Optical properties of Au colloids self-organized into rings via copolymer templates

The investigation of the Localized Surface Plasmon Resonance for plasmonic nanoparticles has opened new perspectives for optical nanosensors. Today, an issue in plasmonics is the development of large scale and low cost devices. We focus here on the Langmuir-Blodgett technique to self-organize gold nanoparticles (~ 7 nm) into rings (~ 60 nm) via polystyrene-b-polymethylmethacrylate templates. In particular, we investigated the optical properties of organized gold nanoparticle rings over large areas and report experimental evidence for plasmon resonances of both individual nanoparticles and collective modes. This paves the way for designing devices with multiple resonances in the visible-Infra-red spectrum and developing optical sensors

Nanoengineered Astronomical Optics

We describe a technology for the fabrication of inexpensive and versatile mirrors through the use of a new type of nanoengineered optical material composed by the spreading of a self-assembling reflective colloidal film spread at the surface of a liquid. These new reflecting liquids offer interesting possibilities for astronomical instrumentation. For example, they can replace mercury in conventional rotating liquid mirrors. The main advantages offered include extremely low cost and, by coating a viscous liquid, the possibility of tilting the mirror by a few tens of degrees. We also have coated ferromagnetic liquids with these reflecting films. The resulting surfaces can be shaped by the application of a magnetic field, yielding reflecting surfaces that can have complicated shapes that can rapidly shift with time. These inexpensive and versatile optical elements could have numerous scientific and technological applications. Among possible astronomical applications, they could be used to make large inexpensive adaptive mirrors exhibiting strokes ranging from nanometers to several millimeters.Comment: Submitted to Astrophysical Journal Letters. 18 pages, 4 figure

Tiltable rotating liquid mirrors: a progress report

Context.We give a progress report on tiltable, nanoengineered, rotating liquid mirrors, which were discussed in previous papers. Aims.We want to develop the technology, improve reflectivities and user-friendliness. The ultimate goal is to demonstrate high-quality liquid mirrors that can be tilted by a few tens of degrees. Methods.We coated hydrophilic liquid substrates that have poor reflectivities with a reflective layer of self-assembling metallic nanoparticles. We analyzed the wavefronts of 1-m diameter mirrors with Ronchi tests, knife-edge tests and point-spread functions (PSFs). Results.There is significant improvement over previous work where the reflecting layer was deposited on hydrophobic oils. While previous work only demonstrated tilted low-reflectivity mirrors, we now test a high-reflectivity 1-m diameter liquid mirror tilted by 45 arcmin. Conclusions.It is considerably easier to coat hydrophilic liquids than hydrophobic ones. We have reached a significant milestone by demonstrating a tilted, highly reflective, liquid mirror. Although this is still an immature technology, it is near the stage where it could be used in astronomy. The remaining technical challenges, for which we propose solutions, are not fundamental and could be overcome with additional work. This will be a worthwhile undertaking, considering the very low cost of liquid mirrors

Infrared reflection-absorption spectroscopy of thin organic films on nonmetallic substrates: Optimal angle of incidence

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Time-Scale Detection of Microemboli in Flowing Blood with Doppler Ultrasound

Small formed elements and gas bubbles in flowing blood, called microemboli, can be detected using Doppler ultrasound. In this application, a pulsed constant-frequency ultrasound signal insonates a volume of blood in the middle cerebral artery, and microemboli moving through its sample volume produce a Doppler-shifted transient reflection. Current detection methods include searching for these transients in a short-time Fourier transform (STFT) of the reflected signal. However, since the embolus transit time through the Doppler sample volume is inversely proportional to the embolus velocity (Doppler-shift frequency), a matched-filter detector should in principle use a wavelet transform, rather than a short-time Fourier transform, for optimal results. Closer examination of the Doppler shift signals usually shows a chirping behavior apparently due to acceleration or deceleration of the emboli during their transit through the Doppler sample volume. These variations imply that a linear wavel..