Sensitive Detection of 4 THz Radiation by Nonlinear Upconversion in an Organic Crystal BNA

Parametric upconversion of terahertz (THz) to near-infrared (NIR) frequencies has been explored as an alternative method for sensitive detection of THz radiation at room temperature [1]–[3]. Here we use this technique to detect THz pulses centered at 4 THz with N-benzyl-2-methyl-4-nitroaniline (BNA), an organic nonlinear crystal with a relatively high second-order nonlinear susceptibility <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\chi^{(2)})$</tex> [4], [5].