Universal antireflection coatings for substrates for the visible spectral region

It is possible to design normal-incidence antireflection coatings that reduce the reflectance of any substrate with a refractive index that lies in the range of 1.48 to 1.75. The performance of such coatings depends on the width of the spectral region over which the reflectance is to be suppressed, on the coating materials used for their construction, and on the overall optical thickness of the layer system. For example, the calculated average spectral reflectance of a set of six different substrates with refractive indices 1.48, 1.55, 1.60, 1.65, 1.70, and 1.75, when coated with a 0.56-μm-thick, eight-layer antireflection coating designed for the 0.40-0.80-μm spectral region, was 0.34%. This is higher than the average reflectance that is attainable with a conventional antireflection coating of similar optical thicknesses designed for a particular refractive index. However, it is an acceptable value for most applications. With the universal type of antireflection coating described, it is thus possible to coat a number of different refractive-index substrates in one deposition run, and this can result in considerable cost and time savings.     

Infrared filters and coatings for the High Resolution Dynamics Limb Sounder (6-18 microm)

We describe the spectral design and manufacture of the narrow-bandpass filters and 6-18-mum broadband antireflection coatings for the 21-channel High Resolution Dynamics Limb Sounder. A method of combining the measured spectral characteristics of each filter and antireflection coating, together with the spectral response of the other optical elements in the instrument, to obtain a predicted system throughput response is presented. The design methods that are used to define the filter and coating spectral requirements, choice of filter materials, multilayer designs, and deposition techniques are discussed.     

Antireflection coating design for plastic optics

The coating of plastics for optical applications is intended to improve the mechanical durability of soft polymers and to serve an antireflection function. Usually a classic four-layer antireflection system is added on top of a single-layer hard coating. With needle optimization, an alternative coating design has been developed. The design is characterized by thin high-refractive-index layers that are almost evenly distributed over the whole stack. Plasma ion-assisted deposition was used to deposit coatings upon poly(methyl methacrylate), polycarbonate, and cyclo-olefin copolymer. Uniform antireflection and high scratch resistance have been achieved.     

Antireflection coatings designed for two different infrared substrates

It is shown that it is possible to design normal-incidence antireflection coatings that simultaneously reduce the reflectance of two different substrates. Although this is at the expense of some deterioration in performance when compared with that of conventional coatings, it can lead to significant time and cost savings in small thin-film production facilities. Numerical examples are presented for ZnS/ZnSe, Si/Ge, and ZnS/Ge substrate pairs. The experimental measurements on one such coating are in good agreement with the calculated performance.     

钼酸铅晶体表面红外增透膜的研究

本文讨论了用于钼酸铅晶体表面的宽带红外增透膜的设计以及其在真空环境中的制备。膜系设计中 ,运用反射率图解法以获得满意的光学性能 ;与传统的热蒸发镀膜工艺相比 ,在真空沉积过程中采用了离子辅助沉积技术 ,从而大大提高了膜层的光学特性及膜层品质。试验表明所镀膜层性能优异 ,在光纤通信领域具有广阔的应用前景     

Oberflächenfunktionalisierung von Kunststoffoptik

Surface Functionalization of Polymer Optics Transparent plastics have been used for optical applications with growing demand. This development is accompanied by a desire for extended surface functionalities like antireflection and hardening. Coating processes well established for glass optics cannot be applied in most cases. A manifold of polymer materials with different chemical surface states require special coating deposition parameters. In the first part of the tutorial the main plastic materials are introduced and their properties which are important for the vacuum deposition processes will be discussed.     

Development of optical coatings for 157-nm lithography. I. Coating materials

In a basic study to identify low-loss optics for applications in F2 lithography, five potential coating materials (AlF3, Na3AlF6, MgF2, LaF8, and GdF3) and three deposition methods (thermal evaporation by a resistance heater and by electron beam and ion-beam sputtering) were investigated in the vacuum ultraviolet (VUV) region. Samples were supplied as single-layer coatings on CaF2 substrates by four Japanese coating suppliers. Refractive indices (n) and extinction coefficients (k) of these coatings at 157 nm were evaluated; the transmittance and the reflectance were measured by a VUV spectrometer and were compared. As a result, resistance heating thermal evaporation is seen to be the optimal method for achieving low-loss antireflection coatings. The relation among optical constants, microstructures, and stoichiometry is discussed.     

Optimal single-band normal-incidence antireflection coatings

Mathematical and computational evidence that strongly suggests that optimal solutions exist to single-band, normal-incidence antireflection coating problems is presented. It is shown that efficient synthesis and refinement techniques can quickly and accurately find such solutions. Several visible and infrared antireflection coating examples are presented to support this claim. Graphs that show the expected optimal performance for different representative substrates, refractive-index ratios, wavelength ranges, and overall optical thickness combinations are given. Typical designs exhibit a pronounced semiperiodic clustering of layers, which has also been observed in the past. Explanations of this phenomenon are proposed.     

Materialien für die Brillenbeschichtung in Aufdampfanlagen

Materials for ophthalmic coatings in PVD – coating equipments In our days we cannot have an isolated view only at the coatings for organic lenses. We need to analyse the interaction of substrates, hardcoats and layerdesigns to deliver a longlife – quality of the complete complex “eyeglases”. Special in the field of organic substrates we could observe in the last years an enormous change. The push to deliver more and more thinner and lighter lenses, produces materials with higher indices. The result from this problem is not the adaptation of the antireflection desin at the substrate index but the adaption at the mechanical and thermal properties of these substrates. The caoting labs influence at the complete system is more or less reduced only by the antireflection system. The substrate‐ and hardcoat material could be influenced only by the “world player” for ophthalmic systems. All the small and middle size coating labs worldwide must buy the substrates‐ and the hardcoat materials and have to accept the quality. The only exertion of influence is in the selection of film materials for the AR‐coating and the process technology. The right choise of coating material in quality, form and costs is crucial for a high quality AR‐ coating. A multitude of factors must be considered for the selection of the adequate material.     

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

Gradient index coatings and optical filters are a challenge for fabrication. In a round-robin experiment, basically the same hybrid antireflection coating for the visible spectral region, combining homogeneous refractive index layers of pure materials and linear gradient refractive index layers of material mixtures, has been deposited. The experiment involved three different deposition techniques: electron-beam evaporation, ion-beam sputtering, and radio frequency magnetron sputtering. The material combinations used by these techniques were Nb(2)O(5)/SiO(2), TiO(2)/SiO(2), and Ta(2)O(5)/SiO(2), respectively. The spectral performances of samples coated on one side and on both sides have been compared to the corresponding theoretical spectra of the designed profile. Also, the reproducibility of results for each process is verified. Finally, it is shown that ion-beam sputtering gave the best results in terms of deviation from the theoretical performance and reproducibility.     

Improving thin-film manufacturing yield with robust optimization

A novel robust optimization algorithm is demonstrated that is largely deterministic, and yet it attempts to account for statistical variations in coating. Through Monte Carlo simulations of manufacturing, we compare the performance of a proof-of-concept antireflection (AR) coating designed with our robust optimization to that of a conventionally optimized AR coating. We find that the robust algorithm produces an AR coating with a significantly improved yield.     

Multilayer optical thin films for use at terahertz frequencies: method of fabrication

A new method of fabricating multilayer optical coatings used at terahertz frequencies has been developed. Using plasma-enhanced chemical-vapor deposition, a multilayer antireflection coating for germanium optics at terahertz frequencies was fabricated. The coating consists of amorphous silicon and silicon-oxide layers. The transmittance and structure of the coating were experimentally investigated. The transmittance spectrum of the coating on the Ge substrate shows a wideband antireflection behavior in the 40-120 cm(-1) region.     

Optical coatings for deuterium fluoride chemical laser systems

The high-power laser system has brought an interesting challenge to the development of optical coatings. A wide variety of coating specifications that are often contradictory have to be fulfilled. The choices of deposition process as well as coating materials are critical to coating loss, damage threshold, long-term stability, and other optical properties. A number of optical coatings being newly applied to deuterium fluoride laser systems are presented. The 3.8-mum laser reflection coatings with high damage threshold, multichromatic beam splitters, antireflection coatings with widely separated dual-wavelength bands, and 0.55-14-mum wide-band reflective coatings have been developed on substrates such as Si, Mo, fused silica, chemical vapor deposition ZnSe. Superior results have been obtained with ion-assisted deposition and electron-beam evaporation. Approaches to coating design and practical aspects of coating development are also discussed.     

Multilayer antireflection coatings for the visible and near-infrared regions

With a high-refractive-index mixed-oxide dielectric material of ZrTiO(4) and ZrO(2) [Substance H2 (Sub2) from E. Merck, Darmstadt, Germany], in combination with magnesium flouride (MgF(2)), design optimization and experimental production of low-loss antireflection (AR) coatings are carried out. Design-optimization studies that make use of these materials as constituents of a seven-layer coating system demonstrate that when the useful bandwidth of an AR coating is extended to cover a wider spectral range, the designs are in general found to have increased integrated reflection loss, higher ripple, and increased spectral instability. The experimental studies on Sub2 material show that the films have excellent optical performance over a wider process window, the advantage of which is demonstrated in the production of different AR coatings on a variety of glasses with refractive indices that range from 1.45 to 1.784 and different mechanical, thermal, and chemical properties. The manufacturing process of AR coatings shows a consistency better than 99% with respect to optical properties and durability.     

Antireflection coating with enhanced anti-scratch property from nanoporous block copolymer template

We prepared a sponge-like nanoporous silica film with a dense skin layer by the infiltration of silica precursor into nanoporous polystyrene-block-poly(methyl methacrylate) copolymer template followed by calcinations at high temperature. This film showed not only excellent antireflection at visible light wavelength range but also very good resistance to scratching compared with antireflection materials made of polymeric film. We expect that this film could be used for antireflection film with anti-scratching property for flat panel displays or touch panels.     

Development of optical coatings for 157-nm lithography. II. Reflectance,absorption, and scatter measurement

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendor's coating design by that vendor's coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.     

Antireflection properties of erbium oxide films

We have studied the optical transmission spectrum of a surface film of erbium oxide and evaluated the effect of clarification for the surface of a silicon-based photovoltaic converter with an antireflection coating of this material. It is established that erbium oxide films are highly transparent in a broad wavelength range from 250 to 1050 nm and ensure a decrease in the coefficient of reflection of a silicon surface down to 1–4.5%. The antireflection coating of erbium oxide increases the short-circuit photocurrent of the silicon-based photovoltaic converter by more than 38%.     

Optical and durability properties of infrared transmitting thin films

Refractive indices and extinction coefficients have been calculated for 14 oxide and fluoride thin films over a wavelength range of 0.6-12 mum. Results from adhesion, abrasion, and humidity testing have been included to characterize the durability of each film. The data allow selection of the best oxide and fluoride materials for IR antireflection coatings, and detailed optical constants are provided for the coating design.     

Enhancement in broadband and quasi-omnidirectional antireflection of nanopillar arrays by ion milling

A new technique is developed to fabricate biomimetic antireflection coatings (ARCs). This technique combines a bottom-up fabrication approach (glancing angle deposition, or GLAD) with a top-down engineering process (ion milling). The GLAD technique is first utilized to produce nanopillar arrays (NPAs) with broadened structures, which are subsequently transformed into biomimetic tapered geometries by means of post-deposition ion milling. This structure transformation, due to milling-induced mass redistribution, remarkably decreases reflection over a wide wavelength range (300-1700 nm) and field of view (angle of incidence < 60° with respect to the substrate normal). The milling-induced antireflection enhancement has been demonstrated in the NPAs made of Si, SiO(x) and TiO(2), illustrating that this integrated technique is readily adapted to a wide variety of materials. Good agreement between simulation and experiment indicates that the enhanced antireflection performance is ascribed to a smoother refractive index transition from the substrate to the air, which improves the impedance match and reduces reflection losses. Additionally, ion bombardment tends to alter the stoichiometry and diminish the crystallographic structure of the NPA materials. The broadband and quasi-omnidirectional antireflection observed establishes the strong competitiveness of this technique with the methods previously reported.     

Vacuum evaporated porous silicon photonic interference filters

Porous materials with nanometer-scale structure are important in a wide variety of applications including electronics, photonics, biomedicine, and chemistry. Recent interest focuses on understanding and controlling the properties of these materials. Here we demonstrate porous silicon interference filters, deposited in vacuum with a technique that enables continuous variation of the refractive index between that of bulk silicon and that of the ambient (n approximately 3.5 to 1). Nanometer-scale oscillations in porosity were introduced with glancing angle deposition, a technique that combines oblique deposition onto a flat substrate of glass or silicon in a high vacuum with computer control of substrate tilt and rotation. Complex refractive index profiles were achieved including apodized filters, with Gaussian amplitude modulations of a sinusoidal index variation, as well as filters with index matching antireflection regions. A novel quintic antireflection coating is demonstrated where the refractive index is smoothly decreased to that of the ambient, reducing reflection over a broad range of the infrared spectrum. Optical transmission characterstics of the filters were accurately predicted with effective medium modeling coupled with a calibration performed with spectroscopic ellipsometry.