Ambient humidity is an important factor to consider when maintaining dielectric films’ component performance. Herein, humidity-influenced experiments were conducted on complex spectral dielectric films based on SiO2 and K9 substrates. Firstly, complex spectral dielectric films’ spectral and surface stresses in different humidity environments were measured. Subsequently, laser-induced damage threshold measurements were carried out on these components. The experimental results indicate that the environmental humidity will induce the evolution of the internal structure of the dielectric films on the mirror, resulting in the deformation of the coating surface and a slight shift of the reflection spectrum. At the same time, the environmental humidity also greatly influences the anti-laser damage performance of the dielectric film mirror. Dielectric films based on SiO2 have excellent damage resistance in high-humidity environments. Conversely, K9-based dielectric films have better damage resistance in low-humidity environments.

Backward light by stimulated Brillouin scattering (SBS) induces the final transport mirror laser damage, which has been considered a bottleneck problem in developing high-power and high-energy laser facilities. In this work, an improved continuous phase plate (CPP) model and a backward SBS model were established based on the G-S algorithm and the Fresnel diffraction transmission algorithm to simulate the backward SBS to the final transport mirror. This study discussed the propagation characteristics of backward SBS. The research results showed that the distribution of the backward SBS transmitted to the final transport mirror was determined by the phase structure of the continuous phase plate attached to the back-transmission process. By optimizing the CPP design, reducing the transmission distance, reducing the intensity modulation, and controlling the phase of the incident beam, the modulation of backward SBS can be suppressed, which has great significance in improving the laser-induced damage threshold to the final transport mirror.

In laser application systems, the optical film is one of the most important parts of the system, as well as its weakest link. Its damage performance determines the output characteristics and safety performance of the laser system. This paper focuses on the fundamental frequency reflection of dielectric films used in large high-powered laser devices. The study of the dielectric film’s initial laser damage performance and laser damage growth performance is carried out through laser damage testing and microscopic morphology testing of the damage. The results show two different damage morphologies: type 1 damage (film discoloration damage) and type 2 damage (cratered damage), and the damage growth behavior between the two is very different, with type 1 damage not growing and type 2 damage growing rapidly under subsequent episodes that trigger their damage fluxes. The difference in the growth behavior is well explained by the micro-zone surface shape of the damage location. The results of this paper help to deepen the understanding of the dielectric membrane element processing process and the damage growth behavior.