Freely propagating terahertz pulses are usually measured by sampling techniques such as photoconductive antenna or electro-optical sampling. Although these sampling techniques provide good signal-to-noise ratios and adequate temporal resolution, they cannot be used for measurement on a single-shot basis. The present invention provides a system for measuring a terahertz frequency pulse propagating in a free-space optical path using an optical streak camera and an electro-optical modulator.
Terahertz (THz) waves occupy a segment of the electromagnetic spectrum between the infrared and microwave bands. As such, they can be used for imaging and sensing in ways that are not possible with conventional technologies such as X-ray and microwave. Because THz radiation transmits through almost anything that is not metal or liquid, the waves can see through most materials that might be used to conceal explosives or other materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks, and book bags. They are also safer than X-rays and microwaves for human tissue.
Electro-optic crystals and photoconductive dipole antennas have been widely used in terahertz (THz) time-domain spectroscopy and related imaging applications. In the standard apparatus used for THz time-domain spectroscopy a separate transmitter and receiver are used for the emission and detection of the THz signal. Because detection is the reverse process of emission, the transmitter and the receiver can be identical devices.