Acousto-optic imaging of a color picture hidden behind a scattering layer.

An imaging technique has been developed to image a color picture hidden behind a 5 mm thick, highly scattering layer with low transmittance of 0.24%. Small vibrations (< 1 µm) were induced in the hidden picture, causing a time-varying speckle pattern on the scattering layer in the front, which is captured by a CCD camera and quantified as speckle contrast difference (SCD). With two lasers at 543 nm and 633 nm, the imaging system raster-scans the front of the scattering layer and the resulting SCD image reveals the color features of the hidden picture.