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Blu-rayTM micro structures resolved - in an ordinary light microscope! (II)

Now you might ask why we were making so much fuss about the Blu-ray in the light microscope? And whether this might be related with the tardigrades in some way? Perhaps you are right.

BUT: we are trying to preserve the reputation of the light microscope!

Nowadays underestimating the light microscope has become kind of a habit. Just give it a try and look around by yourself: a quick search in the internet will reveal a considerable number of publications all of which are using the Blu-ray as a kind of milestone beyond the light microscope resolution [e.g. Huszka 2017, Lai 2016, Lee 2013, Wang 2016, Xiangang 2019]. But this is simply wrong. When properly used, the light microcope is well able to resolve those tiny pits and lands on the Blu-ray disk:


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Fig. 1: Classic light microscopic bright field images of the fine structures of a CD, a DVD and a Blu-ray, with identical magnification. So there can be no doubt that the light microscope is perfectly able to resolve all this down to the Blu-ray fine structure. The images shown were taken by means of normal white light (a low voltage bulb). Some further technical details were already discussed in our recent issue. The Blu-ray image was slightly retouched (some nasty dust particles on the CCD chip surface removed).
[ English keywords: Blu-ray disk, microscope, microscopy, diffraction limit ]

The "first" or primary merit for this resolution achievement apparently can be attributed to Jean-Marc Babalian who published several Blu-ray photomicrographs in 2017 on photography.net. Babalian used a high grade microscope with a N.A. 1.4 Plan objective and differential interference contrast.
We would like to add that similar resolution results can be achieved with more modest equipment, too: The microscope used by us was equipped with a less expensive N.A. 1.30 LOMO Apo oil immersion objective in combination with a decenterable condenser (the latter has fallen into oblivion already many decades ago):



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Fig. 2: a so-called "big" Abbe condenser. Its iris diaphragm (als called aperture iris) can be rotated horizontally and variably decentered. By means of this mechanism the utmost raking light based resolution can be achieved which comes closest to the famous Abbe resolution limit published already in the 19th century.

To sum up and conclude: The fine structure of a Blu-ray disk can be resolved by means of a vintage microscope. But one should know how to use it. It is a big mistake to claim that the Blu-ray pits and lands were ranging beyond the diffraction limit and the reach of a classical light microscope.



Literature

Gergely Huszka et al.: Dielectric microsphere-based optical system for super-resolution microscopy. Conference Paper, June 2017. DOI: 10.1109/TRANSDUCERS.2017.7994464
[therein on p. 2004: "Meanwhile, on the optical image, even the tracks are not distinguishable." (Annotation: this is referring to fig. 2A with the light microcopic image of a Blu-ray DVD)].

Seoungjun Lee et al.: Overcoming the diffraction limit induced by microsphere optical nanoscopy.
Journal of Optics 15 (2013) 125710.
[cf. within the abstract: "The sub-diffraction features of a Blu-ray Disc"]

Hok Sum Sam Lai et al.: Super-Resolution Real Imaging in Microsphere-Assisted Microscopy.
PLoS One. 2016; 11(10): e0165194. Published online 2016 Oct 21. doi: 10.1371/journal.pone.0165194. ["According to the literature [8,1517], a Blu-ray disc has a gap between its tracks that ranges from 100 to 120 nm [8,16,17]. This separation is below the diffraction limit, making it unobservable using normal microscopes and suitable for the super-resolution tests performed in this study."]

Zengbo Wang: Microsphere super-resolution Imaging. Nanoscience 3 (2016) S.193-210.
[therein on p. 201: "a commercial Blu-ray DVD (...). The sub-diffraction-limited 100 nm lines (...)"]

Luo Xiangang: Engineering Optics 2.0 - A Revolution in Optical Theories, Materials, Devices and Systems. Springer Verlag 2013. ISBN-13: 978-9811357541.
[see therein on p. 276: "Then, a sub-diffraction-limited Blu-ray disk (Fig. 6.33c) containing 200 and 100 nm features was used as the imaging objects."]




© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.


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