InGaAs/InP single-photon avalanche diode operated in gated mode for time-resolved diffuse optical spectroscopy up to 1700nm

Time-domain diffuse optical spectroscopy is being applied with increasing success to study highly scattering media, mainly in the fields of non-invasive medical diagnostics and quality assessment of food and pharmaceutical products. The region beyond 1100nm is still largely unexplored by time-domain techniques, probably due to the difficult combination of tunable pulsed sources and suitable single-photon detectors. We extend the spectral range up to 1700 nm thanks to a pulsed supercontinuum laser and a time-gated InGaAs/InP single-photon avalanche diode, with potential applications in medical diagnostics and in the study of scattering materials. A first application on lipids is shown

Time resolved diffuse optical spectroscopy with geometrically accurate models for bulk parameter recovery

A novel straightforward, accessible and efficient approach is presented for performing hyperspectral time-domain diffuse optical spectroscopy to determine the optical properties of samples accurately using geometry specific models. To allow bulk parameter recovery from measured spectra, a set of libraries based on a numerical model of the domain being investigated is developed as opposed to the conventional approach of using an analytical semi-infinite slab approximation, which is known and shown to introduce boundary effects. Results demonstrate that the method improves the accuracy of derived spectrally varying optical properties over the use of the semi-infinite approximation

Exploiting polymorphism in second sphere coordination: thermal transformation, NLO properties and selective mechanochemical synthesis

The racemic organic building block L acting as a first sphere ligand yields a new second sphere adduct [LH]+·[FeCl4]- crystallizing as racemic polymorphs α and β. Solid-state DFT calculations show that polymorph β is the kinetic adduct as observed experimentally. The β-phase crystallizes in the polar space group Pna21 and displays NLO properties. Mechanochemical synthesis yields only the β-phase

Diffuse optical characterization of collagen absorption from 500 to 1700 nm

Reduction in scattering, high absorption, and spectral features of tissue constituents above 1000 nm could help in gaining higher spatial resolution, penetration depth, and specificity for in vivo studies, opening possibilities of near-infrared diffuse optics in tissue diagnosis. We present the characterization of collagen absorption over a broadband range (500 to 1700 nm) and compare it with spectra presented in the literature. Measurements were performed using a time-domain diffuse optical technique. The spectrum was extracted by carefully accounting for various spectral distortion effects, due to sample and system properties. The contribution of several tissue constituents (water, lipid, collagen, oxy, and deoxy-hemoglobin) to the absorption properties of a collagen-rich in vivo bone location, such as radius distal in the 500-to 1700-nm wavelength region, is also discussed, suggesting bone diagnostics as a potential area of interest

Functional modulation of LHCSR1 protein from Physcomitrella patens by zeaxanthin binding and low pH

Light harvesting for oxygenic photosynthesis is regulated to prevent the formation of harmful photoproducts by activation of photoprotective mechanisms safely dissipating the energy absorbed in excess. Lumen acidification is the trigger for the formation of quenching states in pigment binding complexes. With the aim to uncover the photoprotective functional states responsible for excess energy dissipation in green algae and mosses, we compared the fluorescence dynamic properties of the light-harvesting complex stress-related (LHCSR1) protein, which is essential for fast and reversible regulation of light use efficiency in lower plants, as compared to the major LHCII antenna protein, which mainly fulfills light harvesting function. Both LHCII and LHCSR1 had a chlorophyll fluorescence yield and lifetime strongly dependent on detergent concentration but the transition from long- to short-living states was far more complete and fast in the latter. Low pH and zeaxanthin binding enhanced the relative amplitude of quenched states in LHCSR1, which were characterized by the presence of 80 ps fluorescence decay components with a red-shifted emission spectrum. We suggest that energy dissipation occurs in the chloroplast by the activation of 80 ps quenching sites in LHCSR1 which spill over excitons from the photosystem II antenna system

Time-Resolved Diffuse Optical Spectroscopy up to 1700 nm by Means of a Time-Gated InGaAs/InP Single-Photon Avalanche Diode

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