ABSTRACT. Mechanism of two-photon induced oxidation of single-layer graphene on Si/SiO 2 substrates is studied by atomic force microscopy (AFM) and Raman microspectroscopy and imaging. AFM imaging of areas oxidized by using a tightly focused femtosecond laser beam shows that oxidation is not homogeneous but oxidized and non-oxidized graphene segregate into separate domains over the whole irradiated area. Oxidation process starts from point-like "seeds" 2 which grow into islands finally coalescing together. The size of islands before coalescence is 30 -40 nm and the density of the islands is on the order of 10 11 cm -2 . Raman spectroscopy reveals growth of the D/G band ratio along the oxidation. Sharpness of the D-band which persists over large range of oxidation and the maximal value of the intensity ratio of the D-and G-bands (~0.8) indicates that graphene oxidation proceeds by increase of the oxidized area rather than progression of oxidized areas to fully disordered structure. A phenomenological model is developed which explains the observations. According to the model, the probability for oxidation of a site next to already oxidized site is five orders of magnitude higher than oxidation of pristine graphene. Irradiation of an extended area by raster scanning leads to a formation of an irregular nanomesh of oxide islands with a narrow size distribution. The phenomenological model yields similar results as the experiment. This study forms a basis for controlled use of two-photon oxidation for tailoring properties of graphene and patterning it with sub-micrometer resolution.

Algal biomass that is represented mainly by commercially grown algal strains has recently found many potential applications in various fields of interest. Its utilization has been found advantageous in the fields of bioremediation, biofuel production and the food industry. This paper reviews recent developments in the analysis of algal biomass with the main focus on the Laser-Induced Breakdown Spectroscopy, Raman spectroscopy, and partly Laser-Ablation Inductively Coupled Plasma techniques. The advantages of the selected laser-based analytical techniques are revealed and their fields of use are discussed in detail.

In this work we investigate the relationship of the F line and CaF bands with varying Ca and F contents.