Main > A1. CORP. INDEX. O-Om > Oklahoma State University/P > 2005. 10.03.2005. (THz Spectroscop)

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R. Alan Cheville, an associate professor of electrical and computer engineering at Oklahoma State University, Stillwater, described a device known as a photoconductive antenna, which provides an alternative method for generating and detecting THz light. The device consists of an undoped wafer of GaAs that has been patterned lithographically with a pair of long, parallel electrodes separated by some 80 mm. Applying a voltage across the electrodes and focusing pulses from a Ti-sapphire laser in the micrometer-sized gap causes electrons that are liberated by the laser light to be accelerated across the gap. The process generates short bursts of THz light, Cheville explained.

In a similar way, a second antenna device can be used as a detector. The principle is that shining the laser pulses on a semiconductor with a fast response time stirs up photoelectrons--yet there s no flow of current in the absence of an applied voltage or electric field, Cheville pointed out. By adjusting the relative arrival times of the THz and laser pulses, however, researchers can use the electric field associated with the THz light to switch on a short-lived flow of current, which is measured by a current meter to "read" the THz pulse.

After a discussion of other aspects of THz spectroscopy, Cheville displayed a THz generator that was built by undergraduate student Lesley A. Hess. "If you want to build one of these," Cheville told attendees, "you can go to our website (http://THz_spectrometer.okstate.edu), where you ll find an illustrated tutorial with parts lists and step-by-step instructions featuring all kinds of tips and tricks."




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