Dye-doped sol-gel coatings for near-infrared laser protection
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J.A.I. Oksanen and P. Raerinne Defence Forces Research Institute of Technology, Weapons Technology Section, P.O. Box 5, Fin-34111 Lakiala, Finland
J.T. Rantala VTT/Electronics, P.O. Box 1100, Fin-90570 Oulu, Finland (Received 16 October 2000; accepted 25 May 2001)
Sol-gel technology was used to fabricate two types of near-infrared absorbing dye-doped polyceram coatings for eye protection purposes against laser radiation. Tolerance of polycarbonate visors against mechanical and chemical stresses may be enhanced by using these coatings. The visible light transmission maxima of high-quality 35 and 25 m-thick spray-coated polyceram coatings were 70% and 90% for methacrylic and propyl functionalities, respectively. Optical densities at 1064 nm were 4 and 2.
Protection of human eye and optronic devices against laser radiation has become essential due to wide use of lasers both in military and commercial applications. Laser eye protection requires high transmittance at visible wavelengths (400–750 nm). Correspondingly, the optical density (OD) at the laser threat wavelengths should be as high as possible. For the human eye the most dangerous wavelength region is in the near-infrared (NIR), 750–1400 nm. These wavelengths, invisible to human eye, are also focused on the retina of the eye, increasing the laser power density on the retina by five decades, when compared to that on the iris of the eye. Traditionally, laser eye protective materials are made by using incorporation of absorption molecules into an organic polymer matrix.1 However it is well known that organic polymer materials exhibit relatively low chemical and especially poor mechanical resistance. The sol-gel technique2 offers a feasible way of doping NIR-absorbing dyes in chemically and mechanically stable polyceramic coatings.3,4 The introduction of organic functionality to an inorganic network combines the properties of these two types of materials.5,6 Thus, the mechanical and chemical stability of the inorganic materials and the low-temperature processing and flexibility of the organic materials may be achieved at once. The sol-gel process is carried out in the liquid phase providing an adequate way of mixing NIR dyes into the sol-gel network resulting in a homogeneously doped material. The solubility of the dyes in the sol-gel network may be improved by modifying the chemical functionality of the sol-gel network or by variation of the solvents or processing parameters. Typically sol-gel materials 2186
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J. Mater. Res., Vol. 16, No. 8, Aug 2001 Downloaded: 04 Apr 2015
have been prepared from silicon-based alkoxides. High silica content is preferable, since it has been reported to enhance laser damage threshold.7 In this paper, we introduce a sol-gel spray-coating method for fabrication of NIR-dye-doped protection coatings applicable to polycarbonate visors. The coatings possess high visible light transmittance in addition to protection against the 1064 nm laser radiation of the ND:YAG laser. The paper also emphasizes a one-
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