JPH05232314A - Dichroic mirror - Google Patents

Abstract

PURPOSE:To obtain a dichroic mirror which acts as a half mirror for a specified wavelength region and as a total reflection mirror for the rest of wavelength region. CONSTITUTION:This dichroic mirror is obtd. by successively base multilayer film 2 which totally reflects light in <2700nm wavelength region and almost totally transmits light in >2700nm wavelength region, a Ge first surface layer 3, and a ZnS second surface layer 4 on a glass substrate 1. This mirror acts as a total reflection mirror for 1500-2700nm wavelength region (near infrared region) and as a half mirror having about 50% transmittance for about >2700nm wavelength region (medium and far infrared region).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dichroic mirror which reflects only light in a specific wavelength region and transmits light in the remaining wavelength region by utilizing interference of light by a thin film.

[0002]

2. Description of the Related Art Conventionally, by utilizing thin film interference of a multilayer film deposited on a glass surface, a dichroic that reflects only light in a specific wavelength region of light incident on the glass surface and transmits the rest. Mirrors are known.

The above-mentioned multilayer film is formed by alternately laminating a high refractive index substance and a low refractive index substance with a predetermined thickness, and the switching wavelength between reflection and transmission can be controlled by the kind of the substance to be laminated and its film thickness. Are known.

[0004]

When performing spectroscopic measurement of an object using such a dichroic mirror, one of reflected light and transmitted light is made incident on a spectroradiometer and is emitted from the object. The spectral emissivity of light is measured and the other is made incident on the camera to obtain the contour of the object,
Finally, a method of combining these two pieces of information is known.

However, in such a spectroscopic measurement of an object, there is also a great demand for measuring the spectral emissivity of the light emitted from the object with as much light amount as possible over the entire wavelength range. In many cases, the amount of light incident on the camera may be small to some extent because it is sufficient to obtain information about the contour of the object.

For example, of the light from an object that emits heat rays, only the light in a specific infrared wavelength region is made incident on the infrared camera to photograph the contour of the object, and the remaining light is made incident on the spectroradiometer. When obtaining the spectral emissivity of heat rays, the sensitivity of the infrared camera is set to, for example, 3000 to 5000 nm, and only a part of the light in the wavelength region of 3000 to 5000 nm is transmitted by the dichroic mirror to the infrared camera. Make it incident,
It is desirable that the remaining total amount of light be reflected by a dichroic mirror to be incident on a spectroradiometer, and spectroscopic measurement be performed using as much amount of light as possible for all wavelength regions emitted from the object.

The present invention has been made in view of the above circumstances, and provides a dichroic mirror that functions as a half mirror for light in a predetermined wavelength region and as a total reflection mirror for light in the remaining wavelength regions. The purpose is to do.

[0008]

The dichroic mirror of the present invention is such that light in a wavelength region of a predetermined value or less is almost totally reflected on a transparent substrate, and light in a wavelength region of a predetermined value or more is higher than a high transmittance point. A basic multilayer film is formed by alternately laminating a thin layer made of a first substance and a thin layer made of a second substance, which is transmitted at a ratio of 1. Light is transmitted at a rate smaller than the high transmittance point with respect to the time of incidence of the basic multilayer film,
It is characterized in that a surface layer film having one thin layer made of the first substance and one thin layer made of the second substance is provided.

The "high transmittance point" means that the transmittance of light in a wavelength region larger than a predetermined value does not become smaller than this point only by the basic multilayer film, and the surface layer film is provided. For the first time, the reference point of the transmittance that becomes smaller than this point is shown for the first time, and is set to a high transmittance value of 90%, for example.

[0010]

According to the above-described structure, first, a basic multilayer film is formed by alternately laminating thin layers made of a first substance and thin layers made of a second substance on a transparent substrate,
Light in a wavelength region of a predetermined value or less is almost totally reflected, and light in a wavelength region of a predetermined value or more is transmitted at a rate higher than the high transmittance point.

A so-called general dichroic mirror composed only of such a basic multilayer film functions to switch between substantially total reflection and substantially total transmission before and after a predetermined wavelength, and generally,
It has been considered difficult to significantly increase or decrease the transmittance of light in a predetermined wavelength region by increasing or decreasing the number of laminated thin layers.

In fact, according to the applicant's experiments, for example, 20
Up to about a few layers, there is little relation between the increase and decrease in the number of laminated thin layers and the increase or decrease in the above transmittance.
It could not be less than 90%.

However, the Applicant has found that when the surface thin layer made of the first substance and the surface thin layer made of the second substance are provided on the basic multilayer film, the above-mentioned transmittance is greatly reduced, and further, the surfaces thereof are reduced. It was found that the transmittance can be set to 70% or 50% by adjusting the thickness of the thin layer.

The dichroic mirror of the present invention is made on the basis of such a fact, whereby a dichroic mirror as a half mirror having a desired transmissivity for light in a predetermined wavelength region can be used for light in the remaining wavelength region. It becomes possible to function as a normal total reflection mirror.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic view showing the layer structure of the dichroic mirror according to the first embodiment of the present invention. In this dichroic mirror, a basic multilayer film 2, a first surface layer 3 made of Ge (refractive index 4.00) and a second surface layer 4 made of ZnS (refractive index 2.10) are formed on a germanium (Ge) substrate 1 by vapor deposition. The layers are laminated in this order.

The basic multilayer film 2 is formed by laminating 23 thin layers made of ZnS in odd layers and Ge thin layers in even layers, so that the total thickness is about 10 to 15 μm. Has been formed.

The first surface layer 3 made of Ge is 4
nd = 2400 nm, the second surface layer 4 made of ZnS.
Is formed to have a thickness of about 4nd = 2644 nm.

FIG. 1 shows the transmission characteristics of the dichroic mirror according to the first embodiment.

From the transmission characteristics shown in FIG. 1, this dichroic mirror is a total reflection mirror in the wavelength region of 1500 to 2700 nm (near infrared region), and in the wavelength region of about 2700 nm or more (intermediate and far infrared region). Clearly functions as a half mirror with a transmittance of about 50%.

On the other hand, FIG. 3 shows the transmission characteristics of the dichroic mirror having only the basic multilayer film 2 provided on the glass substrate 1 in the layer structure shown in FIG.

From the comparison between FIGS. 1 and 3, the provision of the first surface layer 3 and the second surface layer 4 results in the transmission region (wavelength 2700n).
It was possible to reduce the transmittance in a region of about m or more).

The transmission characteristics of FIGS. 1 and 3 are based on the values when the incident angle is set to 45 °.

Next, FIG. 4 is a schematic view showing the layer structure of the dichroic mirror according to the second embodiment of the present invention.
In this dichroic mirror, a basic multilayer film 12, a first surface layer 13 made of TiO ₂ (refractive index 2.33) and a second surface layer 14 made of SiO ₂ (refractive index 1.47) are formed on a glass substrate 11 by vapor deposition. They are laminated in order.

In the basic multilayer film, a thin layer made of TiO ₂ is used as an odd number layer and a thin layer made of SiO ₂ is used as an even number layer.
It is formed by stacking layers so that the total film thickness is about 10 to 15 μm.

The first surface layer 13 made of TiO _{2 is} also used.
Is about 4nd = 3064 nm, and the second surface layer 14 made of SiO ₂ is formed to a thickness of about 4nd = 2760 nm.

FIG. 5 shows the transmission characteristics of the dichroic mirror according to the second embodiment.

From the transmission characteristics shown in FIG. 5, this dichroic mirror has a total reflection mirror in a wavelength region (visible light region) smaller than about 740 nm, and a transmittance of 70% in a wavelength region of about 740 nm or more (infrared region). It is clear that it acts as a half mirror.

On the other hand, the glass substrate of the layer structure shown in FIG.
FIG. 6 shows the transmission characteristics of a dichroic mirror in which only the basic multilayer film 12 is provided on the substrate 11.

From the comparison between FIG. 5 and FIG. 6, since the first surface layer 13 and the second surface layer 14 are provided, the transmission region (wavelength 740 n
It was possible to reduce the transmittance in a region of about m or more).

The transmission characteristics in FIGS. 5 and 6 are based on the values when the incident angle is set to 13 °.

The dichroic mirror of the present invention is not limited to the above-mentioned embodiment, but the materials and respective films constituting the basic multilayer film, the first surface thin layer and the second surface thin layer. Can take various forms. For example, in the above two embodiments, the first surface layer 3, 13
The transmittance of the transmissive region can be set to a desired value by changing the layer thickness of the second surface layers 4 and 14.

Further, for example, instead of ZnS as the material forming the second surface layer 4 in the first embodiment, ZrO ₂ , TiO ₂ and Si having a substantially similar refractive index to ZnS are used.
It is also possible to use O or the like.

In the above embodiment, the incident angle is 13
Although the angle is set to ° and 45 °, the same effect can be obtained even if the incident angle is set to any angle of 0 to 45 °. Further, although the above-mentioned embodiment describes the case of using as a half mirror, it is also possible to further bond a substrate on the surface layer film and use it as a half prism.

[Brief description of drawings]

FIG. 1 is a graph showing transmission characteristics of a dichroic mirror according to a first embodiment of the present invention.

FIG. 2 is a schematic view showing the layer structure of a dichroic mirror according to the first embodiment of the present invention.

FIG. 3 is a graph showing transmission characteristics when the surface layer film is removed in the dichroic mirror according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing a layer structure of a dichroic mirror according to a second embodiment of the present invention.

FIG. 5 is a graph showing transmission characteristics of a dichroic mirror according to a second embodiment of the present invention.

FIG. 6 is a graph showing transmission characteristics when the surface layer film is removed in the dichroic mirror according to the second embodiment of the present invention.

[Explanation of symbols]

 1,11 Glass substrate 2,12 Basic multilayer film 3,13 First surface layer 4,14 Second surface layer

Claims (1)

[Claims] 1. From a first substance, on a transparent substrate, light in a wavelength region of a predetermined value or less is substantially totally reflected, and light in a wavelength region of a predetermined value or more is transmitted at a ratio of a high transmittance point or more. And a thin layer of the second substance are alternately laminated to form a basic multilayer film, and light having a wavelength region larger than the predetermined value is incident on the basic multilayer film when the basic multilayer film is incident on the basic multilayer film. On the other hand, a surface layer film having one thin layer made of the first substance and one thin layer made of the second substance, which allows transmission at a rate smaller than the high transmittance point, is provided. Characteristic dichroic mirror.