Flat surfaces of reaction bonded SiC and aspheric surfaces of Si clad reaction bonded SiC were polished to yield rms surface roughnesses less than 30a. These surfaces were then overcoated with two formulations of a typical front surface protected silver film and their reflectances and roughnesses compared with highly polished fused silica flat surfaces that were silver coated at the same time. Surface roughness and BRDF measurements performed before and after coating with protected silver indicated no significant increase in surface roughness or measured scatter for either silver coating formulation and a barely detectable measured roughness difference between the two coating formulations.

background

Introduction to Surface Roughness and Scattering

Protected silver coatings for low-scatter SiC and SiC/Si mirror surfaces

This work studied sputter deposited conventional spin valves (SV) and related structures. In SV layered structures, two ferromagnetic layers are separated by a non-magnetic spacer. Under an external magnetic field, the relative orientation of the magnetization changes in the ferromagnets, exhibiting the giant magnetoresistive effect. The controlled switching of ferromagnets in convention SV is facilitated by the exchange bias (EB) effect, which is achieved by depositing an antiferromagnetic layer next to one of the ferromagnetic layers in a magnetic field. Two highly related investigations were performed in this work. In the first part the exchange bias effect in the Ni80Fe20/Fe50Mn50/Co trilayer structure was studied. Samples were deposited in a low field condition that permitted EB to be established in NiFe/FeMn but not in FeMn/Co bilayer structures. Temperature-dependent magnetic measurements were performed on the trilayer sample, as well as the corresponding NiFe/FeMn and FeMn/Co bilayer samples. Recent literature on similar system showed that an AF spiral could be formed in the trilayer, which was probed by relative EB directions of the NiFe and Co layers. In this work, no exchange bias was found to propagate from the NiFe/FeMn system into the FeMn/Co system, showing that the AF spiral was induced by the specific magnetic treatment and was not the cause of EB effect. Besides, exchange bias field and coercivity of the samples indicated the influence of the EB system in the presence of an adjacent EB system. Explanations of the effect were made with some existing EB models. In the second part of the work, conventional SV of target structure Nb/NiFe/Cu/Co/FeMn/Nb was studied in a ‘built-up samples’ strategy. A batch of these built-up samples, which corresponded to the different stages of the deposition of the target top conventional SV structure, were prepared by terminating the sputtering process after a certain number of layers were deposited. These samples were thoroughly characterized by structural, magnetic and electrical measurements. In terms of structural characterization by x-ray techniques, more reliable information concerning the morphology and microstructure of the layers was obtained by probing the built-up samples, instead of relying solely on the information of the full SV structure. For the electric and magnetic measurements, a number of unexpected observations were made in the built-up samples, although the final performance of the full SV structure was of comparable quality to the literature. These results showed the ability of the ‘built-up samples’ strategy in critical characterization and optimization of magnetic multilayered structures.

Metallic magnetic heterostructures

In the design and specification of precision optical components for advanced imaging applications it is necessary that residual optical fabrication errors be specified and measured over the “entire range of relevant spatial frequencies”. This includes the mid-spatial-frequency surface errors that span the gap between the traditional “figure” and “finish” errors. Since surface scatter is merely a diffraction phenomenon, the linear systems formulation of non-paraxial scalar diffraction theory forms the basis of the GHS surface scatter theory: a linear systems formulation of surface scatter theory valid for smooth or rough surfaces, large or small incident and scattered angles and arbitrary surface PSDs. The resulting surface transfer function can be combined with the conventional OTF which then characterizes image degradation due to diffraction effects, geometrical aberrations, and surface scatter effects. The method of determining the composite surface PSD from the metrology data and the method of predicting the bidirectional scattered distribution function (BSDF) from the surface PSD will be discussed as will the process for deriving the optical fabrication tolerances necessary for satisfying specific image quality requirements.

background or methods

The surface PSD and image degradation due to mid-spatial-frequency errors

Im Rahmen dieser Arbeit ist ein neues Mesverfahren zur Online und in-situ-Partikeldetektion auf Oberflachen konzipiert, realisiert und verifiziert worden, das die Detektion der Verunreinigungen durch eine transparente Oberflache hindurch mit Hilfe der Streulichtmestechnik erlaubt. Dieser innovative Schritt erlaubt es, alle Messystemkomponenten unterhalb der transparenten Oberflache anzuordnen. Erstmals wird eine in-situ-Fahigkeit des Mesverfahrens im Gegensatz zu existierenden Oberflachenmestechniken erzielt.

Konzeption und Realisierung eines in-situ und on-Meßverfahrens zur Partikeldetektion auf transparenten Oberflächen

Rugged coatings, originally developed for thermographic purposes in the 8-14 (mu) IR band, have been found to be useful as stray-light suppressants in optical instrumentation. Data on the hemispherical diffuse and goniophotometric reflectances of one formulation of this coating are presented. Diffuse reflectance in the 8-14(mu) wavelength region is below 5 percent, and even lower at 3 (mu) . Normal incidence specular reflectance is below 1 percent in the IR, and increases with angle in accordance with theory for physically rough surfaces. The coatings are moderately electrically conducting. They adhere readily to aluminum, silicon, glass, and other substrates; can be handled routinely with no loss of optical properties; have survived 500 degrees F temperatures at Mach 14; and may be modified to give high absorptivity also in the visible region.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Introduction to Surface Roughness and Scattering

Citations

Protected silver coatings for low-scatter SiC and SiC/Si mirror surfaces

Metallic magnetic heterostructures

The surface PSD and image degradation due to mid-spatial-frequency errors

Konzeption und Realisierung eines in-situ und on-Meßverfahrens zur Partikeldetektion auf transparenten Oberflächen

Durable coating for suppressing stray infrared radiation inside optical instruments

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