13.5nm femtosecond laser induced damage behaviors of Mo/Si multilayer were investigated. In this repo rt, we designed and prepared the Mo/Si mirrors for high reflectivity at 20 degrees. The laser damage test for EUV femtosecond pulses was executed at domestic soft x-ray free-electron laser facility in Shanghai. The EUV central wavelength is 13.5 nm and pulse duration is 300 fs. To understand the influence of absorption distribution in the Mo/Si multilayers, the sample was irradiated at normal incident angle for no reflection status. The damage morphologies were characterized by SEM and TEM. It is found that the most severe absorption area appears bubble-like damage, in which the first ten pairs of Mo/Si bilayer merged thoroughly and the bubble under the multilayers is located at the interface close to the substrate. The absorption distribution in the multilayers was simulated by Monto Carlo method, and that was compared with the electric field distribution simulation. We can conclude from the simulation that the damage locations are consistent with the high absorption layers in the coating stacks.
Tracking the interfacial evolution in Ni/Ti multilayers is a crucial aspect of fabricating neutron supermirrors. According to the Debye–Waller factor, the reflectivity of neutron supermirrors is modulated by the interface width, which includes interface roughness and diffusion characteristics. Significant effort has been devoted to shrinking the interface width using mixed working gases or targets during the sputtering process. To elucidate the interfacial evolution, NiC/Ti and Ni/Ti multilayers with different periods were fabricated using direct-current magnetron sputtering. The NiC layers were deposited by co-sputtering Ni and C targets. The interfacial structure and evolution within the multilayers were characterized by grazing incident x-ray reflectivity and transmission electron microscopy (TEM), respectively. The Ni layers in the Ni/Ti multilayers underwent a higher degree of crystallization, resulting in rough interfaces. Moreover, TEM images of the Ni/Ti multilayers suggest that the interface diffusion in the Ni-on-Ti layers reduces the interface smoothness. However, C doping suppresses the crystallization of the Ni layer to achieve smoother Ni/Ti interfaces, thereby improving the interface quality.
A spectral purity Al/Yb/Al filter for the wavelength range of 50 to 100 nm has been designed, fabricated, and characterized. The spectral analysis and transmittance measurements were performed in the wavelength range of 50 to 80 nm and 50 to 100 nm. The spectral analysis measurement results show that high-order harmonics greater than 10 nm can be efficiently suppressed. Transmittance measurement results show that the filter has the ability of harmonic suppression in the wavelength range of 50 to 95 nm. The fitting result of the transmittance measurement result indicated that lower measured transmittance was mainly caused by the interdiffusion and oxidation of the filter.
Optics manufactured by mechanical grinding and polishing inevitably will bring surface/subsurface damages and defects during the machining process. Laser polishing has been demonstrated as a technique capable of achieving ultra-smooth surface with no damage and low-defects, but by far optics polished by this technology are only sufficient for illumination applications. To achieve high quality optics, high precision laser ablation has been proved to be a promising technology for shape correction. With pulsed CO2 laser, high precision laser ablation can be performed by direct evaporation of unwanted surface asperities. To acquire nanometer scale high precision ablation, an accurate control and meticulous adjustment of temperature should be needed. Herein, a mathematical model has been established to assist the understanding of the thermal mechanism of CO2 laser ablation and subsequently a series of simulations have been extended to investigate the phase change of evaporation. The temperature of fused silica irradiated by CO2 laser can be controlled via laser power and pulse duration. To achieve nanometer ablation depth, a gentle evaporation regime at low laser intensity is necessary. The results indicated that the ablation depth linearly depend on laser fluence and depth control levels of nanometer are obtainable with the control of laser fluence.
We present the design and fabrication approach of a rugate narrow band minus filter. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO2) and high (Al2O3) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. This paper mainly discusses about rugate narrow band minus filter design and fabrication approach. The experimental results show the measured transmittance spectra are in good agreement with the designed value. The laser-induced damage threshold (LIDT) of the narrow band rugate minus filter is measured.
KEYWORDS: Annealing, Particles, Dewetting, Silver, Reflectivity, Sputter deposition, Scanning electron microscopy, Antireflective coatings, High power lasers, Solar cells
The structure properties of random mask of antireflective structure prepared by the thermal dewetting process are investigated. As a low-cost and large-scale technique, the mask obtained in our work has a great prospect in the field of solar cell and high power laser system. Ultrathin films of amorphous Ag are deposited on the fused silica by magnetron sputtering. By fast thermal annealing the structures in Ag film are agglomerated on the substrate and form mask. The influence of different thickness and annealing temperature on the structure properties of random mask are studied. The surface morphologies are characterized by scanning electronic microscopy. The suitable conditions to obtain excellent quality Ag nanomasks with the pebble particles are achieved.
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