Dual-frequency imaging using an electrically tunable terahertz quantum cascade laser.
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.
Dean
Paul
P
School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK. p.dean@leeds.ac.uk
Saat
Nor Kamila
NK
Khanna
Suraj P
SP
Salih
Mohammed
M
Burnett
Andrew
A
Cunningham
John
J
Linfield
Edmund H
EH
Davies
A Giles
AG
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*
D011208:Powders; D010417:Pentaerythritol Tetranitrate; D013395:Sucrose; D005947:Glucose; D007785:Lactose