The sol-gel antireflective films have been applied in Large-scale, high-power laser facility for several years to improve its output capability. While, the loose, porous films are under the baneful influence of contamination. The concentration of contamination and the optical properties of films are difficult to be measured when the laser facility is operated. Therefore, it will be important to study the stability of optical property of the coated substitute optics. To study the optical property stability of films in different environments, the samples coated with technological process at present were placed under 105Pa, 103Pa, 10-3Pa in laser facility, and spectrum transmittance of them was tested before and during the storage. The spectrum transmittance decrease of the films with storage time is described quantitatively. The tested results shows that, the sol-gel antireflective films consequently can maintain its high transmittance under room pressure. The transmittance will be decreased significantly under 10-3Pa owing to plenty of contamination. The test under 103Pa shows that there is much more contaminants on higher fluent. Further experiment after intensified NH3 and HMDS posttreatment has been performed at the same time. The results shows that these samples have lower rate of the transmittance decrease. Both the control of the cleanliness and the intensified post-treatment will extend the lifetime of the sol-gel antireflective films.
Large high-power-laser facility is the basis for achieving inertial confinement fusion, one of whose missions is to make
fusion energy usable in the near future. In the facility, fused silica optics plays an irreplaceable role to conduct extremely
high-intensity laser to fusion capsule. But the surface defect of fused silica is a major obstacle limiting the output power
of the large laser facility and likely resulting in the failure of ignition. To mitigate, or event to remove the surface defect,
wet chemical etching has been developed as a practical way. However, how the surface defect evolves during wet
chemical etching is still not clearly known so far. To address this problem, in this work, the three-dimensional model of
surface defect is built and finite difference time domain (FDTD) method is developed to simulate the evolution of
surface defect during etching. From the simulation, it is found that the surface defect will get smooth and result in the
improvement of surface quality of fused silica after etching. Comparatively, surface defects (e.g. micro-crack, scratch,
series of pinholes, etc.) of a typical fused silica at different etching time are experimentally measured. It can be seen that
the simulation result agrees well with the result of experiment, indicating the FDTD method is valid for investigating the
evolution of surface defect during etching. With the finding of FDTD simulation, one can optimize the treatment process
of fused silica in practical etching or even to make the initial characterization of surface defect traceable.
Fused silica optics were treated by dynamic etching using buffered hydrofluoric acid (BHF) with different etching depths. The transmissivity of fused silica slightly increases in deep UV (DUV) range after dynamic etching. Surface qualities of fused silica were characterized in terms of surface roughness, surface profile and photoluminescence (PL) spectra. The results show that dynamic etching has a slight impact on surface RMS roughness.PL defects gradually reduces by dynamic etching, and laser damage resistance of fused silica continuously increases with etching depth extending. When removal depth increases to ~12μm, the damage threshold is the double that of the unetched surface. However, surface profile continuously deteriorates with etching depth increasing. Appropriate etching amount is very important for improving damage resistance and mitigating surface profile deteriorating of fused silica during etching process simultaneously. The study is expected to contribute to the practical application of dynamic etching for mitigating laser induced degradation of fused silica optics under UV laser irradiation.
The laser-induced damage of fused silica optics significantly restricts the output ability of large laser systems. Hydrofluoric (HF)-based etching is an effective processing to eliminate impurities and mitigate subsurface defects. Traditional polished fused silica samples were etched for different time in a HF-based etchant (2.3% HF and 11.4% NH4F) assisted by a 1.3 MHz megacoustic field. The laser-induced damage thresholds (LIDT) were measured by R-on-1 method, and fourier transform infrared absorption spectras of the samples were obtained. The results of the LIDT demonstrated that the LIDTs of the fused silica samples increased after megacoustic field assisted etching. The more surface materials were removed, the higher LIDT was obtained. The analysis of the infrared spectra illustrated that structural densification materials were removed during the etching, and thus the LIDT can be improved.
Optical assembly and alignment system plays a crucial role for the construction of high-power or high-energy laser facility, which attempts to ignite fusion reaction and go further to make fusion energy usable. In the optical assembly and alignment system, the vibration control is a key problem needs to be well handled and a material with higher damping performance is much desirable. Recently, a new kind of smart magneto-sensitive polymeric composite material, named magnetorheological plastomer (MRP), was synthesized and reported as a high-performance magnetorheological material and this material has a magneto-enhanced high-damping performance. The MRP behaves usually in an intermediate state between fluid-like magnetorheological fluid and solid-like magnetorheological elastomer. The state of MRP, as well as the damping performance of MRP, can be tuned by adjusting the ratio of hard segments and soft segments, which are ingredients to synthesize the polymeric matrix. In this work, a series of MRP are prepared by dispersing micron-sized, magneto-sensitive carbonyl iron powders with related additives into polyurethane-based, magnetically insensitive matrix. It is found that the damping performance of MRP depends much on magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. Especially, the damping capacity of MRP can be tuned in a large range by adjusting external magnetic field. It is promising that the MRP will have much application in passive and active vibration control, such as vibration reduction in optical assembly and alignment system, vibration isolation or absorption in vehicle suspension system, etc.
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