Pic o’ the moment   Leave a comment

As promised, here are some new images.

Last summer, the CD/DVD writer in my computer broke- mechanical failure, not optical. I’ve been slowly disassembling the optical assembly- it’s an amazing piece of technology. The entire optical assembly is approximately 1″ in length, and contains 2 lasers, several mirrors and lenses, a beamsplitter, and two detectors. The front side, the side that faces the CD/DVD, is a floating lens element. Here’s an image of the backside:

The two cylinders on the top are the two laser diodes with collimating lenses. The light from each laser passes through a quarter-wave plate, and then the paths are combined via the beamsplitter (the cube), and directed onto the CD/DVD by a mirror. The returning light is directed to two detectors- one looks like an LED, and the other is all the way on the bottom right of the image, just offscreen.

The lasers still operate- DVDs use a 640nm laser, while the CD laser operates at 780 nm. By connecting the laser diode to a powers supply (3V DC, 500 mA), I can turn the laser on. Here’s the same view of the optical system with the DVD laser on:

The CD laser cannot be seen by eye- and in fact, when I was checking the lasers, I didn’t realize the laser was an infrared laser (I thought the two lasers were red and blue). Fortunately, I didn’t damage my eyes, but I should have been *much* more careful. I checked the laser output with a spectrometer and verified that the diode was operating properly. The Sony camera isn’t sensitive to 780 nm light either, since it has a Bayer filter on top of the CCD, but I have other cameras that should be able to see the light.

here’s a shot of the floating optical element, with the 650 nm laser light coming through:

But the main set of images I have is for the detector just offscreen. It’s the backside of a chip, and may be used for alignment or error correction. Recall, the optical assembly stays aligned to a 0.74 micron wide track, and moves from track to track at speeds up to several centimeters per second. It’s really quite amazing technology that we have taken for granted.

Here’s an image sequence of one of the detectors, taken with the 63mm, 25mm, and 16mm luminar lenses, and then some final images taken at 32X (epi-DIC). The detector element is approximately 0.5mm in the long direction:

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Posted March 11, 2011 by resnicklab in Physics, pic of the moment, Science

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