DD299774A7 - Method for producing climate-stable, laser-radiation-resistant metal layer front surface mirrors - Google Patents

Abstract

The invention relates to a method for producing climate-stable, laser radiation-resistant Metallschichtvorderflaechenspiegel which are required in the optical Geraetebau in cost-effective, structurally simple and small apparatus especially for surveying and medical applications. According to the invention, a 1/4 layer system of the substances cerium fluoride, magnesium fluoride, ceria and silica is thermally evaporated onto the metal layer by depositing the first layer on the substrate at room temperature and all further layers on a substrate previously heated to approximately 550 K, the third with water and the fourth layer are reactive with oxygen vaporized. {High vacuum evaporation; Metallschichtvorderflaechenspiegel, laser radiation resistant, climate-stable; Alternating layer system; cerium fluoride; Magnesium fluoride; ceria; Silica, thermal, reactive}

Description

Field of application of the invention

The invention relates to a method for producing climate-stable, laser-resistant metal layer front surface mirrors, in particular for the production of mirrors with broadband high reflection. Such requirements arise, for example, in optical device construction in structurally simple, small and inexpensive apparatus, especially for surveying and medical applications.

Characteristic of the known state of the art

Metal layer front surface mirrors have the following layer structure for most demanding applications: Substrate adhesion-layer-reflecting metal layer-dielectric protection layer / dielectric multilayer system (with protective and / or reflection-increasing effect). Such mirrors are used in various embodiments with special layer sequences and production processes in DE-OS 2028252, DE-OS 2032452, US-PS 3601471, US-PS 2647441, DD-PS 2'7539, DD-PS 237007, US-PS 3687713, CH-PS 494409 and SU-PS 578634 described in detail. From CH-PS 494409 and dor DE-OS 2028252 the vapor deposition of an aluminum oxide protective layer is known, and in SU-PS 3687713 an aluminum oxide / silica double layer is proposed, which is made by consuming electric tenstrahlverdampfung to the reflection in the visual To improve spectral range. US Pat. No. 2,647,441 proposes, with the same objective, the vapor deposition of a mechanically unstable magnesium fluoride layer, which is tempered in a subsequent process step at about 520 to 700 K in order to improve the stability. In order to improve the reflection rate of a metal layer front surface mirror with respect to a laser wavelength, it has been proposed in US Pat. No. 3601471 to vacuum vaporize a magnesium fluoride / silica alternating layer system onto a previously applied titanium dioxide film.

Similar systems with h ^ .. drem Brechzahlkontrast the alternating layer system are known for stray light gyroscope. In order to increase the mechanical, chemical and climatic stability, the experimentally complex electron beam atomization is used for the production of the silver, titanium dioxide and silicon dioxide layers used (SCHMITT, ROSTECK in DFVLR-FB 86-57 (1986)).

Another common measure for increasing the durability of certain protective layers is their production by electron beam evaporation under ion bombardment (eg Appl. Opt. 22 [1983] 178 and Appl. Opt. 23 [1984] 1116). In addition, dense, amorphous mixed layers of different oxides (Journal Vac, See Technol., 7 [1970] 143) or finely crystalline oxide layers, which are formed at temperatures of more than 630K (Proc. SPIE Vol. 401 [1983] 31) are used , The common disadvantage of all these solutions is that the layer systems only very specific applications, such as either a high broadband reflection in the visual spectral range or high reflection and thus resistance to intense laser light radiation concern. Another common disadvantage of all known solutions is the low mechanical, chemical and thermal stability.

Object of the invention

Ziolder inventions, a possibility for the production of climate-stable, laser-radiation-resistant metal surface front surface mirrors to findon, which can be realisiertl with little technological effort.

Explanation of the essence of the invention

The invention has for its object to provide a method for producing climate-stable, laser radiation resistant metal layer front surface mirror, which improves the reflectivity of the mirror sow jhl for the visible spectral range as well as for the near infrared laser wavelength and the physico-chemical stability of the layers.

According to the invention, the object in a method for producing climate-stable, laser radiation-proof Metallschichtvorderflächenspiogel, wherein a λ / 4-layer system containing a known per se for purely dielectric layer systems layer sequence of magnesium fluoride, ceria and silicon, on a supported by a substrate, as a reflective layer metallized layer is applied, wherein the substrate is first applied a bonding agent layer before the metal layer follows, thereby solved,

that before the end of the vapor deposition process of the adhesion promoter layer at a Restgasdrur.k of less than 1O ^-3 Pa, a simultaneous evaporation of the materials of bonding agent layer and metal layer takes place, which lasts until an approximately 5 nm thick transition region is formed,

- That while maintaining the existing residual gas pressure and the room temperature of the substrate, an approximately 25nm thick Cerfluoridschicht is evaporated,

- That the substrate is heated to about 550 K and held at this temperature for about 30 minutes,

- At constant substrate temperature and the same residual gas pressure, an approximately 75nm thick magnesium fluoride layer is vapor-deposited,

- That while maintaining the high substrate temperature, a water-reactive gas pressure of 5 10 ~ ³ Pa set and the CerdioxidscHcht with oin ^u r geometric thickness of about 55 nm is deposited and

- that Rozip.onten to a residual gas pressure level of less than 1O ^-3 Pa, an oxygen-Reaktivflasdruck of e \ 2.5-10 "after a Ev ikuiorung ^dis. Pa is adjusted in the silicon monoxide is evaporated until an about 210 nm thick Silitiumdioxidschicht has emerged.

With the production method according to the invention, it is possible to produce a broadband from the visible to the near infrared spectral highly reflective and thus laser radiation resistant metal layer front surface mirror, which achieves very good climatic stability by its mechanically, thermally and chemically very stable, four-layer system, exclusively by means of technologically simple thermal evaporation processes. Furthermore, it is noteworthy that the experimentally achieved reflection values clearly exceed the reflection spectra theoretically determined on the basis of interface-smooth and refractive-index-homogeneous layer models

 In addition, the method according to the invention is characterized by a high yield of metal layer front surface mirrors, which meet the required parameters with respect to laser resistance and climatic resistance. The method is also applicable to metal layers which do not have optimal reflectivity.

embodiment

The invention will be explained below with reference to an exemplary embodiment.

As substrates, fused silica or boron-glass are favorably used in order to ensure the required utility value properties of the mirror also substrate-like. The substrate material is provided with a cerium oxide polish prior to the beginning of the sputtering process.

The vapor deposition of all layers of the mirror takes place in a high-vacuum apparatus, which is evacuated after the introduction of the substrate to a pressure of about 1 Pa. At this pressure, a ten-minute Beglimmen the substrate. Because of the broadband high reflectivity in the visual and near infrared spectral range, a front surface mirror with a metal layer of silver should be the subject of the explanations in this embodiment.

Before the start of the production of the layer system, the recipient is evacuated to a residual gas pressure of less than 10 ^-3 Pa. Then the vapor deposition of the primer layer begins, which in this example is obtained by thermal evaporation of chromium and should have a geometric thickness of about 20 nm.

Before completion of the vapor deposition of chromium, the silver evaporation process is initiated, so that by simultaneous evaporation

of chrome and silver, a minimum of 5nm thick transition region from the pure chromium layer to a mixture of chromium and silver is formed into a pure silver layer. The silver evaporation process is continued until an approx.

120 nm thick silver layer is formed. In direct connection, an approximately 25 nm thick cerium fluoride layer (λ / 4 layer for the laser wavelength λ = 165 nm) is applied to the silver layer as the first layer of the λ / 4 layer system.

In the next step, the substrate is heated to a temperature of about 550 K and held in vacuum for about 30 minutes at this temperature, before the 75 nm thick magnesium fluoride layer (λ / 4 layer for the light wavelength λ = 414 nm) is evaporated onto the hot substrate , Thereafter, with the substrate temperature kept constant, a water reactive gas pressure of

5 × 10 ^-3 Pa and the ceria layer with a thickness of approximately 55 nm (λ / 4 layer for the wavelength λ = 464 nm).

deposited. .

Subsequently, the recipient is evacuated to a residual gas pressure level of less than 10 ^-3 Pa and a reactive gas pressure of about 2.5 × 10 ^-2 Pa is set by evaporating silicon monoxide and forming an approximately 210 nm thick silicon dioxide layer (λ / 4 layer for the wavelength of light λ = 1235 nm) is formed.

The entire process control is realized by means of thermal evaporation, compliance with the process parameters within normal tolerances is essential for the realization of the optical and stability properties. The tolerances are technically quite feasible.

For the process product, Table 1 gives the most favorable geometric thicknesses of all layers and the realized optical thicknesses and refractive indices of the layers of the alternating layer system.

Table 1: Layer parameters of the metal layer front mirror according to the invention

layer material geometric optical refractive index episode Thickness (nm) Thickness (nm) (for X = 550nm) substratum quartz glass 1 Cr 20 2 Ag 120 3 CeF ₃ 25 41.25 1.65 4 MgF ₂ 75 103.50 1.38 5 CeO ₂ 55 115.50 2.10 6 SiO ₂ 210 308.70 1.47

This front surface mirror specified in the exemplary embodiment is characterized by particularly high reflection coefficients (> 0.98) over almost the entire visual and the near infrared spectral range and is particularly suitable for the laser wavelength of 1064 nm.

Claims (2)

1. A process for the production of climate-stable, laser-radiation-resistant metal layer front surface mirrors in which a λ / 4-layer system containing a layer sequence of magnesium fluoride, ceria and silica known per se for purely dielectric layer systems is applied by vapor deposition to a metal layer acting as a reflection layer carried by a substrate , wherein on the substrate first a Haflvermittlerschicht is applied before the metal layer follows, characterized in that a) before the end of the vapor deposition process of the adhesion promoter layer at a residual gas pressure of less than 10 ^-3 Pa a simultaneous evaporation of the materials of bonding agent layer and metal layer takes place, which takes so long until an approximately 5 nm thick transition region is formed, b) while maintaining the existing residual gas pressure and the room temperature of the substrate of a about 25nm thick cerium fluoride layer is evaporated, c) the substrate is heated to about 550 K and held at this temperature for about 30 minutes, d) an approximately 75 nm thick magnesium fluoride layer is vapor-deposited at a constant substrate temperature and the same residual gas pressure, e) while maintaining the high substrate temperature, a water reactive gas pressure of 5 × 10 ^-3 Pa is set and the cerium dioxide layer is deposited with a geometric thickness of about 55 nm and f) after an evacuation desRezipienten "an oxygen-reactive gas pressure of approximately 2.5 · 10 ³ Pa" ² Pa is adjusted to a residual gas pressure level of less than 10, by evaporating silicon monoxide until an approximately 210 nm thick silicon dioxide layer is formed. 2. The method according to claim 1, characterized in that in the simultaneous evaporation of chromium and silver are thermally evaporated, chromium being used as a coupling agent and silver as the metal layer.