Badly made green laser pointer damage your vision, and powerful U.S. tech laboratory to help NIST has a home tabletop experiment, separate the good from the dangerous development.
On the Blue Peter Schimmel, we need two plastic cups, a CD and a webcam.
The problem is that some green pointers emit dangerous levels of invisible infrared safe in addition to their level of green. Why?
Well, just have a red red laser pointers inside. But green lasers are expensive, so many green pointer instead of a low-cost (808nm) infrared laser and a few clever physics.
The 808nm laser pumps a crystal of yttrium orthovanadate neodymium (Nd: YVO4) doped, causing the crystal to lower lase (1064) Infrared.
This beam in turn goes through a potassium titanyl phosphate (KTP) frequency-doubling crystal, which halves the wavelength to 532nm - green. All this happens in a tiny module at the tip of the pointer.
NIST says that if the KTP crystal is wrong, or some of the internal reflective coating is too thin, invisible 1064nm are escaping.
From an insult "10mW" green pointer, it is almost 20mW leakage measured by infrared "strong enough to damage the retina, a single cause, before he or she is aware of the invisible light," said NIST.
Apparently green hands are better done not only correctly, but also an infrared-just-in-case-filter on their performance.
The home-test uses a webcam, slightly modified to be sensitive to infrared.
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