Optical attenuation coefficient of skin under low compression.

In various biomedical optics therapies, knowledge of how light is absorbed or scattered by tissues is crucial. Currently, it is suspected that a low compression applied to the skin surface may improve light delivery into tissue. However, the minimum pressure needed to be applied to significantly increase the light penetration into the skin has not been determined.

Absolute and Relative Methods for Fluorescence Quantum Yield Evaluation of Quantum Dots.

Optical spectroscopy techniques are crucial for the evaluation and use of quantum dots (QDs) in life and materials science. In that context, the fluorescence quantum yield (Φ) is an essential parameter in the assessment of the luminescent features of QDs. The fluorescence quantum yield can be defined as the ratio of the number of emitted photons to the number of absorbed photons by a luminescent material.

UV random laser emission from flexible ZnO-Ag-enriched electrospun cellulose acetate fiber matrix.

We report an alternative random laser (RL) architecture based on a flexible and ZnO-enriched cellulose acetate (CA) fiber matrix prepared by electrospinning. The electrospun fibers, mechanically reinforced by polyethylene oxide and impregnated with zinc oxide powder, were applied as an adsorbent surface to incorporate plasmonic centers (silver nanoprisms). The resulting structures - prepared in the absence (CA-ZnO) and in the presence of silver nanoparticles (CA-ZnO-Ag) - were developed to support light excitation, guiding and scattering prototypes of a RL.

Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.

An essential parameter to evaluate the light emission properties of fluorophores is the fluorescence quantum yield, which quantify the conversion efficiency of absorbed photons to emitted photons. We detail here an alternative nonfluorescent method to determine the absolute fluorescence quantum yield of quantum dots (QDs). The method is based in the so-called Thermal Lens Spectroscopy (TLS) technique, which consists on the evaluation of refractive index gradient thermally induced in the fluorescent material by the absorption of light.

Direct three-photon excitation of upconversion random laser emission in a weakly scattering organic colloidal system.

We report the operation and characterization of an upconversion random laser emitting at 560 nm, when directly pumped by three photon excitation at the near IR wavelength of 1350 nm in a colloidal dye solution in the weakly scattering regime. Using a special dye with a high three-photon cross-section and TiO(2) nanoparticles (250 nm diameter), optimized upconverted emission was obtained for particle densities of ~2 x 10(9)/cm3. A strong dependence on the nanoparticle concentration and the pumping area was verified.

Microchip Random Laser based on a disordered TiO2-nanomembranes arrangement.

We developed a new scheme for obtaining coherent random lasing based on a chip consisting of a polymer film doped with Rhodamine 6G, having as scatterers butterfly-like TiO(2) nanomembranes (TiO(2)-NM) supported on a glass substrate. The feedback mechanism for laser action is due to the multiple scattering of light by TiO(2)-NM rather than provided by localized variations of the refractive index in the polymer film. The above-threshold multiple spikes signature indicative of random laser emission with coherent feedback is confirmed.