JPH09292503A - Beam splitting film, nd filter and beam splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a beam splitting film which has smooth transmittance and reflectance characteristics for the all visible ray region and can easily be produced by laminating a Ni thin film layer and a Cr thin film layer, and to obtain a ND filter and a beam splitter using the beam splitting film. SOLUTION: As for this beam splitter (a light flux splitter), the beam splitting film is formed by laminating a Ni single layer coating film 12 and a Cr single layer coating film 13 on a transparent substrate 11. The transmittance- reflectance characteristics can be changed by changing the film thickness ratio of the Ni single layer film 12 to the Cr single layer film 13, and smooth transmittance-reflectance characteristics can be obtd in wavelengths in a visible ray region with any ratio of the transmittance to the reflectance. Especially, smooth transmittance-reflectance characteristics can be obtd. within the range of (2.5:1) to (3.0:1) in film thickness ratio of Ni to Cr. The order of the Ni single layer film 212 and the Cr single layer film 13 in the film forming process may be reversed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light splitting film used for a light splitting device such as a beam splitter or a half mirror of an optical system, an ND (Neutral Density) filter using the light splitting film, and a light splitting device.

[0002]

2. Description of the Related Art Light splitting devices such as beam splitters and half mirrors, or ND filters,
It is formed by adhering a light splitting film on a transparent substrate made of glass or plastic. It is preferable that the light splitting film has transmittance and reflectance characteristics as smooth as possible, but it is difficult for the conventional light splitting film. That is, as the light splitting film, a metal thin film of gold, silver, aluminum, copper, various alloys, a dielectric thin film in which a dielectric coating material is laminated, or a composite thin film of a metal thin film and a dielectric thin film is known. The dielectric light splitting film has variations in transmittance-reflectance characteristics, and smoothness cannot be obtained especially at both ends on the short wavelength side and the long wavelength side in the visible region. The metal light splitting film can obtain more preferable smoothness in the middle of the visible range as compared with the dielectric film, but the transmissivity and the reflectance are reversed at both ends of the short wavelength side and the long wavelength side, Smoothness cannot be obtained. The metal alloy light-splitting film is superior to the dielectric thin film and the metal thin film in transmittance and reflectance characteristics, but it is difficult to keep the composition ratio of the film alloy constant when forming a film. However, there is a problem that it is difficult to manufacture.

[0003]

It is an object of the present invention to obtain a light splitting film, an ND filter, and a light splitting element which can obtain smoother transmittance and reflectance characteristics over the entire visible range and can be easily manufactured. And

[0004]

SUMMARY OF THE INVENTION In the present invention, focusing on the transmittance-reflectance characteristics of Ni thin film and Cr thin film, the reflectance-transmittance characteristics from the short wavelength side to the long wavelength side show the opposite tendency. It has been completed by finding out that a combination of the above-mentioned items can obtain a smooth reflectance-transmittance characteristic in the entire visible range. That is, the light splitting film of the present invention comprises a Ni thin film layer and a C
It is characterized by being laminated with an r thin film layer. The reflectance / transmittance ratio can be changed by changing the film thickness ratio of the Ni thin film layer and the Cr thin film layer. Especially N
The film thickness ratio of the i thin film layer and the Cr thin film layer is 2.5: 1 to 3.0:
When it is set to 1, a characteristic in which reflectance / transmittance ≈ constant is obtained at a wavelength in the visible region.

The ND filter of the present invention is characterized in that a Ni thin film layer and a Cr thin film layer are laminated on a transparent substrate. Further, the light splitting element of the present invention,
It is characterized by having a light splitting film formed by laminating a Ni thin film layer and a Cr thin film layer. In the ND filter and the light splitting element of the present invention, the order of laminating the Ni thin film layer and the Cr thin film layer on the substrate does not matter.

[0006]

2 and 3 show the respective ratios of the transmittance and the reflectance in the visible region with respect to the reference wavelength of a Cr single-layer coating film, and FIGS. 4 and 5 show the Ni single-layer coating. The respective ratios of the transmittance and the reflectance in the visible region with respect to the reference wavelength of the coating film are shown. In these figures, R is the reflectance of light of an arbitrary wavelength, T is the same transmittance, R550 is the wavelength of 550n.
reflectance at m, T550 is transmittance at a wavelength of 550 nm,
λ is an arbitrary wavelength (nm), λ550 is a reference wavelength of 550
means nm.

As is clear from FIGS. 2 and 3, when the transmittance of the Cr single-layer coating film is focused, it is low on the short wavelength side and high on the long wavelength side. On the other hand, it is almost monotonous. Focusing on the reflectance, it is high on the short wavelength side and low on the long wavelength side, and the change is almost monotonous with the increase and decrease of the wavelength.

On the other hand, as is clear from FIGS. 4 and 5, N
Focusing on the transmittance, the i single-layer coat film has a high value on the short wavelength side and a low value on the long wavelength side, and the change is almost monotonous with the increase and decrease in the wavelength. Focusing on the reflectance, the reflectance is low on the short wavelength side and high on the long wavelength side, and the change is almost monotonous with the increase and decrease in the wavelength.

The present invention obtains smooth reflectance-transmittance characteristics by utilizing the reflectance-transmittance characteristics of the Cr single-layer coat film and the Ni single-layer coat. FIG. 1 shows a transparent substrate 1.
FIG. 2 is a schematic diagram of a parallel-plane plate type beam splitter (beam splitting element) in which a Ni single-layer coat film 12 and a Cr single-layer coat film 13 are laminated and formed on 1; The Ni single-layer coat film 12 and the Cr single-layer coat film 13 may be formed in the reverse order. This beam splitter is manufactured as follows, for example.
A transparent vapor deposition substrate (parallel flat glass or resin material) is set in the vacuum vapor deposition device, and Ni is placed in the crucible in the same device.
And Cr coating materials are set. When the inside of the evaporation chamber is evacuated using a vacuum pump and the degree of vacuum inside the evaporation chamber reaches a high vacuum state (for example, about 1.5 × 10 ⁻⁵ Torr), Ni and Cr are formed by an electron beam evaporation method. Do the membrane. As described above, the order of film formation is Ni for the first layer and Cr for the second layer.
However, Cr may be used for the first layer and Ni for the second layer.

FIG. 6 shows a transparent substrate 11 made of glass (BK
7, a refractive index of 1.518 at a wavelength of 550 nm), and a Ni single-layer coating film 12 of about 7 nm on the transparent substrate,
The reflectance-transmittance characteristics are shown when the beam splitter in which the Cr single-layer coat film 13 having a thickness of about 2.3 nm is laminated is placed at an angle of 45 ° with respect to the optical axis. 7 and 8 show the ratio of the transmittance and the reflectance in the visible range with respect to the reference wavelength (550 nm). As is clear from these figures, the spectral ratio between the transmittance and the reflectance in the visible region is approximately 1: 1 and extremely smooth transmittance-reflectance characteristics can be obtained. To obtain a transmittance: reflectance ratio of about 1: 1, the Ni film thickness should be 6.0 to 7.5 nm and the Cr film thickness should be 2.0 to 2.4 nm.

The thicknesses of the Ni and Cr coat films described above are examples for making the spectral ratio of the transmittance and the reflectance in the visible region approximately 1: 1, and other spectral ratios can of course be obtained. It is possible. That is, the transmittance-reflectance characteristic can be changed by changing the film thickness ratio of Ni and Cr, and any spectral ratio can obtain a smooth transmittance-reflectance characteristic in the visible wavelength range. it can. In particular, smooth spectral characteristics can be obtained when the film thickness ratio of Ni and Cr is in the range of 2.5: 1 to 3.0: 1.

[0012]

According to the light splitting film of the present invention, smoother transmittance and reflectance characteristics can be obtained over the entire visible range. Moreover, since the film structure is composed of only two films of Ni and Cr, it is easy to manufacture and the ND filter and the light splitting element can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a beam splitter according to the present invention.

FIG. 2 is a diagram showing reflectance characteristics of a Cr single-layer coating film at a certain wavelength.

FIG. 3 is a diagram showing transmittance characteristics of a Cr single-layer coat film at a certain wavelength.

FIG. 4 is a diagram showing reflectance characteristics of a Ni single-layer coating film at a certain wavelength.

FIG. 5 is a diagram showing transmittance characteristics of a Ni single-layer coating film at a certain wavelength.

FIG. 6 is a diagram showing an example of reflectance-transmittance characteristics of a light splitting film according to the present invention.

FIG. 7 is a diagram showing the same transmittance characteristic.

FIG. 8 is a diagram showing the same reflectance characteristic.

[Explanation of symbols]

 11 Transparent Substrate 12 Ni Single Layer Coat Film 13 Cr Single Layer Coat Film

Claims (10)

[Claims] 1. A light splitting film formed by stacking a Ni thin film layer and a Cr thin film layer. 2. The light splitting film according to claim 1, wherein a film thickness ratio of the Ni thin film layer and the Cr thin film layer is 2.5: 1 to 3.0: 1. 3. An ND filter formed by laminating a Ni thin film layer and a Cr thin film layer on a transparent substrate. 4. The ND filter according to claim 3, wherein the Ni thin film layer and the Cr thin film layer are formed in this order from the substrate side to the Ni thin film layer and the Cr thin film layer. 5. The ND filter according to claim 3, wherein the Ni thin film layer and the Cr thin film layer are formed in order of the Cr thin film layer and the Ni thin film layer from the substrate side. 6. The film thickness ratio between the Ni thin film layer and the Cr thin film layer according to claim 3, wherein the film thickness ratio is 2.5: 1 to 1: 1.
ND filter that is 3.0: 1. 7. A light splitting element having a light splitting film formed by stacking a Ni thin film layer and a Cr thin film layer. 8. The light splitting element according to claim 7, wherein the Ni thin film layer and the Cr thin film layer are formed in this order from the substrate side to the Ni thin film layer and the Cr thin film layer. 9. The light splitting element according to claim 7, wherein the Ni thin film layer and the Cr thin film layer are formed in this order from the substrate side to the Cr thin film layer and the Ni thin film layer. 10. The film thickness ratio between the Ni thin film layer and the Cr thin film layer according to claim 5, wherein the film thickness ratio is 2.5: 1.
~ 3.0: 1 light splitting element.