A method for nonlinear-optical calibration of the terahertz wave spectral brightness

Experimental results are presented for the detection of 0.22 THz radiation from a frequency-doubled impact ionization avalanche transit-time (IMPATT) diode. A procedure is discussed for standard-less measurement of the terahertz wave spectral brightness. The method is based on the use of spontaneous parametric down-conversion of light under the nonlinear-optical detection of terahertz wave radiation.