Softening of the symmetric breathing mode in gold particles by laser-induced heating

The symmetric breathing mode in spherical gold particles has been examined by time-resolved spectroscopy using different intensity pump laser pulses. The results show that the period of the breathing mode increases as the pump laser power increases, up to pump laser powers of 2−3 μJ/pulse. This is attributed to softening of the elastic properties of the particles due to laser-induced heating. At pump laser powers greater than ∼3 μJ/pulse the period versus intensity data flatten off. This most likely arises from saturation of the sample absorption at high pump intensities. The particles studied in these experiments were relatively largebetween 50 and 100 nm in diameter. Large particles were chosen because they have slower heat dissipation times, which means that the temperature in the particles is better defined during the course of the experiment. The particle temperatures were estimated from the laser power density, the heat capacity of gold, and the absorption at the pump wavelengthassuming that the sam...