Terahertz Generation in Non-linear Crystal Powders

Optical rectification (OR) and second harmonic generation (SHG) are second-order non-linear optical processes that can occur simultaneously when an intense electromagnetic wave interacts with a non-centrosymmetric 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 non-linear 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 terahertz time domain spectrometer (THz-TDS) reveal that the polarisation 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.