Dynamic Beam Shaping Research Articles

Investigating the effect of dynamic laser beam oscillations in remote fusion cutting process

The latest research on laser beam fusion cutting has revealed significant improvements in process productivity and cut quality through the use of dynamic beam shaping techniques. While many studies have investigated dynamic beam shaping for proximity cutting, the influence of laser beam oscillations on the remote fusion cutting process remains unexplored. The present work aims to study the effect of dynamic beam shaping on the remote fusion cutting process through analytical modeling, experimental investigations, and in situ high-speed monitoring. Initially, an analytical model based on thermodynamic analysis was developed to assess the influence of circular oscillations on the process zone. This model facilitates the evaluation of process performance from an energetic perspective, providing an estimate of the maximum achievable cutting speed for the remote fusion cutting process across various operating conditions. A significant increment in process productivity could be achieved through beam oscillations. Furthermore, based on theoretical findings, the effect of circular laser beam oscillations superimposed on the processing feed direction was experimentally investigated using a 1 mm thick AISI304 stainless steel material. A 6 kW fiber laser was utilized, alongside a high-speed camera-based system for in situ process monitoring. The experimental results demonstrate a significant increase in the process productivity under dynamic beam shaping conditions, consistent with theoretical findings. Specifically, the maximum achievable cutting speed could be increased from 0.13 to 0.20 m/s. Furthermore, the cut quality of produced samples was evaluated in terms of kerf morphology and profile.

Numerical Verification of a Polarization-Insensitive Electrically Tunable Far Infrared Band-Stop Meta-Surface Filter

Tunable filters have many potential applications in diverse fields, including high-capacity communications, dynamic beam shaping and spectral imaging. Although providing a high-performance solution for actively tunable devices, metasurface combined with tunable materials faces the great challenges of limited tuning range and modulation depth. Here, we propose a far-infrared tunable band-stop filter based on Fabry-Perot (FP) resonators and graphene surface plasmons. By switching the wavelength of the critical coupling condition of the filter via the gate voltage applied on graphene, achieving the dynamically tunable band-stop filtering at the central wavelengths from 12.4 μm to 14.1 μm with a modulation depth of more than 99%. Due to the symmetry of the proposed meta-atoms, the filter is insensitive to the polarization direction of the incident light. And it can realize more than 85% filtering efficiency within 60° angle of incidence around the vertical direction. By adjusting the geometry of the meta-atoms structure, it is feasible to move the operational range from the near-infrared to terahertz bands.

Laser cutting using dynamically modulated intensity distribution

The precise control of the laser beam intensity distribution facilitates the optimization of laser processing performance. This not only presents opportunities for enhancing the process efficiency but also proves advantageous in scenarios where the same laser power level is employed, surpassing traditional methods. This study introduces a novel approach by dynamically modulating the laser beam profile to achieve a non-symmetrical intensity distribution. A detailed investigation into the laser cutting process using modulated beam intensities is conducted by employing a high-speed imaging system. Moreover, the maximum cutting speed, cut edge quality, and cut kerf geometries are evaluated when different strategies are applied. The results demonstrate a noticeable improvement in the cut edge quality compared to a static beam strategy (SBS) and the recently developed conventional dynamic beam shaping (DBS). In addition to laser cutting, examples of such modulation in laser welding and hardening are proposed. This innovative technique offers promising advancements in the field of laser processing.

Design and implementation of dynamic beam shaping in high power laser processing by means of a Deformable Mirror

Optimising the laser intensity distribution in high power laser processes, such as laser welding, laser cladding or laser hardening, can be used to tailor the local thermal fields and thermal cycles which, in turn, determine the final process results. Deformable Mirrors allow to dynamically shape the beam profile and previous studies showed their potential. However, only limited flexibility in achievable beam shapes is shown at higher power levels. In addition the relation between desired laser intensity profiles and required mirror surface profiles is nontrivial. In this work the design and implementation of a dynamic beam shaping system, capable of handling high laser powers (up to 1 kW), is presented and evaluated. To that end, several distinctly different laser intensity profiles are defined, corresponding mirror surfaces are determined and realised with the beam shaping system. Measurements of the laser intensity profiles were compared with laser intensity profiles simulated using a previously presented mathematical framework and showed a good agreement. From the measurements it was concluded that the setup is suitable for high laser powers (up to 1 kW) and is characterised by large depth of focus (<14% change in dimensions at a distance of 100 mm from the focal plane).

Material dependent influence of ring/spot beam profiles in laser powder bed fusion

In recent years, the topic of beam shaping for improved laser material processing has rapidly grown influencing metal laser powder bed fusion (PBF-LB/M). Given the need to reduce the cost and improve control of the PBF-LB/M process to make it more competitive with traditional manufacturing methods, increasing productivity of PBF-LB/M is critical. When research reports a new beam profile (e.g. ring profile) to improve productivity on a specific material, it is often generalised, and assumed to have the capability to improve productivity in PBF-LB/M across the board. In this work, we use both low-fidelity simulations and experimental work to investigate the difference between Gaussian and ring/spot beam profiles on metals with very different thermal properties (a stainless steel and an aluminium alloy). We show that the two materials have opposite responses to the change in beam profile (both in terms of melt pool dimensions and thermal gradients); further, the most beneficial intensity distribution is dependent on the energy input to the material. This exemplifies yet another way in which the PBF-LB/M process is non-linear and contradicts the idea that a ring/spot laser profile is beneficial for all laser processing technologies. This highlights the need for further research into the non-linear effect of varying intensity distributions on laser processing before the benefits of dynamic beam shaping can be truly realised.

Control of meltpool shape in laser welding

In laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.

Azo-carbazole copolymer-based composite films for rewritable vector holograms

Vector holography has emerged as a promising technique that unlocks the polarization degree of freedom of light to be used for generating, storing, and reproducing information. Vector holograms with rewritable capabilities are desirable in applications such as optical computing, data storage, dynamic beam shaping, optical communication, etc. However, the development of materials for rewritable vector holography poses significant challenges. Materials such as photopolymers and metamaterials for vector holograms show good performance and long-term storage capabilities but do not possess rewritable capabilities. On the other hand azo-based polymers, azobenzene liquid crystals, and photorefractive polymers are rewritable but often fail to satisfy other requirements such as higher diffraction efficiency, faster response, stability, and long-term storage, etc., simultaneously. In this study, we have investigated the potentials of azo-carbazole copolymer film for vector holography applications by conducting a thorough study on its polarization recording/reconstruction characteristics, for the first time. We found that the material exhibits a higher diffraction efficiency, reaching up to 85%, with good stability. The recording requires only a short exposure of 5 seconds, using laser power of a few milliwatts/cm2. Our findings indicate that the proposed azo-carbazole polymer material holds great potential for evolving into the ‘rewritable vector holography recording material’ for the future, and is capable of advancing the field of vector holography and related applications.

Response of the melt pool and vapour capillary on dynamic beam shaping in the kHz regime during laser welding

Beam shaping technologies provide the possibility to distribute the optical energy of the laser beam on the workpiece in multiple ways. One of the latest technologies is coherent beam combining (CBC) of 32 fiber lasers, which allows quasi-instantaneous switching of beam shapes during laser material processing with frequencies up to 10 MHz. A study was performed for laser welding of stainless steel 1.4301, to investigate the influence of the switching frequency between two beam shapes on the capillary shape. Therefore, the beam shape was switched between a single spot and four spots, which leads to a maximum intensity variation. Frequencies between 10 Hz and 10 kHz were investigated. The results show, that the melt pool shape and the capillary shape follow the switching frequency until a limit frequency.

Laser beam welding of high thickness sheet metal with highly dynamic beam shaping

Lasers with highly dynamic beam shaping have recently become available on the market. This article examines the question of whether it is possible to influence the welding result in terms of the weld seam formation (upper bead, root) and the microstructure with very high beam oscillation. Four different beam shapes are tested at different frequencies (up to 100 kHz) on material AH36 with a thickness of 8 mm.

Laser cutting of CFRP using novel cutting strategies

Laser cutting of carbon fibre reinforced plastics generates a heat affected zone (HAZ) in the vicinity of the cut, affecting the integrity of the material and therefore the uptake of laser cutting for composite applications. This work uses mechanical testing to determine the effect of laser cutting on material properties and to see if they correlate with the observed HAZ. The potential for an extended-HAZ (exHAZ), where polymer remains but the properties have changed due to the proximity to the laser cut, is considered. This more novel concept of the exHAZ is important in understanding the performance of laser cutting CFRP and enabling wider use. A 2 kW multimode 1070 nm continuous wave fibre laser and a range of cutting strategies have been used to determine the influence of different cutting parameters on the HAZ. Cuts are generated using single and multi-pass (pseudo pulsed) cutting strategies with a range of assist gas pressures. The effect of assist gas has been largely overlooked in laser cutting of CFRP to date. The results obtained will provide guidance for future dynamic beam shaping work.

In-source dynamic beam shaping of Al alloys processed via LPBF: effect of novel beam profiles on surface roughness and microstructure

Next-generation fiber laser sources can dynamically combine Gaussian beams with ring distributions within the source. The irradiance manipulation may add flexibility to the Laser Powder Bed Fusion process, for instance to control microstructure or surface roughness. However, their use is limited by a lack of studies revealing how beam shaping can be exploited in a reproducible manner. Accordingly, this work shows the use of novel beam profiles provided by a multi-core fiber laser source in the LPBF of AlSi7Mg0.6. Irradiance profiles were characterized, then large experiments were conducted to investigate their effect on surface roughness and microstructure of produced parts.

Dynamic beam shaping for LED lighting

We describe an electrically tunable liquid crystal microlens array with a 65 mm clear aperture that allows the dynamic symmetric broadening of white light without mechanical movements. The fundamental mechanism of broadening is demonstrated to involve a spatial twist of molecular orientation. Continuous variations of the light divergence angle are obtained in a very large dynamic range (from 8° to 50°). Particular attention is paid to maintain the desired intensity and color temperature distributions over the angle. The developed lens may be used in various broadband illumination applications based on light-emitting diode-pumped phosphor sources.

Cutting thick aluminum plates using laser fusion cutting enhanced by dynamic beam shaping

Cutting thick plates is affected not only by the laser power but also by the cut kerf width and the melt flow dynamics that determine the ejection of the molten material. Employing the same laser beam intensity distribution for various thicknesses is the limiting factor when cutting thicker plates. This paper investigates fiber laser fusion cutting of 25 mm thick aluminum with dynamic beam shaping (DBS). While both static and longitudinal dynamic intensity distributions fail to cut this thickness with a 4 kW laser power, a cut through is achieved using annular and elliptical intensity distributions. However, an improvement of 45% in cutting speed can be achieved using an elliptical intensity distribution compared to an annular one. In order to understand the effect of the beam shape, an infrared thermal camera is used to study lateral heat propagation when using different process parameters. Moreover, to analyze the melt flow when changing the DBS frequency, high-speed imaging is utilized to observe the molten material inside the cut kerf. Finally, the cut edge quality is investigated for different cutting conditions.

Comprehensive benchmarking of laser welding technologies including novel beam shapes and wavelengths for e-drive copper hairpins

Laser welding is the industrially accepted method for the joining of Cu hairpin windings in the production of electric drives. High brilliance laser beams are scanned over the bare ends of the Cu wires producing a rapid connection through deep penetration remote welding. Despite being an accepted manufacturing method, laser welding of Cu hairpins still requires detailed studies concerning manufacturing productivity and quality. As the availability of novel laser sources with higher power levels, new wavelengths, and beam shaping capabilities increase, the need for benchmarking studies emerges. In this work, six different laser welding systems were compared in terms of process productivity and quality during the welding of Cu hairpins used for automotive traction. The different solutions presented power levels from 3 to 6 kW, with wavelengths from near infrared (NIR) to visible, including in source dynamic beam shaping. The weld bead formation was observed through high-speed imaging. The welds were analyzed in terms of their geometry, internal defects, and most relevantly for their mechanical strength. The results showed advantages of each of the employed system while the laser systems providing the highest irradiance profile produced the fastest weld with more elevated mechanical strength independently from the wavelength.

Dynamic beam shaping requirements for fiber laser cutting of thick plates

A significant improvement in laser cutting productivity and quality can be achieved using dynamic beam shaping (DBS). However, the broad potential of improving the cutting performance of thick plates by employing DBS has not been fully explored. This paper uses an extensive experimental campaign to evaluate laser cutting results using DBS for different industrially relevant materials and thicknesses. Moreover, optimum amplitude and frequency for different material-thickness combinations regarding maximum achievable cutting speed are investigated. In addition, the effects of changing DBS parameters on dross, roughness, heat-affected zone, and kerf area are explored and correlated to the material removal mechanism. Finally, the laser cutting performance using DBS is compared with static beam cutting applied on higher laser powers. The results demonstrate that the performance of a 4 kW laser cutting machine reinforced by DBS is higher than a 6 kW laser cutting machine with a static beam strategy (SBS) when cutting thick plates.

Kirigami‐Inspired Planar Deformable Metamaterials for Multiple Dynamic Electromagnetic Manipulations

AbstractThe Kirigami technique has recently inspired the design of reconfigurable electromagnetic metamaterials that can be easily realized by embedding a patterned cutting array into a supportive substrate. However, these existing designs mainly focus on the 2D‐to‐3D transformable morphology that induces the modulation of the spectral responses. This work proposes a kirigami‐based planar reconfiguration mechanism and extends advanced applications in the dynamic near‐field imaging and tunable double‐foci metalens. These extraordinary tunabilities originate from three meta‐atoms that can be mutually transformed into the morphologies with non‐chirality and opposite chirality under the tensile strain. By utilizing the transmittance characteristics of reconfigurable meta‐atoms, the metamaterial is constructed to achieve three‐foldable near‐field displays and a longitudinal double‐foci metalens empowered with tunable focusing length and intensity ratio. Two anisotropic chiral meta‐atoms in deformed states that possess overwhelming transmittance difference of circularly cross‐polarized components to magnify the focusing intensity ratio of two foci for the proposed metalens are further proposed. The exhibited observations provide typical examples of a wide spectrum of applications of the kirigami‐based reconfiguration mechanism, and it may pave the avenue to spark manifold functional devices for applicable electromagnetic manipulations such as multifunctional hologram display, dynamic beam shaping, and steering, as well as the conformal design of meta‐devices.

Polarization-controlled nonlinear computer-generated holography

Dynamic phase-only beam shaping with a liquid crystal spatial light modulator is a powerful technique for tailoring the intensity profile or wave front of a beam. While shaping and controlling the light field is a highly researched topic, dynamic nonlinear beam shaping has hardly been explored so far. One potential reason is that generating the second harmonic is a degenerate process as it mixes two fields at the same frequency. To overcome this problem, we propose the use of type II phase matching as a control mechanism to distinguish between the two fields. Our experiments demonstrate that distributions of arbitrary intensity can be shaped in the frequency-converted field at the same quality as for linear beam shaping and with conversion efficiencies similar to without beam shaping. We envision this method as a milestone toward beam shaping beyond the physical limits of liquid crystal displays by facilitating dynamic phase-only beam shaping in the ultraviolet spectral range.

Broadband structured light using digital micro-mirror devices (DMDs): a tutorial

Laser beam shaping is a venerable topic that enjoyed an explosion in activity in the late 1990s with the advent of diffractive optics for arbitrary control of coherent fields. Today, the topic is experiencing a resurgence, fuelled in part by the emerging power of tailoring light in all its degrees of freedom, so-called structured light, and in part by the versatility of modern day implementation tools. One such example is that of digital micro-mirror devices (DMDs), for fast, cheap and dynamic laser beam shaping. In this tutorial we outline the basic theory related to shaping light with DMDs, give a practical guide on how to get started, and demonstrate the power of the approach with several case studies, from monochromatic to broadband light.

Programmable freeform optics with extended white light sources: possibilities and limitations.

Freeform optics can be used in lighting applications to generate accurate prescribed illumination patterns from compact light sources such as LEDs. When targeting dynamic illumination systems, a time-variable optical functionality is needed. Phase-only spatial light modulators (SLMs) have been used in the past for various dynamic beam shaping applications with monochromatic, zero-étendue illumination under paraxial conditions. Such limitations can no longer hold when considering lighting applications. In this paper, a novel algorithm for the calculation of smooth phase shift patterns is presented in order to generate arbitrary target patterns from arbitrary incident wave fronts for non-paraxial conditions. When applying such phase shift patterns to SLMs, these devices can be considered as programmable freeform optics. The experimental performance of the calculated phase patterns is analyzed on a real SLM, with a maximal phase shift of 6π, for collimated laser beams and white LEDs. The possibilities and limitations of generating accurate prescribed target patterns are critically discussed in terms of the angular extent of the target pattern, the consider spectrum of the light source and the étendue of the incident light beam.

The influence of novel beam shapes on melt pool shape and mechanical properties of LPBF produced Al-alloy

New generation of multi-core fiber laser sources provide in-source dynamic beam shaping. Such sources can switch between Gaussian and ring beams, providing new irradiance profiles. The new irradiance profiles add up to the process flexibility for controlling the temperature fields generated in the laser powder bed fusion (LPBF) process. On the other hand, they bring further complexity as new process parameters should be defined and their influence on the mechanical properties unveiled. Accordingly, this work studies the use of seven different beam shapes provided by a multi-core industrial fiber laser source with beam diameters varying between 47 μm to 144 μm during the LPBF of AlSi7Mg0.6 alloy. The beam spatial profiles were measured and descriptive irradiance parameters were defined. The Al-alloy constituted a challenging material type due to its high reflectivity and low melting point, hence, more prone to lack-of-fusion and keyhole defects. LPBF experiments were conducted at fixed energy density and peak irradiance levels investigating the influence of the beam shapes on the melt pool geometry in prismatic samples. The results showed that the peak irradiance and the ring intensity had a direct impact on the melt pool aspect ratio (AR) and melt pool depth to layer thickness ratio (h/z). With all the conditions providing adequately dense parts (>99.5 %), the mechanical properties were found to be correlated to the melt pool geometry. The results confirm that the beam shape can be tuned between the central peak and the ring to further manipulate the material properties in LPBF.