UV light of short wavelengths from (2-4x10^-6) m is present in small amounts in sunlight (sunburn), in the light from mercury vapor lamps (sun-beds), and UV-LED's (money tester).

Blue-ray discs use short wavelength blue light to read the information stored as pits on the disc. Because blue light has a shorter wavelength than red, the density of information can be increased by a factor of five. If UV lasers could be made, then another increase in density by a factor of 10 or 20 would become possible. It took forty years to develop a solid state blue laser. How long the next step take?

UV-LED money tester.

> More