Physics Seminar: "New THz Photoconductive Sources Driven at 1550-nm: by E.R. Brown

"New THz Photoconductive Sources Driven at 1550-nm"

Friday, September 26
3:00pm in 204 Fawcett Hall

by: E.R. Brown, Departments of Physics and Electrical Engineering at Wright State University

Perhaps the biggest breakthrough in the THz field during the past 20 years has been the advent of ultrafast semiconductor materials having ultrafast (< 1 ps) electron-hole recombination time and therefore the ability to generate useful levels of THz radiation by laser-excited switching and photomixing. The leading material for this advancement has been low-temperature-grown (LT) GaAs, and the laser technology has been Ti:sapphire mode-locked lasers (for switching) or GaAs-based single-frequency diode lasers (for photomixing), both emitting between 750 and 800 nm. The photonductive mechanism is generally ultrafast intrinsic photoconductivity. This seminar will summarize recent work by our group to develop GaAs-based THz sources driven at 1550-nm where laser sources are much more affordable and easy to integrate into systems large because of devices and components from the 1550-nm fiber-optic telecommunications industry. The mechanism for THz generation in GaAs at 1550-nm is attributed to ultrafast extrinsic photoconductivity. The understanding of this mechanism requires several topics in solid-state physics, including electron transport in metallic-dopant impurity bands, strong sub-band gap radiative absorption by such impurities, strong electron capture cross sections to produce ultrafast lifetime, and of course THz qualification by fabrication and characterization of real devices embedded in planar antennas.