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Re: Idea to test if painting back side and edges of CD has an effect on data

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kcisobderf wrote:

Not all CDP lasers are infrared, and I think most aren't. I had a PDM-60 where the spindle motor stopped spinning. I took it apart to see if I could fix it. I had the whole assembly in my hand when I turned it on. I couldn't find how to get to the spindle motor, but I did see the laser-lens combo move up and down trying to lock on the pits. it was dim, but it was red.

I didn't say infrared. I said near infrared. This is the region that's just outside the visible spectrum above red. The visual spectrum runs from 400nm (violet) to 700nm (red) with blue, green, yellow and orange in between. The CD's based on a 780nm laser.

If the peak output of the laser diode were in the visible red, it wouldn't appear dim to you. It would look about as bright as looking into a red laser pointer (which are usually around 650nm). But the peak output is outside the normal visible spectrum and I'd guess the reason you saw anything at all is because the output of the laser is sufficient to overcome the extreme insensitivity our eyes have at that wavelength or the laser was outputting some small amount of energy at lower, more visible wavelengths.

se





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