ROLE OF HIGHER-ORDER SCATTERING IN SOLUTIONS TO THE FORWARD AND INVERSE OPTICAL-IMAGING PROBLEMS IN RANDOM-MEDIA

From analytical and numerical solutions that predict the scattering of diffuse photon density waves and from experimental measurements of ch anges in phase shift theta and ac amplitude demodulation M caused by t he presence of single and double cylindrical heterogeneities, we show that second-and higher-order perturbations can affect the prediction o f the propagation characteristics of diffuse photon density waves. Our experimental results for perfect absorbers in a lossless medium sugge st that the performance of fast inverse-imaging algorithms that use fi rst-order Born or Rytov approximations might have inherent limitations compared with inverse solutions that use iterative solutions of a lin ear perturbation equation or numerical solutions of the diffusion equa tion. (C) 1997 Optical Society of America.