Absorption coefficient of graphite bulk pressed from 1-5 micrometers size crystalline grains was measured in UV-Vis-NIR range with three different methods: i) determination of pulsed laser ablation rate as the function of laser fluence for different wavelengths ˙(248nm, 337 nm, 532 nm and 1064 nm, respectively); ii) production of aerosol particles by UV laser ablation of the bulk graphite in inert atmosphere and determination of the mass-specific absorption coefficient with a four-wavelength (266 nm, 355 nm, 532 nm and 1064 nm, respectively) photoacoustic spectrometer and iii) spectroscopic ellipsometry in 250-1000 nm range. Taking into account the wide range of the absorption coefficients available in for the different carbon structures, an overall relatively good agreement was observed for the three methods. The ellipsometric results fit well with the ablation rate measurement, the data obtained with photoacoustic method are also similar in the UV and NIR region, however the values were somewhat higher in visible and near-UV range. Taking into account the limitations of the methods, they can be promising candidates for the determination of absorption coefficient when the samples are strongly scattering and there is no possibility to perform transitivity measurements.

Nanostructure formation on bulk metals (copper, gold, and silver) by picosecond (FWHM = 10 ps) Nd:YAG laser irradiation was studied aiming at the production of low-reflectivity surfaces. The experiments were performed at two distinct wavelengths (λ = 355 and 1064 nm) using 20 kHz repetition frequency. The fluence was varied in the 1-11 J/cm 2 range, while the samples were shot by an average pulse number from 0 to 50 depending on the scanning speed of the applied galvanometric scanner. The reflectivity of the treated surfaces was recorded with a visible near-infrared microspectrometer in the 450-800 nm range. Morphological investigations of the irradiated metal surfaces were performed with scanning electron microscope, which showed that mainly two types of nanostructures can be responsible for the reflectivity decrease depending on the type of the illuminated metal. Finite element modeling was performed to simulate the laser absorption-induced heating of the illuminated samples, which helps in the understanding of the structure formation process. It was found that two main processes take place in the production of micro-and nanostructures on the surface; the ejection and falling back of molten metal droplets, and the back scattering and aggregation of nanoparticles.

Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

Static scattering is detrimental to the accuracy of laser speckle contrast analysis (LASCA) measurements on skin when, instead of percentile change monitoring, absolute perfusion values are needed, e.g., for tissue injury examination. Perfusion values were calculated using two evaluation models, while changing the dynamic/static scattering ratio of monitored skin and tissue phantoms. Results were strongly affected by the significant increase of static contribution. Measurements on a modified tissue phantom showed that the changes in the measured perfusion values were mostly caused by the mixed scattering, which was omitted by the tested models. Dynamic ratio values obtained by multi-exposure LASCA could be used for perfusion data correction.

Oil spills pose a significant threat to marine life and finding cost-effective and environmentally friendly solutions is crucial. In this study, pulsed laser ablation (PLA) was applied to produce polymer-based magnetic nanocomposites for oil spill remediation. The selected polymers (polyvinylpyrrolidone, chitosan, and methyl cellulose) are known for their adsorptive removal of polluting residues from various oil species. PLA was performed on pressed tablets containing magnetite nanoparticles (NPs) and polymers, and the generated particles were collected using an external magnetic field. The chemical composition of the ablated products was analyzed using Fourier-transform infrared (FTIR) and Raman spectroscopy, while particle sizes were measured using Leica Image Processing and Analysis System. The study demonstrated that PLA is a single-step, green, and efficient technique for preparing magnetic nanocomposites for oil spill treatment. The average particle size of the composites was in the 1.5–4 µm range, considerably smaller than the initial size of the corresponding polymer. The oil/water separation process using these composites was demonstrated, with separation occurring ~ 1 s after applying the magnetic field. These findings suggest that PLA-generated magnetic nanocomposites have significant potential for oil spill remediation applications.