Free-space electro-optic sampling system achieves 37-TH¥bandwidth
Rensselaer Polytechnic Institute (RPI; Troy, NY) researchers demonstrated a free-space electro-optic sampling system capable of detecting frequencies u¥to 37 THz. Based on zinc telluride (ZnTe), the device essentially operates from the thermal infrared to the millimeter-wave regions. Prior to this work, which is described in CLEO `97 paper #CPD3, the record for coherent detection of free-space terahert¥radiation was 7 THz. Availability of detection u¥to 37 TH¥opens the door for coherent spectroscopy systems.
The RPI sampling system is based on the Pockels effect. A modelocked Ti:sapphire laser pumps a gallium arsenide target with 350-mW, 12-fs pulses at around 800 nm, producing broadband terahert¥radiation. An optical probe pulse train from the Ti:sapphire laser travels collinearly with the terahert¥output to interact simultaneously in the 20-µm-thick ZnTe crystal. The terahert¥beam induces a refractive-index shift in the crystal, and a pair of balanced photodiodes captures the effect of this modulation on the probe pulse. The time-domain waveform of the terahert¥pulse is mapped by varying the delay between pum¥and probe pulses. This technology has been licensed to Molecular Optoelectronics Corp. (Watervliet, NY), which is developing a commercial coherent terahert¥spectroscope for laboratory applications.