Characterization of Scattering Media Using Vector Speckle and High-Order Speckle Correlations

Purdue University, West Lafayette IN

Investigators

Abstract

Spectroscopy makes optical sensing and imaging a powerful tool relative to other modalities. However, a large number of domains of interest have significant degrees of scatter, thereby precluding direct interpretation of optical measurements using standard holographic or spectroscopic techniques. For instance, using light it may be possible to detect tumors at an early stage and to determine blood chemistry using safe and inexpensive instruments, with correct interpretation of the influence of scatter. Environmental sensing applications include measurements of or within aerosols, turbid water, sea ice, and snow. There has also been significant recent interest in random media with optical gain, which may find application in displays and for inexpensive lasers. Coherent light in all these situations can produce speckle. While efforts have been made in some applications to reduce the confounding impact of speckle, such as in optical coherence tomography, speckle has the potential to determine important properties of the scattering medium. They have used frequency correlations of laser speckle to characterize diffusely scattering material. This characterization involves determining impulse response or scattering parameters that can be used to form spatial images and to extract quantitative spectroscopic data. Of particular note, the PIs recently showed that it is possible to use third order speckle intensity correlations to directly determine the impulse response of a scattering medium, independent of a model, extending the second order intensity interferometer concept of Hanbury-Brown and Twiss. This project involves the study of fundamental aspects of speckle, with a view toward several applications. The PIs will extend their single linearly polarized speckle measurement to a set of input/output polarizations, and couple this data to a polarized transport model that will be developed. This should allow treatment of varying degrees of scatter and also characterization of the scatterers. They will also investigate source correlation concepts.