Spherical gold nanoparticles and SiO2/Au core/shell microparticles under intense femtosecond laser excitation: relaxation dynamics of gold nanoparticles and nanostructuring of borosilicate glass using SiO2/Au microparticles

This paper reports surface nanostructuring of borosilicate glass covered with a water layer and the production of ~150 nm diameter pits using SiO2/Au core/shell microparticles under excitation with 50 fs pulses (? = 780 nm) using the optical scheme of an inverted microscope with a 100?, NA = 1.4 objective. We compare the thresholds for hole formation in glass with the use of SiO2/Au and uncoated SiO2 microparticles. The threshold is 0.7 J cm-2 for SiO2/Au and 2.9 J cm-2 for SiO2 microparticles, which coincides with the threshold for nanostructuring by a focused femtosecond pulse without microparticles: 3 J cm-2. Femtosecond pump ? probe spectroscopy has been used to study the relaxation dynamics of laser pulse energy absorbed in a Au nanoparticle and the dynamics of energy dissipation to the ambient medium. The threshold for cavitation bubble formation in water with SiO2/Au has been determined to be 0.06 mJ cm-2, which is a factor of 30 lower than the bubble formation threshold in the case of uncoated SiO2 microparticles.