DE3102301A1 - "INTERFERENCE MIRROR WITH HIGH REFLECTION FOR SEVERAL SPECTRAL BANDS" - Google Patents

Description

Have such highly reflective interference mirrors the lack that - apart from higher interference orders - the desired high reflection only in one narrow spectral range in the vicinity of the wavelength λ m can be achieved. The equilateral reflection of light with wavelengths outside the immediate vicinity of λ m is with these interference mirrors not possible*

Interference mirrors with a small number of layers are known from the same source have a wider reflection range, but their disadvantage is a low degree of reflection. To mirror high reflection for advanced or multiple To obtain Spetetralb'nder at the same time, is also known that different 'Vechseischichtgruppen high number of layers and thus high reflection either on the front and back of a glass plate or are arranged on top of one another on the surface of a layer substrate. Each of these alternating shift groups is different due to the different dimensioning of the optical thicknesses of their A / 4 sub-layers Spectral band with maximum wavelengths to be reflected Am., /.Ϊ́&2··* λ% adapted. (Optics of '.Dhin Films, John Wiley + Sons, London 1976, pp. 143-157; SU copyright certificate 141659} Ch-rat, 4 17997) · The disadvantage here, however, is the fact that the light of the spectral bands, the νjn, is increasingly deeper Alternating layer groups is reflected, before and after the reflection, through the many sub-layers of the alternating layer groups above Spectral bands must go, and thereby suffers considerable losses in comparison due to absorption and light scattering to the light that - related to the direction of incidence of light - already from the foremost or topmost Alternating shift group is reflected. These are

3561 130063/0601

«—-—

l AFTER »..

Interior mirror with high reflection door multiple spectral bands

The invention relates to interference mirrors that for several separate spectral bands result in a high reflection and reflect light in these spectral bands with the lowest absorption and scattering losses. Such Mirrors are mainly used in optical device construction when there is minimal loss of light of several strongly separated spectral lines or spectral bands arrives. One of the most important applications is the use of al3 resonator mirrors in gas lasers with several laser wavelengths, where there are already small losses considerably reduce the output power of the various wavelengths through absorption and scattering.

It is known to build highly reflective mirrors, which act according to the interference principle, from a layer system of many alternating high and low refractive index, low-loss, non-metallic layers which are arranged one above the other on the surface of mirror bodies. The layers have an optical thickness of 74 of the wavelength Am, which is to be maximally reflected, the number of layers having to be high in order to obtain a high reflection. (Zf Physik U £ _t 21 to 41 (1955).)

3561

130063/0601

need to be of great optical thickness. Leading to a total thickness that is unacceptably high for the Gesaratschichtsystem for practical production, whereby the thick sub-layers cause increased losses through absorption and light scattering · In addition, the mechanical The durability of such layer systems is low.

The invention aims to overcome the shortcomings of the known Eliminate technical solutions · It should be specified interference mirrors that for the same time several separate spectral bands result in a high level of reflection with minimal losses due to absorption and light scattering to have.

The invention has for its object to provide interference mirror layer arrangements in which the increase in losses due to absorption and scattering of light for the spectral bands are reflected from deeper gelege- men interference layers can be prevented, and in which the Gesautdicke the layer arrangement is as low as possible .

The inventive solution de; The task is achieved by means of interference mirrors with high R * .- flexion for several spectral bands, consisting of a base on which groups of non-metallic, optically low-loss individual layers are arranged on top of one another in such a way that the individual layers with high and low refractive index alternate, characterized by that one or more non-metallic coupling layers are arranged between adjacent, identically or differently constructed interchangeable layer groups of 2 to 9 single layers. Any change layer groups are tuned to a same measuring wavelength A _0, in that the individual layers of all groups of alternating layer has an optical thickness of ^{one quarter} of this Maßwellen-

3561

130063/0601

lh

- y -

Alternatively, several reflection bands with high * reflection and low absorption and scattering loss on the same side not feasible.

In order to obtain a sufficient width of the reflected band and a steep edge between the reflection and transmission areas, interference filters are known in which so-called transition layers are arranged between two different groups of alternating layers with a high degree of reflection. (CH-Pat. 458780). However, the most significant drawback is that, while wide spectral ranges of low transmittance are reported, which are based, however, in practice, r ι a significant portion on absorption effects for not 1 at a high reflectivity.

Furthermore, simple ⁴ and coupled band-pass filters are known which consist of purely dielectric layers or a combination of metal layers with dielectric layers. (Optics of Thin Films; John Wiley + Sons, London 1976, pages 162 to 177). These band-pass filters have the task of producing a high transmission bandpass range which is limited on both sides by low transmission blocking areas and the function of bandpass filters does not result in any teaching that such layer systems can be used advantageously as a mirror for two S: ektralband compared to the known interference mirrors Areas of high ref lexion (Glaste chn. Ber. 24, 147 to 14-, (1951); SU-Urheberschein 3 "1 055). The main deficiency is that the sub-layers according to the interference order

130063/0601 3561

have length Λ. The optical thickness of the non-metallic coupling layers is an integral multiple of λ _ο / 4.

The measurement wavelength X ₀ is a mean wavelength of the spectral application range in which the reflection bands are to lie, ι

Another feature of the invention is that between adjacent alternating layer groups a coupling layer is arranged, the optical thickness of which is an odd multiple of A / 4, or that two coupling layers between adjacent alternating layer groups are arranged, the optical thickness of which is an even multiple of λ. / 4 » To achieve the object of the invention, it is also possible that a coupling layer is arranged between adjacent alternating layer groups, the op_ table thickness is an even multiple of λτ, / 4 .

The alternating layer groups used according to the invention are expressly those with a small number of individual layers, so that the individual alternating layer group for the measurement wavelength λ does not allow a high reflection, but only a partial reflection, which, however, due to the small number of individual layers over a wide Spectral range is effective, in contrast to alternating layer systems according to the prior art with a high number of individual layers for high reflection, which only act in a relatively narrow spectral range small number of single layers, depending on the respective effective refractive indices, be 2 to 9 individual layers.

3561 130063/0601

Despite the use of changing layer groups the described type achievable high reflection with very low absorption and scattering losses is thus explains that through the coupling according to the invention several such alternating shift groups by one or several coupling layers the non-highly reflective effect of the individual alternating layer groups within its wide reflection range in several spectral bands to a high reflection and to the same extent the already low absorption and scattering losses of such bird layer groups be further minimized These effects are likely to result are based on the fact that the light in all existing spectral bands is already partly from the - to the direction of incidence of light related - anterior alternating shift group or the anterior alternating shift groups largely reflected will. To the lower 7 / lizard! Layer groups, which, however, are obviously indispensable for achieving a high level of reflection, can only be achieved little light, so that this cannot significantly contribute to further losses

The layer arrangements according to the invention can, for example, expediently be produced by the high vacuum process, in which, as is known, suitable layer substances evaporate so that they can be deposited as layers on the surfaces of conventional substrates. In the near UV, / IS and near IR areas, the known layer substances of high refractive index, such as zinc sulfide (ZnS), titanium dioxide (TiO ₂ ), tantalum pentoxide (Ta ₂ Oj-) and the known layer substances of low refractive index, such as cryolite li ? g), magnesium fluoride (MgP ₂ ) or silicon dioxide), etc. can be used.

3561 130063/0601

The invention is to be explained in more detail on the basis of the following examples. Illustrated in the accompanying drawing:

1, 2 and 3 the spectral reflection curves. R (solid Curves) and the spectral transmission curves T (dashed curves) of the invention described in Examples 1, 2 and 3 Interference mirror,

J? Ig · 4 the spectral reflection curve R for comparison (smooth curve) and transmission curve T (dashed curve) of an interference mirror the state of Terhnik.

In all embodiments according to the invention, the spectral position of the reflection bands and their number is given by the measurement wavelength X _Q and by the sum D of the optical thickness of an alternating layer group D and that of a coupling layer D _K (D = D _w + D ^) fixed »There are, for example, three reflection bands with high reflection and very low absorption and light scattering losses with the" / eilenlängen _{Λ η}

Ao * ^u

^ v ₁

-W ²

when the coupling layers have an optical thickness of an odd multiple of A / 4, and is disposed an odd number of coupling layers between adjacent iifechsRlschichtgruppen or when the coupling layers have an optical 4 thickness of an even multiple of A _o / habea and the number of Kopplungaachichte'i is an even number between neighboring groups of layers, Ks gives s / ß. two reflection bands with high reflection and low absorption and light scattering losses

3561

130063/0601

the. ϊ / e ilen lengths

A ₂ _ λΰ. D.

if the coupling layers have an optical thickness of an even multiple, of Λ- / 4 and Between the neighboring groups there is an odd number Number of coupling layers is arranged. The spectral optical details of a given Layer systems can be determined by measuring the produced interference mirrors.

Execution example 1:

With the help of the high vacuum damping, an interference mirror is created produced by an arrangement of alternating layer groups on a base body G (e.g. glass) W and coupling layers E ^. and K-, vapor-deposited that is represented by the formula

can be illustrated. When W bindeIt it is alternating layer groups clotting he number of individual layers, the wave to the Ma ':! Lärr; e A are matched ₀ and / ec from a V .iselfolge of low refractive index _(1ί Λ) and hoehbrechenden (H ) Single layers a with an optical thickness of Λ / 4 exist, γ / obei within W _Q the arrangement N ₀ H ^ ₀ E ₀ is present. Between the alternating layer groups 2 coupling layers are arranged in each case, v / if IC «· = 2H and Kg = 2H _Q , ie in this pallet the coupling layers K ~ and K ™ have an optical thickness of each

Λ _ο / 2. _{The refractive index n G} = 1.52 was taken into account for the glass base _{, n ^ = 1.455 for the low refractive index SiO 2} layers (Ii ₀ ) and the complex refractive index ⁿ h ^ik h ⁼ for the high refractive index TiO ₂ layers (H ₀₎ ² * 315 - i. 0.005 (i = -1) with the one for the

130063/0601 ₃₅₆₁

Responsible for absorption - absorption index k " ~ O _t The absorption index Ic ^ of the low _{refractive index SiO 2} layers v; has been neglected in accordance with practical conditions. The wavelength for the

yt / ^ - layers is ] [ = 520 nm, so that according to the structure of the V / arm layer groups V / and the elastically arranged coupling layers KL and there are 3 reflection bands, which according to the relationships given for A ₁ 2 and A3 with the V / e Ilen lengths Χ., = 693 nm, A2 = 416 nm and Λ ^ ⁼ A ₀ = 520 nm. In FIG. 1, the spectral reflection R (solid upper curve) is shown in the opposite direction to the transmission T (dashed lower curve), so that the hatched area between the curves is a measure of the absorption losses. In the flexion bands, the reflection losses in the working area of the minima are only about; a 1 to 3 % and are therefore only about 2 to 5 times as large as for a single A / 4-TiO ₂ layer.

Embodiment example 2

on the basis of those described in embodiment 1 as a basis Conditions and definitions becomes an interfering mirror with the layer arrangement G /

produced, v / whether the alternate layer group w has the individual layer arrangement H ₀ N ₀ H ₀ , and the alternating layer groups W consist of the layer sequence H IJ HlH. The coupling layers K ^ in this case consist of 5 II layers, ie the coupling layers have an optical thickness of 5 Λ / 4. Eg the same materials were used for the base body G and for the layers as in Example 1.
The Maßv.'ellenlänge for the A _0/4 layers is

Λ = 520 nm, so that in accordance with the structure of the Lechsel layer groups \ Ί and w and the

130063/06 01

ordered coupling layers KL, r? i result in 3 reflection _{bands, which according to the above given relationships for A 1} »Λ2 ^{un <} * Λ3 at aen wavelengths A ₁ ■ 434 nra; ^ ₂ = 65Ο nm and Λ3 = A ₀ * 520 nm lie.

The spectral reflection and transmission properties are graphed in Fig. 2 in the same manner as in Example 1 (Pin x 1). The reflection losses illustrated by the hatched difference area between the R and T curves are 1 to 2VU * in the working area of the minima of the reflection bands

Execution: belapjel 3t

In analogy to example 1, an "interference mirror" ...

with the layer arrangement

where »Y _Q = H ₀ H _Q H ₀ and K ₅₁ = 2H _Q is. Here, too, the same material parameters apply to G,

K and H_, as in example 1.
ο ο * ν

The length for the A _o / 4 layer is

\ a 520 nm, so that in accordance with the structure of the layer arrangement here 2 reflection bands result which, according to the above-mentioned relationships for the main wavelengths of the reflection bands, are λ ^ = and A2 ^a 650 nm.

In Pig. 3, the resulting spectral reflection and transmission characteristics are shown graphically in the same way as in the previous examples. The reflection losses illustrated by the hatched difference area between the R and T curves amount to 1 to 2 % in the working range of the minima of the reflection bands the S'ig. 4 the spectral reflection

130063/0601

- yt -

im ί Transiiilsfiionfjlairven one,?. Interference mirror, as is known from the prior art, is the arrangement of two different alternating layer systems \ * L and VZ _{9 with a} high number of layers on a glass base body G, so that the overall structure

^{G / W} 2 ^W 1

results, where

W ₁ = H ₁ IT ₁ IT ₁ H ₁ = IyA ₁ A single layers and

W ₂ = RrJIp * 9, ..Kk) TJo = 16λ _2/2 individual layers mean, • ^ as the inner V / ax layer system arranged directly on the glass surface. ' ₂ is to the wavelength

2 = 433 nm and adapted to the outer Wechselschichtsyst em ^ ₁ 1st / avelength to the V A ₁ = 650 nm adapted. The same substances were used to make it, and the same! Refractive indices, as the calculation is based on in the examples of the invention, V / ie can be seen from the hatched areas of Pig, 4, are low absorption losses of about 1 to 2% and thus high reflection values only in one spectral band, namely in the vicinity of the matching wavelength λ- = 650 vsd possible because only this spectral band is reflected by the “alternating layer system” IL at the front, based on the direction of incidence of light. In the second spectral band in the vicinity of the wavelength A-) = 433 mn, the reflection is greatly reduced, since the light from this spectral band only passes through a lot _{before and after the reflection from the alternating layer system W 2.} Layers of the Weohselschichtsysterns W ₁ arranged above must go and thereby ^{suffer considerable absorption losses of 10 bio 30 1} ^, which are thus about 10 times higher than with the Interferencspiegel according to the invention,

3561

130063/0601

Blank page

Claims (3)

1. Interference mirror with high reflection for several spectral bands, consisting of a base on which alternating layer groups of non-metallic, optically low-loss Sinzelschiehten are arranged one above the other so that the ßinselschichten with high and low refractive index alternate, characterized in that between neighboring identical or different structures Alternating layer groups of 2 to 9 individual layers one or more non-metallic coupling layers are arranged, the single layers of all ./ Wechselschichtgruppen have an optical thickness of VA of a measurement wavelength Λ _ο and the optical thickness of the non-metallic coupling layers is an integral multiple of λ _ο / 4. 2. interference mirror according to claim 1, characterized in that a coupling layer is arranged between adjacent V / rear layer groups, the optical thickness of which is an odd multiple of A _Q A. 3. interference mirror according to claim 1, characterized in that that between neighboring .Valtering shift groups two coupling layers are arranged, their optical thickness is an even multiple of / 4. 3561 130063/06 01