To meet the requirements for high-performance mirrors in the optical system of laser communication terminal, it is essential to ensure that the film achieves a high reflectivity of > 99% at the target wavelengths of 808 nm and 1550 nm, while also modulating the phase of polarized light, so that the phase difference between s- and p-polarized light remains below 1°. This study aims to overcome the limitations of insufficient phase accuracy in traditional metallic mirrors, develop an enhanced silver-based polarization-maintaining mirror, and verify its reliability in space environments. The designed enhanced silver reflective film for the astronomical telescope plays a crucial role in the optical system development of laser communication terminal.

Using the equivalent-layer design theory, a film structure of “metal + aperiodic multilayer dielectric film” was adopted, selecting silver (Ag) as the metal and TiO₂ and SiO₂ as the dielectric film layer materials. The initial structure was sub |(2TiO₂ 2SiO₂)⁶(TiO₂ SiO₂)⁶Ag| air, and multi-objective optimization was performed with reflectivity and phase difference as the targets. The enhanced silver reflective film samples were prepared using electron-beam evaporation ion-assisted deposition technology, combined with a quartz crystal oscillator and a high-precision optical film thickness monitoring system to control film thickness and deposition rate. After preparation, the samples were subjected to immersion, temperature cycling, adhesion, and damp-heat reliability tests.

The measured reflectance at 808 nm and 1550 nm was ≥ 97.5% for s-polarized light and ≥ 98.95% for p-polarized light (Fig.7, Fig.8). The phase differences in the two bands measured by ellipsometry were 0.65° ± 0.085° and 0.70° ± 0.08°, respectively (Fig.10). All reliability tests were passed (Table 3). The reflectance decreased by approximately 2% compared to the theoretical value, and the phase difference increased by approximately 0.3°, mainly due to scattering caused by the microscopic roughness of the film layers, slightly lower density of TiO₂/SiO₂ layers, and cumulative errors in film thickness.

For the first time, a silver mirror has achieved dual-band high reflectance while maintaining polarization phase control of less than 1°. A film structure of metal plus multilayer dielectric film is used, which is prepared using electron-beam evaporation ion-assisted deposition technology. It plays a key role in the development of the optical system for laser communication terminal. The enhanced silver reflective film undergoes a series of environmental tests, verifying its reliability. The specific processes involved in the design and preparation of this reflective film also provide valuable reference for research on polarization-phase reflective films at other wavelength bands.