Abstract

The design and performance of a fast absorption tomography instrument is presented that is capable of acquiring 100 projections of 100 elements each in <200 ns. The instrument uses time multiplexed, fiber optic fan-beam sources that are sequentially activated in groups to greatly reduce the total number of detectors required to achieve a given resolution. An easily replicated fan-beam generator comprising a UV transmitting silica macrofiber and two microlenses produces a flat fan with a nearly ideal intensity profile. Large area, unencapsulated fast silicon photodiodes developed for this application allow close packing, thus reducing power requirements on the optical fibers and increasing the instrument sensitivity. The optical fibers limit the short wavelength operation of the instrument to 200 nm whereas the detectors limit the long wavelength operation to 1.1 μm. A single-fiber prototype was used to verify the design and establish its sensitivity. The sensitivity is limited by laser speckle noise. The fiber-optic fan-beam generator produced a high degree of interdetector correlation of the projection noise reducing the effect of this noise on the reconstruction. The noise is measured as a function of optical fiber stability and size, laser bandwidth and mode stability, and detector size.

© 1991 Optical Society of America