Development of FOP-HARP imaging device
2010
The high-gain avalanche rushing amorphous photoconductor (HARP) camera tube achieves ultrahigh-sensitivity by
using the avalanche multiplication. The applications of this tube extend beyond broadcasting into other fields. It is
attracting a great deal of attention especially for radiation diagnosis, such as synchrotron radiation microangiography,
because it can obtain high-resolution and high-contrast images with a low dose of radiation. However, in the present
system, a fluorescent screen and the photoconductive film of the HARP tube are connected optically by a lens-coupling
method, and low light throughput remains a big problem. To improve the light throughput by using a fiber-coupling
method, we applied a fiber-optic plate (FOP) to the substrate of a HARP tube. The FOP consists of three types of glass
that have differing hardnesses and elastic coefficients that make it difficult to flatten the FOP surface enough to form the
HARP film. We thus introduced a new mechanical polishing method and succeeded in realizing avalanche multiplication
in the FOP-HARP tube. The results of shooting experiments by applying the FOP-HARP to the microangiography
showed that a spatial resolution of over 20 line pairs/mm was obtained. Moreover, rat femoral arteries of 150-200 μm in
diameter could be visualized as motion pictures with a one-fourth lower concentration of contrast material than that
needed for ordinary microangiography. Another potential application of the FOP-HARP is an ultrahigh-sensitivity nearinfrared
(NIR) image sensor made by fiber-coupling with an image intensifier (I.I.). The image sensor provides highquality
images and should be a powerful tool for NIR imaging.
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