DD153511A3 - INTERFERENCE MIRROR WITH HIGH REFLECTION FOR MULTIPLE SPECTRAL BEFORE - Google Patents

Abstract

The aim is to specify interference levels which at the same time have a high reflection with the least absorption and scattering losses for several separate spectral bands. The object of the invention is to prevent the increase in losses due to absorption and scattering in the spectral bands, which are reflected by deeper interference layers, by means of suitable layer arrangements. The solution according to the invention achieves one or more nonmetallic compounds in each case between two identically or differently constructed non-metallic alternating layer groups with a low degree of reflection and a broad reflection range. Coupling layers are arranged whose optical thickness is an odd or even multiple of the optical thickness of the individual layers in the alternating layer groups. Such interference levels are used in optical equipment, in particular as a resonator, application.

Description

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Title; Interference level with holier yeast reflection for several spectral bands

Field of application of the invention;

The invention relates to interference mirrors which have a high reflection for a plurality of separate spectral bands and reflect light in these spectral bands with the lowest absorption and scattering losses. Such mirrors are used in optical instrumentation especially when it comes to least losses for light from several highly separated spectral lines or spectral bands. One of the most important applications is the use as a resonator mirror in gas lasers with several laser wavelengths, where even small losses due to absorption and scattering considerably reduce the output power of the different wavelengths.

Characteristic of the Known Technical Solutions: It is known to construct highly reflecting mirrors which act on the principle of interference, of a Y / echselschichtsystem of many alternately high and low refractive, low-loss, non-metallic layers which are superimposed on the surface of mirror bodies. The layers have an optical thickness of ^1/4 of the wavelength / Im which is to be maximally reflected, wherein the number of layers must be high in order to obtain a high Heflexion.

(Z.f. Physics j_42, 21 to 41, (1955). '

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Such highly reflective interference mirrors have the defect that - apart from higher interference orders - the desired high reflection can only be achieved in a narrow spectral range in the vicinity of the wavelength m. The simultaneous reflection of light with wavelengths, outside the immediate environment τοη \ m is not possible with these interference mirrors

 Also known from the same source are interference mirrors with a low number of layers which, although having a wider reflection range, have their disadvantage in a low reflectance. In order to simultaneously obtain high reflectance mirrors for extended or multiple spectral bands, it is further known that different high-stratum interleaving layer groups, and hence high reflectivity, are stacked on either the front and back of a glass plate or on the surface of a laminate B. , Each of these alternating layer groups is adapted to a different spectral band with maximum reflectable wavelengths X m., "X nu..." Λ-m by different sizing of the optical thicknesses of their partial sublayers. (Optics of Thin Films, John Wiley + Sons, London 1976, pages 148-157, SU copyrights 141659, CH-Pat 417997).

However, the disadvantage here is the fact that the light of the spectral bands, which is reflected by increasingly lower interlayer groups, must pass through the many sublayers of the overlying alternating layer groups of other spectral bands before and after the reflection, and thereby by absorption and absorption Light scattering suffers considerable losses in comparison to the light which, in the direction of light incidence, is already reflected by the foremost or topmost alternating layer group. In this context,

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se way several reflection bands with high reflection and low absorption and scattering losses simultaneously not feasible

 In order to obtain a sufficient width of the reflected band and a steep edge between the reflection and transmission regions, interference filters are known in which so-called transitional layers are arranged between two different alternating-layer grids of high reflection effect. (CH Pat. 458780). The main shortcoming, however, is that although broad spectral ranges of low transmission are reported, but in practice to a considerable extent based on absorption effects and not on a high reflection.

Furthermore, simple and coupled bandpass filters are known, which consist of purely dielectric layers or a combination of metal layers with dielectric layers. (Optics of Thin Films, John V / iley + Sons, London 1976, pages 162-177). These bandpass filters have the task of producing a bandpass range of high transmission, which is bounded on both sides by blocking regions of low transmission. Again, it is particularly disadvantageous that the blocking effect in the blocking areas in addition to the reflection also based on the absorption effect of the layers. In connection with the production and the function of band-pass filters, there is also no teaching that such layer systems can advantageously be used as a mirror for two spectral bands in comparison to the known interference mirrors.

It also belongs to the state of the art to use alternating layer arrangements in higher interference orders in order to obtain a plurality of regions of high reflection (Glastechn. Ber 24, 147 to 148, (1951), SU-Urheberschθin 381 055). The essential defect is that the partial layers correspond to the Interferenzord-

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must be of great optical thickness. This leads to an unacceptably high total thickness for the overall layer system for practical production, the thick partial layers causing increased losses due to absorption and light scattering. In addition, the mechanical durability of such layer systems is low.

Object of the invention:

The invention aims to eliminate the shortcomings of the known technical solutions. Interference levels are to be specified which at the same time have a high reflection with the least losses due to absorption and light scattering for several separate spectral bands,

Explanation of the essence of the invention;

The invention has for its object to provide interference mirrors with layer arrangements in which the increase in losses due to absorption and light scattering for the spectral bands, which are reflected by deeper interference layers, are prevented, and in which the total thickness of the layer arrangement is minimized.

The object of the invention is achieved by interference mirrors with high reflection for a plurality of spectral bands consisting of a base on which alternating layer groups of 2 to 9 non-metallic optically low-loss individual layers are arranged one above the other so that the individual layers alternate with high and low refractive index, characterized in that one or more non-metallic coupling layers are arranged between adjacent identically or differently constructed alternating layer groups. All alternating layer groups are tuned to the same wavelength X ₀ by the individual layers of all alternating layer groups having an optical thickness of 74 of these wavelengths.

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The optical thickness of the non-metallic coupling layers "is an integer multiple of \ / 4

 The Maßwellenlänge "λ is an average wavelength of the spectral application range in which the reflection bands are to lie.

A further feature of the invention is that a coupling layer is arranged between adjacent elements whose optical thickness is one. odd multiple of * _0/4, or that are located between adjacent Y / echselschichtgruppen two coupling layers whose optical thickness is an even multiple of. "- is _o / 4 In order to realize the object of the present invention, it is also possible that between adjacent WechseIschichtgruppen Coupling layer is arranged, whose optical thickness is an even multiple of \, / 4 "

 The Y / Echselschichtgruppen used according to the invention are expressly those with a small number of Sinzelschichten, so that the individual V / echseIschichtgruppβ for the Maßwellenlänge Λ no high reflection, but only a partial reflection allows, but because of the low An - Number of single layers over a broad spectral range is effective, in contrast to the prior art exchange layer systems with a high number of single layers for high reflection, which act only in a relatively narrow spectral range.

In the interleave layer groups used according to the invention with low reflection but over a relatively broad spectral range, the small number of the single layer can, depending on the particular indices of refraction, comprise 2 to 9 individual layers.

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The achievable despite the use of alternating layer groups of the type described high Heflexion with very low absorption and scattering losses is explained by the fact that the coupling of several such alternating layer groups by one or more coupling layers not highly reflective effect of the individual Viechselschichtgruppen within its wide reflection range in several Spectral bands is amplified to a high Heflexion and to the same extent the already low absorption and scattering losses of such Y / ech se layer group η be further minimized. These effects are probably due to the fact that the light in all existing spectral bands is already partially reflected by the front alternating layer group or the front alternating layer groups with respect to the light incident direction. However, only a few light passes to the lower-lying alternating layer groups, which are obviously indispensable for achieving a high Heflexion, so that they can not contribute significantly to further losses.

The layer arrangements according to the invention can be prepared, for example, expediently by the high-vacuum method, in which, as is known, suitable layer substances are vaporized, so that they can precipitate on surfaces of conventional substrates as layers. In the near UV, VIS and near-IH range, the known layer substances of high refractive index, such as zinc sulfide (ZnS), titanium dioxide (TiO ₂ ), tantalum pentoxide (Ta ₂ O ₅ ) and the known layer substances of low refractive index, such as cryolite CNsuAlFg) , Magnesium fluoride (MgF ₂ ) or silica (SiO 2), etc. may be used.

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EXAMPLES

The invention will be explained in more detail with reference to the following embodiments. The accompanying drawing illustrates:

Fig. 1, 2 and 3, the spectral reflection curves R (solid curves) and the spectral transmission curves T (dashed curves) of the invention described in the embodiments 1,2 and 3, the interference mirror.

FIG. 4 shows for comparison the spectral reflection curve R (solid curve) and transmittance curve T (dashed curve) of a prior-art integer reflection mirror.

In all embodiments according to the invention, the spectral position of the reflection bands and their number by the Maßwellenlänge \ and the sum D of the optical thickness of a Y / Echselschichtgruppe D and a coupling layer Dp- (D = D ^ + D _£ ) is set. For example, there are three reflective bands with high reflectivity and very low absorption and light scattering losses at the wavelengths

1, -

D - hJZ

λ 3 ^{= 7L} o

if the Eopplungsschicht s have an optical thickness of an odd multiple of ^ ₀ / ₄ .-- and between adjacent VÄ igschichtschichtgruppen an odd number of coupling layers is arranged or if the coupling layers an optical thickness of an even multiple of ^ ₀ A and the number of coupling layers between adjacent interface groups is even.

Ss gives e.g. two reflection bands with high reflection and low absorption and light scattering losses

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and

o * D

For example, if the Eopplungsschichten have an optical thickness of an even multiple of ^ / 4 and is arranged between "adjacent groups of alternating layers an odd number of coupling layers." The spectral optical details of a given layer system can be determined by measuring at the produced interference mirrors. earth.

Embodiment 1

By means of the high vacuum attenuation, an interference mirror is formed by evaporating on a base G (e.g., glass) an array of alternating layer groups W and coupling layers K ~ and Kg, which are represented by the formula

can illustrate. In W_ is alternating layer groups with a small number of individual layers which are tuned to the Maßwellenlänge \ and consisting of an alternation of low refractive index (N ₀₎ and high refractive index (H _Q) Individual layers of the optical thickness of \> / 4 consist, wherein within of W _{Q is in} each case the arrangement ^ ₀ ^H ₀ N ₀ ^H ₀ is present.

Coupling layers are arranged between each of the alternating layer groups W, where K ^ = 21T _Q and Krr = 2Η _Λ . ie in this case the coupling

ii O *

Κ layers ~ and Kg an optical thickness of each \ Z2, When refractive indices were taken into account for the glass base n _n = 1.52, ₂ layers for the low refractive index SiO (N ₀₎ tW = 1.455, and (for the high refractive index TIOP layers H ) the complex refractive index - ik _H = 2.315 - i · 0.005 (i ^ = T- "!") ^{with that for the}

ζ. ι ο /

Absorption responsible absorption index kg = 0.005. The absorption index k »of the low - refraction SiOp layers was determined according to the. neglected practical conditions. The measure wavelength for the X / ^ layers is ^ ₀ = 520 nm, so that according to the structure of the alternating layer groups Y / and the coupling layers K, and IC therebetween, there result 3 reflection bands, which according to the given relationships for λ, Λ. and λ -j at the wavelengths X ₁ = 693 nm, I ₂ = 416 nm and T ^ = A ₀ = 520 nm. In Fig. 1 is. the spectral reflection S (solid top curve) is shown opposite to the transmission T (dashed bottom curve), so that the hatched area between the curves is a measure of the absorption losses. In the reflection bands, the reflection losses in the working range of the minima are only about 1 to 3, and are therefore only about 2 to 5 times greater than for a single A / 4 TiO.sub.p layer.

Embodiment 2

On the basis of the conditions and definitions described in Embodiment 1, an interference mirror with the layer arrangement becomes

wherein the alternating layer group w _{Q has} the single layer arrangement .HUH, and the alternating layer groups Vf consist of the layer sequence HNHNH. The coupling layers TL * in this case consist of 5N layers, ie the coupling layers have an optical thickness of 5 λ / 4. The same materials were used for the main body G and for the layers as in Example 1.

The modest wavelength for the λ / 4 layers is λ = 520 nm, so that according to the structure of the interlayer groups w and. Y / _Q and the intervening

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ordered coupling layers K ^ itself. Yield 3 reflection bands which, according to the relationships given above, for λ, _} ^ ₂ and λ ^ at the wavelengths Ii ^ - 434 nm; A ₂ = 650 nm and A ₃ = X _Q = 520 nm lie.

The spectral reflectance and transmission properties are plotted in Figure 2 in the same manner as in Example 1 (Figure 1). The reflection losses illustrated by the hatched difference range between the R and T curves amount to 1 to 3 $ in the working range d 'he minima of the reflection bands.

Embodiment 3

In analogy to Example 1, an interference mirror with the layer arrangement

where W _Q = H ₀ N ₀ H ₀ and E ^ = 2N _Q. Again, the same material parameters apply to G, U ₀ and H ₀ , as in Example 1

The Maßwellenlänge for the λ / 4 layers is \ = 520 nm, so that there are two reflection bands in accordance with the present here structure of the layer arrangement according to the above relations for the main wavelengths of the reflection bands at ^ ₁ = 433nm undÄp = are 650 nm ,

In Fig. 3, the resulting spectral reflectance and transmission properties are plotted in the same manner as in the previous examples. The reflection losses illustrated by the hatched difference range between the R and T curves amount to 1 to 2% in the working range of the minima of the reflection bands.

In order to clarify the progress achieved with the solution to the problem of the invention, the spectral reflectance of the interference gliders according to the invention is shown in FIG.

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and transmission curves of an interference mirror, as known from the prior art. It involves the arrangement of two different alternating layer systems W., and W _{2 of} high number of layers on a glass base G, so that the overall structure ''

GZW ₂ W ₁

where W.β.H.IT. H ^ H ^ = 17 ^ ₁ A Sinzelschichten and

W ₂ = H ₂ IT ₂ ... ..H ₂ N ₂ = 16 L _2/2 mean individual layers. The inner exchange layer system Vi ₂ arranged directly on the glass surface is at the wavelength

) TL ₂ = 433 nm and the outer alternating layer system W. is adapted to the wavelength λ = 650 nm.

For its preparation, the same substances were used, and the same refractive indices, as in the examples of the invention, used in the calculation. As can be seen from the hatched areas of FIG. 5, low absorption losses of about 1 to 23> and thus high reflection values are possible only in one spectral band, namely in the vicinity of the matching wavelength λ-1 = 650 nm, because only this Spectral band of the - referred to the light incident direction - front alternating layer system W is reflected. In the second spectral band in the vicinity of the wavelength X ₂ = 433 nm, the reflection is greatly reduced, since the light from this spectral band before and after reflection from the alternating-layer system W _{2 must} first pass through many layers of the alternating light system W arranged above it, and considerable Absorbs absorption losses of 10 to 30 #, which is about 10 times higher than in the case of the interference mirrors according to the invention

WZ 2 / US / W1

Claims (3)

1. Interference mirror with high reflection for several spectral bands, consisting of a base on the alternating layer groups of 2 to 9 non-metallic, optically low-loss single layers are arranged one above the other so that the individual layers alternate with high and low refractive index, characterized in that between adjacent same or differently constructed alternating layer groups, one or more nonmetallic coupling layers are arranged, the individual layers of all alternating layer groups have q has an optical thickness of ^1/4 of a Maßwellenlänge ^ and the optical thickness of the nonmetallic coupling layers is an integer multiple νοηλ _0/4. ?. Interference mirror according to item 1, characterized in that a coupling layer is located between adjacent groups of alternating layer whose optical thickness is an odd multiple νοηλ _0/4. 2 18793 - Invention claim: 3, interference mirror according to item 1, characterized in that between adjacent alternating layer groups two coupling layers are arranged whose optical thickness is an even multiple of λ _Q / 4. For this ί pages drawings 3561