JPS60114801A - Reflection preventing film - Google Patents

Abstract

PURPOSE:To obtain reflection preventing film having high light resistance usable also for CO2 laser by forming lead fluoride film on chalcogens glass film having a specified refractive index, and forming zinc sulphide film or selen sulphide film on the chalcogens glass film. CONSTITUTION:A material having high refractive index i.e. chalcogens glass 2 which is in amorphous state and having low absorptance, good adhesion and >=2.6 refractive index, is first vapor-deposited on a KRS-5 substrate 1 having 2.37 refractive index with extremely precisely polished surface suitable to optical purpose. Then, PbF2 3 of low refractive index as low as ca. 1.6 and low absorptance is vapor-deposited. Thereafter, a high refractive material 4 i.e. ZnS of 2.2 refractive index or ZnSe of 2.4 refractive index is vapor-deposited thereon in order to protect the chalcogens glass PbF2 of low resistance to environment from the influence of the environment. By this method, a reflection preventing film comprising three-layered structure having low absorptance, high light resistance, and high resistance to environment, is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to thallium iodide (iI) and thallium bromide (TAE).
Infrared optical components (windows) made of a material called KRS-s, for example, a mixed crystal with KRS-s.

It relates to anti-reflection coatings for lenses, optical fibers, etc.

The structure of the conventional example and its problems KH2-5 has a refractive index of 2.37 (wavelength 1o, 5μm
n), the reflection loss at the input and output ends is about 28%. To reduce this, it is desirable to coat the end face with an anti-reflection film.

However, the technology for applying an anti-reflection coating to KH2-5 has not yet been established, and there is almost no literature on it.

Under these circumstances, KR3-s has recently been put into practical use as a light guide (optical fiber) for a carbon dioxide laser scalpel, and there has been an increasing demand for an antireflection film for the purpose of improving its transmittance.

Since the antireflection coating used on the end face of the light guide is irradiated with carbon dioxide laser light, it is first required to have higher light resistance than that of ordinary infrared windows, lenses, etc. Furthermore, in the case of a light guide, the laser light is generally focused and incident on the end face, so the power density at the surface is about two orders of magnitude larger than that of a normal laser optical component. For example, when outputting esoW, the power density at the input end of the light guide is 20KW/c.
It also reaches tA. Therefore, the antireflection film on the end face of the light guide is required to have not only environmental resistance and peeling resistance, but also extremely high light resistance.

Improving light resistance depends first on creating an anti-reflection coating with low absorption.

Conventionally, anti-reflection films made of zinc selenide (ZnSe), gallium arsenide (GaAs), potassium chloride (KCff), etc., which are materials for transparent optical parts for carbon dioxide lasers, have single-layer, double-layer, or three-layer structures. Membrane structures, etc. are being tried. Although it is possible to construct an anti-reflection film with more layers than this, there will be problems with ease of work when forming the vapor-deposited film, and there will be problems such as increased absorption of laser light as the film thickness increases, so it is not recommended in special cases. With the exception of anti-reflection, the number of layers is limited to three.

A single-layer film structure is the easiest to manufacture. According to optical theory, if the condition that the refractive index n is equal to the square root F of the refractive index n8 of the material of the optical component is satisfied, then the optical thickness nd =
λ/4 (for λ=1o, eμm, nd=2.66μm
), the reflectance becomes zero when deposited on a substrate, resulting in a single-layer antireflection film.

There are very few things in nature that satisfy these conditions. The square root of the refractive index n of the KH2-s material, r
Materials with a refractive index close to = , r, 37 + 1.54 are listed in Table 1.

Table 1 Single-layer anti-reflection film for KH2-es As can be seen from Table 1, the single-layer anti-reflection film cannot reduce the reflectance to zero and a reflection of about 1% remains.

ThF4 has excellent environmental resistance, but has the disadvantage of high absorption. In the case of PbF2, absorption is low, but there is a drawback in environmental resistance. That is, the PbF2 vapor-deposited film is weak against water, and if water is accidentally applied to the surface, the film will crack or scattering will increase.

On the other hand, if we consider a combination of two types of dielectric materials that satisfy the conditional expression of the 5-chuster two-layer film structure, it is possible to theoretically reduce the reflectance to zero. If you search for such combinations, you will find something like Table 2.

Table 2 Two-layer antireflection film for KH2-ts As can be seen from Table 2, in the case of a two-layer structure, it is possible to theoretically reduce the reflectance to zero, but it has the drawback of high absorption.

As2Se3/PbF2/AlI2 was prototyped as a combination satisfying Mouchrat's three-layer film structure conditional expression.
The anti-reflection film made of Se3 has a low absorption rate on the order of 0.02% per surface, and has better light resistance than single-layer or double-layer anti-reflection films.

However, chalcogenide glass generally has the disadvantage that it is oxidized and absorbs more when exposed to high temperatures for a long period of time, and its surface is easily scratched during cleaning because it is mechanically soft.

As described above, it has not been possible to obtain an antireflection film with zero reflectance, environmental resistance, long life, low absorption, and high light resistance.

Purpose of the Invention The present invention provides an infrared transmitting material made of a mixture of thallium iodide (Tl) and thallium thallium (T2Br) such as KH2-5, which has excellent environmental resistance, long life, and absorption properties. The object of the present invention is to provide an antireflection film that can be used for carbon dioxide lasers, which has a small amount of light resistance and therefore has high light resistance.

Structure of the Invention The present invention first deposits a high refractive index material, which is chalcogenide glass with a refractive index (n3) of 2.6 or more, on the KH2-5 surface, which exhibits an amorphous state with low absorption and good adhesion, and then deposits a high refractive index material on the KH2-5 surface. PbF2, which is a low refractive index material with a refractive index (n2) of about 1.6, is deposited, and in order to protect the poor environmental resistance of these chalcogenide glasses and PbF2, a material with a refractive index (nl) of 2. ZnS is a material with a high refractive index of 2, or Zn5 has a refractive index (nl) of 2.4.
To provide an antireflection film having a three-layer film structure formed by vapor-depositing E, which has low absorption and therefore has light resistance and excellent environmental resistance.

Description of examples Examples of the present invention will be described in detail below.

Figure 1 shows the wavelength 10 according to the present invention on the KH2-s plane.
．． It is a structural diagram of a three-layer antireflection film for 6 μm.

1 in the figure has a surface that has been optically polished to ultra-precision and has a refractive index ns of 2.
．． 37 KH2-5 board. 2 has a refractive index n3 of 2.
6 or more chalcogenide glass film, where 3 is the refractive index n
It is a PbF2 film where 2 is approximately 1.6. 4 is the refractive index n1
It is a ZnS film with nl of 2.2 or a Zn5e film with nl of 2.4. FIG. 2 is a diagram showing the reflectance wavelength dependence of a typical antireflection film according to the present invention.

Under the above conditions, the film thickness of each of the six sets of three-layer anti-reflection coatings is calculated using Mouchrat's relational formula (Applied 0 pti
csvo2.16. A10. Table 3 shows the results obtained to satisfy P2722).

In each of the examples below, the absorption per surface of the anti-reflection film is about 0.02%, and the absorption per surface of the PbF2 single-layer anti-reflection film, which has the lowest absorption rate among single-layer and double-layer structures, is about 0.02%. 05%
Fewer.

Furthermore, in the above embodiments, the outermost layer exposed to air is made of ZnS or ZnS, e, which is difficult to oxidize, and serves to protect the chalcogenide glass and PbF2 film inside, so it is different from the conventional three-layer antireflection film ( As2S
e3/PbF2/AS2Se3) has better environmental resistance.

Next, in the present invention, the refractive index n of chalcogenide glass
The reason why 3 was specified as 2.6 or more will be explained based on Fig. 3.

Figure 3 shows ZnS, which is the outermost layer of the antireflection film according to the present invention.
Alternatively, it is a diagram showing the relationship between the film thickness of Zn5e and the refractive index of chalcogenide glass, which is the innermost layer. In the figure, 5 is Ge28
Sb12Se60 (nl., 6-226), 6baAll
2S03(n1o, 6-2.8), 7(dGe3oA8
1□Te5oSe23 (“10.6 to 3.1)”.

As explained above, the outermost ZnS, Zn5e film, which is in direct contact with air, etc., has an inner PbF2. and chalcogenide glass, so it is at least about 0.2μ.
A film thickness of m or more is required. What Figure 3 means is that in order to satisfy the conditions for a three-layer anti-reflection film and for the thickness of the outermost layer to be approximately 0.2 μm or more, the refractive index of the bottom chalcogenide glass must be 2.6 or more. If you don't have them, it means you won't be satisfied.

Effects of the Invention As described above, the present invention is a three-layer antireflection film for KH2-5 having a composition of chalcogenide glass/PbF2/ZnS or Zn5e with a refractive index of 2.6 or more, and has the following effects.

1 The absorption rate of the anti-reflection film for carbon dioxide laser light with a wavelength of 10.6μ+/l is as low as 0.02%, and the single-layer P
Since it is better than 0.05% of the bF2 antireflection film, the light resistance is also improved.

2 Compared to the three-layer anti-reflection film whose outermost layer is made of chalcogenide glass, ZnS and Zn5e, which are thermally and chemically stable and mechanically strong, are used, so the inner chalcogenide glass film and PbF film are Because it is chemically and physically protected, it has excellent environmental resistance and has a long life.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the anti-reflection film according to the present invention, FIG. 2 is a diagram showing typical reflectance wavelength dependence of the anti-reflection film according to the present invention, and FIG. 3 is a cross-sectional view showing an embodiment of the anti-reflection film according to the present invention. FIG. 3 is a characteristic diagram showing the relationship between the thickness of the outermost layer and the refractive index of the innermost layer of the prevention film. 1... Substrate to be evaporated, 2... Chalcogenide glass film, 3... PbF2 film, 4...
...ZnS or Zn5e film. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2121 5 Skin length (, u yy2) Figure 3

Claims (1)

[Claims] (1) A lead fluoride (PbF2) film is placed on a chalcogenide glass film with a refractive index of 2.6 or more, and a zinc sulfide (ZnS) film is placed on top of the chalcogenide glass film with a refractive index of 2.6 or more.
) film or a zinc selenide (Zn5e) film. ? ) Is the film thickness of the zinc sulfide film or zinc selenide film 0.2μ?
The antireflection film according to claim 1, wherein the antireflection film is n or more.