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Bouchard S.,Center dOptique Photonique et Laser | Thibault S.,Laval University
Optics InfoBase Conference Papers | Year: 2013

We propose a method to improve the optical efficiency of a planar concentrator used with a single-axis tracker. The low cost for mass producing the system is kept while the performance is improved. Renewable Energy and the Environment Congress. © 2013.

Imitola J.,Brigham and Womens Hospital | Imitola J.,Harvard University | Cote D.,Massachusetts General Hospital | Cote D.,Harvard University | And 15 more authors.
Journal of Biomedical Optics | Year: 2011

Myelin loss and axonal degeneration predominate in many neurological disorders; however, methods to visualize them simultaneously in live tissue are unavailable. We describe a new imaging strategy combining video rate reflectance and fluorescence confocal imaging with coherent anti-Stokes Raman scattering (CARS) microscopy tuned to CH2 vibration of myelin lipids, applied in live tissue of animals with chronic experimental autoimmune encephalomyelitis (EAE). Our method allows monitoring over time of demyelination and neurodegeneration in brain slices with high spatial resolution and signal-to-noise ratio. Local areas of severe loss of lipid signal indicative of demyelination and loss of the reflectance signal from axons were seen in the corpus callosum and spinal cord of EAE animals. Even in myelinated areas of EAE mice, the intensity of myelin lipid signals is significantly reduced. Using heterozygous knock-in mice in which green fluorescent protein replaces the CX 3CR1 coding sequence that labels central nervous system microglia, we find areas of activated microglia colocalized with areas of altered reflectance and CARS signals reflecting axonal injury and demyelination. Our data demonstrate the use of multimodal CARS microscopy for characterization of demyelinating and neurodegenerative pathology in a mouse model of multiple sclerosis, and further confirm the critical role of microglia in chronic inflammatory neurodegeneration. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Bouchard S.,Center dOptique Photonique et Laser | Thibault S.,Center dOptique Photonique et Laser
Applied Optics | Year: 2012

Solar concentrators offer good promise for reducing the cost of solar power. Planar waveguides equipped with a microlens slab have already been proposed as an excellent approach to produce medium to high concentration levels. Instead, we suggest the use of a cylindrical microlens array to get useful concentration without tracking during the day. To use only a seasonal tracking system and get the highest possible concentration, cylindrical microlenses are placed in the east-west orientation. Our new design has an acceptance angle in the north-south direction of ±9° and ±54° in the east-west axis. Simulation of our optimized system achieves a 4.6× average concentration level from 8:30 to 16:30 with a maximum of 8.1× and 80% optical efficiency. The low-cost advantage of waveguide-based solar concentrators could support their use in roof-mounted solar panels and eliminate the need for an expensive and heavy active tracker. © 2012 Optical Society of America.

Bouchard S.,Center dOptique Photonique et Laser | Bouchard S.,Laval University | Thibault S.,Center dOptique Photonique et Laser | Thibault S.,Laval University
Optics Express | Year: 2014

It is generally accepted that small to medium level concentrators could be used as cost-competitive replacements for tracked solar panels. The objective is to design a system that can reach a good level of sun concentration with only one sun-tracking axis and is cheap to fabricate. As the most critical parameter for all concentrator designs, optical efficiency needed improvement to reduce the cost of power produced by our system. By using a graded-index planar waveguide with an index profile similar to SELFOC fiber, the ray's path can be controlled. Also, the concentrator can be fabricated in a single block, which reduces Fresnel reflections. Overall, the optical efficiency can be improved by as much as 33% compared to the same system made with a homogeneous waveguide. Furthermore, the ability to cost-effectively fabricate the concentrator by molding can be preserved, making it possible to reduce the cost of the solar power produced. © 2014 Optical Society of America.

Bouchard S.,Center dOptique Photonique et Laser | Bouchard S.,Laval University | Thibault S.,Center dOptique Photonique et Laser | Thibault S.,Laval University | And 2 more authors.
Journal of Photonics for Energy | Year: 2012

We present an analysis of the degradation of the optical and electrical properties of high-power light-emitting diodes (LEDs) used for general lighting applications. The study was conducted by submitting the LEDs to different current and temperature stress conditions. Those conditions are based on typical operating conditions that can be encountered on LED-based luminaires for general lighting. LEDs were stressed under four different operating currents, and two of those were stressed at two junction temperatures, controlled with a thermoelectric cooler. Results described in this paper indicate that the lumen droop due to an increase in nonradiative recombination is correlated with the stress conditions in accordance with the literature. However, the LED samples showed a forward-voltage droop which seems to be independent of the stresses. For all the stress conditions, the LED forward voltages decreased by about 1% after 1000 h of stress time. A link between forward voltage and lumen output was made through LED efficiency. Also, the yellow peak/blue peak ratio was measured and showed an increase after 1000 to 1200 h. This is attributed to LED chip degradation. These observations suggest the use of both current and voltage control to optimize the use of LEDs in general lighting. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE).

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