High harmonic generation in graphene (Conference Presentation)

Graphene is a remarkable material, a monolayer of carbon atoms bonded together in a honeycomb structure that exhibits extraordinary electronic and optoelectronic properties; such as a zero band gap energy, high electron mobility and ultrahigh mechanical strength. The electronic properties of graphene can lead to nonlinear optical processes such as high harmonic generation. Here, we investigate high harmonic generation in several graphene configurations. We first report on the observation of harmonic generation in monolayer graphene on a quartz substrate. We measured up to the ninth harmonic (233 nm wavelength) from graphene of a mid-infrared femtosecond laser, whose wavelength is 2.1 µm, pulse energy around 6 nJ, pulse duration 85 fs, and repetition rate 18 MHz. Our findings confirm recent observations [1]. We then report for the first time on the observation of harmonics from free-standing graphene supported on TEM grids. Free-standing graphene, in contrast to graphene on a substrate behaves differently; mainly due to the lack of its interaction with the substrate which alters its band gap. We will present major trends of high harmonic generation dependence with laser polarization, intensity and a study on damages issues [2]. [1] Yoshikawa et al., Science 356, 736_738 (2017) [2] Nicolas et al. submitted.