Quantized nanolaminates (QNL) are a material system that was developed, produced and characterized by the LZH in 2016 as an alternative optical material. The idea behind it is that, like a normal mixed material, QNLs have a refractive index that is determined by the ratio of the two materials used. However, the electron mobility is severely restricted by the very thin high refractive index material. This results in a higher band gap and a lower absorption edge of the system. Their properties have been demonstrated on ALD and IBS systems. But the complex and slow coating processes meant that only a few iterations could be produced. We have now developed a process on a magnetron sputtering system with a rotating substrate table that makes it possible to produce QNL layers of SiO2 and Ta2O5 at a very high rate of up to 0.8nm/s. This makes it possible to use these nanolaminates economically as a stand-alone material, even in thick and high layer count designs. Because of the process we were able to produce a variety of QNL with different layer thickness and ratio combinations and perform a variety of measurements such as atomic force microscopy (AFM), total scattering (TIS), transmission electron microscopy (TEM) and Laser induced damage threshold (fs-LIDT) to determine their properties. We were able to use the knowledge gained to coat more complex multilayer systems in a range that would otherwise not have been possible with normal Ta2O5-SiO2 coating systems.
Quantized nanolaminates (QNL) are a new type of metamaterials proposed only recently. The basic properties of QNL single layers have been investigated for various material combinations and deposition techniques. Based on these results the hypothesis was put forward that, thanks to the blueshift of the absorption edge, multilayer interference filters composed of QNL-SiO2 will lead to an increased laser damage threshold in the femtosecond regime compared to standard coatings of the same material combination. In our work we will show a comparison of mirrors with and without QNL designed for the wavelength of 1030nm. For these coatings both standard Ta2O5 and SiO2-Ta2O5 QNL were used as high and SiO2 as low refractive index material. Mirrors consisting of Ta22O5 and SiO2 without QNL were also deposited for reference. The designs used were either quarter-wave designs or designs aiming at reducing the electric field. A magnetron sputter system with a rotating table was used for depositing the multilayer designs. The design of the tool allows to deposit a Ta2O5/SiO2 layer pair at every rotation of the table, which results in a QNL deposition rate higher than the rate for the individual materials. In order to accurately terminate the layers at the design thicknesses, broadband optical monitoring was used. Subsequently, the coatings were investigated by spectrophotometry and femtosecond laser induced damage threshold (LIDT) measurements at 1030nm. These measurements showed that samples with QNL exhibit an improved damage threshold compared to standard high-low mirrors as well as to a commercial ion beam coated fs-mirror. Furthermore, it is shown that the designs with optimized electric field exhibit higher LIDT values than their standard λ/4 design counterparts.
Ion Beam Sputtering systems are well established as state-of-the-art deposition tools for the coating of high quality optical thin films with high density and low losses. These coatings are used for many laser applications, with an ever-increasing demand for higher sustained fluence. Ion Beam Sputtering (IBS) is a known technique to provide such high optical quality thin films. Indeed, it allows to achieve high density layers with low absorption and scattering. In this work, various coatings were developed using Bühler IBS technology. Then, total losses were measured using Cavity Ring Down, absorption using Laser Induced Deflection or Laser thermography, and Total Integrated Scatter using dedicated scatterometers. A correlation between the effect of the chosen deposition method and parameters and the measurement performances were made with the aim of a better understanding of the level and the origin of losses in the coatings. Finally, highly reflecting mirror coatings for 1064 nm wavelength were fabricated with different designs and deposition parameters. The results of the different measurements of absorption, scattering and total losses using different equipment are presented and discussed.
In many laser applications, there is a higher and higher demand for more efficient coatings with reduced losses, in terms of absorption and scattering as those are contributing factors to diverse laser damage regimes. Ion Beam Sputtering (IBS) is a known technique to provide such high optical quality thin films. Indeed, it allows to achieve high density layers with low absorption and scattering. In this work, various coatings were developed using Bühler IBS technology. Then, total losses were measured using Cavity Ring Down, absorption using Laser Induced Deflection or Laser thermography, and Total Integrated Scatter using dedicated scatterometers. A correlation between the effect of the chosen deposition method and parameters and the measurement performances were made with the aim of a better understanding of the level and the origin of losses in the coatings. Finally, highly reflecting mirror coatings for 1064 nm wavelength were fabricated with different designs and deposition parameters. The results of the different measurements of absorption, scattering and total losses using different equipment are presented and discussed.
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