Laser beam shaping

The generation of pure third-order spatial phase is the top requirement for the generation of Airy beams through the Fourier-space beam shaping method. Utilizing coma aberration for inducing such a phase profile is shown to be one of the most appropriate approaches because of providing continuous phase, the capability of working at high laser powers, and low costs. Here, we demonstrate pure tunable third-order spatial generation through aberration control in a positive one-dimensional tilted cylindrical telescopic system, and experimentally verify its quality and tunability by two independent wavefront sensing methods namely moiré deflectometry and fourstep phase-shifting interferometry. The deflectometry method is used for a real-time visual assessment of the quality of the imprinted wavefront, and also for a quantitative analysis of the wavefront and its dependency on the parameters of the system, while, the interferometric method is used for more rigorous measurement of the generated wavefront. It is shown that by changing the tilt angle of the system, the modulation depth of the cubic phase can be tuned. It is also shown that nearly-complete third-order form of the imprinted phase over a large aperture results in high-quality Airy beam generation with a small truncation factor.

The spatial shaping of light beams is the process of redistributing the irradiance of a light beam. A correct beam shaping is essential to optimize a large number of laser-material processing applications and laser-material interaction studies. In this paper, after introducing the basic equations of the classical beam integration method to reshape and homogenize laser beams, we detail the design elements, the experimental performance and the main parameters of a novel transfocal homogenizer that is able to homogenize and reshape any light beam. Then we discuss the reliability of existing international standard parameters to evaluate the "goodness" of nearly flat-top shaped laser beams. Finally, we present examples of successful applications of this new homogenizer technology to ultraviolet irradiation experiments.

Peripheral giant cell granuloma (PGCG) is a non-neoplastic, tumour-like reactive lesion that exclusively involves the gingiva and/or the alveolar crest. The surgical approach with a scalpel has been the golden standard of treatment for PGCG, but the scientific literature reports a high rate of lesion recurrence. Hence, this unique case report aimed to evaluate the efficacy of λ 10,600 nm high-level laser therapy (HLLT) in eradicating persistent, aggressive, and recurrent PGCG that failed to respond to standard surgical treatment. A fit and healthy thirty-four-year-old Caucasian male presented with a two-month history of recurrent episodes of an oral mucosal lesion involving the buccal and lingual interdental papillae between the lower right second premolar (LR5) and lower right first molar (LR6), which was surgically excised with a scalpel three times previously. A λ 10,600 nm-induced HLLT was chosen as a treatment modality at a lower peak power of 1.62 W, measured with a power metre, emitted in gated emission mode (50% duty cycle), whereby the average output power reaching the target tissue was 0.81 W. The spot size was 0.8 mm. Ninety seconds was the total treatment duration, and the total energy density was 7934.78 J/cm 2. Patient self-reporting outcomes revealed minimal to no post-operative complications. Initial healing was observed on the 4th day of the post-laser treatment, and a complete healing occurred at two-weeks post-operatively. The histological analysis revealed PGCG. This unique case report study demonstrated the efficacy of λ 10,600 nm-induced HLLT and its superiority to eradicate persistent aggressive PGCG over the standard surgical approach with minimal to no post-operative complications, accelerating wound healing beyond the physiological healing time associated with no evidence of PGCG recurrence at the six-month follow-up timepoint. Based on the significant findings of this unique study and the results of our previous clinical studies, we can confirm the validity and effectiveness of our standardised λ 10,600 nm laser dosimetry-induced HLLT and treatment protocol in achieving optimal outcomes. Randomised controlled clinical trials with large data comparing λ 10,600 nm with our dosimetry protocol to the standard surgical treatment modality at long follow-up timepoints are warranted.

For intra-cavity laser beam control, a small, low-cost deformable mirror is required. This mirror can be used to correct for time-dependent phase aberrations to the laser beam, such as those caused by thermal expansion of materials. A piezoelectric unimorph design is suitable for this application. The proposed unimorph consists of a copper disc with mirror finish, bonded to a piezoelectric disc. The deformations that the mirror is required to perform are routinely (at least in optical applications) described using Zernike polynomials, which are a complete set of orthogonal functions defined on a unit disc. The challenge is to design a device that can represent selected polynomials as accurately as possible with a specified amplitude. To assist in the design process, numerical modelling is required to predict the deformation shapes that can be achieved by a unimorph mirror with a particular electrode pattern. In this paper a previously proposed axisymmetric Rayleigh-Ritz formulation, is extended to account for non-axisymmetric voltage distributions, and therefore non-axisymmetric displacements. The Rayleigh-Ritz model, which uses the Zernike polynomials directly to describe the displacements, produced a small model (stiffness matrix dimension equal to the number of polynomials used) that predicts the deformations of the piezoelectric mirror with remarkable accuracy. The results using this Rayleigh-Ritz formulation are compared to results from a traditional finite element analysis using a commercial finite element package. Both numerical models were applied to model a prototype deformable mirror and produced good agreement with experimental results.

A plano-convex aspheric lens is designed to collimate the emitted light of the fiber optics. In this paper even orders of general aspheres are used to describe the aspheric surfaces sag. To determine the aspheric coefficient, the even asphere polynomial are fitted on the computed sag data. The surface sag data is determined using genetic algorithm method. The surface sag was analyzed by the commercial optical software package ZEMAX. For typical fiber optics, the numerical aperture (NA) of 0.22 was assumed. With this specification, the expected output spot diagram of 20 mm and the maximum aperture of 25.4 mm have been obtained. A comparison between here presented lens and the similar type of conventional lens has been carried out; the proposed aspheric lens corrected the spherical aberration, which led to increase in the collimated distance.

АННОТАЦИЯ В этой статье рассматривается переход в промышленной обработке и производстве материалов к передовым технологиям производства, уделяя особое внимание точности и устойчивости, необходимым в современных приложениях. В нем подчеркивается, что лазерная резка является выдающимся методом-контролируемым бесконтактным термическим процессом, при котором высокоэнергетический лазерный луч фокусируется для удаления материала путем плавления или испарения. Обсуждаются преимущества лазерной резки, в том числе минимальные потери материала, отсутствие износа инструмента, высокая точность и эффективность. Подчеркивается роль лазерной резки в изготовлении миниатюрных шестерен из нержавеющей стали SS304, имеющих решающее значение в устройствах, требующих движения или передачи энергии. Он решает проблемы достижения желаемого качества поверхности и относительно неисследованную область энергопотребления при лазерной резке. Чтобы восполнить этот пробел, в статье предлагается комплексный анализ параметров процесса лазерной резки на качество миниатюрных шестерен и предлагается дальнейшая оптимизация процесса. ABSTRACT This article examines the transition in industrial material processing and production towards advanced manufacturing techniques, focusing on the precision and resilience required in modern applications. It highlights laser cutting as a prominent method, a controlled, non-contact thermal process where a high-energy laser beam is focused to remove material through № 2 (119) февраль, 2024 г. 20 melting or vaporization. The advantages of laser cutting, including minimal material loss, absence of tool wear, high accuracy, and efficiency, are discussed. The role of laser cutting in fabricating miniature SS304 stainless steel gears, crucial in devices requiring motion or energy transfer is emphasized. It addresses the challenges of achieving desired surface quality and the relatively unexplored domain of energy consumption in laser cutting. To bridge this gap, the paper proposes a comprehensive analysis of the laser cutting process parameters on the quality of miniature gears and suggests further process optimization.

The effect of passive water cooling in laser forming of thin sheets made of AISI 304 stainless steel is experimentally investigated. Indeed, since each laser scan can produce only small bending angles, multiple laser scans are required to produce a given deformation with a significant increase of production time due to cooling between consecutive scans. Therefore, passive water cooling is tested to verify its influence on minimum time between consecutive scans (cooling time), bending angle, and surface quality. A parametric approach is involved in the investigation and main process parameters are changed among the experiments by varying laser scanning speed, laser beam power, sheet thickness, and cooling media among several levels. It was discovered that the employment of passive water cooling in laser forming of thin sheets would be beneficial since the capability to dramatically reduce the cooling time and oxidation of both irradiated and cooled surfaces. In addition, the bending angle is only marginally affected by employment of water cooling. The effect of water cooling on stress and deformations are discussed by developing a numerical model based on finite element model.

Novel compact beam expanders that could be useful for applications such as providing light to flat panel displays are presented. They are based on a planar configuration in which three spatially linear gratings are recorded on one transparent substrate, so as to expand a narrow incoming beam in two dimensions. We present the design and recording procedures along with results, showing a relatively uniform intensity of the wide output beam. Such expanders can serve for illuminating flat panel displays.

A family of orthonormal mode sets arises when Hermite-Gauss modes propagate through lossless first-order optical systems. It is shown that the modes at the output of the system are eigenfunctions for the symmetric fractional Fourier transformation if and only if the system is described by an orthosymplectic ray transformation matrix. Essentially new orthonormal mode sets can be obtained by letting helical Laguerre-Gauss modes propagate through an antisymmetric fractional Fourier transformer. The properties of these modes and their representation on the orbital Poincaré sphere are studied.

PhiPAC project, which gave me more insight about BLAS. Rich Vudoc offered help on choosing the fine-tuned numerical libraries. I thank Eric B. Grann for lending his Ph.D. thesis to me. I also thank Professor Jim Moharam and Philippe Lalanne for answering several questions on RCWA overtelephone and e-mail. I have received support from a lot of people in the semiconductor industry. I thank Joe Bendik, Matt Hankinson, Bob Socha, Ron Kovacs of National Semiconductor for their insights and collaboration. I am grateful to CihanTinaztepeof KLA-Tencor for the summer intemship in 1997. Craig MacNaughton and Anthea Ip of KLA-Tencor helped me with some experimental measurements.

The effect of metal nanoparticles (MNPs) on the electric field strength and distribution for improvement solar cell performance is investigated and simulated. By manipulating the properties of nanoparticles, distribution of the electric field was altered. In this paper, classical solar cell (p-n junction) and improved structure (add an extra layer of SiO2 and gold nanoparticles on the top of p-n junction) is simulated. Different sizes of NPs, thickness of SiO2 sublayer, and spacing distance between NPs is done to improving the electric field and showing plamonic effect. Gold NPs deposition on single crystalline silicon solar cell is modelled by COMSOL 5.2 2D, Electromagnetic wave propagation in the frequency domain with periodic boundary conditions. The best wavelength found in our work is 550 nm. The electric field enhances when the size of NPs increases but it must be limited. When gold NPs are deposited on the SiO2 sublayer, the plasmonic effect appears due to decreasing the refractive index. Moreover, separation distance between NPs affect the electric field enhancement by manipulating the number of NPs, the distance decreases and the plasmonic interaction appears.

We present the electrical and optical design, assembly, and experimental characterization of compact arrays of short-wavelength ultraviolet (UV-C) light-emitting diodes (LEDs) suitable for near-field irradiation. By an appropriate combination of technical arrangements, we have achieved effective thermal management of the LEDs such that long-lasting irradiations are possible without appreciable degradation of UV-C emission. We have successfully used these compact UV-C LED arrays in several applications, two of which are: a) fast inactivation of viruses, including SARS-CoV-2; and b) long-lasting irradiation of plants and fruits, aimed at generating biosynthesis of defensive metabolites that increase their resistance to pathogen attacks.

Цель данной работы состоит в исследовании особенностей процесса плазменной сварки для анализа существования связей параметров процесса. Поставлена цель исследований позволит получить статистические данные для установления зависимостей между основными параметрами плазменной сварки. Знание этих зависимостей необходимо для синтеза гибридного регулятора для системы автоматического управления процессом плазменной сварки. Нечеткий компонент гибридного регулятора может быть создан на основе формализации знаний экспертов. Знания экспертов будет получены на основе исследования зависимостей между основными параметрами плазменной сварки. Для достижения поставленной цели проведены эксперименты и получены зависимости в виде связи силы тока и теплосодержания присадочного и основного металла, а также выполнено исследование зависимости эффективного коэффициента полезного действия источника питания от режима плазменной сварки. Выполнен краткий аналитический обзор известных работ. Результаты анализа показала, что актуальным направлением развития систем управления процессами сварки является применение гибридных регуляторов, как симбиоза классического регулятора, создаваемого с применением методов теории автоматического управления и нечеткого регулятора на основе формализации знаний экспертов. Для исследования связи силы тока и теплосодержания присадочного и основного металла определены параметры режима плазменной сварки в виде тока, длины дуги, диаметра проволоки. Для проведения опытов применена установка для проведения калориметрирования. В результате проводимых опытов было исследовано влияние силы тока плазменной дуги, диаметра присадочной проволоки, диаметра сопла, расстояния от проволоки до изделия, угла ввода проволоки в плазму и точки плавления. Исследовано теплосодержание основного металла и металла шва. В результате опытов получена средняя температура ванны при сварке без присадочной проволоки для разных скоростей сварки. Применив калориметр с «сухим» сосудом в установке для плазменной сварки в СО 2 с присадочной проволокой, оценена эффективность КПД источника питания. Плазменная сварка; защитный газ; параметры; эксперимент; плазменная дуга; зондирование; управление; статистические данные. Al-Shamkhee Ameer Abdulkadhim Oudah, A.F. Shepelev, V.I. Finaev, E.V. Zargaryan STUDY OF THE CONNECTIONS OF PARAMETERS IN PLASMA WELDING The purpose of this work is to study the peculiarities of the plasma welding process for analyzing the existence of relationships between process parameters. The goal of the research is to provide statistical data for establishing relationships between the main parameters of plasma welding. Knowledge of these dependencies is necessary for the synthesis of a hybrid controller for the automatic process control system for plasma welding. The fuzzy component of the hybrid regulator can be created based on the formalization of expert knowledge. Expert knowledge will be obtained on the basis of a study of the dependencies between the main parameters of plasma welding. To achieve this goal, experiments were carried out and dependencies in the form of a coupling between the current strength and the heat content of the filler and base metal were obtained, and the dependence of the effective efficiency of the power source on the plasma welding mode was studied. A brief analytical review of well-known works. The results of the analysis showed that the actual direction of the development of welding process control systems is the use of hybrid regulators, as a symbiosis of the classical regulator created using the methods of the theory of automatic

In the recent years, many different techniques and algorithms have been devised to design diffractive optical elements (DOE’s) for the purpose of beam shaping. This paper demonstrates an approach to realise a 3-D printed radial phase mask to be used in beam shaping to achieve a beam profile closer to the flattop. An iterative algorithm approach is employed to simulate the phase masks in greyscale and subsequently into STL format. These 3-D printed masks are used as an optical element and characterised using an experimental setup. The images of the light after the characterisation are examined and compared with the simulated results. Therefore, this method reduces the complexity as 3-D printing the masks eliminates the need for fabrication, processing time and number of components necessary to obtain a flattop beam profile.

In this article, the strain behaviour of the depressed inner core triple clad single mode optical fiber is investigated. Both tensile and compressive types of axial strain are considered in simulations. The modal analysis of the fiber structure is based on linear polarization (LP) approximation method. Mode field diameter (MFD) of the fiber is selected as the indirect parameter for strain sensing task and investigating the MFD behaviour of the fiber, the strain sensitivity is augmented through independent adjustment of the structural parameters. Subsequently, a design procedure based on evolutionary genetic algorithm (GA) is introduced for consideration of simultaneous effect of all hyper-parameters of the fiber which yields the strain sensitivity of 15.96 pmµɛ-1. The substantial sensitivity attained is as the inherence of complicated configuration in multilayer fiber as well as the GA based method. Furthermore, negligible temperature sensitivity of-6.97×10-7 pmC-1 removes the temperature compensation technique which is inevitable stage of fiber optic measurement systems. Additionally, the simulation results admit the stable strain response of the proposed structure.

We present an experimental demonstration of a class of beams, namely Frozen Waves, that can carry predetermined longitudinal intensity profiles in the presence of modeled loss. These waveforms consist of a superposition of equal frequency Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator addressed by computer-generated hologram. Attenuation-resistant Frozen Waves can address challenges associated with light-matter interaction in absorbing media encountered in imaging, remote sensing, and particle micro-manipulation, to name a few.

Fresnel lenses based on liquid crystals, because of LC's large birefringence & also tunable optical properties, have attracted considerable attention in photonics. Precise controlling of focal length in a lens, can be kind of remarkable tools in photonics. In this article, we introduce a layout printing way for producing Fresnel zone on 1294-1b liquid crystal doped with dye. With layout printing technique, we recorded 25 zones on cell with λ=532nm diode laser. After producing, DDLC Fresnel lens have 33 cm focal length at 0 v and 225 cm focal length at 20 v.

Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10-100 times greater than the diffraction limit. This inevitably restricts their wider use in 'direct-diode' applications in materials processing and biomedical photonics. We report here a 'super-focusing' characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a 'needle' beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of mul...

We present experimental results on the intracavity generation of radially polarized light by incorporation of a polarization-selective mirror in a CO 2-laser resonator. The selectivity is achieved with a simple binary dielectric diffraction grating etched in the backsurface of the mirror substrate. Very high polarization selectivity was achieved, and good agreement of simulation and experimental results is shown. The overall radial polarization purity of the generated laser beam was found to be higher than 90%.

New methods of laser metrology (interferometry and microscopy) based on applications of beams with special structures provide increased resolution and efficiency. To generate a beam with linear singularity (dark beam) we recently proposed a beam shaping method using a bi-prism-like element within the laser resonator. There we have studied resonators that are traditionally designed to oscillate on the fundamental mode designed within the range of configuration parameters, 0.5 1 G. In the present work we extend the approach and show that the choice of specific configurations, outside the above range of configuration parameters, can lead to much better results for our application. This is the case in particular for an approximately semi-concentric resonator (G ~-1).The optimal dark beam is obtained for a bi-prism angle about twice that obtained for the earlier configurations. For this case the difference between the losses of the first odd mode and other modes is 0.12-0.15, which is adequate for oscillation on this mode in lasers with any type of active media.

We demonstrate optical trapping of rare earth-doped NaYF4:Er/Yb nanorods of high aspect ratio (length 1.47 μm and diameter 140 nm) using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips. Propulsion or trapping of the nanorods is demonstrated using either single or dual fiber nano-tip geometries. The optical force exerted on the trapped nanorods, their velocities, and their positions have been analyzed. We determine the trap stiffness for a single nanorod to be 0.12 pN/μm (0.003 pN/μm) by power spectrum analysis and 0.13 pN/μm (0.015 pN/μm) by Boltzmann statistics in the direction perpendicular to (along) the fiber axes for an average optical power of 34 mW. The experiments illustrate the advantage of using a QBB for multiple nanorod trapping over a large distance of up to 30 μm.

High-quality optical resonant cavities require low optical loss, typically on the scale of parts per million. However, unintended micron-scale contaminants on the resonator mirrors that absorb the light circulating in the cavity can deform the surface thermoelastically, and thus increase losses by scattering light out of the resonant mode. The point absorber effect is a limiting factor in some highpower cavity experiments, for example, the Advanced LIGO gravitational wave detector. In this Letter, we present a general approach to the point absorber effect from first principles and simulate its contribution to the increased scattering. The achievable circulating power in current and future gravitational-wave detectors is calculated statistically given different point absorber configurations. Our formulation is further confirmed experimentally in comparison with the scattered power in the arm cavity of Advanced LIGO measured by in-situ photodiodes. The understanding presented here provides an important tool in the global effort to design future gravitational wave detectors that support high optical power, and thus reduce quantum noise.

We demonstrate optical trapping of rare earth-doped NaYF4:Er/Yb nanorods of high aspect ratio (length 1.47 μm and diameter 140 nm) using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips. Propulsion or trapping of the nanorods is demonstrated using either single or dual fiber nano-tip geometries. The optical force exerted on the trapped nanorods, their velocities, and their positions have been analyzed. We determine the trap stiffness for a single nanorod to be 0.12 pN/μm (0.003 pN/μm) by power spectrum analysis and 0.13 pN/μm (0.015 pN/μm) by Boltzmann statistics in the direction perpendicular to (along) the fiber axes for an average optical power of 34 mW. The experiments illustrate the advantage of using a QBB for multiple nanorod trapping over a large distance of up to 30 μm.

An in-process optical technique is described for accurately monitoring the end point in plasma etching processes. A grating pattern is lithographed somewhere in the film to be etched. The grating modulation decreases as the film is etched out and the process may be monitored by measuring the diffraction of a low power He-Ne laser beam aimed at the grating. The etching end point is accurately detected by the disappearance of all diffracted orders. The laser beam does not need to be directed at normal incidence and so any available plasma etching equipment is suitable. The detection is carried out with low cost photovoltaic detectors but simple visual inspection is satisfactory also. Comparative experimental results are presented.

Доктор технических наук, профессор, заведующий кафедрой* Е-mail: rot44@yandeх.ru *Кафедра металлургии цветных металлов Запорожская государственная инженерная академия пр. Ленина 226, г. Запорожье, Украина, 69006 Представлені результати аналітичного дослідження з контролю параметрів і прогнозування технологічних відхилень в алюмінієвих електролізерах з метою зниження енергоємності виробництва алюмінію. Обговорюються технологічні параметри, що дозволяють підвищити ефективність управління процесом електролізу та прогнозу технологічних відхилень у ванні. Показано, що постійне вимірювання додаткових технологічних параметрів на електролізері дозволяє прогнозувати настання технологічних відхилень Ключові слова: алюмінієвий електролізер, струм, електроліт, напруга, анодний ефект, МГД-нестабільність Представлены результаты аналитического исследования по контролю параметров и прогнозирования технологических отклонений в алюминиевых электролизерах с целью снижения энергоемкости производства алюминия. Обсуждаются технологические параметры, позволяющие повысить эффективность управления процессом электролиза и прогноза технологических отклонений в ванне. Показано, что постоянное измерение дополнительных технологических параметров на электролизере позволяет прогнозировать наступление технологических отклонений Ключевые слова: алюминиевый электролизер, ток, электролит, напряжение, анодный эффект, МГД-нестабильность

Vibrations are periodic or random motion from an equilibrium position. In the steel industry, vibrations are an undesirable phenomenon, as they waste energy and create unwanted noise. For example, vibrations affect steel strips during rolling and transportation, producing random or periodic vertical movements of the strips as they move forward along a roll path. The consequences of these vibrations are particularly harmful for 3-D reconstruction and flatness measurement based on non-contact techniques. Vibrations corrupt the height profiles, causing an erroneous reconstruction of the 3-D surface. The flatness measurement is also distorted because the estimated lengths of the strip fibers with vibrations are different. This paper analyzes how vibrations in steel strips affect flatness measurement, and proposes methods to remove or reduce these effects. The shape of steel strips is firstly modeled including the two most common flatness defects: wavy edges and center buckle. Then, different types of vibrations are added to the strip models, and their effects on the resulting flatness measurement are analyzed. The method proposed to reduce the effects of vibrations is a combination of a low-pass filter and geometric transformations. Finally, these methods are applied to data from real strips.

This paper presents a feasibility study of laser-induced breakdown spectroscopy (LIBS) for the development of an in-situ diagnostic for the characterization of deposition layers on plasma-facing components in fusion devices. Preferentially, LIBS would be applied in the presence of a toroidal magnetic field and under high vacuum conditions. The impact of the laser-energy densities on the laser-induced plasma parameters and correspondingly on the number of emitted photons and on the reproducibility of the LIBS method has been studied in laboratory experiments and in TEXTOR on fine-grain graphite (EK98) as well as on bulk W samples coated with carbon and metallic-containing deposits. The effect of magnetic fields and of ambient pressures in the range from 2 × 10-4 Pa to 10 Pa on the carbon plasma plume produced by the LIBS technique has been studied on TEXTOR between plasma pulses. The possibility of applying this method to ITER is discussed.

Time and costs for manufacturing prototypes can be significantly decreased by using stock lenses. An f-θ lens design based on our approach and a comparison to the Zemax stock lens matching tool are presented. The designed lens is used for a high power laser cleaning application, and the requirements of this application are discussed in detail.

An off-axis reflective collimation system design for application in Radar systems is presented. The crosssection of the system has a round configuration for compactness. Based on the spatial analytic geometry and the reflection law (in vector form), space propagation rules for laser beam are derived. The optical design is simulated and optimized using MATLAB. The highly collimated results are presented.

Decomposition of a general arbitrary field into a set of Gaussian beams has been one of the challenges in the Gaussian beam decomposition method for field propagation through optical systems. The most commonly used method in this regard is the Gabor expansion, which decomposes initial fields into shifted and rotated Gaussian beams in a plane. Since the Gaussian beams used have zero initial curvatures, the Gabor expansion method does not utilize the ability of the Gaussian beams to represent the quadratic behavior of the local wavefront. In this paper, we describe an alternative method of decomposing an arbitrary field with smooth wavefront into a set of Gaussian beams with non-zero initial curvatures. The individual Gaussian beams are used to represent up to the quadratic term in the Taylor expansion of the local wavefront. This significantly reduces the number of Gaussian beams required for the decomposition of the field with smooth wavefront and gives more accurate decomposition results. The proposed method directly gives the five ray sets representing the parabasal Gaussian beams, which can then be directly used for propagation of the Gaussian beams through optical systems. To demonstrate the application of the method, we have presented results for the decomposition of fields with strongly curved spherical wavefronts, a cone shaped wavefront, and a wavefront with large spherical aberration. The numerical comparison of the input field with the field reconstructed after the decomposition shows very good agreement in both amplitude and phase profiles. We also show results for the far field intensity distributions of the decomposed wavefronts by propagating in free space using the Gaussian beam propagation method.

For the first time, to the best of our knowledge, we experimentally demonstrated the new scheme for a coated Plano-convex lens (CPCL) fiber with a maximum coupling efficiency \((\eta\)max). In the single-mode solid core fiber (SMSCF), the fiber coupling efficiency is ~ 68% injected pump power 632.8 nm (1.5-dB loss was measure with a laser diode) which is difficult to achieve by using conventional technology, and also we reported, without fiber tapering technology has been used to realize low loss coupling from CPCL to SMSCF at low power level, and compare with published data. This is very useful for implementing all optical fiber systems. In addition, it also investigates the effect of bending the output power and beam profile of SMSCF. The Gaussian-like output beam profile is maintained up to \(\cong 7cm\) bending radius. The output mode field with good beam quality shows the mode filtering characteristics of SMSCF. Finally, the result of the fiber coupling efficiency (FCE) illustr...

Propulsion is required for satellite motion in outer space. The displacement of a satellite in space, orbit transfer and its attitude control are the task of space propulsion, which is carried out by rocket engines. Electric propulsion uses electric energy to energize or accelerate the propellant. The electric propulsion, which uses electrical energy to accelerate propellant in the form of plasma, is known as plasma propulsion. Plasma propulsion utilizes the electric energy to first, ionize the propellant and then, deliver energy to the resulting plasma leading to plasma acceleration. Many types of plasma thrusters have been developed over last 50 years. The variety of these devices can be divided into three main categories dependent on the mechanism of acceleration: (i) electrothermal, (ii) electrostatic and (iii) electromagnetic. Recent trends in space exploration associate with the paradigm shift towards small and efficient satellites, or micro-and nano-satellites. A particular example of microthruster considered in this paper is the micro-cathode arc thruster (µCAT). The µCAT is based on vacuum arc discharge. Thrust is produced when the arc discharge erodes some of the cathode at high velocity and is accelerated out the nozzle by a Lorentz force. The thrust amount is controlled by varying the frequency of pulses with demonstrated range to date of 1-50 Hz producing thrust ranging from 1 µN to 0.05 mN.

This paper presents the numerical analysis of an optical resonator which has in one side a flat coupling mirror and, in the other side, a convergent lens and a flat reflector emulating a concave total reflector mirror. Between the lens and the total reflector flat mirror there is a chopper to promote q-switching operation. This resonator was conceived to be installed in a CW CO2 laser. Two analysis were performed: stability and mode formation. The stability was done by using ray tracing (ABCD matrix) and evaluating the configurations the stability criteria is observed. The mode formation analysis was done by using the Fox and Li formalism. It was concluded that it is possible to find a range of parameters (mirrors and lens distances and focal lengths) that allows stable operation and a convergence to the fundamental mode in just few round-trips inside the resonator. These characteristics are quite desirable for pulsed operation in the TEM00 mode.

The growth in terahertz frequency applications utilising the quantum cascade laser is hampered by a lack of targeted power delivery solutions over large distances (>100 mm). Here we demonstrate the efficient coupling of double-metal quantum cascade lasers into flexible polystyrene lined hollow metallic waveguides via the use of a hollow copper waveguide integrated into the laser mounting block. Our approach exhibits low divergence, Gaussian-like emission, which is robust to misalignment error, at distances > 550 mm, with a coupling efficiency from the hollow copper waveguide into the flexible waveguide > 90%. We also demonstrate the ability to nitrogen purge the flexible waveguide, increasing the power transmission by up to 20% at 2.85 THz, which paves the way for future fibre based terahertz sensing and spectroscopy applications.

Laser beam shaping offers remarkable possibilities to control and optimise process stability and tailor material properties and structure in laser-based welding and additive manufacturing. However, little is known about the influence of laser beam shaping on the complex melt-pool behaviour, solidified melt-track bead profile and microstructural grain morphology in laser material processing. A simulation-based approach is utilised in the present work to study the effects of laser beam intensity profile and angle of incidence on the melt-pool behaviour in conduction-mode laser melting of stainless steel 316L plates. The present high-fidelity physicsbased computational model accounts for crucial physical phenomena in laser material processing such as complex laser-matter interaction, solidification and melting, heat and fluid flow dynamics, and free-surface oscillations. Experiments were carried out using different laser beam shapes and the validity of the numerical predictions is demonstrated. The results indicate that for identical processing parameters, reshaping the laser beam leads to notable changes in the thermal and fluid flow fields in the melt pool, affecting the melt-track bead profile and solidification microstructure. The columnar-to-equiaxed transition is discussed for different laser-intensity profiles.

Laser acceleration of monoenergetic protons in a thin hydrocarbon target with protons as a minority species is studied theoretically and by simulation. We found there are two distinct stages of acceleration: radiation pressure acceleration of the target as a whole, followed by electron screened Coulomb repulsion of protons by carbon ions. The instabilities are largely suppressed, and the acceleration time with these combined mechanisms lasts ten times longer than with radiation pressure acceleration alone. We developed analytical theory, solved the proton equations of motion for the screened Coulomb acceleration, and compared with the simulation. Excellent agreement was obtained between the simulation result and the numerical solution. We found that the proton acceleration due to Coulomb repulsion in the second stage is effective. With 10% protons, a proton beam of more than ten billion in number can be accelerated to close to 1 GeV for a laser with less than 7 petawatt power over t...

The tight focusing properties of an azimuthally polarized Bessel Gaussian beam phase modulated by annular Walsh function filter is studied numerically by vector diffraction theory. It is observed that upon suitable optimization of order and annular obstruction ratio of an annular Walsh function filter, one can generate multiple sub wavelength scale optical tubes (optical holes) with super long focal depth. Such a focal system is usable for Nanolithography, particle trapping and transportation, as well as confocal and STED microscopy, microstructure fabrication etc.

ITER J. Karhunen1, A. Hakola1, J. Likonen1, A. Lissovski2, P. Paris2, M. Laan2, C. Porosnicu3, C.P. Lungu3, K. Sugiyama4 and JET EFDA Contributors∗ 1 VTT Technical Research Centre of Finland, Association Euratom-Tekes, 02044 VTT Finland 2 Institute of Physics, University of Tartu, 51010 Tartu, Estonia 3 INFLPR, MEdC EURATOM Association Magurele-Bucharest, 077125, Romania 4 MPI fur Plasmaphysik, EURATOM Association, D-85748 Garching, Germany ∗See the Appendix of F. Romanelli et al., Proceedings of the 24th IAEA Fusion Energy Conference 2012, San Diego, US Introduction Laser-induced breakdown spectroscopy (LIBS), based on studying the spectrum emitted in a laser ablation process, is a potential method for in situ studies of the compositions of mixed layers deposited on the first walls of future fusion reactors [1]. By LIBS, these layers could be monitored in between plasma discharges without the need for removing any wall components. In this contribution, the aim is to find optimal ex...

ITER J. Karhunen1, A. Hakola1, J. Likonen1, A. Lissovski2, P. Paris2, M. Laan2, C. Porosnicu3, C.P. Lungu3, K. Sugiyama4 and JET EFDA Contributors∗ 1 VTT Technical Research Centre of Finland, Association Euratom-Tekes, 02044 VTT Finland 2 Institute of Physics, University of Tartu, 51010 Tartu, Estonia 3 INFLPR, MEdC EURATOM Association Magurele-Bucharest, 077125, Romania 4 MPI fur Plasmaphysik, EURATOM Association, D-85748 Garching, Germany ∗See the Appendix of F. Romanelli et al., Proceedings of the 24th IAEA Fusion Energy Conference 2012, San Diego, US Introduction Laser-induced breakdown spectroscopy (LIBS), based on studying the spectrum emitted in a laser ablation process, is a potential method for in situ studies of the compositions of mixed layers deposited on the first walls of future fusion reactors [1]. By LIBS, these layers could be monitored in between plasma discharges without the need for removing any wall components. In this contribution, the aim is to find optimal ex...

We present a scalar variational method for the analysis of light-propagation characteristics in thermally diffused expanded core (TEC) fibers. The method leads to simple closed-form expressions regarding the mode field diameter, numerical aperture, waveguide dispersion as well as coupling losses produced by radial, longitudinal and angular misalignments. The dependence of coupling losses on the 'taper ratio' and normalized frequency is investigated and previous predictions that TEC fibers transmit light more effectively in free space over the order of millimeters, is confirmed. The coupling losses between small core diameter step-index fibers typically used in most erbium-doped fiber amplifiers and TEC-fibers is also considered.

We present a theoretical and experimental investigation of a very simple binary Diffractive Optical element referred as a phase slit. The latter is made up of two transparent plates of glass in which a phase step has been patterned using ion beam etching. The two phase steps are set parallel and are able to slide each on the other so that one can adjust continuously the width of the phase shifting zone that suffers an incident Gaussian beam. It is shown that the phase slit is able to make a 1-D transformation of a Gaussian beam either into a uniform profile or a hollow profile having a central depression whose depth can be continuously adjusted just by changing the width of the slit.

This paper presents a numerical investigation and statistical analysis of laser bending of Titanium sheets. The aim of the present simulation is to identify the response through response surface methodology related to bending angle and characterize the effects of input parameters: laser power, spot diameter, scanning speed and plate thickness. The numerical simulations are carried out based on the four factors, central composite face centered design. The statistical software Design-Expert® is used to create the design layout and to obtain the final regression equation. The numerical simulation is carried out by implementing a Gaussian surface heat flux, and convection-radiation boundary conditions through a commercial finite element software COMSOL MULTIPHYSICS. Investigations reveal that bending angle increases with laser power and decreases with the increase in scanning speed, spot diameter and plate thickness. The optimum process parameters for the target bending angle are also found based on misimisation of processing time and operating energy.

Necessary and sufficient conditions are presented that determine a generalized class of propagation-invariant wave fields. The existence of wave fields with transverse distributions that are periodically reproduced with different azimuthal orientations is demonstrated. These fields are conveniently described in the longitudinalazimuthal frequency representation. An interesting subclass is characterized by aperiodic rotated selfimages, in the sense that they never return to their original orientation along the propagation. Other subclasses include the conventional self-imaging wave fields, the so-called nondiffracting beams, and the rotating wave fields.

In this paper, we start from the well known DurninÕs experimental setup, finding general analytical formulae to investigate generation and propagation of nondiffracting beams. Our general formula makes possible considering any kind of angular modulation. As an example we discuss the Mathieu beams. Moreover, in the study of Bessel beams we consider the width of the slit to compare with the ideal case represented by a Dirac d transmittance function.

Various methods have been employed to produce Bessel beams (BBs), with axicon-based techniques remaining the most efficient. Among the limitations of axicons are manufacturing defects such as oblate tips and difficulty in tuning the generated BBs. In this work, we combine the effect of a blunt-tip axicon with refraction using various combinations of liquid media to generate variable BB intensity profiles. The output BBs from the axicon are made to pass through a custom-built fluid chamber and magnified using a telescope system. When traversing an empty chamber, the Bessel beam core diameter is measured to be 773.8 µm at propagation distance z’ = 30 cm. The core diameter increases as the beam passes through a chamber containing different liquids as a result of an effective axicon–telescope distance produced by the indices of refraction of the pertinent fluids. Bessel beams modified by the fluid chamber maintain the properties of non-diffraction and self-healing.