Patent
1981-01-25
1984-01-10
Henry, Jon W.
350164, G02B 528
Patent
active
044250223
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The application concerns a reflection-reducing layer on highly reflecting surfaces and a process for the preparation of such layers.
It is known to prepare masks, diaphragms, slits, gratings or coding arrangements by applying them in the form of a thin, impermeable layer to a transparent carrier, for example, lenses or plane parallel plates. This is effected in most cases by vapor deposition in a high vacuum or by sputtering. Metals, particularly aluminum or chromium, have been found suitable as coating materials.
A disadvantage of the method is the relatively high reflectivity at the interfaces between the metal and the adjacent media, because the reflections produced may lead to various interferences, such as for example contrast reductions, light scattering or signal falsification.
In the case of a layer with an optical thickness of .lambda..sub.o /4 the following condition must be satisfied to completely eliminate reflection components. ##EQU1## wherein:
n.sub.1 --the refractive index of an absorption-free incident medium,
n.sub.2 --the refractive index of an absorption-free reflection-reducing layer,
n.sub.3 --the real portion of the refractive index of the highly reflective material,
k.sub.3 --the absorption coefficient of the highly reflective material and
.lambda..sub.o --the wave length at which the reflection disappears.
The refractive indices resulting from this equation for the coating materials are, however, substantially higher than those available for practical applications.
In order to overcome this objective difficulty, it has already been proposed to provide multiple layers in place of a single coating, which consist, for example, of a plurality of .lambda..sub.o /4- and .lambda..sub.o /2- layers and the refractive indices of which are adjusted to the optical constants of the highly reflective material and the adjacent medium. The disadvantage of this proposed solution consists of the fact that the effective spectral range is relatively narrow.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to avoid the disadvantages of the known coatings and to eliminate for a relatively broad spectral range the interfering reflections which occur.
The object is attained according to the invention with a reflection-reducing layer (8) of the above-mentioned type in that the reflection-reducing layer comprises a first and a second substance, wherein the first substance has a refractive index n.sub.2 which is equal to or at least approximately equal to n.sub.1, and wherein the second substance comprises a strongly absorbing material. The layer(s) can be a single homogeneous layer (total thickness D.apprxeq.n.sub.2 .multidot.d.sub.2) or a sandwich-like laminate (total thickness given by ##EQU2## whereby l is the number of all partial layers) and is structured so that the .lambda..sub.o /4 condition is satisfied. The necessary absorption of the reflection-reducing layer is provided by the relative proportions of the two substances. It is possible that the reflection-reducing layer consists of at least two partial coatings. It may be convenient in this regard to provide a first partial layer deposited directly onto the highly reflective surface, consisting of an absorption-free material and having a refractive index n.sub.2 with the relationship n.sub.2 =n.sub.1 or at least N.sub.2 .perspectiveto.n.sub.1, together with a second partial layer consisting of an absorbent material and arranged on the first partial layer. Advantageously, the first partial layer consists of the same material as the incidence medium, for example, of germanium, and the second partial layer consists of the same material as the highly reflective surface, for example, chromium.
According to a further embodiment of the invention, the reflection-reducing layer may also consist of a homogenous, binary mixture of material, which is composed of a first material corresponding to the incidence medium, and a second material corresponding to the highly reflective surface.
The reflectio
REFERENCES:
patent: 2519722 (1950-08-01), Turner
patent: 2590906 (1952-04-01), Tripp
patent: 4101200 (1978-07-01), Daxinger
patent: 4180954 (1980-01-01), Gell
Sov. Journ. of Quantum Electronics, vol. 8, No. 2, Feb. 2, 1978, V. V. Apollonov et al., pp. 262-264.
Ernst Leitz Wetzlar GmbH
Henry Jon W.
LandOfFree
Antireflection coating on a surface with high reflecting power does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Antireflection coating on a surface with high reflecting power, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Antireflection coating on a surface with high reflecting power will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-451407