Accurate threshold curves of laser-induced damage (7-ns single shot at 1.064 µm) are measured in bulk and at the surfaces of optical components such as substrates, thin films, multilayers, and liquids. The shapes and the slopes of the curves are related to the spot size and to the densities of the nanodefects that are responsible for damage. First, these densities are reported for bulk substrates. In surfaces and films the recorded extrinsic and intrinsic threshold curves permit the discrimination of the effects of microdefects and nanodefects. In all cases the density of nanocenters is extracted by means of a phenomenological approach. Then we test liquids and mixtures of liquids with controlled defect densities. The results emphasize the agreement between measurement and prediction and demonstrate the validity of the presence of different kinds of nanocenter as the precursors of laser damage.

We report on extensive femtosecond laser damage threshold measurements of optical materials in both bulk and thin-film form. This study, which is based on published and new data, involved simple oxide and fluoride films, composite films made from a mixture of two dielectric materials, metallic films, and the surfaces of various bulk materials: oxides, fluorides, semiconductors, and ionic crystals. The samples were tested in comparable conditions at 1030 nm, 375 to 600 fs, under single-pulse irradiation. A large number of different samples prepared by different deposition techniques have been tested, involving classical materials used in the fabrication of optical thin film components (Ag, ${\mathrm{AlF}}_3$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, ${\mathrm{HfO}}_2$, ${\mathrm{MgF}}_2$, ${\mathrm{Nb}}_2{\mathrm{O}}_5$, Pt, ${\mathrm{Sc}}_2{\mathrm{O}}_3$, ${\mathrm{SiO}}_2$, ${\mathrm{Ta}}_2{\mathrm{O}}_5$, ${\mathrm{Y}}_2{\mathrm{O}}_3$, and ${\mathrm{ZrO}}_2$) and their combination with codeposition processes. Their behaviors are compared with the surfaces of bulk materials (${\mathrm{Al}}_2{\mathrm{O}}_3$, ${\mathrm{BaF}}_2$, ${\mathrm{CaF}}_2$, Ge, KBr, LiF, ${\mathrm{MgF}}_2$, NaCl, Quartz, Si, ZnS, ZnSe, and different silica glasses). Tabulated values of results are presented and discussed.

We report on the laser damage resistance of ion beam—sputtered oxide materials (${\mathrm{Al}}_2{\mathrm{O}}_3$, ${\mathrm{Nb}}_2{\mathrm{O}}_5$, ${\mathrm{HfO}}_2$, ${\mathrm{SiO}}_2$, ${\mathrm{Ta}}_2{\mathrm{O}}_5$, ${\mathrm{ZrO}}_2$) and mixtures of ${\mathrm{Al}}_2{\mathrm{O}}_3\text{-}{\mathrm{SiO}}_2$, ${\mathrm{Nb}}_2{\mathrm{O}}_5\text{-}{\mathrm{SiO}}_2$, ${\mathrm{HfO}}_2\text{-}{\mathrm{SiO}}_2$, ${\mathrm{Ta}}_2{\mathrm{O}}_5\text{-}{\mathrm{SiO}}_2$, and ${\mathrm{ZrO}}_2\text{-}{\mathrm{SiO}}_2$, irradiated by single 500 fs pulses at 1030 nm. Laser-induced damage threshold (LIDT), refractive index, and bandgaps of the single-layer coatings are measured. For pure oxide materials a linear evolution of the LIDT with bandgap is observed. The results are in accordance with our simulations based on photo-ionization and avalanche-ionization. In the case of mixtures, however, deviations from the previous behaviors are evidenced. The evolution of the LIDT as a function of the refractive index is analyzed, and an empirical description of the relation between refractive index and LIDT is proposed.

An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 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 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.

A self-consistent approach is proposed to determine the temperature dependent thermal conductivity k(T) of fused silica, for a range of temperatures up to material evaporation using a CO2 laser irradiation. Calculation of the temperature of silica using a two-dimensional axi-symmetric code was linked step by step as the laser power was increased with experimental measurements using infrared thermography. We show that previously reported k(T) does not reproduce the temporal profile as well as our adaptive fit which shows that k(T) evolves with slope discontinuities at the annealing temperature and the softening temperature.

The knowledge of optical properties of tungsten at high temperatures is of crucial importance in fields such as nuclear fusion and aerospace applications. The optical properties of tungsten are well known at room temperature, but little has been done at temperatures between 300 K and 1000 K in the visible and near-infrared domains. Here, we investigate the temperature dependence of tungsten reflectivity from the ambient to high temperatures (<1000 K) in the 500–1050 nm spectral range, a region where interband transitions make a strong contribution. Experimental measurements, performed via a spectroscopic system coupled with laser remote heating, show that tungsten’s reflectivity increases with temperature and wavelength. We have described these dependences through a Fresnel and two Lorentz–Drude models. The Fresnel model accurately reproduces the experimental curve at a given temperature, but it is able to simulate the temperature dependency of reflectivity only thanks to an ad hoc choice of temperature formulae for the refractive indexes. Thus, a less empirical approach, based on Lorentz–Drude models, is preferred to describe the interaction of light and charge carriers in the solid. The first Lorentz–Drude model, which includes a temperature dependency on intraband transitions, fits experimental results only qualitatively. The second Lorentz–Drude model includes in addition a temperature dependency on interband transitions. It is able to reproduce the experimental results quantitatively, highlighting a non-trivial dependence of interband transitions as a function of temperature. Eventually, we use these temperature dependent Lorentz–Drude models to evaluate the total emissivity of tungsten from 300 K to 3500 K, and we compare our experimental and theoretical findings with previous results.