A high quality mirror was required to operate in an optical projection system. The mirror was required to give a high reflectivity over a wide angle of incidence and wavelengths.

Specification

Reflectivity: >97% : 420 nm - 490 nm, >94% : 490 nm - 700 nm

Angular range: 0 - 50 degrees

Polarisation: Within specification for all angles at both s and p polarisation states.



Durability: The coating must withstand the MIL specifications: Mil-M-13508, temperature cycling, adhesion, abrasion, and humidity.

Design Review

Due to the combination of a wide range of wavelengths and angles over which the mirror must operate a dielectric mirror was not appropriate. Furthermore, the need to operate at both s and p polarisation states added to the design difficulty.

Using Essential Macleod our in-house design team produced a theoretical model for an enhanced silver mirror that met the performance criteria.

Figures 1a, 1b and 1c illustrate the theoretical performance obtained for 0 degrees, 20 degrees and 40 degrees.