quality of composite parts. In this study, a theoretical model-based Super-Gaussian profile beam in the laser irradiation area was established to obtain the heat flux distribution on the curved surface. The effect of curvature on the surface scattering reflection, temperature distribution, and surface morphology were investigated and verified the validity of the theoretical model. Furthermore, the influence of the laser intensity distribution, laser inclination and curvature radius on the power density distribution and distribution uniformity were studied. Research indicated that the power density increases as the distance from the origin increase resulting from the variation of the irradiance and absorptance along the circumference. The flatter the intensity distribution of the laser beam in the height direction, the less uniform the power density distribution. Accordingly, the typical Gaussian profile beam significantly ameliorates the power density distribution. This research provides a novel understanding of using heat sources during laser heating thermoplastic tape placement.

Study on Propagation Properties of Orbital Angular Momentum Modes in Plasma Sheath Turbulence for Power-Exponent-Phase Airy Beams

The theory of random phase screen is adopted to establish the propagation model of power-exponent-phase airy (PEPA) beams in plasma sheath turbulence (PST) conditions. The propagation model can determine the changes in intensity, phase, and orbital angular momentum (OAM) mode distribution of PEPA beams under PST. Simulation results reveal that PEPA beams in multiple OAM modes at the source field can better suppress PST than the conventional vortex beams because the influence of turbulence is dispersed in different OAM modes. Moreover, compared with power-exponent-phase Laguerre–Gaussian (PEPL) beams, PEPA beams are better suited for transmission under plasma turbulence because of their self-focusing and self-healing properties. The results provide a theoretical basis for studying communication problems during PST.

Оценка возможности определения поперечного профиля медицинского электронного пучка методом многоуглового сканирования для повышения точности проведения радиотерапевтических процедур

This study is aimed at assessing the applicability of the proposed method of multiangle beam scanning for determining the transverse profile of an electron beam. The application area of the proposed approach will be control of the therapeutic beams spatial and dose characteristics in order to increase the irradiation accuracy and, as a result, reduce the side effects of radiation therapy. One of the main applied problems to be solved by the proposed approach is to determine the beam characteristics during electron beam therapy. For carrying out of electron beam therapy procedures it is necessary to form electron beams with the complex shape of transverse profile. The need to precisely control beam shapes throughout all irradiation stages determines the relevance of this study. The integral transform method was used in this study to obtain distributions of medical electron beam intensity. For the study, we used electron beam transverse pro-files calculated on the basis of a radiation therapy planning system for real clinical cases. The method was applied both theoretical beam profiles with sharp edge and to ones experimentally obtained with real medical electron beams. Integral transforms were performed for a different number of scan projections. Due to this, the optimal number of projections was calculated for each considered profile. The results of the study demonstrate that the multiangle beam scanning method needs 12 scan projections which corresponds to an angular displacement of 15° to control the medical electron beam profile.

Mitigating thermal blooming effect of seawater using self-rotating beam

When the high-power lasers propagate in seawater, the thermal blooming (TB) effect can cause wavefront distortion, which severely affects the beam quality. Here we proposed a potential approach to reduce the thermally-induced wavefront distortion by using the self-rotating beam in seawater. This approach using the self-rotating beam can directly rotate the intensity distribution of the laser beam and thus break the accumulation path of thermally-induced wavefront distortion, contributing to the improvement of beam quality. Results show that, the self-rotating beam with an appropriate rotation frequency can well mitigate the thermal blooming effect in seawater, exhibiting excellent performance in reducing beam expansion, beam centroid drift and beam quality degradation.

Nondestructive evaluation (NDE) of multilayered attenuative structures using ultrasonic Bessel beams

In this article Nondestructive Evaluation (NDE) of structures with attenuative coating or a layer of thermal protection system is presented utilizing various designs of acoustic axicons. Generation of ultrasonic Bessel beam in single-layered and multi-layered structures to overcome the ultrasonic attenuation is discussed. The possible modulation and the effective increase of the acoustic energy inside the attenuative layer are investigated using axicons, which are proposed to be an ad-hoc element to the existing ultrasonic transducers. Upon confirming the existence and generation of the ultrasonic Bessel beam in an arbitrary host media the spatial intensity distribution of the zeroth-order Bessel beam is studied. Further, we show how the generated Bessels beams propagate and penetrate deep inside the multi-layered structures comprising of different material properties. It is shown that the intensity of the Bessel beams and their possible deep penetration capabilities are altered when the geometrical properties of the axicon and material properties of the media are changed. We also report the numerical characterization of the different degrees of Bessel beams with a unique multi-annular shaped axicon. Modulating the axicon angles and the geometry, the long-distance propagation of the Bessel beam is ensured. Such beam can correspond to the field of Nondestructive Evaluation (NDE) for investigating materials with attenuative layers.

A New Approach for Sensitive Characterization of Semiconductor Laser Beams Using Metal-Semiconductor Thermocouples

This paper presents the results of beam investigations on semiconductor IR lasers using novel detectors based on thermocouples. The work covers the design, the fabrication of detectors, and the experimental validation of their sensitivity to IR radiation. The principle of operation of the manufactured detectors is based on the Seebeck effect (the temperature difference between hot and cold junctions induced voltage appearance). The devices were composed of several thermocouples arranged in a linear array. The nano- and microscale thermocouples (the hot junctions) were fabricated using a typical Si-compatible MEMS process enhanced with focused ion beam (FIB) milling. The performance of the hot junctions was tested, focusing on their sensitivity to IR radiation covering the near-infrared (NIR) radiation (λ = 976 nm). The output voltage was measured as a function of the detector position in the XY plane. The measurement results allowed for reconstructing the Gaussian-like intensity distribution of the incident light beam.

Paraxial propagation of cosine-hyperbolic-Gaussian beams in a chiral medium

The properties of a linearly polarized cosine-hyperbolic-Gaussian beam (ChGB) propagating in a chiral medium are investigated theoretically by using the Huygens-Fresnel diffraction integral. Beam intensity distribution characteristics in the chiral medium are discussed with numerical examples. The linearly polarized ChGB is found to split into a superposition of left and right circularly polarized Gaussian components, and its intensity pattern exhibits a variable shape depending on the chirality factor and decentered parameter b. The output beam can exhibit a richer intensity pattern compared to the Gaussian beam. The results could be beneficial for the application of ChGB in beam shaping and optical micromanipulation.

Perturbation of V-point polarization singular vector beams

The structured beams of light endowed with vector field singularities can be expressed as a superposition of spin and orbital angular momentum states. This article investigates the effect of perturbation of vector field singularities by superposing it with a homogeneously polarized beam and discusses its possible applications in studying the chiroptical effects. This perturbation leads to the splitting of vector field singularities (V-points) into stable lower-index ellipse field singularities (C-points). The strength of perturbation decides the separation between the two C-points in the resultant beam. It is found that the unfolding of V-points into lower-index C-points is always accompanied by a measurable centroid shift in the total and component intensity distribution of the resultant beam. Moreover, the centroid shift is more pronounced in the component intensity, whose state of polarization matches the state of polarization of the perturbing beam. The strength of perturbation can be measured by analyzing the radial shift in the centroid of the beam. It is observed that in the process of perturbation, the polarization singularity index is always conserved while the net helicity in the resultant beam is decided by the helicity of the perturbing beam. The strength of the perturbing beam can be modified by introducing a chiral sample in the beam path which may be useful to investigate the chiroptical effects.

Melanin effect on light beam intensity distribution in skin as a function of wavelength and depth from 200 to 1000 nm using Monte Carlo simulation

Light beam propagation inside biological tissue, is crucial for many fields. Giving that, we had investigated the effect of melanin, on light propagation inside different type of tissue. We had constructed phantoms that approximates a real tissue and mimic its reaction to light. The skin model of seven layers takes into consideration the volume fractions and optical properties of blood, water, and melanin content. We developed a Monte Carlo simulation to investigate the intensity distribution inside tissues of a light beam. The study is done for different Fitzpatrick skin types. We provide the intensity distribution and the penetration depth in the 200–1000 nm wavelength range.

Terahertz vortex beams generated by the ring-arranged multilayer transmissive metasurfaces

We propose a multilayer “H” type cell structure to construct a vortex beam metasurface generator. Based on the Pancharatnam-Berry phase theory, we propose a uniform annular arrangement to achieve a vortex beam with high transmission efficiency. At 0.1 THz frequency, the transmission efficiency reaches 62%. We further utilized printed circuit board technology to prepare samples of vortex beam generators. Using a self-built terahertz test platform, we tested the transmission beam intensity distribution characteristics of the sample. The metasurface vortex beam generator can realize the miniaturization and integration characteristics of the device, and is expected to be applied to the field of terahertz communication.

Generation, Transmission, and Amplification of OAM Modes in the PbSe-Doped Ring-Core Fiber Carrying 3D Printed Spiral Phase Plate

Vortex beams carrying orbital angular momentum (OAM) have increasingly attracted attention in the field of optical communication. However, transmission is still an issue due to transmission loss, especially in optical fibers. In this work, we proposed, designed, and fabricated micro spiral phase plates (SPPs) directly on an end facet of a piece of PbSe-doped ring-core fiber (RCF) through two-photon polymerization, realizing the integration of OAM beam generation, transmission, and amplification. The prepared RCF comprises a double-clad structure with a core-clad refractive index difference of 2.2% and the fluorescence range is 1150 nm–1700 nm. The intensity distribution of the OAM beam and the spiral interference fringes were obtained, which indicated that the OAM mode (|l|=1, 2, 3, 4) was generated and transmitted directly within the fiber. The small-signal amplification of four OAM modes was accomplished at 1550 nm under a pump power of 634 mW. The on–off gain is >13.2 dB for all modes and the differential mode gain (DMG) is <1.7 dB. The SPP-carrying RCF structure demonstrates the integration of generation, transmission, and amplification of higher-order OAM modes in all-fiber systems.