Sensitive mid-infrared detection in wide-bandgap semiconductors using extreme non-degenerate two-photon absorption

Identifying strong and fast nonlinearities for today’s photonic applications is an ongoing effort1. Materials2–5 and devices6–9 are typically sought to achieve increasing nonlinear interactions. We report large enhancement of two-photon absorption through intrinsic resonances using extremely non-degenerate photon pairs. We experimentally demonstrate two-photon absorption enhancements by factors of 100–1,000 over degenerate two-photon absorption in direct-bandgap semiconductors. This enables gated detection of sub-bandgap and sub-100 pJ mid-infrared radiation using large-bandgap detectors at room temperature. Detection characteristics are comparable in performance to liquid-nitrogen-cooled HgCdTe (MCT) detectors. The temporal resolution of this gated detection by two-photon absorption is determined by the gating pulse duration.