Fig 4 10 shot solid symbols higher lidt values and

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Fig. 4. 10-shot (solid symbols, higher LIDT values) and 100,000- shot damage thresholds (open symbols, lower LIDT values) of ultrafast mirrors as a function of the maximum design field strength inside the stack with respect to the incident field. The material of the different mirrors is color-coded. Fig. 2. (a) Spectral reflectivity curves of the test mirrors listed in Table 1 . (b) Spectral group delay dispersion curves of the test mirrors for the design angle of incidence. In the case of 45° mirrors, p polarization is considered. Fig. 5. LIDT comparison for the best-performing multilayer optics in this study for 10-shot and 100,000-shot experiments. 342 Vol. 57, No. 2 / January 10 2018 / Applied Optics Research Article
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design provides a higher reflectivity bandwidth with a maximum reflectivity at 99.2% (Fig. 2 ). By comparing Ta 2 O 5 SiO 2 structures, it can be seen that increasing the number of layers from 41 to 81 in order to achieve a broader reflectivity (see Table 1 and Fig. 2 ), the dam- age threshold decreases by some 13%, as expected. This is because the design cannot be optimized for low maximum fields and broad bandwidth at the same time, as evidenced by Fig. 4 . As expected, the reference coating that is anti-reflective for 800 nm outperforms all the HRs with a LIDT value exceeding 2 J cm 2 . However, damage tests with its design HR at 400 nm wavelength are expected to yield more comparable LIDT values to our HR at 800 nm mirrors. In order to sum up the LIDT results of this study, we provide an overview of the 4 mirrors and one AR coating with the highest LIDT in each category in Fig. 5 showing the superior performance of silica/hafnia stacks (due to the highest bandgap of the high-index material in the stack) but also the high LIDT values achievable with hybrid metal dielectric structures. 3. CONCLUSIONS In summary, our experiments have shown that durable compo- nents for femtosecond applications can be produced with a combination of high-bandgap materials and advanced coating techniques, particularly if the electric field distribution inside the stack is optimized and high standing-wave electric fields at layer interfaces are avoided. As a result, the best HR damage threshold in the current batch of samples was above 1.5 J cm 2 involving an optimized silica/hafnia stack. This conclusion is also true for metal dielectric hybrid mirrors with only slightly worse LIDT values exceeding 1.2 J cm 2 . AR coatings can sig- nificantly exceed even these values with a LIDT of 2.0 J cm 2 . We also found that LIDT decreases with similar tendency with the increasing number of shots, regardless of the choice of the high-index material. The ratio of damage thresholds between 10 and 100,000 shots is approximately the same for any of these mirrors and does not exceed 14% difference in these cases.
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  • Fall '19
  • APPLIED OPTICS, SPIE, Ultrashort pulse

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