The images below are visualizations of the average path taken by photons as they move from the source to the detector. The sample is a homogeneous slab 0.5 cm thick, irradiated by an infinitely thin laser in the center. The material has an absorption coefficient of 1 cm-1 and a scattering coefficient of 90 cm-1. The anisotropy factor "g" = 0.75, so this material scatters light predominately in the forward direction. ( g = average of the cosine of the scattering angle ) This material is very transparent compared to Simulations 1 and 2, and we see the light samples a very much larger volume before emerging from the top and being detected.
The images are not exactly cross-sections through the slab, rather, they are plots of the log of photon intensity versus radius (horizontal) and depth (vertical). The laser hits the sample at the upper left corner, and the intensity is maximum at this point. The 0-60 numbers are an artifact of the contouring program; the actual scale is 0 to 5 mm in both directions. The contour lines span 8 decades; each pair of lines spans a factor of 10 in intensity.
An artifact of the program is visible on the right-hand edge of these images. This occured because, in this simulation, the photons suffered very little attenuation as they moved. If the photon traveled outside the simulated region (5 mm in each direction), the remaining intensity was added to the last set of cells in the region. This results in an incorrect increase in intensity at the right edge of the images.
Click on each picture for a larger version.
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| Total detected photons, photons that escaped between 0-1 mm , and photons that escaped between 1-2 mm (0-12 and 12-24 on the horizontal scale). | ||
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| Photons that escaped between 2-3 mm, 3-4 mm, and 4-5 mm (24-36, 36-48, and 48-60 on the horizontal scale). | ||