title: Dual-frequency imaging using an electrically tunable terahertz quantum cascade laser.
abstract: We report dual-frequency transmission imaging of polycrystalline materials using an electrically tunable terahertz (THz) frequency quantum cascade laser (QCL). Using our system we are able to obtain images at both 3.05 THz and 3.24 THz in a single two-dimensional scan of a sample. By taking the difference of the natural logarithms of the transmission coefficients obtained at each frequency, the difference-attenuation coefficient is determined, and evaluated for samples of lactose monohydrate, glucose monohydrate, sucrose, and the high explosive PETN. We also demonstrate difference-intensity imaging at these frequencies by combining amplitude modulation of the QCL bias with lock-in detection. Owing to the specific molecular absorption spectra of these materials in the THz frequency range, the samples can be distinguished using our technique.
authors.affiliation: School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK. p.dean@leeds.ac.uk
authors.forename: Paul
authors.initials: P
authors.lastname: Dean
authors.forename: Nor Kamila
authors.initials: NK
authors.lastname: Saat
authors.forename: Suraj P
authors.initials: SP
authors.lastname: Khanna
authors.forename: Mohammed
authors.initials: M
authors.lastname: Salih
authors.forename: Andrew
authors.initials: A
authors.lastname: Burnett
authors.forename: John
authors.initials: J
authors.lastname: Cunningham
authors.forename: Edmund H
authors.initials: EH
authors.lastname: Linfield
authors.forename: A Giles
authors.initials: AG
authors.lastname: Davies
mesh_terms: D005947:Glucose / Q000737:chemistry; D007785:Lactose / Q000737:chemistry; D054023:Lasers, Semiconductor; D055095:Optics and Photonics; D010417:Pentaerythritol Tetranitrate / Q000737:chemistry; D011208:Powders; D011789:Quantum Theory; D013395:Sucrose / Q000737:chemistry; D055053:Terahertz Radiation; D055068:Terahertz Spectroscopy / Q000379:methods*
chemical_list: D011208:Powders; D010417:Pentaerythritol Tetranitrate; D013395:Sucrose; D005947:Glucose; D007785:Lactose