Fig. 4: Wavelength-dependent time-refraction effect.
From: Broadband frequency translation through time refraction in an epsilon-near-zero material
a–e Experimentally measured maximum redshifts and blueshifts at different wavelengths λ0 as a function of peak pump intensities. f The red line denotes the fractional redshift |Δfred|/f0 as a function of probe beam’s central frequency f0 at a peak pump intensity ~450 GW cm−2. The real part of the linear permittivity Re(ε) of ITO film at the corresponding central frequency f0 is shown in the top axis. The black line shows the total fractional shift (redshift plus blueshift) measured at the maximum pump intensities before the onset of higher-order nonlinear optical effects. We find that both the maximum fractional redshift and the total shift occur near the zero-permittivity wavelength.
