Gas-fusion mirrors for atmospheric lidar

Design analysis and test results of two 610 × 432 × 57 mm (24 × 17 × 2.25 in) light-weighted octagonal mirrors and a mounting system for a scanning 1.54-micron wavelength elastic backscatter lidar will be presented. The mirrors were designed to replace damaged gold-coated Zerodur mirrors and fit inside an existing mechanical scanner structure also known as a beam steering unit. Finite element analysis was performed to confirm that the design would meet the required flatness of 3 He:Ne (633 nm) laser wavelengths over the clear aperture. The mirrors were fabricated through a gas-fusion process for weight reduction and flexure stage mounts were designed to compensate for differences in the coefficient of thermal expansion of the borosilicate glass mirrors and aluminum enclosure. Enhanced aluminum coatings will be applied for high reflectivity at 1.54 microns wavelength and durability. Engineering design analysis results, including measurements of the polarization characteristics of the mirror coatings, will be described and field results from a whole system test of the lidar using the new mirrors will be presented.