Ultrafast nano-photonics science is emerging thanks to the extraordinary progress in nano-fabrication and ultrafast laser science. Nanotechnology enables the engineering of photonic structures at the nanometer scale for enhancing light-matter interaction, exploited in photonic applications.
Our research is motivated by the novel fundamental processes occurring while a semiconductor is submitted to a strong laser field. Electrons start to oscillate in coherence and are accelerated by the laser in the Brillouin zone. After recombination, high order harmonics are emitted, carrying precious information about the fundamental process[1]. Strategies to boost and control these coherent phenomena are of recent focus[2,3].
We propose new routes to boosting the non-linear response using nanostructured photonic crystals. We demonstrate field amplification through light confinement in ZnO nano-structured 3D waveguides. Using our novel “nano-amplifiers”, we have observed the amplification of high harmonics from mi-infrared laser-crystal interaction by up to 2 orders of magnitude. Compared to previous works[3], we extend enhancement of high harmonic to the highly non-perturbative regime. Amplification of up the 15th harmonic order is reported[4].
Nanostructuring semiconductors makes it possible to control the properties of the generated high-harmonic light. We will present strategies to manipulate the orbital angular momentum of light.
Finally, we investigate high harmonic generation in 2D semiconductors. High harmonic generation from graphene on substrate has been reported very recently[5]. Here, we report for the first time on the generation of high harmonics from free-standing graphene. We study the laser polarization dependence of the harmonics to reveal the impact of the band-gap opening induced by the substrate.

[1]: Ghimire, S. et al., Nat. Phys. 7, 138–141 (2011).; Luu, T. T. et al., Nature 521, 498–502 (2015); Sivis, M. et al., Science 357, 303–306 (2017); Ndabashimiye, G. et al, Nature 534, 520–523 (2016).
[2]: Han, S. et al., Nat. Commun. 7, 13105 (2016); Vampa, G. et al., Nat. Phys. 13, 659–662 (2017).
[3]: Sivis, M. et al., Science 357, 303–306 (2017).
[4]: Franz et al., submitted to Science Advances, arXiv:1709.09153
[5]: Naotaka Yoshikawa, Tomohiro Tamaya, Koichiro Tanaka, Science 356, 736–738 (2017).