A High Resolution Terahertz Spectrometer for Chemical Detection

摘要

Goodrich has been developing a high resolution, broad band spectrometer that operates in the Terahertz (THz) region of the spectrum with the intent of performing chemical detection. THz spectroscopy exploits rotational resonances for detection of gas phase compounds. High resolution THz spectroscopy can improve detection and identification through increased probability of detection and reduced false alarms. The Goodrich THz spectrometer is based upon CW photomixer technology in a heterodyne configuration. The current Goodrich design offers continuous tunability across a 0.1 THz to 1.2 THz frequency range. One of the unique aspects of the Goodrich spectrometer is laser system control that has demonstrated difference frequency line widths on the order of 1.5 MHz with stability measured over long time scales. Absolute frequency accuracy is of the order of 4 MHz. The spectrometer design enables high THz energy densities with narrow line widths tunable over a broad spectrum. The system has demonstrated SNR better than a cryogenically cooled hot electron bolometer. This capability allows the Goodrich system to accurately determine absorption signatures of multiple chemicals with exceptional performance. Goodrich has completed initial system testing and verified performance. Initial tests were completed to determine SNR of the heterodyne photomixer transceiver. System performance was also verified for laser line width, stability, and repeatability. The spectrometer was tested against various toxic industrial chemicals. Preliminary data for HCN, HCl, NH_3, and SO_2 is presented.