JPH06208004A - Antireflection film for ir laser - Google Patents

Abstract

PURPOSE:To provide the antireflection film having excellent safety in production and low absorptivity by having a first layer consisting of at least either of PbTe and CdTe and a second layer consisting of at least either of ZnSe and ZnS on this first layer. CONSTITUTION:A ZnSe substrate 1 is prepd. and after this substrate is installed in a vacuum vapor deposition device, vacuum vapor deposition is executed under respective prescribed conditions of a pressure in a reaction chamber and substrate temp. to grow the PbTe thin film 2 of a prescribed thickness on the ZnSe substrate 1. The electric conductivity of the PbTe thin film 2 is lowered by optimizing the substrate temp. and the growth speed of the PbTe thin film 2. The vacuum vapor deposition is then continuously executed under the respective prescribed conditions of the pressure in the reaction chamber and the substrate temp., by which the ZnSe thin film 3 of the prescribed thickness is further grown on the PbTe thin film 2. As a result, the PbTe thin film 2 and the ZnSe thin film 3 are laminated on the ZnSe substrate 1, by which the optical window coated with the antireflection film on the surface is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film for infrared laser, and more particularly to an antireflection film coated on the surface of an optical component of an infrared laser represented by CO ₂ laser or the like.

[0002]

_2. Description of the Related Art A CO ₂ laser is a kind of gas laser capable of continuous oscillation with high output, and is used for fine processing such as welding and cutting. The oscillation wavelength of an infrared laser such as a CO ₂ laser is near the infrared region (10.6 μm), and its efficiency is high.

FIG. 3 is a schematic diagram showing the basic structure of a CO ₂ laser processing machine which has been conventionally used.

As shown in FIG. 3, the CO ₂ laser processing machine includes a laser oscillator 10, a partial reflecting mirror 11 and a beam splitter 1 in order to perform work such as welding or cutting.
2, a plurality of metal mirrors 13, a parabolic mirror 14, a circular polarization mirror 1
5, various optical components such as the condenser lens 16 are appropriately combined and configured.

On the surface of the optical parts used in such a CO ₂ laser processing machine, especially the optical parts such as the partial reflecting mirror 11, the beam splitter 12 and the condenser lens 16 through which the beam light is transmitted. A transparent antireflection film 20 for vertical incidence or oblique incidence is coated to prevent light reflection and minimize light loss.

As shown in FIG. 4, an antireflection film 20 for vertical incidence which has been generally used up to now has a thickness of 1 made of ThF ₄ which is a fluoride on a base material 21 made of ZnSe which is a chalcogen compound. 0.04 μm thin film 22 and Zn
The thin film 23 made of Se and having a thickness of 0.23 μm is laminated.

[0007]

Normally, when a CO ₂ laser is used for a long time for work such as welding or cutting, the laser light emitted from the laser oscillator 10 is partially reflected by the partial reflecting mirror 1.
1, the beam splitter 12, the condenser lens 16, and other regions near the center of optical components are transmitted in a concentrated manner. As a result, in the optical component through which the laser light penetrates, only a part of the region expands due to the absorbed heat, and the solid density becomes nonuniform. Along with this, a phenomenon occurs in which the refractive index and the shape of the optical component slightly change.

Since the conventional antireflection film 20 described above is not set to have a sufficiently small absorptance, it tends to cause a temperature rise on the surface of the optical component due to absorbed heat accompanying the transmission of light, and the above phenomenon is further caused. It tended to encourage.

Therefore, in the conventional optical component coated with the antireflection film 20, the operating time becomes long,
Further, if the number of times of use is repeated, the characteristics thereof are likely to change, and, for example, the focal length of the condenser lens 16 largely changes, which causes a problem that precise work cannot be performed.

Accordingly, if an attempt is always maintained high accuracy CO ₂ laser processing machine, the optical components of the short-term use is necessary new components and Tokaeru occurs, the life of the expensive optical components had become shorter.

Further, since ThF _{4 which} is a fluoride used as a film material of the conventional antireflection film 20 is a radioactive substance, it must be handled with care during film production, and there is a problem in terms of work safety. Had. Therefore, there has been a long-felt demand for an antireflection film using a film material having excellent safety.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an antireflection film which is excellent in manufacturing safety and has a lower absorptance.

[0013]

In order to solve the above-mentioned conventional problems, the antireflection function is not deteriorated,
It is desired to further reduce the absorption rate of the antireflection film coated on the surface of the optical component.

It has been known so far that the absorptance of the antireflection film is controlled by the product of the absorptance of the film material forming the film and the film thickness of the film made of the film material. The smaller the product of the absorptivity of the film material forming the film and the film thickness of the film made of the film material, the smaller the absorptivity. From this, in order to keep the absorptance of the antireflection film small, firstly, how to select a film material having a low absorptivity and secondly how to keep the film thickness small. Becomes important.

Therefore, as a result of repeated studies on the above two points, the inventor selects PbTe or CdTe having a particularly high refractive index among the chalcogen compounds as the film material, as shown in the following examples. By this, without degrading the high antireflection function,
The present invention has been completed by succeeding in obtaining an antireflection film capable of further suppressing the light absorption rate in the vicinity of the oscillation wavelength (10.6 μm) of the infrared laser.

The antireflection film used for the optical component of the infrared laser device according to the present invention is formed on a base material made of at least one of ZnSe and ZnS, and is formed on the base material and PbTe. And a first layer made of at least one of CdTe and a second layer formed on the first layer and made of at least one of ZnSe and ZnS.

In the present invention, the first layer can be formed in a desired thickness on the substrate by using a vacuum vapor deposition method, an ion cluster beam vapor deposition method, an ion assisted vapor deposition method or the like.

The second layer can be further formed on the first layer with a desired thickness by using a vacuum vapor deposition method, an ion cluster beam vapor deposition method, an ion assisted vapor deposition method or the like.

When forming the first layer or the second layer, the number of carriers is suppressed by optimizing the temperature of the base material and the growth rate of the film so that the electrical conductivity of the first layer or the second layer is reduced. The conductivity can be suppressed to be smaller.

Further, in the present invention, by appropriately setting the thicknesses of the first layer and the second layer, it is possible to secure a desired antireflection function required in the optical component of the infrared laser device. it can.

[0021]

As shown in the following examples, in the antireflection film formed on the substrate made of at least one of ZnSe and ZnS, the chabogen compound Pb
First made of at least one of Te and CdTe
Form a sandwich structure sandwiched between a base material and a second layer made of at least one of ZnSe and ZnS, and the film thicknesses of the first layer and the second layer are as follows. It has been found that by setting an appropriate size according to the film thickness determining method as shown, the light absorption rate can be further reduced while ensuring a desired antireflection function.

In the film thickness determining method used in the present invention, the optical admittance (refractive index) of the substrate is defined as η _m ,
The optical admittance (refractive index) of the material forming the layer of η ₁ , the optical admittance (refractive index) of the material forming the second layer η ₂ , and the optical admittance of the air (refractive index) η ₀ (where derives by a an eta ₀ = 1 If the vacuum), an optical film thickness [delta] ₂ of the first layer optical thickness [delta] ₁ and the second layer of the following equation (1) and (2).

[0023]

[Equation 1]

Further, by substituting the optical admittance η ₁ of the material forming the first layer and the optical film thickness δ ₁ of the first layer into the following equation (3), the physical film of the first layer is obtained. Thickness d ₁
Can be asked.

Similarly, by substituting the optical admittance η ₂ of the material forming the second layer and the optical film thickness δ ₂ of the second layer into the following equation (4), the physical properties of the second layer are calculated. Film thickness d ₂
Can be asked.

[0026]

[Equation 2]

That is, according to the present invention, by selecting at least one of PbTe and CdTe, which has a low absorptivity and a particularly high refractive index among the chalcogen compounds, as the film material, predetermined optical characteristics can be obtained. Since the film can be obtained with a film thickness smaller than that of the film made of ThF ₄ which is a fluoride, the absorptance of the entire antireflection film can be further suppressed. In addition, Pb selected as the film material
Since Te or CdTe is a chalcogen compound, it has good codeability with a substrate made of a chalcogen compound.

Therefore, when the antireflection film according to the present invention is used, even if the infrared laser is used for a long time or repeatedly, the characteristics of the optical parts are hardly changed by the temperature change due to the absorption of light. The reliability of the optical component is further improved.

Moreover, since the film material is not a radioactive substance but a non-radioactive substance, the safety in manufacturing the antireflection film and the ease of handling are significantly improved.

Further, PbTe or CdTe selected as the film material also has an excellent property that it generally has low water absorption.

Therefore, the antireflection film according to the present invention comprises:
In addition to the antireflection function, it can also serve as a protective film that protects the surface of the optical component from the external environment. As a result, the influence of moisture, impurities, etc., which causes deterioration of the characteristics of the optical component, from the external environment can be suppressed to an extremely small level.

[0032]

【Example】

Example 1 A ZnSe substrate having a diameter of 38.1 mm and a thickness of 3 mm was prepared and placed in a vacuum vapor deposition apparatus. Pressure in the reaction chamber is about 10 ⁻⁷ to 10 ⁻⁵ Torr, substrate temperature is 100 to 300 ° C.
Under the conditions described above, vacuum deposition was performed to grow a PbTe thin film having a thickness of 0.20 μm on the ZnSe substrate. Here, by optimizing the substrate temperature and the growth rate of the PbTe thin film, the electrical conductivity of the PbTe thin film is kept low.

Then, the pressure in the reaction chamber is about 10 ^-7 to 10 ^-5.
Vacuum deposition was continuously performed under the conditions of Torr and the substrate temperature of 100 to 300 ° C. to further grow a ZnSe thin film having a thickness of 1.40 μm on the PbTe thin film.

As a result, as shown in FIG.
By stacking the PbTe thin film 2 and the ZnSe thin film 3 on the substrate 1, an optical window having a surface coated with an antireflection film was obtained.

Comparative Example In order to compare with the above-mentioned example, the diameter is similarly 38.1 m.
A ZnSe substrate having a thickness of 3 mm and a thickness of 3 mm is prepared, a ThF ₄ thin film having a thickness of 1.04 μm is deposited on the substrate according to a known conventional method, and then a ZF having a thickness of 0.23 μm is deposited on the ThF ₄ thin film.
An nSe thin film was deposited.

As a result, as shown in FIG.
The ThF ₄ thin film 22 and the ZnSe thin film 23 are formed on the substrate 21.
By laminating, an optical window having a surface coated with a conventional antireflection film was obtained.

The absorptance of light in the optical windows obtained in Examples and Comparative Examples was measured by the calorimetry method.

As a result, the optical window obtained in the comparative example had a light absorptance of about 0.20%. On the other hand, in the optical windows obtained in the examples, the light absorptance was a value of about 0.13%.

As is apparent from these results, it was shown that the use of the antireflection film according to this example can reduce the light absorption rate to about 2/3 of that of the conventional antireflection film.

In order to compare the antireflection function, the transmission spectrum in the infrared region was examined using the optical windows obtained in the examples and the comparative examples. The results are shown in FIGS. 2 and 5. In the graphs shown in FIGS. 2 and 5,
The vertical axis shows the light transmittance (%), and the horizontal axis shows the wavelength of light (μ
m).

From the results of FIG. 2 and FIG. 5, the antireflection film obtained in the example shows a high transmittance close to 100% in the infrared region (wavelength around 10 μm) like the conventional antireflection film. Therefore, it was confirmed that the antireflection function is kept high.

[0042]

When the antireflection film according to the present invention is used, the absorptance of the optical component can be suppressed to a lower level than when the conventional antireflection film is used. Therefore, by using an optical component such as a lens, a window, or the like, the surface of which is coated with the antireflection film according to the present invention, it is possible to suppress variations in characteristics due to temperature changes due to absorption of laser light,
Precision processing with higher dimensional accuracy is possible.

Further, since the characteristic deterioration of the optical parts can be suppressed to a small level, the life of expensive optical parts can be extended.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of an antireflection film according to an embodiment of the present invention.

FIG. 2 is a diagram showing an infrared transmission spectrum of a ZnSe window coated with an antireflection film according to an example of the present invention.

FIG. 3 is a schematic diagram showing a basic configuration of a conventional infrared laser processing machine.

FIG. 4 is a cross-sectional view showing a structure of a conventional antireflection film.

FIG. 5: ZnSe coated with a conventional antireflection film
It is a figure which shows the infrared transmission spectrum of a window.

[Explanation of symbols]

 1 ZnSe Substrate 2 PbTe Thin Film 3 ZnSe Thin Film In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An antireflection film used for an optical component of an infrared laser device, which is formed on a base material made of at least one of ZnSe and ZnS, and formed on the base material. And a first layer made of at least one of PbTe and CdTe, and ZnSe and ZnS formed on the first layer.
An antireflection film for infrared laser, comprising a second layer made of at least one of the above.