Galvo Scanner Research Articles

Two-photon polymerization-based fabrication of millimeter-sized precision Fresnel optics

Two-photon polymerization (2PP) is known to be the most precise and highest resolution additive manufacturing process for printing optics, but its applicability is restricted to a few applications due to the limited size of printable objects and low throughput. The presented work is intended to demonstrate the performance of printing millimeter-scale optics by implementing appropriate stitching methods into a setup that combines a Galvo scanner and translational axes. In this work, specifically, Fresnel axicons with a diameter of 3.5 mm are manufactured by 2PP to substantiate the applicability of the process. Manufacturing Fresnel optics instead of volumetric optics allows for attaining acceptable process times with durations of tens of hours highlighting the appeal of 2PP for rapid prototyping in optics. The suitability of the Fresnel axicons for beam shaping is confirmed through illumination with a laser beam. The resulting ring-shaped intensity distribution in the far field behind the Fresnel axicon is captured using a beam profiler. Furthermore, the influence of different stitching parameters on the resulting intensity distribution is investigated. The experimental results are validated by simulations, where the intensity distribution in the far field behind an axicon was calculated by Fourier transformation. Simulations were carried out to discuss the effect of manufacturing errors on the far field intensity distribution.

Experimental Investigation on the Effect of Nickel-plating Thickness on Continuous-wave Laser Welding of Copper and Steel Tab Joints for Battery Manufacturing

The welding of dissimilar materials, such as copper and steel, holds significant industrial significance in the production of electric vehicle batteries. These materials are commonly used in the case of connections between busbars and cylindrical cells inside a battery pack. To optimize welding and guarantee protection against corrosion, nickel is commonly used in the form of a coating. In this paper, the effect of nickel plating thickness on copper-to-steel welds made with laser technology is investigated. The initial phase consists of a statistical characterization of the nickel plating thickness of the busbar in order to identify the thickness ranges. Experiments were conducted using two different fiber laser sources (a single-mode laser source and a beam-shaping laser source) equipped with a Galvo scanner head; the fluence value and the thickness of nickel plating varied during the experiments. The study conducted has revealed that the thickness of nickel plating plays a crucial role in the weld bead interface, particularly when using a single-mode source. Furthermore, when using the beam-shaping laser source, the fluence employed can have a significant impact on both the depth of penetration and the interface width.

Ultrashort pulse laser micro processing strategies for fast beam deflection with acousto-optical deflectors

Acousto-optical deflectors (AOD) enable laser pulse-synchronous beam deflection up to the MHz range, which can deviate from the usual path control and raster scan strategies. Where the small working field of the AODs is not sufficient, a combination with a galvo scanner or an axis system can be used. Laser micromachining with modern ultrashort pulse lasers with a high pulse repetition rate is increasingly faced with the challenge of applying the laser power to the workpiece without too much heat remaining locally in the surface. AOD-based beam deflection can help here by quickly distributing the laser pulses on the surface, which is equivalent to a locally reduced laser pulse repetition rate without reducing the laser’s repetition rate. We provide an overview of the technology and present examples of innovative machining strategies resulting from the use of acousto-optical laser beam deflection.

High speed laser cutting of ultrathin metal foils for battery cell production

Laser-based manufacturing has become a key enabling technology in the production of batteries and battery cells for the e-mobility field. Several applications, in fact, have already been industrialized, such as laser-based welding, cutting, stripping, and cleaning. Among all those technologies, laser cutting, in particular, has to deal with several very stringent constraints: the presence of highly reflective materials (aluminum and copper), very low thicknesses (6–12 μm), on-the-fly processing, and high quality of the cutting surface. According to those considerations, the present paper deals with the application of remote cutting of 12 μm thick aluminum and 6 μm thick copper foils by means of a galvo scanner and two different fiber laser sources: single mode constant wave and nanosecond pulsed wave ones. The experimental activity is devoted to understanding the feasibility of the process and to point out the pros and cons of the two different lasers involved. The cutting edges are analyzed by means of optical and SEM microscopy, in order to characterize cutting quality. The process is also characterized in terms of maximum achievable speed in order to understand the limits of both lasers and galvo scanning systems.

Infrared pulsed fiber laser-produced gold and silver-109 nanoparticles for laser desorption/ionization mass spectrometry of steroid hormones.

Hormones are compounds that perform many important functions in the human body, but above all their task is to maintain homeostasis by adapting them to the constantly changing environmental conditions. Even minor hormonal disorders have a negative effect on the body, leading to physical or mental changes. Therefore, monitoring these changes and precise quantification of hormones are essential for the early diagnosis of diseases related to hormonal disorders. Application of monoisotopic silver-109 and gold nanoparticles obtained by PFL (pulsed fiber laser) 2D GS (galvo-scanner) LGN (laser-generated nanomaterial) for high-resolution laser desorption/ionization mass spectrometry (LDI-MS) and mass spectrometry imaging (MSI) of steroid hormones is presented. Four steroid hormones, estrone, prednisolone, corticosterone and progesterone, were used as test compounds for quantitative analysis with matrix-assisted LDI time-of-flight MS apparatus. Moreover, comparison of manual measurements and semiautomatic MSI with both types of nanoparticles was performed. Methods were also tested on spiked human blood serum for quantification of steroid hormones and for estimation of the matrix effect. Hormones were directly tested in 1000 000-fold concentration change conditions ranging from 1mg/mL to 1ng/mL which equates to 300 ng to 300 fg of hormone per measurement spot. For almost all tested hormones MSI allowed one to obtain equal or lower limit of detection value than manual LDI-MS. The best results judged by lowest limit of detection values are found for silver-109 nanoparticles. The results of the quantitative analysis of steroid hormones using silver-109 and gold nanoparticles prepared with PFL 2D GS LGN for LDI-MS and semiautomatic LDI-MSI are presented. It has been proven that nanoparticles obtained by laser synthesis can be successfully used for the analysis of steroid hormones in a wide range of concentrations.

Surface Laser Micropatterning of Polyethylene (PE) to Increase the Shearing Strength of Adhesive Joints

In the introduction, we present an overview of previous research on this subject in order to help the reader review possible technological solutions regarding the joining of construction materials. The original research presented in this article concerns the results of increasing the shear strength of adhesive joints of plastics using various types of surface preparation (laser texturing). Laser texturing consists in developing the surface by applying various geometric patterns of appropriate shapes and depths, as well as its density on the surface. The above parameters are currently selected in an empirical way as research is still being developed as part of a research project. The textures obtained in this way are subjected to microscopic examination. Then, a layer of glue is applied, and the samples prepared in this way, after drying, are subjected to various destructive tests, e.g., tensile, shear, and bending. In this article, we attempted to test the strength of the bonded joint of polyethylene (PE). The impact of a laser beam with ultrashort picosecond pulses was used in the research. Tools in the form of a TRUMPF TruMicro 5325c device integrated with a SCANLAB GALVO scanning head were used. This enabled ablative material removal without the presence of a heat affected zone (HAZ) in the non-laser part. Ultrashort laser pulses remove material without melting the non-exposed area by the laser beam. On the basis of the tests performed (in this article and previous research works of the authors), it was shown that the method increases the shear strength of the glued joints made in the tested construction materials. This is confirmed by laboratory results of tribological tests. The laser treatment parameters used, which are shown in this article, did not lead to the appearance of cracks in the micromachined materials. Research has shown that the connections between elements with a properly selected micropattern are characterized by a several-fold increase in the strength of joints, unlike materials without a micropattern. The presented method may be helpful for use as a technology for joining plastics.

Active-Feedback 3D Single-Molecule Tracking Using a Fast-Responding Galvo Scanning Mirror.

Real-time three-dimensional single-particle tracking (RT-3D-SPT) allows continuous detection of individual freely diffusing objects with high spatiotemporal precision by applying closed-loop active feedback in an optical microscope. However, the current tracking speed in RT-3D-SPT is primarily limited by the response time of the control actuators, impeding long-term observation of fast diffusive objects such as single molecules. Here, we present an RT-3D-SPT system with improved tracking performance by replacing the XY piezoelectric stage with a galvo scanning mirror with an approximately 5 times faster response rate (∼5 kHz). Based on the previously developed 3D single-molecule active real-time tracking (3D-SMART), this new implementation with a fast-responding galvo mirror eliminates the mechanical movement of the sample and allows a more rapid response to particle motion. The improved tracking performance of the galvo mirror-based implementation is verified through simulation and proof-of-principle experiments. Fluorescent nanoparticles and ∼1 kB double-stranded DNA molecules were tracked via both the original piezoelectric stage and new galvo mirror implementations. With the new galvo-based implementation, notable increases in tracking duration, localization precision, and the degree to which the objects are locked to the center of the detection volume were observed. These results suggest that faster control response elements can expand RT-3D-SPT to a broader range of chemical and biological systems.

Video-rate mid-infrared photothermal imaging by single-pulse photothermal detection per pixel.

By optically sensing absorption-induced photothermal effect, mid-infrared (IR) photothermal (MIP) microscope enables super-resolution IR imaging of biological systems in water. However, the speed of current sample-scanning MIP system is limited to milliseconds per pixel, which is insufficient for capturing living dynamics. By detecting the transient photothermal signal induced by a single IR pulse through fast digitization, we report a laser-scanning MIP microscope that increases the imaging speed by three orders of magnitude. To realize single-pulse photothermal detection, we use synchronized galvo scanning of both mid-IR and probe beams to achieve an imaging line rate of more than 2 kilohertz. With video-rate speed, we observed the dynamics of various biomolecules in living organisms at multiple scales. Furthermore, by using hyperspectral imaging, we chemically dissected the layered ultrastructure of fungal cell wall. Last, with a uniform field of view more than 200 by 200 square micrometer, we mapped fat storage in free-moving Caenorhabditis elegans and live embryos.

Galvanometer driven optical system for laser dynamic focusing.

This paper proposes a novel dynamic focusing module driven by galvanometers to position the laser focus with high speed and high precision. Thanks to the extremely high repeatability and the fast response time of galvanometers, the repeatability of the laser focus positioning is far less than the Rayleigh length of the beam and its response time is around 600 µs. An important feature of the proposed module lies in that it can be further integrated to an XY galvo scanner to realize a 3-axis laser scanning system. Due to the same galvanometers of the dynamic focus module and the XY scanner, the laser focus could be positioned in a simultaneous, rapid and precise manner in all three axes. Various simulation and experimental results demonstrate the feasibility and performance of the proposed dynamic focus module and the processing capability of the 3-axis scanning system with the proposed module.

Iterative closest point-based data fusion of non-synchronized in-situ and ex-situ data in laser powder bed fusion

With the development of additive manufacturing (AM) processes, a variety of methods and technologies for process monitoring and post-process inspection have become available. These, together with modern computerized machines, generate large amounts of data about the process. Hence, efficient analysis methods for extracting useful information and knowledge from these datasets are needed. This paper presents a method for automated data fusion of machine input toolpath commands, on-axis intensity monitoring, and Computed Tomography (CT) scan measurement data in laser metal powder-bed fusion AM. The iterative closest point (ICP) point-clouds registration method is used for fine spatial alignments of (1) on-axis intensity measurements with machine input toolpath commands and (2) machine input toolpath and CT scan. The input-toolpath point cloud is selected as the reference point cloud. We further propose a post-processing method that can correct part of the wrong connections between measurements and toolpath points as results of ICP registration. The proposed method is suitable for merging data where there is no temporal synchronization between the machine commands and the monitoring system, and where the actual laser scan path may deviate from the machine input toolpath commands, e.g., due to dynamics constraints of scanning galvo mirror system. The method is designed to handle dynamic changes in input process parameters such as dynamic changes in laser power and scan speed, which lays a solid foundation for advanced AM process control, qualification and certification. A practical solution for organizing and storing the fused data, which allows for efficient analysis, is also presented. The results show that the method can spatially align all three different types of data and find the corresponding input toolpath command for each measurement point. The alignment of on-axis measurements and machine input toolpath commands has been improved by using a clustering algorithm. The main limitation is that, for estimating the improvement and error of spatial alignment, the average difference between the closest points of two point clouds is used, but this metric does not give an exact value of an actual registration error. The estimation of connectivity error is based on a visual comparison of registration results.

Energy consumption and performance optimisation of laser cleaning for coating removal

Selective removal of coatings by lasers can facilitate the reuse of coated tools in a circular economy. In order to optimise and control the process, it is essential to study the impact of process input variables on process performance. In this paper, coating removal from tooling was carried out using a picosecond a pulsed fibre laser, in order to investigate the effects of laser pulse energy, pulse frequency, galvo scanning speed and scanning track stepover. A fractional factorial design of experiments and analysis of variance was used to optimise the process; considering cleaning rate, specific energy consumption and surface integrity as assessed by changes in surface roughness and composition of the tooling after laser cleaning. The results shows synergy between cleaning rate and specific energy with the laser pulse frequency and galvo scanning speed as the two most significant factors, while the laser pulse energy had the greatest contribution to changes in surface composition. Based on extensive experiments, the relationship between processing rate and system specific energy consumption was mathematically modelled. The paper contributes a new specific energy model for laser cleaning and provides a benchmark of the process energy requirements compared to other manufacturing processes. Additionally, the generic scientific learning from this is that the rate of energy input is a key tool for maximising cleaning rate and minimising specific energy requirements, while the intensity of energy applied, is a key metric that influences surface integrity. More complex factors, influence the surface integrity.

LIPSS and DLIP: From hierarchical to mutually interacting, homogeneous, structuring

Direct Laser Interference Patterning (DLIP) and Laser Induced Periodic Surface Structures (LIPSS) are two distinct, key technologies for texturing of surfaces with structures in the range comprised between some hundreds of nm and few µm. Based on different physical phenomena, they enable structures often showing distinct morphologies and pitches. It has been shown the possibility of superposing LIPSS over DLIP with a final multi-scale, hierarchical morphology where the two structures coexist. Here, we report an experimental study showing that it is possible to turn from a hierarchical to mutual interacting texturing where DLIP and LIPSS give rise to a novel, uniform texturing having a homogeneous morphology with highly regular periodicity and low orientation dispersion. Moreover, we show that our approach makes possible an unexpected, significant reduction of the LIPSS period from the conventional values (roughly comprised between 0.7λ – 0.9 λ) to ∼0.45λ. In addition, for all the tests an industrial set-up has been used including an IR, ps laser, an f-theta lens with relatively high NA and a galvo scanner making possible the extension of the process over large area. Results are discussed in the light of different LIPSS generation models. We believe that our results represent a significant step forward through the further miniaturisation of laser induced morphologies opening the possibility for innovative surface functionalisations (anti-reflective, wide spectrum antimicrobial activity) to be exported in an industrial environment.

Infrared pulsed fiber laser-produced silver-109-nanoparticles for laser desorption/ionization mass spectrometry of amino acids.

Application of monoisotopic cationic 109Ag nanoparticles (109AgNPs) obtained by pulsed fiber laser (PFL) 2D galvo-scanner (GS) laser generated nanomaterial (LGN) for both high resolution laser desorption/ionization mass spectrometry and mass spectrometry imaging of amino acids is presented. Four amino acids, alanine, isoleucine, lysine, and phenylalanine were used as test compounds for quantification with matrix-assisted laser desorption/ionization mas (MALDI)-type mass spectrometer. Comparison of commonly made manual measurements with semiautomatic mass spectrometry imaging (MSI) was performed providing very interesting findings. Amino acids were directly tested in 1000 000-fold concentration change conditions ranging from 1mg/ml to 1ng/ml, which equates to 500 ng to 500 fg of amino acid per measurement spot. Methods were also tested on samples of human blood plasma for quantification of endogenous amino acids.

Infrared pulsed fiber laser-produced silver-109-nanoparticles for laser desorption/ionization mass spectrometry of carboxylic acids

Application of monoisotopic cationic 109Ag nanoparticles (109AgNPs) obtained by PFL (pulsed fiber laser) 2D GS (galvo-scanner) LASiS (laser ablation synthesis in solution) for high resolution laser desorption/ionization mass spectrometry and mass spectrometry imaging of carboxylic acids is presented. Six acids, azelaic, 3-methylhippuric, linoleic, oleic, arachidic and erucic acid were used as test compounds for quantification with a MALDI-type mass spectrometer. Comparison of commonly made manual measurements with semi-automatic MSI was performed providing very interesting findings. Carboxylic acids were directly tested in 1 000 000-fold concentration change conditions ranging from 1 mg/mL to 1 ng/mL, which equates to 300 ng to 300 fg of carboxylic acid per measurement spot. Methods were also tested on samples of spiked human blood serum for quantification of carboxylic acids and verification of the influence of biological matrix on the measurement.

Illumination angle correction during image acquisition in light-sheet fluorescence microscopy using deep learning.

Light-sheet fluorescence microscopy (LSFM) is a high-speed imaging technique that provides optical sectioning with reduced photodamage. LSFM is routinely used in life sciences for live cell imaging and for capturing large volumes of cleared tissues. LSFM has a unique configuration, in which the illumination and detection paths are separated and perpendicular to each other. As such, the image quality, especially at high resolution, largely depends on the degree of overlap between the detection focal plane and the illuminating beam. However, spatial heterogeneity within the sample, curved specimen boundaries, and mismatch of refractive index between tissues and immersion media can refract the well-aligned illumination beam. This refraction can cause extensive blur and non-uniform image quality over the imaged field-of-view. To address these issues, we tested a deep learning-based approach to estimate the angular error of the illumination beam relative to the detection focal plane. The illumination beam was then corrected using a pair of galvo scanners, and the correction significantly improved the image quality across the entire field-of-view. The angular estimation was based on calculating the defocus level on a pixel level within the image using two defocused images. Overall, our study provides a framework that can correct the angle of the light-sheet and improve the overall image quality in high-resolution LSFM 3D image acquisition.

Ruled surfaces generated by gimbaled mirrors: II. A comparative study of gimbaled mirrors with the dual axis galvanometric scanners for XY scanning.

The theory developed in the first part of this study [J. Opt. Soc. Am. A38, 1884 (2021)JOAOD60740-323210.1364/JOSAA.435621] is extended to an investigation of the ruled surface produced by a gimbaled mirror and its applications to formulate a new criterion that uses the base curve of the ruled surface as a reference scale to divide the scan field into near and far zones and to investigate ruled surfaces produced by the 1D mirror-scanning systems, such as the monogon, the polygon, and the galvanometric scanners as the special cases of that produced by a gimbaled mirror. Results obtained from the two applications described above lead to placing the ruled surface produced by scanners of different architectures on a platform and then bridging them up by the ruled surfaces they produced for a performance comparison. Although all these scanners may have very different scanning geometries and different application areas, there is one thing making them comparable: the key parameters of the ruled surfaces they produced. As an example, we compare the ray deviation power of a gimbaled mirror with that achievable by a dual galvo scanner for XY scanning by way of the key parameters of the ruled surfaces they produced.

Submicrometer surface shaping and surface repair of metals via laser ablation

Metal foils with precise thicknesses are required for use as laser targets in high energy density physics experiments. To achieve the micrometer scale tolerances accompanying these applications, the authors have developed a laser ablation technique utilizing burst pulses from a femtosecond laser operated in concert with a high-speed galvo scanning system. For authors’ application, an optimum laser processing format consisted of 250 fs laser pulses arranged in pairs, with the pulse separation in each pair equal to 400 ps and high galvo scanning speeds (∼2000 mm/s). These parameters enable the authors to thin and shape metals (depleted uranium, beryllium, tantalum, and iron) and remove unwanted variations in foil thickness over meaningful foil sizes. Double femtosecond pulses enable ablation that mitigates some undesirable pre-existing surface structures such as residual scalloping and scratches and lead to a surface roughness near 300 nm. Precise ablation rates were correlated to laser processing area and foil thickness. Finally, ablation rates were correlated to bulk surface temperature by tracking workpiece heating during ablation. These techniques yield the ability to apply highly controlled thickness maps with micrometer accuracy and tens of nanometer precisions. This control has demonstrated the ability to level foils with micrometer scale thickness deformities and create various programmed patterns that are difficult or out of reach of traditional machining methods.

High-rate laser processing with ultrashort laser pulses by combination of diffractive elements with synchronized galvo scanning

AbstractThe combination of diffractive optical elements or spatial light modulators with fully synchronized galvo scanners offers a possibility to scale up machining processes with ultra-short pulses to several 100 W of average power with minimal thermal impact. This will be demonstrated with the high-rate applications multi-pulse drilling on the fly and material removal with special intensity distributions up to an average power of 162 W and a removal rate of 16.5 mm3/min. Based on the experimental results strategies to achieve drilling rates of several 10,000 holes/s or removal rates of multiple 10 mm3/min will be discussed.

Experimental investigation on the effect of spot diameter on continuous-wave laser welding of copper and aluminum thin sheets for battery manufacturing

Welding of dissimilar materials, particularly copper and aluminum alloys, has gained considerable industrial interest in many different electric and electronic fields, such as the production of lithium-ion batteries for automotive applications. The differences in physical and chemical properties of these materials make fusion welding processes difficult to apply due to the formation of hard and brittle intermetallic compounds that impair both mechanical and electrical performance. In this paper, the effect of spot diameter on dissimilar laser autogenous lap-welding of copper and aluminum was studied. Experiments were conducted using a mid-power fiber laser source equipped with a galvo scanner and two different focal lengths to obtain two different spot diameters. The results showed that a smaller spot diameter promoted the formation of sound weld beads with better control of penetration depth, reduced mixing of the base metals and lower laser power requirements. By selecting the correct process parameters, good mechanical properties and low contact resistance could be obtained with both focal lengths. SEM-EDX analysis confirmed that a smaller spot diameter minimized the formation of copper rich phases in the weld bead.

High-speed wide-angle interleaved scanning technique for a 3D imaging lidar

In this paper, we describe a novel interleaved scanner for an eye-safe 3D scanning lidar system to measure aerodynamic phenomena in a wind tunnel using elastic backscatter from seeding particles. The scanner assembly consists of a rotating polygon scanner for line scanning along the fast axis, a galvanometer (galvo) scanner for scanning along the slow axis, angular position sensors, and motor controllers. The polygon scanner sweeps the lidar beam at up to 10,000 lines/s across a 27 deg angular field of regard in the fast axis, while the galvo scanner covers an angular range of 20 deg in the slow axis. Using this scanner, the lidar can perform nonintrusive flow visualization, velocimetry, and hard target mapping at millimeter-scale spatial resolution to a standoff range of 5 m at an update rate of 50 Hz for the full field of regard. An interleaved scanning methodology for the acquisition of two snapshots of 3D lidar intensity data with a 100 µs time offset is discussed. The design of the control and data acquisition electronics is described. The effects of rapid scanning on the response of a narrow field-of-view lidar are addressed. The design of the scanner is scalable and can be tailored to meet the requirements of other applications by increasing or decreasing the standoff range, angular field of regard, and scan rate.