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Laser corneal reshaping is an eye surgery utilizes UV lasers to modify a targeted corneal surface to correct vision disorders such as myopia, hyperopia and astigmatism. The most commonly used laser type in such treatment is a pulsed gas laser namely argon fluoride (ArF) excimer laser (193 nm). A mixture of Argon, Fluorine and high percentage of Neon gas is utilized for producing the required laser. However, the availability of Neon gas is currently very limited due to the existent Russian-Ukraine war as this region is considered the main supplier of pure Neon gas. The present work provides a novel alternative system for the commercially available corneal reshaping eye surgery devices with a special opening for entering the operational laser beam from external sources. The proposed system is a flying spot platform coupled with a solid state laser, that is a forth harmonic of Nd: YAG laser. The aperture in the system's design enables it to take in the generated UV-laser beam (266 nm) from the external Nd: YAG laser source. The beam is then modified and directed at the treatment area. The device was tested for hyperopia laser profile algorithm on different targets. Furthermore, the hyperopia profile procedure was also applied to the ex-vivo rabbit eye to investigate the ablation effect on the corneal tissues. The obtained results showed an appropriate ablation effect for hyperopic correction via a complete corneal reshaping platform. Although, the device's current state may not be appropriate for immediate clinical use. It holds significant value as a training and educational platform. [ABSTRACT FROM AUTHOR]

To elucidate whether it is feasible to use porcine eyes from scalded, abattoir-acquired animals for refractive femtosecond laser research. An infrared laser (FS 200) and an ultraviolet laser (prototype version) were tested for their applicability on scalded pig eyes. Fifty porcine eyes were divided into two equally-sized groups and assigned to either the infrared or the ultraviolet laser. Both laser groups were comprised of five subgroups of n = 5 eyes each. Group A: non-scalded eyes (negative control); group B: eyes taken from tunnel-scalded animals; group C1: eyes taken from tank-scalded animals without opaque corneal lesion; group C2: eyes taken from animals with opaque corneal lesion; group D: eyes scalded in toto in the laboratory (positive control). In each group the lasers were employed to create a stromal flap. The quality of the laser cuts and the resulting flap beds, as well as of the porcine corneas themselves, was examined by anterior segment optical coherence tomography and scanning electron microscopy. All scalded specimens exhibited substantial corneal swelling, most pronounced in group C2. After ultraviolet laser application, the tank- and tunnel-scalded samples displayed marked irregularities and an increased degree of surface roughness in the flap beds. After infrared laser application, this was only the case in the tank-scalded specimens. It is not recommended to use eyes taken from scalded pigs for ultraviolet femtosecond laser experiments. For infrared femtosecond lasers, eyes taken from tunnel-scalded animals may represent an acceptable alternative, if non-scalded eyes are not available. [ABSTRACT FROM AUTHOR]

High (15–25) harmonic generation in the vacuum ultraviolet spectral range (83–50 nm) has been realized by focused (NA = 0.033) near-infrared femtosecond laser radiation (wavelength λ = 1.24 μm) with a vacuum intensity of ~7.5 × 1014 W/cm2 irradiating a dense gas jet. It has been shown experimentally that the use of such a high-numerical aperture focusing requires high (up to 10 bar) gas jet pressures to optimize phase matching. The use of the dense gas jet results in a noticeable manifestation of nonlinear propagation effects for generating radiation, which affect the generation process through the change in the phase matching conditions. Furthermore, it has been shown that the prechirping of the generating pulse makes it possible to compensate a chirp appearing due to self-phase modulation and to increase the harmonic generation efficiency because of the nonlinear compression of the generating pulse. This approach has allowed 17th (73 nm) harmonic generation with an energy of 2 pJ in a pulse and a generation efficiency of 5.4 × 10–9. The estimates obtained have shown that this radiation can be used for single-pulse maskless photolithography in the extreme ultraviolet range. [ABSTRACT FROM AUTHOR]

Nonlinear infrared (IR) crystals for radiation conversion are of paramount importance for realization of advanced laser spectrometers for medical diagnostics, environmental monitoring, and advanced sensing. However, performance of such crystals suffers from substantial surface reflectivity coming from rather high (over 2.5) refractive index of the key nonlinear materials used. Here, based on the example of promising BaGa4Se7 nonlinear crystal, we attested direct surface patterning with ultraviolet (257 nm) femtosecond laser pulses used to engrave anti-reflective microstructures (ARMs) directly on both output sides of the crystal. Imprinted surface nanotrenches arranged into a fish-net morphology with a periodicity down to 500 nm was found to increase transmittance of the crystals from 65% to 84% within a practically relevant shortwave IR spectral range. Formation of the ARMs with an optimized geometry is expected to weakly reduce the laser damage threshold of a pristine crystal material as it was also evidenced from supporting full-wave simulations and tests. [ABSTRACT FROM AUTHOR]

Rationale: Boron isotopes are a powerful tool for pH reconstruction in marine carbonates and as a tracer for fluid–mineral interaction in geochemistry. Microanalytical approaches based on laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) often suffer from effects induced by the sample matrix. In this study, we investigate matrix‐independent analyses of B isotopic ratios and apply this technique to cold‐water corals. Methods: We employ a customized 193 nm femtosecond laser ablation system (Solstice, Spectra‐Physics) coupled to a MC‐ICP‐MS system (Nu Plasma II, Nu Instruments) equipped with electron multipliers for in situ measurements of B isotopic ratios (11B/10B) at the micrometric scale. We analyzed various reference materials of silicate and carbonate matrices using non‐matrix matched calibration without employing any correction. This approach was then applied to investigate defined increments in coral samples from a Chilean fjord. Results: We obtained accurate B isotopic ratios with a reproducibility of ±0.9‰ (2 SD) for various reference materials including silicate glasses (GOR132‐G, StHs6/80‐G, ATHO‐G and NIST SRM 612), clay (IAEA‐B‐8) and carbonate (JCp‐1) using the silicate glass NIST SRM 610 as calibration standard, which shows that neither laser‐induced nor ICP‐related matrix effects are detectable. The application to cold‐water corals (Desmophyllum dianthus) reveals minor intra‐skeleton variations in δ11B with average values between 23.01‰ and 25.86‰. Conclusions: Our instrumental set‐up provides accurate and precise B isotopic ratios independently of the sample matrix at the micrometric scale. This approach opens a wide field of application in geochemistry, including pH reconstruction in biogenic carbonates and deciphering processes related to fluid–mineral interaction. [ABSTRACT FROM AUTHOR]

The deconvolution of low-resolution time-of-flight data has numerous advantages, including the ability to extract additional information from the experimental data. We augment the well-known Lucy-Richardson deconvolution algorithm using various Bayesian prior distributions and show that a prior of second-differences of the signal outperforms the standard Lucy-Richardson algorithm, accelerating the rate of convergence by more than a factor of four, while preserving the peak amplitude ratios of a similar fraction of the total peaks. A novel stopping criterion and boosting mechanism are implemented to ensure that these methods converge to a similar final entropy and local minima are avoided. Improvement by a factor of two in mass resolution allows more accurate quantification of the spectra. The general method is demonstrated in this paper through the deconvolution of fragmentation peaks of the 2,5-dihydroxybenzoic acid matrix and the benzyltriphenylphosphonium thermometer ion, following femtosecond ultraviolet laser desorption. [ABSTRACT FROM AUTHOR]

• Safe stained-glass laser cleaning protocols are designed using a fs UV laser. • Cleaned crust thickness control is improved using a multi scan series process. • Laser cleaning has been applied on 15th century samples from Cuenca cathedral (Spain). • Hydrated and anhydrous sulphates, and apatite have been identified as the principal components of the unwanted crust deposits. Laser irradiation enables the removal of unwanted surface deposits from different materials in a safe and controllable manner. Laser parameters should be carefully selected to achieve the removal of the target contaminants without inducing damage to the substrate. Ultra-short pulse lasers have opened new opportunities for safe and controlled decontamination of cultural heritage materials because the thickness of material that is affected by the laser is limited. In this study, an ultraviolet femtosecond pulsed laser was used for the removal of unwanted encrustation formed on the surface of an historical colourless stained-glass sample from the Cuenca Cathedral in Spain. One of the sides of this glass exhibits a reddish-brown grisaille that also has to be preserved. A laser cleaning process has been designed to avoid heat accumulation while controlling the thickness of ablated material. In this context, a multi-step process was selected in order to be able to eliminate, in a controlled way, the crust layer without damaging the grisaille layer, or the glass substrate. In this case, laser irradiation in beam scanning mode with a pulse repetition frequency of 10 kHz proved to be effective for the safe cleaning of the glass. The latter was analysed before and after laser cleaning by optical and confocal microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence, and Raman spectroscopy, confirming that the crust layer was effectively eliminated without damaging the surface. [Display omitted] [ABSTRACT FROM AUTHOR]

Ultra-short laser pulses (1030 nm/230 fs) were used to laser ablate the surface of crystalline sapphire (Al2O3) at high intensity per pulse 20–200 TW/cm 2 /pulse. Laser-ablated patterns were annealed at a high temperature of 1500  ° C. Surface reconstruction took place, removing the ablation debris field at the edges of ablated pits in oxygen flow (O2 flow). Partial reconstruction of ripples was also observed when multi-pulse ablated surfaces were annealed at high temperature in O2 flow. Back-side ablation of a 0.5-mm-thick Al2O3 produced high surface roughness ∼ 1 μ m which was reduced to ∼ 0.2 μ m by high-temperature annealing at 1500  ° C for 2 h in O2. Improvement of surface quality was due to restructuring of the crystalline surface and sublimation, while the defined 3D shape of a micro-lens was not altered after HTA (no thermal morphing). [ABSTRACT FROM AUTHOR]

Texturing can be used to functionalize the surface of plastic parts and, in particular, to modify the interaction with fluids. Wetting functionalization can be used for microfluidics, medical devices, scaffolds, and more. In this research, hierarchical textures were generated on steel mold inserts using femtosecond laser ablation to transfer on plastic parts surface via injection molding. Different textures were designed to study the effects of various hierarchical geometries on the wetting behavior. The textures are designed to create wetting functionalization while avoiding high aspect ratio features, which are complex to replicate and difficult to manufacture at scale. Nano-scale ripples were generated over the micro-scale texture by creating laser-induced periodic surface structures. The textured molds were then replicated by micro-injection molding using polypropylene and poly(methyl methacrylate). The static wetting behavior was investigated on steel inserts and molded parts and compared to the theoretical values obtained from the Cassie–Baxter and Wenzel models. The experimental results showed correlations between texture design, injection molding replication, and wetting properties. The wetting behavior on the polypropylene parts followed the Cassie–Baxter model, while for PMMA, a composite wetting state of Cassie–Baxter and Wenzel was observed. [ABSTRACT FROM AUTHOR]

A novel technology for the precise fabrication of quartz resonators for MEMS applications is introduced. This approach is based on the laser-induced chemical etching of quartz. The main processing steps include femtosecond UV laser treatment of a Cr-Au-coated Z-cut alpha quartz wafer, followed by wet etching. The laser-patterned Cr-Au coating serves as an etch mask and is used to form electrodes for piezoelectric actuation. This fabrication approach does not alter the quartz's crystalline structure or its piezo-electric properties. The formation of defects, which is common in laser micromachined quartz, is prevented by optimized process parameters and by controlling the temporal behavior of the laser-matter interactions. The process does not involve any lithography and allows for high geometric design flexibility. Several configurations of piezoelectrically actuated beam-type resonators were fabricated using relatively mild wet etching conditions, and their functionality was experimentally demonstrated. The devices are distinguished from prior efforts by the reduced surface roughness and improved wall profiles of the fabricated quartz structures. [ABSTRACT FROM AUTHOR]

The impact of wavelength and pulse duration in laser cleaning of hard blackish contaminants crust from archaeologically significant Pleistocene bone is investigated in this research. The objective is to determine the practical cleaning procedures and identify adequate laser parameters for cleaning archaeological bone from Sima de los Huesos (Spain) based on conservation and restoration perspectives. Bone surface cleaning was performed utilizing two Q-switched Nd:YAG lasers: sub-nanosecond pulsed lasers with emission wavelengths at 355 nm and 1064 nm, respectively, and a Yb:KGW femtosecond pulsed laser with an emission wavelength in the third harmonic at 343 nm. In all experiments, the laser beam scanning mode was applied to measure cleaning efficiency in removing contaminants and degradation products while assessing the underlying substrate surface damage. Several properties, including wavelength-dependent absorption, pulse repetition rate, and thermal properties of the material, are analyzed when evaluating the ability of these lasers to boost the cleaning efficiency of the deteriorated bone surface. Bone surface morphology and composition were studied and compared before and after laser irradiation, using Optical Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) characterization methods. The results indicate that 238-femtosecond UV laser irradiation with 2.37 TWcm−2 is significantly safer and more efficient toward surface contaminant desorption than sub-nanosecond laser irradiation. The results herein presented suggest that these types of fs lasers may be considered for realistic laser conservation of valuable historic and archaeological museum artifacts. [ABSTRACT FROM AUTHOR]

The femtosecond (fs) laser ablation of metals is a precise method used to create microfeatures on the surface of the material with a minimized heat-affected zone (HAZ). Despite its many advantages, fs laser ablation often requires extensive trial-and-error experimentation before finding the optimal laser strategy for a desired geometry with minimal HAZ. The pulse-based two-temperature model (TTM) can significantly shorten this process by predicting the ablated geometry based on a set of material and laser parameters. However, this model has only been validated for percussion drilling and single lines. In this study, the pulse-based TTM is tested against parallel line experiments and subsequently modified to include geometry-dependent material parameters. More specifically, the threshold fluence and reflectivity of the material are modified to incorporate the temperature increase inside the standing features between parallel lines. The introduced geometry-dependent factors are fitted with experimental data and their inclusion in the model is shown to have a positive impact on the simulation results. The results show a clear amelioration in the shape and depth of the simulated profiles, with the error on the average depth and width of the modified TTM being lower than the average standard deviation on the experiments. [ABSTRACT FROM AUTHOR]

Strain sensing technology using fibre Bragg grating (FBG) sensors is an attractive capability for aerospace structural health monitoring (SHM) and assessment because they offer resistance to harsh environments, low maintenance, and potential for high density and high strain sensing. The development of FBG inscription techniques through the fibre polymer coating using infrared (IR) lasers has overcome the mechanical weaknesses introduced by removal of the fibre coating, which is typically required for conventional UV laser inscription of FBGs. Type I and Type II femtosecond gratings are fabricated using through-coating inscription techniques, but the higher laser energy used for Type II gratings damages the glass fibre core, impacting mechanical performance. This paper investigates the fatigue performance of Type I and Type II through-coating FBG sensors with different fibre geometries and photosensitisation approaches to evaluate their overall reliability and durability, with a view to assess their performance for potential use in civil and defence SHM applications. The fatigue performance of FBG sensors was assessed under high-strain and high-frequency mechanical loading conditions by using a custom-designed electro-dynamically actuated loading assembly. In addition, pre- and post-fatigue microscopic analyses and high-resolution reflection spectrum characterisation were conducted to investigate the failure regions of the fibres and the effect of fatigue loading on reflection spectrum features. As expected, Type I gratings had a significantly higher fatigue life compared to Type II gratings. However, Type II gratings performed significantly better than conventional UV laser-inscribed FBGs and electrical foil strain gauges. Type II gratings withstand higher temperatures, and are therefore more suitable for application in harsh environments. [ABSTRACT FROM AUTHOR]

Nonresonant multiphoton ionization by femtosecond laser pulses can be applied to any molecule virtually, thereby greatly enhancing the scope of Stark decelerated molecules. For comparison, we detect decelerated and trapped ammonia molecules using two different schemes: (i) nonresonant multiphoton ionization using intense femtosecond (fs) pulses in the near infrared, and (ii) resonance-enhanced multiphoton ionization using nanosecond (ns) pulses from a tunable UV laser. The observed number of ions per shot for both schemes is similar. The fs laser detection scheme suffers from an increased background, which can be effectively eliminated by subsequent mass and velocity selection. To determine the detection volume of the ns laser detection scheme, we present measurements in which the decelerated ammonia molecules are bunched to a packet with a longitudinal spread well below ∼100 ÎĽm. It is concluded that the detection volume for the ns laser detection scheme is 1.5â€"2 times larger than that of the fs laser detection scheme. [ABSTRACT FROM AUTHOR]

Ultrafast laser processing has recently emerged as a new tool for processing fiber-reinforced polymer (FRP) composites. In the astronautic industry, the modified epoxy resin (named 4211) and the modified cyanate ester resin (known as BS-4) are two of the most widely used polymers for polymer-based composites. To study the removal mechanism and ablation process of different material components during the ultrafast laser processing of FRPs, we isolated the role of the two important polymers from their composites by studying their femtosecond UV laser (260 fs, 343 nm) ablation characteristics for controllable machining and understanding the related mechanisms. Intrinsic properties for the materials' transmission spectrum, the absorption coefficient and the optical bandgap (Eg), were measured, derived, and compared. Key parameters for controllable laser processing, including the ablation threshold (Fth), energy penetration depth (δeff), and absorbed energy density (Eabs) at the ablation threshold, as well as their respective "incubation" effect under multiple pulse excitations, were deduced analytically. The ablation thresholds for the two resins, derived from both the diameter-regression and depth-regression techniques, were compared between resins and between techniques. An optical bandgap of 3.1 eV and 2.8 eV for the 4211 and BS-4 resins, respectively, were obtained. A detectable but insignificant-to-ablation difference in intrinsic properties and ablation characteristics between the two resins was found. A systematic discrepancy, by a factor of 30~50%, between the two techniques for deriving ablation thresholds was shown and discussed. For the 4211 resin ablated by a single UV laser pulse, a Fth of 0.42 J/cm2, a δeff of 219 nm, and an Eabs of 18.4 kJ/cm3 was suggested, and they are 0.45 J/cm2, 183 nm, and 23.2 kJ/cm3, respectively, for the BS-4 resin. The study may shed light on the materials' UV laser processing, further the theoretical modeling of ultrafast laser ablation, and provide a reference for the femtosecond UV laser processing characteristics of FRPs for the future. [ABSTRACT FROM AUTHOR]

A close-packed micro-lens array (MLA) is widely used not only in novel optical systems but also in various engineering fields, such as semiconductors and display devices. In this paper, we present a simple and efficient method for fabricating MLAs on a glass substrate via laser ablation with a single femtosecond laser pulse and chemical wet etching in a hydrofluoric acid solution. The shapes of concave micro-lenses were optimized for laser pulse energy and etching time, and ∼70 000 micro-lenses with 15 µm diameter were formed. The shape of the micro-lens varies significantly with respect to the etching time in accordance with an initial ablated area (or laser energy), which is a key feature in fabricating micro-lenses of several tens of μm. Using the glass MLA as a mold, a polydimethylsiloxane convex-plano lens array was replicated, and the performance of the optical imaging and beam integrator was then examined. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fast and sensitive multi-elemental mapping of laser-deposited Hastelloy coating using UV-fs-LA-ICP-TOFMS. • Spatial distributions of major, minor and trace elements in the Hastelloy coating, interface and carbon steel substrate. • Detection of elements from external corrosive agents with heterogenous spatial distributions within the Hastelloy coating. • Quantification approach to determine the elemental concentrations in the Hastelloy coated carbon steel. Ultraviolet Femtosecond Laser Ablation-Inductively Coupled Plasma-Time of Flight Mass Spectrometry (UV-fs-LA-ICP-TOFMS) is critically evaluated for fast multi-elemental mapping of Hastelloy coated carbon steel that was immersed in a liquid corrosive environment for two months. The Hastelloy coating, which is a multi-elemental Cr-Fe-Ni-Mo-W matrix, is produced using laser cladding technology. A UV-fs laser is employed to reduce the ablation thermal effects improving the spatial resolution in the elemental analysis of the coating, interface and substrate. Moreover, the TOFMS is equipped with ion beam attenuation grids to expand its linear dynamic range, allowing the determination of major, minor and trace elements. In particular, spatial distribution of major (e.g., Co, Ni, Fe), minor (e.g., Mn, Si) and trace (e.g., Cu, In, Zn) elements from two sequential mapping analysis were determined. Quantification is achieved through Relative Sensitivity Factors calculated using matrix-matched external reference materials and making use of measurements carried out by SEM-EDX to determine the concentration of internal standard elements. Qualitative and quantitative elemental maps highlight diffusion processes at the coating-substrate interface. Moreover, correlated spatial distributions of ion signals from external corrosive elements (e.g., 32S, 138Ba, 202Hg, 205Tl, and 209Bi) were detected in localized regions within the material and on the external surface. [ABSTRACT FROM AUTHOR]

The Modulation Transfer Function (MTF) offers an objective measure to assess the imaging performance of streak cameras. This study aims to enhance the diagnostic precision of streak camera used in laser-driven inertial confinement fusion research. We introduce a novel method for evaluating the MTF of a recently developed large imaging area streak tube. This method integrates the electron optical MTF theory and the production of a reticle plate-type photocathode. Using ultraviolet and femtosecond lasers, we established two calibration platforms for the streak camera in both static and dynamic modes. We measured the radius of the electrons reaching fluorescent screen and obtained MTFs. Our findings reveal that the ultimate spatial resolutions at off-axis distances of 1.2, 4.7, 8.2, and 11.7mm are 28.5, 27.2, 26.4, 24.9 lp/mm (static) and 25.0, 22.8, 23.0, 21.2 lp/mm (dynamic). Notably, we successfully charted the ultimate spatial resolution distributions across the streak camera's full imaging area in both modes. • A novel method for calibrating the MTF of a large imaging area streak tube is reported. • The radius of the electrons reaching fluorescent screen and the static and dynamic MTFs are measured. • The ultimate spatial resolution distributions across the streak camera's full imaging area in both image modes are obtained. [ABSTRACT FROM AUTHOR]

This Letter reports a femtosecond ultraviolet laser absorption spectroscopy (fs-UV-LAS) for simultaneous in situ measurements of temperature and species. This fs-UV-LAS technique was demonstrated based on X2Π-A2Σ+ transitions of OH radicals near 308 nm generated in low temperature plasmas and flames. The fs-UV-LAS technique has revealed three major diagnostic benefits. First, a series of absorption features within a spectral bandwidth of ∼3.2 nm near 308 nm were simultaneously measured and then enabled simultaneous multi-parameter measurements with enhanced accuracy. The results show that the temperature and OH concentration could be measured with accuracy enhanced by 29–88% and 58–91%, respectively, compared to those obtained with past two-narrow-line absorption methods. Second, an ultrafast time resolution of ∼120 picoseconds was accomplished for the measurements. Third, due to the large OH X2Π-A2Σ+ transitions in the UV range, a simple single-pass absorption with a 3-cm path length was allowed for measurements in plasmas with low OH number density down to ∼2 × 1013 cm−3. Also due to the large OH UV transitions, single-shot fs absorption measurements were accomplished in flames, which was expected to offer more insights into chemically reactive flow dynamics. [ABSTRACT FROM AUTHOR]

The demand for precise and high-quality machining of wide-bandgap materials, such as glasses and crystals, is of considerable significance in science and industry. Among these materials, sapphire stands out as an appealing choice due to its exceptional mechanical and optical attributes, high thermal conductivity and stability, low electrical conductivity, and resilience against harsh chemicals. Despite its hardness, sapphire is brittle, making it prone to cracking during conventional machining attempts. Recently, alternative non-contact approaches, like laser ablation, have emerged as potential solutions to improve the machining quality. However research of laser processing of wide-bandgap materials, especially utilizing the high harmonics of femtosecond solid-state laser systems, remains incomplete. Our study focuses on investigating the nonthermal laser ablation of c-cut sapphire crystals using femtosecond (300 fs) deep UV (206 nm) laser pulses and comparing the results with traditional IR femtosecond ablation. The publication encompasses a comprehensive depiction of the ablation process and a review of the various achieved morphologies with accompanying scanning electron microscope images. Our findings indicate that efficient ablation with surface roughness below 100 nm can be achieved through a single-step process within specific laser processing parameter ranges. The ablation process of sapphire encompasses a strong incubation effect, hence the pulses need to be tightly overlapped. Additionally, we provide a detailed description of methodology used to extract surface roughness which was utilized in all the presented research and offers a practical framework for characterizing ablation results obtained from diverse laser systems. • Deep ultraviolet femtosecond pulses minimize thermal effects in sapphire ablation. • Ultraviolet wavelengths surpass infrared for achieving low surface roughness. • The ablation process exhibits a significant incubation effect. • Efficient ablation regime produces deep structures with low roughness. • Ablation originates from impurities and breakup mechanism is photomechanical. [ABSTRACT FROM AUTHOR]

• The electronic responses of single-crystal silicon irradiated by different wavelengths (800, 400 and 46.9 nm) are compared. • Tunneling ionization in silicon is difficult to happen under EUV irradiation due to the high laser frequency. • The impact ionization rate of 46.9 nm is greater than 800 and 400 nm. • The 46.9 nm laser may be a promising approach to removing atomic layers without destroying the surface lattice. The phenomenon of laser-induced electronic evolution in semiconductors is an essential issue in laser fabrication, which has been extensively investigated within the near-infrared and visible spectral ranges. However, electronic evolution at short wavelength laser has neither been systematically investigated. In this paper, time-dependent density functional theory is employed to investigate the response in silicon under laser irradiation of different wavelengths. The result shows that shorter wavelength induces the excitation of electrons to higher energy levels, consequently leading to increased impact ionization rates. Such a moderate excitation of energetic electrons even at low-medium intensity is considered as a distinctive feature of extreme ultraviolet light laser, which is expected to further enhance the quality of laser processing. [ABSTRACT FROM AUTHOR]

The use of cyclopropenone derivatives as latent photo-released strained cyclic alkynes is reported for the covalent printing of complex patterns on cellulose paper. Two different approaches using either a UV LED or a laser as light irradiation source are discussed. While the high intensity of the laser damages the grafted molecular layer, the use of a simple UV LED allows the printing in only 8 min at room temperature with a good resolution at the micrometer scale with negligible diffusion. The validity of this strategy is demonstrated through the sequential printing of a QR code and a logo on the same paper sheet. [ABSTRACT FROM AUTHOR]

Superconducting Nb thin films have been nanostructured by means of a femtosecond UV laser. Laser induced periodic surface structures (LIPSS) with lateral modulation of ≈ 250 nm and depth smaller than amplitude (≲ 20 nm from crest to trough) are obtained for optimized laser scanning conditions over the film surface, i.e. power, frequency, scanning speed and polarization. This provides a fast and scalable procedure of surface control at the nanoscale. In thin films, control over the kinetics of the LIPSS formation process has been crucial. Untreated and laser-patterned samples have been characterized by electron and atomic force microscopy as well as by local and global magnetometry. The superconducting properties reveal anisotropic behavior in accordance with the observed topography. The imprinted LIPSS define channels for anisotropic current flow and flux penetration. At low temperatures, magnetic flux avalanches are promoted by the increased critical current density, though flux tends to be channeled along the LIPSS. In general, directional flux penetration is observed, being a useful feature in fluxonic devices. Scalability allows us to pattern areas of the order of cm 2 /min. [Display omitted] • Surface periodic nanostructures are induced in Nb thin films by femtosecond laser pulses. • Achieving the fine-tuning of laser irradiation conditions is critical for patterning thin films. • Magneto optical imaging reveales the induced anisotropy of laser patterned samples. • The surface topography allows to control the vortex dynamics in superconducting films. [ABSTRACT FROM AUTHOR]

Nano/microfabrication experiments on the surface of silicon solar cell are performed by ultraviolet femtosecond laser in the fluence range from 0.10 to 0.70 J/cm2. The surface morphology change of sample was observed by a laser scanning microscopy and a scanning electron microscope. The crystallinity of surface irradiated by laser pulses was evaluated by Raman spectroscopy. The ablation threshold for silicon was estimated to be 0.10 J/cm2. We successfully produced nano‐structures on the surface of silicon solar cell maintaining single‐crystalline with the irradiation at the laser fluence of 0.10 J/cm2. [ABSTRACT FROM AUTHOR]

Real-time monitoring of temperatures over extensive free-form surfaces of precision machines, smart products, and human bodies with a high resolution can provide invaluable information for smart manufacturing, Internet-of-Things, and advanced healthcare. However, traditional rigid thermistors could not be conformally attached on arbitrarily curved surfaces. In this study, a high-resolution flexible graphene thermistor is demonstrated by transforming wood into laser-induced-graphene via ultrafast laser pulses and subsequent transfer to flexible substrates. This thermistor provides a 16-times higher resolution than the state-of-the-art counterparts which was applied to precise temperature monitoring of an electric motor, glass cup, and human hand. [ABSTRACT FROM AUTHOR]

Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH2=CHBr, are probed using femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy. Strong-field ionization is initiated with an intense femtosecond, near infrared (NIR, 775 nm) laser field. Femtosecond XUV pulses covering the photon energy range of 50-72 eV probe the subsequent dynamics by measuring the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. Spectral signatures are observed for the depletion of neutral C2H3Br, the formation of C2H3Br+ ions in their ground (X ) and first excited (à ) states, the production of C2H3Br++ ions, and the appearance of neutral Br (2P3/2) atoms by dissociative ionization. The formation of free Br (2P3/2) atoms occurs on a timescale of 330 ±150 fs. The ionic à state exhibits a time-dependent XUV absorption energy shift of ∼0.4 eV within the time window of the atomic Br formation. The yield of Br atoms correlates with the yield of parent ions in the à state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C2H3Br+ (à ) ions undergoes intramolecular vibrational energy redistribution followed by the C-Br bond dissociation. The C2H3Br+ (X) products and the majority of the C2H3Br++ ions are relatively stable due to a deeper potential well and a high dissociation barrier, respectively. The results offer powerful new insights about orbital-specific electronic processes in high field ionization, coupled vibrational relaxation and dissociation dynamics, and the correlation of valence hole-state location and dissociation in polyatomic molecules, all probed simultaneously by ultrafast table-top XUV spectroscopy. [ABSTRACT FROM AUTHOR]

Femtosecond lasers emit short pulses whose temporal width is in the range of less than a picosecond to a few femtoseconds (fs), thereby enabling extremely high peak-power machining with minimum thermal damages. Herein, we employed femtosecond laser pulses as a versatile tool for surface processing of 2 polymers commonly used in textile industry, Polyethylene terephthalate (PET), and Polyamide66 (PA66). This work focuses on a comparison of ultraviolet (UV, 257 nm) and infrared (IR, 800 nm) femtosecond laser irradiation at the surface of the polymers PET and PA66. The polymers are modified topographically and chemically, by direct laser irradiation, through different ablation routines, with direct bond breaking for UV fs laser irradiation, and multiphoton absorption for IR fs laser irradiations. The interaction strongly depends on the laser beam operation conditions, such as laser fluence, number of pulses, wavelength etc, as illustrated by post mortem analysis based on optic microscopy, Scanning Electron Microscopy and Raman spectroscopy. This work defines the change in the characteristics of the polymers as a function of the laser wavelengths. UV fs laser processing appears to be more advantageous, offering a large process window and a high precision in ablation. [ABSTRACT FROM AUTHOR]

The ablation plume dynamics arising from ablation of silver with a 500 fs, 248 nm laser at ∼2 J cm-2 has been studied using angle-resolved Langmuir ion probe and thin film deposition techniques. For the same laser fluence, the time-of-flight ion signals from femtosecond and nanosecond laser ablation are similar; both show a singly peaked time-of-flight distribution. The angular distribution of ion emission and the deposition are well described by the adiabatic and isentropic model of plume expansion, though distributions for femtosecond ablation are significantly narrower. In this laser fluence regime, the energy efficiency of mass ablation is higher for femtosecond pulses than for nanosecond pulses, but the ion production efficiency is lower. [ABSTRACT FROM AUTHOR]

This paper focusses on understanding laser-NBR rubber interactions in particular the effect of laser wavelength and pulse width on material removal and thermal damage. Three lasers with wavelengths at 355 nm, 795 nm and 1064 nm and pulse duration at 30 ns, 10 ps and 130 fs, respectively, have been investigated for their optical absorption, heat conduction and their material removal mechanisms in high aspect ratio drilling of NBR rubber. It is interesting to find that under certain conditions, the ultrashort pulse lasers (both the femtosecond and picosecond lasers) did not lead to better results than the nanosecond UV laser in drilling hole profile (straightness and thermal damage), aspect ratio and amount of the ablated material re-deposition on the substrate surfaces. The results implied that there is heat conduction and thermal damage even with ultrashort laser pulses when the processing conditions are not appropriate. Firing laser pulses intermittently was shown to reduce thermal accumulation. Experimental studies showed that the 355-nm Nd:YAG laser (UV laser) achieved higher material removal rate with high aspect ratio as compared to the ultrashort laser pulses in drilling the NBR substrates. [ABSTRACT FROM AUTHOR]

Thirteen organochlorine pesticides in a standard sample mixture were measured by gas chromatography combined with mass spectrometry using an ultraviolet femtosecond laser (267 nm) as the ionization source, and the observed mass spectra were compared with the corresponding spectra obtained using an electron ionization source. When an ultrashort optical pulse was used for ionization, molecular ions were typically produced which was preferential for reliably identifying the analytes. The ionization mechanism was studied based on three models constructed for resonance-enhanced two-photon ionization, non-resonant two-photon ionization, and non-resonant three-photon ionization. The optimal conditions for observing a molecular ion were investigated using data obtained for three pulse widths. The results suggest that two-photon ionization with minimum excess energy would be optimal for observing a molecular ion. [ABSTRACT FROM AUTHOR]

Soot, which is produced through the rapid growth of hydrocarbon molecules in fuel-rich flames, has been proved to be responsible for global warming and harmful to the respiratory system of human. However, the complex formation process of soot in flames has not been understood yet because of the lack of efficient time-resolved methods for monitoring soot and its precursor species. We present here a viable pump–probe approach to measure ultrafast processes of the soot particles in flames with femtosecond time resolution. The scattering of femtosecond ultraviolet (UV) light pulses is used to monitor soot particles along alkanol–air diffusion flames from the inception phase up to the burnout region after the formation of a femtosecond laser filament in the flames. The time evolution of the scattered UV signal reveals unexpected ultrafast swelling and shrinking of soot particles induced by the femtosecond laser filament in the different flame regions. Our in situ and time-domain measurements of soot particles with the femtosecond time resolution unveil their unique properties in the flames. [ABSTRACT FROM AUTHOR]

Laser lift‐off (LLO) is commonly applied to separate functional thin films from the underlying substrate, in particular light‐emitting diodes (LEDs) on a gallium nitride (GaN) basis from sapphire. By transferring the LED layer stack to foreign carriers with tailored characteristics, for example, highly reflective surfaces, the performance of optoelectronic devices can be drastically improved. Conventionally, LLO is conducted with UV laser pulses in the nanosecond regime. When directed to the sapphire side of the wafer, absorption of the pulses in the first GaN layers at the sapphire/GaN interface leads to detachment. In this work, a novel approach towards LLO based on femtosecond pulses at 520 nm wavelength is demonstrated for the first time. Despite relying on two‐photon absorption with sub‐bandgap excitation, the ultrashort pulse widths may reduce structural damage in comparison to conventional LLO. Based on a detailed study of the laser impact as a function of process parameters, a two‐step process scheme is developed to create freestanding InGaN/GaN LED chips with up to 1.2 mm edge length and ≈5 μm thickness. The detached chips are assessed by scanning electron microscopy and cathodoluminescence, revealing similar emission properties before and after LLO. [ABSTRACT FROM AUTHOR]

The effects of water vapor ionization on the nonlinear propagation of femtosecond laser pulses with a 248 nm wavelength are numerically investigated in this paper. It is found that ionization of H2O molecules plays a significant role in air ionization, which seriously affects the dynamic and energy deposition of filamentation. The propagation of femtosecond pulses in air with different humidity levels are compared. The total number of electrons and total deposited pulse energy increase with the humidity increases. However, they tend to be saturated in high humidity conditions. Results presented here are conducive to characterizing the long-range propagation of filaments under atmospheric conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Femtosecond pulse laser cleaning of Makrana marble. • Comparison of laser wavelength from infrared, green and ultraviolet irradiations. • Laser cleaning with ultraviolet irradiation presents high risk of melting the stone. • Infrared and green wavelengths are safer for laser cleaning. • Successful cleaning of contaminants and dirt using femtosecond pulse laser. We studied femtosecond pulse lasers for cleaning Makrana marble, used in the construction of Soami Bagh Samadh, Agra, India. We investigated laser irradiation at different wavelengths (1029 nm, 515 nm, and 343 nm) and found that ultraviolet radiation had the lowest ablation threshold at 0.23 J cm−2, followed by green at 0.34 J·cm−2, and infrared at 1.3 J·cm−2. Green irradiation was the most efficient, ablating marble at 0.9 mm3·(min W)–1 at 4 J·cm−2 compared to 0.73 mm3·(min W)–1 at 12 J·cm−2 for 343 and 1029 nm. We evaluated the wavelength's effect on the stone. Infrared irradiation, having a higher ablation threshold, allowed for a broader range of laser fluence for the safe removal of contaminants, without risking inducing any chemical or morphological changes to the stone, and thus was selected for cleaning. We explored the cleaning effectiveness of infrared femtosecond laser pulses on a sculpted Makrana marble covered by environmental soiling. Optical and scanning electron microscopy, optical profilometry, Raman spectroscopy, and colorimetry demonstrated that satisfactory cleaning was achieved, with the removal of the unwanted layers without causing damage or chemical alteration to the marble structure. This study demonstrates the potential of femtosecond lasers for safe and effective heritage marble cleaning. [ABSTRACT FROM AUTHOR]

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are suspected to be highly carcinogenic and mutagenic compounds that are present in the environment. Gas chromatography combined with mass spectrometry (GC-MS) is the most frequently used technique for trace analysis. The electron ionization techniques that are currently used in MS, however, typically do not result in the formation of a molecular ion, thus making the determination of these compounds more difficult. In this study, we report on the use of a compact highly-repetitive (low-pulse-energy) ultraviolet (UV) femtosecond laser as the ionization source in combination with a miniature time-of-flight mass analyzer and a time-correlated ion counting system. The UV laser pulses emitted at 343, 257, and 206 nm were produced by harmonic generations of a femtosecond Yb laser emitting at 1030 nm and were utilized for single-color multiphoton ionization. A combination of the 343-nm and 257-nm pulses was further employed to achieve two-color two-photon ionization. This technique was found to be more useful for sensitive detection and also resulted in the formation of a molecular ion. A pump-and-probe technique using these pulses was examined in a proof-of-concept study to measure the femtosecond lifetimes of the nitro-PAHs separated by GC, providing additional information for use in the characterization of the analyte. The developed technique was applied in the analysis of an authentic sample, an organic solvent extract from diesel exhaust particulates. The nitro-PAHs contained in a standard reference material (SRM1975) were determined on a two-dimensional GC-MS display, suggesting that this technique would be useful for the practical trace analysis of nitro-PAHs in environmental samples. [Display omitted] • Nitro-PAHs were measured by gas chromatography combined with mass spectrometry. • A two-color femtosecond laser was utilized for ionization in mass spectrometry. • A two-dimensional display of GC-MS was employed for comprehensive analysis. • An excited-state lifetime was measured for the characterization of nitro-PAHs. • A standard reference material was measured for the determination of nitro-PAHs. [ABSTRACT FROM AUTHOR]

The PICOSEC detection concept consists in a "two-stage" Micromegas detector coupled to a Cherenkov radiator and equipped with a photocathode. A proof of concept has already been tested: a single-photoelectron response of 76 ps has been measured with a femtosecond UV laser at CEA/IRAMIS, while a time resolution of 24 ps with a mean yield of 10.4 photoelectrons has been measured for 150 GeV muons at the CERN SPS H4 secondary line. This work will present the main results of this prototype and the performance of the different detector configurations tested in 2016–2018 beam campaigns: readouts (bulk, resistive, multipad) and photocathodes (metallic+CsI, pure metallic, diamond). Finally, the prospects for building a demonstrator based on PICOSEC detection concept for future experiments will be discussed. In particular, the scaling strategies for a large area coverage with a multichannel readout plane, the R&D on solid converters for building a robust photocathode and the different resistive configurations for a robust readout. [ABSTRACT FROM AUTHOR]

Different from cascaded second-order nonlinear frequency conversion which is a common way to obtain ultraviolet (UV) laser only through noncentrosymmetric crystal, the optical properties of the phase-matched direct third-harmonic generation (THG) in the centrosymmetric calcite crystal was studied. A femtosecond laser was taken as the pumping source in the type-I (ooo→e) and type-II (ooe→e) phase-matched experiment, and a nanosecond laser was also used for comparison. Polarization angle ρ, phase-matching angle θ and azimuth angle φ in direct THG were determined and verified. Strong third-harmonic at 266 nm was observed in calcite crystal pumped by femtosecond laser. Compared with type-I phase-matched, Type-II was more efficient for energy conversion. The shortest harmonic wavelength obtained was about 213 nm, which was close to deep-UV region. The maximal output energy was 19.3 μJ (average power, ～19.3 mW) and the maximal conversion efficiency was 1.25% at 266 nm, which was the highest conversion efficiency at present. These results may indicate a wider application field for centrosymmetric crystals and another method to produce laser in UV and even deep-UV region. [ABSTRACT FROM AUTHOR]

[Display omitted] • Large-area and high-quality microdisk arrays were processed by femtosecond laser direct writing. • The coupling of material excitons and the optical mode density in cavities using transient optical spectroscopy. • The optical properties of rhodamine 6G molecules can be manipulated within microcavity. Femtosecond laser technology is developing into a powerful and flexible tool for manufacturing polymeric photonic devices. Micro-nano precision is obtained by ultrafast laser ablation and minimal thermal damage to materials. Coupling optical microcavities of luminescent molecular materials have been a trending approach to advanced optical applications by harnessing light-matter interaction. Molecular materials with facile processibility are natural candidates with integrability, whilst nanocavity fabrication on these materials, partially for reproducible large-scale fabrication, is challenging. In this study, we use a femtosecond laser processing technique to ablate PMMA films doped with dye molecules to give high-quality Whispering-Gallery-Mode microcavity arrays with uniform morphology, vertical cavity wall, and no residue. Experimental and simulation studies suggest that the luminescence and electronic dipole properties of the material can be manipulated within microcavity diameters that determine the resonance wavelengths. The effectiveness of laser processing techniques is demonstrated in regulating the luminescence properties of optical materials for applications in nanophononics and optoelectronics. [ABSTRACT FROM AUTHOR]

• A CO 2 laser-induced LPFG in the DTP has been proposed, which provides a low-cost and simple way to replace femtosecond and UV lasers, and breaks the limitation that CO 2 laser could not fabricate LPFG with shorter period. • The LPFG induced in thin SMF can be applied to subsequent work and practice due to its good sensing characteristics and greater attenuation loss peaks of 20 dB. • Considering the mechanical strength, the average RI sensitivity of 2117.12 nm/RIU could be achieved in the RI range of 1.33222 to 1.39018 by combining reducing cladding diameter and making LPFG work near DTP. A CO 2 laser-induced long-period fiber grating (LPFG) in the dispersion turning point (DTP) has been proposed in this work, which has demonstrated the possibility of fabricating LPFG with a shorter period of 115 μm in a thin single-mode fiber (SMF) without etching cladding. The LPFG working near DTP was also induced in a conventional SMF by CO 2 laser after etching cladding, whose grating period was 196 μm. Then, the refractive index (RI) sensitivity of LPFG based on thin SMF was optimized by fully combining DTP and cladding reduction. Considering the sensor probe's mechanical strength comprehensively, the thin SMF cladding was etched to 51.03 μm to ensure cladding mode LP 1,6 work near DTP, which can result in an average RI sensitivity of 2117.12 nm/RIU in the RI range of 1.33222 to 1.39018. Based on its excellent RI sensing performance, the proposed LPFG is a prospective sensor that can be applied to significant fields such as environmental, chemical, or biological parameters measurement. At the same time, this study provides a low-cost path to fabricate LPFG worked in DTP for most researchers. [ABSTRACT FROM AUTHOR]

• Improving the LIDT of SiO 2 thin films with fs laser irradiation. • Enhancing hardness and young's modulus with fs laser. • Leaving the composition of SiO 2 films unchanged after fs laser irradiation. • Decreasing hydroxyl group (OH) density with fs laser. Femtosecond laser (@1030nm, 280fs) was applied to irradiate SiO 2 thin films in the hope of improving damage resistance of films to nanosecond ultraviolet (UV) laser light (@355nm, 4ns). The optical and mechanical properties of laser strengthened SiO 2 thin films were characterized and laser-induced damage threshold (LIDT) results show that femtosecond laser irradiation can significantly improve LIDT of the films to nanosecond UV laser light from 5.45 J /cm2 to 28.96 J /cm2 by a factor of 5. Fluorescence and Fourier Transform Infrared (FTIR) spectra indicate that the LIDT improvement is attributed to the decrease in hydroxyl group's(OH) density in SiO 2 thin films resulting from femtosecond laser irradiation. [ABSTRACT FROM AUTHOR]

We investigate the second harmonic generation (SHG) and third harmonic generation (THG) processes of femtosecond (fs) laser that occurred in type Ⅰ phase-matched K 3 B 6 O 10 X (X = Cl, Br; KBOC and KBOB) crystals. The high average power of 515 nm green and 343 nm ultraviolet (UV) fs lasers output were efficiently generated from these two crystals with an incident fundamental 773 fs 1030-nm laser source. Experimental results show that the highly effective nonlinear coefficient of the KBOC crystal causes higher harmonic conversion efficiency than that of KBOB crystal in the same fundamental laser parameters. The average power of 10.4 W 515 nm green and 4.6 W 343 nm UV lasers output were obtained from two pieces of 4.5 mm KBOC crystals, corresponding to 42.3 % and 19.7 % high optical conversion efficiency respectively, without temporal pulse walk-off time compensation between 1030 nm and 515 nm laser pulses. Our research will stimulate in-depth research on nonlinear frequency conversion in nonlinear optical systems and have potential applications in future applications. [ABSTRACT FROM AUTHOR]

• Fast and sensitive multi-elemental mapping of thin tissue sections of a liver metastasis, from colorectal cancer patient, after oxaliplatin-based chemotherapy, using UV-fs-LA-ICP-TOFMS. • Useful analytical tool for examining highly heterogeneous cancer tissues, allowing for more effective elemental mapping over multiple locations, including cancer cells and tumor microenvironment cells. • Importance of UV-fs laser operating parameters to achieve proper ablation conditions of thin tissue sections. • Spatial distributions of elements at cellular level, superimposing UV-fs-LA-ICP-TOFMS elemental mappings on original histological images of the tumoral tissue, taken before the laser ablation process. The characterization of the multi-elemental distributions within a thin tissue section of a liver metastasis from colorectal cancer patient after oxaliplatin-based chemotherapy, is critically evaluated using Ultraviolet Femtosecond Laser Ablation Inductively Coupled Plasma-Time of Flight Mass Spectrometry (UV-fs-LA-ICP-TOFMS). Different femtosecond laser ablation conditions, in terms of spot size and energy per pulse, were investigated to achieve proper ablation of the formalin-fixed paraffin-embedded tumor sections, while also trying to minimize the ablation of the glass substrate. Moreover, histological images of the tissues before and after the ablation processes were combined with UV-fs-LA-ICP-TOFMS elemental mapping to achieve multi-elemental spatial distributions at cellular level. For instance, spatial distributions of endogenous 31P, 56Fe, 63Cu and 64Zn analytes were determined within the thin tissue section. Furthermore, spatial distribution of elements such as 24Mg, 28Si, and 40Ca were employed to study glass substrate ablation during tissue analysis. Additional analytes, which might be partially associated to compounds employed on hematoxylin and eosin tissue staining processes, such as 23Na, 27Al, 32S, 39K, 79Br and 127I, were also detected. Finally, the accumulation of the oxaliplatin-based chemotherapy products in the stroma was confirmed from the spatial distribution of 196Pt ion signals within the tissue. [ABSTRACT FROM AUTHOR]

We present a new photonic magnetic sensor that can yield information on the spatial angle of rotation of the sensor within a given static magnetic field that based upon an optical fiber platform that has a wavelength-encoded output and a demonstrated sensitivity of 543 pm/mT. This optical fiber magnetic field sensor combines a conventional, UV-laser inscribed long period grating (LPG) with a magnetostrictive material Terfenol-D that coats and fills 50-μm micro-slots running adjacent and parallel to the fiber central axis. The micro-slots are produced using a femtosecond laser and selective chemical etching. A detection limit for a static magnetic field strength of ±50 μT is realized in low strength DC magnetic field (below 0.4 mT), this performance approaches the Earth’s magnetic field strength and thus, once optimized, has potential for navigation applications. Our method addresses the major drawback of conventional sensors, namely their inadequate sensitivity to low strength, static magnetic fields and their inability to provide information about the orientation and magnitude. [ABSTRACT FROM AUTHOR]

Purpose To characterize corneal wound healing in a rabbit model after flapless refractive lenticule extraction with a 345 nm ultraviolet femtosecond laser. Setting Departments of Ophthalmology and Anatomy II, University of Erlangen-Nürnberg and Wavelight GmbH, Erlangen, Germany. Design Experimental study. Methods Flapless refractive lenticule extraction was performed in 1 eye each of 20 New Zealand white rabbits (−5.0 diopters). Groups of 4 animals were euthanized after 48 hours, 1 week, 2 weeks, 4 weeks, and 3 months, respectively. Corneal samples were prepared for histology and fluorescence microscopy. To assess corneal cell death, proliferation, and myofibroblastic transdifferentiation, terminal uridine deoxynucleotidyl nick end-labeling (TUNEL) assay as well as immunostaining for Ki67 and α-smooth muscle actin (αSMA) were performed on sagittal cryosections. Results Histology revealed a zone of keratocyte depletion with a thickness of approximately 50 μm around the extraction site. At 48 hours, pronounced TUNEL staining of keratocytes was detected around the interface (159.9 cells/mm ± 18.4 [SD]), which steadily decreased to 74.9 ± 19.8 cells/mm at 1 week and 5.7 ± 4.8 cells/mm at 2 weeks. Ki67 staining of keratocytes was evident at 48 hours (10.0 ± 3.8 cells/mm), which then decreased at 1 week (5.2 ± 1.7 cells/mm) and 2 weeks (0.4 ± 0.5 cells/mm). From 4 weeks onward, no TUNEL or Ki67 staining was detected. The corneal stroma was αSMA-negative at all timepoints. Conclusion Application of the 345 nm laser showed no signs of problematic repair processes in the cornea, which supports the initiation of the clinical phase. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) femtosecond lasers with a high repetition rate have important applications, especially in processing brittle materials. However, the group velocity walk-off limits the tripling efficiency of the 1 μ m femtosecond pulse. Without effective compensation, the tripling efficiency was generally less than 1%. In this study, by optimizing a birefringent BBO crystal to compensate the temporal walk-off in the 1. 03 μ m tripling process, a maximum output power of 1.9 W with a repetition rate of 145 kHz at 344 nm was obtained, which implied a conversion efficiency of 30.5% from infrared (IR) to UV. The generated UV laser showed good power stability of 0.19% rms over 1 h and beam quality of M 2 < 1.2. Using this scheme for other IR femtosecond lasers is promising for achieving high tripling efficiency. [ABSTRACT FROM AUTHOR]

• The second harmonic reflected the femtosecond laser ablation penetration. • 'Cold laser', femtosecond laser, caused overheating on bone. Temperature control is the key factor for its application on laminectomy. • Larger power, 20 W, created high energy input, however, 15 W was proved to be more eligible for both penetration and overheating prevention. • Deep learning helped to lock the laser spot region, and defocus was benefit for penetration control (4 mm). Orthopedic diseases are increasingly becoming a prominent problem threatening human health. Traditional mechanical osteotomy causes mechanical and thermal damages, which are believed to increase the safety risk of orthopedic surgery. Femtosecond lasers provide a safe and efficient method for laminectomy. In this study, the experiments were conducted on femtosecond laser ablation operations aided by convolutional neural network and collaborative control. The various spectra during femtosecond laser bone ablation were detected by using isolated porcine ribs. An optical fiber spectrometer was used to monitor the spectrum, which was proved to reflect the laser ablation process. The spectral composition during femtosecond laser bone ablation was analyzed. The second harmonic was related to the penetration. The temperature distribution indicated that 15 W with cooling was the best parameter for preventing carbonization. Defocusing the laser improved safety because the ablated effect was very limited when the defocus distance was 4 mm. Although large energy input resulted in better efficiency, it also caused carbonization due to overheating. [ABSTRACT FROM AUTHOR]

Polymethylpentene (PMP) polymers can be used to make advanced optics, especially for midinfrared (MIR) ultrafast optics. In this study, an optical parametric converter pumped by a Ti sapphire femtosecond laser was used to investigate the polymer. The thermal effect generated by loosely focused femtosecond near mid-infrared (MIR) pulses in bulky materials is observed in real-time, and the polymer exhibits thermal stability and conformability. To avoid strong linear absorption and to increase the nonlinear damage threshold, the spectral region for ultrafast applications is 1310 nm (0.95 eV)–1350 nm (0.92 eV). For the process in region VI, there is a sign of stronger coupling for short-wavelength photons, and the pulse duration is recommended to be lower than 160 fs. In the ultraviolet (UV) region, filamentary writing using a low-focused beam, the laser peak power was selected in the range of 2.2 MW–9.2 MW. High-density bulky gratings were written. The refractive-index modulation was significant, and the polymer exhibited highly nonlinear features. This study provides insights into the applications and production of PMP polymers in laser optics and laser engineering. • In situ thermal observation on filamentation built by near MIR femtosecond pulses in polymer. • Using super-continuum spectra to characterise filamentary process of PMP. • Writing bulky gratings with tightly focused beam. [ABSTRACT FROM AUTHOR]