A Terahertz Detector and optical parametric generator for remote sensing applications

摘要

Terahertz remote-sensing applications require high sensitivity detectors and high-power terahertz sources. The reason for this is that terahertz signals can be quickly attenuated by water molecules present in the target, as well as in the environment between the source and the target. Of the many terahertz source technologies available, the one based on the optical parametric generation technique seems to be the most promising, as it is portable and can produce a relatively high-power terahertz beam. At present we are developing a terahertz source based on an optical parametric technique. We have used a Nd:YAG Q-switched laser as the pump source, and a LiNbO_3 crystal as the optical parametric medium. With LiNbO_3 our generator could produce a terahertz beam over the frequency range of 100 GHz through 3 THz. The output power was highly dependent on the properties of the material. For terahertz detection we have used a Si-bolometer or an electro-optic (EO) detector, which was specifically developed to detect CW terahertz signals. In addition to the EO sensor, we are presently developing a new detector based on a quantum-dot structure, whose noise equivalent power (NEP) is expected to be about 10~(-21) W/(Hz)~(1/2). This is several orders of magnitude better than the sensitivity of our bolometer (10~(-13) W/(Hz)~(1/2)) at 4.2 K, or our EO detector (10~(-12) W/(Hz)~(1/2) ) at room temperature.