The human eye is an incredible instrument can accurately distinguish smaller, subtle color differences. When the human eye stands in an area, it seems short in others, such as the perception of the smallest details to drop because of the natural limits of human perspective.
In an article published today in the new revised Optica strong influence of the Optical Society, a research team at the University of Stuttgart in Germany and the University of Eastern Finland in Joensuu, Finland, operated powers color detection human eye the eye's ability to distinguish between objects that to differ in the thickness of not differ by more than a few nanometers or about the thickness of a cell membrane or a particular virus.
This ability to go beyond the diffraction limit of the human eye has been. By teaching a small group of volunteers, the subtle differences in color light that shown to identify by thin layers of titanium dioxide in lighting conditions very controlled and specific The result was a remarkably consistent set of tests that a previously untapped potential, one that can be measured as ellipsometry minutes with sophisticated tools, the optical thicknesses, competes revealed.
"We showed that the human eye is able to reduce the thickness of a thin film material only a few nanometers thick by determining simply observing the color that shows it in certain lighting conditions," said Sandy Peterhansel, University of Stuttgart, Germany, and lead author of the article. The real test was conducted at the University of Eastern Finland.
The color and the thickness of thin films
Thin films for a variety of commercial and industrial applications, including anti-reflective coatings for solar collectors. These films may be thick as small as a few tens of nanometers. Thin films were used in this experiment, from the application layer, after a layer of atoms formed on the surface. Although precise, this is a method, timing, and other techniques such as vapor deposition used in the industry.
The optical properties of thin films means that when light with surfaces in interaction produces a wide range of colors. This is the same phenomenon that produces brilliant colors on a soap bubble and oil films on the water.
Produced by this process special color depends strongly on the composition of the incoming light material properties, thickness, and. This sensitivity to both the material and the thickness was sometimes. By engineers to quickly estimate the film thickness at a level of about 10 to 20 nanometers
This observation inspired the research team to test the limits of human vision, to see how small it was possible to detect a change in the ideal conditions.
"Even if the power of spatial resolution of the human eye is too low by orders of magnitude to directly characterize film thickness interference colors are known very sensitive to fluctuations in the film to be," said Peterhansel.
Test facility
The configuration of this experiment was remarkably easy. A series of thin films of titanium dioxide in a layer at a time prepared by atom deposition. Although long, this method allowed the researchers carefully check the thickness of the samples, the limits on how a small change could test identifying research topics.
The samples were then placed in a liquid crystal display configured to display a pure white, with the exception of a reference color range that can be calibrated to match the colors of the visible surface of thin films have different thicknesses.
Then the color of the reference field is modified by the subject until the reference sample A perfect match: to identify the correct color meant that he also determined its thickness correctly. This could be done in less than two minutes, and for some test samples and approximate thickness only submit two fifty-nine nanometer is different from the actual measured by conventional means. This accuracy is far beyond the normal human vision.
Compared to conventional automated method for determining the thickness of a thin film that can be done five to ten minutes per sample using some techniques, the human eye compares very favorable performance.
Because the human eye tire easily, it is unlikely that the process of replacing the automated methods. However, it may serve as a quick check by an experienced technician. "The aim of our study was to determine not only the human color perception to compare more sophisticated methods," said Peterhansel. "Discover how this approach may be necessary, was the primary motivation for our work."
Researchers believe that it may be possible to detect even finer variations when other control factors are determined. "People often underestimate the human meaning and value in technology and science. This experiment demonstrates that our vision was born, of course, exceptional tasks usually affect only the expensive and complicated machinery," says Stephane Peterhansel.
More info. Peterhansel Laamanen H., J. Lehto Lahti Mr. Kuittinen, W. East, J. Tervo, "human color perception provides precision thin film thickness nanometric characterization" Optica, 2, 7, 627 (2015). DOI: 10.1364 / OPTICA.2.000627
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