From Thermo- to Plasma-Mediated Ultrafast Laser-Induced Plasmonic Nanobubbles

The laser-induced generation of vapor bubbles around gold nanoparticles (AuNPs) is a promising diagnostic and therapeutic avenue for various pathologies. The physical mechanism that leads to their formation strongly depends on the time regime of the irradiation. While the plasmonic nanobubbles induced by nanosecond and picosecond laser pulses are known to be triggered by the energy that is absorbed in the nanoparticles and diffused in the medium (thermo-mediated cavitation), we show that a different plasma-mediated mechanism occurs in the case of femtosecond pulses. In this paper, we present experimental evidence that the dimensions of laser-induced bubbles depend on the polarization of the incident laser pulse when the pulse duration is reduced below similar to 1 ps. This result cannot be explained by the standard thermo-mediated cavitation process and, thus, reveals the onset of a new mechanism in the ultrafast regime. We further show that the discrepancy between the dimensions of bubbles generated from linearly and circularly polarized laser pulses can be explained using a simple model, revealing the polarization cavitation dependence as a clear signature of the plasma mechanism. This paper presents in detail the transition between both cavitation regimes and provides insight into the precise control of the cavitation dynamics at the nanoscale.