using your cd-rom to test for anthrax

CD-ROM drives don't have the sort of photodetector you'd need to run that kind of spectrogram. It's an urban legend.

The same channel that runs "Ghost Hunters"?Look, CD-ROM drives don't work that way. They detect the way pits on the reflective CD surface cause the laser to interfere with itself on its way back to the photodetector.It's not an optical scanner, it's an interferometer. You can't just shine it at an arbitrary surface and get signal back. If you shone it at your goofy anthrax test mixture, the laser would simply disappate. You'd get no reflection back to the detector optics so the CD-ROM head would have nothing to detect.It's not possible, RR. It's a hoax, like the spaghetti crop or the vinyl-based LP-ROM drive.

There's no way the CD ROM could measure opacity. It doesn't have that kind of photodetector, and it's mounted in the wrong place.

Look, it's a simple matter of optics. CD-ROM's read by bouncing a laser of wavelength w at a reflective disc rotating k*w distance away. Data is encoded onto the disc by depressing the reflective surface such that it is moved k*w+1/2w away from the laser, so that as the beam returns from the reflective disc, it's 180 degrees out of phase and so the beam cancels itself out. A simple photodiode detects the difference between the beam being reflected and the beam being out of phase.Shooting the beam through a transparent disc to try to detect some biological colony isn't going to work, because there's no photodetector above the disc in a CD-ROM drive. And even if there were, what's the point of this? The best you get is a picture of a disc with fungus growing on it, and you can get that from putting it on a flatbed scanner.

How? There's no detector at the top of the drive. All the optics are at the bottom.

I don't understand what's doing the reflecting.