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Another possible explanation may be that since the tested fused silica samples were not the same, depending on the fabrication and polishing process the samples may have different properties. In our case the damage threshold of the fused silica sample is 4.85 J/cm 2 . 3. Results and discussion To present the results, we will make the distinction between the ’internal’ LIDT and ’measured’ LIDT of the samples. The ’internal’ LIDT, or intrinsic LIDT of the material, corresponds to the measured data that are rescaled in order to take into account the electric field distribution in the sample, using the following definition: Fig. 3. Comparison of the laser-induced damage thresh- old measured by different groups on the surface of fused silica samples at 800 or 1053 nm. Measurements at the pulse duration of the experiments are given (dashed bars) and also rescaled values with the scaling law given in the text for comparing the results at 500 fs (gray bars). Data are extracted from references [22, 26–35]. The present measurement is given on the right (dark gray bar). LIDT internal = | E max /E inc | 2 LIDT measured (2) with E max /E inc the ratio of the maximum of the electric field distribution in the samples to the in- cident field. This correction factor is applied to the coating samples, since there are interference effects in the film, but also to the case of the bulk sam- ples to compare all samples on the same basis (in this case ’ E max ’ is the value on the surface). Note that in a case of a half wave layer, bulk and coating data could be compared directly since the ratio is the same. 3.A. Films of simple oxides and fluorides The LIDT measured on the different dielectric thin film samples are reported on Fig. 4 and Fig. 5. The LIDTs are plotted on Fig. 4 as a function of the measured gap, since the main property that drives the laser damage resistance is the optical bandgap. For applications, the interesting material parameter for the design of multilayer optical component being the refractive index we report also in Fig. 5 the LIDTs and their relation to the refractive index. A linear dependency of the LIDT with respect to the bandgap value has been observed on IBS oxide films (Al 2 O 3 , HfO 2 , SiO 2 , Ta 2 O 5 , TiO 2 ) and de- scribed by a phenomenological model by Mero et al. [3]. This linear dependency is also observed in our experiments on an extended range of materials
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5 Fig. 4. LIDT of optical thin film materials tested in single shot at 500 fs and 1030 nm, as a function of the measured optical bandgaps. The values are given as the internal LIDT, i.e. by taking into account the electric field distribution in the film. Each point corresponds to a different sample. The plain and dotted lines corresponds to the plot of equation 3 with its error margin. See table 2 for data and references.
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  • Fall '19
  • refractive index, bandgap, Ultrashort pulse, LIDTs

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