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 effort(1). Materials(2-5) and devices(6-9) 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.