Terahertz Generation in Nonlinear Crystal Powders

Optical rectification (OR) and second harmonic generation (SHG) are second-order nonlinear optical processes that can occur simultaneously when an intense electromagnetic wave interacts with a noncentrosymmetric material. Specially, OR has been used to generate terahertz (THz) waves and SHG for laser frequency conversion. In both cases, bulk crystals are generally used as nonlinear media. In SHG, however, powder crystals have also been employed. In contrast, this has not been confirmed either experimentally or theoretically for the case of OR. Thus, we propose and present here for the first time, the feasibility of generating THz signals by OR in tablets specifically made from powdered sugar. Experimental results obtained with a THz time domain spectrometer reveal that the polarization of the generated electromagnetic field is linear. They also showed, in the best case, a signal with a spectrum extending up to 3 THz with a dynamic range of 40 dB. These findings were validated by a proposed theoretical model.