RESUMEN
An international round-robin experiment has been conducted to test procedures and methods for the measurement of angle-resolved light scattering. ASTM E2387-05 has been used as the main guide, while the experience gained should also contribute to the new ISO standard of angle-resolved scattering currently under development (ISO/WD 19986:2016). Seven laboratories from Europe and the United States measured the angle-resolved scattering from Al/SiO2-coated substrates, transparent substrates, volume diffusors, quasi-volume diffusors, white calibration standards, and grating samples at laser wavelengths in the UV, VIS, and NIR spectra. Results were sent to Fraunhofer IOF, which coordinated the experiments and analyzed the data, while ESA-ESTEC, as the project donor, defined conditions and parameters. Depending mainly on the sample type, overall good to reasonable agreements were observed, with largest deviations at scattering angles very close to the specular beam. Volume diffusor characterization unexpectedly turned out to be challenging. Not all participants provided measurement uncertainty ranges according to the Guide to the Expression of Uncertainty in Measurement; often, a single general scatterometer-related measurement uncertainty value was stated. Although relative instrument measurement uncertainties close to 1% are sometimes claimed, the comparison results did not support these claims for specular scattering samples as mirrors, substrates, or gratings.
RESUMEN
The intensity of scattered light is extremely sensitive to even small changes of illumination wavelength, incident angle, polarization states, or even the measurement position. To obtain light scattering distributions with varied parameters, time-consuming sequential measurement procedures are typically employed. Here, we propose a concept for the measurement of multiple properties at the same time. This is achieved by tailoring orthogonal frequency division multiplexing (OFDM) for light scattering measurement techniques to the required low inter-channel crosstalk performance. The concept is used for a highly-robust roughness and contamination characterization, to derive one-shot roughness information, as well as to characterize color and appearance.
RESUMEN
Grating waveguide structures have been prepared by the deposition of a high refractive index broadband antireflection coating onto a patterned fused silica substrate. Aluminum oxide and hafnium oxide as well as mixtures thereof have been used as coating materials. Optical reflection measurements combined with atomic force microscopy have been used to characterize the structures. Upon illumination with a TE wave, the best structure shows a narrow reflection peak located at 633 nm at an incidence angle of about 17°. The peak reflectance of that sample accounts for more than 89%. Off-resonance interference structures appear strongly suppressed in the spectrum between 450 and 800 nm because of the characteristics of the designed antireflection layer. The structure thus possesses a notch filter spectral characteristic in a broad spectral range.
RESUMEN
Aluminum layers protected with fluoride coatings have been deposited by evaporation and characterized with respect to their suitability as vacuum ultraviolet (VUV) mirrors. Optical characterization has been performed by spectrophotometry, while the surface quality of the layers has been judged by means of x ray reflection, scanning electron microscopy, and atomic force microscopy. In particular, protection with aluminum fluoride results in superior VUV reflection properties. VUV reflectance values between 80% and nearly 90% have been verified even two years after deposition and exposure to the atmosphere.
RESUMEN
Light-scattering measurements on rugate coatings made out of mixtures of Si(x)Ta(y)O(z) and Si(x)Hf(y)O(z) were performed. Through successive optimization steps for the substrate roughness and deposition parameters, the overall scattering loss could be reduced by 96% to 3.5 ppm. In order to analyze the relevant scattering mechanisms in such coatings, different theoretical models for scattering from bulk and surface imperfections are compared to measured data. The best accordance between simulated and measured data could be achieved for the theory based on bulk imperfections, while the classical roughness based theory, which is used for conventional multilayer systems, gives reasonable good results.
RESUMEN
The realization of ultra low-loss dielectric reflection gratings with diffraction efficiencies between 7% and 0.02% is presented. By placing the grating beneath the highly reflective layerstack scattering was significantly reduced. This concept allows the all-reflective coupling of high laser radiation to high finesse cavities, thereby circumventing thermal effects caused by absorption in the substrate.
RESUMEN
A method for characterizing the microroughness of samples in optical coating technology is developed. Measurements over different spatial-frequency ranges are composed into a single power spectral density (PSD) covering a large bandwidth. This is followed by the extraction of characteristic parameters through fitting of the PSD to a suitable combination of theoretical models. The method allows us to combine microroughness measurements performed with different techniques, and the fitting procedure can be adapted to any behavior of a combined PSD. The method has been applied to a set of ion-beam-sputtered fluoride vacuum-UV coatings with increasing number of alternative low- and high-index layers. Conclusions about roughness development and microstructural growth are drawn.
RESUMEN
An international round-robin experiment has been conducted among laboratories in different countries to test the measurement and the data-analysis procedures in the International Organization for Standardization draft standard ISO/DIS 13696 for measuring total scattering from low-scatter laser optics. Ten laboratories measured total backscattering from high-reflectance mirrors, 50% beam splitters, and antireflection-coated windows. Results were sent to the Laser Zentrum Hannover, which acted as coordinator and analyzed all the backscattering data. The results showed that the procedure in the draft standard was useful for measuring and reporting backscattering for low-scatter optics. Problems encountered in the round-robin experiment included the accumulation of particles on the surfaces, particularly on the high-reflectance mirrors.
RESUMEN
Scattering characteristics of multilayer fluoride coatings for 193 nm deposited by ion beam sputtering and the related interfacial roughnesses are investigated. Quarter- and half-wave stacks of MgF(2) and LaF(3) with increasing thickness are deposited onto CaF(2) and fused silica and are systematically characterized. Roughness measurements carried out by atomic force microscopy reveal the evolution of the power spectral densities of the interfaces with coating thickness. Backward-scattering measurements are presented, and the results are compared with theoretical predictions that use different models for the statistical correlation of interfacial roughnesses.
RESUMEN
The surface roughness of polished glass substrates and optical thin-film coatings is studied with atomic force microscopy and x-ray scattering. It is demonstrated that both methods permit the determination of power spectral density functions in a wide range of spatial frequencies. The results are in good quantitative agreement.
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Thin films of SiO(2), TiO(2), Ta(2)O(5), ZrO(2), and the mixed oxide H4 (Merck) have been deposited onto nonheated glass substrates by electron-beam evaporation in commercial coating plants. All depositions have been carried out with ion assistance provided by three different ion or plasma sources (end-hall, plasma, and cold-cathode sources). The optical film properties such as index of refraction, extinction coefficient, light scattering, and absorption have been examined by spectrophotometry, laser calorimetry, and total integrated light-scatter measurements. Surface morphology has been investigated by atomic force microscopy studies. Furthermore, films have undergone sand erosion tests for the determination of relative wear resistance. The film properties are compared for the three different ion sources.
RESUMEN
For a variety of UV optical coatings, surface roughness was measured by use of an atomic-force microscope (AFM) to study its dependence on the film material and thickness, coating design, and deposition process. After analyzing the corresponding power spectral density functions, we propose a simple classification model for coatings according to the contributions of substrate roughness and intrinsic film roughness to the scattering. Results of scattering measurements on different types of coatings are presented and are found to be in good agreement with predictions based on the AFM data. Consequences for a scatter reduction strategy are discussed.
RESUMEN
To meet the requirements of comprehensively characterizing the morphology of thin films and substrates, a suitable combination of different measuring techniques should be chosen, i.e., a nonoptical surface profile measurement should be used together with optical analysis. It is demonstrated on selected examples of fluoride and oxide films that the use of atomic force microscopy and light scattering fulfills the demand of appropriate quantitative characterization over a sufficiently large range of bandwidths.
RESUMEN
Special substrate-film designs are used to measure roughness-induced scattering and scattering from the volume of optical thin films separately. So theoretical models of surface roughness and volume scattering become applicable to the experimental data, and quantitative information on thin-film microstructure can be derived. Measuring total integrated and angle-resolved scattering on oxide, fluoride, and chalcogenide films of different film thicknesses yields the evolution law of microstructural growth, which for the majority of investigated films roughly follows a square-root dependence on film thickness. Packing densities of fluoride films calculated from volume-scattering data are found to agree with results from quartz-crystal monitoring.
RESUMEN
A theoretical model is presented that describes the volume scattering in thin optical films, particularly in typical columnar structures. It is based on a first-order perturbation theory that concerns the fluctuation of the dielectric permittivity in the film. For evaporated PbF(2) films that show a pronounced columnar morphology, angular as well as total integrated scattering measurements at lambda = 633 nm have been performed on a special layer design to suppress roughness-induced scattering. A comparison of the predicted theoretical and the measured experimental values leads to such structural parameters as packing density and the evolutionary exponent of the columns.