Optical Properties Of Coatings Research Articles

Improved properties of optical coatings through substrate pre-treatment

Optical films were deposited onto float glass substrates following initial pre-treatment via a Hall-type ion source within a conventional magnetron sputtering system. Films of titania, and zinc oxide were deposited via reactive magnetron sputtering. Film properties were analysed using a range of techniques including AFM, XRD, spectrophotometry, scratch testing and wear resistance. Coatings deposited onto glass that was pre-treated with the ion source exhibited enhanced mechanical properties in comparison with those deposited onto untreated glass. In particular, film durability was increased substantially and surface roughness was reduced, without any detrimental effect on the optical properties of the films. The effects of ion source gas species, ion energy and exposure time were studied systematically, and optimum conditions were derived to provide maximum film property enhancement. This study has demonstrated the potential to enhance coatings via the incorporation of an ion source for pre-treatment of glass within a standard production system.

The effect of crystal structure and morphology on the optical properties of chromium nitride thin films

We study the microstructure of various CrxNy (1<x<2, y∼1) coatings grown by unbalanced reactive magnetron sputtering (UBRMS), using X-ray diffraction (XRD) and reflectivity (XRR). The coatings consist of various CrN phases, depending on the growth conditions. XRD has shown that a Cr adhesion layer below CrxNy eliminates the stress and promotes the growth of bigger grains. XRR determined the film density, which can be used also for the phase identification. We found that the UBRMS can produce single-phase CrN and Cr2N coatings with density equivalent to the corresponding single-crystals. The optical properties of the coatings were studied by spectroscopic ellipsometry (SE). The variations of optical properties of CrxNy coatings have been evaluated from SE data using the combined Drude–Lorentz model, which describes the optical response of the conduction and valence electrons, respectively, and provides the conduction electron density and the energy positions of the interband transitions. Finally, the optical properties were used to quantify the volume fractions of each phase using effective medium theories.

Improved mechanical properties of optical coatings via an enhanced sputtering process

Magnetron sputtering is the process of choice for the deposition of a wide range of industrially important coatings. However, current processes have inherent limitations in terms of controlling, independently, the flux and energy of particles incident at the substrate at each stage of the deposition process. Consequently, film properties may not be optimal. In order to overcome this limitation, studies are being made of an enhanced sputtering system, which incorporates a grid-less linear ion source suitable for use in a reactive gas environment. The impact of this source on the structure and properties of dielectric coatings, in comparison with films grown in a standard system, is reported here. Coatings have been characterised in terms of their structures, optical properties and mechanical properties using a range of techniques including atomic force microscopy, X-ray diffraction, spectrophotometry, critical load scratch testing and wear testing. Results to date demonstrate that the enhanced system improves the flexibility of control of the growth parameters in a magnetron sputtering system.

Scandia optical coatings for application at 351 nm

The recent interest in high-power UV lasers, as energy source to study nuclear fusion in confinement, has motivated the design of new high-index materials highly resistant to UV radiation. Such materials were to be deposited on optical surfaces and used as components for lenses, mirrors, protective layers, polarizers, etc., devices. Quarter-wavelength thickness (i.e. 351/4 nm) optical thin films of scandia, hafnia and zirconia xerogels, produced from sol–gel chemistry, have been prepared on fused silica substrates by dip coating. The initial scandia-based particles were lozenge-shaped platelets (i.e. 70×40×5 nm). These were highly stable in suspension in alcohols, and did not change their morphology after calcination at 773 K. Hafnia- and zirconia-based particles were spherical and less than 5 nm in dimension. Structures and surface topographies of coatings were characterized by atomic force microscopy and photothermal deflection. X-ray photoemission spectroscopy investigation allowed for the determination of the thin film chemical composition. Optical properties of coatings were deduced from UV-transmittance and ellipsometry measurements. Resistance to laser radiation at 351 nm in N-on-1 and R-on-1 modes are reported in detail. Each xerogel thin film was of high optical quality, exhibited a low surface roughness, and had excellent transparency at 351 nm. Scandia thin films were successfully purified by solvent extraction and thermal treatment. Annealing the scandia-based coatings at 773 K induced a densification of the xerogel network to cubic Sc2O3, exhibiting a refractive index of 1.85. Except for the dense scandia layer, other coatings exhibited laser-induced damage threshold (LIDT) above the resistance of the bare fused silica substrate (LIDT>11 J/cm2), suggesting that they could all be used as component for UV optical devices.

Optical Properties of Coatings with Cu and Copper Oxide Colloidal Particles in a SiO&lt;sub&gt;2&lt;/sub&gt; Matrix

SiO 2 coatings prepared by the sol-gel method containing various amounts of copper have been annealed under two different atmospheres to produce colloidal copper based particles embedded in a SiO 2 matrix. The particle composition depended on: the amount of copper added to the stating solutions, the atmosphere in which the samples were annealed and the annealing temperature. The optical properties of the colloidal coatings were determined using the model proposed by Mie, using effective values for the optical constants of the colloidal particles.

Study of the optical properties of diamond-like coatings prepared by Laser-Arc

The Laser-Arc as a controlled pulsed arc plasma source was used to prepare diamond-like coatings (DLC) for optical applications. DLC films with a thickness of up to 500 nm were deposited on different substrate materials (ZnSe, NaCl, KCl, Ge) using special preparation techniques for enhancing the substrate-film adhesion. Coating was performed at room temperature in a vacuum of 10 −4 Pa. A special moving substrate holder was used to deposit an all-round protective DLC that covered the complete surface of the salt substrates including the rims. The optical properties of the coating were determined by spectrophotometry and laser calorimetry. On the basis of the photometric transmission measurements, the refractive indices were calculated. The optical absorption at 10.6 μm ranges from 200 to 900 cm −1 and depends on the film thickness and on the substrate material. The results demonstrate that the controlled arc evaporation by Laser-Arc is suitable for the preparation of DLC with optical quality.

Antireflection coatings on KCl single-crystal optical elements for optical systems of continuous and pulsed technological lasers

Several single- and double-layer 3ntireflection coatings on KCl single crystal plates were deposited in vacuum by thermal evaporation. The optical properties of the coatings (reflectance, transmittance and absorption) were theoretically investigated using iterative and matrix methods. Experimental studies of the optical, mechanical and moisture-resistant properties of the antireflection coatings in combination with the theoretical results show that the best coating system is PbF 2/ZnSe/KCl. The surface reflectance of this coating is about 0.05% and the absorption of KCl plate with such a coating is 0.05%, which is an acceptable value for CO 2 laser systems with powers 10 kW and over.

Optical properties of glass coatings containing Fe and Co

Glass films of SiO 2M x O y (M = Fe, Co, FeCo) have been prepared on soda-lime-silica flat glass by sol-gel employing the dip-coating technique. Different parameters affecting solution preparation and application and coating processing (H 2O/TEOS and R-OH/TEOS ratios, type of catalyst, time and temperature of thermal treatment) were studied, determining the limits in the R-OH, H 2O, TEOS diagram within which good coatings can be produced. Film thickness varies from 0.2 to 0.9 μm and its dependence on viscosity and oxide concentration in the solution and on the withdrawal rate has been studied. Furthermore, it has been determined the relation between film thickness and microcracks appearance using ROM. Optical properties of coatings have been investigated by spectrophotometric techniques, optical parameters obtained being compared with the corresponding parameters of soda-lime-silica glasses containing the same oxides. From these measurements, the coloration mechanism in each case has been determined.

The Electrolytic-Coloured, Anodized Aluminium Selective Absorber Coating and its Optical Properties

This paper describes the technology and optical properties of the selective absorber coating prepared on industrial pure aluminium or aluminium alloys by the anodizing and colouring method. The optical properties of the coating are solar absorptance αs = 0.94 (AM2) and normal thermal emittance e = 0.10; the coating was stable during the ageing test. Scanning electron micrographs of surface morphology and fracture section as well as Auger depth profiling data of the coating are given. Based on this information, a coating structure model of Ni particle pigmented A12O3 film is proposed in which the Ni concentration has a graded distribution. Bruggeman effective medium theory and multilayer matrix technique are used to calculate the spectral reflectance of the coating in the wavelength range 0.3 to 20 μm. The result shows that the theoretical value is approximately in agreement with the experimental data. The effect of morphology on the optical properties of coatings is also discussed.

Methods for estimating the influence of the departure from design parameters on the optical properties of interference coatings

Two methods are suggested for estimating the influence of errors occuring in the course of fabrication of interference coatings on the optical properties of these coatings. These methods deal with two types of error, one of which is dependent and the other independent. It is shown that the most general method is mathematical modeling. A description is given of a computer program, which can be used to estimate the probability that the optical properties of multilayer coatings fall within a specified range if the sensitivity of the recording instrument is known. Examples are given of the modeling of the fabrication of some coatings which are widely used in quantum electronics.

Optical Properties of Coatings. Effect of Pigment Concentration

Optical Properties of Coatings. Effect of Pigment Concentration