Fabrication of UV-Curable Polysiloxane Coating with Tunable Refractive Index Based on Controllable Hydrolysis.

In order to improve laser transmission efficiency at 1053 nm and 527 nm, a potassium deuterium phosphate (DKDP) crystal (a key component of high-power laser systems) needs a bi-layer antireflection coating system on its incident surface. UV-curable polysiloxane coatings with a refractive index varying from 1.500 to 1.485 were prepared through the polycondensation of a methacryloxy propyl trimethoxylsilane (MPS) monomer with a controllable degree of hydrolysis. Additionally, the influence rule of the coating structure on the refractive index was intensively studied, and the primary factors that dominate the hydrolysis process were discussed. Further refractive index adjustment was achieved using only a small amount of dopant based on the polysiloxane coating with refractive index of 1.485, allowing for high antireflection of the bi-layer coating system at desired wavelengths to be achieved. In addition, high laser damage resistance and remarkable mechanical properties of the coating were simultaneously realized through the incorporation of a minor quantity of dopants, which benefited from the successful modulation of the intrinsic refractive index of the polysiloxane coating.

Damage analysis and mechanism study of sol-gel coating over KDP crystal under multi-pulse of laser irradiation at low flux.

The purpose of this study is to analyze the damage of antireflective (AR) coating over potassium dihydrogen phosphate (KDP) crystal subjected to multi-pulse laser irradiation at low flux under vacuum. Fresh silica AR was characterized as a reference; Atomic Force Microscope (AFM), Scanning Electron Microscopy (SEM), profilometer, and Scanning Near-Field Optical Microscope Photo-induced Force Microscope (SNOM-PiFM) were employed to analyze the characteristics of coatings. The experimental results indicated that the damage of AR coating over the KDP crystal was mainly caused by partial exfoliation, which exposed silica particles beneath the surface. It was found that the accumulated tensile stress led to coating damage with the increase of laser pulse. The initial coating damage was observed to extend and interconnect to form large-area exfoliation. Splitting mechanism of SiO-Si TO3 was observed at vibration mode peaks of 1064 cm-1 and 1096 cm-1showing progressing irradiation damage. Based on this study, it would be helpful to suppress the damage probability of AR coating over KDP crystal applied in high-power laser systems. Moreover, the applicability of SNOM-PiFM method to study the Infrared Radiation (IR) spectra of ultra-thin coatings with transparent substrates was proposed.

Template-Free Fabrication of Refractive Index Tunable Polysiloxane Coating Using Homogeneous Embedding Strategy: Application in High-Power Laser System.

A refractive index (RI) tunable polysiloxane coating was fabricated based on the cross-linked network structure embedded with mesoporous silica nanoparticles (MSNs), in which the MSNs were utilized to modulate the RI as well as to support the interior structure of the polysiloxane coating. The Si-O-Si inorganic backbone structure in combination with characteristics from the photopolymerization of active bonds produced the main cross-linked network structure, and controllable embedding of MSNs constructed the network-sphere structure. This approach eliminated the high-temperature post-treatment that was needed to remove the template, which ensures the safe application for temperature-sensitive laser crystal substrates and avoids coating structure collapse. In addition, degradation of the resulting coating can be minimized due to the similar chemical formation between MSN and polysiloxane coating. Hereby, a polysiloxane coating with expected spectral and laser damage-resistant properties can be obtained. This will facilitate the fabrication and application of a laser component with both high-transmission and high-flux capability for a high-power laser system.

Fabrication of Refractive Index Tunable Coating with Moisture-Resistant Function for High-Power Laser Systems Based on Homogeneous Embedding of Surface-Modified Nanoparticles.

Moisture-resistant silicone coatings were prepared on the surface of potassium dihydrogen phosphate (KDP) crystal by means of spin-coating, in which hydrophobic-modified SiO2 nanoparticles were embedded in a certain proportion. The refractive index of such coating can be tuned arbitrarily in the range of 1.21⁻1.44, which endows the KDP optical component with excellent transmission capability as well as the moisture proof effect. A dual-layer anti-reflective coating system was obtained by covering this silicone coating with a porous SiO2 coating which is specially treated to enhance the moisture resistance. Transmittance of such a dual-layer coating system could reach 99.60% and 99.62% at 1064 nm and 532 nm, respectively, by precisely matching the refractive index of both layers. Furthermore, the long-term stability of this coating system has been verified at high humidity ambient of 80% RH for 27 weeks.