Interference No. 104,649
Page No. 10
to
31432
34
35
33
WMk=8 LWP
M.3
In Figure 3 above, incident light passes through finger platen 10 having a sheet prism underside
and an interface surface 26, which is contacted by a finger 11, whereupon the incident light is
directed back through the sheet prism to form a working image. According to Keagy:
In FIG. 3, because of the difference in the indices of refraction between air and
flesh, rays that impinge on air in the valleys between fingerprint ridges, such as
rays 31, 33 and 35, are totally internally refracted and proceed back down through
the optical surface to form the rays of the working image. The remaining rays
which impinge upon the flesh of a fingerprint ridge, pass out of the plastic of the
platen 10, enter the flesh and escape thereby forming a contrast in the working
image between the ridges and surrounding valleys of the fingerprint.
(Keagy'969, col. 7, lines 43-52, underline added).
F20. Keagy Figure 7A is said to depict a ray diagram explaining the formation of a working
image with a preferred optical surface. Keagy Figure 7A is provided below:
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Last modified: November 3, 2007