Individual Nanoflakes of Two Dimensional Materials Harmonic Generation with Ultralow Pump Power

Two dimensional materials with nonlinear optical response are of interest for bioimaging and optical information processing. However, achieving a measurable second order nonlinear signal in thin films and two dimensional materials has relied on using pulsed lasers and intense optical focusing, which limits potential applications require nonlinear response by using low laser power or from nanoscale materials. Here we achieved second harmonic generation from nanoflakes of two dimensional materials with lateral size smaller than the diffraction limit by using a double nanohole plasmonic optical tweezer with a low-power continuous-wave laser. The plasmonic double nanohole aperture enhances the local field intensity and allows for single nanoflake trapping and significant second harmonic generation at the nanoscale. The two dimensional property of nanoflakes allows for positioning in an area with high local field intensity and achieving higher nonlinear response than bulk nonlinear nanoparticlesWe observed an increase in second harmonic generation power two orders of magnitude higher than. other bulk materials such as lithium niobate nanoparticles. This allows for having strong nonlinear generation at the nanoscale for applications such as subwavelength nonlinear imaging or information processing.