Time-Domain Terahertz - Toptica

(c) SynView GmbHTerahertz ApplicationsWavenumber (1/cm)04.010 20 30 40 50 602.03.51.53.02.51.0ε 1ε 22.00.51.51.00.0 0.3 0.6 0.9 1.2 1.50.01.8Frequency (THz)SpectroscopyVarious applications of terahertz spectroscopy exist, as many gas molecules and organicsolids, including chemical agents and explosives, exhibit “fingerprints” at terahertzfrequencies. A spectrum can be acquired using either pulsed or cw terahertz radiation,and yields information on the complex refractive index of the sample. A time-domain(pulsed) measurement demonstrates an absorption signature with a decrease of theamplitude and a delay of the terahertz pulse. In a frequency-domain (cw) experiment, thesignature presents an attenuated signal and a phase shift of the terahertz wave.Since terahertz rays penetrate opaque materials such as paper, and are hardlyattenuated by aerosols, spectroscopy can aid in observing “inaccessible” settings (e.g.,through sealed envelopes or black smoke).Real part ε 1(black, left axis) andimaginary part ε 2(blue, right axis) ofthe dielectric constant of α-lactosemonohydrate, measured with cw-THzspectroscopy.(M. Grüninger, University of Cologne,Germany)4 | www.toptica.com