Laser Research Articles

Fluidic laser beam shaper based on thermal lens effect in MoS2 and its application in optical trapping

In this work, we develop a fluidic laser beam shaper based on the thermal lens effect in MoS2 suspensions. It is demonstrated that another weak unfocused Gaussian beam (probe beam) is transformed into an annular beam due to the thermal lens effect resulting from a strong focused Gaussian beam (pump beam). The time evolution of the generated annular beam is studied, and the result shows that the annular beam exhibits asymmetric caused by heat convection with the high pump beam power. In addition, the tunability of the generated annular beam is investigated. Furthermore, the optical trapping of micro-sized particles in air using the annular beam is researched. It is found that this method exhibits stable performance capture for 3 h. The advantages of adjustable size, flexible setup and low cost of annular beam generated method are significant for lots of laser applications, such as optical trapping, optical imaging and laser machining.

Mitigation of laser plasma filamentation by rotating beam smoothing scheme

The propagation of intense laser beams in plasma inevitably gives rise to laser plasma instabilities, which have a significant impact on the illumination uniformity of the focused spot on the target in inertial confinement fusion (ICF) facilities. Here we propose an ultrafast smoothing scheme using a rotating beam (RB) to mitigate the laser plasma filamentation. Using the propagation model of the rotating beam in plasma for the laser-plasma self-focusing (SF) and filamentation, the filamentation characteristics of laser spots were analyzed. The results indicate that the rotating beam smoothing scheme, operating at picosecond timescale, exhibits superior mitigation effect of laser plasma filamentation.

Fiberoptic Laser-Induced Breakdown Spectroscopy System for in situ Measurement in a Hazardous Environment

We report the development of a novel fiberoptic laser-induced breakdown spectroscopy (FOLIBS) system for material characterization applications. The system utilizes a 1000-µm optical fiber to transport the laser beam to remote locations for elemental analysis via laser-induced breakdown spectroscopy. Air-fiber interface damage, internal damage, and air breakdown issues during laser-fiber coupling are identified and corresponding solutions are presented. For evaluating the physical properties of the plasma generated by the FOLIBS system, spectroscopic characterization is carried out using a titanium sample. The spectral features collected from a natural uranium sample are also presented. Hence, this rapid, remote, and flexible measurement technique is promising for in situ measurements in hazardous environments in nuclear energy, nuclear safeguards, and nonproliferation applications.

The change of the absorptance at the transition from partial- to full-penetration laser welding

AbstractFull-penetration laser welding processes are necessarily associated with significant changes of the geometrical properties of the keyhole at the beginning of the process when the keyhole expands all the way through the workpiece and finally pierces the bottom of the sheet. The impact that this transition has on the absorptance was investigated by means of X-ray imaging to determine the geometry of the keyhole and subsequent raytracing to calculate the distribution of the absorbed irradiance. The results show a significant drop of the overall absorptance when the bottom of the capillary opens through the rear side of the workpiece which in practice is noticed by an unstable behavior of the keyhole. Since the drop of the absorptance is less pronounced for smaller diameters of the keyhole, one may recommend the application of laser beams with small diameters at least during the initial phase until the keyhole is fully developed and reliably reaches through the bottom surface of the welded sheet.

The importance of adjusting the processing parameters for the resulting material density of PBF-LB AISI 316L lattice structures

Lattice structures are becoming more commonly used in the design of components for additive manufacturing. This is due to their ability to reduce the weight of manufactured parts, minimize material consumption, and achieve specific properties by modifying their geometry. As the applications of lattice structures continue to evolve, it is essential to determine whether the process parameters used in the PBF-LB (Laser Beam Powder Bed Fusion) process for manufacturing these structures should be the same as or different from those used for larger cross-sectional components. An analysis of the existing literature revealed insufficient data on this subject, which inspired this study. Experiments conducted using AISI 316L stainless steel showed that lattice structures can be produced with significantly lower volumetric energy density, while maintaining a high relative material density. In the experiment on lattice structures made of BCCZ and gyroid unit cells, a relative material density of over 99.5% was achieved with a volumetric energy density of approximately 33 J/mm3. These findings are significant for the fabrication of lattice structures. The lower volumetric energy density typically allows for greater geometric accuracy and reduced internal stresses. Furthermore, it has been proven that the nodes of the structure are critical places exposed to porosity formation.

Efficient spatial separation for chiral molecules via optically induced forces.

We investigate an efficient spatial enantioseparation method of chiral molecules in cyclic three-level systems coupled with three optical fields using optically induced forces. When the overall phase differs by π between two enantiomers, significant variations in the magnitude and direction of the optically induced forces are observed. The manipulation of the center of mass of chiral molecules in optical fields can be achieved through the induced gauge force, primarily generated from the variations in the chirality-dependent scalar potentials created by the three inhomogeneous laser fields. By appropriately configuring the system, we can completely separate the slow spatial and fast inner dynamics, making instantaneous eigenstates of the inner Hamiltonian independent of the transverse profiles of the laser beams. Compared to previous methods, which required adiabatic conditions to be satisfied, the proposed method overcomes the limitations of the adiabatic approximation by utilizing a specific system configuration. This allows for increased flexibility in the transverse profiles of the laser beams and relaxes the constraints on the velocity of chiral molecules, leading to significantly greater spatial separations achievable across a broader range of parameters.

A Case Study of a Laser Beam Welding Model for the Welding of Inconel 718 Sheets of a Dissimilar Thickness

A Case Study of a Laser Beam Welding Model for the Welding of Inconel 718 Sheets of a Dissimilar Thickness

Influence of laser power and beam path under nonuniform AC electric fields on 3D microvortex flow

This paper describes the effect of optical light on the generation and manipulation of microvortex flow named ‘twin opposing microvortex’ (TOMV) flow. This opto-electrohydrodynamic (OEHD) technique combines optical light, i.e. infrared (IR) laser (1064 nm), with non-uniform AC electric fields generated from a pair of indium tin oxide (ITO) electrodes. When the IR laser beam passes through the electric fields, a rapid and three-dimensional (3D) vortex flow is generated in a microchamber. When the laser beam passes through the electric fields, especially the exposed ITO electrode, the direction of the TOMV flow as well as its strength are controlled. With an AC signal of 107 kHz and various voltages below a peak-to-peak voltage of 10 V, laser power is varied up to 1.5 W and the path of a laser beam relative to the electrode (300 μm long and 16 μm wide) is manipulated. The maximum in-plane velocity outside the electrode region was obtained by micron-resolution particle image velocimetry (μPIV). When the laser beam passes through the left or right side of the lower electrode, the TOMV flow field rotates counterclockwise or clockwise, respectively. Applying optical light on an ITO electrode creates in situ and on-demand microvortex flow, which increases the feasibility of OEHD technique in various biological and chemical applications (e.g., mixing and delivering nanofluids in microfluidic devices).

Enhancing payload capacity to low earth orbit via a relay solution trajectory with laser-powered vehicles

ABSTRACT Low Earth Orbit (LEO) stands as the primary access point for deep space exploration endeavors, encompassing a variety of space missions such as communication satellites, Earth observation platforms, and scientific research missions. In light of the expanding scope of human activities in space, the cost associated with accessing LEO has emerged as a critical focal point for spacecraft designers. Within the spectrum of proposed solutions, laser-powered vehicle has emerged as a viable avenue toward achieving cost-effective launch options. In order to significantly augment the payload capacity of laser-powered launch vehicles destined for LEO, this study introduced a novel Relay Solution Trajectory Flight Scheme. Central to this scheme was the implementation of a relay mirror system affixed to a satellite, which served to stabilize the incident angle of the laser beam directed toward the laser-powered vehicle, thereby ensuring continuous alignment between the laser beam and the vehicle’s axis throughout the duration of the flight. Following the development of comprehensive structural, propulsive, aerodynamic, and trajectory models tailored for the laser-powered vehicle, an optimization of its flight trajectory was conducted, comparing this innovative strategy with two conventional flight strategies. The outcomes of this analysis showcased a notable enhancement of 269.29% in payload capacity compared to conventional strategies that lacked a relay satellite system, within a designated 400 km LEO flight scenario. This endeavor underscored the transformative potential of advanced relay systems in reshaping payload delivery mechanisms and elevating mission feasibility levels, notwithstanding the intricate coordination challenges posed by intricate satellite systems.

Analysis of centroiding algorithms for non-diffracting structured and hollow structured laser beams: errata

Analysis of centroiding algorithms for non-diffracting structured and hollow structured laser beams: errata

Correction to: The influence of laser separation distance on the mechanical properties of 2219 aluminum alloy T joint in double‑sided laser beam oscillation filler welding

Correction to: The influence of laser separation distance on the mechanical properties of 2219 aluminum alloy T joint in double‑sided laser beam oscillation filler welding

Early Peri-Implant Bone Healing on Laser-Modified Surfaces with and without Hydroxyapatite Coating: An In Vivo Study

(1) Objective: The aim of this study was to assess the biological behavior of bone tissue on a machined surface (MS) and modifications made by a laser beam (LS) and by a laser beam incorporated with hydroxyapatite (HA) using a biomimetic method without thermic treatment (LHS). (2) Methods: Scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDX) was performed before and after installation in the rabbit tibiae. A total of 20 Albinus rabbits randomly received 30 implants of 3.75 × 10 mm in the right and left tibias, with two implants on each surface in each tibia. In the animals belonging to the 4-week euthanasia period group, intramuscular application of the fluorochromes calcein and alizarin was performed. In implants placed mesially in the tibiofemoral joint, biomechanical analysis was performed by means of a removal torque (N/cm). The tibias with the implants located distally to the joint were submitted for analysis by confocal laser microscopy (mineral apposition rate) and for histometric analysis by bone contact implant (%BIC) and newly formed bone area (%NBA). (3) Results: The SEM showed differences between the surfaces. The biomechanical analysis revealed significant differences in removal torque values between the MSs and LHSs over a 2-week period. Over a 4-week period, both the LSs and LHSs demonstrated removal torque values statistically higher than the MSs. BIC of the LHS implants were statistically superior to MS at the 2-week period and LHS and LS surfaces were statistically superior to MS at the 4-week period. Statistical analysis of the NBA of the implants showed difference between the LHS and MS in the period of 2 weeks. (4) Conclusions: The modifications of the LSs and LHSs provided important physicochemical modifications that favored the deposition of bone tissue on the surface of the implants.

Parametric Analysis and Optimization on Fiber Laser Micro-Milling on AZ31 Magnesium Alloy

One of the proficient machining technologies to create micro-features in a variety of materials is the laser micro-milling process. This procedure involves irradiating a highly concentrated laser beam on the sample and performing laser cutting at various cutting patterns to change the surface conditions and enhance the characteristics of that surface tribology. In this work, an effort has been made to mill magnesium alloy (AZ31) material using a laser. The pulse frequency, laser beam power, cutting speed, number of passes, and transverse feed are among the different process variables taken into account for the current research effort. Measured results include depth of cut and surface roughness. To ensure the validity of the established empirical models, this paper also presents experimental data. Several surface plots have been used to examine the test data. To get the lowest values of surface roughness and depth of cut, multiperformance optimization is also utilized. The influence of process factors on response has also been examined using optical microscopic images. Gray relational analysis approach is also applied to obtain the multiobjective optimization parametric combination and based on the calculated results of gray relational grade, it is revealed that improvement in the value of gray relational grade at predictive setting is 0.054 compared to the initial parametric combination.

Multi-gas sensing system based on miniaturized cruciform photoacoustic cell

Photoacoustic spectroscopy has the advantage of multi-gas sensing with only one sound detector because of its non-selectivity. A photoacoustic cell (PAC) is an important part of the system as it amplifies the intensity of sound pressure. In this paper, we report on the development of a multi-gas sensing system based on a specially designed cruciform photoacoustic cell (CF-PAC), whose structure contains two beam paths and is suitable for multiple laser beams incident from different directions independently. It is especially suitable where beams are not easy to combine due to large wavelength differences. The structure of the cell is carefully designed using the finite-element method (FEM) and the resonant frequency of it is about 5050 Hz and the external dimension is only 67×60×40 mm with the inner volume of about 24 cm3. We also present a contrast experiment between the CF-PAC and the conventional “H-type PAC” with similar parameters and the result shows that the former sacrifices only a small amount of performance, but adds beam path effectively. The sensor is designed to detect methane (CH4), nitrogen dioxide (NO2), and carbon dioxide (CO2), and the minimum detection limit (MDL) with a 5 s integration time are 113 ppb, 2.1 ppm, and 1.6 ppm, respectively. The 1σ normalized noise equivalent absorption coefficients (NNEA) of the three gases are 2.54×10−9 cm−1 W Hz−1/2, 5.70×10−8 cm−1 W Hz−1/2, and 2.31×10−6 cm−1 W Hz−1/2, respectively. Modified formulas based on nonlinear regression will be given to make the detection results more accurate in the multi-component gas environment.

Wavelength-tolerant generation of Bessel-Gaussian beams using vortex phase plates

With their nearly non-diffracting and self-healing nature, Bessel-Gaussian beams (BGBs) are attractive for many applications ranging from free-space communications to nonlinear optics. BGBs can successfully be generated on background laser beams by imprinting and subsequently annihilating multiply charged optical vortices followed by focusing the resulting ring-shaped beam with a thin lens. For high-power applications optical vortices are preferentially created by spiral phase plates because of their high damage threshold. These are fabricated to realize an azimuthal change of the accumulated phase of a multiple of 2π at a predetermined wavelength. This raises the expectation that the use of spiral phase plates for the generation of BGBs is limited to the design wavelength and therefore not applicable to broadband applications involving short-pulse lasers. In this paper we present experimental data showing that this limitation can be overcome in a broad spectral range around the design wavelength. Experimental cross-sections of the BGBs for several off-design wavelengths are found in a good quantitative agreement with the theoretical Bessel functions at distances up to 540 cm after the focus of the lens.

Deep Cryogenic and Thermal Aging Treatments of Ti–5Al–5Mo–5V–3Cr Alloy Additively Manufactured by Powder Bed Fusion–Laser Beam

The properties of 3D‐printed components via powder bed fusion–laser beam (PBF–LB) depend strongly on the processing parameters, particularly due to the rapid solidification conditions involved. In this study, an innovative post‐treatment strategy combining deep cryogenic treatment (DCT) and thermal aging treatments are introduced to enhance the properties of Ti–5Al–5V–5Mo–3Cr alloy (Ti‐5553) alloy fabricated by PBF–LB. In the results, it is revealed that DCT of as‐built material can refine the grain size and introduce defects and sub‐grain boundaries, thereby improving strength and ductility without significantly altering the microstructure or phase composition. However, applying DCT after aging can significantly improve ductility and maintain strength, primarily by refining β‐phase grains. Conversely, thermal aging followed by DCT of as‐built materials tends to increase strength at the expense of ductility, due to the formation of the ω phase and defects induced by the cryogenic treatment that in turn promote the development of more abundant and finer α phase within grains during aging. In the findings of this research, significant insights and valuable methodologies are offered for optimizing the mechanical properties of Ti‐5553 alloy manufactured by PBF–LB via an extra DCT following thermal aging.

Experimental study on the keyhole dynamic evolution and porosity formation during laser welding of Ti-6Al-4V alloy

Keyhole dynamic evolution significantly affects laser welding quality. For observing the keyhole’s dynamic behaviors directly, a sandwich workpiece that consists of a piece of quartz glass and a piece of Ti-6Al-4V alloy is used in experiments of this study, and the dynamic behaviors of the keyhole are recorded with a high-speed camera. The experimental results show that, in the first 5 ms of welding, the depth and width of the keyhole increase linearly and, at about 70 ms, a relatively stable keyhole is formed. A keyhole typically exhibits the shape of a “7” character in a short period after it forms. At this stage, the laser beam is reflected by the wall of the keyhole repeatedly until it reaches the bottom, which results in some tiny pore formations in the middle part of the keyhole. In subsequent welding, the collapsing and rebuilding process of the keyhole are observed, and big pores are formed at the bottom of the keyhole. The results of this research are helpful to understand the mechanism of the keyhole dynamic evolution and porosity formation during titanium alloy laser welding.

Laser nanofabrication inside silicon with spatial beam modulation and anisotropic seeding

Nanofabrication in silicon, arguably the most important material for modern technology, has been limited exclusively to its surface. Existing lithography methods cannot penetrate the wafer surface without altering it, whereas emerging laser-based subsurface or in-chip fabrication remains at greater than 1 μm resolution. In addition, available methods do not allow positioning or modulation with sub-micron precision deep inside the wafer. The fundamental difficulty of breaking these dimensional barriers is two-fold, i.e., complex nonlinear effects inside the wafer and the inherent diffraction limit for laser light. Here, we overcome these challenges by exploiting spatially-modulated laser beams and anisotropic feedback from preformed subsurface structures, to establish controlled nanofabrication capability inside silicon. We demonstrate buried nanostructures of feature sizes down to 100 ± 20 nm, with subwavelength and multi-dimensional control; thereby improving the state-of-the-art by an order-of-magnitude. In order to showcase the emerging capabilities, we fabricate nanophotonics elements deep inside Si, exemplified by nanogratings with record diffraction efficiency and spectral control. The reported advance is an important step towards 3D nanophotonics systems, micro/nanofluidics, and 3D electronic-photonic integrated systems.

AscentAM: A Software Tool for the Thermo-Mechanical Process Simulation of Form Deviations and Residual Stresses in Powder Bed Fusion of Metals Using a Laser Beam

Due to the tool-less fabrication of parts and the high degree of geometric design freedom, additive manufacturing is experiencing increasing relevance for various industrial applications. In particular, the powder bed fusion of metals using a laser beam (PBF-LB/M) process allows for the metal-based manufacturing of complex parts with high mechanical properties. However, residual stresses form during PBF-LB/M due to high thermal gradients and a non-uniform cooling. These lead to a distortion of the parts, which reduces the dimensional accuracy and increases the amount of post-processing necessary to meet the defined requirements. To predict the resulting residual stress state and distortion prior to the actual PBF-LB/M process, this paper presents the finite-element-based simulation tool AscentAM with its core module and several sub-modules. The tool is based on open-source programs and utilizes a sequentially coupled thermo-mechanical simulation, in which the significant influences of the manufacturing process are considered by their physical relations. The simulation entirely emulates the PBF-LB/M process chain including the heat treatment. In addition, algorithms for the part pre-deformation and the export of a machine-specific file format were implemented. The simulation results were verified, and an experimental validation was performed for two benchmark geometries with regard to their distortion. The application of the optimization sub-module significantly minimized the form deviation from the nominal geometry. A high level of accuracy was observed for the prediction of the distortion at different manufacturing states. The process simulation provides an important contribution to the first-time-right manufacturing of parts fabricated by the PBF-LB/M process.

Design framework of a computer-generated hologram that performs volumetric beam shaping for advanced laser processing

Axial beam shaping is very effective for material laser processing, typically laser cutting, drilling, and grooving. We demonstrate a framework for designing a computer-generated hologram (CGH) that performs volumetric beam shaping. The procedure performs axial beam shaping with a continuous intensity distribution, unlike our previous research in which only discrete focal points were arranged three-dimensionally. This research is the more general approach for volumetric beam shaping. An important point in this research is finding an optimal interval in the optical axis direction and in calculating the CGH design. The design interval is half of the focusing length (the full width at half-maximum of the laser beam profile in the axial direction) given by the diffraction limit of the optical system. The optimal value is obtained using an axially shaped beam that is the reconstruction of the CGH calculated from Zernike polynomials. We also demonstrate that the optimal interval for evaluating the axially shaped beam is also half of the beam length. Following the CGH design procedure, we demonstrate CGHs that generate long-focus beams with an arbitrary axially shaped beam. We found a tradeoff relation between the focusing length and the intensity of the long-focus beam, suggesting that the use of a focused beam with an appropriate length according to the purpose will lead to improved processing efficiency.