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A gateable, image-intensified laser system that permits detection of latent fingerprints under high background light is described. The system is intended for crime-scene work and for daylight conditions.
Offers up-to-date treatment of fingerprint detection with lasers, including basic principles and equipment, established photoluminescence-based detection techniques and a range of emerging techniques. This second edition summarizes information on time-resolved fingerprint detection, transition selection rules, image intensifiers and CCD cameras, uses of photoluminescence in criminalistics, and scientific principles underlying figerprint detection.
Fingerprints constitute one of the most important categories of physical evidence, and it is among the few that can be truly individualized. During the last two decades, many new and exciting developments have taken place in the field of fingerprint science, particularly in the realm of methods for developing latent prints and in the growth of imag
Fingerprint development techniques that use blue-green laser light suffer from high background fluorescence on substrates such as cardboard, wood, leather, and some metals and plastics. These substrates tend to exhibit little or no fluorescence under ultraviolet light, prompting us to search for procedures that yield visible fluorescence under this illumination. Specifically, chemical development with dansyl chloride and vapor staining with 9-methylanthracene were found to be useful when dealing with these substrates. Fluorescence excitation was possible either with an ultraviolet lamp or an argon-ion laser operating in the ultraviolet. Coumarin 535 vapor staining following 9-methylanthracene staining was also found effective.
Laser detection of fingerprints, as described in an earlier paper [1], entails exposure of crime scene exhibits to laser light and photography (or direct viewing) of any fingerprints thereby induced. The Ontario Provincial Police Force has initiated laser examination of exhibits for fingerprints to evaluate the effectiveness of this technique and to obtain additional data that might further exploit the luminescence of fingerprints on materials under examination. Glass, metal, wood, cloth, stone, and plastic exhibits were examined for fingerprints under laser light. Many of these surfaces yielded localized luminescence that may or may not have been the result of fingerprint deposit.
In 1976 a method for the detection of latent fingerprints by their inherent luminescence using continuous-wave (CW) argon-ion laser excitation [1] was discovered at Xerox Research Centre of Canada, where the first detection by this method of an identified print from an actual criminal exhibit (a fingerprint on the sticky side of a piece of black electrical tape) was also achieved. Basically, the laser procedure involves illumination of the exhibit under scrutiny with the blue-green light from the argon-ion laser and photography of the resulting yellow-green fingerprint luminescence. The viewing and photography are carried out in a darkened room. A filter is used to block the laser light scattered from the exhibit to prevent eye damage and film exposure by the laser light. Spectroscopic and chromatographic features of fingerprint material indicate that riboflavin is one of several inherent luminescers in fingerprint residue and our findings suggest potential for fingerprint age determination [2].