Spherical gold nanoparticles and SiO{sub 2}/Au core/shell microparticles under intense femtosecond laser excitation: relaxation dynamics of gold nanoparticles and nanostructuring of borosilicate glass using SiO{sub 2}/Au microparticles

This paper reports surface nanostructuring of borosilicate glass covered with a water layer and the production of ∼150 nm diameter pits using SiO{sub 2}/Au core/shell microparticles under excitation with 50 fs pulses (λ = 780 nm) using the optical scheme of an inverted microscope with a 100{sup ×}, NA = 1.4 objective. We compare the thresholds for hole formation in glass with the use of SiO{sub 2}/Au and uncoated SiO{sub 2} microparticles. The threshold is 0.7 J cm{sup -2} for SiO{sub 2}/Au and 2.9 J cm{sup -2} for SiO{sub 2} microparticles, which coincides with the threshold for nanostructuring by a focused femtosecond pulse without microparticles: 3 J cm{sup -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 SiO{sub 2}/Au has been determined to be 0.06 mJ cm{sup -2}, which is a factor of 30 lower than the bubble formation threshold in the case of uncoated SiO{sub 2} microparticles. (nanostructures)