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Invar 36 alloy has an extremely low coefficient of thermal expansion and is suitable for preparing a fine metal mask (FMM) for the evaporation of silicon-based organic light emitting display microdisplays. The higher the resolution and the greater the number of pixels, the finer and more delicate the holes required. Femtosecond laser processing technology is an effective technical means for processing Invar 36 alloy FMM due to its characteristics of extremely short pulse width, extremely high pulse energy density, smaller heat-affected zone, and more regular machining edges. The femtosecond laser processing parameters directly affect temperature distribution and then affect the manufacturing quality and efficiency of Invar 36 alloy FMM. At present, femtosecond laser processing of Invar 36 alloy FMM is still in the exploration stage, and the processing mechanism and technology are not clear. In this paper, a simulation model of single-pulse femtosecond laser processing Invar 36 alloy is established based on the two-temperature equation. By comparing the ablation morphology of the simulation output with the experimental measurement results, the validity of the simulation model is verified and the processing mechanism is preliminarily explored. Based on the simulation model, the effects of femtosecond laser energy density, pulse duration, and spot diameter on the electron temperature field, lattice temperature field, and ablation morphology of the craters are explored. The process window of laser processing parameters is determined. A full-factor test is conducted. Take the minimum length of the heat-affected zone, the maximum depth of the ablation crater, and the minimum diameter of the ablation crater as three optimization objectives and obtain Pareto optimal solutions based on genetic algorithm. The optimization of single-pulse femtosecond laser drilling Invar 36 alloy is realized. [ABSTRACT FROM AUTHOR]

In this work, laser‐induced periodic surface structures (LIPSS) are generated on the surface of thin films of poly(trimethylene terephthalate) (PTT) fabricated by spin coating on silicon. Previous studies have shown the appearance of LIPSS in this type of materials with femtosecond laser pulses in the near‐infrared region of the spectrum, despite the extremely low absorption of the polymer. The present work consists of an exploration of the effect of adding complexity to the femtosecond laser fields employed for irradiation. Changes in the repetition rate of the pulse train, the pulse duration, and the pulse temporal chirp are explored, and conditions for optimum LIPSS formation are identified. The effects of these modifications on the polymer surface topography, assessed by atomic force microscopy, are described and discussed. [ABSTRACT FROM AUTHOR]

Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study investigates their durability against acetone, ethylene glycol, and UV radiation. The laser-structured surfaces were immersed in the respective liquids for up to 48 h. The results indicate limited durability of the superhydrophobic and icephobic layers when submerged in acetone and ethylene glycol, with more favorable results for petrol treatment than vacuum treatment. Similar results were obtained after 100 h of UV exposure, showing a decrease in superhydrophobic properties and an increase in ice adhesion. However, repeated vacuum treatments conducted after the chemical durability tests revealed the potential for partial recovery of the hydrophobic and icephobic properties. XPS analysis was performed throughout the experiments to evaluate changes in surface chemistry resulting from the post-laser treatments and the durability tests. [ABSTRACT FROM AUTHOR]

This work demonstrates a method to design photonic surfaces by combining femtosecond laser processing with the inverse design capabilities of tandem neural networks that directly link laser fabrication parameters to their resulting textured substrate optical properties. High throughput fabrication and characterization platforms are developed that generate a dataset comprising 35280 unique microtextured surfaces on stainless steel with corresponding measured spectral emissivities. The trained model utilizes the nonlinear one‐to‐many mapping between spectral emissivity and laser parameters. Consequently, it generates predominantly novel designs, which reproduce the full range of spectral emissivities (average root‐mean‐squared‐error < 2.5%) using only a compact region of laser parameter space 25 times smaller than what is represented in the training data. Finally, the inverse design model is experimentally validated on a thermophotovoltaic emitter design application. By synergizing laser‐matter interactions with neural network capabilities, the approach offers insights into accelerating the discovery of photonic surfaces, advancing energy harvesting technologies. [ABSTRACT FROM AUTHOR]

Femtosecond laser processing technology is an advanced sub-micro-processing technique that enables the non-contact processing of various materials. This technology can be used to apply sub-micro structures for purposes such as hydrophilicity enhancement, optical transmittance improvement, and photonics detection. However, when it comes to processing micro/nanostructures on highly brittle materials using femtosecond lasers, there are challenges such as low processing efficiency, generation of debris, and microcracking. In this paper, we propose a method called the out-of-focus femtosecond laser direct writing technique combined with wet etching. This method offers simplicity, speed, and flexibility in preparing dense, large-area sub-microstructured surfaces on the brittle material sapphire. Our detailed investigation focuses on the impact of laser processing parameters (direct writing period, distance of focusing, direct writing speed, etc.) on the sub-microstructures of Al2O3 surfaces. The results demonstrate that this method successfully creates embedded sub-microstructures on the sapphire surface. The microholes, with a diameter of approximately 2.0 μm, contain sub-micro structures with a minimum width of 250 ± 20 nm. Additionally, we conducted experiments to assess the optical transmittance of sapphire nanostructures in the range of 350–1200 nm, which exhibited an average transmittance of approximately 77.0%. The water contact angle (CA) test yielded a result of 52 ± 2°, indicating an enhancement in the hydrophilicity of the sapphire nanostructures with only a slight reduction in optical transmittance. Our efficient fabrication of sub-microstructures on the sapphire surface of highly brittle materials offers a promising method for the production and application of brittle materials in the field of micro-optics. [ABSTRACT FROM AUTHOR]

Featured Application: The obtained knowledge can be useful for understanding and optimizing various technologies with glass-forming materials under local fast laser excitations. The ability to control the temperature distribution T (t , r) and the rate of temperature change R t , r inside glasses is important for their microstructuring. The lattice temperature is considered at time t , exceeding the electron–phonon thermalization time, and at a distance r from the center of the model spherical heating zone. In order to describe thermal excitations, the heat capacity of glasses must be considered as a function of time due to its long-term relaxation. A method for the analytical calculation of T (t , r) and R (t , r) for glasses with dynamic heat capacity c d y n (t) is proposed. It is shown that during laser microstructuring, the local cooling rate − R (t , r) significantly depends on the time dispersion of c d y n (t) . It has been established that at the periphery of the model heating zone of the laser beam focus, the local cooling rate can reach more than 1011 K/s. Strong cooling rate gradients were found at the periphery of the heating zone, affecting the microstructure of the material. This effect is significantly enhanced by the time dispersion of c d y n (t) . The effect associated with this time dispersion is significant, even well above the glass transition temperature T g , since even short relaxation times of the dynamic heat capacity c d y n (t) are significant. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) is widely used in many research fields because of its excellent properties. The femtosecond laser has been proven to be an effective method for achieving high-quality and high-efficiency SiC micromachining. In this article, the ablation mechanism irradiated on different surfaces of 6H-SiC by a single pulse under different energies was investigated. The changes in material elements and the geometric spatial distribution of the ablation pit were analyzed using micro-Raman spectroscopy, Energy Dispersive Spectrum (EDS), and an optical microscope, respectively. Moreover, the thresholds for structural transformation and modification zones of 6H-SiC on different surfaces were calculated based on the diameter of the ablation pits created by a femtosecond laser at different single-pulse energies. Experimental results show that the transformation thresholds of the Si surface and the C surface are 5.60 J/cm2 and 6.40 J/cm2, corresponding to the modification thresholds of 2.26 J/cm2 and 2.42 J/cm2, respectively. The Raman and EDS results reveal that there are no phase transformations or material changes on different surfaces of 6H-SiC at low energy, however, decomposition and oxidation occur and then accumulate into dense new phase material under high-energy laser irradiation. We found that the distribution of structural phase transformation is uneven from the center of the spot to the edge. The content of this research reveals the internal evolution mechanism of high-quality laser processing of hard material 6H-SiC. We expect that this research will contribute to the further development of SiC-based MEMS devices. [ABSTRACT FROM AUTHOR]

The field of bone tissue engineering is steadily being improved by novel experimental approaches. Nevertheless, microbial adhesion after scaffold implantation remains a limitation that could lead to the impairment of the regeneration process, or scaffold rejection. The present study introduces a methodology that employs laser-based strategies for the development of antimicrobial interfaces on tricalcium phosphate–hydroxyapatite (TCP-HA) scaffolds. The outer surfaces of the ceramic scaffolds with inner porosity were structured using a femtosecond laser (λ = 800 nm; τ = 70 fs) for developing micropatterns and altering local surface roughness. The pulsed laser deposition of ZnO was used for the subsequent functionalization of both laser-structured and unmodified surfaces. The impact of the fs irradiation was investigated by Raman spectroscopy and X-ray diffraction. The effects of the ZnO-layered ceramic surfaces on initial bacterial adherence were assessed by culturing Staphylococcus aureus on both functionalized and non-functionalized scaffolds. Bacterial metabolic activity and morphology were monitored via the Resazurin assay and microscopic approaches. The presence of ZnO evidently decreased the metabolic activity of bacteria and led to impaired cell morphology. The results from this study have led to the conclusion that the combination of fs laser-structured surface topography and ZnO could yield a potential antimicrobial interface for implants in bone tissue engineering. [ABSTRACT FROM AUTHOR]

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2–4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis. [ABSTRACT FROM AUTHOR]

In recent years, superhydrophobic surfaces have attracted significant attention due to their promising applications, especially in ice prevention, reduction in air resistance, and self-cleaning. This study utilizes femtosecond laser processing technology to prepare different surface microstructures on polytetrafluoroethylene (PTFE) surfaces. Through experiments, it investigates the relationship between the solid–liquid contact ratio and surface hydrophobicity. The shape of water droplets on different microstructure surfaces is simulated using ANSYS, and the relationship between surface microstructures and hydrophobicity is explored in the theoretical model. A superhydrophobic surface with a contact angle of up to 166° was obtained by machining grooves with different spacings in polytetrafluoroethylene sheets with femtosecond laser technology. Due to the micro- and nanostructures on the surface, the oleophobicity of the processed oleophilic PTFE surface is enhanced. [ABSTRACT FROM AUTHOR]

Two-photon lithography (TPL) is a laser-based additive manufacturing technique that enables the printing of arbitrarily complex cm-scale polymeric 3D structures with sub-micron features. Although various approaches have been investigated to enable the printing of fine features in TPL, it is still challenging to achieve rapid sub-100 nm 3D printing. A key limitation is that the physical phenomena that govern the theoretical and practical limits of the minimum feature size are not well known. Here, we investigate these limits in the projection TPL (P-PTL) process, which is a high-throughput variant of TPL, wherein entire 2D layers are printed at once. We quantify the effects of the projected feature size, optical power, exposure time, and photoinitiator concentration on the printed feature size through finite element modeling of photopolymerization. Simulations are performed rapidly over a vast parameter set exceeding 10,000 combinations through a dynamic programming scheme, which is implemented on high-performance computing resources. We demonstrate that there is no physics-based limit to the minimum feature sizes achievable with a precise and well-calibrated P-TPL system, despite the discrete nature of illumination. However, the practically achievable minimum feature size is limited by the increased sensitivity of the degree of polymer conversion to the processing parameters in the sub-100 nm regime. The insights generated here can serve as a roadmap towards fast, precise, and predictable sub-100 nm 3D printing. [ABSTRACT FROM AUTHOR]

Bacterial infection is one of the most common and harmful medical issues following the implantation of materials and devices in the body leading to antibiotic resistance of diverse bacterial strains. In this work, a novel approach is presented combining adopted laser-based patterning method in addition to doping (Mg and Zn) metal ions to prepare calcium phosphate ceramic substrate, applicable in medicine, with enhanced surface antimicrobial characteristics. The preparation of tablets containing Mg (8.44 mol%) and Zn (2.63 mol%) β-tricalcium phosphate involved biomimetic precipitation of amorphous calcium phosphate in media of simulated body fluid enriched with Mg2+ and Zn2+ ions as well as the presence of valine as an organic additive, followed by step-wise calcination up to 1000 °C. The results from laser processing showed formation of deeper patterns with increased surface roughness (from 4.9 µm to 9.4 µm) as laser power and velocity increase, keeping constant the hatch sizes of 50 µm. The textured surfaces consist of peaks and valleys arrangement that change the morphology of Escherichia coli cells and decrease of cell viability. Our study reveals the possibilities of the application of ultra-short laser radiation as a potential alternative therapy for controlling the antimicrobial effect of the ceramic surface. [ABSTRACT FROM AUTHOR]

Micro‐optical components exhibit significant potential applications in various fields such as imaging, optical fiber communication, and aerospace owing to their small size, light weight, and flexible design. It is imperative to fabricate micro‐optical components on hard brittle materials to improve stability and broaden the optical transmission range. Therefore, femtosecond laser processing technology is demonstrated to be an efficient processing strategy for preparing refractive/diffractive micro‐optical components on hard brittle materials compared to other established micromachining techniques. This study reviews recent advances in refractive/diffractive micro‐optical components using femtosecond laser processing technologies. The applications of refractive/diffractive micro‐optical components with high accuracy, efficiency, and quality in the fields of imaging, sensing, display, and integration are also summarized. Moreover, the challenges of femtosecond laser processing technologies and the outlook of micro‐optical components are highlighted. [ABSTRACT FROM AUTHOR]

Large-area nanostructuring of glasses using intense laser beams is a challenging task due to the material's extreme non-linear absorption of laser energy. Precise optimization of the process parameters is essential for fabricating nanostructures with large-area coverage. In this study, we report the findings on creating high-spatial-frequency LIPSS (HSFL) on borosilicate glass through direct laser writing, using a femtosecond laser with a wavelength λ = 800 nm, pulse duration τ = 35 fs, and repetition frequency frep = 1 kHz. We measured the single-pulse ablation threshold and incubation factor of Borosilicate glasses to achieve high-precision control of the large-area surface structuring. Single-spot experiments indicated that, when there was higher fluence and a larger number of irradiated laser pulses, a melt formation inside the irradiated area limited the uniformity of LIPSS formation. Additionally, the orientation of the scan axis with the laser beam polarization was found to significantly influence the uniformity of LIPSS generated along the scan line, with more redeposition and melt formation when the scan axis was perpendicular to the laser beam polarization. For large-area processing, the borosilicate glass surface was scanned line-by-line by the laser beam, with a scan orientation parallel to the polarization of the laser. The optical characterization revealed that the transmittance and reflectance of the borosilicate glass decreased significantly after processing. Additionally, the surface's wettability changed from hydrophilic to super-hydrophilic after processing. These chemical contamination-free and uniformly distributed structures have potential applications in optics, microfluidics, photovoltaics, and biomaterials. [ABSTRACT FROM AUTHOR]

Among metallic biomaterials, near-equiatomic NiTi is one of the most promising intermetallic system applicable for biomedical applications, thanks to its high biocompatibility and unique superelasticity (or pseudoelasticity), offering a complete recoverable strain up to 8%. In the prospective uses for bio-devices, the surface processing of NiTi medical components plays a fundamental role for guaranteeing both a Ti oxide passivizing layer for avoiding Ni ion release into the human body and surface morphology for controlling the cell proliferation. Mechanical polishing, thermal, chemical or electro-chemical treatments are typically performed for surface modifications. Recently, laser texturing has been successfully applied for different materials, included NiTi shape memory alloys, and also for tuning the surface properties, such as wettability. In the present work, ultrashort laser surface modification was carried out, through the use of a femtosecond laser, for the surface texturing of commercial superelastic NiTi plates. The main goal is to investigate the correlation among morphology, chemical composition and wettability with the principal process parameters, such as average power and scanning velocity in high power ultrashort laser texturing. Laser patterned surfaces were characterized by means of scanning electron microscopy, 3D-profilometry, XPS analysis and wetting measurements. After the laser treatments, both surface morphology and Ni/Ti ratio were largely modified from the initial surface, depending on the adopted process parameters. The wettability of the laser textured surfaces can be also varied with respect to the initial surface, due to the roughness values and grooves induced by the laser beam scans. The laser texturing process induced a combination between micro and nano structures, depending on the input energy. In details, the surfaces were tuned to lower roughness values (from 0.4 μm to 0.3 μm) with a laser power of 1 W, while it was increased up to 0.65 μm with a laser power of 13 W. The laser surface modification promoted a change of the contact angle from 70° of the untreated condition up to 135° to the surface laser treated with a power of 13 W. [ABSTRACT FROM AUTHOR]

In this study, we developed a one-step method for fabricating hydrophobic surfaces on copper (Cu) substrates. Cuprous oxide (Cu2O) with low free energy was successfully formed after low-fluence laser direct irradiation. The formation of Cu2O enhanced the hydrophobicity of the Cu substrate surface, and the contact angle linearly increased with the proportion of Cu2O. The Cu2O fabricated by low-fluence laser treatment showed the same crystal plane orientation as the pristine Cu substrate, implying an epitaxial growth of Cu2O on a Cu substrate. [ABSTRACT FROM AUTHOR]

A novel multifunctional material with efficient wicking and evaporative functionalities was fabricated using hierarchical surface nano-/microstructuring by femtosecond laser micromachining. The created material exhibits excellent multifunctional performance. Our experiments in a wind tunnel demonstrate its good wicking and evaporative functionalities under the conditions of high-temperature airflows. An important finding of this work is the significantly enhanced evaporation rate of the created material compared with the free water surface. The obtained results provide a platform for the practical implementation of Maisotsenko-cycle cooling technologies for substantially increasing efficiency in power generation, thermal management, and other evaporation-based technologies. The developed multifunctional material demonstrates long-lasting wicking and evaporative functionalities that are resistant to degradation under high-temperature airflows, indicating its suitability for practical applications. [ABSTRACT FROM AUTHOR]

Femtosecond laser machining of materials has transformed into a mature high‐precision technology, giving access to a wide range of applications. Yet, for a complete exploitation of its full potential, a detailed knowledge of the complex laser–matter interaction processes is required. For the case of the application‐relevant material steel, a complete study of the electron dynamics and material transformation upon single laser pulse irradiation (800 nm, 120 fs) is reported. Detailed analysis of the obtained time‐ and fluence‐dependent reflectivity map reveals that ultrafast electron heating during the pulse is directly followed by energy transfer to the lattice within a few picoseconds, reaching fluence‐dependent peak temperatures from below melting threshold to above the boiling point. Moreover, an innovative approach to obtain the ultrafast‐evolving 3D structure of a femtosecond laser excited material is reported, unraveling the dynamics of complex processes as melting, ablation, and solidification. Combined with modeling, the evolving optical properties, multilayer structure, and expansion velocities can be precisely determined. The information obtained from this study will contribute to further increase the achievable precision and wealth of structures that can be produced by designing efficient pulsed energy deposition schemes for selective re‐excitation of the material. [ABSTRACT FROM AUTHOR]

In recent years, many novel optical phenomena have been discovered based on perovskite materials, but the practical applications are limited because of the difficulties of device fabrication. Here, we propose a method to directly induce localized lattice modification inside the potassium tantalate niobate crystal by using the femtosecond laser. This selective modification at the processed regions and the surrounding areas is characterized by two-dimensional Raman spectrum mapping. The spectrum variations corresponding to specific lattice vibration modes demonstrate the lattice structure deformation. In this way, the lattice expansion at the femtosecond laser irradiated regions and the lattice compression at the surrounding areas are revealed. Furthermore, surface morphology measurement confirms this lattice expansion and suggests the extension of lattice structure along the space diagonal direction. Moreover, the existence of an amorphization core is revealed. These modifications on the sample lattice can induce localized changes in physicochemical properties; therefore, this method can realize the fabrication of both linear diffraction and nonlinear frequency conversion devices by utilizing the novel optical responses of perovskite materials. [ABSTRACT FROM AUTHOR]

As a laser technology, the femtosecond laser is used in biomedical fields due to its excellent performance—its ultrashort pulses, high instantaneous power, and high precision. As a surface treatment process, the femtosecond laser can prepare different shapes on metal surfaces to enhance the material's properties, such as its wear resistance, wetting, biocompatibility, etc. Laser-induced periodic surface structures (LIPSSs) are a common phenomenon that can be observed on almost any material after irradiation by a linearly polarized laser. In this paper, the current research state of LIPSSs in the field of biomedicine is reviewed. The influence of laser parameters (such as laser energy, pulse number, polarization state, and pulse duration) on the generation of LIPSSs is discussed. In this paper, the applications of LIPSSs by femtosecond laser modification for various purposes, such as in functional surfaces, the control of surface wettability, the surface colonization of cells, and the improvement of tribological properties of surfaces, are reviewed. [ABSTRACT FROM AUTHOR]

The dependence of the ablation rate on the laser fluence was measured in femtosecond laser processing of polydimethylsiloxane, and the slope of the ablation rate tended to change to three ablation regimes. The laser-irradiated area was analyzed using Raman and photoluminescence spectroscopy to investigate the cause of the changes in the slope in terms of chemical structural changes. We will show that microscopic observation of the cross-sectional sample enables the analysis of grooves with a high aspect ratio that could not be measured by conventional observation from the sample surface. This allows us to discuss the correlation between the ablation rate and chemical structural changes over a wide range of fluences up to the high fluence regime. As a result, it was found that in the low fluence regime, the photochemical process is dominant with the gentle slope of ablation rate, while both photochemical and photothermal processes lead to an increase in the slope in the middle fluence regime. Moreover, the steep slope in the high fluence regime was induced by high temperatures where carbon–carbon bond formation takes place. [ABSTRACT FROM AUTHOR]

Temporary scaffolds that mimic the extracellular matrix's structure and provide a stable substratum for the natural growth of cells are an innovative trend in the field of tissue engineering. The aim of this study is to obtain and design porous 2D fibroin-based cell matrices by femtosecond laser-induced microstructuring for future applications in muscle tissue engineering. Ultra-fast laser treatment is a non-contact method, which generates controlled porosity—the creation of micro/nanostructures on the surface of the biopolymer that can strongly affect cell behavior, while the control over its surface characteristics has the potential of directing the growth of future muscle tissue in the desired direction. The laser structured 2D thin film matrices from silk were characterized by means of SEM, EDX, AFM, FTIR, Micro-Raman, XRD, and 3D-roughness analyses. A WCA evaluation and initial experiments with murine C2C12 myoblasts cells were also performed. The results show that by varying the laser parameters, a different structuring degree can be achieved through the initial lifting and ejection of the material around the area of laser interaction to generate porous channels with varying widths and depths. The proper optimization of the applied laser parameters can significantly improve the bioactive properties of the investigated 2D model of a muscle cell matrix. [ABSTRACT FROM AUTHOR]

The anti-reflection properties of hard material surfaces are of great significance in the fields of infrared imaging, optoelectronic devices, and aerospace. Femtosecond laser processing has drawn a lot of attentions in the field of optics as an innovative, efficient, and green micro-nano processing method. The anti-reflection surface prepared on hard materials by femtosecond laser processing technology has good anti-reflection properties under a broad spectrum with all angles, effectively suppresses reflection, and improves light transmittance/absorption. In this review, the recent advances on femtosecond laser processing of anti-reflection surfaces on hard materials are summarized. The principle of anti-reflection structure and the selection of anti-reflection materials in different applications are elaborated upon. Finally, the limitations and challenges of the current anti-reflection surface are discussed, and the future development trend of the anti-reflection surface are prospected. [ABSTRACT FROM AUTHOR]

Ultrashort pulse lasers have significant advantages over conventional continuous wave and long pulse lasers for the texturing of metallic surfaces, especially for nanoscale surface structure patterning. Furthermore, ultrafast laser beam polarization allows for the precise control of the spatial alignment of nanotextures imprinted on titanium-based implant surfaces. In this article, we report the biological effect of beam polarization on human mesenchymal stem cell differentiation. We created, on polished titanium-6aluminum-4vanadium (Ti-6Al-4V) plates, a laser-induced periodic surface structure (LIPSS) using linear or azimuthal polarization of infrared beams to generate linear or radial LIPSS, respectively. The main difference between the two surfaces was the microstructural anisotropy of the linear LIPSS and the isotropy of the radial LIPSS. At 7 d post seeding, cells on the radial LIPSS surface showed the highest extracellular fibronectin production. At 14 days, qRT-PCR showed on the same surface an increase in osteogenesis-related genes, such as alkaline phosphatase and osterix. At 21 d, mineralization clusters indicative of final osteoinduction were more abundant on the radial LIPSS. Taken together, we identified that creating more isotropic than linear surfaces enhances cell differentiation, resulting in an improved osseointegration. Thus, the fine tuning of ultrashort pulse lasers may be a promising new route for the functionalization of medical implants. [ABSTRACT FROM AUTHOR]

Microstructures with a given topology were created on the surface of pure chitosan films and the same films with nanometer Ti- and Zn-containing layers deposited by magnetron sputtering. These structures were obtained using two methods: proton lithography and femtosecond laser processing. The quality of the structures (the sharpness of the walls and the thickness of the channel) is comparable to the quality of the structures obtained in the classical synthetic resist for proton lithography (polymethylmethacrylate, PMMA). A thin metal layer on the surface of the biopolymer matrix (resist) does not interfere with the formation of structures by the proton beam writing method. Laser treatment allows us to create repeating structures that control the biocompatibility of the treated surface. [ABSTRACT FROM AUTHOR]

Advances in femtosecond laser-material interaction facilitate the extension of maskless optical processing to the high efficiency and deep-subwavelength scale. Here, a hybrid plasmon lithography technique has been demonstrated by irradiating near-infrared femtosecond laser pulses onto the Si material coated with thin Cr films in a vacuum chamber, and superior nanograting structures are found to deeply penetrate through the thin Cr film into the underlying Si substrate. In stark contrast to the common ripple structures formed on the Si surface, the Cr-layer mediated Si nanograting structures not only exhibit the spatially super-regular arrangements with a deep-subwavelength period of 355 nm but also present the nonsinusoidal sharp-edged groove geometry with a large depth-to-width aspect ratio of 2.1. Theoretical analyses and calculations reveal that the anomalous structure characterizations are physically ascribed to the excitation of dual-interface coupled plasmons in the thin metal layer, which possess the squeezed spatial wavelength and the periodic columnar intensity distributions. Moreover, the further deepening of periodic nanostructures into the Si substrate is also elucidated by the simulation of electric field enhancements at the bottom of shallow grooves under irradiation of subsequent laser pulses. In combination with a wet etching process, the Si nanograting structures can be modified into the smooth and narrow-mouthed V-profiles, whose optical measurements show a near omnidirectional antireflection especially in the visible range of 565–750 nm, which is expected for the design of advanced photonic devices. [ABSTRACT FROM AUTHOR]

Reconstruction of bone tissue defects is a problematic area of the modern world. Temporary "platforms" of various materials for improving cell adhesion and proliferation have been extensively researched in recent decades. β-tricalcium phosphate (β-TCP) is a suitable biocompatible, biodegradable material used for bone regeneration. The creation of scaffolds with specifically designed surface structures will enable bone engineering applications that require navigated cell proliferation on a substrate with pre-set geometric limits. In this study, an innovative laser-based technique for surface modification was applied to improve the morphological properties of the surface of β-TCP pellets for proper cell surface environment creation. The obtained topographies with diverse processing parameters were compared. Homogenous microgroove structures, less than 100 µm, without the onset of melting and crack formation, were produced. The contribution from the accumulation effect of a diverse number of laser pulses (N = 1–100) on the final structure dimensions was examined. The microstructured scaffolds were investigated by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. We studied the effect of the patterned surface of the material on the mouse calvaria osteoblast (MC3T3) cells' viability and cytotoxicity from 1 to 7 days. The results indicated that cell behavior was affected by microscale dimensions of the surface. [ABSTRACT FROM AUTHOR]

Investigating the wettability of the tool surface made of cemented carbide is of great significance to improve its working life and quality. The micropit array was processed on the surface of cemented carbide YT15 by a 1064 nm femtosecond pulse laser. Then, the optical microscope, the optical profilometer, and the contact angle measuring instrument were applied to measure the surface morphology and the surface contact angle of micropits. The influence of different laser parameters on surface morphology and the surface contact angle was studied. The geometric morphology model of the micropit was established. The influence of the morphology of micropits on the surface contact angle is analyzed based on the Wenzel theory. The results show that the radius and depth of micropits have a positive correlation with the average laser power and scanning times. As the spacing increases, the surface roughness factor and the surface contact angle decrease. There is a strong correlation between the characterization parameters kurtosis, skewness, and surface wettability in a 3D height parameter system. The smaller the kurtosis, the greater the skewness and the better the surface hydrophilicity. [ABSTRACT FROM AUTHOR]

Combining femtosecond laser exposure with chemical etching enables the fabrication of arbitrary 3D shapes in fused silica with micron precision. Here, we investigate the use of this process combined with additional tuning of the material properties for controlling the vibrational behavior of silica microcantilevers through an acoustic black hole (ABH) effect. This effect, caused by a tapered profile at the cantilever's end, enables the trapping of propagating acoustic waves. Such cantilevers with ABH design show a remarkable amplitude decrease in the resonance peak without adding any damping material as demonstrated experimentally. Finally, using Fourier‐transform infrared spectroscopy (FTIR), we observe residual effects of the laser exposure at the surface of the specimen that have noticeable influence on the dynamic behavior of the device. [ABSTRACT FROM AUTHOR]

A new 3D nanofluidic biochip for the study of cancer cell migration and invasion is proposed. In this design, femtosecond laser‐assisted etching is applied to create embedded microfluidic channels, with a base thickness of less than 100 µm for high‐resolution imaging using inverted microscopes. The glass deformation is thermally controlled during fabrication to create pillar‐like formations separated by narrow constricted channels with widths of less than 1 µm spanning lengths of more than tens of microns, mimicking the 3D intravasation–extravasation configuration. Time‐lapse microscopy is used to observe the behavior of prostate cancer (PC3) cells in chemoattractant‐free media over long time intervals as the cells invade the narrow spaces. The PC3 cells are observed to be capable of breaching the fabricated submicrometric intravasation‐like barriers while retaining their viability and proliferation activity. The cells are further able to penetrate the extravasation‐like confining spaces, confirming their dynamic adaptability as they pass through constricted channels with volumes much less than that of the cell nucleus. [ABSTRACT FROM AUTHOR]

The benefits of micro-textures on cutting tools have been confirmed widely in implementing sustainable machining. However, the derivative cutting processes induced by the sharp edges of textures weakened the potential benefits. In our preliminary work, the newly designed curvilinear micro-grooved cutting tool has been proved to eliminate derivative cutting processes and implement sustainable machining than non-textured tools by three-dimensional (3D) finite element (FE) simulations. In this paper, the curvilinear micro-groove structures were optimized and fabricated to further improve the cutting performance of minimizing specific cutting energy. The results indicated that all the micro-groove parameters, including the width, spacing, depth, and edge distance (the distance from cutting edge to the micro-grooved area), showed obvious influence on specific cutting energy in their own ways. Specific cutting energy of the metal cutting processes can be effectively reduced by the optimal curvilinear micro-grooved cutting tools, although the optimal structures used in rough and finish turning conditions were different. In addition, a new two-step method was developed in this work to prepare curvilinear micro-grooves on carbide tools with femtosecond laser. The optimal curvilinear micro-grooved cutting tools were fabricated and used in cutting experiments, which verified the simulative results. [ABSTRACT FROM AUTHOR]

In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil. [ABSTRACT FROM AUTHOR]

It is demonstrated that the wettability of liquid metal (LM) on a substrate is very different from the water wettability. Superhydrophobic and superhydrophilic silicon and polydimethylsiloxane surfaces, respectively, are obtained by femtosecond laser processing and proper chemical modification. All of the structured surfaces have excellent LM repellence, that is, supermetalphobicity, in spite of superhydrophobicity or superhydrophilicity. The experimental comparison and contact model analysis reveal that surface microstructure actually plays a crucial role in endowing a surface with supermetalphobicity while surface chemistry has a little influence on the formation of supermetalphobicity, because the liquid/solid contact is replaced by a solid/solid contact mode for a LM droplet on a textured substrate. It is believed that the established principle for creating supermetalphobic surfaces will enable to accelerate the application progress of LM materials in flexible circuits and liquid robots. [ABSTRACT FROM AUTHOR]

Besides the optimization of the laser and processing parameters, the adaptation of the focal intensity distribution offers great potential for a well-defined control of laser processing and for improving the processing results. In this paper, different tailored intensity distributions were discussed with respect to their suitability for femtosecond laser material processing on the micro- and nanoscale such as cutting, marking, and the generation of laser-induced periodic surface structures. It was shown by means of laser processing of stainless steel that the numerical simulations for the beam shaping unit are in good agreement with the experimental results. Also, the suitability of the beam shaping device to work with a scanner and an F-theta lens as commonly used for material processing was demonstrated. In this context, the improvement of the machining results was shown experimentally, and a significant reduction of the machining time was achieved. [ABSTRACT FROM AUTHOR]

To improve the intensity and reliability of the emission fluorescence spectrum signal of petroleum pollutant samples, we designed multiple microchannel sample pools to replace traditional sample pool with square section. First, the microchannel structure of the sample pool was designed. Second, we analyzed the pulse intensity distribution and laser ablation volume (LAV) of a femtosecond laser. Then, based on the LAV, we tested the oblique motion of the laser focus at a 45° angle combined with the change in laser power, ablated a specific length region on the quartz glass surface, and indirectly determined the processed depth of the hole inside the quartz glass. Finally, using quartz glasses of 2, 5, and 10 mm in thickness as substrates, we separately varied the processing speed in the x‐direction, feed rate in the y‐direction, and laser output power of the laser processing platform, and obtained the shape‐structure of the microchannel inside the quartz glass under different processing parameter combinations. The experimental results demonstrate that the proposed method is effective at processing a specific hole depth inside the quartz glass. Experiments show that the sample cell can be used for comparative detection of fluorescence signals. [ABSTRACT FROM AUTHOR]

A simple structured ultra-highly sensitive fiber optic gas pressure sensor with low temperature cross sensitivity is proposed and demonstrated. The sensor is composed of two cascaded Mach–Zehnder interferometers (MZIs), which consist of single mode-multimode-single mode fiber structure with a micro-machined air cavity in each multimode fiber. The micro air cavities are drilled by a femtosecond laser and act as a gas pressure sensing element. Interference happens between the beams transmitting along the air cavity and the remaining silica core of the multimode fiber. The difference between the fringe intervals of the two MZIs are small enough for generating Vernier effect in gas pressure measurement. The same configuration employed in the two MZIs is to obtain the same temperature response, so that preventing the Vernier effect from appearing in temperature changes. Therefore, the proposed sensor can achieve a high gas pressure sensitivity but is insensitive to temperature variation. Experimental results show that the sensitivity for gas pressure measurement is −82.131 nm/MPa. [ABSTRACT FROM AUTHOR]

We demonstrated a simple single-exposure method of fabricating phase-shifted fiber Bragg gratings (PSFBGs), in which a non-photosensitive SMF-28 fiber was irradiated by a femtosecond laser beam passing through a uniform period phase mask. The phase-shifted structure in the FBG was formed by shielding a small region of the incident femtosecond laser beam during its irradiation. The fabricated PSFBG exhibited a 0.2 nm narrow resonant frequency band, 88% peak reflectance, and 77% extinction ratio. All-optical switching based on cross-phase modulation was demonstrated in the PSFBG at 1549.625 nm. A switching extinction ratio of more than 40% was achieved for 0.6 kW pulse peak power. [ABSTRACT FROM PUBLISHER]

Stress dynamics, stress wave and thermal stress, after photoexcitation inside glass a by tightly focused ultrashort laser pulse were investigated by a pump-probe polarization microscope and Transient Lens (TrL) method. The observation by the pump-probe polarization microscope revealed transient birefringence distributions of a laser-induced stress wave and thermal stress. The directions of compressive stress by a stress wave and thermal stress were radial from the photoexcitation, and the amplitudes of the stress estimated from the retardance of the birefringence were as high as several hundreds MPa. The observation by the TrL measurement showed the propagation of a laser induced stress wave as an oscillating TrL signals. From the pulse duration dependence of the oscillation amplitudes of the TrL signals, we found that the threshold and sensitivity to pulse energy of the stress wave become higher at longer pulse duration. We interpreted the pulse duration dependence in terms of different ionization mechanism; multiphoton ionization should be dominant for shorter pulse durations, while avalanche ionization should be dominant for longer pulse duration. [ABSTRACT FROM AUTHOR]

Ultra-short pulse laser with unique advantages in micromachining, especially on the hard brittle material becomes the focus of study on micro-structure processing. Theoretical and experimental researches are taken from the ablation properties of micro-channel in the quartz glass by femtosecond laser. As the ablation depth of quartz glass has not relationship obviously with defocusing distance within LAV effective range, a new way to control precisely the ablation depth of quartz glass is present in the study. With fixed laser power, the ablation depth could be known easily by the length of the ablation streak while moving the femtosecond laser focus along the straight line with a 45-degree angle from the quartz glass surface within the LAV range. Research is carried out to study laser pulse power, scanning velocity and step distance to do something with micro-channel ablation quality. According to the parameters of test, the micro-channel with rectangle cross section of the quartz glass is processed, and then we analyze the ablation morphology and processing efficiency. The results provided a important suggestion to process micro-structure precisely for quartz glass by femtosecond laser. [ABSTRACT FROM AUTHOR]

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In this paper, we reviewed the fabrications of functional microcavity lasers in soft materials such as polymer and protein by femtosecond laser processing. High-quality ( Q) microdisks with a laser dye (Rhodamine B, RhB) acting as gain medium were fabricated that produced whispering-gallery-mode (WGM) lasing output. We also obtained unidirectional lasing output with a low lasing threshold in a deformed spiral microcavity at room temperature. Photonic-molecule (PM) microlasers were prepared to investigate the interaction and coupling effects of different cavities, and it was found that the distance between the two disks plays an important role in the lasing behaviors. Single-mode lasing was realized from a stacked PM microlaser through Vernier effect. Furthermore we adopted the biocompatible materials, RhB-doped proteins as a host material and fabricated a three-dimensional (3D) WGM microlaser, which operated well both in air and aqueous environment. The sensing of the protein micro-lasers to NaSO concentration was investigated. Our results of fabricating high- Q microlasers with different materials reveal the potential applications of femtosecond laser processing in the areas of integrated optoelectronic and ultrahigh sensitive bio-sensing devices. [ABSTRACT FROM AUTHOR]

We report a 680-nm photoluminescence (PL) from a femtosecond-laser-modified region inside silicon. Light-emitting structures were formed inside silicon by femtosecond laser irradiation in an air atmosphere. The formation of light-emitting structures arose from laser-induced oxygen doping, and the doping depths of a few hundred micrometers could be reached. PL intensities increased with increasing depth in the laser-modified region. The effects of the laser powers and scanning velocities were investigated. The peak positions of PL spectra showed almost no change after annealing. According to the Raman spectroscopy analysis, the defect states between the silicon nanocrystals and SiO2 matrix contribute to the PL. [ABSTRACT FROM PUBLISHER]

Heat resistant FBG sensors were developed by femtosecond laser processing to apply them to high-temperature- operated piping system of nuclear power plants. The FBG sensor was installed on the surface of a steel blade and a vibration test was conducted to detect the resonant vibration frequency of the vibrating blade. The FBG sensor had the heatproof performance at 600 °C. A frequency stabilized sensing system using a tunable laser was tested for structural health monitoring in daily operation of nuclear power plants. The FBG sensor was installed on the surface of a steel blade for vibration induced strain measurements. Welding, brazing, soldering and noble metal powder adhesive were discussed for molding the FBG sensors. [ABSTRACT FROM AUTHOR]

When a femtosecond laser pulse is focused inside a LiF single crystal, four cracks are generated in the <100> directions from the photoexcited region. The time-resolved observation have elucidated that the tensile stress in the laser induced stress wave induces the generation and propagation of the cracks. In this study, to investigate the possibility of control of laser induced cracks inside single crystals, the interference of stress waves were generated by simultaneous fs laser irradiation at multiple spots inside a LiF crystal, and the effects to the crack formation were investigated. We found that the crack lengths depended on the photoexcited spots' distribution. The dependence was explained by different transient density distributions by different interference of stress waves. The simulated density distribution indicated that a compressive stress at a crack tip could prevent the crack from propagating further and an expansive stress along a crack could facilitate the crack propagation. [ABSTRACT FROM AUTHOR]

Arrays of microlenses have been created on the surface of thin amorphous films of As2S3by localized photoexpansion induced by femtosecond laser pulses. The profile of a typical microlens has been mathematically described. Ray-tracing analysis has been performed to determine the focal points in the red and near-infrared spectrum of electromagnetic radiation. These lie at distances of 1.21 μm atλ = 650 nm and 1.33 μm atλ = 1.5 μm above the top of the microlens. It is suggested that the microlenses could be used in two-dimensional optoelectronic circuits or in fibre optics. [ABSTRACT FROM AUTHOR]

Time resolved spectral interferometry shows that both the trapping time of electrons excited in the conduction band is strongly dependent on the doping nature (e.g. Ge, P or F) event for very low concentrations on the order of 1 at%. This is agreement with the birefringence threshold (T2) that exhibits a significant dependence on the used dopants. In contrast, we observed that the permanent isotropic index change threshold (T1) is not significantly dependent on the doping. This indicates that the T1 threshold is not determined by a "critical" excited electron density neither a self-trapped exciton density. Another criterion more appropriate for T1 would be the absorbed energy per pulse and its subsequent transfer to the glass network. [ABSTRACT FROM AUTHOR]

Femtosecond laser-assisted etching is a promising technique as micro three-dimensional removal processing. This technique consists of two-steps: the first step is irradiation of focused femtosecond (fs) laser pulses along the pre-designed pattern, and next step is wet etching. Provided the modified region is etched faster than the unmodified host material, the modified region is selectively removed. However, when this technique was applied to volume etching of sapphire, there was a problem of incomplete removal (residues remain after etching). In the present report, we pro-pose and demonstrate a new strategy of two-cycle process, i.e., repeating {irradiation-etching} cycle two-times. The region that should be removed was divided into two. Outer layer was etched at the first cycle and inner volume was etched at the second cycle. In this way, the etching capability was improved as well as suppressing undesirable side effects of cracks and surface pits. [ABSTRACT FROM AUTHOR]

Bimetallic, initially spherical Ag/Au nanoparticles in glass prepared by ion implantation have been irradiated with intense femtosecond laser pulses at intensities still below the damage threshold of the material surface. This high-intensity laser processing produces dichroism in the irradiated region, which can be assigned to the observed anisotropic nanoparticle shapes with preferential orientation of the longer particle axis along the direction of laser polarization. In addition, the particle sizes have considerably been increased upon processing. [ABSTRACT FROM AUTHOR]

The article focuses on the demonstration of parallel femtosecond laser processing with a computer generated hologram displayed on a liquid crystal spatial light modulator (SLM). The SLM enables the performance of an arbitrary and variable patterning in laser processing. The hologram uses multiplexed phase Fresnel lenses that is optimized by changing the center phase and size of each lens.

Recent research and development on the femtosecond laser has shown that it is a powerful tool for high precision micromachining. However, the femtosecond laser-material interaction is fast and complex due to its ultrashort pulse duration. Consequently, it is not an easy task to optimize process parameters and to ensure high-quality fabrication. In this context, we propose an in-line monitoring technique based on plasma plume diagnostics. By analyzing the spectra of the femtosecond laser-induced plasma, which was detected and analyzed using a spectrometer, the plasma temperature of the copper sample was estimated. As drilling holes and cutting lines are two common applications in industry, the relationship between the emission light and the geometry of the fabricated structure was investigated based on the time-varying signals from the photodetector. These results will help us to understand the mechanism of femtosecond laser ablation so as to achieve high quality micromachining. [ABSTRACT FROM AUTHOR]