The Focusing of Light Scattered from Diffuse Reflectors Using Phase Modulation

“Indirect photography was recently demonstrated for imaging hidden scene information through the collection and radiometric modeling of light reflecting off of visible reflecting surfaces. The ability to focus the beam that reflects off the visible surface to a tight spot on the hidden object is theorized to simulate a direct line of sight from the light source to the object, reducing the radiometric model to that of the previously demonstrated dual photography. Experiments involving the focusing of light transmitted through highly scattering media have been adapted to the case of reflection. The focusing of a HeNe laser reflected off diffusely scattering surfaces to a tight spot is demonstrated using phase control. A liquid crystal spatial light modulator assigns pixelated phase delay to the beam to conjugate the scattering properties of the reflector. Intensity enhancement values between 13.8 and 122.3 are achieved for the surfaces studied. Samples with relatively strong specular reflection achieve higher enhancement for a given geometry. More diffusely reflecting materials achieve higher enhancement in regions of nonspecular scatter, facilitating non-mechanical beam steering