Coherent Optical Tomography

The methods of conventional (X-ray) tomography have, in the past, been employed in a number of applications in optics such as combustion diagnostics [1] and con-destructive evaluation of strongly refracting objects such as optical fibers [2]. In these applications a laser is employed much in the same way as an X-ray source is employed in X-ray tomography [3]. For example, in combustion diagnostics [1] a narrow laser beam is made to scan through the object of interest and a photo detector records the transmitted light intensity thereby yielding a "projection" of the object’s attenuation profile. The algorithms of X-ray tomography such as ART or the filtered backprojection algorithm [3] can then reconstruct a cross-section of the attenuation profile from the measured data. In the case of strongly refracting objects [2] the goal is to reconstruct the object’s velocity profile from optical path length measurements of the transmitted optical field. These measurements yield a "generalized projection" of the real part of the object’s complex index of refraction profile. Although the reconstruction algorithms of X-ray tomography cannot be employed due to the refraction of the probing optical field, generalized reconstruction algorithms based on a ray model of the optical field have been developed [2] that can yield reconstructions of the real part of the index of refraction from the "generalized projections".