CD DVD and Blue-ray imaging craziness

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cmtalb01
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CD DVD and Blue-ray imaging craziness

#1 Post by cmtalb01 » Tue Jan 23, 2018 4:26 am

I recently saw on the internet an interesting article with microscope images of CD tracks. Given the challenges, I thought this an interesting experiment. The images (attached PDF file) for the CD and Blue-ray were computer screen captures to reduce size, but otherwise are directly from the camera with no alterations or “photo shopping”. The image for the DVD is again without alterations or enhancements except for photostacking of 5 image depths.

A little background as I understand it from Wikipedia. Blue-ray architecture although similar in principle, physically is quite different from CD and DVD architecture. Blue-ray uses a 405nm laser which is more purple than blue. However, the smaller wavelength (CD IR 780 nm and DVD 650 nm) means that smaller-sized data peaks and valleys can be used to record the information which allows for significantly enhanced data storage capacities. These smaller storage elements however, mean that a thinner substrate must be used to protect the “data” and reduce the diffraction scattering of the laser beam.

Imaging of these peaks and valleys are still a huge challenge for the optical microscopist as the physical sizes of these elements, for all three data formats (CD, DVD, and Blue-ray), are a challenge to resolve with the standard NA objectives. For example the typical “peak” area for a CD is 600X800nm (orange-red to IR light), for a DVD it is 320X 400nm (UV to violet-blue light), and for a Blue-ray disc the peak area is 130X150nm (vacuum ultraviolet). What’s more, the data elements of these discs are protected below a polycarbonate substrate (1100um for CD, 600um for DVD, and 100um for Blue-ray) which adds additional limits to the working distance and hence the maximum magnification of objective that can be used.

The Blue-ray disc was by far the most difficult to image, and I had to throw resolution to the wind and move far into the area of “useless magnification.” Differential Interference Contrast (DIC) was used with 16X and 40X epi-illuminated objectives with an additional magnification of 2X through a Zeiss optovar magnification system to obtain the best possible imaging. In addition, 4X digital zoom of a 24.3 megapixel APS-C camera element was added to extend the magnification well beyond what is even normally considered on such an optical system. This puts the magnification theoretically somewhere around 1280X for the 16X objective with NA of 0.35 and 3200X for the 40X objective with NA of 0.85. The 16X objective with the longer working distance was used to image the CD and DVD with 1.1mm and 600 um polycarbonate substrates respectfully. The 40X objective was used to image the Blue Ray with the 100um hard coat.

Conclusion: imaging nanometer-sized items through relative thick substrates can be a challenge for the microscope optics as well as the "luck" of the microscopist. However, with a little patience and throwing resolution to the wind, some interesting images can be had.

Would greatly appreciate any comments or suggestions.
Attachments
Blue-ray approx 3200X
Blue-ray approx 3200X
Blue-Ray 3200x.jpg (21.26 KiB) Viewed 3023 times
DVD approx 1280X
DVD approx 1280X
DVD 1280X.jpg (8.65 KiB) Viewed 3023 times
CD image approx 1280X
CD image approx 1280X
CD 1280X.jpg (18.27 KiB) Viewed 3023 times
Image file.pdf
Image file
(473.92 KiB) Downloaded 291 times

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patta
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Re: CD DVD and Blue-ray imaging craziness

#2 Post by patta » Thu Nov 18, 2021 4:05 am

Some time after, here we go again
I've cut some slide-size pieces of DVD and bluray, to use them as resolution test

I'd recommend it, if you have some of those obsolete things hanging around.

Different from previos post, I've peeled away the protective layer, so the track bits are exposed, so objectives with short working distance can be used, can put a coverslip of right thickness etc.
It was also useful to scratch or scribble the surface so to get something to focus on, otherwise is very difficult.
I'm using transmitted illumination, that may solve some of the issues of previois post.

WARNING the definition of "resolution" needed here to resolve the bits on the disk is the track pitch (distance between two lines), NOT the width of a single line.
Pretty often in scientific papers titles they cheat and claim "resolved 90 nanometer" when actually they have observed two lines each 90nm wide... but distant 250 nm. This is 250nm resolution imho, not 90.
One can resolve 90 nm thin lines with naked eyes if they're bright enough and one meter apart.

About the DVD, funny discovery:
the track distance is 0.7 micron; should be a piece of cake for a 40x 0.65 objective.... is it?
Nope! visually, with 10x eyepiece I couldn't see nothing. Blank despair!
But then, with afocal camera (over same eyepiece!) here there are the well resolved dots.
Back with the eyes, and with some patience, yes, the lines are visible but sooo tiny that I didn't noticed them before. So tiny, so many. So thin focus depth.
Moral: with 10x eyepiece, my eyes are the weak link in the optical chain. Need to reassess my crave for more Planapo objectives; a 30x eyepiece may be more effective.

About Bluray disk
track distance is 0.32 micron
they should be visible with high NA, like oil immersion
With 0.550 um light, in principle already NA 0.75 could do.
But scarce success until now, I can just see some littlebit twiggling, no neat separation of lines. Only spreading the bluray with mayonnaise seemed to split some bits.
Good excuse to splurge for a new planapo with some NA 1.45?

Photos maybe coming

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