Nonlinear and Extreme Photonics at the Fraction of a Wavelength

Metals and high index dielectrics pave the way for manipulating light well below the diffraction limit. By squeezing light at the fraction of a wavelength new opportunities for nonlinear and high-intensity photonics emerge. Firstly, I will present a first demonstration of nonlinear light generation in van der Waals 3R-MoS₂ metasurfaces. Bulk 3R-MoS₂ owing to its asymmetric layered nature and unique electronic band structure exhibits high second order nonlinearity. I will show that 3-R MoS₂ metasurfaces allow for efficient phase mismatch-free generation of second harmonic with over 150-fold enhancement in less than 100 nm thick structures when pumped below bandgap. I will further discuss a three-fold interplay between excitonic-driven enhancement of light generation, optical extinction, and structural resonances. Conditions for efficient second harmonic generation will be outlined. Secondly, I will present our study of high intensity light interaction with nanoplasmonic structures. As light intensity increases, a range of non-equilibrium phenomena at different time scales emerge. I will show that plasmonic nanostructures are ideally suited for creating structured solid-density plasmas for taming high intensity femtosecond beams. Detailed particle-in-cell time-resolved study of high-energy femtosecond pulse coupling with nanostructures with subsequent excitation of plasmons and energetic electron clouds will be presented. Spill-out of electrons outside of nanostructures, plasmon decay rate, generation of highly energetic electrons will be discussed. For high energy nanosecond pulses light-materials interaction is even more complex and involves materials heating and phase transitions. In particular, I will show that resonant nanostructures allow controlling time-resolved dynamics of photo-thermal interaction, as well as controlling phase transitions.