Experimental study of light focusing through strongly scattering media using binary amplitude spatial light modulator

Abstract

Current paper considers light focusing through strongly scattering medium using binary amplitude modulation of the incident light. The focusing was performed using a simple sequential algorithm. It consisted of the successive estimation of the influence of every pixel of the spatial light modulator on the intensity of the focal spot and making the decision on its target state. Also, noise characteristics of the imaging system camera-frame-grabber were estimated with further investigation of their influence on the focusing quality. Modulation of the incident light was performed by the liquid crystal spatial light modulator. For more efficient usage of the incident beam energy, pixels were combined in groups (so-called superpixels) and were controlled as one separate segment. We estimated the influence of the size of superpixel on the intensity enhancement in the focal spot maintaining the constant size of the illuminated area. The focusing at different distances behind the sample was performed. It was shown that the size of the focal spot at small focusing distances is determined by the properties of the imaging system lens. Starting from some certain distance, the size of the focal spot depends on the focusing distance and the size of the illuminated area of the sample. Hence, the scattering medium operates like a lens.