Laser Energy Input Research Articles

Molecular dynamics research on the effect of selective laser melting parameters on porosity and properties of parts

Selective laser melting (SLM) is considered as a new production technology which has the potential to produce amorphous alloy parts. However, pores are often observed in parts prepared by SLM, which seriously affect the properties and life of the parts. In this work, an atomic model for SLM forming of Cu50Zr50 amorphous alloy is established. The effects of laser power and scanning speed on the porosity and mechanical properties of parts fabricate by SLM are researched using molecular dynamics methods. The results indicate that increasing laser power or reducing laser scanning speed could enhance the laser energy input of the molten pool and increase the molten pool temperature, which could improve the fluidity of the metal melt and prolong the existence time of the molten pool. The molten metal could fully fill the gaps between powders, which reduces the porosity and is beneficial to obtain dense parts. The tensile strength of samples formed by SLM is positively correlated with their porosity. Stress concentration occurs in the system with through holes and internal pores. Defects expand and interconnect rapidly under stress concentration, which leads to a decrease in strength and plasticity. The porosity could be reduced by adjusting the process parameters, thus improving the mechanical properties of the parts. This study provides a theoretical reference for a deeper understanding of the formation mechanism of SLM pores and the development of advanced alloys with high density.

Tailored porosity in additive manufacturing of 7075 aluminum alloy for crack suppression and high strength

Laser-directed energy deposition (LDED) additive manufacturing of 7075 aluminum (Al) alloy is highly challenging due to the inherent poor printability and high cracking tendency. Here, we disclose a new approach to suppress cracking in LDED-processed 7075 Al alloy by engineered porosity (about 1.14 %). The crack-free 7075 Al alloy was achieved by slightly sacrificing the densification. Further increasing the density of the material by increasing laser energy input leads to cracking. The mechanisms of minor pores in alleviating cracks are mainly reflected in three aspects: (i) pores disrupt the epitaxial growth of columnar grains; (ii) free-form surfaces surrounding pores could release the accumulated residual stress, and (iii) more dislocations near pore drive nucleation of near equiaxed grains. The LDED-processed crack-free 7075 Al alloy after heat treatment shows an ultimate tensile strength of 464 ± 12 MPa and break elongation of 9.7 ± 1.2 %, attaining a good strength-ductility synergy among many additively manufactured 7075 Al alloys in the current literature. Unlike the mainstream additive manufacturing of metallic materials, which pursues high densification to attain high-performance components, this work demonstrates the positive roles of pores in the additive manufacturing of cracking-sensitive materials. The findings of this work highlight new insights regarding the balance between pores and cracks for better manufacturability and higher mechanical performance of materials.

Novel processing of micro-channels in micro-grinding with automated laser-assistance

AbstractMicro-structures are widely utilized in various fields such as optical, medical, defense, and aerospace. The accuracy and performance of micro-structures depend on fabrication methods, including conventional and non-conventional machining. High-quality micro-channel fabrication is challenging by conventional micro-grinding (CMG) which uses a micro-pencil grinding tool during micro-machining. However, in CMG, high-cutting forces act in the machining zone leading to tool deflection, tool failure, high temperature, and poor surface finish. The challenges of CMG can be overcome by using automated laser-assisted micro-grinding (LAMG), one of the modern micro-machining processes for fabricating high-quality, precise micro-channels. The novel processing of micro-channels in this work is through the in tandem use of LAMG and CMG. In this, the laser structuring is performed using LAMG followed by a micro-pencil grinding tool processing in a sequential manner on a same machine tool to achive high-quality parts and accuracy. This helps in fabrication of a micro-channel directly in one go without the need to remove the part to perform the two operations on two different machining setups, thereby reducing systematic fixturing errors which are significant when we are working at the micro-scale. This paper thus investigates the effect of various parameters viz. laser input energy densities and laser power on cutting forces and surface roughness on the tool as well as the work surface with two distinct scan patterns. In LAMG, at lower laser input energy density (pattern 1), the tangential and normal forces decreased by 10.3% and 20.5%, and surface roughness Sa and Sq reduced by 24% and 22% compared to CMG. Similarly, a normal force decreased by 20.5% in pattern 1 and 38% less in pattern 2. Still, the higher laser energy density (pattern 2) is unsuitable for structure due to an increase in Sa and Sq by 11% and 14.6%, respectively. Results have shown a maximum reduction in the normal and tangential force magnitude by 31 and 44% at 25 W compared to CMG. The work concludes that LAMG with novel laser assistance scan patterns has lower dynamic deflections resulting in better dimensional accuracy and surface finish compared to CMG with a lower tool.

Repairability and effectiveness in direct energy deposition of 316L stainless steel grooves: A comparative study on varying laser strategy

Direct energy deposition (DED) has gained attention in the field of metal repair because of its ability to integrate additively deposited material with preexisting components. Having the beneficial aspects of depositing right material, DED is evaluated the best option for repair deposition. Machining grooves in damaged components is the common first to repair, which is necessary to remove cracked or damaged material and provide suitable geometry for deposition. Preprocessing as grooving is commonly applied to prevent the propagation cracks or tears. However, challenges such as dimensional error and crack induced by residual stress emerge owning to complex interactions between the DED parameters and groove geometry during repair deposition. This study investigates effective deposition strategies for repairing 316L stainless steel grooves with wall-angles of 90° and 135° by exploring the relationship between the repair integrity and parameters such as groove angles, laser energy input, and powder supply, all with reference to the underlying mechanism of metallurgical bonding in angled areas. Based thereon, a modified effective repair strategy is proposed, using enhanced dual laser power to address bonding issues in the angled areas. Samples repaired using this method exhibit a defect-free groove–deposit interface and a continuous columnar-grained microstructure with abrupt changes in grain size between the repaired area and groove. This microstructural heterogeneity results in an exceptional combination of strength and ductility when compared to the base material and samples repaired using a single laser strategy. The findings of this study provide insights into the optimization of DED strategies for achieving robust metallurgical bonding within grooves, thereby advancing technological maturity in the field of metal repair.

Experimental investigation of nanosecond pulsed laser ablation of polycrystalline diamond composite

A fundamental understanding of the laser ablation of polycrystalline diamond composite (PCD) at different laser energy intensities is indispensable for extending these findings to practical applications where, through appropriate parameter combinations, a substantial amount of material with minimal thermal damage should be removed. The objective of this study is to investigate experimentally the nanosecond ablation of polycrystalline diamond composite at different laser pulse energies and input energy densities. The research comprised two distinct categories of experiments: (1) single-point and (2) line experiments. In single-point tests, the number of the incidence pulses (N.P) was varied from 1 to 100 pulses with different pulse energies (Ep) ranging from 40 to 200 µJ. As the N.Ps increased, the ablation depth increased as well. No considerable enhancement in ablation depth was observed with the increase in pulse energies. For the line experiments, the results emphasized the differences in ablation depths by nearly a factor of 2, resulting in a corresponding change in laser input densities from 6.5 J/mm2 to 1.3 J/mm2. The ablation difference was pronounced as the number of repeats of the scanning path increased. The results emphasize that the ablation depth varies at the same pulse energy when the pulse overlap decreased from 100 % to lower percentages. Based on these results, a constant laser energy density with three different combinations of laser inputs—namely, scanning speed and average power—was selected to evaluate the ablation depth and quality. The results show that in moderate numbers of scan repeats (here 20, 30 & 40 times), it is advisable to adopt a minimum pulse energy when the same ablation depth is achieved compared to higher pulse energies. The ablation pile-up was also evaluated in these repeat ranges, indicating that higher pulse energies and repeats do not result in ablation improvement and cause excessive melt deposition.

Elucidating the transfer dynamics of high-viscosity silver paste for laser-induced forward transfer of continuous line

Laser-induced forward transfer (LIFT), as an innovative 3D direct-write method, has been increasingly applied for various material printing in many applications. Elucidating the transfer process of paste is crucial to manipulate the printing quality. In this work, the transfer dynamics of high-viscosity silver paste in LIFT of continuous line was systematically investigated based on the cumulative effect from images obtained over hundreds of laser pulses. The influences of process parameters, including the laser energy input (single pulse energy, repetition frequency, and scanning speed) and the thickness of paste film, on the bump height and expansion velocity of bump front were analyzed. With increasing the single pulse energy or repetition frequency, or decreasing the scanning speed or film thickness, the evolution of bump morphology and sputtering varies from just a tiny bump with no sputtering, to a moderate-sized bump with a small amount of sputtering and rebounding, and further to a large bump with intense sputtering and rebounding. A non-dimensional group in terms of Reynolds and Weber numbers was proposed to categorize different evolution regimes and claim the physical mechanism on LIFT of continuous line. When the Reynolds number is greater than 0.01 and the Weber number is greater than 0.1, the inertial effect is sufficient to resist the viscous and capillary effects, inducing the paste to bulge and transfer downwards. A moderate-sized bump with no visibly fragmented sputtering is desirable for the transfer of continuous grid lines. The forming status of grid lines can be predicted according to the behavior of paste transfer, and the predicted grid line state agrees well with the actual state. This can provide process and theoretical references for printing continuous grid lines with LIFT.

Isofield plasma expansion in kJ petawatt laser-driven ion acceleration with a tailored fast electron temperature

Kilojoule-class relativistic intensity lasers, having multi-picosecond (ps) pulse durations, enable efficient ion acceleration in the interaction with thin foil targets. The foil plasma expands under the laser energy input over picoseconds where fast electrons keep increasing their effective temperature, while they convert a part of the energy into fast ions through generation of a sheath electric field. The temporal evolution of the sheath electric field is the key to understanding the efficient ion acceleration seen in kJ-class laser experiments. Here, we extend the non-isothermal plasma expansion model by introducing a temporal function of the effective temperature of fast electrons to obtain the sheath electric field in the expanding plasma. We theoretically derived that when the effective temperature of fast electrons increases in proportional to the square of the time, the strength of the sheath electric field is kept constant without depletion during the expansion. This ‘isofield’ expansion is confirmed by a quasi-one-dimensional particle-in-cell simulation. The isofield expansion results in a high energy ion acceleration with a small expansion length, which is favorable for realizing an efficient ion acceleration with less lateral energy loss in multi-dimensional situations.

Laser-beam powder bed fusion of magnetostrictive Fe81Ga19 alloys: parameter optimization, microstructural evolution and magnetostrictive properties

Magnetostrictive Fe-Ga alloys, featuring with good machinability, high Curie temperature, and high permeability, have received increasing attention in fields such as actuators, implants, and energy harvesting. Unfortunately, bulk polycrystalline Fe-Ga alloys usually suffer poor magnetostrictive strains compromised by the randomness of grain structure and the intricate phase constitution. The current study was centered on the fabrication of bulk polycrystalline Fe81Ga19 alloys with tailored grain morphology and phase arrangement utilizing laser-beam powder bed fusion (LPBF) technology. Particular emphasis was laid on investigating the repercussions of LPBF process parameters on the microstructure and magnetostrictive performance. The findings illustrated a non-linear interplay between laser power and the relative density of laser powder bed fusion-fabricated (LPBFed) Fe81Ga19 alloys, marked by an initial augmentation followed by a subsequent decrement. Similarly, a consistent trend was observed for the LPBFed alloys at varying scan speeds. In particular, the LPBFed Fe81Ga19 alloys exhibited a highest density at optimized process parameters (laser power set at 120 W paired with a scan speed of 100 mm s−1) due to suitable laser energy input during LPBF process. It was experimentally shown that elongated columnar grains and disorder A2 phase structures were obtained within the alloys attibutes to the high temperature gradient and rapid cooling kinetics intrinsic to LPBF, contributing to a desirable magnetostrictive strain of ∼87 ppm for bulk polycrystalline Fe81Ga19 alloys. Moreover, a good dynamic magnetostrictive response of the LPBFed alloys was confirmed by the near-synchronous variations between magnetostrictive behavior and alternating magnetic fields. It can be derived from these findings that LPBF process may be a promising method to prepare bulk magnetostrictive Fe-Ga alloys for versatile applications.

Realizing Crack Inhibition of Haynes 230 Alloy during Laser Powder Bed Fusion by Grain Refinement under Decreased Energy Density

Nickel-based superalloys (Haynes 230) fabricated by laser powder bed fusion suffer from high cracking susceptibility, leading to a decrease in mechanical performance. In this study, the cracking mechanism of Haynes 230 was investigated based on microstructural and thermodynamic calculations. It was found that C and carbide-forming elements (such as Mo and Cr) were segregated at the grain boundaries, which increased the solidification range and impeded liquid film backfalling by forming nano-carbides. Additionally, the coalescence of high-angle grain boundaries (>15°) requires a higher undercooling ΔTbthan that of low-angle grain boundaries (2–15°), which increases the susceptibility to hot cracking. Through gradually reducing laser energy input, the grain size is significantly decreased from 27.86 μm (47.40 J/mm3) to 14.66 μm (31.81 J/mm3). Moreover, the calculated cooling rate |dT/dt| and temperature gradient |dT/ds| gradually increase with decreasing energy input, which reduces the duration of dendrite merging and shortens the length of the liquid film. Compared with cracked samples, the optimized sample showed superior mechanical properties, including high yield strength (678 MPa), ultimate tensile strength (943 MPa), and elongation to failure (19.2%), which increased by 16.1%, 9.7%, and 77.7%, respectively.

Powder bed fusion–laser beam (PBF-LB) three-dimensional (3D) printing: Influence of laser hatching distance on the properties of zolpidem tartrate tablets

Laser sintering, known as powder bed fusion–laser beam (PBF-LB), offers promising potential for the fabrication of patient-specific drugs. The aim of this study was to provide an insight into the PBF-LB process with regard to the process parameters, in particular the laser hatching distance, and its influence on the properties of zolpidem tartrate (ZT) tablets. PHARMACOAT® 603 was used as the polymer, while Candurin® Gold Sheen and AEROSIL® 200 were added to facilitate 3D printing. The particle size distribution of the powder blend showed that the layer height should be set to 100 µm, while the laser hatching distance was varied in five different steps (50, 100, 150, 200 and 250 µm), keeping the temperature and laser scanning speed constant. Increasing the laser hatching distance and decreasing the laser energy input led to a decrease in the colour intensity, mass, density and hardness of the ZT tablets, while the disintegration and dissolution rate were faster due to the more fragile bonds between the particles. The laser hatching distance also influenced the ZT dosage, indicating the importance of this process parameter in the production of presonalized drugs. The absence of drug-polymer interactions and the amorphization of the ZT were confirmed.

Shock compression experiments using the DiPOLE 100-X laser on the high energy density instrument at the European x-ray free electron laser: Quantitative structural analysis of liquid Sn

X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼1% at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

Molecular dynamics simulations of nanoparticle sintering in additive nanomanufacturing: The role of particle size, misorientation angle, material type, and temperature

Additive nanomanufacturing, where nanoparticles (NPs) are generated via laser material ablation and sintered via laser, permits the fabrication of novel electronic devices with adequate flexibility, such as tunable material composition, adjustable sintered state, and a wide selection of substrates—including biodegradable ones—to name a few. The laser energy input often needs to be carefully balanced between achieving adequate sintering and avoiding substrate damage. The sintered state of NPs, a key influencing factor of the resistivity of electronic circuits, depends not only on temperature (the result of laser energy input), but also on NPs size, size ratio, and crystallographic misorientation. While the minuteness of NPs and the transient nature of their sintering (typically within a nanosecond) make direct experimental evaluation of such parameters challenging, the length and time scales are uniquely suitable for molecular dynamic (MD) studies. This study utilizes MD to investigate the sintering characteristics of silver and copper NP doublets at different temperatures and examines the effects of NP size, size ratios, misorientation angle (including both tilt and twist), and material type. A mathematical framework to describe the characteristic sintering time, i.e., time needed for a NP doublet to achieve a given normalized neck size, was proposed based on MD results.

Laser additive manufacturing of TiB2-modified Cu15Ni8Sn/GH3230 heterogeneous materials: Processability, interfacial microstructure and mechanical performance

Cu/Ni heterogeneous materials integrate excellent thermal conductivity and high-temperature mechanical properties, enabling them to be widely used in the aerospace domain. Differences in the thermal and physical properties of the Cu and Ni materials, however, make them difficult to be processed using the laser powder bed fusion (LPBF) additive manufacturing process. This study systematically examines the effects of various LPBF process parameters on microstructure, element diffusion, bonding strength and microhardness at the Cu/Ni interface, as well as investigating the mechanisms of defect formation within Cu/Ni heterogeneous materials. The results indicate that a reasonable control of laser energy input (<100 J/mm3) facilitates the Cu/Ni components through strong interfacial metallurgical bonding without pore defect formation. Compared to single-material Cu alloy, the ultimate tensile strength (UTS) of the horizontally bonded Cu/Ni specimen increased by 55.25 %, without significant reductions in elongation. The vertically bonded Cu/Ni tensile specimen fractured in the middle of the Cu region rather than the interfacial region, indicating superb interfacial bonding strength. Another advantage lies in the enhancement of thermophysical properties, with a 109.5 % increase in thermal conductivity achieved in the LPBF-fabricated Cu/Ni heterogeneous materials compared to the single-material Ni alloy. Quasi-static compression experiments indicated that the Cu/Ni lattice structure could absorb more energy when compressed parallel to the build direction (BD), compared to being perpendicular to the BD. This study provides guidance for the design and manufacture of high-performance Cu/Ni heterogeneous components via LPBF.

Research on thermal efficiency and weld forming coefficient prediction of ultra-high strength steel welded joint under different energy inputs

As an ultra-high strength steel, Al–Si coated 22MnB5 hot stamping steel is widely used in the manufacturing of body-in-white structural parts. Compared with traditional welding technology, laser welding is widely used in the field of automobile body-in-white manufacturing due to its high energy density, small heat affected zone, and high weld quality. For ultra-high strength steel laser welded joints, the weld forming coefficient is an important index to reflect the welding quality. In order to investigate the influence of weld forming coefficient on the Al content and the thermal efficiency, laser welding experiments of ultra-high strength steel under different laser energy inputs are carried out. The melting of the base metal and coating under different laser energy inputs is also considered. Particle swarm optimization (PSO) algorithm is introduced into radial basis function (RBF) neural network model to optimize the central parameters as the RBF neural network model alone is not sufficient in predicting the outcomes. The results shows that if the laser power density is constant (7 × 105 W/cm2), when laser energy inputs are 400 J/cm to 1200 J/cm, the Al content in welded joints is 1.458%–1.886%, the melting efficiency of welded joints is 0.23–0.26, the energy conversion efficiency of welded joints is 0.45–0.46. When the laser energy inputs are lower than 522 J/cm, the Al content of the laser welded joint increases gradually. When the laser energy inputs are higher than 522 J/cm, the Al content of the laser welded joint decreases. The root mean square error(RMSE) of PSO-optimized RBF neural network testing sets prediction results is 0.1551, R-square (R2) is 0.771 and mean absolute percentage error (MAPE) is 2.758%. The prediction accuracy of the PSO-optimized RBF neural network model for the upper surface weld width, waist weld width, and lower surface weld width is 93.9%, 91.1%, and 92.2%.

Numerical investigations of water jet-guided laser cutting of silicon

To investigate the interaction mechanism between a laser, water jet, and substrate, a model is developed to simulate the temperature field evolution and removal process during water jet-guided laser (WJGL) cutting of silicon. The model accounted for the temperature-dependent properties of the silicon absorption coefficient, as well as the physical processes of solid-liquid-gas phase change. A three-dimensional finite volume model of WJGL cutting of silicon is created, incorporating laser energy input, water jet impact-cooling, and silicon phase transition and removal. The volume of fluid (VOF) method is employed to trace the interphase interface and obtain the groove shape. The validity of the model is verified by comparing simulation results with experimental data. The simulation results show that the groove cross section is characterized by a “V” shape. The groove depth nonlinearly increases from 52 to 385 μm with an increasing number of cuts. Additionally, the residual temperature of the silicon substrate rises from 837 to 1345 K as the number of scans increases from 1 to 10. The findings offer valuable insights into WJGL cutting research, specifically shedding light on the intricate details of the laser-water jet-substrate interaction mechanism.

Finite element simulation of selective laser melting based on the layer thickness-dependent shrinkage ratio model

During selective laser melting (SLM), a powder undergoes a transition to a molten state and subsequently solidifies. Using a finite element (FE) model to investigate temperature evolution during SLM manufacturing is an efficient and reliable method for parameter and process optimization. However, factors such as the powder layer porosity and material evaporation induced by the laser energy input lead to volume shrinkage of each layer in SLM, which dramatically influences the precision of the FE model. This work investigates the shrinkage in the deposition direction of SLM-fabricated TC4 components with different powder layer thicknesses using a step-shaped substrate. According to the obtained shrinkage ratio, an FE model is used to establish a layer thickness-dependent volume shrinkage ratio. A comparison is made with the commonly used fixed 50% shrinkage ratio model. The study demonstrates that the shrinkage in the deposition direction of components fabricated by SLM using commercial TC4 powder is greatly affected by powder layer thickness. Introducing a layer thickness-dependent shrinkage ratio enhances the precision of the FE model, and it improves the predictive accuracy of the optimized process parameters.

Influence of optical grating on the triggering efficiency of VCSI silicon carbide photoconductive semiconductor switch

In this article, we present a new configuration of opposed-contact vanadium-compensation semi-insulating (VCSI) 4H–SiC photoconductive semiconductor switch (PCSS) to reduce the input laser energy for operation. The configuration is made up of three parts: the PCSS with optical grating, the convex lens in front of PCSS, and the additional reflector behind PCSS. Periodic surface structures were fabricated on the VCSI 4H–SiC substrate by ultrafine femtosecond laser direct writing to etch optical gratings. The microstructure on the lower surface plays the role of reflection grating, so that the laser forms a specific distribution pattern and enhances the laser absorption. Experiments and simulations show that the triggering efficiency increased 3.7 times compared to PCSS without grating at 532 nm laser. And output voltage can reach 90 % of the input bias voltage. This SiC PCSS optical system significantly reduces the laser energy without reducing the electrodes spacing.

Spectral emission characteristics of single point exposure LPBF process

Despite the advantages of laser powder bed fusion (LPBF), part defects may arise from inaccurately chosen process parameters or heat accumulation during the scanning of complex geometries. Amongst different monitored entities the chemistry or the process fingerprints related to the material requires further attention. Monitoring the spectral content of light emitted from the laser-material interaction provides insight into thermal conditions and chemical composition of the processed material. This work implements an off-axial spectral monitoring setup for Optical Emission Spectroscopy (OES) in LPBF. Single-point experiment was conducted on AISI316L and Ti-6Al-4V. The study showed that the variation of laser energy input causes consequent variation of spectral emission intensity, as well as that the developed setup successfully captures spectral peaks of alloying elements. Principal Component Analysis demonstrated clear differentiation between the two materials. These findings prove the potential of OES for monitoring alloying elements of processed material and processing conditions in LPBF.

Effect of processing parameters on the microhardness, shear, and tensile properties of layer-cladded Inconel 718

Inconel 718 alloy (IN718) is a popular choice for aerospace hot-end components due to its exceptional mechanical properties. This study investigates the impact of processing parameters (i.e., laser power, powder feeding rate, and scanning speed) on the microhardness, bond strength, and tensile strength of layer-cladded IN718. The results show that IN718 coatings have high microhardness (277.15 HV0.1), strong metallurgical bonding strength (33.97 kN), substantial yield strength (794.09 MPa), impressive ultimate tensile strength (1171.81 MPa), and notable elongation at failure (8.24 %) under laser power is 1.2 kW, powder feeding rate is 250 mg/s, and scanning speed is 4.5 mm/s. In particular, decreased laser energy input enhances microhardness, yield strength, and ultimate tensile strength but reduces bonding strength and elongation. This is attributed to improved Nb element segregation, the reduction of the Laves phase, and grain refinement. However, inadequate energy input leads to cracks and unmelted powder, negatively affecting metallurgical bonding strength. The shear and tensile fracture mechanism of the IN718 coatings is a typical ductile fracture with a microvoid accumulation fracture. The study can facilitate the fabrication of the IN718 coatings with the excellent mechanical properties and the applications in the engineering field.

Polarization of the third harmonic emission from the filamentation of femtosecond cylindrical vector beams.

We experimentally generate a third harmonic (TH) vector optical field in deep ultraviolet wavelength range using femtosecond vector laser beams. The generated TH beams are characterized by analyzing the Stokes parameters with different input laser energies. The results show that the TH predominantly preserves the vector polarization distribution of the fundamental frequency beam. Moreover, the intensity profile of the TH exhibits a multiple-ring structure. A hybrid polarization pattern is observed in the TH, where the ellipticity is influenced by the input laser energy. Our work provides an effective and straightforward method for producing TH vector optical fields, which may facilitate potential applications such as micro/nanofabrication and super-resolution microscopy.