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Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

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Figure 11 Transmission electron microscopic images of a gold nanorods solutionwith a mean aspect ratio of 4.1 after exposure to the same energy femtosecond (a) andnanosecond (b) laser pulses. (c) and (d) are TEM images of nanoparticles produced <strong>by</strong>irradiation with high-energy femtosecond and nanosecond laser pulses, respectively.(Fig. 11b) is a ‘‘f-shape,’’ indicating only partial melting compared to thenanodots (Fig. 11a) produced <strong>by</strong> femtosecond pumping [27,57]. This comparisonleads to the conclusion that femtosecond laser pulses are moreeffective in inducing a complete shape transformation than nanosecondpulses. This observation can be explained <strong>by</strong> the fact that with femtosecondlaser pulses, the energy is rapidly absorbed <strong>by</strong> the nanorods and the meltingthen occurs after heating the lattice via electron–phonon interactions. In thecase of nanosecond pumping, cooling of nanorods (time constant f100 ps)can compete with heating induced <strong>by</strong> relatively long 7-ns laser pulses [26,27].<strong>Copyright</strong> <strong>2004</strong> <strong>by</strong> <strong>Marcel</strong> <strong>Dekker</strong>, <strong>Inc</strong>. <strong>All</strong> <strong>Rights</strong> <strong>Reserved</strong>.

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