DD286434A5 - REFLEX-REDUCING LAYER WITH LOW PHASE SHIFT IN TRANSMISSION - Google Patents

Abstract

The invention relates to an antireflective layer with low phase shift in transmission, which is used in particular on optically effective surfaces of polarization lenses and condensers for the visible spectral range. The antireflective layer according to the invention consists of five partial layers which satisfy the following conditions: S / n1d1 / 4, n2d20.64 / 4, n3d30.25 / 4, n2d40.7 / 4, * where n11, 64, n22, 0.05 and n31, 38, and t has a value in the range of 0.75t1.2 for varying the optical thickness of the second sublayer n2d2, and is w1 or, advantageously, w4t for varying the optical thickness of the last sublayer. In addition to a low residual reflection R * and a small phase shift of Df (1) 1, the coating according to the invention is characterized in particular by the possibility of varying the optical thickness of the second partial layer with respect to these parameters for various applications. {Antireflection coating ; Phase shift; Residual reflection; color point; Polarizing microscope}

Description

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Field of application of the invention

The invention can be used above all where it is important for a reflection-reducing effect of optical surfaces and where at the same time a small and variable phase shift Δφ is required between parallel and perpendicular polarized waves when passing through the optical surfaces. The invention therefore finds particular application in the antireflecting of optical surfaces in polarized lenses, condensers and other optical systems in which a particular polarization direction and a certain phase shift are to be maintained or intentionally changed. Use as an antireflection layer with a variable course of reflection R (λ) for optimizing the antireflection effect in optical devices is likewise possible.

Characteristic of the prior art

In an optical system, one or more optical surfaces are located in the optical path. At all optical interfaces (transition air-substrate and vice versa), a portion R of the incident light I _{0 is} reflected. The reflection is generally unacceptably large for non-mirrored optical surfaces (eg for optical glass of the type BK7R = 0.042I ₀ ). Both the reflections and the reduction of the transmitted light I have a negative effect, especially if several optical surfaces k are present:

I = I ₀ (IR) ^k

Therefore, in most optical devices, the optical surfaces are provided with anti-reflection coatings. These Antireflection coatings, which consist of one or more individual layers, lead to a reduction, but also spectral Dependence of the reflected light R (λ). Low-refraction λ / 4 monolayers with R s 1.5% are used for the spectral range from 400 to 700 nm, 4-layer Antireflection coating with alternating high and low refractive index layers H and L according to the notation S / HLHL / A,

where S is the substrate and Ada's outer medium (generally air) and the reflectance R is £ 0.75% for the spectral range of 450 to 660nm and e-layer antireflective coating S / HLHLHLHL / A with RS 0.75% for 430 to 700nm, where none of the high and low refractive layers has an optical thickness of λο / 4 or a multiple of λο / 4 of the

Has focal wavelength A _{0 of} the application area. By applying such antireflection coatings on optical substrates but also the polarization state of

continuous light changed. This effect is particularly disturbing when working in the optical system with polarized light, such. B. with polar lenses.

The phase shift Δφ, the coated optical surfaces at a light incidence angle U ₀ between vertical

and parallel component of the polarization of the transmitted light, leads to an increase of the

Erasure coefficient E, which describes the ratio of light intensities in crossed and parallel polarizers. E (A, β) = a ² (A, β) + [Δφ (A, β) / 2] ' ₍ if α, Δφ <«1 In this case, α describes the rotation of the polarization plane as a function of the azimuth angle β and the aperture A. In the case of antireflection coating with good antireflection effect (R (λ) <0.5%, 43Giim <λ <700nm), the influence of Phase shift Δφ in the above equation to the extinction coefficient E. Therefore, in optical systems, where working with polarized light, in addition to the antireflection effect of Anti-reflective coating also used the phase shift to characterize an anti-reflective coating.

Particularly suitable is a λ / 4 - λ / 2 - λ / 4-Wechselschichtbelag according to DD-WP 223540, the λ / 2 layer of ZRO ₂ with η = 2.05 is formed. A problem is here the λ in / 2-ZrOrSchicht at η · d "λ" / 4 occurring refractive index inhomogeneity between η (nd <A ₀ Al) "2.05 and η (nd> A ₀ AJ)" 1, 95 has a steady transition and reduces the anti-reflection effect. Possibilities for suppressing this inhomogeneity are provided by interposed interlayers spaced nd - V8 with an optical thickness of nd = 1 ... 6nm (GB-PS 1497636), mixed layers of ZrO ₂ and ZrTiO ₄ (Steuer, Esselborn: New materials for optical thin Films, Appl. Opt, vol.15 [10] 1976, p.2315ff.), a reactive vapor deposition atmosphere (GB-PS 1466640) or activating the substrate surface by ion bombardment (Martin, McLeod: lon-beam-assisted deposition of thin films Appl. Opt., Vol. 22 [1] 1983, p. 178 ff.).

All these solutions either have the disadvantage of a very high expenditure on equipment in the production (ion source) or a strong scattering and absorption of the correspondingly modified coating due to the irregular growth of the layer due to the admixtures to ZrO ₂ . In addition, in these solutions, the course of the residual reflection R (λ) and the phase shift Δφ (λ) of the anti-reflection layer produced is clearly defined and can not be varied for optimization purposes.

Object of the invention

The aim of the invention is an antireflective coating for optically active surfaces, in particular of polar lenses and condensers, with a phase shift of Δφ (λ) s 1 ° at an angle of incidence of U ₀ = 40 "and a residual reflection of R (λ): s 0.5% in the visible spectral range from 450 nm to 700 nm, which does not have the disadvantages of the prior art, in particular can be produced without additional expenditure on equipment and can be optimized for different applications.

Explanation of the essence of the invention

The invention is based on the object to provide a reflection-reducing layer for optically active surfaces, in which the low residual reflection R (λ) in the visible spectral range and the minimum phase shift Δφ (λ) between the parallel and the vertical component of the transmitted light are spectrally displaceable in order to achieve a minimum extinction coefficient E, a favorable color locus and a high antireflection effect for an optical system. This object is achieved by an anti-reflection layer with low phase shift in transmission between parallel and perpendicular to the plane of incidence oscillating light waves, which is applied to the optically active surface of an optical component and sublayers of different optical thickness η · d as a product of refractive index η and geometric layer thickness d expressed in values of λ _o / 4 of a centroid wavelength λ ₀ , solved by being composed of five partial layers satisfying the following conditions:

S / n, d, = V4, n ₂ dj = 0.64t * A ₀ M, n ₃ dj = 0.25 W 4, n ₂ d ₄ = 0.7λο / 4, n ₃ d ₆ = 1.07 V4 / L, where n, = 1.64, n ₂ = 2.05 and n ₃ = 1.38 and t to

Variation of the optical thickness of the second sub-layer n ₂ d ₂ assumes a value in the range of 0.75 <t <1.2 and S for substrate

and I stand for air.

With the help of a large series of experiments on the invention, consisting of five sub-layers reflex-reducing S rhicht,

It was found that by varying the optical thickness of the second sub-layer by changing the parameter t, the wavelength-dependent phase shift Δφ (λ) of the transmitted light at an incidence angle of U ₀ = 40 ° at

Keeping the good antireflection properties continuously change. By a theoretical evaluation of the

Antireflection layer according to the invention with the computer neither the reflection course R (λ) nor the phase shift Δρ (λ) could be modeled.

Presumably, the refractive index ratios in the material transitions of the three middle sub-layers are no longer with the

to describe a simple step model.

With the variable optical thickness of the second part-layer within the stated limits, the invention allows

Refraction-reducing layer on the one hand when applied in transmission by optimal adaptation of the phase shift Δφ (λ) to the specific application of a polarization optical system achieving a minimum extinction coefficient E and on the other hand by optimal adjustment of the reflection curve R (λ) influencing the color location and the residual reflection of the entire optical system. The use of the antireflective coating according to the invention is especially important

Substrate breaking numbers (n,), 1.44 <n, s 1.6, in question. Possible asymmetries in the reflection curve, depending on the type of measurement of the layer thicknesses (SQ, photometry Single layer, photometry total layer) occur during the evaporation process, can advantageously by slight variation of the

optical thickness of the last air-tight Tbilschicht according to the Formet n ₃ d ₆ = 1.07 · w · λο / 4 are compensated, wherein

w = ⁴ vT.

embodiment

The Eifindung will be explained in more detail using Ausführungson. Show it

1 shows the continuous change in the reflection R (λ, t) of an antireflection coating according to the invention 2 shows the phase shift (Δφ (λ, t) of a reflection-reducing layer according to the invention at an incident angle U ₀ = 40 ° 3: the correction of the reflection profile of an Ao / 4-MgF ₂ coating by an inventive antireflection coating 4: the compensation of the phase shift of a V * MgF ₂ coating at Δφ (560 μm) by means of an inventive method

FIG. 5: the correction of a reflection course of a reflection-reducing layer according to the invention by additional variation of the optical thickness de; FIG. plumbed sublayer

Bet game 1

An inventive relfexmindernde layer for the Schwerpi / nktwellenlänge A ₀ = 520 nm has the following structure:

S / n, d, = λ o / 4, n ₂ d ₂ = 0.64 x t x V 4, n ₃ d ₃ = 0.25 Δ ₀ Al

n ₂ d ₄ - 0.7 · A ₀ M, n ₃ d = 1.07 V4 / L, where n, = 1.64 (eg Al ₂ O ₃ ), n ₂ = 2.05 (ZfO ₂ ) and n ₃ = 1.38 (MgF ₂ ).

In Fig. 1, curves 1 a-1 d, the experimentally determined reflection curve R (λ) of this antireflection layer for t, = 0.83, t _b = 1, t «= 1.12 and t _d = 1.2 hot vertical incidence of light (angle of incidence U ₀ = 0 °). From the curves it can be seen that a very good antireflection effect is obtained for the parameters "t t _b 0.83 st S 1 in the entire visible Spektralboreich of 430nm to 700ηm. The antireflective layer with the parameters t "and td can be used to compensate the color locus of known antireflection coatings (see Example 3).

Example £

An anti-reflection layer according to the invention according to Example 1 was examined with passage of light at an angle of incidence of U ₀ = 40 ° with respect to the phase shift Δφ (λ). The curves 2 a to 2 d of FIG. 2 show that the phase shift at A ₀ = 520nm of -0.4 ° to + 1 ° can be variiart by varying the parameter t of the coating according to the invention. This situation can also be exploited for compensation purposes (see Example 4).

Example 3

In Fig. 3, curve 3a, the reflection curve of a known λ / 4 MgF ₂ -Entspiegelungsbelages on a substrate of refractive index n, = 1.72 at a centroid wavelength X ₀ = 560nm and a light incidence angle U ₀ = 0 ° is shown. This coating exhibits higher residual reflection values in the blue spectral range with λ <500 nm and in the red spectral range with λ> 620 nm than in the medium spectral range. Will oine optically effective surface in the same optical system with an inventive reflection-reducing layer of A ^wf construction

S / m / d, = λο / 4 n ₂ d ₂ = 0.64 · 1.06 · λο / 4, n ₃ d ₃ = 0.25 A ₀ M n ₂ d ₄ = 0.7 λο / 4, n ₃ d ₆ = 1.07 λο / 4 / L, wohei as

Al ₂ O ₃ layer materials (n _t = 1.64), ZrO ₂ (n ₂ = 2.05) and MgF ₂ (n ₃ = 1.38) are used and the substrate has a refractive index of n ₂ = 1.51 and A ₀ = 520 nm (curve 3b), a color correction of the reflected light of the A ₀ M MgF ₂ coating succeeds. The resulting reflection curve shows curve 3 b.

Example 4

In an optical system in which on an optically active surface of a substrate with n, = 1.72, an A / 4 MgF _r layer is applied, the passage of the light at an incident angle of U ₀ = 40 °, a wavelength-dependent phase shift Δφ (λ) (see curve 4a), becomes an optically active surface of a substrate with n, = 1.51 with an inventive antireflective layer of the structure

S / n, d, = λο / 4, n ₂ d ₂ = 0.64 × 1.12 × A ₀ M, n ₃ d ₃ = 0.25 A ₀ AJ n ₂ d ₄ = 0.7 Ao / 4 , n ₃ d ₅ = 1.07 λο / 4 / L for A ₀ = 520nm

occupied, the phase shift Δφ (A) from curve 4 b can be seen.

The resulting phase shift of both linings shown in curve 4c makes it clear that for the Center wavelength A ₀ = 560nm a compensation of the phase shift Δφ (560nm) = 0 is achieved. A compensation of the residual reflection R or the phase shift Δφ, as described in Examples 3 and 4 applies

however, exactly only for plane-parallel optical surfaces and in a good approximation for weakly curved optical surfaces. For optical surfaces with small radii of curvature separate calculations have to be made.

Example 5 An antireflective coating, for example, having a through-1.1 varied optical thickness of the second sub-layer n ₂ d ₂

according to the invention additionally modified with respect to the optical thickness de ^ last sub-layer n ₃ d ₅ = 1.07 · w A ₀ M by means of parameter w = ⁴ Vt = 1.025.

The modification of the optical thickness of the last partial layer with the parameter w is advantageously carried out in that Aufdampfprozeß measuring the optical thickness using a photometer as a termination condition for the evaporation process R = Rmtn is selected. From the reflection course of the modified layer according to the invention (see curve 5b) it becomes clear that a correction of the

otherwise asymmetric curve has been achieved.

For other measuring methods and termination conditions (eg quartz oscillator, volumetric evaporation ...) must be considered

be that the sole variation of the parameter t of the optical thickness of the second sub-layer leads to a low asymmetry) in the reflection curve (see curve 5a).

Claims (2)

1. A reflection-reducing layer with a low phase shift in transmission between the parallel and perpendicular to the plane of incidence oscillating light waves, which is applied to the optically active surface of an optical component and from sub-layers of different optical thickness η · d as the product of refractive index η and geometric layer thickness d, expressed in terms of X ₀ M of a centroid wavelength X ₀ , characterized in that it consists of five sublayers satisfying the following conditions: S / n ^! = Aq / 4, n ₂ d ₂ = 0.64t · A ₀ M, n ₃ d ₃ = 0.25 X ₀ M, n ₂ d ₄ = 0.7 λο / 4, n ₃ d ₆ = 1.07 V4 / L, where n, »1.64, n ₂ « 2.05 and n ₃ «1.38 and t for the variation of the optical thickness of the second sub-layer n ₂ d ^ has a value in the range of 0.75 <t <1.2 and S stands for substrate and L for air. 2. A reflection-reducing layer according to claim 1, characterized in that the optical thickness of the last, air-adjacent sub-layer with n ₃ d ₅ = 1.07 · w · λο / 4 is also variable, wherein w = VF is.