When irradiated at its resonance frequency, a metallic nanoparticle efficiently converts the absorbed energy into heat which is locally dissipated. This effect can be used in photothermal treatments, e.g., of cancer cells. However, to fully exploit the functionality of metallic nanoparticles as nanoscopic heat transducers, it is essential to know how the photothermal efficiency depends on parameters like size and shape. Here we present the measurements of the temperature profile around single irradiated gold nanorods and nanospheres placed on a biologically relevant matrix, a lipid bilayer. [1] We developed a novel assay based on molecular partitioning between two coexisting phases, the gel and fluid phase, within the bilayer. [2, 3] This assay allows for a direct measurement of local temperature gradients, an assay which does not necessitate any pre-assumptions about this system and is generally applicable to any irradiated nanoparticle system. The nanorods are irradiated with a tightly focused laser beam at a wavelength of 1064 nm where biological matter exhibits a minimum in absorption. By controlling the polarization of the laser light we show that the absorption of light by the nanorod and the corresponding dissipated heat strongly depends on the orientation of the nanorod with respect to the polarization. Finally, by comparing to spherical gold nanoparticles, we demonstrate how a change in shape, from spherical to rod like, leads to a dramatic enhancement of heating when using near infrared light.
A novel method is presented to inject the light of millimeter-sized high-brightness blue LEDs into light guides of submillimeter
thickness. Use is made of an interference filter that is designed to pass only those modes that will propagate in
the light guide by total internal reflection. Other modes are reflected back to the LED cavity and recycled, leading to an
increased brightness.
With this method a collimator has been designed and made that is only 1mm thick, with a diameter of 6.5mm. It creates a
beam of 26deg Full Width at Half Maximum. Presently, collimators with these characteristics have a thickness of 10-20mm and a diameter of 20-30mm and require careful mounting and alignment. The new collimator contains a
4.5micron thick interference filter made of 54 layers of Nb2O5 and SiO2 layers. The filter is optically coupled to the LED
with Silicone adhesive which makes the configuration very robust. A cylindrical lightguide, tapered from 6.5mm to
2.5mm diameter and 1mm thick captures the light that passes the filter, folds the light path and redirects the beam.
Measurements on collimator prototypes show good agreement with the designed characteristics. This promising
approach enables much more compact collimators optics that offer material cost savings and design freedom.
A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light
guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Largeangle
emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be
as thin as 0.3mm for an LED of 1x1mm2, and the best coupling efficiency is estimated to be around 80%. With this
approach, a backlight system can be greatly simplified but also compact collimators can be realized. In this paper the
optical design and testing of the filter is described, and a 1mm thick, 6.5mm diameter collimator is presented that emits
in a cone of 2×13°. Measurements on prototypes show good agreement with the designed characteristics.
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