Optical rectification for terahertz generation

The applications of terahertz-frequency electromagneticradiation are growing rapidly, driven by developments insources, detectors and optics suited to the THz-frequencyregion. Much of the advance is in the field of THz time-domainspectroscopy in which ultrashort pulses of near-infraredradiation are used in a pulse-probe arrangementto realise both the emission and detection of the THz radiation.Methods for ultrafast THz pulse generation includephotoconductivity, transient currents or optical rectification.While optical rectification has been known forsome time, earlier theoretical and experimental resultshave been limited to simple crystallographic directions.