A cross-correlation spectroscopy in subterahertz region using an incoherent light source

A subterahertz (sub-THz) spectroscopic system using a multimode laser diode and photoconductive antennas (PA) has been proposed. It employs a random fluctuation of the light intensity to produce the subterahertz radiation from the emitter PA and also to trigger the detector PA. The signal is obtained as the cross correlation between the sub-THz radiation amplitude and laser light intensity. The decrease in the amplitude and phase delay of the radiation due to transmission from a sample can be calculated from the signal in a broad spectral region of sub-THz. This system is applied to the measurement of the complex refractive indices of Si wafers. The obtained dispersion of the refractive indices is well explained by the Drude model.