Laser Irradiation Process Research Articles

Fabrication of modified laser-induced graphene using activated carbon and polyamic acid coating for flexible and high-performance microsupercapacitors

In this study, we developed a method to combine polyamic acid (PAA) and activated carbon (AC), which were then coated on laser-induced graphene (LIG). The material was heated to facilitate the conversion of PAA–AC into polyimide (PI)–AC. Then, the resulting material was subjected to a second laser irradiation process to obtain AC–LIG composite materials. The resulting material features a robust and flexible electrode architecture with a high surface area, improved ion accessibility, and enhanced charge transfer kinetics. In tests conducted with a three-electrode setup, the AC–LIG configuration exhibited a considerably high specific capacitance, reaching 97.2 mF cm−2 at 0.2 mA cm−2, which is approximately fourteen times larger than that of pristine LIG (7.1 mF cm−2). When integrated into a flexible microsupercapacitor using a polyvinyl alcohol (PVA)–H2SO4 (sulfuric acid) gel-type electrolyte, AC–LIG exhibited a higher specific capacitance (68.4 mF cm−2 at 0.3 mA cm−2) than d-LIG (17.1 mF cm−2 at 0.3 mA cm−2). Furthermore, AC–LIG showed good Coulombic efficiency (98.5 %) and capacitance retention (90.0 %) after 10,000 cycles. These results highlight the potential of AC–LIG as a viable alternative for advanced supercapacitor (SC) applications, providing improved energy storage capacities and a reliable performance.

Quantifying laser irradiation-induced temperature field of particle reinforced metal matrix composites

While particle-reinforced metal matrix composites (PMMCs) are composed of particles and matrix with distinctly different thermomechanical properties, the thermal differences and coupled interactions between individual phases greatly determine the thermal characteristics of PMMCs under laser irradiation. In this work, we quantify the temperature evolution characteristics within SiCp/Al under laser irradiation by microstructural thermal finite element simulations and experimental investigation. Specifically, a 2D thermophysical FE model of laser-SiCp/Al interaction for the two-phase PMMCs material under laser irradiation is developed, which incorporates the temperature-dependent thermophysical properties of particles, matrix and interfaces, along with the considerations of the shape and distribution characteristics of particles, as well as the comprehensive thermal conditions. Furthermore, a 3D equivalent thermal FE model for experimental validation of predicted laser-induced temperature of SiCp/Al is developed, based on the derived equivalent properties. Meanwhile, an in-situ temperature measurement system is constructed for exploring temperature evolution characteristics during the on-going laser irradiation process, which validates a derivation of 1.7 % of predicted temperature by the equivalent thermal FE model. Finally, the impact of laser processing parameters on the temperature field of SiCp/Al is addressed. These findings provide valuable insights for understanding the thermal mechanisms of PMMCs under laser irradiation, and also the parameter optimization for laser processing of PMMCs.

Real-time microwave transmittance variation of glass fiber composites subjected to laser irradiation

Laser irradiation may have a significant impact on the microwave transmission properties of glass fiber composites. In this study, a two-dimensional microwave transmission transient model of glass fiber composites during the complete laser irradiation process was developed. The numerical results indicate that carbonization during irradiation causes a significant increase in dielectric loss, thus resulting in a decrease in transmittance. After irradiation, the dielectric loss decreased due to the decrease in temperature, which, in turn, led to an increase in transmittance. The increased transmittance after cooling was lower than the original value due to the generation of pyrolytic carbon with a high dielectric loss. The numerical results were verified by conducting an experiment wherein the microwave transmittance of glass fiber composites was measured in real time before, during, and after laser irradiation. In addition, the effects of different laser parameters on the real-time microwave transmittance during laser irradiation were investigated experimentally and numerically. For the same total energy, a laser with a high power density and short irradiation time had a more significant effect on the attenuation of transmittance.

Laser‐Induced Graphene Toward Flexible Energy Harvesting and Storage Electronics

AbstractEnergy harvesting and storage devices play an increasingly important role in the field of flexible electronics. Laser‐induced graphene (LIG) with hierarchical porosity, large specific surface area, high electrical conductivity, and mechanical flexibility is an ideal candidate for fabricating flexible energy devices which supply power for other electronic components. Through a simple laser irradiation process with designable routes, abundant precursors (or substrates) rapidly transform into patterned LIG without any other treatments. The structure and physicochemical properties of LIG can be regulated by controlling the processing strategies and parameters, enabling the optimization of device performance. The laser scribing method, as a non‐contact and in situ technique, proves to be efficient in integrating different LIG‐based devices, resulting in all‐in‐one flexible power platforms. Here, a systematic summary of recent advancements in LIG‐based flexible energy electronics is presented. The controllable synthesis of LIG, functional LIG, and 3D architectures are described by elucidating corresponding mechanisms and processing strategies. An overall review of flexible energy conversion and storage devices based on LIG is presented. Eventually, the challenges and opportunities of LIG‐based materials in flexible energy conversion and storage are briefly discussed.

ВИЗНАЧЕННЯ ТЕХНОЛОГІЧНИХ ПАРАМЕТРІВ ЛАЗЕРНОГО ВИПРОМІНЕННЯ ДЛЯ ОТРИМАННЯ СУБМІКРО- ТА НАНОСТРУКТУР У ЗМІЦНЮВАЛЬНИХ ПОКРИТТЯХ НА СТАЛЯХ

Using the previously developed model of theoretical processes in the zone of laser irradiation, where thermal and thermomechanical processes are described, including the influence of crystallization energy and other internal energies during the formation of nanostructures at various temperature levels, further investigation of the thermal and thermomechanical characteristics of different structural steels during the formation of nanostructures on their surfaces using laser irradiation was conducted. To validate the model, temperature fields were determined in the zone of laser irradiation on steel 20 (Fig. 1a) and steel 50 (Fig. 1b), considering both heating and cooling processes. Calculations were performed for heat flux densities and durations of exposure close to those necessary for obtaining nanostructures (500...2000 K) and with temperature rise rates exceeding 10^7 K/s. As a result of calculations using the refined thermal model, temperature distributions at a depth of 1 μm during laser irradiation on steel with different carbon contents (steel 20, 38Х, 50, and У8) at various peak heat flux densities in the surface layer were obtained. A spatiotemporal distribution of temperatures along the radius of the laser spot and over time during laser irradiation with a heat flux density of q=3∙10^8 W/m^2 at a spot radius of 0.1 mm was constructed. Zones of nanostructure formation were identified depending on the heat flux density over the duration of laser irradiation. Theoretical investigations using the updated thermal model confirmed the need to consider the temperature rise rate, as exceeding it increases the likelihood of thermomechanical failure. At the same time, due to insufficient temperature rise rates during laser nanostructure formation in the surface layers of carbon steels, more micro- and sub microstructures are formed.

Morphological and size tuning of biogenic Ag and Au nanoparticles induced by laser irradiation

Since size and shape of the metal nanoparticles (NPs) determine its physical and chemical properties, such could be relevant for specific applications; it is critical to have adequate control over such features. In this work, a facile bottom-up, bio-inspired synthetic route for noble metal nanoparticles (NPs) preparation is presented. Specifically, Ag and Au monometallic nanoparticles were synthesized by bio-reduction with Citrus paradisi (Grapefruit) aqueous extract. Besides, conventional chemical reduction synthesis using NaBH4 and PVP as capping agent was also performed for comparison purposes. Characterization accomplished by UV–vis spectroscopy and electron microscopy over the synthesized nanoparticles shown that, although that unimodal (in the case of Ag NPs) or almost unimodal (Au NPs) size distributions were obtained, thanks to stabilizing effect of the ligand acting-biomolecules present in the extract; and the narrower size distribution in comparison with the conventional chemical synthesis route were observed, several morphologies were found for both metals. In order to modify such features, the obtained noble metal NPs were submitted to pulsed (30 ps, 10 mJ) Nd:YAG laser irradiation process; after that, the spherical shape seems to be the predominant morphology in both metal nanoparticles, whereas the population of particles smaller than 15 nm became increases considerably.

Wearable textile with laser-induced hydrophilic porous graphene oxide coating for rapid adsorption of volatile organic compounds

As the global epidemic eases today (2023), the high economic and environmental costs brought about by excessive production of masks are further disrupting global society. This study explores a unique approach to endow common commercial surgical masks with efficient volatile organic compounds (VOCs) adsorption properties as well as recyclability. A near-infrared laser irradiation method was developed for the formation of laser-induced porous graphene oxide coating on polypropylene masks. Graphene oxide coating can absorb laser energy and “explode”, thus realizing the transition from smooth coating to porous coating. This mask with porous graphene oxide coating can be directly used as an excellent VOCs filter material. The laser irradiation process in the air environment endows the porous coating with rich oxygen-containing groups, which makes the mask highly hydrophilic and breathable. In addition, the excellent absorbance of graphene oxide coating enables it to rapidly heat up under solar, allowing the mask to be desorbed and reused. Compared to traditional powder spraying methods, the coating of porous graphene oxide is more stable as a whole. This method can not only solve the problem of excess masks after the epidemic, but also provide a new idea for wearable protective textiles for VOCs.

Full laser irradiation processed Pb-graphene nanocomposite electrodes toward the manufacturing of high-performance supercapacitors

Facile and scalable manufacturing of metal decorated carbon electrodes is highly expected for next-generation energy-storage devices. Inspired by unique processing characteristics of laser-induced graphene (LIG) as well as electrochemical advantages of Pb, a full-laser protocol is developed for assembling Pb doped LIG (Pb-LIG) electrodes through two separate laser-irradiation processes to selectively irradiate polyimide (PI) for forming graphene framework and to selectively melt-and-recrystallize Pb powders. Along with high-efficient production and customizable sizes and shapes, Pb dosage and laser power are systematically investigated as two critical parameters to understand the process-structure relationship. By simultaneously considering the two factors, an interesting two-regime effect has been discovered, which is guiding for achieving optimized Pb content of 77.77 wt% as long as laser fluence per Pb dosage is around 100 J mg−1. Owing to clear redox faraday reaction, the integrated Pb content is indeed fundamental for promoting capacitive performance, by realizing a six-fold enhancement of areal capacitance from 25 to 128 mF cm−2. Finally, multiple Pb-LIG supercapacitors are facilely combined either in series or in parallel to expand its performance for energy-storage applications.

Bi-layered plasmonic photothermal nanocomposite heater for laser-irradiation based rapid digital annealing of metal and oxide films

A photonic annealing technique implanting highly energetic photons provides the characteristic advantage of triggering designated chemical/physical evolutions in materials along with suppressing undesired side reactions in a kinetically controlled way. However, the effectiveness of the photonic annealing technique is determined essentially by the optical property of the material itself and can become almost negligible for optically transparent inorganic films. To resolve this critical impediment, we have designed a photothermal nanocomposite heater that can convert the optical energy into a thermal energy and can transfer efficiently the thermal energy to the target materials regardless of the optical properties of the materials. The photothermal nanocomposite heater is designed to have a bi-layered structure with a silver nanoparticle-populated dense bottom layer and a porous carbon upper layer. It is revealed by time-dependent photothermal simulation that the silver nanoparticles with a plasmonic absorption behavior have a significant role in generating the thermal energy from the photons implanted by the green laser irradiation process, while a number of air voids prevent the thermal energy from being dissipated into the outer surroundings. The digitally designable annealing is conducted up to temperatures as high as 800 °C at a ramping rate as fast as 1300 °C/sec. The thermal profiles including the temperature, duration time and heating/cooling rate are adjustable accordingly depending on the laser processing parameters of the laser power, scan speed and number of loops in a single scan. It is demonstrated that a photothermal heater-based green laser irradiation process enables a rapid digital annealing for optically different particulate metallic and vacuum-deposited oxide films, generating their conductive nature and highly improved ferroelectric property, respectively.

Effect of Laser Printing Mode on Surface Topography, Microstructure, and Corrosion Property of Additive‐Manufactured NiTi Alloy

Laser powder bed fusion (LPBF) is an emerging metal additive manufacturing method that can pave a pathway for manufacturing NiTi shape memory alloys (SMAs) with high performance. Considering the unique characterizations of LPBF process, the position and sequence of laser irradiation are different under different laser scanning modes, which will affect the performance of as‐built samples. Herein, four different chessboard sizes are utilized to fabricate NiTi parts. The surface quality and relative density first increase and then decrease with the increasing chessboard size, obtaining the optimal surface roughness of 9.95 μm and relative density of 99.7%, respectively, at a chessboard size of 5 mm. As the chessboard size increases, the more pronounced precipitation of Ni4Ti3 with a higher quantity induces a strengthening effect, leading to a higher microhardness value of ≈290 HV0.2 at a chessboard size of 9 mm. The electrochemical test shows a better corrosion resistance with a corrosion potential of 0.101 V and a corrosion current density of 1.670 × 10−5 A cm−2 at a chessboard size of 5 mm. The corrosion mechanism is further revealed. This work emphasizes the importance of chessboard size as a reference for optimizing the process of additive‐manufactured NiTi SMAs.

Upper temperature limit for nanograting survival in oxide glasses.

The thermal stability of self-assembled porous nanogratings inscribed by an infrared femtosecond (fs) laser in five commercial glasses (BK7, soda lime, 7059, AF32, and Eagle XG) is monitored using step isochronal annealing experiments. Their erasure, ascertained by retardance measurements and attributed to the collapse of nanopores, is well predicted from the Rayleigh-Plesset (R-P) equation. This finding is thus employed to theoretically predict the erasure of nanogratings in the context of any time-temperature process (e.g., thermal annealing, laser irradiation process). For example, in silica glass (Suprasil CG) and using a simplified form of the R-P equation, nanogratings composed of 50 nm will erase within ∼30m i n, ∼1µs, and ∼30n s at temperatures of ∼1250∘ C, 2675°C, and 3100°C, respectively. Such conclusions are expected to provide guidelines to imprint nanogratings in oxide glasses (for instance, in the choice of laser parameters) or to design appropriate thermal annealing protocols for temperature sensing.

Optimization of laser irradiation process parameters for 40Cr steel based on back propagation neural network and genetic algorithm

40Cr is a significant material in the manufacturing of gears. However, this process is plagued by uneven distribution of quenching layers and excessive residual stress, leading to a decline in the precision of the workpiece, deformation, and cracking. Relying solely on the trial-and-error method in experiments is inadequate for effectively revealing the evolution mechanism of the laser quenching process. This approach is detrimental to improving research and development efficiency. In this study, a multi-field coupled numerical model for the multi-track overlapping laser quenching of the 40Cr gear steel is established. This model quantitatively reveals the coupling evolution laws of the temperature field, stress field, and phase transformation field during the laser quenching. The focus is on calculating the size of the tempering zone under different overlapping rates and conducting correlation analysis between parameters. Based on the artificial neural networks and genetic algorithms, the width and depth of the tempering zone are selected as target values for parameter optimization. The aim is to find the nonlinear relationship between the laser power, spot diameter, scanning speed, laser overlapping rate, and the size of the tempering zone, which can accurately predict the size of the tempering zone. The material microstructure of 40Cr gear steel was characterized by the scanning electron microscope, microhardness tester and friction and wear tester. The results show that the training error and testing error of the output parameters in genetic algorithm optimized back propagation network can accurately predict the size of the tempering zone. It is found that the higher the lap rate, the more uniform the hardness of the phase transformation hardening layer surface, and the tempering softening zone becomes larger. The parts surface is easy to produce defects, which can provide a theoretical basis for optimizing the laser quenching process parameters.

Femtosecond Laser-Driven Phase Engineering of WS2 for Nano-Periodic Phase Patterning and Sub-ppm Ammonia Gas Sensing.

Laser-driven phase transition of 2D transition metal dichalcogenides has attracted much attention due to its high flexibility and rapidity. However, there are some limitations during the laser irradiation process, especially the unsatisfied surface ablation, the inability of nanoscale phase patterning, and the unexploited physical properties of new phase. In this work, the well-controlled femtosecond (fs) laser-driven transformation from the metallic 2M-WS2 to the semiconducting 2H-WS2 is reported, which is confirmed to be a single-crystal to single-crystal transition without layer thinning or obvious ablation. Moreover, a highly ordered 2H/2M nano-periodic phase transition with a resolution of ≈435nm is achieved, breaking through the existing size bottleneck of laser-driven phase transition, which is attributed to the selective deposition of plasmon energy induced by fs laser. It is also demonstrated that the achieved 2H-WS2 after laser irradiation contains rich sulfur vacancies, which exhibits highly competitive ammonia gas sensing performance, with a detection limit below 0.1ppm and a fast response/recovery time of 43/67 s at room temperature. This study provides a new strategy for the preparation of the phase-selective transition homojunction and high-performance applications in electronics.

Laser-Induced Graphene in Polyimide for Antenna Applications

Laser-induced graphene (LIG) has gained considerable attention recently due to its unique properties and potential applications. In this study, we investigated using LIG in polyimide (PI) as a material for antenna applications. The LIG-−PI composite material was prepared by a facile picosecond laser (1064 nm) irradiation process, which resulted in a conductive graphene network within the PI matrix. Furthermore, LIG formation was confirmed by Raman spectroscopy and sheet resistance measurements. Finally, a patch antenna from LIG with 2.45 GHz microwaves was simulated, produced and tested. These findings suggest that LIG−PI composites have great potential for use in high-frequency electronic devices and can provide a new avenue for the development of flexible and wearable electronics.

Influence of CO2 laser beam modelling on electronic and electrochemical properties of paper-based laser-induced graphene for disposable pH electrochemical sensors

Laser-induced graphene (LIG) allows for the fabrication of cost-effective, flexible electrodes on a multitude of recyclable and sustainable substrates, for implementation within electrochemical biosensors. This work expands on current LIG research, by experimentally modeling the effects of several CO2 laser irradiation variables towards resulting conductive and electrochemical properties of paper-derived LIG. Instead of relying on the established paradigm of manipulating power and scan speed of the laser irradiation process for optimized outcomes, modeling of underlying laser operation principles for pulse modulation, regarding pulse repetition frequencies, pulse duration and defocus are presented as the key aspects dominating graphitization processes of materials. This approach shows that graphitization is dominated by appropriate pulse durations, dictating the time the substrate is exposed to each laser pulse, with laser fluence and irradiation defocus influencing the resulting conductive properties, with sheet resistances as low as 14 Ω sq−1. Similarly, fabrication settings controlled by these parameters have a direct influence on the properties of LIG-based electrochemical three-electrode cells, with optimized fabrication settings reaching electrochemically active surface area as high as 35 mm2 and heterogeneous electron transfer rates of 3.4 × 10−3 cm.s−1. As a proof-of-concept, the production of environmentally friendly, accessible, and biocompatible pH sensors is demonstrated, using two modification approaches, employing riboflavin and polyaniline as pH-sensitive elements.

A Surface Conformal Laser‐Assisted Alloying Reaction for 3D‐Printable Solid/Liquid Biphasic Conductors

Recently, electronics research has made major advances toward a new platform technology facilitating form factor‐free devices. 3D printing techniques have attracted significant attention in the context of fabricating arbitrarily shaped circuits. Herein, a 3D‐printable metallic ink comprising multidimensional eutectic gallium indium (EGaIn)/Ag hierarchical particles is proposed to fabricate arbitrarily designable solid/liquid biphasic conductors that can be inherently self‐healed/chip bonded and do not suffer from liquid flood out due to their liquid and solid nature, respectively. The EGaIn/Ag hierarchical particles are designed to have plasmonic optical absorption at the visible green–red wavelength regime, which is elucidated by an optical simulation study, and also enable the direct transfer of thermal energy, generated in the vicinity of the Ag nanoparticles, to the surface of the EGaIn particles. The 3D surface conformal green laser irradiation process activates the evolution of the biphasic conductive layer from the as‐printed insulating particulate one. The chemical/physical evolution is elucidated along with a photothermal simulation study for clarifying the suppression of undesirable side reactions. It is demonstrated that the biphasic conductors formed by successive 3D printing and the surface conformal green laser irradiation process exhibit electrical properties that have thus far been unexplored in solid metallic conductors.

Laser-irradiated carbonized polyaniline-N-doped graphene heterostructure improves the cyclability of on-chip microsupercapacitor.

Laser-irradiated graphene-based heterostructures have attracted significant attention for the fabrication of highly conducting and stable metal-free energy storage devices. Heteroatom doping on the graphene backbone has proven to have better charge storage properties. Among other heteroatoms, nitrogen-doped graphene (NG) has been extensively researched due to its several advanced properties while maintaining the original characteristics of graphene for energy storage applications. However, NG is generally prepared via chemical vapor deposition or high temperature pyrolysis method, which gives low yield and has a complex operation route. In this work, first a polyaniline-reduce graphene oxide (PANI-rGO) heterostructure was prepared via in situ electrochemical polymerization, followed by the deposition process. In the next step, laser-irradiation process was employed to carbonize polyaniline as well as doping of nitrogen on the graphene film, simultaneously. For the very first time, laser-irradiated carbonization of PANI on NG (cPANI-NG) heterostructure was utilized for microsupercapacitor (MSC). The as-prepared cPANI-NG-MSC shows extremely high cycling stability with a capacitance enhancement of 135% of its initial capacitance after 70 000 continuous charge-discharge cycles. It is very interesting to know the origin of the capacitance enhancement, which results from the change of pyrrolic N in NG-MSC to the pyridinic and graphitic N. An on-chip NG-MSC exhibits an excellent charge storage capacitance of 43.5 mF cm-2 at a current density of 0.5 mA cm-2 and shows impressive power delivery at a very high scan rate of 100 V s-1. The excellent rate capability of the MSC shows capacitance retention up to 70.1% with the variation of current density. This unique approach to fabricate NG-MSC can have a broad range of applications as energy storage devices in the electronics market, as demonstrated by glowing a commercial red LED.

Experimental and numerical investigation of laser-assisted electrodeposition based on amorphous forming: Laser-electrodeposition correlation and explanation of enhancing mechanism

In this study, the laser parameters including laser power, scanning rate, scanning line distance, pulse width, frequency, and scanning area were used as the influencing factors, and the temperature, current density, and force impact effect were used as the response indexes to discuss the correlation between laser irradiation and electrochemical deposition (ECD) amorphous-forming process. The results show that in the preparation area ranges of 5 × 5, 10 × 10, and 20 × 20 mm, the laser power, scanning rate, and scanning line distance are the most significant parameters affecting the ECD process performance. The laser power affects the rising range and vibration amplitude of the current density, whereas the scanning rate and line distance influence the rising range, vibration amplitude, and variation period. The current density and force signal change periodically and stably over the suitable processing range. Compared with ECD NiP coating, the comprehensive performance of the coating prepared by the representative parameters selected according to the optimized parameter range are better. This study can provide ideas for the parameter optimization of the laser-enhanced ECD for different materials and processing sizes. In the future work, the influence of laser parameters on the ECD reduction process from a microscopic perspective will be discussed for establishing the correlation between laser parameters and coating performance. Moreover, the periodic current waveform formed by the laser is expected to prepare multilayer gradient structures with alternating grain sizes.

Interaction between the mid-infrared continuous wave laser with a center wavelength of 3.8 µm and fused silica.

The absorption coefficient of fused silica for a mid-infrared (IR) laser is higher than that for a near-IR laser, but smaller than that for a far-IR laser. Therefore, the energy coupling efficiency of the mid-IR laser is higher than that for the near-IR laser, while the penetration depth is higher than that for the far-IR laser. Thus, the mid-IR laser is highly efficient in mitigating damage growth. In this study, a deuterium fluoride (DF) laser with a center wavelength of 3.8 µm was used to interact with fused silica. The temperature variation, changes in the reflected and transmitted intensities of the probe light incident on the laser irradiation area, and the vaporization and melting sputtering process were analyzed. The results demonstrate that when the laser intensity was low (<1.2 kW/cm2), no significant melting was observed, and the reflection and transmission properties gradually recovered after the end of the laser irradiation process. With a further increase in the laser intensity, the sample gradually melted and vaporized. At a laser intensity above 5.1 kW/cm2, the temperature of the sample increased rapidly and vapors in huge quantity evaporated from the surface of the sample. Moreover, when the laser intensity was increased to 9.5 kW/cm2, the sample melted and an intense melting sputtering process was observed, and the sample was melted through.

Investigation of structural transformation and residual stress under single femtosecond laser pulse irradiation of 4H–SiC

Silicon carbide (SiC) is an attractive semiconductor material for devices that operate under extreme conditions. However, its high hardness and chemical stability hinder micromachining. Femtosecond laser has been proposed extensively as an effective micromachining tool for SiC. However, the fundamental mechanisms of laser-material interaction during femtosecond laser irradiation process remain elusive. This paper presents a comprehensive study of the structural transformation and residual stress induced by irradiating a 4H–SiC target with a single-pulse femtosecond laser. The energy dependence of the structural characteristics at the spot center and the spatial distribution across the laser spot were determined using optical microscopy and micro-Raman spectroscopy. The effect of the laser fluence on the residual stress was discussed. The obtained results showed that no structural changes occurred at low energy, whereas bond breaking occurred among crystalline SiC (c-SiC) at high energy. A central disk with no structural transformation and no residual stress was formed for the fluence of 22.2 J/cm 2 , owing to phase explosion-induced spluttering. Meanwhile, an inhomogeneous distribution of the structural transformation was generated from the spot centre to the edge. Based on this, threshold fluences for modification and structural transformation were proposed and calculated. The fundamental mechanisms for different laser-fluence regimes are discussed, and some suggestions for improving the surface quality are put forward. This study provides deep insights into the laser-material interaction mechanisms and is beneficial for optimising the utilisation of femtosecond laser for 4H–SiC micromachining. • Structural characteristics and residual stress at the spot centre depend on laser energy. • Spatial distribution of structural transformation from the spot centre to the edge is inhomogeneous. • Threshold fluences for modification and structural transformation are proposed and calculated. • The fundamental mechanisms of laser-material interaction for different laser-fluence regimes are analysed. • The residual stress in central disk region vanishes for the laser fluence of 22.2 J/cm 2 , owing to explosive boiling.