Near Field Enhanced Nanoplasma Formation around Gold Nanoparticles Irradiated by Off-Resonance Femtosecond Laser and its Application as Durable Nanolens for Cavitation

Michel Meunier Dept of Engineering Physics, Polytechnique Montreal, Montreal, Canada Christos Boutopoulos Dept of Engineering Physics, Polytechnique Montreal, Montreal, Canada Ali Hatef Dept of Engineering Physics, Polytechnique Montreal, Montreal, Canada Remi Lachaine Dept of Engineering Physics, Polytechnique Montreal, Montreal, Canada

Plasmonic nanoparticles (NPs) can lead to extreme confinement of the light in the near field. This unique ability can be used to generate nanobubbles when plasmonic nanoparticles are immersed in a liquid. Irradiating a plasmonic nanoparticle at the plasmon peak could lead to nanocavitation but also to the deformation and even fragmentation of the nanoparticles due to the strong energy absorption by the NPs. In this work, we demonstrate experimentally and theoretically that 100 nm AuNPs irradiated by off-resonance femtosecond (fs) (λ = 800 nm), can act as durable nanolenses in liquid and provoke nanocavitation while remaining intact because of the low energy absorption. The irradiation of the AuNP by the off-resonance femtosecond laser leads to the production of an optical breakdown in the liquid and nanoplasma formation around the NP due to the near field enhancement [1,2,3]. We have employed combined ultrafast shadowgraphic imaging, in-situ dark field imaging and dynamic tracking of AuNP Brownian motion to ensure the study of individual AuNPs/nanolenses under multiple fs laser pulses. Using this approach we demonstrate that 100 nm AuNPs can generate multiple, highly confined (radius down to 550 nm) and transient (life time < 50 ns) nanobubbles. The important role of the near field enhancement in the nanocavitation mechanism was further confirmed by investigating its effect when using AuNPs of various sizes (30 nm to 210 nm). The experimental results have been correlated with theoretical modeling [1,3] to provide an insight to the AuNP-safe cavitation mechanism as well as to investigate the deformation mechanism of the AuNPs at high laser fluences. These durable nanolenses are of significant importance for future development of AuNP-assisted laser nanosurgery and theranostic applications [4].

[1]E Boulais, R Lachaine, M Meunier, Nano letters 12 (9), 4763-4769 (2012)

[2] R Lachaine, E Boulais, M Meunier, ACS Photonics 1 (4), 331-336 (2014)

[3] E Boulais, R Lachaine, A Hatef, M Meunier, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 17, 26-49 (2013)

[4] J Baumgart, L Humbert, É Boulais, R Lachaine, JJ Lebrun, M Meunier, Biomaterials 33 (7), 2345-2350 (2012)

michel.meunier@polymtl.ca









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