Figure 4: The broadband focusing capability from visible to infrared.

(a) Characterization of the broadband focusing ability of a GO lens (a₁=3.3 μm, N=3). Both FWHM_lateral (black spheres) and focusing efficiency (red spheres) are measured over a broadband illumination of the wavelengths from 450 to 1,500 nm. The error bars on both FWHM_lateral and efficiency are determined via resampling. Theoretical predictions of FWHM_lateral (black solid line) are also presented matching well with the experimental results. Insets: Cross-sectional intensity distributions along the lateral direction captured by two CCDs operating at the visible and infrared, respectively. Different colours indicating different input wavelengths schematically. Scale bar, 1 μm. (b–d) Focusing ability of a GO lens (a₁=1.2 μm, N=3) under a white light illumination. Measured cross-sectional intensity distributions along the lateral (b) and axial (c) directions under a white light illumination. The intensity distributions along the red dashed line in b and blue dashed line in c are also plotted (red and blue spheres in d) and fitted (red and blue solid lines in d), respectively. Scale bar, 1 μm.