Ultrafast detector senses both near-IR and terahertz pulses

By John Wallace
Senior Editor

http://www.laserfocusworld.com/articles/print/volume-49/issue-09/newsbreaks/ultrafast-detector-senses-both-near-ir-and-terahertz-pulses.html

A photodetector has been created that responds with precise timing to both near-IR and terahertz radiation. Developed by researchers at the University of Erlangen-Nuremberg, Technical University Dresden, and Helmholtz-Zentrum Dresden-Rossendorf (all in Germany) and the University of California, Santa Barbara, the detector is designed for simultaneously resolving optical and terahertz pulses for terahertz-pump/optical-probe experiments, as well as characterizing high-peak-power (30 kW) terahertz pulses.

The field-effect-transistor (FET)-based detector has an area of 345 μm2 and is located on the flat of a plano-convex silicon lens; near-IR light accesses the device directly through air, while terahertz radiation is incident from the opposite direction and is sensed after being focused through the lens. (In an alternate configuration, both near-IR and terahertz light are incident from the same direction in free space on a device with an area of 1.17 mm².) Terahertz radiation from 0.24 to 4.9 THz was detected with a detection time constant of shorter than 30 ps, while the time constant for near-IR light (pulses emitted by a Ti:sapphire laser) was 150 ps. The smallest dimensions of the FET devices were quite large at 3 μm, allowing easy fabrication. The detectors can be used in either pulsed or continuous-wave tabletop experiments. Contact Sascha Preu at sascha.preu@physik.uni-erlangen.de.