Fig. 2. Frequency-correlation between the entangled photon pair.

(A) Case of quasi-CW laser. (B) Case of pulsed laser. All panels are computed from eq. S4 in section S1. The panels on the left present the pump envelope ${\mathrm{\alpha }}_{\mathrm{p}}({\mathrm{\omega }}_1+{\mathrm{\omega }}_2)$, the panels on the middle present the phase matching function $\mathrm{\varphi }({\mathrm{\omega }}_1,{\mathrm{\omega }}_2)$, and the panels on the right are the two-photon amplitude $f({\mathrm{\omega }}_1,{\mathrm{\omega }}_2)={\text{ζα}}_{\mathrm{p}}({\mathrm{\omega }}_1+{\mathrm{\omega }}_2)\mathrm{\varphi }({\mathrm{\omega }}_1,{\mathrm{\omega }}_2)$. For clarity, panels (A) and (B) are plotted using different values of the entanglement time $T_{\mathrm{e}}$ to highlight the contrast between positive and negative frequency correlations.