Gas bubbles in liquids are important in biomedical applications such as ultrasound imaging, drug release, or photothermal therapy. We create vapor nanobubbles in liquids around laser-heated gold... Show moreGas bubbles in liquids are important in biomedical applications such as ultrasound imaging, drug release, or photothermal therapy. We create vapor nanobubbles in liquids around laser-heated gold nanoparticles and investigate their time-dependent properties using optical techniques. Vapor nanobubbles can show explosive behavior on the (sub-)nanosecond (10^-9s) time scale, even under continuous heating. They are highly sensitivity to acoustic pressures. From our study, we conclude that vapor nanobubbles are very interesting systems for fast all-optical light modulation and for nanoscale acoustic-wave sensing. Conjugated polymers are important organic materials in organic light emitting diodes, thin-film transistors, solar cells, or as chemical sensors. We use photothermal microscopy to study the optical absorption of single conjugated polymer molecules (MEH-PPV). Immersing the molecules in supercritical xenon as the photothermal transducing medium, we detect single conjugated polymer molecules via their absorption, and correlate this signal with photoluminescence. We measure the number of monomers in individual polymer chains and the apparent quantum yield of single conjugated molecules. The information provided by our technique will generate a better understanding of trapping and non-radiative deactivation channels of optically-induced excitations in conjugated polymers and thus facilitate the design and optimization of devices based on this important class of materials. Show less
We study the technique of photothermal microscopy by which we can detect single nano-objects by their absorption at room temperature. We optimize the sensitivity of this technique and demonstrate... Show moreWe study the technique of photothermal microscopy by which we can detect single nano-objects by their absorption at room temperature. We optimize the sensitivity of this technique and demonstrate the first optical detection of a single molecule by its absorption at room temperature. Moreover, we combine photothermal, luminescence and scattering of individual nano-objects (organic dye nanoparticles and gold nanoparticles) at single-particle level to gain insight into their radiative and nonradiative properties. Single organic nanoparticles exhibit a complex excitation power-dependent luminescence quantum yield due to singlet-singlet or singlet-triplet annihilation, and their luminescence quantum yield can be as high as 10^(__2). In contrast to organic dye nanoparticles, gold nanoparticles yield very stable optical signals. Gold nanoparticles are also easily detectable by their photoluminescence. We find that the luminescence quantum yield of single gold nanoparticles is nearly independent of their volumes and can be as high as ~10^(-5) for nanorods with a plasmon resonance of ~650 nm. We further investigate the sensitivity of a single gold nanorod to an approaching dielectric surface. We show that the nanorod exhibits significant red-shift in its plasmon resonance wavelength for distances less than 400 nm pointing the way towards the possible application of nanorods as distance sensors. Show less
