Fig. 5: Emission spectra of a semi-infinite planar slab made of SiC with a time-varying susceptibility externally perturbed under a time-harmonic modulation (Ω = 1.5 THz and δχ = 0.025).

At finite temperature (T = 300 K), thermal emission spectra display remarkable differences depending on the regime in which one perform the measurement: a far-field (100 μm); b intermediate-field (1 μm); c near-field (0.1 μm). The physical features brought about by the time-modulation lead to an enhancement of the emission spectra in the ENZ frequency regime (noticing their shift due to the modulation), which results as a direct consequence of the non-local character of the current density correlations in time-varying media. This enables a mechanism for overcoming the black-body spectrum in the far-field (dashed black curves), as well as for connecting near-to-far field radiation effects. Likewise, the spectra at T → 0 K show the potential of time-modulation to produce dynamical vacuum amplification effects at the same time that reveal the quantum nature of the ENZ-induced strong releasing of radiation.