Fig. 3: Simulated THG efficiency in THz QCL pumped SLG-CSRR.
a Field enhancement in SLG-CSRR as a function of frequency, for different resonator array quality factors (Q), representing the SLG-CSRR absorption normalized by AG. Different colors correspond to Q = 75 (purple), 48 (blue), 13 (red), 6 (black). b AG0 and AG3 (right axis) calculated as the ratio between average optical field in- and out-side of the SRR gap, extracted from the FEM simulation for the fundamental (black) and third harmonic modes (gray), shown alongside the respective Q (left axis) labeled as Q0 (red) and Q3 (blue), as a function of SRR array period. c Electric field on SLG-CSRR as a function of frequency, obtained from the convolution of the field enhancement of a) and the optical beam intensity in the inset of c, assuming 1 W total emission power focused on a 700 μm diameter circular spot, whose frequency distribution is shown in the inset, for different Q. The color code is the same as in panel a. Inset: d Electric field, calculated at the fundamental frequency (red dots) in SLG-CSRR and SLG (no SRR, blue star), as a function of Q, corresponding to the p values of b. e, f Normalized transmittance variation as a function of frequency, ΔT/T0 (ν), in the pumped SLG-CSRR, assuming an incident effective electric field as in c, following Eq. (3), at the fundamental QCL frequency ν0(d), and at 3ν0 (e), for different Q values (same code as in a). g THG efficiency, defined as ΔT/T0 (3ν0) in the SLG-CSRR, as a function of impinging electric field (bottom axis) and total power (top axis), assuming an incident beam diameter of 700 μm, calculated at different Q (same color code is the same as in a).
