Femtosecond Laser Irradiation Research Articles

Glass Surface Modification Was Induced by the Combination of Coating Technology and Femtosecond Laser Assisted Chemical Etching

Due to its high hardness and high transmittance, ultra-white glass has a strong application prospect in the fields of optoelectronics industry and experimental instruments. However, because of its brittleness, it was still a difficult problem in the machining industry. Surface modification provides a basic research idea for ultra-white glass microstructure processing. An effective method to obtain surface modified area on ultra-white glass was presented. The modified zone on the surface of ultra-white glass was induced by the technique of coating and femtosecond laser-assisted chemical etching. The method combines vacuum coating with femtosecond laser irradiation. Next, the modified glass was processed with highly selective potassium hydroxide solution. In order to control the surface size more efficiently, the optimization experiment of laser parameters and chemical parameters on the machining process was carried out. The experimental results show that the method made the surface modification of ultra-white glass more easily and provides basic research for fabricating microchannels on the material.

Femtosecond laser sintering Al nanoparticles: A multiscale investigation of combined molecular dynamics simulation and two-temperature model

The sintering process of Al nanoparticles subject to femtosecond laser irradiation is investigated by using a multiscale approach combining molecular dynamics simulation at atomistic scale and two-temperature model at continuum scale. The temporal evolutions of electron temperature and lattice temperature, atomistic snapshot and structural transformation are calculated to reveal the detailed spatiotemporal information on femtosecond laser sintering Al nanoparticles. Moreover, by studying the temporal evolutions of mean square displacement, radius ratio, shrinkage rate and gyration radius during the sintering process, the impacts of absorbed laser fluence and laser pulse width on the sintering process of Al nanoparticles are probed. The absorbed laser fluence is found to crucially induce whether the Al nanoparticles are to be sintered. Furthermore, the critical absorbed laser fluence to trigger sintering is determined. Whereas, the laser pulse width is found to bring almost no distinctive differences on the process and result of Al nanoparticles sintering.

Generation of 56.5 W femtosecond laser radiation by the combination of an Nd-doped picosecond amplifier and multi-pass-cell device.

We demonstrate the generation of high average power femtosecond laser radiation by combination of an Nd-doped picosecond amplifier and a multi-pass cell device. With this efficient and robust scheme, the pulse duration of a picosecond amplifier is compressed from 9.13 ps to 477 fs, corresponding to a compression factor of 19.1. The average power before and after pulse compression is 77 W and 56.5 W respectively, so the overall transmission reaches 73.4%. The presented scheme offers a viable route toward low-cost and simple configuration high power femtosecond lasers driven by Nd-doped picosecond amplifiers.

Simultaneous measurement of salinity and temperature based on Fabry-Perot interference and anti-resonance effect

In this work, we demonstrate a novel cascaded fiber-optic structure depending on Fabry-Perot interference and anti-resonance (AR) effect for seawater salinity and temperature simultaneous measurement. An in-fiber microchannel Fabry-Perot interferometer (FPI) is obtained in a single-mode fiber (SMF) by using femtosecond laser radiation and hydrofluoric acid corrosion, which is filled with thermosensitive polymer and able to measure the temperature. A section of hollow-core fiber (HCF) is fused between the SMFs with the square micro-slots ablated on the ends, and the liquid can easily flow into the HCF. To our knowledge, this is the first time that the capillary-type HCF was used as a microfluidic device to measure seawater salinity. Through model analysis and experimental tests, it is confirmed that the proposed sensor can simultaneously measure the salinity and temperature, the corresponding minimum detectable resolutions reach 0.0008‰ and 0.001 ℃, respectively. The performance tests show that the sensor has accurate measurement results, good stability, and repeatability. Besides, the proposed HCF-based internal liquid analysis structure is a promising approach for highly reliable and ultrasensitive biochemical sensing.

Femtosecond laser induced one-step nanopatterning and preparation of rGO/RuO2 electrodes for high-performance micro-supercapacitors

Due to the tremendous importance of miniaturized energy harvesting devices for implantable and wearable electronics, numerous new materials and electrode architectures for micro-supercapacitors (MSCs) have emerged in recent years. Hybrid electrodes based on transition metal oxides and carbon-based materials are considered to be promising candidates to overcome the relatively low energy density of pure carbon materials. However, the complicated preparation process limited its development. Herein, a facile method of simultaneous nanopatterning and preparation of reduced graphene oxide (rGO)/RuO2 nanocomposite electrodes by femtosecond laser irradiation is proposed. The RuO2 nanoparticles and filaments structures are successfully anchored to rGO surfaces through a redox reaction of graphene oxide (GO) and RuCl3. On this basis, the binder-free, metal current collector-free rGO/RuO2 electrodes are constructed. The as prepared rGO/RuO2 MSCs deliver an areal capacitance of 2.35 mF/cm2 and 90% capacitance retention after 4000 charge-discharge cycles. The synergic effect between rGO and RuO2 nanoparticles enables the high-performance of rGO/RuO2 hybrid electrodes. This research enables the one-step manufacturing of carbon/pseudocapacitor hybrid electrodes, showing great promise for next generation flexible displays and wearable electronic devices.

Formation of Metallic Ag on AgBr by Femtosecond Laser Irradiation

Laser irradiation of materials induces changes in their structure and functional properties. In this work, lattice heating and electronic excitation on silver bromide (AgBr), provoked by femtosecond laser irradiation, have been investigated by finite-temperature density functional theory and ab initio molecular dynamics calculations by using the two-temperature model. According to our results, the electronic temperature of 0.25 eV is enough to excite the electrons from the valence to the conduction band, whereas 1.00 eV changes the structural properties of the irradiated AgBr material. Charge density simulations also show that an Ag clustering process and the formation of Br3− complexes take place when the electronic temperature reaches 2.00 eV and 5.00 eV, respectively. The present results can be used to obtain coherent control of the extreme nonequilibrium conditions due to femtosecond laser irradiation for designing new functional materials.

Ways of Measuring the Parameters of a Laser-Induced Plasma Channel Formed by Femtosecond Laser Radiation in an Argon Medium at Different Pressures

Ways of Measuring the Parameters of a Laser-Induced Plasma Channel Formed by Femtosecond Laser Radiation in an Argon Medium at Different Pressures

Coupling Localized Laser Writing and Nonlocal Recrystallization in Perovskite Crystals for Reversible Multidimensional Optical Encryption.

The ability to generate and manipulate photoluminescence (PL) with high spatial resolution has been of primary importance for applications in micro-optoelectronics, while the emerging metal halide perovskites offer novel material platforms where diverse photonic functionalities and fine structuring are constantly explored. Herein, micro-PL patterns consisting of highly luminescent CsPbBr3 nanocrystals (NCs) in nonluminescent perovskite crystals are directly fabricated by focused femtosecond laser irradiation. Further modulation with a moisture field leads to the selective dissolution of the laser-destabilized perovskite structures as revealed by density functional theory simulations, thus allowing for facile control of the reversible PL from the recrystallization of moisture-induced CsPbBr3 NCs. By leveraging the coupled laser writing and moisture modulation, multimodal information encryption is realized by reversible encryption-reading and repeatable erasing-refreshing. This optical storage mechanism is also extended to 3D and 4D by realizing spatially and temporally resolved optical encryption. The coupled multifield modulation on perovskite crystals can enable potential applications in optical storage and encryption, and offer a novel solution for the creation and manipulation of localized PL structures with high temporal and spatial resolutions.

Preliminary Study on the Optimization of Femtosecond Laser Treatment on the Surface Morphology of Lithium Disilicate Glass-Ceramics and Highly Translucent Zirconia Ceramics.

All-ceramic restorations have become increasingly popular in dentistry. Toward ensuring that these restorations adhere to the tooth structure, this study determines the optimal femtosecond laser (FL) treatment parameters for lithium disilicate glass-ceramics and highly translucent zirconia ceramics with respect to surface morphology. For both the ceramics, the following surface conditions were investigated: (1) as-sintered; (2) Al2O3 sandblasted; (3) FL treatment (dot pattern with line distances of 14, 20, and 40 µm); (4) FL treatment (crossed-line pattern with a line distance of 20 and 40 µm). Surface roughness parameters were estimated using a 3D confocal laser microscope; microstructures were analyzed using a scanning electron microscope. Peak fluence (Fpeak) values of 4 and 8 J/cm2 and irradiation numbers (N) of 20 and 10 shots were selected to create dot patterns in highly translucent zirconia and lithium disilicate glass-ceramics, respectively. Furthermore, Fpeak = 8 J/cm2 and N = 20 shots were chosen to obtain crossed-line patterns in both ceramics. Our results show that lithium disilicate glass-ceramics and highly translucent zirconia exhibit a similar surface morphology under each of the surface treatment conditions. Therefore, FL irradiation of dot or crossed-line patterns (at a distance of 20 and 40 µm) are potential candidates for future investigations.

Inactivation of SARS-CoV-2 by a chitosan/α-Ag2WO4 composite generated by femtosecond laser irradiation

In the current COVID-19 pandemic, the next generation of innovative materials with enhanced anti-SARS-CoV-2 activity is urgently needed to prevent the spread of this virus within the community. Herein, we report the synthesis of chitosan/α-Ag2WO4 composites synthetized by femtosecond laser irradiation. The antimicrobial activity against Escherichia coli, Methicilin-susceptible Staphylococcus aureus (MSSA), and Candida albicans was determined by estimating the minimum inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC). To assess the biocompatibility of chitosan/α-Ag2WO4 composites in a range involving MIC and MBC/MFC on keratinocytes cells (NOK-si), an alamarBlue™ assay and an MTT assay were carried out. The SARS-CoV-2 virucidal effects was analyzed in Vero E6 cells through viral titer quantified in cell culture supernatant by PFU/mL assay. Our results showed a very similar antimicrobial activity of chitosan/α-Ag2WO4 3.3 and 6.6, with the last one demonstrating a slightly better action against MSSA. The chitosan/α-Ag2WO4 9.9 showed a wide range of antimicrobial activity (0.49–31.25 µg/mL). The cytotoxicity outcomes by alamarBlue™ revealed that the concentrations of interest (MIC and MBC/MFC) were considered non-cytotoxic to all composites after 72 h of exposure. The Chitosan/α-Ag2WO4 (CS6.6/α-Ag2WO4) composite reduced the SARS-CoV-2 viral titer quantification up to 80% of the controls. Then, our results suggest that these composites are highly efficient materials to kill bacteria (Escherichia coli, Methicillin-susceptible Staphylococcus aureus, and the yeast strain Candida albicans), in addition to inactivating SARS-CoV-2 by contact, through ROS production.

Polaron lifetime enhancement of P3HT thin film under femtosecond laser irradiation and its ultrafast mechanism

The morphology and properties of poly (3-hexylthiophene) (P3HT) thin films after femtosecond laser irradiation with various fluences were studied. Two types of final ablation morphology were characterized through optical microscope (OM), atomic force microscope (AFM) and scanning electron microscope (SEM). At lower fluences, nano-bumps were formed in the central area. At higher fluences, nano-bumps were formed in the entire irradiated area and the material in the center disintegrated. Time-resolved pump–probe system was used to investigate laser − P3HT ultrafast interaction and the principle of morphological differences, which revealed that the Coulomb explosion was the reason for the morphology change with fluence increasing. Photoluminescence (PL) spectra indicated that the transition of the PL signal from enhancement to quenching with various laser fluences was related to the effect of laser on morphology and molecular exciton. A maximal 2 fold lifetime enhancement of bound polaron pair dissociation and 1.3 fold lifetime improvement of defect trapping were achieved at higher fluences, which contributed to obtaining more effective free carriers and subsequent photocurrent. These results promote the potential applications of femtosecond laser on P3HT and other organic semiconductors, especially organic photovoltaics (OPV) devices.

Single-shot femtosecond bulk micromachining of silicon with mid-IR tightly focused beams

Being the second most abundant element on earth after oxygen, silicon remains the working horse for key technologies for the years. Novel photonics platform for high-speed data transfer and optical memory demands higher flexibility of the silicon modification, including on-chip and in-bulk inscription regimes. These are deepness, three-dimensionality, controllability of sizes and morphology of created modifications. Mid-IR (beyond 4 µm) ultrafast lasers provide the required control for all these parameters not only on the surface (as in the case of the lithographic techniques), but also inside the bulk of the semiconductor, paving the way to an unprecedented variety of properties that can be encoded via such an excitation. We estimated the deposited energy density as 6 kJ cm−3 inside silicon under tight focusing of mid-IR femtosecond laser radiation, which exceeds the threshold value determined by the specific heat of fusion (~ 4 kJ cm−3). In such a regime, we successfully performed single-pulse silicon microstructuring. Using third-harmonic and near-IR microscopy, and molecular dynamics, we demonstrated that there is a low-density region in the center of a micromodification, surrounded by a “ring” with higher density, that could be an evidence of its micro-void structure. The formation of created micromodification could be controlled in situ using third-harmonic generation microscopy. The numerical simulation indicates that single-shot damage becomes possible due to electrons heating in the conduction band up to 8 eV (mean thermal energy) and the subsequent generation of microplasma with an overcritical density of 8.5 × 1021 cm−3. These results promise to be the foundation of a new approach of deep three-dimensional single-shot bulk micromachining of silicon.

Study of surface wettability on fused silica by ultrafast laser-induced micro/nano-surface structures

Glass materials integrated with advanced functions, such as anti-fogging and self-cleaning functions, are urgently demanded in applications such as vehicle windshields, eyeglasses, goggles, electronic device screens, and windows. Inspired by nature, researchers have found multiscale surface structures to be a crucial factor in determining a material's surface wettability. The ultrafast pulsed laser is a promising tool to induce such surface structures and subsequently control the surface functionalities on different materials. The behavior of surface wettability with different micro/nano-scale surface structures created by femtosecond laser irradiation on fused silica is investigated in this research. The effects of laser fluence, overlapping ratio, and repetition rate on the structure morphology are studied. Seven different sorts of structures can be created by manipulating these parameters: (S1) micro-dots array, (S2) micro-dots array covered with laser-induced periodic surface structures (LIPSSs), (S3) LIPSSs, (S4) microgrooves covered with LIPSSs, (S5) microgrooves covered with irregular nanostructures, (S6) micro-channels and (S7) micro-channels covered with LIPSSs. Investigations into the static contact angle show that hydrophilic and superhydrophilic surfaces can be generated through the introduction of these laser-induced hierarchical structures. The relationship between laser parameters, surface structures, surface roughness, and surface wettability is established. Different distinctive mean static contact angle values are identified for different surface structures.

Femtosecond Laser Direct Writing of Gradient Index Fresnel Lens in GeS2-Based Chalcogenide Glass for Imaging Applications

Chalcogenide glasses have attracted growing interest for their potential to meet the demands of photonic applications in the Mid-Wavelength InfraRed (MWIR) and Long-Wavelength InfraRed (LWIR) transmission windows. In this work, we investigated the photosensitivity to femtosecond laser irradiation of a dedicated chalcogenide glass, along with its possible applications in micro-optics. In order to address the SWaP problem (Size, Weight and Power), this work took advantage of recent techniques in femtosecond laser direct writing to imprint flat and integrated optical systems. Here, we wanted to simplify an infrared multispectral imaging system which combines a lens array and a filter array. Each channel has a focal length of 7 mm and an f-number of 4. We show in this paper that the chosen GeS2-based chalcogenide glass is very promising for the fabrication of graded index optics by fs-laser writing, and particularly for the fabrication of Fresnel lenses. We note a very important phase variation capacity in this infrared material corresponding to refractive index variations up to +0.055. A prototype of Fresnel GRIN lens with a refractive index gradient was fabricated and optically characterized in the Vis range.

The role of glass composition in the 3D laser fabrication of lithium niobate single crystal in lithium niobosilicate glass

Spatially selective growth of lithium niobate (LiNbO3) crystals deep within lithium niobosilicate (LNS) glass can be achieved via femtosecond laser irradiation, wherein these crystals could serve as optical elements in photonic integrated circuits. In practice, it is challenging to achieve continuous, single-crystal growth of LiNbO3 within LNS glass. This work reports on progress in overcoming this challenge by exploring how the formation of single-crystal LiNbO3 is influenced by the incongruent composition of the glass matrix. An investigation of the parameter space of glass composition ((100 – x) LiNbO3 – x SiO2 for x = 22, 26, 30, and 34), laser scanning speed, and laser power leads to the observation of several growth modes: continuous growth at an optimal speed, segmented growth below it, and polycrystalline growth above it. For certain glass compositions, a balance of long incubation time and high crystal growth rate results in the ability to grow indefinitely long (∼cm) single crystal lines at the optimal scanning speed. Guidance for predicting which glass compositions are most suitable for single crystal growth based on the LNS composition diagram is provided.

Generation of micro/nano hybrid surface structures on copper by femtosecond pulsed laser irradiation

The delamination of copper lead frames from epoxy molding compounds (EMC) is a severe problem for microelectronic devices, as it leads to reduced heat dissipation or circuit breakage. The micro/nanoscale surface structuring of copper is a promising method to improve the copper–EMC interfacial adhesion. In this study, the generation of micro/nano hybrid structures on copper surfaces through femtosecond pulsed laser irradiation is proposed to improve interfacial adhesion. The micro/nano hybrid structures were realized by generating nanoscale laser-induced periodic surface structures (LIPSS) on microscale parallel grooves. Several types of hybrid surface structures were generated by changing the laser polarization direction, fluence, and scanning speed. At a specific aspect ratio of microgrooves, a latticed structure was generated on the sides of microgrooves by combining LIPSS formation and direct laser interference patterning. This study provides an efficient method for the micro/nanoscale hybrid surface structure formation for interfacial adhesion improvement between copper and EMC.

High photocatalytic activity of Ag/Ag3PO4:W heterostructure formed by femtosecond laser irradiation

In this work, the W-doped Ag3PO4 was prepared by the chemical coprecipitation method and irradiated with a femtosecond laser (FL). The successful formation of the Ag/Ag3PO4:W heterostructure was confirmed by XRD analysis. A higher structural disorder in the [PO4] clusters was observed for the FL irradiated sample (Ag3PO4:W-FL), indicating the formation of Ag metallic from the Ag3PO4 structure. The photocatalytic activity of the samples was studied by photodegradation of rhodamine B under visible light irradiation. The formation of Ag nanoparticles on the surface of Ag3PO4:W led to a degradation rate constant 3.54 times higher than the nonirradiated sample. This higher photocatalytic activity was related to the surface plasmon resonance effect of the Ag metallic, which acts by capturing photoexcited electrons from the Ag3PO4:W, avoiding the recombination of electron-hole pairs, and thus improving the photocatalytic activity.

Insights into the Correlation between Residual Stresses, Phase Transformation, and Wettability of Femtosecond Laser-Irradiated Ductile Iron.

Despite numerous studies on the wettability behavior of ductile iron after ultrafast laser structuring, the correlation between the phase change due to the interaction with an intense pulse and wettability is not yet well understood. In the present work, phase transformations of ductile iron substrates after femtosecond laser irradiation are investigated and correlated with the wettability behavior. Laser parameters such as fluence (F), cumulative fluence (CH), number of pulses (N), and scan speed were varied to produce hierarchical structures with different morphologies and phase concentrations. Our outcomes indicated that substrates with higher concentrations of austenite in the absence of hierarchical structures have a superhydrophilic nature despite being stored in an ambient atmosphere for several days and the application of a vacuum process. In addition, we measured the concomitant residual stresses after laser irradiation using the X-ray diffraction (XRD) method and established a relationship with the doses of CH and induced micro/nanostructures. Transmission electron microscopy (TEM) revealed that laser-structured surfaces are covered with oxides; moreover, phase transformation occurs at the near-subsurface layer.

Atomic‐Level Insight into the Formation of Subsurface Dislocation Layer and Its Effect on Mechanical Properties During Ultrafast Laser Micro/Nano Fabrication (Adv. Funct. Mater. 15/2022)

Atomic Structures In article number 2108802, Jianfeng Yan and co-workers investigate the formation of the subsurface dislocation layer and its effect on mechanical properties during ultrafast laser fabrication at the atomic level. Three layers with different atomic structures, the recast layer, dislocation layer, and unaffected layer, are found after femtosecond laser irradiation. The subsurface dislocation layer is formed by laser-induced stress waves, and the effect on the mechanical properties of the metal is studied.

Tightly Focused Femtosecond Laser Radiation Induces DNA Double-Strand Breaks in Human Tumor Cells.

We studied the formation of double-strand DNA breaks (DNA DSB) induced by femtosecond laser radiation in A549 human lung adenocarcinoma cells using immunocytochemical staining of the resulting tracks of a specific DSB marker protein phosphorylated ATM kinase (phospho-ATM). Additionally, colocalization of phospho-ATM tracks with γH2AX protein tracks was studied. The results of immunocytochemical analysis showed that 30 min after irradiation of cells with femtosecond pulses with energies of 1 and 2 nJ (radiation power density 2×1011 and 4×1011 W×cm-2, respectively), the formation of tracks consisting of phospho-ATM and γH2AX proteins located in sites where the laser beam passes through the cell nuclei was observed. The presence of phospho-ATM tracks co-localized with γH2AX allows us to conclude that exposure to focused femtosecond infrared laser radiation with a pulse energy of 1-2 nJ leads to the formation of DNA DSB in irradiated cells.