Fig. 3: Single-pulse (SP) fifth harmonic generation reveals the non-perturbative regime and high damage thresholds of resonant metasurfaces.

a A setup for SP-HHG back focal plane (BFP) imaging. Single pulses from an optical parametric amplifier (OPA) pass through a mechanical shutter, split into the main beam (sample irradiation) and the pick-off beam (individual pulse power calibration). The diffracted harmonics are collected by an objective lens with a numerical aperture of NA = 0.42 and detected in the BFP configuration by triggered camera exposure. b A typical BFP image of the H5 from the resonant sample at non-destructive intensities. c Zeroth diffraction order intensity of the H5 as a function of MIR pump intensity for five different metasurfaces with resonances at \({\lambda }_{{\rm{res}}}\), from the farthest from (blue circles) to the closest to (purple triangles) the driver wavelength. Solid lines: best fits to the power law \({I}^{(5)}=a{I}^{b}\). Deviation from the expected \({I}^{(5)} \sim {I}^{5}\) indicates the saturation of nonlinear response. Inset: power exponent \(b\) vs. resonance wavelength \({{\rm{\lambda }}}_{{\rm{res}}}\). The mask damage threshold and the metasurface damage threshold are shown for the most resonant metasurface \({\lambda }_{{\rm{res}}}={\lambda }_{{\rm{res}}}^{(0)}=\lambda\).