Looking through walls and around corners

It is shown theoretically that under appropriate conditions a visually opaque, multiply scattering optical barrier can be made to serve as a thin lens which produces a near perfect, real, paraxial image of objects lying behind the barrier. Preliminary experimental results are described which verify the validity of the underlying assumptions. The barrier can also be made to serve as various other types of optical instruments, such as mirrors, polarizers, optical Fourier analyzers, theodolites, etc. Thus it is now clear that multiply scattering media should no longer be considered barriers to optical propagation, but are more properly to be regarded as potential high-precision optical instruments.