Nonlinear absorption of glass doped with PbS nanocrystals is studied and application of this composite material as a saturable absorber for mode locking in lasers is discussed. By using time resolved absorption pump-probe investigation, bleaching due to filling of discrete states caused by quantum confinement in the nanocrystals as well as induced absorption are revealed and characterized. The origin of the induced absorption is discussed. Kinetics of the transient absorption is studied. Two components observed in the decay of the nonlinearities are observed and interpreted in terms of the carrier trapping.

Coherent anti-Stokes Raman scattering (CARS) of carbon nanostructures, namely, highly oriented pyrolytic graphite, graphene nanoplatelets, graphene oxide, and multiwall carbon nanotubes as well CARS spectra of thymine (Thy) molecules adsorbed on graphene oxide were studied. The spectra of the samples were compared with spontaneous Raman scattering (RS) spectra. The CARS spectra of Thy adsorbed on graphene oxide are characterized by shifts of the main bands in comparison with RS. The CARS spectra of the initial nanocarbons are definitely different: for all investigated materials, there is a redistribution of D- and G-mode intensities, significant shift of their frequencies (more than 20 cm-1), and appearance of new modes about 1,400 and 1,500 cm-1. The D band in CARS spectra is less changed than the G band; there is an absence of 2D-mode at 2,600 cm-1 for graphene and appearance of intensive modes of the second order between 2,400 and 3,000 cm-1. Multiphonon processes in graphene under many photon excitations seem to be responsible for the features of the CARS spectra. We found an enhancement of the CARS signal from thymine adsorbed on graphene oxide with maximum enhancement factor about 105. The probable mechanism of CARS enhancement is discussed.

Graphene-enhanced Raman scattering (GERS) spectra and coherent anti-Stokes Raman scattering (CARS) of thymine molecules adsorbed on a single-layer graphene were studied. The enhancement factor was shown to depend on the molecular groups of thymine. In the GERS spectra of thymine, the main bands are shifted with respect to those for molecules adsorbed on a glass surface, indicating charge transfer for thymine on graphene. The probable mechanism of the GERS enhancement is discussed. CARS spectra are in accord with the GERS results, which indicates similar benefit from the chemical enhancement.

Theranostics is the emerging field of medicine that uniquely combines diagnostic techniques and active agents to diagnose and treat medical conditions simultaneously or sequentially. Finding a theranostic agent capable to cure the affected cells and being safe for the healthy ones is the key for successful treatment. Here, we demonstrate that agglomerated single-walled carbon nanotubes (SWCNTs) are promising theranostic agent that enables photo-activated ‘cold’ destruction of the cancer cells keeping their environment alive. The absorption of picosecond pulses by SWCNT agglomerates results in the mechanical (due to photoacoustic effect) rather than photothermal cancer cell destruction, which was visualized by micro-Raman and ultrafast near-infrared CARS. The developed theoretical model allows us to distinguish photothermal, photoacoustic, and photothermoacoustic regimes of the cancer cell destruction, and also to optimize SWCNT-based theranostics recipe.

Coherent anti‐stokes Raman scattering microscopy (CARS) was applied to visualize carotenoids in microalgae and cyanobacteria. Nonlinear light–matter interaction utilized in CARS microscopy inevitably induces a number of competing nonlinear processes, such as multiphoton excitation fluorescence. Microalgae and cyanobacteria being an intrinsically well‐fluorescent object generates a strong two‐photon‐excitation fluorescence (TPEF) signal which should be effectively suppressed during the CARS experiment. Using an energetically balanced duel‐wavelength excitation scheme and spectral purification of detecting signal, the TPEF was completely blocked providing a possibility to probe microalgae and cyanobacteria in a fingerprint region of the CARS spectrum. Microspectroscopy experiments were carried out with three species ‐ cyanobacteria Nostoc Commune, Nostoc sp. and Chlorella sp. Distinct bands obtained in CARS spectra of such species were assigned to carotenoids and were taken as spectral markers in the imaging experiment. CARS imaging known as a chemical selective and label‐free technique allows non‐invasion monitoring of accumulation and movement of chemical compound at the subcellular level. Obtained high‐resolution images of carotenoid distribution in algae and cyanobacteria clearly demonstrate the potential of CARS microscopy for spatially resolved analysis of the natural products stored in the microalgae and cyanobacteria cell. Copyright © 2013 John Wiley & Sons, Ltd.