JPS60263902A - Antireflecting film for rotassium chloride - Google Patents

Abstract

PURPOSE:To improve the environmental resistance, etc. of an antireflecting film consisting of the three-layered films, i.e., As2S3/PbF2/As2S3 formed on a KCl substrate by providing a protective film consisting of BaF2, YbF3 or ThF4 between the substrate and the three-layered films. CONSTITUTION:The protective film 1 which consists of anh among barium fluoride, ytterbium trifluoride or thorium tetrafluoride, is chamically stable and is mechanically strong is formed on the surface of the potassium chloride substrate 5. The arsenic trisulfide film 2, lead fluoride film 3 and arsenic trisulfide are successively formed thereon to manufacture the intended antireflecting film for potassium chloride. The protective film 1 is interposed to avoid the contact of the substrate 5 and arsenic trisulfide chalocogenide glass 2 and therefore the oxidation of the chalcogenide glass 2 by the H2O molecules and OH<-> ions absorbed by the substrate 5 having high moisture absorptivity is prevented.

Description

[Detailed description of the invention] It has low absorption and good transmittance even for 0.6328 μm wavelength laser light, and has excellent environmental resistance. This invention relates to an antireflection film for potassium chloride that has excellent properties.

Conventional configurations and their problems Conventionally, the materials for transparent optical parts for carbon dioxide lasers have been zinc selenide (ZnSe) and gallium arsenide (QAAs).

Examples include potassium chloride (KCI).

Compared to other materials, KCI has a wavelength of 1086μm,
Transparent at 0.6328 μm wavelength with low optical distortion.
Although it has many advantages such as being non-toxic and cheap,
It has the major drawback of being deliquescent. Therefore, it has the disadvantage that it cannot be used for long periods of time in humid environments. On the other hand, a NaF single layer film was considered as the simplest structure for an antireflection film for KCI. The refractive index of NaF is 1.2
3 and the square root of the refractive index of KCI (〆1..'4'5' =
1. ．． 204), the optical film thickness nd
If -λ/4 = 2.65 μm is deposited, a reflectance of 0.05% can be expected, which is close to the ideal optical properties, but since this NaF film itself has deliquescent properties, it is not satisfactory in terms of water resistance. I have no choice but to conclude that it is useless and has no practical use.

There is no substance other than NaF that satisfies the requirements for a single-layer anti-reflection film, and therefore anti-reflection films with a two-layer or three-layer structure are being considered. The anti-reflection coating material for KCI must satisfy 9 conditions: it is insoluble in water, transparent at wavelengths of 106 μm and 0.6328 μm, has good adhesion to engravings, and in a thin film state, :゛Cage exhibiting an amorphous structure that is difficult to form V1 holes,
・Envy must be chosen. Promising materials include chalcogenide glasses such as arsenic trisulfide (AS2S3) + arsenic triselenide (As2Se3) and thorium tetrafluoride (ThF4). The following structures can be considered for two-layer and three-layer antireflection films using these materials.

A) KC1zGATs/AszS3 0) KCl7As2s3/ThF4 C) KCI/A32S3/PbFz =) KC17A8zs3/PbF2//ASzS3 All of the structures shown in A) are composed of chalcogenide and lath, so they have excellent moisture resistance. Wavelength 106μ
Although it has the advantage of having a low absorption rate at m, GA
TS (Ge2gAs2+Te29Sez2) has wavelength 0
．． The 13 layers, which have the disadvantage of not transmitting He-1'Je light of 6328 μm, are all materials that exhibit an amorphous structure and have excellent moisture resistance, and the outermost layer, ThF4, has strong mechanical strength, so it is Although it has the advantage of not being easily scratched, it has the disadvantage that it is difficult to obtain a deposited film 1 with low absorption. ) structure ゛t' can reduce absorption, but the outermost layer P b F2
It has strong crystallinity and is prone to pinholes in a thin film state, and furthermore, it itself has somewhat poor moisture resistance, so it does not exhibit satisfactory moisture resistance as an anti-radiation film.

! The disadvantage of PbF2 is that it has poor moisture resistance, but chalcogenide glass, which is less likely to form pinholes, is A S 2 S 3.
Because it is protected by water, it has excellent moisture resistance and little absorption, making it the best of the examples a) to 2) above. However, chalcogenide glasses are generally susceptible to oxidation at high temperatures, and in particular the presence of H20 molecules or OH- ions significantly affects their behavior. This oxidation phenomenon of chalcogenide glass increases the light absorption of 10.6 μm light, so improvement is desired. However, K.C.
L is highly hygroscopic and it is difficult to completely remove H20 molecules and OH ions adsorbed on the surface. For this reason, KCI
In the case of anti-reflection films, there is a problem of deterioration due to increased absorption due to oxidation by H20 molecules or oH- ions of the first layer of chalcogenide glass in contact with the KCI substrate.

Purpose of the Invention The present invention is directed to the conventional AS2S3/PbF2/AS2S3
The anti-reflection coating has many advantages, such as low absorption for carbon dioxide laser light with a wavelength of 6 μm, excellent moisture resistance, and transparency for He-Ne laser light. The purpose of this method is to capture the first layer of AS2S3 Calco i, which is in contact with the KCI substrate, which has its drawbacks, without compromising its drawbacks.

Structure of the Invention The present invention forms a film of barium fluoride, ytterbium trifluoride, or thorium tetrafluoride on a KCI substrate, and then deposits an arsenic trisulfide film, an arsenic trifluoride film, a lead chloride film, and a trisulfide film on the KCI substrate. This anti-reflection coating for KCI consists of a four-layer structure in which arsenic films are sequentially formed.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an antireflection film according to the present invention. In the figure, 5 is a KCI substrate with a refractive index n8 of 145, which has a number of ultra-precise optical layers on both sides. This KCI
On the substrate 1, first, a chemically stable and KCI substrate 5 with a refractive index n+ = 1. ．． Liumium fluoride (BaF2) with a refractive index close to 45 nl-1,40, ytterbium trifluoride (YbF3) nl = 1.38 or thorium tetrafluoride (ThF4) nl = 1.35
A β substance film made of one of these is formed as the protective film 1. The optical film thickness nld to be formed is 0.140 μm in the case of the BaFz film.

In the case of YbF3 film, it is 0.138 μm, T h F
In the case of 4 films, it is 0.135 μm. 2 is the first arsenic trisulfide (AS2S3) film, which is a high refractive index material with low light absorption, water insoluble refractive index n2 of 2.31, and optical film thickness n.
It is 2d2-2494 μm. 3 is lead fluoride (P), which is a low refractive index material with low light absorption and a refractive index of n3/1.67.
bF2) 1F, optical thickness n3d3 = 1.336
It is pm. 4 is a second As2 with a refractive index n4 of 231
Optical thickness of S3 film @:rr4 d4 = 0.994
It is 11m. The protective film 1 protects the KCI substrate and the AS2S3 film 2, which is chalcogenide glass, from having poor anti-ring resistance, and preferably has a refractive index close to the refractive index of the KCI substrate, 1.45.

Figure 2 shows the wavelength 10.6 μm depending on the deposited film thickness of each film when a BaF2 film with a refractive index of 1.40 is used as the protective film 1 and a ThF4 film with a refractive index of 1.35 is used.
FIG. 3 is a characteristic diagram showing changes in reflectance at

The thicknesses of AS2S3 film 2, PbFz film 3, and AS2S3 film 4 are 2.494 μm and 1.336 μm, respectively.
m and 0.994. It is l1m. In the figure, 6 is a curve when the protective film 1 is a BaF2 film, and 7 is a curve when the protective film 1 is a T h F4 film. As can be seen from the figure, even if the thickness of any protective film is twice as thick as the set value d, -〇, 1 μm, the refractive index is close to that of KCI, so the reflectance is only 0.02%, which is extremely It can be seen that the constraints on film thickness control are weak. In addition, the film thickness d1 is set to d1=0.5 μm, which is the set value of 5.
Even if it is twice as thick, the reflectance of BaF2 is 0.02'% and that of ThF4 is 0.08'%, so this is a small increase in the total reflectance as an antireflection film, and for practical purposes it is Even if it is twice as thick, there is no difference.

, Car 3 shows the optical thickness n1dl-40 as the protective film 1.
μm BaF2 is provided, AS2S3/PbF2/ASz
8. When the thickness of the three-layer Sa film is the same as in the embodiment shown in FIG. When each film thickness is increased by 3%, 9 and 3%
When it is reduced to 100, the wavelength dependence of the reflectance is eliminated. According to this, the reflectance at a wavelength of 10.6 μm is about 0.4% even if the film' is increased or decreased by 3 factors, so even when both sides have anti-reflection coatings, the total reflectance is as low as 0.8% for practical use. There is no problem above.

As is clear from these figures, the BaF2 film + Y that constitutes the first layer of the antireflection film for KCI according to the present invention
The film thickness of bFa or ThF4 protective film is d, = 0
．． 1 μm to 0.5 μm, loose constraints on film thickness control,
Easy to manufacture. Furthermore, the optical film thickness from the second layer is within the range of ±3 inches as shown in Figure 3, that is, the first A
S2S3 film has n2 d2 = 2.419 μm ~ 2.5
69 μm, PbFz film has n3d3 = 1.296
~1.376 μm.

The second AS2S3 film is +14d4 =, 0.964μm
A range of −1,024 μm is preferable.

FIG. 4 shows the transmittance spectrum of the sample obtained according to the present invention. The measured values in the wavelength range from 8 μm to 13 μm are in good agreement with the calculated values1.Next, the output coupling mirror manufactured according to the present invention was mounted on a 500W laser oscillator, and a continuous laser beam irradiation test was conducted. I will describe the results after one Saturday. The output coupling mirror was mounted on a well-insulated jig for the purpose of conducting an acceleration vehicle test, and after o o o time had elapsed, the output coupling mirror was taken out and the transmittance spectra before and after laser beam irradiation were measured.

1] (1 As a result, as shown in Fig. 5, 11 and 12, the conventional anti-h+1 prevention film (As2S3/PbFz/As25
3) was used and irradiated with laser light for 800 hours. The increase in absorption due to oxidation14 seen in 13 was not observed, and by adding a protective film, the anti-reflection film was better than the conventional anti-reflection film using chalcogenide glass. It was found that it has excellent environmental resistance and is sufficiently durable for practical use.

Effects of the Invention As described above, the present invention provides Ba on the surface of a potassium chloride substrate.
Form a protective film of either F2, YbF3 or T h F4, and then AS2S3/PbF2/
This is an antireflection film for potassium chloride that has a three-layer A32S3 film, and has the following effects.

(1) KCI and chalcogenide glass are combined with chemically stable and mechanically strong ThF4. YbF3. Alternatively, since BaFz is used to prevent direct contact and the sicalcogenide glass film is chemically protected, it has excellent environmental resistance.

(2) Beam alignment is easy because it is transparent to He-Ne laser light with a wavelength of 0.6328/jm.

(3) ThF4. YbF3. Alternatively, even if the optical thickness of the BaF2 protective film increases 2 to 5 times from the set value, the reflectance at a wavelength of 106 μm is at most 0.02 to 0.08.
By only increasing the thickness by '%, the restrictions on film thickness control are very loose and manufacturing is easy.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an anti-reflection film for KCI in an embodiment of the present invention, and FIGS. 2 to 5 are optical characteristic diagrams of the anti-reflection film for KCI in an embodiment of the present invention, respectively. 1-...Protective film 2...AS2S3 film 3...PbFz film 4...
...A S 2 S 3 film 5 ... KCI substrate patent applicant Director of the Agency of Industrial Science and Technology Kawa 1) Yube 1 Figure 2 Film thickness d+ (pm) Figure 3 Thickness (pm) Figure 4 Wavelength input (pm) Figure 5 Te length (am) - wave number (C)

Claims (1)

[Claims] (1) A film of barium fluoride, ytterbium trifluoride, or thorium tetrafluoride is formed on at least one surface of a potassium chloride substrate, and arsenic trisulfide film, fluoride, lead oxide film, and trisulfide film are formed on at least one surface of the potassium chloride substrate. A chloride film characterized by the sequential formation of arsenic films. 11 Anti-reflection coating for use with cameras.