Terahertz (THz) spectroscopy and imaging methods have strong potential to non-invasively and non-destructively detect explosives and chemical/biological warfare agents. This goal will be realized by two objectives. In the first, layered gallium phosphide (GaP) nonlinear crystals will be developed and characterized to increase the useable spectral bandwidth of THz time-domain spectrometers by a factor of two. The GaP devices will provide pulsed THz radiation generation and detection from 0.1 to =7 THz (3 to =233 cm-1) with no absence of spectral content and with no degradation in spectral resolution. This objective will yield sensors and detectors with unprecedented ability to obtain THz spectra with simultaneous high spectral resolution and wide spectral bandwidth. These new devices will enhance accessibility to valuable chemical information, particularly the hydrogen-bonding interactions ubiquitous in biological systems. In the second objective, the devices will be used to investigate the THz spectra of condensed-phase biologically relevant materials, focusing on hydrogen-bond stretching and bending vibrations observable above 3 THz. This underutilized spectral region will yield THz signatures for molecules and ultimately aid in the rational construction of spectral libraries for use in the rapid detection and identification of compounds of interest to the intelligence community.
