Chirped optical beam electro-optically measures terahertz pulses

A group at Rensselaer Polytechnic Institute (Troy, NY) has used a linearly chirped optical probe pulse in a free-space electro-optic detection system to measure the temporal waveform of a terahertz pulse and has demonstrated a single-shot (single pulse) coherent measurement of such a pulse. X.-C. Zhang and Zhiping Jiang copropagated a chirped optical probe pulse (820 nm and 30 ps long) and a terahertz pulse through a zinc telluride (ZnTe) crystal. Polarization of different spectral components of the chirped pulse was rotated by a different portion of the terahertz pulsed field by the Pockel's effect. Using an optical analyzer, the polarization modulation was converted to the amplitude modulation, and a grating-lens combination was used to disperse and focus the collimated probe beam on a linear diode array (which had 1024 pixels). By measuring the spectrum difference of the probe beam with and without pulsed electromagnetic field modulation, a temporal measurement of the terahertz waveform was obtained without a moving element (such as a mechanical translation stage) for the time delay. This differential distribution reconstructs both amplitude and phase of the terahertz pulse.