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Tightly focused, highly spatially multiplexed femtosecond laser pulses, coming at sub-MHz repetition rates, were used to mask-less pattern thin plasmonic films film at ultrafast rates, approaching 25 million of microelements per second. For this purpose, the initial pulses were multiplexed by fused silica diffractive optical elements into linear arrays of 31, 51 and 101 circular light spot and then scanned over the films by a galvanometric scanner through a long-focus objective or high-NA aspherical lens. These optical scheme and 5-μJ pulse energy supported the only 31- and 51-beam micro-patterning, with the corresponding aperture, field-of-view and sub-100 nJ energetic limitations for the laser processing of the film. The resulting large (~105–106 holes per array) arrays of micro-holes of variable diameters and periods in thin films of different thickness and diverse plasmonic materials - Ag, Cu, Al and Au-Pd alloy (80%/20%) - were for the first time systematically characterized in the broad IR-range (1.5–25 μm) in terms of plasmonic effects in extraordinary optical transmission, indicating for the increasing wavenumber a smooth transition from the common Bethe-Bouwkamp transmission to its plasmon-enhanced analogue, ending up with common geometrical (wave-guide-like) transmission. Finally, promising label- and luminescence-free laboratory-scale, robust and high-sensitivity sampling of chemicals and biosamples via plasmonic and chemical contributions, uneven and structurally-sensitive regarding different functional groups of the model analyte molecules and band structure of the plasmonic metal, was demonstrated for the large IR-sensing arrays of micro-holes in plasmonic films, with the obvious perspectives for down-scaling of sensing elements for vis-IR surface-enhanced spectroscopies.

The experimental study of the single-shot 1030-nm femtosecond laser ablation of bulk silicon and silver in air and liquid media (deionized water, isopropyl alcohol) is reported. The main laser ablation mechanisms were studied via analysis of the resulting microcrater surface morphology and elemental composition in single- and multi-shot (number of pulses N = 10, 100) regimes by scanning electron microscopy with a built-in module for energy-dispersive X-ray spectroscopy. It was concluded, that multi-shot ablation in liquids leads to the lesser extent of the processed surface oxidation, than in dry conditions. The monitoring of the ablative plumes dynamics was implemented with the use of time-resolved emission spectroscopy in the non-filamentation regime, corresponding to the formation of nanoparticles without fragmentation of the ablation products. It was demonstrated, that the lifetime of the plume emission in liquid is significantly shorter, than in air: 5 and 15 ns, correspondingly, for silicon, and 10 and 30 ns for silver.

The effect of laser pulsewidth, tuned in the range τ = 0.3–10 ps, on infrared (IR) laser ablation (LA) thresholds of bulk gold, silver and silicon in air and in liquid environments (deionized water, isopropyl alcohol (IPA)) was studied in this work. The influence of laser pulsewidth on the morphology and yield of the ejected nanoparticles (NPs), as well as its impact on the efficiency of NP generation, was studied by UV–vis spectral measurement of the extinction coefficient spectra of NP colloids, fabricated by multi-pass ablation of bulk targets in both solvents at different pulse duration values, by analytical disc centrifuge and by high-resolution scanning electron microscopy. The ablation thresholds are raising with the increase of laser pulsewidth, exhibiting sublinear dependences. The extinction coefficient dependence on τ exhibited a non-monotonous character in case of water medium for all materials, and was gradually descending in case of LA in IPA. Additional MD-TTM (molecular dynamics- two-temperature model) modeling was performed for single-shot laser exposition of bulk Au target in air with τ = 0.3 ps and 4 ps, which allowed distinguishing the main mechanisms of the material removal, the formation of NPs, and the observed crater topography. The performed simulations supported the trend on the ablation threshold increase with the increase of laser pulse duration.

Selenium and silicon nanoparticles were obtained by nanosecond laser ablation in distilled water and characterized by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy. The antibacterial properties of their coatings regarding Gram-positive and Gram-negative bacteria were demonstrated. The presence of singlet oxygen and other reactive oxygen species on the surface of the silicon nanoparticles, leading to oxidative damage to bacterial membranes and further death of the bacteria, was considered a possible mechanism of their antibacterial modality.

Using aluminum as an example, ultrafast sub-ablative broad-range (EUV-IR) spectral tuning of surface plasmon resonance in metals by IR femtosecond laser pulses was demonstrated by theoretical modeling of prompt surface optics for strongly photoexcited materials and of their surface plasmon-polariton (SPP) dispersion curves, as well as by experimental multi-shot laser imprinting of surface plasmon-polaritons as large-scale regular surface ripples with minimal sub-diffraction periods down to 200 nm. According to laser-pump self-reflection and charge emission experiments, the key issue in the prompt optical tuning (spectral red-shifting) of EUV surface plasmon resonance in aluminum by the IR laser pulses is related to ultrafast surface charging of its surface via intense electron emission during the laser pump pulse, depleting its surface electron density and simultaneously decreasing its surface/bulk plasma frequencies, at the corresponding negligible surface ablative etching.

We report the facile synthesis of colloidal Si@Au and Si@Ag nanoparticles (NPs) through nanosecond IR laser plasma-mediated reduction of 0.03 mM aqueous solutions of chloroauric acid (HAuCl4) and silver nitrate (AgNO3) at different laser intensities on the surface of Si NPs during the ablation of the silicon wafer. The resulting hybrid colloidal NPs were analysed by UV–vis transmission spectroscopy, dynamic light scattering, scanning electron microscopy, energy-dispersive x-ray and x-ray photoelectron spectroscopy.

Milligram-per-second production of selenium nanoparticles in water sols was realized through 7-W, 2 MHz-rate femtosecond laser ablation of a crystalline trigonal selenium pellet. High-yield particle formation mechanism and ultimate mass-removal yield were elucidated by optical profilometry and scanning electron microscopy characterization of the corresponding crater depths and topographies. Deposited selenium particles were inspected by scanning and transmission electron microscopy, while their hydrosols (nanoinks) were characterized by optical transmission, Raman and dynamic light scattering spectroscopy. 2D patterns and coatings were ink-jet printed on thin supported silver films and their bare silica glass substrates, as well as on IR-transparent CaF2 substrates, and characterized by electron microscopy, energy-dispersive x-ray spectroscopy, and broadband (vis-mid IR) transmission spectroscopy, exhibiting crystalline selenium nanoparticles with high refractive index as promising all-dielectric sensing building nanoblocks in nanophotonics.

Food pathogens (Staphylococcus aureus, Listeria monocytogenes, and Pseudomonas aeruginosa) in planktonic form were subjected to bactericidal treatment by colloidal nanoparticles. NiOx colloidal nanoparticles, as anti-biotic nanomaterial, were produced by laser ablation in deionized water and air, and comprehensively characterized by x-ray diffraction, scanning electron microscopy, energy dispersive X-ray, Raman, Fourier transformed infrared (FT-IR) spectroscopy, dynamic light scattering size and zeta-potential measurements. Normalized Fourier transformed infrared (FT-IR) spectra of the nanoparticle-inactivated bacteria deposits exhibit for the larger, positively charged water-borne nanoparticles pronounced enhancement of IR-absorption in molecular fragments, comprising the bacterial membrane, which appears to be unfavorable for the inactivation of the food bacteria strains. In contrast, smaller and less charged air-borne nanoparticles exhibit less influence in IR-absorption, but pronounced TEM-envisioned penetration inside these pathogenic bacteria, resulting, according to the complementary microbiological tests, in their efficient inactivation. The study will help to understand the possible mechanisms responsible for the death of bacteria at their interacting with antibacterial nanoparticles.

High-pressure Si-XII and Si-III nanocrystalline polymorphs, as well as amorphous Si phase, appear consequently during multi-shot femtosecond-laser exposure of crystalline Si wafer surface above its spallation threshold along with permanently developing quasi-regular surface texture (ripples, microcones), residual hydrostatic stresses and subsurface damage, which are characterized by scanning and transmission electron microscopy, as well as by Raman micro-spectroscopy. The consequent yields of these structural Si phases indicate not only their spatially different appearance, but also potentially enable to track nanoscale, transient laser-induced high-pressure, high-temperature physical processes – local variation of ablation mechanism and rate, pressurization/pressure release, melting/resolidification, amorphization, annealing – versus cumulative laser exposure and the related development of the surface topography.

Deep sub-wavelength, large-scale surface nanopatterning of silicon (Si) wafers immersed in water or carbon disulfide, in the form of ultrafine nanoripples was performed by multi-shot 1030-nm femtosecond laser exposures. Our simulations indicate the key role of surface plasmons, with their extreme wavenumbers tunable versus the dielectric permittivity of the contact dielectric fluids. The factors of the squared optical refraction index of fluids, excitation and interference of counter-propagating surface plasmons were revealed to provide in both these fluids the ultimately small (~100 nm) periods of the nanoripples. The realized advanced wet laser nanopatterning of Si surfaces, unattainable via dry laser processing, paves the way toward nanoscale laser lithography.

Ambient-air single-shot ablative femtosecond laser surface processing of an advanced Al-alloy AA5083 was characterized by non-contact broadband ultrasonics, scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, and Vickers microhardness tests. The characterization indicates that the generated Mbar-level shock waves induce not only a strong structural modification of the processed micron-thick surface layer with sub-GPa-level residual compressive and tensile stresses, raising its microhardness by almost 45%, but also significant depth-dependent chemical modification within the layer.