Graphite optics combines high reflectivity of graphite with the required focusing shape. High stability makes it useful for harsh environments.
Detail information about
Graphite Optics see at the following pages.
Graphite Optics can be optimized for the required task by varying characteristics of the PG layer and the optics shape.
Graphite optics consists of a thin flexible Graphite Crystal (a layer of specially annealed well-aligned PG) deposited on a substrate of a focusing shape. Graphite optics is used as focusing and monochromatizing element between an X-ray source and an object or as a dispersion element or broad band filter between an object and a detector in X-ray experiments and commercial set-ups.
There are two types of Graphite Optics, that differ
by a modification of graphite crystal used as a reflecting layer:
HOPG-OPTICS
HAPG-OPTICS
To improve resolution, Graphite Optics are mainly used in von-Hamos geometry
Cylindrical HAPG-optics on glass substrates
Elliptical HOPG-optics
on an aluminium substrate
Logspiral HOPG-optics
on a PMMA substrate
Spherical HOPG-optics
on a glass substrate
Conical HAPG-optics on a glass substrate
Mosaicity of Graphite Optics depends on the form of Pyrolytic Graphite used as reflecting layer:
HOPG optics is made of thin films of HOPG-flex which adhere to each other and to a substrate, creating a layer of the required thickness. Mosaicity of the reflecting layer depends on the layer thickness and the number of the deposited films.
Substrate quality and material do not influence mosaicity of the HOPG-optics, but affect the adhesion of graphite layer to the substrate. The film adhere to optically polished glass, quartz and PMMA without additional adhesives. Various metal substrates (aluminum or copper alloys, stainless steel) usually require an adhesive, but it does not influence mosaicity and performance of this type of the optics.
HAPG optics are made of a single film of a specially annealed Pyrolytic Graphite called HAPG (Highly Annealed Pyrolytic Graphite). The film thickness and hence the thickness of the reflected layer in HAPG optics is limited by 100µm. The roughness of the substrate strongly affected mosaicity of HOPG optics. Best results are achieved with optically polished glass or quartz. Metal substrates lead to increased optics mosaicity due to imprinting the substrate relief on the crystal surface. A graphite layer with a mosaicity of 0,2° on an aluminium substrate reduces its mosaicity down to 0,1° being re-deposited on optically polished glass. The influence of the substrate on the mosaicity of HAPG-optics is illustrated on figure below (left). The integral reflectivity of HAPG layer on a glass substrate is represented in figure below (right).
To increase resolution, Graphite Optics are used in von Hamos geometry. Under these conditions, the energy smearing is determined by the geometrical aberration, the source size and the Darwin width of small crystallites (intrinsic broadening). Crystal mosaicity affects geometrical aberrations.
Optics up to 100x100 mm in size are made from a single crystal. Larger sizes can be discussed individually or assembled from several crystals.
Optically polished glass or quartz lens as well as polished aluminum are the most common substrates for Graphite Optics. The quality of the substrate surface drastically affects HAPG optics, and is not so important for HOPG optics of moderate mosaicity (for more details, see page Mosaic Spread of Graphite Optics).
An optically polished glass lens usually
used as substrate for graphite optics
A metal substrate of a complex shape mainly used for
HOPG-optics of moderate mosaicity
Although Optigraph does not produce substrates for Graphite Optics, there is a number of long-terms partners, who manufacture custom shape substrates upon our request. Please note that some shapes are available only in a certain minimum quantity. In this case, the costs of this minimal set of the substrates will be included in the price of the optics, regardless of the number of the optics requested.
An uncoated glass or quartz lens from the lens manufacturer's catalog can be used as a substrate. These lenses are significantly cheaper than custom-made substrates, and their delivery time is much shorter. Contact us, if you find a lens of a suitable shape.
You may offer us a substrate for coating. The geometry as well as the surface roughness of such a substrate should be agreed with us before manufacturing. Please note that the specified roughness does not guarantee crystal adhesion. Metal substrates, even with a surface roughness less than 100nm, may require an adhesive layer.