Fig 10 internal lidt of single layers of mixture ma

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Fig. 10. Internal LIDT of single layers of mixture ma- terials tested under single irradiation at 500 fs and 1030 nm, as a function of the refractive index at 1030nm. If we analyze now the LIDT as a function of the refractive index of the mixture film (Fig. 10), we can observe that with the exception of Sc 2 O 3 - SiO 2 mixtures the behavior of the mixture films is the same that the simple films. The mixture materials fill the gap between the simple thin film materi- als. For the case of Sc 2 O 3 - SiO 2 mixture sam- ples, a clear deviation form the general tendency is observed. This is associated with a change in the damage morphology with the occurrence of more pronounced thermal effects when the content Sc 2 O 3 is increased. The relatively high damage threshold compared to other materials makes Sc 2 O 3 - SiO 2 mixtures an interesting choice for the high index material to produce optical interference coatings for high power applications in the femtosecond pulse duration range. However we have to keep in mind that the results are obtained for single pulse irra- diation. For low refractive index materials, fluoride films exhibit a quite low damage threshold when compared to their bulk counterparts, however by introducing a small amount of an oxide (Al 2 O 3 in AlF 3 in the case shown in Fig. 8) improves no- tably the properties of the film and a high LIDT compared to silica can be obtained. 4. Conclusion We have reported on an extensive experimental study on the laser damage resistance of thin films and bulk optical materials at 1030nm, 500fs. In the case of simple materials a clear ranking of materials can be established based on their bandgap values with a linear evolution of the LIDT, as observed in previous studies. Surface of bulk and thin film materials were found to have the same evolution and comparable laser damage resistance. Accord- ingly the deposition parameters were found to be not very critical, at least for single shot irradiation which were the conditions of these tests. In the case of mixture films however, a more complex behav- ior is observed that cannot be described by simple models (rate equation) or simple phenomenologi- cal laws based on the first order dependency on the bandgap of the the materials. In some cases (Sc 2 O 3 - SiO 2 for instance) the combination of the mate- rials gives specific properties to the film and very high damage threshold can be achieved. The re- sults reported in this paper were however restricted to one particular condition (1030nm, 500fs, single shot irradiation) and will be further extended to other irradiation parameters (different wavelength, multishot irradiation) with the same methodology to be useful for applications. Acknowledgments The results presented in this paper have been ob- tained thanks to the contribution of different people that have been implied in the preparation and char- acterization of the samples. The authors would like to acknowledge their support: D.B. Douti, B. Mangote, F. Lemarchand, C.
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9 Hecquet, M. Lequime from Institut Fresnel- France M. Mende, H. Ehlers, L. Jensen, M. Jup´
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  • Fall '19
  • refractive index, bandgap, Ultrashort pulse, LIDTs

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