Broadband High-Reflection Coating at 50 Degrees
In the paper,|
The goal is to design a high reflector which operates in the wavelength range 400-800 nm at a 50 degree angle of incidence. Because this coating is at 50 degrees, the reflectance of S polarization will be much higher than P. Hence, we can concentrate on controlling the reflectance for P polarization. The coating, composed of layers of L (index 1.45) and H (index 2.35), is to be deposited on glass G (index 1.52). The incident medium is air (index 1.0).
The formulas in the paper lead to a 3-stack (7 periods/stack) design whose stacks are centered at wavelengths 705, 555, and 437 nm. To increase the reflectance, the authors add one additional H layer next to the substrate. The result is a 43-layer coating whose average P reflectance is 98%.
TFCalc can be used to design and refine this type of coating. The starting design is a 43-layer coating with the stack formula
If all layers are optimized to improve the reflectance, the average P reflectance stays approximately the same; however, the minimum reflectance is substantially higher, as shown below.
Here is the last design, with the first layer closest to the substrate and thickness given in nm.
H 97.87 L 171.35 H 80.56 L 152.15 H 74.35 L 154.04 H 83.10 L 178.45 H 72.02 L 129.75 H 85.36 L 141.64 H 82.96 L 141.89 H 71.17 L 137.71 H 69.96 L 104.04 H 55.42 L 113.89 H 71.53 L 121.61 H 63.21 L 111.11 H 61.47 L 121.69 H 63.51 L 101.69 H 56.86 L 101.16 H 52.26 L 82.60 H 46.62 L 94.22 H 53.49 L 90.92 H 46.16 L 86.62 H 51.59 L 91.80 H 45.96 L 80.64 H 49.35
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