Epithelium

• But the imprint your finger leaves on the surface of the button is actually a 3D structure called a fingermark.
• A 2D fingerprint neglects the depth of the fingermark, including pores and scars buried in the ridges of fingers that are difficult to see.
• I’m an educator and scientist who studies holography, a field of research that focuses on how to display 3D information.

Fingermark types

• Patent fingermarks are the most visible type – bloody fingerprints at crime scenes are one example.
• Plastic fingermarks are found on soft surfaces, such as clay, Play-Doh or chocolate bars.
• Cyanoacrylate makes super glue in its liquid form, but as a gas it can make latent fingermarks visible.

Finally, Level 3 features, such as pores, scars and creases, are too small for the human eye to resolve. This is where optical techniques like holography come in handy, since optical wavelengths are in the order of microns, small enough to make out small details on an object.

Developing fingermark holograms

• Since fingermarks are usually collected as 2D pictures, and holograms display 3D information, my team wanted to develop a technique that can show all the 3D topological characteristics of a fingermark.
• Columnar thin films are dense pillars of glassy material that uniformly cover the fingermark, like a dense growth of identical trees in a forest.

• To make a hologram of something like a 3D fingermark, researchers split light from a laser into two parts.
• One part, called the reference wave, shines directly on a digital camera.
• The other wave shines on the object, in this case the fingermark.

Picking up fingermarks

• In 2017, our collaboration reported our first results, where we made 3D pictures of latent fingermarks using the CTF technique.
• We recorded holograms of the CTF-developed fingermarks with two different wavelengths of light – green and blue – generated from a laser.
• The Miami Valley Regional Crime Lab in Dayton, Ohio, has graded the quality of the fingermarks captured by Lakhtakia’s research group.

Partha Banerjee’s Holography and Metamaterials (HaM) Lab has used Digital Holography for many applications funded by DARPA, Air Force and Army. The current joint work on fingermarks is supported by a grant from the Criminal Investigations and Network Analysis (CINA) Center of the Department of Homeland Security (DHS).