Detection of nanometer size differences through human color vision

Speaker : Sandy Peterhänsel, Stuttgart University

Venue    : Thu 6 Oct 2016, 3pm (Murdoch University, Senate Room)

We study how accurately a naked human eye can determine the thickness of thin films and the geometric parameters (height and width) of optical gratings from the observed color. Our approach is based on color-matching experiments, where a sample with unknown parameters is observed next to a reference field of same size. The study of the limits of color discrimination and their dependence
on surrounding conditions for human eyes are one of the major trends in color science [1]. For thin lms this is done by placing the  sample in direct contact to a LCD display, see Fig. 1. For matching of gratings the setup is more complex, as shown in gure 2. This is due to the fact, that only the zeroth order should be observed, as higher orders will lead to an angular dispersion of the wavelengths present in the spectrum of the light source.

In both cases, the color of the reference field is matched by several test persons. From their selection the geometric properties of the thin films, as well as of the gratings are reconstructed via rigorous simulation. We found that the human color observation provides an extremely accurate evaluation of the lm thickness and is comparable to sophisticated instrumental methods in this case. Even for the more complex reconstruction of the grating parameters an accuracy in the range of much more sophisticated methods like scanning  electron microscopy could be observed. Our results suggest that for a wide range of structures, the  color observation may help to get quick, but still accurate, results, without any sophisticated instrumentation.
[1] R.G. Kuehni, Color Res. Appl. 33(324), (2008).
[2] S. Peterhänsel, H. Laamanen, J. Letholahti, M. Kuittinen, W. Osten and J. Tervo, Optica 2(7), (2015)
[3] S. Peterhänsel, H. Laamanen, M. Kuittinen, J. Turunen, C. Pruss, W. Osten and J. Tervo, Opt. Lett. 39(3547), (2014)