JPS6361202A - Optical thin film for infrared ray - Google Patents

Abstract

PURPOSE:To prevent the spectral characteristic from being shifted in accordance with circumstances of the use and to improve the abrasion resisting property by overcoating an optical thin film for infrared rays with a diamond-shaped carbon having a prescribed thickness as the spectral characteristic shift preventing film. CONSTITUTION:An interference filter or a multilayered mirror 2 formed on a substrate 1 is overcoated with a diamond-shaped carbon film 3. It is preferable that this coat covers not only the upper face of the optical thin film but also the overall surface including its peripheral end face, and the optical thin film is not taken out to the air after being formed and is coated in a vacuum chamber as it is. If the thickness of the film 3 is thinner than 0.7mum, the film 3 is ineffective; and >10mum thickness is improper because the film forming time is extended and the film is easily peeled with the internal stress of the film if the thickness of the film exceeds 10mum. Though the film 3 may be a single layer, the film 3 is more effective if multilayered structure is given to the film 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an infrared optical thin film whose spectral characteristics do not shift, that is, an infrared interference filter or an infrared multilayer mirror.

(Prior art) Infrared interference filters and infrared multilayer mirrors generally use a crystal material such as germanium, silicon, sapphire, or fluorite as a substrate, and based on optical interference theory, a high refractive index material (e.g. sb, s, , G e % S i ,
) and low refractive index materials (e.g. B a F t , M
g F t , S i O, etc.) of i”l[He are alternately stacked from several layers to several tens of layers. In this case,
Each layer is formed by vacuum thin film deposition techniques such as vacuum evaporation, sputtering, ion blasting, and CVO.

(Problem to be solved by the invention) However, when the formed optical thin film is taken out of the vacuum chamber and left in the air, the spectral characteristics (spectral curve)
The first problem is that the entire wavelength is shifted toward longer wavelengths.

Therefore, in the past, the optical thickness of each layer was controlled during film formation in anticipation of the shift to the long side. However, this manufacturing method is prone to miscalculations,
The drawback was that the reproducibility of spectral characteristics was poor.

In addition, when these infrared optical thin films are used under high vacuum conditions or under high temperature conditions such as when used near a light source, they tend to shift toward shorter wavelengths. There was a second problem with shifting. For example, the third
When an optical thin film with the spectral characteristics shown by the solid line in the figure is irradiated with a high-intensity laser beam, the spectral characteristics shift to the shorter wavelength side as shown by the dotted line B in Figure 3. The transmittance will change.

In particular, the problem of this shift is remarkable and serious in infrared interference filters and multilayer mirrors, and an early solution to the problem has been desired.

Furthermore, these infrared optical thin films have a third problem of being easily scratched.

An object of the present invention is to prevent the above-mentioned shifts in spectral characteristics and to prevent susceptibility to scratches.

(Means for Solving the Problem) As a result of intensive research, the present inventors found that when an optical thin film is overcoated with a diamond-like carbon film of a predetermined thickness,
It was discovered that the present invention is effective in preventing shifts in spectral characteristics and preventing scratches, leading to the completion of the present invention.

Therefore, the present invention provides a diamond-like carbon film with a thickness of 0.7 to 10 μm as a film for preventing shifts in spectral characteristics in an infrared optical thin film consisting of an infrared interference filter or an infrared multilayer mirror formed on a substrate. The present invention provides an infrared optical FJ film characterized by being overcoated with:

(Function) FIG. 1 is a conceptual diagram showing a vertical cross section of the infrared optical thin film of the present invention, in which an interference filter or multilayer mirror 2 formed on a substrate l is overcoated with a diamond-like carbon film 3. There is.

It is preferable to coat not only the upper surface of the optical thin film but also the entire surface including the peripheral edge end surface. In this case, after forming the optical thin film, it should be coated before leaving it in the air to change the spectral characteristics to the long wavelength side, and after forming the optical thin film, it should be coated in the vacuum chamber without taking it out into the air. It is preferable.

The diamond-like carbon film itself is known and is formed, for example, by plasma CVD or ion beam sputtering. The thickness of the carbon film is 0.7 to 10
If it is thinner than 0.7 μm, it will not be effective, and if it exceeds 10 μm, ■ The film formation time will be longer.
(2) It is unsuitable because the internal stress of the film makes it easy for rr and Il to separate. In addition, by appropriately selecting l<J> within this range, the transmittance at the reference wavelength can be increased, decreased, or made equal to that without the diamond-like carbon film. □ The diamond-like carbon film itself may be a single layer, but it may also have a multilayer structure as shown in FIG. A multilayer structure may be more effective than an identical single layer film.

Moreover, the film thickness of the diamond-like carbon film is 0.7 to 1
A film thickness having an antireflection effect can be selected between 0 μm, and it is preferable to do so in the case of an interference filter.

Hereinafter, the present invention will be specifically explained with reference to Examples.

(Example 1) First, in order to manufacture an interference filter 2 that transmits light with a wavelength of 4000 nm or more, an optical designer created an optical design diagram of a 21-layer structure as shown in FIG. 6 (reference wavelength λ = 290 nm).
0nm) was designed.

In Figure 6, H indicates a layer of germanium with a high refractive index (n = 4.0), and L indicates a layer of 5iO with a low refractive index (n = 1.8).
The numbers ro, 125 j and ro, 25 j indicate the thickness of the monolayer H or L shown to the right. However, the unit is refractive index n x actual film thickness d ÷ wavelength λ.

It is.

A sapphire substrate was prepared as the substrate 1, and a high refractive index material and a low refractive index material were alternately deposited on the sapphire substrate according to the design diagram shown in FIG. 6 to create an interference filter 2.

After the fabrication, the spectral characteristics were measured in vacuum without being taken out of the vacuum chamber into the air. The solid line A in Figure 4 shows the results.
Indicated by

Subsequently, a diamond-like carbon film 3 having a film thickness of 1 μm was overcoated on the interference filter 2 by plasma CVD to complete the infrared optical thin film of this example.

The result of measuring this spectral characteristic is shown by the dotted line B in FIG.
. ” The 12ii pass rate at 4000 nm was set to the same value as the solid line A, so the result is as expected.

The spectral characteristics of B in Figure 4 do not shift even if this optical thin film is left in the air for 6 months, and lk
There was no shift at all after 72 hours of irradiation with light from an infrared lamp.

(Comparative Example) An infrared optical thin film was prepared in exactly the same manner as in Example 1, except that the diamond-like carbon film 3 was not provided.

This is because the spectral characteristics shifted when irradiated with light from an lkw infrared lamp for 72 hours.

(Example 2) After producing the interference filter 2 in the same manner as in Example 1, the spectral characteristics were measured in vacuum without being taken out of the vacuum chamber into the air. The results are shown by solid line A in FIG.

Subsequently, a diamond-like carbon film 3 having a film thickness of 0.96 μm was overcoated on the interference filter 2 by plasma CVD to complete the infrared optical thin film of this example.

The results of measuring this spectral characteristic are shown by dotted line B in FIG.

In this case, the reference wavelength λ. The transmittance at -4000 nm is improved by several percent compared to the actual LIAA.

The spectral characteristics of B in Figure 5 do not shift even if this optical thin film is left in the air for 6 months, and lk
There was no shift at all even after 72 hours of irradiation with light from an infrared lamp.

On the other hand, regarding the infrared optical GI films of Example 1 and Comparative Example,
Tested for scratch resistance. The test was conducted using the falling sand test method. The test conditions are shown in Table 1.

Table 1 As a result of the crushing test, there was no change in Example 1, which was overcoated with a diamond-like carbon film, but in Comparative Example, which had no overcoat, the substrate was exposed.

(Effects of the Invention) As described above, the present invention has no shift in spectral characteristics due to the environment in which it is used, which was a drawback of conventional infrared optical (W) films, and also has high scratch resistance.

In addition, it has sufficient environmental resistance, so its spectral characteristics do not change depending on the environment in which it is used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram showing a vertical cross section of an infrared optical thin film showing an embodiment of the present invention. FIG. 2 shows an infrared optical FJ showing another embodiment of the present invention.
115! FIG. FIG. 3 is a graph showing the spectral characteristics of one conventional infrared optical thin film. FIG. 4 is a graph showing the spectral characteristics of the infrared optical thin film according to Example 1. FIG. 5 is a graph showing the spectral characteristics of the infrared optical thin film according to Example 2. FIG. 6 is an explanatory diagram showing the structure of the interference filter created in Examples 1 and 2. (Explanation of symbols of main parts)

Claims (1)

[Claims] 1. In an infrared optical thin film formed on an infrared interference filter or an infrared multilayer mirror formed on a substrate, a diamond-like carbon film with a thickness of 0.7 to 10 μm is used as a spectral characteristic shift prevention film. An infrared optical thin film characterized by being overcoated with. 2. The infrared optical thin film according to claim 1, wherein the diamond-like carbon film has a multilayer structure.