title: Terahertz tomography using quantum-cascade lasers.
abstract: The interfaces of a dielectric sample are resolved in reflection geometry using light from a frequency agile array of terahertz quantum-cascade lasers. The terahertz source is a 10-element linear array of third-order distributed-feedback QCLs emitting at discrete frequencies from 2.08 to 2.4 THz. Emission from the array is collimated and sent through a Michelson interferometer, with the sample placed in one of the arms. Interference signals collected at each frequency are used to reconstruct an interferogram and detect the interfaces in the sample. Because of the long coherence length of the source, the interferometer arms need not be adjusted to the zero-path delay. A depth resolution of 360 µm in the dielectric is achieved with further potential improvement through improved frequency coverage of the array. The entire experiment footprint is <1 m × 1 m with the source operated in a compact, closed-cycle cryocooler.
authors.affiliation: Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. awmlee@longwavephotonics.com
authors.forename: Alan Wei Min
authors.initials: AW
authors.lastname: Lee
authors.forename: Tsung-Yu
authors.initials: TY
authors.lastname: Kao
authors.forename: David
authors.initials: D
authors.lastname: Burghoff
authors.forename: Qing
authors.initials: Q
authors.lastname: Hu
authors.forename: John L
authors.initials: JL
authors.lastname: Reno