Patent ID: 6894284

Claim:
A method of detecting a low lead impurity level in a below 200 nm transmitting optical fluoride crystal said method comprising: providing a below 200 nm wavelength transmitting optical fluoride crystal having a crystal light transmission path length, said below 200 nm wavelength transmitting optical fluoride crystal light transmission path length ≧2 mm, providing a light transmission spectrophotometer having a light source for producing a transmission test wavelength in the range 200 to 210 nm and a transmission detector for measuring transmission of said test wavelength, transmitting said transmission test wavelength in the range 200 to 210 nm through said below 200 nm wavelength transmitting optical fluoride crystal light transmission path length and measuring the transmission of said 200 to 210 nm test wavelength through said path length to provide a lead ppb impurity level measurement less than 900 ppb.