Electro-optic effect enables free-space sampling of terahert¥beams
Free-space electo-optic probe characterization of propagating terahert¥beams has been demonstrated by researchers at Rensselaer Polytechnic Institute (Troy, NY). Unlike alternative methods such as photoconductive antennas and far-infrared interferometric techniques, free-space electro-optic sampling can provide knowledge of the entire terahert¥waveform, including both amplitude and phase. The method is based on the nonlinear coupling between a low-frequency electric field (terahert¥pulse) and a laser beam (optical pulse) in a zinc telluride (ZnTe) crystal. Modulating its birefringence by applying a polarized electric field will modulate the polarization of ellipticity of the optical probe beam passing through the crystal. The ellipticity modulation of the optical beam is then polarization-analyzed to provide information on both the amplitude and phase of the applied electric field.
Preliminary data with ZnTe probes indicate subwavelength spatial resolution, femtosecond temporal resolution (177-fs pulse duration), and 4-TH¥bandwidth. X.-C. Zhang of Rensselaer says the simplicity of the detection geometry, capability of optical parallel processing, and excellent signal-to-noise ratio (greater than 5000) make these probes suitable for real-time 2-D subpicosecond far-infrared imaging applications.