Photo-physical mechanism of near-IR femtosecond laser-induced refractive-index change in PMMA.

Micromodification in bulk undoped polymethylmethacrylate (PMMA) by single focused (numerical aperture (NA) = 0.25), 1030-nm 250-fs laser pump pulses was explored by pump self-transmittance; optical, 3D-scanning confocal photoluminescence (PL); Raman micro-spectroscopy; and optical polarimetric and interferometric microscopy. Starting from the threshold pulse energy  = 0.

Multi-Wavelength Raman Differentiation of Malignant Skin Neoplasms.

Raman microspectroscopy has become an effective method for analyzing the molecular appearance of biomarkers in skin tissue. For the first time, we acquired in vitro Raman spectra of healthy and malignant skin tissues, including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), at 532 and 785 nm laser excitation wavelengths in the wavenumber ranges of 900-1800 cm and 2800-3100 cm and analyzed them to find spectral features for differentiation between the three classes of the samples. The intensity ratios of the bands at 1268, 1336, and 1445 cm appeared to be the most reliable criteria for the three-class differentiation at 532 nm excitation, whereas the bands from the higher wavenumber region (2850, 2880, and 2930 cm) were a robust measure of the increased protein/lipid ratio in the tumors at both excitation wavelengths.

FT-IR Analysis of Bacteria Inactivation by Femtosecond IR Laser Radiation.

We report the successful inactivation of strain by femtosecond infrared (IR) laser radiation at the resonant wavelengths of 3.15 μm and 6.04 μm, chosen due to the presence of characteristic molecular vibrations in the main structural elements of the bacterial cells in these spectral ranges: vibrations of amide groups in proteins (1500-1700 cm), and C-H vibrations in membrane proteins and lipids (2800-3000 cm).

Direct Bactericidal Comparison of Metal Nanoparticles and Their Salts against . Culture by TEM and FT-IR Spectroscopy.

We report the bactericidal effect of Ag and Cu NPs with different concentrations on methicillin-resistant strain in comparison to the effect of AgNO and CuCl solutions, characterized by microbiological tests, TEM and Fourier-transform infrared spectroscopy. NPs were produced by nanosecond laser ablation in distilled water and characterized by scanning electron microscopy, UV-vis, energy dispersive X-ray, FT-IR spectroscopy, as well as X-ray diffraction, dynamic light scattering size and zeta-potential measurements. Microbiological tests showed antibacterial activity of NPs and metal ion-containing salts.

Spectrally-selective mid-IR laser-induced inactivation of pathogenic bacteria.

Micrometer-thick layers of bacteria were prepared on fluorite substrates and scanned by focused mid-IR femtosecond laser radiation that was spectrally tuned to achieve the selective excitation of either the stretching C-H vibrations (3 μm), or stretching C = O, C-N vibrations (6 μm) of the amide groups in the bacteria. The enhanced biocidal efficiency of the latter selective excitation, compared to the more uniform 3-μm laser excitation, was demonstrated by performing viability assays of laser-treated bacterial layers. The bacterial inactivation by the 6-μm ultrashort laser pulses is attributed to dissociative denaturation of lipids and proteins in the cell membranes and intra-cell nucleic acids.

Few Percent Efficient Polarization-Sensitive Conversion in Nonlinear Plasmonic Interactions Inside Oligomeric Gold Structures.

The backscattering spectra of a 500 nm thick gold film, which was excited near the 525 nm transverse localized plasmon resonance of its constituent, self-organized, vertically-aligned nanorods by normally incident 515 nm, 300 fs laser pulses with linear, radial, azimuthal and circular polarizations, revealed a few-percent conversion into Stokes and anti-Stokes side-band peaks. The investigation of these spectral features based on the nanoscale characterization of the oligomeric structure and numerical simulations of its backscattering response indicated nonlinear Fano-like plasmonic interactions, particularly the partially degenerate four-wave mixing comprised by the visible-range transverse plasmon resonance of the individual nanorods and an IR-range collective mode of the oligomeric structure. Such oligomeric structures in plasmonic films may greatly enhance inner nonlinear electromagnetic interactions and inner near-IR hotspots, paving the way for their engineered IR tunability for broad applications in chemosensing and biosensing.

Polarization-Sensitive Surface-Enhanced In Situ Photoluminescence Spectroscopy of Bacteria on Gold Nanospikes.

We report the possibility of a time-resolved bacterial live/dead dynamics observation with the use of plasmonic nanospikes. Sharp nanospikes, fabricated on a 500-nm thick gold film by laser ablation with the use of 1030-nm femtosecond pulses, were tested as potential elements for antibacterial surfaces and plasmonic luminescence sensors. bacteria were stained by a live/dead viability kit, with the dead microorganisms acquiring the red colour, caused by the penetration of the luminescent dye propidium iodide through the damaged cell membrane.

Surface-Enhanced IR-Absorption Microscopy of Bacteria on Bactericidal Nanostructured Si Surfaces.

Surface-enhanced IR absorption (SEIRA) microscopy was used to reveal main chemical and physical interactions between bacteria and different laser-nanostructured bactericidal Si surfaces via simultaneous chemical enhancement of the corresponding IR-absorption in the intact functional chemical groups. A cleaner, less passivated surface of Si nanoripples, laser-patterned in water, exhibits much stronger enhancement of SEIRA signals compared to the bare Si wafer, the surface coating of oxidized Si nanoparticles and oxidized/carbonized Si (nano) ripples, laser-patterned in air and water. Additional very strong bands emerge in the SEIRA spectra on the clean Si nanoripples, indicating the potential chemical modifications in the bacterial membrane and nucleic acids during the bactericidal effect.

Nanosecond-Laser Generation of Nanoparticles in Liquids: From Ablation through Bubble Dynamics to Nanoparticle Yield.

A comprehensive picture of the nanosecond-laser generation of colloidal nanoparticles in liquids is nowadays the demand of their high-throughput industrial fabrication for diverse perspective biomedical, material science, and optoelectronic applications. In this study, using silicon as an example, we present a self-consistent experimental visualization and theoretical description of key transient stages during nanosecond-laser generation of colloidal nanoparticles in liquids: plasma-mediated injection of ablated mass into the liquid and driving the vapor bubble, finalized by the colloid appearance in the liquid. The explored fundamental transient stages envision the basic temporal and spatial scales, as well as laser parameter windows, for the demanded high-throughput nanosecond-laser generation of colloidal nanoparticles in liquids.