Abstract
An all-optical switchable twisted nematic liquid crystal system has been designed for use as a laser protection filter, which takes advantage of light-induced modification of liquid crystal order. The filter employs photochromic azo-doped liquid crystal mixtures that have been optically characterized and incorporated into a laser filter device. The ability to switch between transmission and blocking modes is shown to occur, even for incredibly low intensity (0.5 mW) irradiation with a continuous 405 nm laser. The blocking-state extinction is defined only by the polarizer extinction ratio, and sub-second switching is demonstrated for these low laser intensities. The response is sufficiently fast to provide protection for CCD cameras against laser damage. The optical switching time is shown to depend on both temperature and laser power. This automatic photo-switchable device offers an exciting approach for passive laser protection.
Highlights
The accessibility of high-powered hand-held lasers has led to an increase in accidental and malevolent exposure of cameras and eyes to high intensity radiation
Differential scanning calorimetry (DSC, 10 °Cmin−1) data demonstrates that TNI increases with increasing concentration of BAAB2 dopant, as expected since BAAB2 has a higher TNI than 5CB
The same trends for TNI are observed using white-light polarizing optical microscopy (POM, 2 °Cmin−1), coupled with a red filter to prevent the broadband light from photoisomerising the BAAB2 molecules; the 1 °C difference in the transition temperatures is attributable to the absolute accuracy of each measurement method ( ± 1 °C)
Summary
The accessibility of high-powered hand-held lasers has led to an increase in accidental and malevolent exposure of cameras and eyes to high intensity radiation. Laser powers >5 mW can potentially cause damage to eyesight or camera systems [1,2], with lower intensities still presenting a dazzle threat. To provide protection the device must be switchable, rapid, and have high optical densities. The use of liquid crystals (LC) in laser protection has been clearly demonstrated [3,4,5], with their electro-optical properties providing an excellent base for an electrically switchable filter. There is clear potential for using light-matter interactions in photochromic LCs to provide automatic, passive laser protection. We demonstrate a new LC device that includes a photosensitive azo-LC as a passive all-optical switchable protection against continuous (CW) laser threats
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