Many Protective Glasses Not Tested on Ultrafast Pulsed Lasers, NIST Warns
Many laser eyewear products are not being tested with ultrafast pulsed lasers, the type that increasingly supply light for biomedical applications and imaging, materials processing, industrial micromachining, and that means the eyewear may not provide adequate protection for the technical workers who depend on them, researchers found.
Many laser eyewear products are not being tested with ultrafast pulsed lasers, the type that increasingly supply light for biomedical applications and imaging, materials processing, and industrial micromachining, which means the eyewear may not provide adequate protection for the technical workers who depend on it, researchers at the National Institute of Standards and Technology have found. They published a study in Journal of Laser Applications on 24 samples of protective filters used in eyewear from five different manufacturers and found "some of them are good, but some did not perform even close to their own specs when used with ultrafast lasers," said NIST researcher and study co-author Ted Heilweil.
NIST posted a news release about the findings Nov. 28.
It says typical test procedures and standard measurements widely followed by eyewear makers to set their product specifications use low-power, continuous light sources, so they don't capture many potential hazards of actual high-power, pulsed-laser working conditions. Also, end users infrequently test how their eyewear performs in particular applications before using it.
For example, a filter claiming a certain optical density, which indicate the proportion of light it blocks, actually provided 10,000 times less light reduction than specified. Some other eyewear products blocked the specific wavelength for which they were rated but transmitted much more light at nearby wavelengths.
This happens because ultrafast pulsed lasers emit light pulses lasting femtoseconds (one is a millionth of a billionth of a second). As the pulses get shorter, the range of wavelengths expands.
The researchers were initially supported by NIST's Office of Safety, Health and Environment to investigate how well filters in protective eyewear performed in stopping light from femtosecond pulses.