title: Measuring the reflectance of hidden color objects with acoustically modulated laser speckle.
abstract: We demonstrate a technique to measure the reflectance of colored objects, including blue, green, and yellow, hidden behind an opaque slab based on acoustically modulated laser speckle. One colored paper at a time was placed behind a 1 cm thick opaque slab with an air gap of 5 mm. Small periodic movements (nanometer scale) at 200 Hz were induced in the colored paper. A coherent red He-Ne laser illuminated the front of the slab, producing acoustically modulated speckle patterns, which were captured by a CCD camera. The magnitude of the time-varying speckle intensity is indicative of the hidden colored paper's reflectance.
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, London WC1E 6BT, UK. t.leung@ucl.ac.uk
authors.forename: Terence S
authors.initials: TS
authors.lastname: Leung
authors.forename: Shihong
authors.initials: S
authors.lastname: Jiang
mesh_terms: D003116:Color; D007834:Lasers; D055620:Optical Phenomena; D010209:Paper