Laser beam can not pass through clear tape? (experiment)

I have used a test CD-R for that experiment (just out of curiosity):
I have stuck transparent clear tape on a portion of a disc.

The result is that the disc is entirely unreadable on that portion, as if the tape were black instead of transparent.

I know, this is not a situation that would encounter in real life, but I am still curious:

How come a thin layer of clear tape (that is nearly invisible with the naked eye) is enough to make the disc entirely unreadable (until removed)?

Clear tape isn’t transparent, not to a low energy 780nm beam of light, or to the naked eye for that matter;
The beam from the laser would scatter, so focus on the pits and lands of the media would be impossible.

Clearly, you have too much spare time on your hands. :slight_smile:

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Thanks for the response.

Except for some after-tests, the experiment took less than five minutes, actually.

I think you are mixing up translucent with transparent. You can clearly see the tape on the media, therefor it is not transparent.There are few things on earth that is transparent, clean air, fresh and pure still water. Even some ultra high quality glass is not completely transparent.

The tape is translucent, even if only slightly, it’s enough to defuse the light coming from the laser.

You can’t see the tracks on a CD as they are only 1.6 microns. The human eye can’t see anything smaller than 40 microns.

To get things into perspective, The average diameter of a human hair is 0,06 mm

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To make a non-scientific demonstration of what happens when you stick the tape on the disc, please try to put a piece of same tape on a mobile phone camera and compare what happens to level of details captured by the sensor.

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Very interesting. Makes a person wonder if a layer of that on your eye glasses can throw off the recognition scanning? Or the retinal scan recognition at the least? I know that if you put a couple of the invisible LED that is used on tv remotes on the edges of your glasses, where the hinge mounts, it throws of facial recognition from the cameras.

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All transparent substances have multiple effects on light. They can reflect, split, refract (bend), and temporarily slow down light if the medium is a different density to air. The lenses in optical writers and similarly with your glasses are tailored to make the most of these effects, but only if they’re focused and correctly aligned etc. as everything has its limits.

Oh, and welcome to the forums!

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