I. N. Saraeva

Nanoscale surface boiling in sub-threshold damage and above-threshold spallation of bulk aluminum and gold by single femtosecond laser pulses

The sub and near-threshold topographic signatures of the spallation of nanometer-thick melt layers during single-shot femtosecond laser ablation of bulk aluminum and gold were experimentally observed for the first time, using scanning electron microscopy with high spatial resolution. The novel ablative nanofeatures—sub-threshold boiling nanopits, the partially detached ultrathin solidified melt layer, and the lamellar surface structure under the layer along the spallative crater border, as well as the foam-like nanostructure of the crater bottom—indicate the boiling origin of the spallation threshold, rather than the thermomechanical rupture of the molten surface layer in a propagating unloading wave. These ablative surface nanofeatures were also revealed in trenches of single-shot, near-wavelength normal interference ripples on the aluminum surface, indicating their spallative nature and being promising for biosensing applications.

Nonlinear absorption mechanisms during femtosecond laser surface ablation of silica glass

Spatial profiles of single-shot microcraters produced by tightly focused femtosecond laser pulses with variable pulse energies are measured by means of a laser confocal microscope. Dependences of crater depth on laser intensity at different pulse energies appear as overlapping saturating curves with the same threshold, indicating the presence of nonlinear absorption and absence of nonlocal ablation effects. A monotonic twofold increase in absorption nonlinearity is related to the transition from minor defect-band absorption to fundamental band-to-band absorption.

Background-free, highly sensitive surface-enhanced IR absorption of rhodamine 6G molecules deposited onto an array of microholes in thin silver film

Selective IR absorption at 1261 cm−1 enhanced by 455 times, was demonstrated for rhodamine 6G molecules, covering a 2D-photonic crystal, represented by a regular array of 4-micron wide holes in a 30 nm thick silver film on a CaF2 substrate. The reference absorption lines were taken near 2900 cm−1, where the IR radiation is freely channeling through the microholes, indicating the reference substrate coverage by the dye molecules for its relative internal calibration. The limit of background-free detection for the analyte was determined at the level ~10−2 monolayer.

Diffraction microgratings as a novel optical biosensing platform

Using a micro-hole grating in a supported silver film as a laser-fabricated novel optical platform for surface-enhanced IR absoprtion/reflection spectroscopy, characteristic absorption bands of Staphylococcus aureus, in particular, its buried carotenoid fragments, were detected in FT-IR spectra with 10-fold analytical enhancement, paving the way for the spectral express-identification of pathogenic microorganisms.

Single-shot femtosecond laser ablation of gold surface in air and isopropyl alcohol

Single-shot IR femtosecond-laser ablation of gold surfaces in ambient air and liquid isopropyl alcohol was studied by scanning electron microscopy characterization of crater topographies and time-resolved optical emission spectroscopy of ablative plumes in regimes, typical for non-filamentary and non-fragmentation laser production of nanoparticle sols. Despite one order of magnitude shorter (few nanoseconds) lifetimes and almost two orders of magnitude lower intensities of the quenched ablative plume emission in the alcohol ambient at the same peak laser fluence, craters for the dry and wet conditions appeared with rather similar nanofoam-like spallative topographies and the same thresholds. These facts envision the underlying surface spallation as one of the basic ablation mechanisms relevant for both dry and wet advanced femtosecond laser surface nano/micro-machining and texturing, as well as for high-throughput femtosecond laser ablative production of colloidal nanoparticles by MHz laser-pulse trains via their direct nanoscale jetting from the nanofoam in air and fluid environments.Single-shot IR femtosecond-laser ablation of gold surfaces in ambient air and liquid isopropyl alcohol was studied by scanning electron microscopy characterization of crater topographies and time-resolved optical emission spectroscopy of ablative plumes in regimes, typical for non-filamentary and non-fragmentation laser production of nanoparticle sols. Despite one order of magnitude shorter (few nanoseconds) lifetimes and almost two orders of magnitude lower intensities of the quenched ablative plume emission in the alcohol ambient at the same peak laser fluence, craters for the dry and wet conditions appeared with rather similar nanofoam-like spallative topographies and the same thresholds. These facts envision the underlying surface spallation as one of the basic ablation mechanisms relevant for both dry and wet advanced femtosecond laser surface nano/micro-machining and texturing, as well as for high-throughput femtosecond laser ablative production of colloidal nanoparticles by MHz laser-pulse trains v...

Electrochemical Fabrication of Hybrid Plasmonic-dielectric Nanomaterial Based on Gold-diamond Clusters

Hybrid plasmonic-dielectric materials were fabricated by micro-discharge through water sols of sub-micrometer-sized diamonds mixed with HAuCl4 acid. Primary characterization of their deposits on a silicon wafer surface by means of electron microscopy and energy-dispersive x-ray spectroscopy indicate close proximity of gold nanoparticles and diamond particles, which is supported by photoluminescence studies demonstrating strong – almost two-fold – damping of diamond luminescence owing to the attachment of gold nanoparticles. UV-near IR spectroscopy of their sols consistently exhibits small red spectral shifts for the fabricated nanomaterials, comparing to bare gold nanoparticles.

Non-linear increase and saturation of third-harmonic yield from supported silver nanostructures excited by IR femtosecond laser pulses

A second-power yield of resonantly enhanced third harmonic and three-photon luminescence of 744 nm femtosecond laser pump pulses, weakly focused onto a layer of silver nanorolls on a silica substrate, was spectrally detected in the fluence range of 4–20 mJ cm−2, saturating at higher fluences. The third-harmonic yield and its saturation were explored in terms of ultrafast carrier dynamics, based on direct three-photon or cascade one- and two-photon transitions balanced by Auger recombination (and the final band-filling effect) which limited the radiative recombination output in the form of the third harmonic and three-photon luminescence.

SINGLE BACTERIUM DETECTION USING SERS

This work is devoted to the study of a single Staphylococcus aureus bacterium detection using surface-enhanced Raman spectroscopy (SERS) and resonant Raman spectroscopy (RS). It was shown that SERS allows increasing sensitivity of predominantly low frequency lines connected with the vibrations of Amide, Proteins and DNA. At the same time the lines of carotenoids inherent to this kind of bacterium are well-detected due to the resonance Raman scattering mechanism. The reproducibility and stability of Raman spectra strongly depend on the characteristics of nanostructured substrate, and molecular structure and size of the tested biological object.

Laser Nanostructuring and Three-Dimensional Ink-Jet Printing of Nanocoatings

High-production laser ablation is used to prepare nano-ink that is colored colloidal solutions of nanoparticles in water, characterized by a variety of physicochemical properties. Using the nano-ink, singleand multi-layered nanocoatings are printed by a jet technique and studied in detail.

Laser-ablative fabrication of nanoparticle inks for 3D inkjetprinting of multifunctional coatings

We report the fabrication of multifunctional coatings via inkjet printing using water-based nanoinks in the form of selenium (Se) and gold (Au) nanoparticle (NP) colloids, prepared by laser ablation of solid targets in deionized water or 50%-isopropyl alcohol solution. Nanoparticles and NP-based coatings were deposited onto silver films, magnetronsputtered to silica-glass substrates, and characterized by means of scanning and transmission electron microscopy (SEM, TEM), UV-vis-IR, Raman and energy-dispersive X-ray spectroscopies.