Short and long term surface chemistry and wetting behaviour of stainless steel with 1D and 2D periodic structures induced by bursts of femtosecond laser pulses

We investigate the short and long term wettability of laser textured stainless steel samples in order to better understand the interplay between surface topography and chemistry. Very different 1D and 2D periodic as well as non-periodic surface patterns were produced by exploiting the extreme flexibility of a setup consisting of five rotating birefringent crystals, which allows generating bursts of up to 32 femtosecond laser pulses with fixed intra-burst delay of 1.5 ps. The change of the surface morphology as a function of the pulse splitting, the burst polarization state and the fluence was systematically studied. The surface topography was characterized by SEM and AFM microscopy. The laser textured samples exhibited, initially, superhydrophilic behaviour which, during exposure to ambient air, turned into superhydrophobic with an exponential growth of the static contact angle. The dynamic contact angle measurements revealed a water adhesive character which was explained by XPS analyses of the surfaces that showed an increase of hydrocarbons and more oxidized metal species with the aging. The characteristic water adhesiveness and superhydrophobicity of laser textured surfaces can be exploited for no loss droplet reversible transportation or harvesting

Double- and multi-femtosecond pulses produced by birefringent crystals for the generation of 2D laser-induced structures on a stainless steel surface

Laser-induced textures have been proven to be excellent solutions for modifying wetting, friction, biocompatibility, and optical properties of solids. The possibility to generate 2D-submicron morphologies by laser processing has been demonstrated recently. Employing double-pulse irradiation, it is possible to control the induced structures and to fabricate novel and more complex 2D-textures. Nevertheless, double-pulse irradiation often implies the use of sophisticated setups for modifying the pulse polarization and temporal profile. Here, we show the generation of homogeneous 2D-LIPSS (laser-induced periodic surface structures) over large areas utilizing a simple array of birefringent crystals. Linearly and circularly polarized pulses were applied, and the optimum process window was defined for both. The results are compared to previous studies, which include a delay line, and the reproducibility between the two techniques is validated. As a result of a systematic study of the process parameters, the obtained morphology was found to depend both on the interplay between fluence and inter-pulse delay, as well as on the number of incident pulses. The obtained structures were characterized via SEM (scanning electron microscopy) and atomic force microscopy. We believe that our results represent a novel approach to surface structuring, primed for introduction in an industrial environment

Laser-induced breakdown spectroscopy in cultural heritage science

The potential of Laser-Induced Breakdown Spectroscopy (LIBS) for micro-destructive analysis of cultural heritage objects has been widely demonstrated, and the technique is now ready to be integrated in the permanent instrumentation of conservation laboratories. This chapter presents a review of recent results obtained by LIBS researchers with a focus on three main applications that exemplify the most representative contributions of this technique to cultural heritage science: noninvasive stratigraphic analysis of multilayered samples; feasibility and field studies with portable instrumentation; and underwater LIBS of submerged samples. An overview on the principles of LIBS and employed instrumentation is also provided, together with a discussion on its advantages and drawbacks as compared to well-established techniques for the analysis of cultural heritage

Calibration-free inverse method for depth-profile analysis with laser-induced breakdown spectroscopy

The Calibration-free inverse method (CF-IM) is a variant of the classical CF approach that can be used for the determination of the plasma temperature using a single calibration standard. In this work, the IM was suitably modified in order to test its applicability to the depth-resolved elemental analyses of stratified samples. The single calibration standard was used as a sort of reference sample to model the acquisition conditions of the spectra, to investigate the effect of the acquisition geometry, and to account for possible crater-induced changes in the acquired spectra and plasma parameters. Thus, a depth profile of the standard sample was performed in order to obtain a plasma temperature profile, which in turn was employed, together with the experimental electron density profile, for the depth profile calibration-free analysis. The methodology was also applied to archaeological samples, with the purpose of testing the method with weathered and layered samples, and compared with the results of classical LIBS with calibration lines

Minimally invasive medical diagnosis through Laser-Induced Breakdown Spectroscopy (LIBS) coupled with machine learning

Untargeted spectroscopic methods allow interrogating biomedical samples without prior hypotheses about specific pathways, and therefore they are a powerful diagnostic tool for poorly understood or initially asymptomatic diseases. In this work, we analyzed micro- drops of biological fluids from patients and animal models with Laser-Induced Breakdown Spectroscopy (LIBS) and coupled the spectra with supervised classification algorithms to distinguish healthy and diseased individuals. LIBS is the optical emission spectroscopy of laser-induced plasmas, and it can provide the elemental fingerprinting of a wide variety of samples [1]. In [2], we designed a voting algorithm based on the use of LIBS difference spectra, that we employed as a data-pretreatment and feature-selection method to couple with Quadratic Discriminant Analysis for Alzheimer's Disease diagnosis in living patients

Micro-invasive depth profile analysis by laser-induced breakdown spectroscopy (LIBS): The case of mercury layers on Sasanian coins

Laser-Induced Breakdown Spectroscopy (LIBS) was used for depth-profile analysis of one Sasanian coin of the emperor Khusro II (591-628) from the Coin Collection of the Kunsthistorisches Museum of Vienna. The peculiarity of this coin, also found in analogous samples of the same and other collections, was the presence of an external Hg layer. The thickness and homogeneity of the Hg layer were characterized with the calibration-free inverse method, a variant of the classical calibration-free LIBS approaches in which one sample of known concentration is used to determine the plasma temperature. We demonstrated the feasibility of the inverse method also in cases of unknown samples with matrices different from that of the employed standard. In this work, the standard was a Cu-based alloy and the sample was an Ag-based alloy, also containing Hg and other minor components. The LIBS results were in good agreement with two previous independent micro-XRF measurements performed with a destructive approach, i.e. using a cross section of the same sample. This confirmed the applicability of the inverse method to unconventional matrices, for which the use of matrix-matched standards may be unfeasible. The conclusions of this work strongly support the use of laser ablation techniques for calibration-free and micro-invasive analysis of layered samples, in particular when the integrity of samples has to be preserved

The role of Continuum radiation in Laser Induced Plasma Spectroscopy

This paper focuses on the interpretation of the origin of the continuum radiation in Laser Induced Plasma (LIP) emission spectra, a subject that has received little consideration in the literature when compared to the analysis of the line emission spectrum. The understanding of the spectral peculiarities observed immediately after the laser pulse, when the continuum radiation prevails on discrete emission lines, can be extremely important to retrieve the initial conditions of LIP and to correlate the produced plasma to the ablation mechanism. In this work, in addition to a qualitative interpretation of the LIP continuum in the initial stage of expansion, a methodology is proposed for a better measurement of the atomic temperature in the expansion stage of the LIP. Such methodology is based on the analysis of the combined Boltzmann and Planck plots. The results obtained stress once again the importance of considering non equilibrium effects in the initial stage of LIP expansion

Diagnosis of Alzheimer's disease using laser-induced breakdown spectroscopy and machine learning

Alzheimer's disease (AD) is a progressive incurable neurodegenerative disease and a major health problem in aging population. We show that the combined use of Laser-Induced Breakdown Spectroscopy (LIBS) and machine learning applied for the analysis of micro-drops of plasma samples of AD and healthy controls (HC) yields robust classification. Following the acquisition of LIBS spectra of 67 plasma samples from a cohort of 31 AD patients and 36 healthy controls (HC), we successfully diagnose late-onset AD (> 65 years old), with a total classification accuracy of 80%, a specificity of 75% and a sensitivity of 85%