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 combine optical trapping and far-field optical detection techniques in a novel approach to study single metal nanoparticles in solution. We demonstrate the first measurements of the acoustic... Show moreWe combine optical trapping and far-field optical detection techniques in a novel approach to study single metal nanoparticles in solution. We demonstrate the first measurements of the acoustic vibrations of single gold nanoparticles optically trapped in water, and find evidence for intrinsic damping mechanisms. Additionally, we explore the potential of single gold nanorods as ultra-small mechanical actuators: we quantify the optical forces and torques on a single trapped gold nanorod (25 nm diameter and 60 nm length) and show that the rod can simultaneously exert forces and torques that would be large enough to manipulate single (macro-) molecules. We developed techniques to measure the combined translational and rotational Brownian motion of a trapped nanorod. We determine the rod's heating by the trap beam and show that translational and rotational Brownian motion of a hot particle are described by different effective temperatures and viscosities. Show less
