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17 Jun 2002
Liquid crystal-based films will protect human eyes and optical sensors from intense light and continuous glare while still allowing them to see. Iam-Choon Khoo of Penn State University, US described an 'optical limiting film', which could be used on car windscreens in the future, at the annual meeting of the Materials Research Society in Boston on 2 December 1999.
Liquid crystals let in dramatically less light if there is a laser flash or a strong glare, such as on a car windscreen, because they respond to light in a nonlinear way. The optical limiting film can reduce light with the intensity of 140 milliwatts to only 5 microwatts. It can protect against continuous, long-term light that is below the level that will permanently damage the human eye or optical sensors, but too intense to see through.
The film consists of a liquid crystal material sandwiched between two sheets of glass. A small amount of a dye, methyl red, is mixed with the liquid crystal to enhance its sensitivity to low levels of light.
In addition to car windscreens, the film has potential applications in communications satellites, sunglasses and photographic systems. It will also help welding, protecting both the optical sensors on welding robot and the eyes of the operators.
Khoo and colleagues have already developed an optical switch based on liquid crystal that shuts out damaging laser flashes in a fraction of a nanosecond.
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