Efficient THz-to-NIR upconversion detection for quantum-level THz detection
We demonstrate room-temperature terahertz (THz) detection schemes that combine parametric upconversion and engineered photonic structures to achieve ultrahigh sensitivity. Using a GaP nonlinear crystal, we detect THz pulses with energies as low as 1.4 zeptojoules (~1.5 photons per pulse) at 2 THz when averaged over jus...