JPS633281B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in an optical system in which a multilayer film is formed on the surface of an optical element made of glass having poor chemical durability. Conventionally, glasses with poor chemical durability, such as SK16 and LaK13, are often used as materials for optical elements such as lenses and mirrors in terms of optical design.
Generally, these glasses often have a refractive index of 1.60 to 1.70. By the way, as is known from Japanese Patent Application Laid-Open No. 52-60142, the spectral characteristics of multilayer films, which are the superimposition of the spectral sensitivity characteristics of the photoreceptor and the spectral wave characteristics of the light source, are biased towards the short wavelength side or the long wavelength side in copying machines and the like. It is used to correct for almost uniform spectral characteristics. In general, selenium-based photoreceptors are used on the shorter wavelength side.
CdS photoreceptors have spectral characteristics biased toward longer wavelengths. Such multilayer films, especially multilayer films with five or more layers,
When mounted on glass with poor chemical durability such as SK16 or LaK13, the film often peels off or becomes cloudy over time, and optical elements such as lenses with multilayer films may become less durable. It had become something missing. This is because in a multilayer film, the surface of the glass serving as the substrate is easily corroded due to the influence of its internal stress, hygroscopicity, and the film material constituting the film. An object of the present invention is to solve the above problems and provide an optical system with improved chemical durability. This objective is achieved by depositing a transparent aluminum oxide layer on the surface of glass such as SK16 or LaK13 by vacuum evaporation, sputtering, etc., and forming a conventional multilayer film thereon. Hereinafter, the present invention will be described in detail using the accompanying drawings. FIG. 1 shows an embodiment of an optical system according to the present invention. A transparent single-layer aluminum oxide layer 1' is deposited on a glass substrate 1 having poor chemical durability, such as SK16 or LaK13. The refractive index of aluminum oxide is 1.65, which is almost equal to 1.62 for SK16 and 1.69 for LaK13. On the aluminum oxide layer 1', conventional multilayer films 2 to 14 shown in the table, namely high refractive index dielectric layers and low refractive index dielectric layers, are laminated alternately starting from the high refractive index layer. High refractive index dielectric layers include CeO ₂ , ZrO ₂ , TiO _{2 ,} etc., and low refractive index dielectric layers include MgF ₂ , SiO ₂ , etc. In the table, λ is the design wavelength. Glass surfaces such as SK16 and LaK13, which have poor chemical durability, are protected by the vapor-deposited aluminum oxide film and have improved chemical durability, but this is due to the following properties of aluminum oxide. (i) When a vapor-deposited film is formed, the film is not porous but dense. (ii) It has high strength, especially hardness and adhesion, and is chemically stable. (iii) The refractive index is approximately equal to the refractive index of the glass serving as the substrate, and does not affect the optical properties of the multilayer film formed thereon. Such aluminum oxide film has at least 100
A thickness of Å or more is appropriate. Figure 2 A shows 13 alternating layers, starting from the high refractive index layer, with _two CeO layers as a high refractive index dielectric layer and _two MgF layers as a low refractive index dielectric layer on the surface of a lens using LaK13 as a substrate. Optical characteristics of a conventional optical system (curve b) and optical characteristics of an example of an optical system according to the present invention in which an aluminum oxide layer is deposited on LaK13 and the conventional 13 alternating layers are directly formed thereon. (Curve a) is compared. Here, the vertical axis is transmittance (%) and the horizontal axis is wavelength (mμ). It is clear from this that there is almost no difference in the optical properties between the two. This is because there is no large difference between the refractive index of the glass and the refractive index of aluminum oxide, and they are almost equal. In Figure 2 A, the transmittance decreases on the short wavelength side, making it suitable for use with selenium-based photoreceptors in copying machines, etc. However, in order to apply it to CdS-based photoreceptors, the transmittance decreases on the long wavelength side. A multilayer film may be used. The chemical durability of the sandwiched aluminum oxide layer between the glass substrate and the first layer of a conventional multilayer film has been improved through environmental resistance tests at a temperature of 45°C and a humidity of 95%.
As a result of being left for 200 hours under the conditions of This was demonstrated by good results with no problems. This is glass (SK16,
This is because the aluminum oxide layer itself is chemically stable and resistant to corrosion, and has good adhesion to the glass when deposited on the glass. Similar results were confirmed for the optical systems shown in the table. FIG. 2B shows a comparison of the optical characteristics of the optical system shown in the table with a conventional example, and there is no difference between the two. Curve c relates to the present invention, and curve d shows the optical characteristics of a conventional optical system. FIG. 3 is an explanatory diagram of a system in which the present invention is applied to a copying machine. The original 16 is illuminated in the form of a slit by the illumination light source 17, and the original light is reflected by the object-side reflecting mirrors 19 and 20, then reflected by the lens 21 and the image-side reflecting mirror 22, and is imaged on the drum 23. be done. Here, the lens 21 has a multilayer film deposited on the front and the front. The optical system according to the present invention can be formed on each surface of the lens 21, the object side reflecting mirrors 19 and 20, and the image side reflecting mirror 22. That is, it can be applied not only to transmission type optical systems but also to reflection type optical systems. As described above, according to the present invention, an optical system made of a multilayer film using glass as a substrate, which has poor chemical durability, can be made to have excellent chemical durability and not affect conventional optical characteristics.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a diagram of an embodiment of an optical system according to the present invention.
FIGS. 2A and 2B are comparison diagrams with the conventional example in terms of spectral characteristics, and FIG. 3 is an explanatory diagram of a system in which the present invention is applied to a copying machine. In the figure 1...Glass, 1'...Aluminum oxide layer,
2, 4, 6, ..., 14... high refractive index dielectric layer,
3, 5, 7,..., 13...Low refractive index dielectric layer.

Claims (1)

[Claims] 1. In an optical system in which a multilayer film is formed on the surface of an optical element made of glass having a refractive index of 1.60 to 1.70, which has poor chemical durability, the surface of the optical element and the first layer of the multilayer film are An optical system characterized in that an aluminum oxide layer having a refractive index substantially equal to the refractive index of the glass is deposited therebetween. 2. The optical system according to claim 1, wherein the optical element is a transmission lens. 3. The optical system according to claim 1, wherein the multilayer film is composed of dielectric layers, and the odd-numbered layers including the first layer are high refractive index dielectric layers, and the even-numbered layers are low refractive index dielectric layers. .