By Harnessing the Human Eye’s Ability to Detect Remarkably
Subtle Color Differences, Researchers have Shown that Normal Human Vision can
Accurately Identify ‘Thin Films’ that Differ in Thickness by a Few Nanometers,
about the Width of a Single Virus
(July 9, 2015) The
human eye is an amazing instrument and can accurately distinguish between the
tiniest, most subtle differences in color. Where human vision excels in one
area, it seems to fall short in others, such as perceiving minuscule details
because of the natural limitations of human optics.
In a paper published today in The Optical Society’s new,
high-impact journal Optica, a research team from the University of Stuttgart,
Germany and the University of Eastern Finland, Joensuu, Finland, has harnessed
the human eye’s color-sensing strengths to give the eye the ability to
distinguish between objects that differ in thickness by no more than a few nanometers
— about the thickness of a cell membrane or an individual virus.
This ability to go beyond the diffraction limit of the human
eye was demonstrated by teaching a small group of volunteers to identify the
remarkably subtle color differences in light that has passed through thin films
of titanium dioxide under highly controlled and precise lighting conditions.
The result was a remarkably consistent series of tests that revealed a hitherto
untapped potential, one that rivals sophisticated optics tools that can measure
such minute thicknesses, such as ellipsometry.
“We were able to demonstrate that the unaided human eye is
able to determine the thickness of a thin film — materials only a few
nanometers thick — by simply observing the color it presents under specific
lighting conditions,” said Sandy Peterhänsel, University of Stuttgart, Germany
and principal author on the paper. The actual testing was conducted at the
University of Eastern Finland.