Optical Microscopy and Spectroscopy of Single Molecules and Single Plasmonic Gold Nanoparticles

Physics Colloquium 19th February 2016 delivered by Professor Michel Orrit Optical signals provide unique insights into the dynamics of nano-objects and their surroundings. I shall present some of our experiments of the last few years. i) At low temperatures, single molecules present very sharp lines which enable quantum optical experiments or nanoscale probing, for example of mechanical deformations (see Fig.1). ii) Photothermal microscopy opens the study of non-fluorescent absorbers, down to single-molecule sensitivity. Combining this contrast with photoluminescence, we can measure the luminescence quantum yield on a single-particle basis. The high signal-to-noise ratio of this technique enables uses of individual gold nanoparticles for local plasmonic and chemical probing. iii) Gold nanorods generate strong field enhancements near their tips. Matching the rods’ plasmon to a dye’s spectra, we observe enhancements in excess of thousand-fold for the fluorescence of single Crystal Violet molecules. This method generalizes single-molecule fluorescence to a broad range of weak emitters. iv) We recently studied the dynamics of vapor nanobubbles created in the liquid surrounding a single immobilized gold nanosphere. We found that these nanobubbles form in an instable, explosive process before collapsing (see Fig.2). Nanobubbles can react to reflected sound waves such as those released in the explosion [5].

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The Department of Physics public lecture series. An exciting series of lectures about the research at Oxford Physics take place throughout the academic year. Looking at topics diverse as the creation of the universe to the science of climate change. Features episodes previously published as: (1) 'Oxford Physics Alumni': "Informal interviews with physics alumni at events, lectures and other alumni related activities." (2) 'Physics and Philosophy: Arguments, Experiments and a Few Things in Between': "A series which explores some of the links between physics and philosophy, two of the most fundamental ways with which we try to answer our questions about the world around us. A number of the most pertinent topics which bridge the disciplines are discussed - the nature of space and time, the unpredictable results of quantum mechanics and their surprising consequences and perhaps most fundamentally, the nature of the mind and how far science can go towards explaining and understanding it. Featuring interviews with Dr. Christopher Palmer, Prof. Frank Arntzenius, Prof. Vlatko Vedral, Dr. David Wallace and Prof. Roger Penrose."