Optical resistance of sapphire

Vibrational Spectroscopy

“…α-Al 2 O 3 (corundum) is the crystalline form of alumina. Reflectivity measurements on corundum single crystals showed that the band positions and intensities of amorphous surface layers were strongly dependent on the lattice deformations and on the thickness of the surface layer [130]. Additional forbidden bands at 385, 436, 450, 480, 571, 592, 637, 650, 770 and 806 cm −1 were explained by the relaxation of selection rules within a thin, damaged surface layer on the crystal, thus showing the high sensitivity of IR spectroscopy to defects in the crystal lattice [129].…”

Importance of surface topography on pulsed laser-induced damage threshold of Sapphire crystals

“…We have performed tests on Sapphire crystals grown with the Czochralski technique and which surface has been prepared following two different procedures. As a general view, the process for surface preparation (polishing) is an abrasive technique that may yield chemical contamination, surface and sub-surface alterations or stress depending on the level of aggressiveness of the compounds and tools used 1 , 9 – 12 . Surface alterations induced by the process of polishing may also provide local sites for attracting pollution or absorbing contaminants.…”

“…Surface alterations induced by the process of polishing may also provide local sites for attracting pollution or absorbing contaminants. Afterward, when the material surface is exposed to laser irradiation, the defects resulting from the process of surface preparation promote locally enhanced absorption of the laser field or reduce the resistance of the material to fracture 9 , 13 – 16 , 29 , 30 , 36 .…”

“…As Sapphire is extremely difficult to machine making delicate the realization of high-quality optical devices, one will also find interest in the accurate determination of the fluence levels required to modify the surface of Sapphire under a wide range of laser exposure conditions. Otherwise, the last step of fabrication of an optical component, consisting in the preparation of the material surface to provide the optics with optimal optical properties, is essential 9 – 11 . Indeed, the initial conditions of the surface, such as the roughness, topography and chemical and geometrical structure (contaminants, lattice deformation, inclusions), may have an influence on the absorption of the laser light, acting as absorption precursor or enhancement factor.…”

“…Indeed, the surface finish is different in this last case, since the doping prevents to obtain the same quality of the surface. Even if the process of surface finish may promote additional pollution of the sample and also modify its sub-surface structure 9 , 10 , 12 – 16 , we focus here our study on the particular influence of the characteristics of surface topography on the energy level requested for macroscopic surface modification. We first use Atomic Force Microscopy (AFM) for detailed surface characterization and we further expose the samples to femtosecond, picosecond, and nanosecond laser illumination conditions in single pulse regime at visible and near-infrared wavelengths.…”