Advances in Fingerprint Technology.pdf

laser
Figure 6.6 Block diagram of phase-shift/demodulation apparatus for time-resolved
imaging.
Fingerprint Treatments
Fingerprint treatments suitable for time-resolved imaging began to be
explored in the late 1980s. At first, transition metal complexes that yield
charge-transfer phosphorescences were successfully examined and applied to
fingerprint development by dusting or staining. 15 However, such complexes
could not be utilized for chemical fingerprint development, thus limiting the
approach primarily to smooth surfaces. Next, lanthanide-based procedures
were explored. These have the potential of forming a universal photoluminescence
approach to fingerprint detection, being applicable, in principle, to
all types of surface and to fingerprints of any age. They have by now reached
a reasonable level of maturity. However, problems persist with the lanthanide
(rare earth) approaches, thus prompting more recent investigation of photoluminescent
semiconductor nanocomposites.
Lanthanide-Based Procedures
modulator
delay
sine
wave
generator
MCP
CCD
fingerprint
sample
computer
The concept of time-resolved fingerprint detection for purposes of background
fluorescence suppression actually dates back to 1979. 16 Its feasibility
then was explored using a rotating cylinder with slots cut into it to turn the
laser illumination on and off. The photographic camera was placed such that
the sample would come into its view at a time after laser cut-off, as shown
in Figure 6.7. The arrangement resembles a phosphoroscope, a device that
dates back to the 19th century. The sample was a fingerprint dusted with a
powder that contained a Tb 3+ complex, yielding a green luminescence of
millisecond-order lifetime. The fingerprint was located on yellow notepad