Martti Silvennoinen

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.

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.

Formation of luminescence centers and nonlinear optical effects in silver-containing glasses under femtosecond laser pulses

It is experimentally shown that irradiation of silver-containing silicate glass by IR femtosecond laser pulses leads to generation of free electrons in glass as a result of multiphoton ionization. Free electrons, being captured by charged molecular silver clusters, transform them into the neutral state, as a result of which the luminescence intensity along the laser-pulse track significantly increases. When a laser pulse propagates in glass, cubic nonlinearity dominates in the initial portion of the path, which leads to pulse self-focusing and filamentation. In the final portion of the path, the dominant process is self-defocusing, which is caused by the local decrease in the refractive index as a result of multiphoton generation of free electrons.

Parallel femtosecond laser processing using intensity modulated diffraction pattern produced with spatial light modulator

Due to technical development of the adaptive optics, use of them in various laser processing applications has become possible. These techniques based on the adaptive optics have been applied with various lasers to generate diffraction patterns with equal intensity spots. In this paper ultrashort laser pulse ablation with intensity modulated diffraction pattern is presented. Diffraction patterns are generated with the Computer Generated Holograms (CGH) created using the Spatial Light Modulator (SLM). Applied CGHs are designed using method based on the Iterative Fourier Transform Algorithm (IFTA). Added to this Fresnel lenses are used to avoid problems with 0th-diffraction order. With this kind of designing procedure it is possible to generate diffraction patterns with intensity variation between diffracted spots. By intensity modulating the diffracted beams it is possible to ablate virtually arbitrary patterns with depth variation into the different materials. In this paper different kinds of CGHs are designed to generate various diffraction patterns with intensity modulation. These patterns are used to ablate greyscale images directly into the silicon using ultrashort pulses.Due to technical development of the adaptive optics, use of them in various laser processing applications has become possible. These techniques based on the adaptive optics have been applied with various lasers to generate diffraction patterns with equal intensity spots. In this paper ultrashort laser pulse ablation with intensity modulated diffraction pattern is presented. Diffraction patterns are generated with the Computer Generated Holograms (CGH) created using the Spatial Light Modulator (SLM). Applied CGHs are designed using method based on the Iterative Fourier Transform Algorithm (IFTA). Added to this Fresnel lenses are used to avoid problems with 0th-diffraction order. With this kind of designing procedure it is possible to generate diffraction patterns with intensity variation between diffracted spots. By intensity modulating the diffracted beams it is possible to ablate virtually arbitrary patterns with depth variation into the different materials. In this paper different kinds of CGHs are desi...

Optical Sensing of Attached Fibrinogen on Carbon Doped Titanium Surfaces

The adsorption/desorption of Human Plasma fibrinogen (HPF) molecules on biosurfaces was measured in spectroscopic cuvette by a diffractive optical element- (DOE-) based sensor. To characterize the surfaces, the basic parameters as surface tension was obtained by sensing of a contact angle of water droplet and dielectric constant was measured by ellipsometry in the absence of HPF molecules. It was observed a significant correlation between the adsorption ability of HPF molecules (sensed by DOE on the basis of the changes in optical roughness () of studied surface in the absence and presence of HPF molecules), and dielectric constant (measured by ellipsometry) of differently treated titanium surfaces, where the permittivity and dielectric loss have the known linear relation. These findings with carbon-treated biomaterial surfaces can help us to understand mechanisms behind attachment of HPF molecules on biomaterial surfaces to realize and extend variety of implants for hard tissue replacement.

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.

Sensing of parameters behind attachment of human plasma fibrinogens on carbon doped titanium surfaces: an optical study

Polished titanium surface and four differently carbon doped titanium surfaces are investigated to characterize adsorption and desorption of human plasma fibrinogen (HPF) molecules. The surface tension and surface energy of carbon doped titanium and other comparative titanium surfaces used in the experiments were observed by measuring optically the contact angle of water droplet on the treated surfaces. The dielectric constant of each bulk surface was measured utilizing ellipsometry in dry environment. Whereas the temporal adsorption or desorption of HPF molecules on test surfaces in background electrolyte with and without HPF molecules were measured using an optical correlator, which utilizes a diffractive optical element (DOE) in non-contact domain. The optical correlator operates in coherent and in non-coherent mode, which allows sensing of optical path differences providing information on the optical roughness (Ropt), contrary to the mechanical roughness obtained from atomic force microscope (AFM) profilometer, and reflectance of the surfaces immersed into a liquid. The knowledge of the parameters helps us to understand mechanisms behind attachment of HPF molecules on biomaterial surfaces in hard tissue replacement.

Electrically pumped microdisk lasers with semitransparent conducting pyrolytic carbon film

Electrically driven microdisk lasers with top contacts made of a semitransparent conducting pyrolytic carbon film are developed. Electrical properties of the pyrolytic carbon contact to a p-type doped GaAs epitaxial layer are studied. Room temperature electroluminescence spectra from an array of the microdisk lasers and a single 27 μm in diameter microdisk laser are demonstrated.

Femtosecond laser processing and spatial light modulator

The use of the femtosecond laser enables generation of small spot sizes and ablation features. Ablation of the small features usually requires only a small amount of laser power to be delivered to the ablation spot. When using only a one beam for the ablation of the small features this process is bound to be time consuming. The spatial light modulator (SLM) together with the computer generated holograms (CGH) can be used for manipulating and shaping of the laser beam in various applications. In laser micromachining, when using laser with relatively high power, the original beam can be divided up to hundreds beams and still have the energy of the individual beam above the ablation threshold of the material. This parallel laser processing enables more efficient use of the laser power regardless of the machining task.