DE3134477A1 - Reflection-free metallic film - Google Patents

Abstract

A metallic anti-reflection film is described which consists of a relatively thick, i.e. light-impervious metal layer and on which there is at least one thin second metallic layer. The second metallic layer on one or else on both sides of the thick metal layer appropriately consists of chromium oxide. The anti-reflection film described facilitates production, especially when it is used for stray light diaphragms or annular slits in optical instruments such as endoscopes or microscopes.

Description

Non-reflective metallic film

The invention relates to a (largely) reflection-free metallic film according to the preamble of claim 1. In particular, it is These are films (layers) on the surface of optical components such as diaphragms or annular gap elements, such as those used for endoscopes or microscopes or similar optical instruments can be used. They are supposed to prevent light is reflected from the surface.

Usually a diaphragm or a Annular gap, as required for an endoscope or microscope, a lens surface or a flat glass surface painted with black paint and an opening part, to allow light to pass through, cut out to peel off the paint. Man but can also be applied to the lens surface to produce the diaphragm or the annular gap or evaporate a metal film onto the flat glass surface, in which case onto the Surface of the metal film is applied a dielectric anti-reflective film and then an opening was formed by photo-rolling. In this photo aemethod of education the dielectric film and the metal film had to be placed separately under the opening Use of different etching solutions for the dielectric film or for the Metal to be etched.

The invention is based on the object of a formed from metal to create non-reflective film, its individual films or layers, viz the anti-reflective layer and the metallic layer, using a photo-etching process at the same time can be treated.

This object is achieved by the film characterized in claim 1.

The non-reflective film described here can be particularly advantageous for a lens hood or for one ltinc3spal L is used will.

Thus, according to the invention, a non-reflective film is made from a first metallic layer formed with such a thickness that it is substantially does not let light through, and at least one thin layer on the first metallic layer second metallic layer arranged. Preferably at least one is thin dielectric layer arranged on the second metallic layer, which is made of Chromium oxide consists. The second metallic layer is on one or both Surfaces of the first metallic layer arranged so that each desired reflection protection results.

The invention is explained in more detail using various exemplary embodiments. The drawing shows: FIGS. 1 to 3 sectional views of a first, second or

third embodiment of the invention; Figure 4 to 6 the curves of the spectral reflection factor, which can be found in the three exemplary embodiments mentioned result; and FIG. 7 shows the course of the spectral reflection factor for a sample without anti-reflective measures.

The invention is intended to prevent the reflection of light from its metal surface with a metallic film. This is based on the following principle when, as shown in FIG. 1, a metallic film I is applied to a metallic substrate in the form of film II: If the complex index (refractive index or "reflection index") of the metallic film I n2 = n2 - ik2, die Film thickness d1, the complex index of the metallic film II n3 = n3 - ik3 and the index of the medium (air or a glass plate) over the surface A of the metallic film I n1, the reflection factor based on the total thickness corresponds to at perpendicular to the surface A. incident light of the following relationship (1): So that reflection can be prevented, the factors n2, k2 and d1 can be chosen so that they satisfy the amplitude relationship and the phase relationship according to the following two formulas (2) and (3): # 2e2k2 # + # ²e-2k2 # - 2 # 12 # 23 = 0 (2) 12 23 # 23 - # 12 - 2n2n = ## (3) Even if the above formula (2) should not be strictly fulfilled, if the formula (3) is fulfilled, it is an extensive one Reflection prevention possible if the factors n2, k2, n3 and k3 are kept within the following limits for 1 # n <2: 1.7 # n2 # 4, 0 <k2 # 0.7 0.5 # n3 # 4, 2 # k3 # 10 In the In practice, it can even suffice if the formula (3) is likewise not strictly, but only essentially or approximately fulfilled.

To prevent reflection on both surfaces, according to FIG 2 the metal film II is used as a base and on each of its two surfaces each a non-reflective metallic film or III can be applied. With G-ist in Figure 2 denotes a glass plate.

The above explanations were based on single-layer films. Of the but first film I can also have multiple layers including a dielectric Layer included.

If, in the case of a multilayer film, it is then made up of the corresponding Combination resulting equivalent complex index within the limits given above is held for n2 and k2, the same anti-reflection effect is obtained like a single shift. In the case of such a multilayer film, moreover a metal can be used particularly expediently for the first layer (film I), in which the above limits for the metal are adhered to.

Details of the exemplary embodiments described are given below explained. In the first embodiment shown in FIG. 1, the film I has one complex index from 2.4 to 0.41, a thickness of 44.7 m and consists of Cm30 ,. Film II is thick enough that essentially no light penetrates through the film can, has a complex index of 1.97 to 3.31 and is made of an alloy (Inconel) composed of 75.3% Ni, 15.6% Cr, 7.7% Fe and 1.4% other elements. A glass plate with index n1 = 1.52 is on the incident side of film I. The curve the spectral reflectance factor of a non-reflective film thus formed is shown in FIG. There curve a shows actually measured values and the curve b calculated values. The illustration shows that the actual neutrally measured values do not deviate significantly from the calculated values.

The film formed according to the second embodiment is shown in FIG 2 shown. Here both surfaces of the thick metallic film are supposed to be reflection prevent, which is why the opposite side of film II to film I a non-reflective film III is applied.

The indices and thicknesses of the films in question have the following values: Air n1 = 1 film I Cr2O3 n2 = 2.4 - 0.4i, d1 = 47.2mµ film II Cr n3 = 2.86 - 4.4i, d2: sufficiently thick film III Cr2O3 n4 = 2.4 - 0.4i, d3 = 50.2 mg glass plate n5 = 1.52 The characteristics of the spectral reflectance factor (calculated values) of the second Exemplary embodiments are shown in FIG. There the curve represents a1 the general reflection factors on the side in contact with air and the curve a2 those on the glass side.

In addition and for comparison, FIG. 7 shows the reflection factor curves of samples not protected against reflection.

Here, too, curve a1 represents the factors on the air side and the curve a2 those on the glass side.

The remarkable antireflective effect achieved according to the invention works from a comparison of FIGS. 7 and 5 clearly emerges.

The third embodiment of a film formed in accordance with the present invention is shown in FIG. Here the metallic anti-reflective FiJ-m consists of two layers The indices and film thicknesses have in this embodiment the following values: Air n = 1 film I r; 2 '= 2.4 - 0.4i, d2' = 45mµ n2 "= = 1.97 - 3.3i, d2" = 5.1mµ film II n3 = 0.82 - 5.99i, d3: sufficiently thick Die spectral reflection factor curves (calculated values) of the third embodiment are shown in FIG. According to the invention, reflection can also be used in this case can be prevented although a metallic film composed of two or more layers is used will.

Claims (6)

Non-reflective metallic film claims 1. at least partially metallic film with a first metallic layer of a such a thickness that it is essentially impervious to light, d a d u r c h e k e k e n n n z e i c h n e t that on the first metallic layer (film II) at least one thin second metallic layer (film I) is arranged. 2. Film according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that on the second metallic layer (film I) at least one thin dielectric Layer is arranged. 3. Film according to claim 1 or 2, d a d u r c h g e -k e n n z e i c n e t that on both surfaces of the first metallic layer (film II) respectively thin second metallic layers are arranged. 4. Film according to claim 1 or 2, d a d u r c h g e -k e n n z e i c h n e t that the index (of the reflection) n = n '- ik of the second metallic layer the following relationship satisfies: 1.7 # n '# 4 and 0 <k # 0.7 5. Film according to claim 1 or 2, d a d u r c h g e -k e n n n z e i c h n e t that the second metallic layer consists of chromium oxide. 6. The film of claim 1 or 5, d a d u r c h g e k e n n -z e i c h n e t that the thickness of the second metallic layer is chosen so that im essentially the phase relationship # 23 - # 12 - 2n2 # = is fulfilled, where n2 is the index of the second metallic layer.