DE3026370A1 - MIRROR - Google Patents

Description

PATENT Attorney DIPL.-ING. H. STRAW BAR

8000 MÜNCHEK 60 MUSÄUSSTRASSE 5 TELEPHONE (089) 881608

7/11/1980-SSe (5) 190-1587P

mirrors

The invention relates to a mirror for reflecting only radiation that is convergent or divergent from a Direction or from a limited number of directions and within a narrowly limited wavelength band or a limited number of such wavelength bands.

The invention is thus concerned with a so-called "dark mirror", which should only reflect the radiation that comes from certain, predetermined directions and within certain, predetermined and narrowly limited wavelength ranges.

The term "dark mirror" in this context relates to the fact that other portions of the wavelength range than the portions for which the mirror is made are suppressed to the greatest possible extent. These other sections appear hence as dark to an observer or a measuring instrument. "Dark mirrors" made up of selective, narrow-band interference filters are constructed, have the disadvantage of sensitivity to the angle of incidence of the radiation, wherein especially the reflected wavelength to shorter wavelengths

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is shifted towards when the angle of incidence increases. This wavelength shift is a function of the cosine for the angle of incidence within the interference filter stack. The result is that "dark mirrors" constructed in this way can be used over a narrow range for the angle of incidence and are limited to almost parallel incident radiation. This inevitably leads to difficulties if the incident radiation comes from several different directions, and if such a mirror acts as a selective filter, So if you want to work in a convergent or divergent radiation path, it can be difficult to achieve the required degree to obtain narrowly limited wavelength bands. This is because the reflection bands of the interference mirror are used for adaptation the entire angular range of the incident radiation must be made so wide that radiation at wavelengths outside the desired and selected wavelength range within the same angle of incidence through the mirror is reflected.

The invention is therefore based on the object of a mirror to create the type mentioned above, which is not subject to the above-mentioned restrictions and also with different Incidence angles reflected radiation emits only within precisely limited wavelength bands.

The object set is achieved according to the invention by a mirror as specified in claim 1; advantageous Further developments and refinements of the invention emerge from the subclaims.

The improvement achieved by the invention is essentially based that a mirror with an interference mirror layer or a holographic mirror layer on its front side with an absorption filter layer with transmission for one or multiple desired wavelength bands and absorption in others

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is provided by the mirror layer reflected wavelengths. By arranging the mirror layer on an optical component from a material transparent to the radiation used, such as glass, plastic, silicon or the like. and arrangement of one or more relatively incidence independent absorption filters on the front face can have a tight limitation around the desired wavelength bands be achieved. If, in addition, the optical component is designed in a wedge shape, the arrangement the mirror layer on the back of this component does not direct desired reflections at the boundary layers between absorption layers and optical elements in other directions than in the direction in which the light to be reflected by the mirror is to be emitted.

A mirror of this type can be used wherever a limited wavelength band is reflected from an object should, which can be, for example, a display screen. Such a mirror is particularly suitable for use in aircraft, to display symbols in the pilot's field of view, which are then displayed on one or more display screens. Such arrangements have difficulties in keeping solar radiation off the display screen and in the Preventing ambient radiation from entering the optical System, which can result in reflections and contrast reductions, which are perceived as extremely annoying. If several If display screens are used, it must be possible to place the symbols on all of these screens in one and the same picture plane reflect.

When the mirror is inserted into convergent or divergent radiation and the reflective surface is an interference mirror has, then according to the invention it is possible to use different sections of the interference layer To allow angles of incidence for the radiation by the interference layer is formed so that they are on different

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Share their surface with different reflective properties shows. In addition, according to the invention, it is possible to reduce the attenuation of the various layers with respect to the direction of incidence and the radiation reflection and consequently on the radiation path by the respective layers as well as the attenuation for the radiation within a desired wavelength range and also with regard to the curve shape for the mirror layers used in each case to be taken into account by the thickness of the absorption layer is varied along the surface.

In a simple embodiment, the mirror has a Plate with an interference mirror layer or a holographic mirror layer on the front and one or more absorption filter layers arranged on top. When the mirror is in a convergent or divergent beam path with inclined light is to be inserted on the mirror, the absorption layers are preferably wedge-shaped.

In the drawing, the invention is illustrated by way of example; show it:

Fig. 1 shows a first embodiment of an inventive formed mirror in a cut perpendicular to its various layers;

Fig. 2 shows a wedge-shaped second embodiment with a schematic representation of incident and reflected radiation;

FIG. 3 shows a third exemplary embodiment for the invention in a representation corresponding to FIG. 2; FIG.

Fig. 4 shows a fourth embodiment with again plane-parallel Arrangement of the layers as in Fig. 1.

The first embodiment shown in Fig. 1 for an inventive formed mirror has a holographic mirror layer or an interference mirror layer 1 with a Reflectivity curve based on that represented by the Mirror to reflect a wavelength range

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Reflection area has an angle of incidence range of about + 5 ° around the main direction for the incident radiation includes. This means that the range of reflectivity for the mirror layer 1 must be considerably wider than the actual wavelength range for the mirror. Plus, it's totally impossible to have an interference mirror or a Manufacture holographic mirror that does not also have a certain reflectivity outside of the intended reflection area having. Rather, there always remains a weak reflectivity over essentially the entire wavelength range.

For this reason, in Fig. 1, the mirror layer 1 is applied to the back of an absorption filter 2, 3, which as in the drawing may comprise combination filters, which are composed of several absorption filters that are connected to each other are cemented by means of an adhesive layer 4, which are also kept colored and thus also as an absorption filter can work. The absorption filter has a transmission interval which stretches narrowly around the actual wavelength range in which the mirrors are reflective target. Furthermore, the mirror of FIG. 1 is provided on its front side with an anti-reflective layer 5 of the usual design.

The reason for using an interference mirror layer or a holographic mirror layer is that it it is very difficult to obtain a sufficiently narrowly limited wavelength band with absorption filters alone. The curve for that The reflectivity of the mirror layer and the transmission curve for the absorption filter are therefore matched to one another so that a limiting wavelength of the mirror layer, preferably the longest wavelength, close to a limiting wavelength for the transmission range of the absorption filter, so that the range within which the mirror has reflectivity, is limited by these two limit wavelengths. As a result of the properties of an interference filter mirror or a

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holographic mirror, it is difficult for certain smaller reflection peaks to appear within the rest of the section to be avoided in the transmission range of the absorption filter. The mirror layer is dimensioned so that it is within this area shows such small reflection peaks how this is practically achievable. If this is not achievable, can this range also outside the spectral sensitivity range for the human eye or a collector used Light detector or close to the limit for this sensitivity range. Both the mirror layer and the absorption filter are also dimensioned so that their characteristics for the reflectivity or for the transmission close to the limits for the desired reflection range of the mirror have a steep slope.

If the incident radiation is collected at the mirror, the direction of incidence is the same for the entire mirror surface, and consequently the mirror layer 1 is then constructed in such a way that they have the same properties over its entire surface having. This means that when the mirror layer 1 is an interference mirror, the various ones provided in this mirror dielectric layers have the same thickness over the entire mirror surface. When the one in the mirror incident radiation, on the other hand, is divergent or convergent, becomes the angle of incidence or, in practice, the angle of incidence range different at different points on the mirror surface. The dielectric ones provided in an interference mirror Layers are then made with different thicknesses at different points on the mirror surface in order to adapt the reflection curve for the mirror to the different angles of incidence. fit. For example, if at one edge of the mirror the angle of incidence is 35 ° + 3 ° and at the other edge of the mirror 45 ° + 3 °, then the reflection curve in the direction of shorter wavelengths would be about 0.1% compared to the wavelength to be reflected shifted, if not the thickness of the dielectric layer

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ten in the mirror would be adapted.

Interference layers with varying across the surface Thickness can be determined by evaporation in a vacuum by means of suitable alignment of the surface to be evaporated with respect to the evaporation source and / or obtained by inserting suitably designed masks between the surface to be vaporized and the vaporization source.

On the back of the mirror layer 1 in FIG. 1 there is also a carrier substrate 61 of considerably greater thickness than all the others Layers shown in dashed lines. This carrier substrate 61 is necessary if one consists only of absorption layers and mirror layers built up mirrors would not be completely mechanically stable. The support substrate 61 consists of a rigid material such as glass or plastic with a smooth surface. If it's a tee substrate 61 is required, the interference mirror layer 1 is expediently vapor-deposited onto the surface of the carrier substrate 61, and the absorption filter 2 is on a support with interference mirror layers puttied up. When the carrier substrate 61 is off Glass consists, its underside can be frosted or have a non-transparent surface layer.

In the second exemplary embodiment shown in FIG. 2 for a mirror designed according to the invention, the mirror layer is 1 on the back of a wedge-shaped carrier 6 made of a material that is transparent to the light used, such as optical Glass, silicon or the like. arranged. On the front of the carrier 6 are two slightly wedge-shaped absorption filter disks 7 and 8 cemented on by means of adhesive layers 9 and 10. One of these absorption filters can be a long pass filter with a sharp edge at the limiting wavelength, and the other The filter is then a bandpass filter that is chosen so that there is a sharp edge at the upper limit for the intended

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Has wavelength range. The order of these filters is not important, provided the filters have otherwise similar properties exhibit. If, for example, one of the filters changes in its transmission behavior under the influence of incident should experience ultraviolet radiation that others could prevent the passage of this radiation, it goes without saying that the first of these two filters is to be arranged after the second.

In Fig. 2, the mirror shown is shown inserted into a divergent radiation flux, which from the left on the Mirror hits, with the incident beam on one side an angle of incidence α ... and on the other side an angle of incidence a "has. In the example shown, the materials have the same refractive index for the individual layers 6 to 10 of the mirror, and therefore the beam direction changes by refraction only when the beam enters and exits the composite mirror. This is of course not a prerequisite for the implementation of the invention, but it proves to be very useful if the absorption layers must be given a shape other than a pure wedge shape in order to fulfill their control function. The incident Radiation is reflected on the mirror layer 1, passes through the various layers 6 to 10 again and then occurs at an exit angle α_ or α. the end.

As the illustration in Fig. 2 readily shows, rays pass through at different angles of incidence with respect to the mirror paths of different lengths through the absorption layers, if these are perfectly plane-parallel, which leads to different attenuation for the radiation which has passed through this at different sections of the mirror. In order to remedy this, the absorption layers are designed with a thickness that varies over the surface, so that a uniform Attenuation is achieved for the entire beam. Here can

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it will of course be difficult to obtain more complicated forms of variation for the thickness in the two absorption layers, as there are precise requirements with regard to the grinding of the respective surfaces of the absorption layer and optisehen Components are connected. A good approximation for a solution to this problem is therefore the arrangement of wedge-shaped absorption layers, with the wedge tip lying in the plane of incidence for the incident ray and facing away from the direction where the radiation converges. In the illustration in FIG. 2, the wedge tip for the absorption filter points to the right. In addition, in Fig. 2 indicated by arrows 11 and 12 drawn in dashed lines that the reflected on the front side of the carrier 6 Radiation as well as the radiation reflected on the various filter layers and on the upper edge of the carrier 6 in is reflected in a completely different direction than the radiation that is reflected by the mirror layer 1 and after Passage is made usable through further optical components not shown in the drawing.

Furthermore, in Fig. 2, an additional absorption layer 13 is shown in dashed lines, which by means of an adhesive layer 14 is inserted between the filter 7 and the carrier 6. It goes without saying that the mirror layer 1 can be formed in such a way that that it has reflection bands for several wavelength ranges. This can be indicated, for example, when the mirror to The purpose of reflecting images on the screen of a color picture tube is to filter the images contained in these images Colors red, blue and green are supposed to effect. This gives an extremely sharp picture. As shown in 2 mirrors provided with the additional absorption layer 13 is suitable for reflecting two colors, the filter 7, for example, being a long-pass filter with a sharp transmission edge at the lower limit wavelength for the lower range, the filter 8 can be a pass band in the lower wavelength range and a pass band area or a long pass area in the upper

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ren wavelength range and the filter 13 has a passband that extends over both actual wavelength ranges, or two or more passbands, two of which extend over each of the wavelength ranges for which the Mirror is adapted.

The mirror layer 1 has reflection bands for the actual wavelength ranges made as narrow as possible by having only a part of each reflection band of interest within a transmission range for the absorption filter combination lies.

The third exemplary embodiment shown in FIG. 3 for a mirror structure according to the invention is for reflecting radiation determined by two different radiation sources with different or similar wavelength ranges in the comes in the same direction and, viewed in the direction of radiation, is intended to fall into one and the same optics behind the mirror. In Fig. 3 is similar to FIG. 2, a wedge-shaped carrier 16 made of a material such as glass that is transparent to the intended light an insert of the mirror for reflecting visible light on its lower side in the drawing with an interference mirror layer 17 provided. On the other side of the carrier 16 is an absorption layer 18 by means of an adhesive layer 19 glued. In the exemplary embodiment shown, however, further adhesive layers 23 are above this layer 18 and 24 additional absorption layers 20 and 21 cemented on, of which the layer 20 on its lower side with an interference mirror layer 22 is provided. As the radiation path shown in FIG. 3 shows, this should be from the layers 16 to 22 composed overall structure drawn in dashed lines, of one in the drawing at the top left assumed radiation source reflect incoming radiation, while the layers 20, 21 and 22 should reflect radiation , which is drawn in dash-dotted lines and from a radiation source assumed in the drawing on the right

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whereupon the radiation path after the reflection towards the mirror for the radiation originating from both radiation sources should be essentially similar. The two radiation sources do not need to lie in the plane of the drawing in FIG. 2, but rather one of them can be arranged above and the other below the plane of the drawing.

In order to achieve the desired effect, the layers 20, 21 and 22 have a high permeability for the wavelength range the right radiation source so that this radiation is not noticeably attenuated. Since the absorption layer 18 of the Radiation from the right radiation source is matched, the tip of its wedge is to the left as seen from the radiation source directed. The two absorption layers 20 and 21 are adapted to the radiation from the left radiation source. You can be both bandpass filters, their essential passbands being around the radiation coming from the radiation source on the right, however, there are weaker passbands around other wavelength ranges, which in this case around the wavelength range for the radiation from the left radiation source, the filters are made sufficiently thin that they act as bandpass filters for the radiation from the left radiation source. The different angles of incidence for the incidence of the Radiation on the mirror are chosen so that the radiation coming from the left radiation source with a wavelength for which the absorption layer 18 is permeable, does not lie within the direction of incidence range for which the mirror layer 22 acts reflective.

In Fig. 4 still another embodiment of the invention is shown, in which on the back of a stack from absorption filters 26, 27 and 28 cemented to one another by means of adhesive layers 29 and 30, a holographic mirror 25 is arranged. For a holographic mirror it is true that its mirror normal does not have to be the same as the normal

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paint for the actual layer forming the hologram. With the so-called. Thick-film holograms, the form in which holographic optical components are usually produced, moreover, several different holograms can be superimposed on one another in one and the same film. This offers the possibility of producing a holographic mirror in such a way that one and the same layer can reflect radiation incident in different directions or, as in the case shown in FIG Directions on the mirror. The mirror shown in FIG. 4 is shown inserted in a convergent radiation path of two radiation sources, one of which, the radiation of which is shown in dash-dotted lines, is further to the left than the other, the radiation of which is shown in dashed lines. Both radiation sources are monochromatic and their radiation can have the same wavelength or different wavelengths. Both beam paths are reflected by the holographic mirror in the direction which is indicated in FIG. 4 by the beam path shown with solid lines. As in the case of interference mirrors, holographic mirrors are highly sensitive to changes in the wavelength of the incident light and, in particular, react in such a way that a change in wavelength results in a change in the direction of reflection for the incident radiation. If the mirror is now to be able to reflect radiation with two different colors from two different predetermined directions, then an absorption filter stack 26, 27, 28 with transmission for the respective colors must be provided on the front of the mirror.

A mirror, the radiation of the wavelength / \ = 543 πιμ at angles of incidence between 15 and 45 ° with largely uniform

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Variation over the surface with a mean angle of incidence of 20 ° on the one hand and 36 ° on the other side and at each point with a reflected angular range of about 15 ° for the actual wavelength can reflect in accordance with the basic principles of the invention according to the embodiment shown in Fig. 2 can be produced. Then, using the designations for glass types and thicknesses according to the Schott glass catalog, layer 8 consists of BGSo _{1 n} and layer 7 of 0G530. ,. The interference mirror layer 1 consists of 25 layers, with TiO "with a refractive index of about 2.40 and SiO- with a refractive index of about 1.45 ^{alternating in the order (H / 2) (LH) 11} L (H / 2), in the L for a Si0 "layer with a thickness of 875 Å in the middle ■ - in the drawing, H for a Ti0 ₂ ~ layer with a thickness

of 518 Å and H / 2 for a Ti0_ layer with a thickness of 259 Å stand. On the one hand, with the larger mean angle of incidence, the thickness of each layer increases by about 4% while on on the other hand, with the smaller angle of incidence, the thickness of each layer is reduced by about 2%.

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Claims (9)

PATENT Attorney DIPL.-ING. H. STRAW BAR 80C0 MUNICH 60 MUSÄUSSTRASSE 5 TELEPHONE (0 89) 881608 07/11/1980-SFSe (5) 190-1587P t 1 _T Mirror for reflecting only radiation which is convergent or divergent and is incident from one direction or from a limited number of directions and lies within a narrowly limited wavelength band or a limited number of such wavelength bands, characterized in that a mirror with an interference mirror layer (1 ; 17) or a holographic mirror layer (25) on its front side with at least one absorption filter layer (2, 3; 7, 8, 13; 18, 20, 21; 26, 27, 28) with transmission for the desired wavelength band or bands and absorption is provided at other wavelengths reflected on the mirror layer. 2. Mirror according to claim 1, characterized in that the mirror layer (1) of the mirror has such a wide reflection area around the wavelength band (s) to be reflected, that at least all of the angular ranges within which the desired radiation impinges on the mirror layer can, accommodated by the reflection tape of the mirror layer and that on the side of the mirror layer facing the incident radiation one or more absorption filters (2, 3) with transmission for the wavelength ranges is or are arranged where around this wavelength range the absorption filter layer or the combination of such layers has a narrowly limited transmission range with a high gradient of the transmission 030063/0959 sion characteristic results at the border areas. 3. Mirror according to claim 1 or 2, characterized in that the reflection tape for at least one of the reflection areas of the mirror the mirror layer a limiting wavelength edge within the transmission range of the absorption filter and that this wavelength range extends over a part of the reflection band of the mirror layer, which extends through the limiting wavelength edge of the reflection band of the mirror layer and a limiting wavelength edge of the absorption filter is limited in the actual transmission range. 4. Mirror according to one of claims 1 to 3, characterized in that that the mirror layer (1; 17) on the side facing away from the incident radiation is a transparent layer for this radiation Support element (6; 16) is arranged and that both opposite sides of this support element have a certain Have inclination relative to one another, so that the radiation reflected on the side facing the incident radiation in is reflected in a different direction than the radiation reflected on the mirror layer. 5. Mirror according to one of claims 1 to 4 with an interference mirror layer as a mirror layer, characterized in that the reflectivity of the interference mirror layer (1; 17) varies along the surface of the mirror, so that each ray of the beam coming from the mirror despite the over the Surface varying direction of incidence in each of the desired wavelength ranges over the entire mirror surface experiences essentially the same reflection across the board. 6. Mirror according to one of claims 1 to 5, characterized in that that the thickness of the absorption layers (7, 8; 18, 20, 21) varies along the surface of the mirror, so that each at Mirror reflected beam de_. Beam in each individual 030063/0959 NEN desired wavelength band experiences a predetermined desired radiation absorption determined by the thickness of the absorption layers. 7. Mirror according to one of claims 1 to 6, characterized in that that when the mirror layer is designed as a holographic mirror (25) it has at least two superimposed holograms which are each assigned to their own mirror for mutually different wavelength bands with different reflection directions. 8. Mirror according to one of claims 1 to 5, characterized in that that at least one absorption layer (20) with an interference mirror layer (22) with transmission for the wavelength ranges and the angles of incidence and reflection for the radiation is provided, which is behind it as seen in the direction of incidence arranged mirror layer (17) is to be reflected. 9. Mirror according to one of claims 1 to 5, characterized in that the absorption filter comprises two layers, of which the outer layer consists of BG36 .. “and the layer arranged on the other side of it consists of 0G5 30 _g , and that the mirror layer has 25 sub-layers , in which Ti0 "and Si0" alternate according to the sequence (H / 2) (LH) 11L (H / 2), in which L for a Si0 "layer with a thickness varying between 859 and 179 Å and H for a Ti0 “Layer with a thickness varying between 508 and 537 Å. 030063/0959