Highly sensitive multi-stage terahertz parametric detector.

In this Letter, we developed a high-sensitivity multi-stage terahertz (THz)-wave parametric detection system that operates at room temperature. This detection system has high sensitivity over a wide wavelength range through upconversion of a THz wave to near-infrared light. The broadband noise associated with parametric generation limited the detection sensitivity in the previous setup; however, in the multi-stage configuration using multiple crystals, the THz parametric detection sensitivity was improved by spatially eliminating the broadband noise using an iris between the former and latter stages. With this improvement, the minimum detectable sensitivity at 1.05 THz approached 130 zJ (=10), which is equivalent to 90 photons or less. Furthermore, by combining this detector with an injection-seeded THz-wave parametric generator, which is a high-power, tunable THz-wave source, the THz-wave measurement system achieved a maximum dynamic range of 125 dB.