JP4192308B2 - Optical element manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an optical element for ultraviolet rays.
[0002]
[Prior art]
Conventionally, an optical element for ultraviolet rays has been manufactured by, for example, grinding and polishing quartz glass, which is a typical material thereof. When using ultraviolet rays, particularly ultraviolet rays having a wavelength of 300 nm or less, quartz glass is very expensive because required characteristic values such as transmittance and refractive index homogeneity are severe.
[0003]
Also, depending on the optical element, when shaping the shape by grinding or polishing, it may be necessary to cut out from a large member, in which case there are many useless parts, which increases the cost of processing time and the cost of materials. was there.
[0004]
[Problems to be solved by the invention]
Therefore, a method for manufacturing an optical element by heating and softening optical glass and transferring a mold having an optical function surface or a shape close to the optical function surface by pressure is generally used. Attempts were made to produce a glass optical element, but a new problem arose by raising the quartz glass to its softening temperature.
[0005]
That is, generally, when a quartz glass optical element is irradiated with ultraviolet rays of 300 nm or less, a sudden decrease in transmittance occurs due to a change in physical properties inside the element. The concentration is 1 × 10 ¹⁸ (pieces / unit cubic cm) or more.
However, by heating the quartz glass to its softening temperature, the hydrogen molecule concentration becomes about 1/10 to 1/20 of the initial state, the ability to suppress changes in physical properties is extremely lowered, and the transmittance is consequently reduced. It has been found.
[0006]
[Means for Solving the Problems]
Therefore, a method for manufacturing an optical element in which quartz glass that suppresses a decrease in transmittance is heated and softened and a mold having an optical function surface or a shape close to the optical function surface is transferred by pressure is manufactured. In order to apply to the method, by mixing hydrogen gas into the atmosphere during molding, hydrogen molecules in the quartz glass are not reduced during heating, molding, and cooling, 1 × 10 ¹⁸ (pieces / unit cubic cm) or more I found out that I was holding.
[0007]
In order to solve the above problems, in the present invention, first, in claim 1, an installation step of installing quartz glass in a container, a heating step of heating the installed quartz glass, and the heated quartz glass And a pressurizing step of pressurizing with a mold, wherein the atmosphere in the container in the heating step is a mixed gas of inert gas and hydrogen gas or hydrogen gas, and the pressurization The method for producing an optical element is characterized in that the atmosphere in the container in the process is a vacuum.
According to a second aspect of the present invention, in addition to the first aspect, the method further includes a cooling step of cooling the quartz glass pressurized in the pressurizing step, and the atmosphere in the container in the cooling step includes an inert gas and hydrogen. Provided is a method of manufacturing an optical element, which is a mixed gas with gas or hydrogen gas.
According to a third aspect of the present invention, there is provided the method for manufacturing an optical element according to the first or second aspect, wherein the inert gas is argon.
According to Claim 4 of the present invention, in the method of manufacturing an optical element according to Claim 1 or 2, the mixed gas has a ratio of the hydrogen gas to the inert gas of 0.1 to 99.9%. An optical element manufacturing method is provided.
By using this production method, the problem of reducing the concentration of hydrogen molecules was solved, and an optical element using ultraviolet light, particularly ultraviolet light having a wavelength of 300 nm or less, could be produced. In addition, this manufacturing method has realized a significant cost reduction.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
There are many types of optical elements made of quartz glass. In the present embodiment, a method for manufacturing a fly-eye lens made of quartz glass will be described in detail below.
[0009]
【Example】
In order to heat and soften quartz glass and pressurize a mold having an optical functional surface or a shape close to the optical functional surface to transfer the functional surface or a shape close to the functional surface, as shown in FIG. For example, a quartz glass member 1 is prepared by polishing the upper and lower surfaces of a width 30 mm × depth 30 mm × height 20 mm and grinding the side surfaces.
[0010]
And this member 1 is installed in a container (not shown) so that it may be pinched | interposed between the upper mold | type 2 and the lower mold | type 3. FIG. The upper mold 2 and the lower mold 3 are made of a sintered body having durability at a high temperature, for example, represented by tungsten. The upper mold 2 and the lower mold 3 have optical function surfaces 2a and 3a on the side in contact with the quartz glass member 1, respectively. is doing. Here, the optical functional surfaces 2a and 3a to be transferred are often polished, but a grinding surface can be substituted when transferring a shape approximate to the optical functional surface.
[0011]
The configuration of the molding apparatus of this embodiment is shown in FIG. The molding apparatus is formed of a main body unit 10 having a heating and pressurizing mechanism, an exhaust unit 20, and an atmospheric gas introduction unit 30.
The quartz glass member 1, the upper mold 2, and the lower mold 3 shown in FIG. 1 are arranged in a container, and are housed in the molding apparatus shown in FIG. In other words, the work 13 is installed on the platform 11 in the vacuum vessel 14. Then, after closing the atmospheric gas introduction valve 31, the valve 26 is opened, and the air in the vacuum vessel 14 is roughed by the oil rotary pump 21.
[0012]
After this roughing, the valve 26 is closed, the valve 23 is opened, and the valve 24 is opened, so that the air in the vacuum vessel 14 is drawn by the oil diffusion pump 22. When the vacuum gauge 27 for measuring the degree of vacuum in the vacuum vessel 14 becomes, for example, 5 × 10 ⁻³ Pa or less, the valve 24 is closed and the atmospheric gas introduction valve 31 is opened.
Then, for example, an atmospheric gas having a mixing ratio of 80% hydrogen gas and 20% argon gas is introduced into the vacuum vessel 31 through the opened valve 31, and when the pressure in the vacuum vessel 14 becomes atmospheric pressure, the heater 12 Start heating.
[0013]
The heating by the heater 12 is performed, for example, according to the schedule shown in FIG. That is, it is heated to 1450 ° C. in 50 minutes and held for 10 minutes. At this time, atmospheric gas is constantly introduced into the vacuum container 14, and the valve 25 is opened and closed while the vacuum gauge 27 is checked so that the internal pressure does not exceed atmospheric pressure.
Further, just before the pressurization start time (from 50 minutes to 55 minutes), the atmosphere gas introduction valve 31 is closed again, the valve 26 is opened, and the oil in the vacuum vessel 14 is opened by the oil rotary pump 21. Roughen.
[0014]
After this roughing, the valve 26 is closed, the valve 23 is opened, and the valve 24 is opened, so that the air in the vacuum vessel 14 is drawn by the oil diffusion pump 22.
Then, when the vacuum gauge 27 for measuring the degree of vacuum in the vacuum vessel 14 becomes, for example, 5 × 10 ⁻³ Pa or less, pressurization is started. The reason why the vacuum vessel 14 is evacuated before pressurization is that the optical function surfaces 2 a and 3 a of the upper mold 2 and the lower mold 3 have a concave shape with respect to the quartz glass member 1. When the concave shape is pressed and molded in the atmosphere, there is no escape path for the atmospheric gas near the center of the recess, and as a result, an air pocket is formed near the center of the recess and an optical functional surface cannot be obtained.
[0015]
As a matter of course, when the optical functional surfaces 2a and 3a have a convex shape, the step of evacuating the vacuum container 14 as described above is unnecessary.
The cylinder 16 is actuated 5 minutes after the pressurization is maintained at 1450 ° C., and the upper mold 2 of the work 13 is pushed down by the pressure of 70 kgf / cm ² through the pressing shaft 15. Thereafter, pressurization is performed for 10 minutes as shown in FIG. 3, and the temperature is decreased from 60 minutes so that the temperature at the completion of pressurization is 1100 ° C. At this point, the valve 24 is closed again, and the atmospheric gas introduction valve 31 is opened. Thereafter, the workpiece is cooled in an atmospheric gas to a temperature at which the workpiece can be taken out, and the molding is completed.
[0016]
By removing the work 13 from the vacuum vessel 14 and taking out the upper die 2 and the lower die 3 from the vessel (not shown), a desired molded quartz glass optical element can be obtained. FIG. 4 shows a typical shape of a molded quartz glass optical element, that is, a fly-eye lens.
Since the quartz glass optical element obtained by the manufacturing method described above is heated in an atmosphere gas mixed with hydrogen gas, the concentration of hydrogen molecules inside the element is 1 × 10 ¹⁸ (pieces / unit cubic cm) or more. I am letting. The amount of this hydrogen molecule can be easily calculated from the intensity of the peak obtained by Raman spectroscopy. For this reason, even when an ultraviolet ray of 300 nm or less is irradiated, a sudden decrease in transmittance does not occur due to a change in physical properties inside the element.
[0017]
When the obtained quartz glass optical element has an optical functional surface, it is used as it is, and when it has a shape approximated to the optical functional surface, the actual optical system is obtained by finishing the optical functional surface by a light polishing process. As a result of performance evaluation, the optical performance was sufficiently achieved.
That is, it is possible to apply the molding process to a quartz glass optical element that can only be handled by conventional grinding and polishing processes, and the manufacturing cost of the quartz glass optical element can be greatly reduced.
[0018]
In the above embodiment, an atmosphere gas having a mixing ratio of 80% hydrogen gas and 20% argon gas is used. However, the atmosphere gas is mixed with an inert gas other than argon gas. (The mixing ratio can be selected between 0.1 to 99.9% hydrogen gas) or only hydrogen gas may be used.
[0019]
【The invention's effect】
In the method for molding a quartz glass optical element as described above, the atmosphere during heating and cooling is a mixed gas of inert gas and hydrogen gas, or hydrogen gas, and vacuum or inert gas is used during molding. Since it is a mixed gas of hydrogen and hydrogen gas or hydrogen gas, it is possible to reliably use the optical element as an optical element for ultraviolet rays, particularly ultraviolet rays having a wavelength of 300 nm or less.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an installation state when a fly-eye lens is obtained by molding.
FIG. 2 is a diagram illustrating a state in which the molding of the present invention is performed.
FIG. 3 is a diagram showing a schedule in an embodiment of the molding method of the present invention.
FIG. 4 is a fly-eye lens obtained by an embodiment of the molding method of the present invention.
[Explanation of symbols]
1: Quartz glass member 2: Upper mold 2a: Upper mold optical functional surface 3: Lower mold 3a: Lower mold optical functional surface 10: Molding apparatus main body 11: Mounting table 12: Heater 13: Workpiece 14: Vacuum container 15: Press Shaft 16: Cylinder 20: Molding device exhaust unit 21: Oil rotary pump 22: Oil diffusion pump 23: Valve 24: Valve 25: Valve 26: Valve 27: Vacuum gauge 30: Molding device atmosphere gas introduction unit 31: Valve

Claims (4)

An installation process for installing quartz glass in the container;
A heating step of heating the installed quartz glass;
A method of manufacturing an optical element comprising a pressing step of pressing the heated quartz glass with a mold,
The atmosphere in the container in the heating step is a mixed gas of inert gas and hydrogen gas or hydrogen gas,
The method of manufacturing an optical element, wherein the atmosphere in the container in the pressurizing step is a vacuum. A method for producing an optical element according to claim 1,
A cooling step of cooling the quartz glass pressed in the pressing step;
The method of manufacturing an optical element, wherein the atmosphere in the container in the cooling step is a mixed gas of inert gas and hydrogen gas or hydrogen gas. The inert gas, method of manufacturing an optical element according to claim 1 or claim 2, characterized in that argon. The gas mixture, method of manufacturing an optical element according to claim 1 or claim 2 ratio of the hydrogen gas to the inert gas, characterized in that a 0.1 to 99.9%.

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