Low Efficiency of Laser Heating of Gold Particles at the Plasmon Resonance: An X-ray Calorimetry Study

Laser excitation of nanoparticles provides an appealing tool for particle engineering as well as nanoscale-localized photothermal material modification. In the case of plasmonic nanoparticles like gold, mostly on-resonant excitation is used as it appears to be the most efficient channel for laser heating. Yet, as will be shown in this paper, in the case of an excitation with picosecond pulse duration a drastic reduction of the energy uptake efficiency of gold nanoparticles is observed at on-resonant excitation with 532 nm compared to interband excitation at 400 nm. This observation is found irrespective of varied gold nanoparticle size or different synthesis methods. Based on the nanocalorimetry of laser-excited suspended gold nanoparticles with time-resolved X-ray scattering the transient particle temperature, heat-induced relaxation and particle expansion and nonreversible particle transformations were disentangled. At first glance, the lower heating efficiency appears related to ultrafast plasmon bleaching and its recovery in the picosecond range. Yet, following a caloric heat balance a significant residual dissipation channel remains in the case of on-resonant excitation, which is absent at interband excitation. Consequently, photothermal applications may suffer from lower heat generation at the expense of irreversible channels.