JPS60263901A - Antireflection film for rotassium chloride - Google Patents

Abstract

PURPOSE:To improve the moisture resistance of a titled antireflection film made of the three-layered structure consisting of an As2S3 film, PbF2 film and As2S3 film formed successively on a KCl substrate by increasing the thickness of at least one As2S3 film by 1/2 wavelength. CONSTITUTION:The 1st As2S3 film 2 is formed on the IR transmittable substrate 1 consistint of the KCl substrate and further the As2S3 film 5 having the thickness equiv. to 1/2 wavelength is additionally formed thereon. The PbF2 film 3 and the 2nd As2S3 film 4 are successively formed thereon to manufacture the intended antireflection film for KCl. The thickness of the 2nd film 4 may be increased by 1/2 wavelength and the thicknesses of both the 1st and 2nd films 2, 4 may be increased in place of increasing the thickness of the 1st film 2. The resultant antireflection film is highly resistant to moisture and is small in the absorptivity per surface and is therefore usable for a CO2 laser of 10kW level.

Description

[Detailed description of the invention] Industrial field of application The present invention is applied to potassium chloride fields, which are the materials for optical parts (windows, lenses, beam sprues, etc.) used in infrared light equipment such as carbon dioxide lasers. The present invention relates to an antireflection film for use in commercial applications.

Conventional Structure and Problems Conventionally, Zn5e, GaAs, and the like have been used as substrate materials for transparent optical parts such as windows, lenses, and beam spiriters for high-power carbon dioxide lasers.

For Zn5e, the wavelength is 10.6 pm and 0.6328
Although it has the advantage of being transparent in micrometers, has excellent water resistance, and can obtain large crystals, it has the disadvantages of being expensive, having large optical distortion caused by high-power irradiation, and using toxic U2SE gas when growing Western crystals. It is difficult to handle for safety reasons, such as the generation of toxic selenium-based gas during the surface polishing process.

GaAS is transparent at a wavelength of 10.6 μm, its thermal conductivity is about three times better than Zn5e, and it has excellent ice cutting properties. He-IlIJe with a wavelength of 0.6328 pm for isotropic light superposition, which is not available, does not transmit laser light. Furthermore, it has a number of drawbacks, including the fact that it contains a harmful element called As (As), which requires safety measures during growth and processing.

On the other hand, 'C'l has the advantages of being transparent at wavelengths of 10.6 μm and 0.6328 μm, has low optical distortion, is non-toxic, and is inexpensive. The main reason why it is not used as a substrate for other products (such as the following) is that it is deliquescent and dissolves in water, so it cannot withstand long-term use in humid environments.

The anti-reflection coating added to the surface has the drawback of being vulnerable to water, but it also has optical properties such as a reflectance close to zero and being transparent to a wavelength of 0.6328 μm.
If water resistance can also be provided, KCI windows and lenses with many of the above-mentioned advantages can be realized.

Currently, antireflection coatings for windows and lenses using KCI that are commercially available are composed of a single layer of NaF.

The refractive index of NaF is 123 and the square root of the refractive index of KCI (white, 4-5--1.204
), the optical film thickness nd-λ/4=2
．． If a thickness of 65 μm is deposited, a reflectance of 0.05% can be expected, which is close to the ideal value. Actual commercially available diameter 1
KC1 with NaF anti-reflection coating on both sides, inch, thickness 5m1n
When the reflectance of g was measured at a wavelength of 10.6 μm, it was approximately 0.
4%, I! It was found that the yield of 31° was approximately 0.3°, which was sufficient for practical use in terms of optical properties, but the temperature was 45°C.
, relative humidity; In an environmental test of 95% freezing, after 6 hours Na
Peeling of the F film was clearly observed. Therefore, we have no choice but to judge that the water resistance is not satisfactory and is not practical.

−j, ; A single layer that satisfies the requirements for an antireflection film is Na.
, F. Since there is no such thing outside the tail, two-layer or three-layer antireflection coatings are being considered. The conditions that must be met as a material for an anti-reflection film are that it is not soluble in water and has a wavelength of 10.
It is transparent at 6 μm and 0.6328 μm, has good adhesion to the substrate, and has no pinholes when formed into a thin film.

A substance that exhibits an amorphous state that is difficult to form must be selected. Therefore, arsenic trisulfide (A) is a promising material.
S2S3. ), chalcogenide glasses such as selenium trisulfide (As2Se3) and thorium tetrafluoride (ThF4).
).

Regarding the structure of the two-layer antireflection film, the following can be considered.

b) KC1/GATS/AS2S3 0) KC17As2S3/ ThF4 c) KCI/
AS2S3/PbF2 (a) Structures are all made of chalcogenide glass, so they are water resistant and heat generated (wavelength: 10.6 μm).
7: GATS
has a 'L point that does not transmit light with a wavelength of 0.6328 μm. O) are both amorphous state 1 and T
h F4 has the advantage of strong mechanical strength, but T
hF4 has the disadvantage that it is radioactive and difficult to use, and that it is difficult to obtain high-purity materials with low absorption. Although c) has low absorption, it has the disadvantage that P b F2 does not form a thin film in an amorphous state and is sensitive to water.

In order to solve the above-mentioned drawbacks, the present inventors studied an antireflection film having a three-layer structure as shown in FIG. T of low refractive index material
h Since F4 cannot be used, P b with low absorption
The basic idea was to use the F2 film 3 to protect the sandwich portion between the A3283 layers 2 and 4, which are less susceptible to pinholes, and to further secure the KCI board 1 with the three-layer film. As for the effect, A32S3 with less light absorption has KCI
P b F 2 has good adhesion to water and acts as a protective film against water.
A S 2 is added to further explain its disadvantage of being vulnerable to water.
We have realized a high-power antireflection film that is protected by S3 and satisfies the antireflection film requirements of zero reflectance, and is also transparent to light with a wavelength of 0.6328 μm.

The characteristics of this antireflection film are as follows.

(1) The absorption rate of the anti-reflection film by carbon dioxide laser light having a wavelength of 10.6 μm is on the order of 0.015%, and it can be used satisfactorily even with irradiation with a high power of 20 KW.

(2) Even after 650 hours of environmental testing at a temperature of 45° C. and a relative humidity of 95° C., the anti-reflective film was not damaged in any way and is a practical anti-reflective film.

(3) Even if the optical thickness of each of the three layers is simultaneously increased or decreased by three factors, the reflectance can be kept below 0.4%.

(4) The anti-reflection film does not suffer any damage even if it is irradiated with a laser beam with a laser density of 70 KW/cm for 2 minutes.

(5) Beam alignment is easy because it is transparent to He-Ne laser light with a wavelength of 0.632811 m.

As described above, this anti-reflection film has many advantages, but it has the disadvantage that it penetrates and melts the KCI substrate 1, and as a result, the anti-reflection film partially peels off from the KCI substrate 1.

Object of the Invention The present invention is directed to the conventional AszS3. The purpose of the present invention is to provide an anti-reflective coating for KC, l with the purpose of improving water resistance for cram schools without sacrificing the many advantages of anti-reflective coatings using PbF2.

Structure of the Invention The present invention provides an A S 2 layer in the first layer in contact with the potassium chloride substrate.
S3 film, PbF2 film for second layer, A S2 film for third layer
Using the S3 film, the thickness of at least one of the first and third As25e3 layers was increased by 1/2 wavelength = i
Film structure: Anti-reflection film for potassium chloride.

DESCRIPTION OF EMBODIMENTS The present invention will be described below in detail based on embodiments.In order to improve the clarity, in the present invention, the maximum thickness of A S 2 S 3 is expressed as an optical thickness nd-λ/2 (λ is 106 μm). If so, increase it by 5.3 μm). In this case, the question is which layer should be increased by nd-2. In this case, important points to consider are that the absorption does not increase by one lapse of width, and that it is easy to control the film thickness so that the reflectance becomes rust at a wavelength of 10.6 μm.

Possible cases are shown in FIGS. 2, 3, and 4.

Figure 4 shows that when the first AS2S3 layer 2nd-λ/2 is added in contact with the KCI board 1, A
s2S35, 5' is a configuration diagram of an antireflection film when nd-λ/2 is added.

In each figure, 2 is the optical thickness nd-2,540
pm AS2S3 film, 3 has optical thickness nd=1,311
pm PbF2 film, 4 is optical thickness nd = o, 9'l
It is an A S 2 S 3 film with a thickness of 5 μm. The optical thickness of each of these films is determined so as to satisfy Mouchart's relational expression, but even if they are increased or decreased by 4%, the reflectance will hardly increase and practicality will not be impaired. Therefore, A
S2 S3 film 2, PbF2 film 3, AS2S
Optical film thickness of 3 film 4 p 2.23/1m ”'-2
, 86μm, 1.264! m ~1.36 μm.

East 16 μm to 1.04 μm is suitable.

15-The material of the AS2S3 films 5, 5' in each figure is A
Since it is the same as the s2S3 film 2゜4, the second
The figure shows an A82S3 film on a KCI substrate with an optical thickness of 7.
AS2S3 films 2 and 5 are formed from one animal with a thickness of 53 μm to 8.16 μm. Figure 3.

The same applies to small 4th drawings.

Figure 5 shows the transmittance (spectrum, numbered 6, 7, 8.9 in the figure) of a KCI window in which anti-reflection films of the respective configurations shown in Figures 1 to 4 are formed on both sides of the KC1 substrate. correspond to the spectra of the KCI windows with antireflection coatings shown in FIGS. 1, 2, 3, and 4, respectively.

As can be seen from the spectrum in Figure 5, AS2S3 is nd-λ
When adding /2, the film structure shown in Figure 2, that is, adding it to the first layer A S 2 S 3 layer in contact with KCI has the least change in transmittance with respect to wavelength. It was found that it is easy to bring the point at which the ratio becomes 100% to a wavelength of 106 μm, and it is highly possible to realize the entire area in terms of film thickness control. In this configuration, the absorption rate per surface of the anti-reflection film was approximately 0.04%, which was found to be sufficient for practical use when the absorption rate was measured by carbon dioxide laser beam irradiation. On the other hand, the absorption rate per surface of the antireflection film shown in Figure 4 is 00
7. Since the absorption is large, it is unsuitable for high-output carbon dioxide lasers, but it is sufficient for medium to low-output carbon dioxide lasers. It can be argued that the reflective film has superior moisture resistance compared to the film structure (film structure), does not have a large increase in absorption, and is easy to control the film thickness.

Effects of the Invention As described above, the present invention provides A82S on a KCI substrate.
3 membranes.

A three-layer film consisting of a lead fluoride film and an A S 2 S 3 film is formed, and the optical thickness of the A S 2 S 3 film in the first and third layers is increased by at least -Q') by 7. The A S 2 S 3 film in contact with the KCI is three times thicker than that of the conventional example, so it has excellent moisture resistance and has a very low surface absorption rate.
It can also be used with KW level carbon dioxide lasers and has a long life.
Making CI optical components possible.

[Brief Description of the Drawings] Fig. 1 is a sectional view of a conventional three-layer anti-reflection film for KCI according to the invention of the present inventors, and Figs. 2 to 4 are three-layer anti-reflection films for KCI according to the present invention. Example 2...A
82 S3 film 3...PbF2 film 4...A S2S3 film 5.5'...
・・AS2S3 membrane

Claims (3)

[Claims] (1) A first layer is placed on an infrared transparent substrate made of a potassium chloride substrate.
an arsenic trisulfide film, a lead fluoride film, and a second arsenic trisulfide film of An anti-reflection film for potassium chloride characterized by an added film thickness. (2) The antireflection film for potassium chloride according to claim 1, wherein the thickness of the first arsenic trisulfide film is increased. (3) The optical thickness of the first arsenic trisulfide film, lead fluoride film, and second arsenic trisulfide film is 753 μm to 8.16 μm, respectively.
m, 1.26μm -1.36μm, 0°96.1
Claim 1 selected from 7m to 1.0411m
Anti-reflective coating as described in section.