Asynchronous Optical Sampling for the Investigation of Noble Metal Nanoparticles: Vibrational Dynamics and Heat Dissipation Studies

In this thesis, I will describe the technique of Asynchronous Optical Sampling and its use in a variety of experimental spectroscopic methodologies, as well as the results and theories both of and behind these experiments. The primary investigations are focused on the acoustic vibrations of gold nanoplates. These vibrational modes are launched at both external and internal boundaries intrinsic to the systems being investigated. For measurements on single structures, the lifetimes of the modes provide invaluable information about the dissipation of the energy in the systems into the environment. Accurate lifetime measurements prove a considerable challenge in conventional ultrafast experiments that rely on mechanical delay stages, something ASOPS avoids in its entirely due to its unique configuration. ASOPS uses a piezo stage internal cavity to regulate its repetition rates, simulating an effect functionally identical to using a mechanical delay stage to change the beam path. Without the influence of the delay stage the measurements are completed on a time scale an order of magnitude shorter than previously with many more points than can feasibly be measured with the traditional technique. Using ASOPS in this manner the acoustic resonance of the gold nanoparticles was able to not only be investigated but also the heat dissipation of nanowires into a variety of environments. Additionally, ten nanoseconds of temporal range are afforded to the ASOPS technique were with the delay stage that would be equivalent to ten feet of bench space and many hours per scan for any reasonable amount of averaging, completely sidestepped by the variable repetition rates of ASOPS. This temporal range allows for a complete examination of the oscillation from the nanoparticle being investigated. The technique has also been utilized by my group to investigate the energy dispersion of nanowires into a series of environments that provide incredible insight into the mechanisms of the heat dissipation. ASOPS proves itself exceedingly useful in these and similar studies and this thesis will detail the initial results and examinations of that utility in a pump probe spectroscopic setting, with a focus on vibrational dynamics of gold nano particles and heat dissipation in nanowires.