JP2006259124A - Cold mirror - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold mirror which has the fewer number of layered layers and further provides high reflectance of visible light. <P>SOLUTION: The cold mirror A has: a substrate 1; a dielectric multilayered film 3 where thin films having refractive indices different from each other are alternately layered; and an IR transmission film 2 having a refractive index higher than the refractive index of any thin film forming the dielectric multilayered film 3. The IR transmission film 2 is interposed between the substrate 1 and the dielectric multilayered film 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a cold mirror that reflects visible light and transmits infrared light.

Conventionally, as a mirror used for light sources with infrared rays (heat rays) such as halogen lamps and metal halide lamps, cold mirrors that use a dielectric multilayer film to reflect visible rays and transmit unnecessary infrared rays to dissipate heat are known. It has been. This cold mirror is one in which a low-refractive index thin film and a high-refractive index thin film having a higher refractive index than this thin film are alternately laminated on a substrate, and reflects visible light by utilizing interference of light waves. In order to obtain the reflectance of visible light, it was necessary to stack many thin films having the same optical thickness. (For example, refer to the upper right column on page 3 of Patent Document 1).
JP-A-63-311301

However, as the number of thin film layers increases, the number of processes increases and labor is required for manufacturing, and the film thickness increases in proportion to the number of stacks, and the thin film is likely to peel off.

The present invention has been made in order to solve the above-described problems, and provides a cold mirror capable of obtaining a high visible light reflectance with a small number of stacked layers.

The means according to claim 1 includes a substrate, a dielectric multilayer film in which thin films having different refractive indexes are alternately laminated, and an infrared ray having a refractive index higher than a refractive index of any thin film constituting the dielectric multilayer film. A cold mirror having a configuration in which the infrared transmission film is interposed between the substrate and the dielectric multilayer film.

According to a second aspect of the present invention, there is provided the cold mirror according to the first aspect of the invention, wherein the infrared transmission film is made of any one material selected from silicon (Si) and germanium (Ge).

According to a third aspect of the present invention, in the invention of the first or second aspect, the optical film thickness of the infrared transmitting film is λ _IR / 2 (λ _IR is the designed center wavelength of infrared light to be transmitted). A cold mirror of the configuration.

In the cold mirror of the present invention, since the infrared transmission film is interposed between the substrate and the dielectric multilayer film, the number of thin films constituting the dielectric multilayer film is small, while transmitting heat by transmitting unnecessary infrared rays. Even if it exists, it becomes possible to obtain the reflectance of a high visible ray.

An embodiment of the present invention will be described with reference to FIG.
The cold mirror A of the present invention includes a substrate 1, an infrared transmission film 2, and a dielectric multilayer film 3, and the infrared transmission film 2 is interposed between the substrate 1 and the dielectric multilayer film 3. It has a configuration.

The substrate 1 supports the infrared transmission film 2 and the dielectric multilayer film 3 formed on the substrate 1 and transmits infrared rays as heat rays, or once absorbs and dissipates heat from the back surface A1 side of the cold mirror A. It is also a medium. Accordingly, the substrate 1 is made of an infrared transmitting material such as glass or plastic when transmitting infrared rays, and has a good thermal conductivity and heat dissipation such as metal and ceramics when absorbing infrared rays once. Material is used.

The aforementioned infrared transmission film 2 has a refractive index higher than that of any of the thin films constituting the dielectric multilayer film 3 to be described later, and reflects infrared rays and transmits infrared rays, for example, silicon (Si), germanium A material such as (Ge) is used.

The optical film thickness of the infrared transmission film 2 is preferably (2m−1) × λ _IR / 2 (λ _IR is the designed center wavelength of infrared light to be transmitted and m is a natural number). Infrared reflected light at the interface b between the dielectric multilayer film 3 and the infrared transmitting film 2 and infrared reflected light at the interface a between the infrared transmitting film 2 and the substrate 1 interfere with each other, and the infrared reflection is weakened. It is. Preferably, λ _IR / 2 (m = 1) is used. This is because the same effect can be obtained with a thinner infrared transmitting film 2.

The dielectric multilayer film 3 described above is formed by alternately laminating thin films having different refractive indexes. For example, a low refractive index thin film 4 as a thin film having a different refractive index and a higher refractive index than the low refractive index thin film 4. The high-refractive-index thin films 5 are stacked alternately. In addition, a material that transmits the entire wavelength band of visible light is preferable. Silicon dioxide (SiO ₂ ), silicon oxide (SiO), magnesium fluoride (MgF ₂ ), titanium dioxide (TiO ₂ ), tantalum pentoxide (Ta) ₃ O ₅ ), niobium pentoxide (Nb ₃ O ₅ ), zirconium oxide (ZrO ₂ ), hafnium oxide (HfO ₂ ), magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ) and the like are used.

Further, the optical film thickness of each thin dielectric multilayer film 3 is _{(2n-1) × λ 0} /4 (λ 0 is the design center wavelength of visible light desired to be reflected, n represents a natural number), preferably _{λ 0/4 (n = 1} ) is used. This is because the same reflection effect can be obtained with a thinner thin film.

Note that the number of stacked dielectric multilayer films 3 is preferably 6 or more. This is because if the number of layers is less than 6, the color shift from the white of the reflected light z reflected by the cold mirror increases due to the influence of the reflection characteristics of the infrared transmission film 2 itself, for example, a reddish light color.

Next, the manufacturing method of the cold mirror which concerns on this invention is demonstrated. First, the surface of the substrate 1 is washed with alcohol or the like, and then an infrared transmission film 2 is formed on the substrate 1 to a predetermined thickness. Thereafter, for example, the low refractive index thin film 4 described above is formed on the infrared transmission film 2, and the high refractive index thin film 5 is further formed on the low refractive index thin film 4. Hereinafter, the low refractive index thin film 4 and the high refractive index thin film 5 are formed. Are alternately stacked so as to have a predetermined number of layers. Further, as a method for forming the infrared transmission film 2, the low refractive index thin film 4, and the high refractive index thin film 5, for example, a vacuum vapor deposition method, a sputtering vapor deposition method, or other known techniques are used.

In the above description, the low refractive index thin film 4 is formed on the upper surface of the infrared transmitting film 2 and the high refractive index thin film 5 is alternately formed. However, the high refractive index thin film is formed on the upper surface of the infrared transmitting film 2. 5 may be formed, and the low refractive index thin films 4 may be alternately formed below. Further, the thin film on the surface A2 of the cold mirror A after the predetermined lamination may be either the low refractive index thin film 4 or the high refractive index thin film 5.

Next, the operation of the cold mirror A according to the present invention will be described.

When the cold mirror A is irradiated with incident light x including visible light and infrared light, the low refractive index thin film 4 and the high refractive index thin film 5 constituting the dielectric multilayer film 3 are used for visible light in the incident light x. Is reflected by interference of light waves. That is, by setting the optical thickness of the low refractive index thin film 4 and a high refractive index thin film 5 and _{(2n-1) × λ 0} /4, the high refractive index film 5 adjacent to the upper surface of the low refractive index thin film 4 The visible light reflected at the interface c and the visible light reflected at the interface d between the low refractive index thin film 4 and the high refractive index thin film 5 adjacent to the lower surface of the low refractive index thin film 4 have the same phase, and intensified reflection occurs. Further, visible light reflected at the interface d with the low refractive index thin film 4 adjacent to the upper surface of the high refractive index thin film 5 and reflected at the interface c between the low refractive index thin film 4 adjacent to the lower surface of the high refractive index thin film 5 are reflected. Since the same phase is applied to visible light, the reflection occurs in the same manner.

The reason why a large number of the low refractive index thin films 4 and the high refractive index thin films 5 are alternately laminated is to increase the number of the interfaces c and d. The visible light is reflected and reflected by these interfaces c and d. This is to increase the rate.

By the way, a part of the visible light passes through the dielectric multilayer film 3 and reaches the infrared transmission film 2, but most of the visible light is reflected by the interface b. This is because the infrared transmission film 2 has a higher refractive index than any of the thin films constituting the dielectric multilayer film 3.

On the other hand, most of the infrared light of the incident light x incident on the cold mirror A passes through the dielectric multilayer film 3 and the infrared transmission film 2 and reaches the interface a between the substrate 1 and the infrared transmission film 2. This is because any thin film constituting the dielectric multilayer film 3 is transparent to infrared rays, and there is no interference (reflection) by these thin films, and silicon (Si) or the like is used as the material of the infrared transmission film 2 This is because infrared rays are transmitted. In addition, by setting the optical film thickness of the infrared transmission film 2 to (2m−1) × λ _IR / 2, the infrared rays reflected by the interface b and the infrared rays reflected by the interface a are 180 ° out of phase with each other. Counteracting infrared reflection is further suppressed.

As described above, by providing the infrared transmission film 2 between the substrate 1 and the dielectric multilayer film 3, the reflectance can be increased by providing the infrared transmission film 2 for visible light. In this case, it can be transmitted for heat dissipation.

Examples of the present invention will be described below.

(Embodiment) FIG. 1 is a schematic diagram showing the construction of an embodiment of the present invention. A cleaned glass plate having a thickness of 3 mm is used as the substrate 1, and silicon (Si) is deposited on the substrate 1 by vacuum deposition so that the optical film thickness is λ _IR / 2 (λ _IR is 1500 nm). Thus, an infrared transmission film 2 was formed. Furthermore, the dielectric multilayer film 3 was formed by alternately laminating the low refractive index thin film 4 and the high refractive index thin film 5 on the infrared transmitting film 2 by vacuum vapor deposition so that the number of laminated layers becomes 10. Further, the low refractive index thin film 4 is an optical film thickness of λ _0/4 (λ ₀ is 500 nm) and silicon dioxide (SiO ₂₎ thin film of a high refractive index thin film 5 optical thickness of lambda _0/4 dioxide A titanium (TiO ₂ ) thin film was obtained. The total film thickness L1 (the sum of the film thickness of the infrared transmission film 2 and the film thickness of the dielectric multilayer film 3) is 0.88 μm.

FIG. 2 shows the spectral characteristics of reflectance when the incident angle of the incident light x is 0 degree in the cold mirror A of this embodiment.

(Comparative Example 1) FIG. 3 shows a schematic diagram of the structure of Comparative Example 1. Comparative Example 1 is an example in which the infrared transmission film 2 of the example is not provided, and the configuration other than the infrared transmission film 2 is the same as that of the example. The configuration and manufacturing method of the substrate 1 and the dielectric multilayer film 3 are the same as those in the embodiment, and the same reference numerals are given to the same parts, and detailed description is omitted.

FIG. 4 shows the spectral characteristics of the reflectance when the incident angle is set to 0 degree in the cold mirror of Comparative Example 1, but the infrared transmittance is substantially the same when compared with the above-described embodiment. On the other hand, it can be seen that the reflectance of visible light is small. In other words, the reflectance of visible light can be increased by providing the infrared transmission film 2 as in the embodiment.

(Comparative Example 2) FIG. 5 shows a schematic diagram of the structure of Comparative Example 2, and FIG. 6 shows the spectral characteristics of the reflectance of Comparative Example 2 at an incident angle of 0 degrees. Comparative Example 2 is an example in which the number of layers of the low refractive index thin film 4 and the high refractive index thin film 5 of Comparative Example 1 is increased, and a visible light reflectance substantially equivalent to that of the example can be obtained. The number was 24 layers (2.4 times that of the example), and the total film thickness L2 (thickness of the dielectric multilayer film 3) was required to be 1.58 μm (1.8 times that of the example).

1 is a schematic diagram showing the configuration of an embodiment of the present invention. It is a figure which shows the spectral characteristic of the reflectance of the cold mirror of FIG. 6 is a schematic diagram showing a configuration of a cold mirror of Comparative Example 1; It is a figure which shows the spectral characteristic of the reflectance of the cold mirror of FIG. 6 is a schematic diagram showing a configuration of a cold mirror of Comparative Example 2; It is a figure which shows the spectral characteristic of the reflectance of the cold mirror of FIG.

Explanation of symbols

A Cold mirror 1 Substrate 2 Infrared transmitting film 3 Dielectric multilayer 4 Low refractive index thin film 5 High refractive index thin film x Incident light z Reflected light

Claims (3)

A substrate,
A dielectric multilayer film in which thin films having different refractive indexes are alternately laminated;
An infrared transmission film having a refractive index higher than the refractive index of any thin film constituting the dielectric multilayer film;
Have
A cold mirror, wherein the infrared transmission film is interposed between the substrate and the dielectric multilayer film. 2. The cold mirror according to claim 1, wherein the infrared transmission film is made of any one material selected from silicon (Si) and germanium (Ge). 3. The cold mirror according to claim 1, wherein an optical film thickness of the infrared transmitting film is λ _IR / 2 (λ _IR is a designed center wavelength of infrared light to be transmitted).

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