# Dr Alberto Perez

To achieve this purpose, we explore the possibility of use a cheap material like single doped silicon and germanium to triple THz radiation from 1.7 to 5 THz (which is available from Quantum Cascade Laser diodes). The presence of the dopants modifies substantially the optical properties of the semiconductors, generating large nonlinear coefficients at THz frequencies. Samples of bismuth doped silicon and phosphorus, arsenic and antimony doped germanium has been characterised using frequency-domain and time-domain spectroscopy, and finally the optical nonlinear coefficient of Si:Bi has been measure by a Four Wave Mixing (FWM) experiment. We have found that the nonlinear susceptibility $\chi^{(3)}$ of Si:Bi at resonance is the highest ever reported for a bulk material.