Novel Uses of Boron Phosphide Films
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easurements were made using a single impact jet apparatus (SIJA) with 10 impacts/sight and 0.8mm diameter jet. Solid impact resistance is also expected to be significantly better as DLC/BP on multispectral zinc sulphide has been demonstrated to be better than silicon [4]. Multispectral zinc sulphide itself is poor in this regard. tU.GUmSon91(=Rarnwb#
Optical Figure 1 compares the measured and theoretical transmittance for a 5mm silicon substrate coated with DLC/10itm BP on one face and a high efficiency antireflection coating on the other.
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Figure 2 Angular performance of DLC/BP on Si
Mat. Res. Soc. Symp. Proc. Vol. 555 0 1999 Materials Research Society
DLC/BP on Silicon (AR on rear lace)
Such a system also has good performance at high angles as shown in Figure 2. This shows the calculated transmittance averaged over 3 to 5 jim, both with an ideal internal antireflection coating and with a practical internal antireflection coating.
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The fact
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DLC/BP COATED ZINC SELENIDE Zinc selenide is a highly transparent optical material but its durability is poor. We are studying how much improvement can be afforded by using it in conjunction with a DLC/BP coating. Durability Rain Impact SIJA studies have indicated that the DTV(10 impacts) can be increased from 75m/s for uncoated zinc selenide to 200m/s for zinc selenide coated with 10pm of BP. This improvement has been confirmed by whirling arm rain erosion tests at Defence Evaluation and Research Agency (DERA) Farnborough (Figure 3). This shows that even a thin layer of -2pm of BP provides some protection whilst more is provided by 7.4prm of BP.
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Figure 3 Rainfield 25mm/hr, 1.8mm diameter; Speed 223m/s
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Optical particularly interesting A coating, from the optical point of view, can be made if a low index form of DLC (EDLC) is used in conjunction with BP on a zinc selenide substrate (Figure 4). Such an approach is more attractive than a zinc selenide sulphide/zinc sandwich because it is more cost effective and can be formed into domes relatively
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-v6&Vth (ffa) Figure 4 Calculated Optical Performance of EDLC/BP on ZnSe
BP ON GERMANIUM FOR LOW SPEED NAVAL APPLICATIONS Durability For naval applications the durability requirements are very different from the airborne environment. In particular, high speed erosion is not usually a problem but chemical corrosion can be a severe problem. Germanium optics are subject to corrosion in a salt fog atmosphere
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