Excitation of metal nanoparticles with sub-picosecond laser pulses causes a rapid increase in the lattice temperature, which can impulsively excite the phonon modes of the particle that correlate with the expansion co-ordinates. The vibrational periods depend on the size, shape and elastic constants of the particles. Thus, time-resolved spectroscopy can be used to examine the material properties of nanometer sized objects. This article will provide a brief overview of our recent work in this area of research, specifically, how the vibrational modes observed in the experiments are assigned and what information can be obtained from the measurements. Our work has mainly been concerned with noble metal particles (gold and silver) in aqueous solution. The different shapes that have been examined include spheres, rods and triangles, all with different sizes.
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