ADMEP · Dynamics of femtosecond laser ablation of trapped dielectric and metallic nanoparticles

Dynamics of femtosecond laser ablation of trapped dielectric and metallic nanoparticles

In many applications in research, industry and healthcare, pulsed lasers are used to cut, remove or deposit material. In even more extreme examples, pulsed lasers are used to trigger nuclear fusion or more practically, to generate EUV light for a new generation of lithography machines. What all the above processes have in common is that so much energy is deposited in the target that its optical properties change during an individual laser pulse. Thus, to predict/optimize the energy absorption in this regime, one needs to understand the complex interplay between the laser and the dynamically changing material. The ADMEP project aims to theoretically and experimentally study the dynamics of the material properties in nano- to micro-scale particles and their influence on the optical properties upon irradiation with femtosecond (1 fs = 10-15 s) laser pulses. By using fs-laser pulses, we can ensure that the shape of the particle does not change during the pulse interaction, allowing us to focus on studying mainly the carrier dynamics of the particle. To isolate the effects of the dynamics of the carrier density and temperature from the effects of their spatial inhomogeneity, we perform experiments on small spherical nanoparticles. For small enough spheres, the transient material properties can be assumed to remain homogeneous inside the particles. Hence, they are the ideal platform to investigate the transient material properties while interacting with fs-laser pulses. The objectives of the project involve the study of nanoparticles in three different scenarios in order to address specific questions: • Influence of the laser-induced carrier density on the scattering cross-section of small spherical nanoparticles under ablation conditions. • Scattering and absorption by microparticles under ablation conditions. • Plasma dynamics of trapped nanoparticles upon fs-laser irradiation. Main outputs: • We have designed and built a working experimental apparatus that allows us to study the interaction dynamics of fs-laser pulses with levitating nanoparticles. In this way we have studied the ultrafast optical response of single gold nanoparticles upon fs-laser irradiation and its laser-induced evaporation. • We have developed a method that combines a theoretical model with a numerical algorithm that successfully predicts the dynamics of the energy deposition of femtosecond laser pulses in dielectrics under tight focusing conditions. We have benchmarked this method by studying the transient optical properties of a laser-induced electron plasma micro-disk in water.

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