Laser fingerprint scanner does away with dusting

Published 19 November 2007

Breakthrough in finger printing: Indian scientists develop a laser-based finger printing device; devices uses optical coherence tomography (OCT), which is often described as an optical version of ultrasound imaging

News on the finger printing front. Scientists in India have developed a portable device that could scan fingerprints in microseconds. The system, which works using a technique called optical coherence tomography, holds the promise of improvement over existing fingerprint detection methods since it does not require any chemical processing. Optical coherence tomography (OCT) is like an optical version of ultrasound imaging. The technique is already routinely used in medicine, but has not had a forensic application until now. The New Scientist’s Belle Dumé writes that the technique provides a transparent 3D structural picture by sending light though the pattern of natural secretions left on a surface by a finger and combining the reflected beam with a “reference beam” produced by bouncing light from a laser off a mirror. This produces an interference pattern at a photodetector — the same as those found in a digital camera — which can then be used to reconstruct an image of the original fingerprint.

The new device, developed by Satish Kumar Dubey and Dalip Singh Mehta of the Indian Institute of Technology, New Delhi, is a “swept-source” OCT, which uses a rapidly scanning laser. The key advantage of the design is that undesired reflections can be filtered out using a mathematical approach called selective Fourier filtering. This, in turn, helps the system detect fingerprints from surfaces which do not reflect light well, such as paper. Conventional techniques require chemical processing to enhance the contrast of fingerprint impressions.

The device currently uses a low frame-rate digital camera as its photodetector, so its response time is limited. “This can be improved using a high speed camera with smaller pixel size, which means the device will have the speed of a few microseconds,” Mehta told New Scientist. “OCT is a 3D instrument, hence excellent for the job,” says Haida Liang of Nottingham Trent University, an expert on the technique. “The technique reported here is trying to image fingerprints with better sensitivity and clarity. There’s certainly potential in using OCT for fingerprint detection and very little has been done on this application.”