Tunable thermoresponsive TiO2/SiO2 Bragg stacks based on sol-gel fabrication methods

Thermoresponsive TiO2/SiO2 one-dimensional photonic crystals (Bragg stacks) fabricated via sol-gel processing methods represent a promising class of environmentally responsive nanostructures featuring optically encoded temperature and humidity detection. The thermo-optic response of the layer materials is amplified by their inherent porosity owing to adsorption/desorption of ambient humidity into the mesoporous multilayer structure. Based on a comprehensive analysis of the impact of layer thickness, refractive index and thermo-optic coefficient on the stop band position, and width of various Bragg stack architectures, design criteria for thermoresponsive Bragg stacks operating in the visible range of the optical spectrum are put forward. A large and well-defined thermo-optic signature is expected for material combinations featuring individually high thermo-optic coefficients with the same sign or allowing for large changes in the effective refractive indices due to water adsorption in the porous layers reinforcing the thermo-optic response, as observed in the TiO2/SiO2 couple. Important practical aspects of the performance of thermoresponsive Bragg stacks are addressed, including the hysteresis properties of TiO2/SiO2 Bragg stacks during multiple heating/cooling cycles, as well as response and recovery times (similar to 2-4 s) of the multilayer system during external changes in ambient humidity

Bringing one-dimensional photonic crystals to a new light: an electrophotonic platform for chemical mass transport visualisation and cell monitoring

Photonic sensor technologies represent an important milestone in monitoring complex physical, chemical and biological systems. We present an integrated chemo- and bio-photonic sensing scheme drawing on the integration of one-dimensional (1D) stimuli-responsive photonic crystals (PCs) with an electrophotonic visualisation platform. We demonstrate various modi operandi, including the real-time mapping of spatial concentration distribution of a chemical analyte and the in situ monitoring of adhesive cell cultures, enabled by the modular combination of stimuli-responsive 1D PCs with various light emitters and detectors

Tunable thermoresponsive TiO2/SiO2 Bragg stacks based on sol-gel fabrication methods

Thermoresponsive TiO2/SiO2 one-dimensional photonic crystals (Bragg stacks) fabricated via sol-gel processing methods represent a promising class of environmentally responsive nanostructures featuring optically encoded temperature and humidity detection. The thermo-optic response of the layer materials is amplified by their inherent porosity owing to adsorption/desorption of ambient humidity into the mesoporous multilayer structure. Based on a comprehensive analysis of the impact of layer thickness, refractive index and thermo-optic coefficient on the stop band position, and width of various Bragg stack architectures, design criteria for thermoresponsive Bragg stacks operating in the visible range of the optical spectrum are put forward. A large and well-defined thermo-optic signature is expected for material combinations featuring individually high thermo-optic coefficients with the same sign or allowing for large changes in the effective refractive indices due to water adsorption in the porous layers reinforcing the thermo-optic response, as observed in the TiO2/SiO2 couple. Important practical aspects of the performance of thermoresponsive Bragg stacks are addressed, including the hysteresis properties of TiO2/SiO2 Bragg stacks during multiple heating/cooling cycles, as well as response and recovery times (similar to 2-4 s) of the multilayer system during external changes in ambient humidity

Photonic Hydrogel Sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified

Improved plasma performance on Large Helical Device

Since the start of the Large Helical Device (LHD) experiment, various attempts have been made to achieve improved plasma performance in LHD [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. Recently, an inward-shifted configuration with a magnetic axis position R_ax of 3.6 m has been found to exhibit much better plasma performance than the standard configuration with R_ax of 3.75 m. A factor of 1.6 enhancement of energy confinement time was achieved over the International Stellarator Scaling 95. This configuration has been predicted to have unfavorable magnetohydrodynamic (MHD) properties, based on linear theory, even though it has significantly better particle-orbit properties, and hence lower neoclassical transport loss. However, no serious confinement degradation due to the MHD activities was observed, resolving favorably the potential conflict between stability and confinement at least up to the realized volume-averaged beta of 2.4%. An improved radial profile of electron temperature was also achieved in the configuration with magnetic islands, minimized by an external perturbation coil system for the Local Island Divertor (LID). The LID has been proposed for remarkable improvement of plasma confinement like the high (H) mode in tokamaks, and the LID function was suggested in limiter experiments

Reduction of Ion Thermal Diffusivity Associated with the Transition of the Radial Electric Field in Neutral-Beam-Heated Plasmas in the Large Helical Device

Recent large helical device experiments revealed that the transition from ion root to electron root occurred for the first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. A clear reduction of ion thermal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory when the neoclassical ion loss is more dominant than the anomalous ion loss

Thermal transport barrier in heliotron-type devices (Large Helical Device and Compact Helical System)

In the discharges of the Large Helical Device [O. Motojima et al., Proceedings of the 16th Conference on Fusion Energy, Montreal, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 3, p. 437], a significant enhancement of the energy confinement has been achieved with an edge thermal transport barrier, which exhibits a sharp gradient at the edge. Key features associated with the barrier are quite different from those seen in tokamaks (i) almost no change in particle (including impurity) transport, (ii) a gradual formation of the barrier, (iii) a very high ratio of the edge temperature to the average temperature, (iv) no edge relaxation phenomenon. In the electron cyclotron heating (ECH) heated discharges in the Compact Helical System [K. Matsuoka et al., in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, France, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411], the internal electron transport barrier has been observed, which enhances the central electron temperature significantly. High shear of the radial electric field appears to suppress the turbulence in the core region and enhance the electron confinement there

Photonic hydrogel sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified