Speaker
Description
Nonlinear frequency upconversion of terahertz (THz) radiation into the near infrared (NIR) or visible offers a highly sensitive approach to THz detection. This method is particularly appealing because it avoids the need for bulky cryogenic systems to suppress thermal background noise. Considerable effort has gone into developing nonlinear THz detection schemes, exploring a wide range of materials to improve both sensitivity and accessible bandwidth. Recent advances in organic crystals have been especially promising, since their large optical nonlinearity and favorable phase matching properties enable efficient THz to NIR upconversion at optical frequencies extending up to 25 THz.
Here, we present an approach for nonlinear frequency upconversion detection around 10 THz using the organic crystal N-benzyl-2-methyl-4-nitroaniline (BNA). The upconverted photons resulting from the interaction of a THz pulse with a near-infrared pulse in the crystal are spectrally resolved with a monochromator and detected using a commercial silicon-based single-photon detector. A polarizer, spatial filter and a spectral filter also enhance the detection sensitivity towards the single-photon level. We can accurately estimate the detection sensitivity by calibrating the measured SFG photon counts against the THz photon number extracted from standard electro-optic sampling. We further characterize the optical losses and the detector quantum efficiency to obtain the internal conversion efficiency in the crystal. Initial measurements at 4 THz show that a single THz pulse containing 60 photons can be detected with more than 50% probability. At higher THz frequencies, improved conversion efficiency is expected to further enhance sensitivity. Measurements are underway to extend the characterization up to ~12 THz. This work provides a practical route to a room-temperature, single-photon-level upconversion detection scheme near 10 THz for THz quantum optics.
| Keyword-1 | THz detection |
|---|---|
| Keyword-2 | Organic nonlinear crystals |
| Keyword-3 | Sum-frequency generation (SFG) |