International audienceAn experimental and numerical study of the laser-induced damage of the surface of optical materialin the femtosecond regime is presented. The objective of this work is to investigate the differentprocesses involved as a function of the ratio of photon to bandgap energies and compare the resultsto models based on nonlinear ionization processes. Experimentally, the laser-induced damagethreshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system.Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damagethreshold with the bandgap and photon energy. A model based on the Keldysh photo-ionizationtheory and the description of impact ionization by a multiple-rate-equation system is used toexplain the dependence of laser-breakdown with the photon energy. The calculated damage fluencethreshold is found to be consistent with experimental results. From these results, the relativeimportance of the ionization processes can be derived depending on material properties and irradiationconditions. Moreover, the observed damage morphologies can be described within the frameworkof the model by taking into account the dynamics of energy deposition with one dimensionalpropagation simulations in the excited material and thermodynamical considerations

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A principal possibility to overcome fundamental (intrinsic) limit of pure optical materials laser light resistance is investigated by designing artificial materials with desired optical properties. We explore the suitability of high band-gap ultra-low refractive index material (n less than 1.38 at 550 nm) in the context of highly reflective coatings with enhanced optical resistance. The new generation all-silica (porous/nonporous) SiO2 thin film mirror with 99% reflectivity was prepared by glancing angle deposition (GLAD). Its damage performance was directly compared with state of the art hafnia/silica coating produced by Ion-Beam-Sputtering. Laser-Induced Damage Thresholds (LIDT) of both coatings were measured in nanosecond regime at 355 nm wavelength. Novel approach indicates the potential for coating to withstand laser fluence of at least 65 J/cm2 without reaching intrinsic threshold value. Reported concept can be expanded to virtually any design thus opening a new way of next generation thin film production well suited for high power laser applications.

In this work a possibility of selective GaN and InGaN layer etching via femtosecond laser ablation was investigated. The samples of different indium concentrations were grown by metal organic chemical vapor deposition (MOCVD) technique on sapphire substrates. Prior to the laser treatment all samples were characterized by the means of photoluminescence and X-ray diffraction techniques. Further the laser-induced damage thresholds (LIDT) were estimated in multiple pulse (S-on-1) and single pulse (1-on-1) regimes for 1030, 515, and 343 nm wavelengths covering NIR–UV spectral regions. Experimental results indicated a strong interrelation between LIDT, indium concentration and band-gap. An abrupt change in single pulse LIDT is observed when the multi-photon absorption experiences transition from three to two photon absorption. Furthermore an overview of typical laser induced damage morphologies is performed and discussed. A selective smooth etching of GaN and InGaN layers was obtained when exposing with multiple pulses in UV range.