Sol-gel SiO2 antireflective (AR) film is an important part of the components in "SG II" high power laser device, which plays a technical support in the inertial confinement fusion experiment. Due to its high porosity and large specific surface, it is susceptible to complex environmental conditions during the operation of the device, including humidity change, which will lead to uncertainty in the results of physical experiments. The degree of influence about humidity conditions on the various key properties of SiO2 AR film can be systematically understood by tracking and testing the changes in water contact angle (WCA), transmittance, laser induced damage threshold (LIDT), etc. of that under different humidity conditions for about 24 weeks. Results show that the contact angles and transmittances of SiO2 AR films decrease with increasing humidity. The WCA of the films decrease from 120° to 89.2°, and the peak transmittances decrease by about 0.2% when the relative humidity is 49%, the films had a trend of hydrophilic and becoming thinner. SiO2 AR films have an improving effect on the surface roughness of components, the surface roughness of the components with SiO2 AR film is less than 1 nm, and basically not affected by humidity environment. While the LIDTs of SiO2 AR films increase with the increasing humidity. In order to ensure the long-term stability of the key properties of the components with SiO2 AR films, the ideal storage and working humidity environment for components with SiO2 AR films is 24%~49% based on the test results of various performance factors.
Cleanliness management is essential for the safe operation of high power laser systems. In order to maintain the transmittance and minimize the optics damage, we should protect the optics surface with coatings from contamination. Large aperture optics in the vacuum is easily contaminated by airborne molecular from material outgas. In this paper, we introduce the techniques of cleanliness management in SG-II-UP laser facility. The online monitoring of surface airborne molecular contaminant is carried out with quartz crystal microbalance. We investigated the influence of the airborne molecular contaminant on the 351nm transmittance of fused silica optics with sol-gel coatings.
Neodymium phosphate glass (Nd:glass) is the typical gain medium in the large clear aperture slab amplifiers, and provide more than 99% energy of a high power laser facility. Cladding structure is employed for decreasing the amplified spontaneous emission (ASE) and parasitic oscillation (PO) which are the key limits for the gain of large clear aperture slab amplifier. Polymer cladding is generally used since it was proposed.
Polymer is an organic glue which has risk to decompose and fracture under high flash-lamp irradiation while the irradiation is a common condition in the operation of a high power laser facility. Once the polymer glue falls off, the suppression of ASE and PO of cladding structure would be damaged. In addition, the impurities existing in the glue may form the counteractive scattering sources and reduce the suppression of the cladding structure. Moreover, the decomposer of the organic glue may affect the cleanliness of the slab cavity. Thus, an inorganic edge cladding structure based on hydroxide-catalysis bonding (HCB) was proposed which can match the requirements of the cladding structure and evade the organic glue in the high flash-lamp irradiation slab cavity. An antireflective film was used as the medial material whose refractive index was matched with the cladding structure. Bonded samples were prepared based on HCB and confirmatory experiment under high flash-lamp irradiation was finished.
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