Tical applications as for fundamental research in

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tical applications as for fundamental research in this field, experimental measurements of the laser- induced damage threshold of optical materials are * Corresponding author: [email protected] of main interest. These data can be used for the design of multilayer coatings or for the comparison with theroretical models. However in only few stud- ies dedicated to the sub-picosecond regime different optical materials have been investigated and com- pared: Stuart et al [1] have reported LIDT for high bandgap materials (SiO 2 , CaF 2 , MgF 2 , BaF 2 , LiF), Simanovskii et al [2] have also studied high bandgap materials (CaF 2 , MgF 2 , BaF 2 , LiF) and ZnSe, in the study of Mero et al. [3] dielectrics optical coat- ings were investigated (TiO 2 , Ta 2 O 5 , HfO 2 , Al 2 O 3 , SiO 2 ) and in the study of Watanabe et al [4] inter- mediate bandgap materials were studied (SrTiO 3 , ZrO 2 , LaAl 2 O 3 , MgO, Al 2 O 3 ). Nevertheless the results are difficult to compare because laser dam- age measurements were made in different conditions which can be source of discrepancies. Therefore the objective of the present paper is to report on an extensive study of optical materials in bulk and thin film forms that have been characterized and damage-tested in similar conditions. A large part of the results in the case of coatings have been re- ported in different published works from our group [5–12], the interest of the present paper being to
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2 compare and discuss all these experimental results on the same basis using scaling laws that will be described. Additionally these data have been com- pleted with other coating and bulk materials (see appendix). Particularly the relationship between the damage resistance and the bandgap on the one hand and on the refractive index on the other hand are investigated. The first dependency is indeed of main interest for the study of the physical processes involved [3] and the former is of main importance for the design of high laser damage resistance mul- tilayer coatings [13]. In this paper however we re- strict our investigations on the case of single shot ir- radiation. In the case of multiple pulses the damage threshold is decreasing with the number of pulses, an effect called incubation or fatigue. This decrease of the damage resistance is directly related to the number of incident pulses, but also on other irradi- ation parameters such as the pulse duration, as ob- served in IBS oxide coatings [14, 15], and possibly repetition rate. The process involved being depen- dent on native and laser-induced electronic defects, extensive systematic studies are then also needed on this point to study these behaviors for different coating materials and deposition processes, but is beyond the scope of this paper. 2. Materials and methods 2.A. Samples Dielectric films of different oxides and fluorides available for optical coatings - AlF 3 , Al 2 O 3 , HfO 2 , MgF 2 , Nb 2 O 5 , Sc 2 O 3 , SiO 2 , Ta 2 O 5 , TiO 2 , Y 2 O 3 and ZrO 2 - were investigated. They were produced with various state-of-the-art deposition techniques:
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  • Fall '19
  • refractive index, bandgap, Ultrashort pulse, LIDTs

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