Ultrasensitive, Room Temperature Detection of THz Radiation Using Nonlinear Parametric Conversion

We demonstrate ultrasensitive, room temperature optical detection of terahertz by using nonlinear parametric upconversion. Terahertz radiation is mixed with pump light at 1550 nm in quasi-phase-matched GaAs crystal to generate an optical sideband or idler wave that is coupled into optical fiber and detected using a Geiger-mode APD. The resulting terahertz detector has a noise equivalent power of 78 fW/Hz^1/2 with a timing resolution of 1 ns.