This document discusses various techniques for developing latent fingerprints, including the application of lasers. It describes how argon lasers can cause fingerprints to fluoresce without treatment due to components like riboflavin and pyridoxine in sweat. However, post-treatment is usually needed to improve fluorescence. Methods include using luminescent materials or chemicals that react with sweat to form luminous products. Other techniques discussed are forensic light sources, chromatic white light sensors, and x-ray fluorescence radiography which detects fingerprint ridge patterns through fluorescence of elements like sodium and potassium in sweat.

1. Application of Laser and Other
Radiations to Develop Latent
Fingerprints
By: CHHAVI KAUSHAL
M.Sc Forensic Science & Criminology
4 Semester

2. Contents
 Fingerprints
 Types of fingerprints found
 Latent fingerprints
 Application of Lasers to Fingerprint Detection
 Argon laser
 Post treatment and other radiation methods
 Forensic light sourse
 Chromatic white light sensor
 X-ray fluroscence radiography
 References

3. Fingerprints
 Fingerprints are patterns formed by the raised papillary ridges on
fingertips, which contain rows of pores that connect to sweat glands.
The basic patterns of fingerprints are loops, whorls and arches that
can be found in fingerprints. Fingerprints have been the gold
standard for personal identification within the forensic community.
 Fingerprint patterns are genetically determined and remain
unchanged from birth till death. They are unique, immutable,
universal, easy to classify. Fingerprints collected from a crime scene
can be used to identify suspects, victims and other persons who
touched the surface.

4. Types of Fingerprint Found
 There are three types of fingerprints that can be
found:
 Latent
 Patent and
 Plastic

5. Latent Fingerprints
 Latent prints are the most viable fingerprints
amongst patent and plastic prints as these are not
visible to the naked eye, and substantially consist
of only the natural secretions of human skin.
 Also, there is impact of location on the latent
fingerprint development as porous surfaces
(Human skin, paper, fabric, unfinished wood, etc.)
are more difficult as compared to non- porous
surfaces (Glass, plastic, finished wood etc.).

6. Continue...
 In the past, powder dusting, ninhydrin dipping,
iodine fuming and silver nitrate soaking were the
most commonly used techniques for latent print
development. These traditional techniques are quite
effective for many surfaces. However, these
traditional methods for latent print detection are not
always effective and scientists have attempted to
improve the existing methods for the visualization
of latent prints.

7. Application of Lasers to
Fingerprint Detection
 Laser detection of latent fingerprints is an extremely sensitive technique with a
wide range of applicability.
 The methodology is based on the principle that a luminescent fingerprint,
impinged on a non-luminescent surface, produces laser-excited fluorescence. The
fluorescence so produced provides intrinsically such high sensitivity that
fingerprints may be detected on difficult and unusual surfaces. The method also
ensures detection of weak, as well as old latent fingerprints. Laser technique is
often used as a supplement to conventional procedures of fingerprint detection.

8. Argon Laser
 The most common device used for the detection of latent fingerprints on difficult surfaces is the argon laser (Ar-laser). The surface
impinged with the fingermark is illuminated with the blue-green beam from the Ar-laser. Before it strikes the surface, the beam is
made to pass through a lens.
 This serves two purposes;
 Firstly, it enlarges the area of coverage of the beam, so that the whole fingerprint impression becomes exposed to the laser light.
 Secondly, the expanded beam protects the surface from burning. The imprint is observed through a safety filter. Such filters absorb the
short wavelength components and transmit the longer ones, thus protecting the observer’s eyes. After the fingerprint is identified, it is
photographed through the same filter. The identification of the fingerprint, as well as its photography is carried out in a dark room.

10. Continue...
 In order that light from the fingerprint ridges alone reaches the eye, the surface containing the impression should be non-fluorescent. If the
surface itself is luminescent, then the ridge pattern is post-treated with a chemical reagent so as to generate the ridge fluorescence which is either
stronger than the background or of a different color. Alternately, the surface fluorescence may be blocked by using an appropriate filter.
 The use of lasers for fingerprint detection dates back to 1977, when it was reported that inherent luminescence of sweat deposit may be
illuminated by an Ar-laser. No fingerprint treatment reagent was used in this investigation. The fact that fingerprint residue contains luminescers,
such as riboflavin (I) and pyridoxine (II), was considered as a possible route to fingerprint detection. However, the luminescent components in
the sweat deposit are present in trace amounts and, therefore, the method had limited utility.

11. Continue...
 It thus became evident that laser technique can be
used for resolution of ridge pattern only after the
latent imprint is given a post-treatment. Two broad
post treatment procedures may be used.
 1. The latent fingerprint may be treated with a
luminescent material.
 2. The latent fingerprint may be treated with a
chemical reagent which reacts with a sweat
component to form a luminous reaction product.

12. Post Treatment & Other
Radiation Methods

13. Forensic Light Source
 Forensic light source techniques have been successfully utilized for revealing latent prints on these and many other types of textured surfaces,
backgrounds which mask ridge detail, fragile surfaces, and contaminated surfaces.
 Different wavelengths (color bands) are required for processing different types of surfaces making a forensic light source with tunable or multiple
wavelengths a required tool for any crime scene investigator. In many cases the background surface will also glow under light source
illumination. In these cases it is necessary to tune to a wavelength of light that causes the processed print to glow (fluoresce) and not the
background. The quality and quantity of evidence revealed is proportional to the output power and the extent of wavelength tunability of the light
source. This ability is exclusive to a forensic light source, UV lights or Blue lights cannot offer this selectivity due to their limited number of
wavelengths and low power.

14. Images showing
detection of
fingerprints at
different
wavelengths of light

15. Chromatic White Light Sensors
 The chromatic white light (CWL) sensor generates a topographic image of the sample by using chromatic aberration of light. These
sensors are used to localize marks on various nonporous substrates and to separate overlapped finger marks.
 These sensors can also be used to estimate the age of latent fingerprints left on a variety of surfaces.
 Some authors used contactless CWL sensors for determining the age of a fingermark. They observed that different factors such as
composition of sweat, humidity, temperature, ultraviolet (UV) radiation, type of substrate, presence of water-containing substance on
fingertip, scan resolution, and measured area size affect the results.
 However, time and pressure of contact between fingertip and substrate are less effective parameters.

16. X-Ray Fluroscence Radiography
 In the standard approach to lifting fingerprints from a crime scene, known as contrast enhancement, a sample is treated with a substance--either vapor, liquid or
powder--that adds color to a fingerprint and allows it to stand out from its background. Prints left on such surfaces as leather, plastic or fibrous textiles, can
sometimes be difficult to detect, however.
 The technique developed by Chris Worley of the Los Alamos National Laboratory and his colleagues is a noninvasive one that relies on a process known as
micro-x-ray fluorescence (MXRF).
 When a surface is exposed to a thin beam of x-rays, the MXRF instrument detects elements such as sodium, potassium and chlorine, which are present as salts in
human sweat. Because the salts are deposited along the ridges present in a fingerprint, the fluorescence can be used to assemble a digital image of a print. "This
process represents a valuable new tool for forensic investigators that could allow them to nondestructively detect prints on surfaces that might otherwise be
undetectable by conventional methods.

17. Limitation
MXRF cannot detect all the prints that conventional techniques do,
because some prints won't contain enough of the necessary
elements. But it might find some prints that would otherwise be
missed: the researchers' tests illustrated that MXRF successfully
identified prints from subjects whose hands were exposed to
sunscreen, lotion or saliva, which could interfere with contrast
enhancement.
Currently, this method can only test samples that can physically be
transported to a laboratory that has an MXRF machine.

18. References
 7206-Latent-Fingerprint-on-Human-Skin-A-Silent-
Diagnosis
 Pgpathshala.com
 jasuja2016.pdf
 https://www.scientificamerican.com/article/researche
rs-use-x-rays-to/


19. THANKYOU