title: Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector.
abstract: Terahertz (THz) imaging can see through otherwise opaque materials. However, because of the long wavelengths of THz radiation (λ = 400 μm at 0.75 THz), far-field THz imaging techniques suffer from low resolution compared to visible wavelengths. We demonstrate noninvasive, near-field THz imaging with subwavelength resolution. We project a time-varying, intense (>100 μJ/cm(2)) optical pattern onto a silicon wafer, which spatially modulates the transmission of synchronous pulse of THz radiation. An unknown object is placed on the hidden side of the silicon, and the far-field THz transmission corresponding to each mask is recorded by a single-element detector. Knowledge of the patterns and of the corresponding detector signal are combined to give an image of the object. Using this technique, we image a printed circuit board on the underside of a 115-μm-thick silicon wafer with ~100-μm (λ/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity, it is possible to detect fissures in the circuitry wiring of a few micrometers in size. THz imaging systems of this type will have other uses too, where noninvasive measurement or imaging of concealed structures is necessary, such as in semiconductor manufacturing or in ex vivo bioimaging.
authors.affiliation: School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Rayko Ivanov
authors.initials: RI
authors.lastname: Stantchev
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Baoqing
authors.initials: B
authors.lastname: Sun
authors.affiliation: School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Sam M
authors.initials: SM
authors.lastname: Hornett
authors.affiliation: School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.; QinetiQ Limited, Cody Technology Park, Ively Road, Farnborough GU14 0LX, UK.
authors.forename: Peter A
authors.identifier: 0000-0001-6240-0702
authors.initials: PA
authors.lastname: Hobson
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Graham M
authors.initials: GM
authors.lastname: Gibson
authors.affiliation: School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Miles J
authors.identifier: 0000-0001-6643-0618
authors.initials: MJ
authors.lastname: Padgett
authors.affiliation: School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
authors.forename: Euan
authors.initials: E
authors.lastname: Hendry
mesh_terms: D055095:Optics and Photonics; D055069:Terahertz Imaging / Q000295:instrumentation / Q000379:methods*; D055053:Terahertz Radiation
keywords: Compressed sensing; imaging; near-field; noninvasive; optics; single-pixel detection; terahertz