Thermal stability of volume Bragg gratings in chloride photo-thermo-refractive glass after femtosecond laser bleaching.

We demonstrate that the Joule heating of the volume Bragg grating recorded in chloride photo-thermo-refractive glass can be suppressed by bleaching the silver nanoparticles with intense ultrashort laser pulses. Measurement of the bleached grating angular selectivity showed that, at the signal wavelength at 972 nm, the spectral drift is 0.5 nm at the CW laser diode beam intensity as high as 145 W/cm2. Thus, the bleaching of silver nanoparticles results in the improved thermal stability of transmission gratings, allowing one to employ them to control the powerful CW laser radiation.

Fluorescent clusters in chloride photo-thermo-refractive glass by femtosecond laser bleaching of Ag nanoparticles.

We report photoluminescence in bulk chloride photo-thermo-refractive glass under irradiation with femtosecond laser pulses. The fluorescence originates from the bleaching of silver nanoparticles precipitating in the glass. Similarly to the conventional process of the femtosecond re-shaping of metal inclusions with diameter tens of nanometers, irradiation of the smaller nanoparticles results in a fast shrinking size with an ellipsoidal shape via photofragmentation. Under UV excitation, remaining sub-nanometer silver molecular clusters show visible and near IR fluorescence, which increases with chlorine concentration. The observed bleaching of silver nanoparticles in bulk glass-metal nanocomposite can find applications in data storage and bleaching of volume Bragg gratings.

Parallel femtosecond laser ablation with individually controlled intensity.

The use of computer generated holograms together with spatial light modulator (SLM) enable highly parallel laser micromachining. Usually SLM is used for splitting the original laser beam to desired number of beams with equal intensity. However, this technique also enables that the intensity of every beam can be controlled individually. Example of the hologram designing procedure for separation of the original beam to 400 beams with individually controlled intensity is presented. The proposed technique is demonstrated by femtosecond laser ablation of grayscale pictures so that grey scale of the pixel is addressed with corresponding beam intensity in the ablated picture.

Control of cultured human cells with femtosecond laser ablated patterns on steel and plastic surfaces.

The purpose of the present study is to explore topographical patterns produced with femtosecond laser pulses as a means of controlling the behaviour of living human cells (U2OS) on stainless steel surfaces and on negative plastic imprints (polycarbonate). The results show that the patterns on both types of material strongly affect cell behaviour and are particularly powerful in controlling cell spreading/elongation, localization and orientation. Analysis by fluorescence and scanning electron microscopy shows that on periodic 1D grating structures, cells and cell nuclei are highly elongated and aligned, whereas on periodic 2D grid structures, cell spreading and shape is affected. The results also show that the density and morphology of the cells can be affected. This was observed particularly on pseudo-periodic, coral-like structures which clearly inhibited cell growth. The results suggest that these patterns could be used in a variety of applications among the fields of clinical research and implant design, as well as in diagnosis and in cell and drug research. Furthermore, this article highlights the noteworthy aspects and the unique strengths of the technique and proposes directions for further research.

Diffractive-optics-based sensor as a tool for detection of biocompatibility of titanium and titanium-doped hydrocarbon samples.

Adsorption of the elongated human plasma fibrinogen (HPF) and globular human serum albumin molecules on a titanium-based surface is monitored by analyzing permittivity and optical roughness of protein-modified surfaces by using a diffractive optical element (DOE)-based sensor and variable angle spectro-ellipsometry (VASE). Both DOE and VASE confirmed that fibrinogen forms a thicker and more packed surface adlayer compared to a more porous and weakly adsorbed albumin adlayer. A linear relation of the permittivity (ε(')) and dielectric loss (ε('')) was found for some of the dry titanium-doped hydrocarbon (TDHC) surfaces with excellent HPF adsorption ability. We discuss some aspects of TDHC's aging and its possible effects on fibrinogen adsorption.

Sensing of human plasma fibrinogen on polished, chemically etched and carbon treated titanium surfaces by diffractive optical element based sensor.

Adsorption of human plasma fibrinogen (HPF) on 6 differently treated titanium samples (polished, polished and etched, and 4 titanium carbide coatings samples produced by using plasma-enhanced chemical vapour deposition (PECVD) method) is investigated by using diffractive optical element (DOE) sensor. Permittivity (susceptibility) change and fluctuation in optical roughness (R(opt)) of treated titanium surface in the presence of background electrolyte without and with HPF molecules are sensed by using DOE sensor and optical ellipsometry. Correlation between transmitted light and thickness of molecule layer was found. The findings allow to sense temporal organization and severity of adsorption of nano-scale HPF molecules on polished, on polished and etched, and on titanium carbide surface.