LECTURER: Prof. Hamed Merdji, CEA Saclay

TIME: 18.10.2017 /WEDNESDAY/ 18:40



We will present recent results in strong laser field science and nanoplasmonics. Our research is at the frontier of two large and highly successful fields of modern research: ultrafast science and nanoscale physics. On the one hand, ultrafast science produces and analyses the electronic motion at the shortest space (sub-nm) and time scales (attoseconds, with an unprecedented control of the atomic or molecular nonlinear response. On the other hand, nanoscale research opens new routes in extreme optics, from the low to the strong field regime. By bringing together ultrafast laser-matter interactions and nanophysics, We have discovered new routes in boosting the non-linear response using nanostructured photonic crystals. This is a very vast domain of research that encompasses all sorts of nano-objects, as well as meta-materials whose structure can be engineered so as to display some particular electromagnetic properties. Plasmonics is a very fast growing field which already finds practical applications in numerous aspects of day to day life. An incident laser field, coupled with ad hoc resonant structures, can excite surface plasmons, i.e. charge oscillations at the interface between a metal and a dielectric.

By carefully shaping the metallic structure at the nanometre scale, it is possible to manipulate those oscillations, in order for instance to locally enhance by several orders of magnitude the strength of the electromagnetic field radiated by the oscillation of the charges. While this effect has been applied to multiple nonlinear optics processes (like second harmonic generation, four wave mixing), the extension to HHG has been hampered by two main factors. First the low damage threshold of metallic nanoparticles at IR and mid-IR wavelengths. Second, a difficulty in designing appropriate large amplifying volume resonant structures. Indeed, the bowtie geometry that has been mostly used up to now, while offering a very high localized field enhancement (by up to 3 orders of magnitude), presents nm3 scale volume. We will present two strategies to increase the field enhancement volume by 3 to 6 orders of magnitude. Using our novel “nano-amplifiers”, we have observed the amplification of high harmonic generation from infrared1 and mi-infrared2 laser-crystal interaction by up to 2 orders of magnitude. Our results open the way towards strong field physics at high repetition rates with low cost small scale femtosecond lasers (oscillators, fibre lasers). Potential applications range from nanoscale imaging, efficient storage and transfer of information to nanoplasmonics (optical filters, waveguides), novel photon and particle sources, and even biomedical sciences.

1. Rana et al, submitted to Scientific Reports
2. Franz et al. submitted to Light Science and Applications. arXiv:1709.09153

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