JPH0210770B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to ultraviolet transmitting glass used, for example, in laser fusion. Recently, in laser fusion experiments, it was found that the shorter the wavelength of laser light, the smaller the energy required to cause implosion. 3ω light) laser light is being used. The problem in this case is that the glass used as the optical element in conventional laser systems
BK-7 (optical glass manufactured by Schott, West Germany) has a wavelength
The light transmittance of 0.35 μm is low and solarization occurs, so it cannot be used. On the other hand, as a glass with high light transmittance at a wavelength of 0.35 μm and excellent solarization resistance,
_SiO2 60~70, _B2O3 15~25, _{Al2O3 1} ~ ₅ , _R2O
(R=K, Na, Li) 10-20, R′O (R′=Mg, Ca,
Borosilicate glass having a composition of 0 to 5 (Sr, Ba, Zn, Pb) is known. Furthermore, in high-output laser systems such as laser fusion, anti-reflection treatment on the surface of optical glass is essential in order to efficiently extract output.
Conventional vacuum-deposited multilayer anti-reflection coatings have a low damage threshold against laser light, which limits the output of laser systems. On the other hand, Japanese Patent Laid-Open No. 58 (1982) proposed a method for manufacturing an antireflection film with a high laser damage threshold by treating the glass surface in a weak alkaline solution containing polyvalent cations.
It is reported in Japanese Patent No. 69746 that it is possible to form a film with low reflectance at any wavelength using silicate glass containing at least 5% by weight of alkali metal. However, since the borosilicate glass having the above composition has a high content of Al ₂ O ₃ , a good antireflection film cannot be formed by the treatment method disclosed in the above publication. This is because glass with a high content of Al ₂ O ₃ has a strong glass structure and is difficult to erode, making it impossible to obtain a sufficiently porous film. In view of the above, an object of the present invention is to provide a glass for transmitting ultraviolet rays which has a high light transmittance at a wavelength of 0.35 μm and can form a porous antireflection film on its surface. Here, the inventors of the present invention have discovered that by adding 0.1 to 6% by weight of _F2 to the glass having the above composition, a glass with high light transmittance at a wavelength of 0.35 μm can be obtained, and this can be obtained at a pH of 8. When treated with a buffered solution containing no polyvalent metal ions between 7 and 10.0, _F2
Due to the action of glass, the glass structure becomes loose and becomes susceptible to erosion, which causes it to dissolve into the solution.
F ^- promotes erosion, while Al ³⁺ leached into the solution controls the erosion of the glass, thereby creating a porous glass surface with optically uniform, low reflectance and high laser damage threshold. It was discovered that an antireflection film of Note that if the _F2 content is less than 0.1% by weight, the light transmittance at a wavelength of 0.35 μm will not improve and a good antireflection film cannot be formed, while if it is more than 10%, the glass will easily devitrify. . That is, the ultraviolet transmitting glass according to the present invention contains SiO ₂ 60 to 70, Al ₂ O ₃ 1 to 5, and B ₂ O ₃ 15 in weight percent.
~25, _R2O (R=K, Na, Li) 10~15, R′O
(R'=Mg, Ca, Sr, Ba, Zn, Pb) has a composition of 0 to 5 and F2 of 0.1 to ₆ in terms of outer division. Further, the ultraviolet transmitting glass according to the present invention has the above composition and has a porous antireflection film formed on its surface. The following table shows composition examples of glasses according to the present invention (sample
Nos. 2 to 8) are shown together with conventional glass that does not contain F ₂ (sample No. 1), and both samples Nos. 1 to 8 and BK-7 transmit light at a wavelength of 0.35 μm through 10 cm thick glass. Show rate. The glasses of Samples No. 2 to 8 are made of silica powder purified by acid washing, aluminum fluoride, aluminum hydroxide, anhydrous borax, boric acid, potassium carbonate, potassium nitrate, lithium carbonate, zinc white, and acid fluoride. After accurately weighing and mixing the potassium chloride so that it has the composition of each glass, it was melted in a platinum crucible at 1450℃ for 3 hours and stirred for 30 minutes during the melting, and after cooling to 1350℃, it was placed in a cast iron frame. The glass was poured into a glass container, slowly cooled using the usual method, and then ground and polished in the cold to obtain a 10cm thick glass. In addition, the iron content in glass has a wavelength
Since it has a large effect on the light transmission of 0.35 μm, the raw material mixture was kept at a so-called batch stage to 2 p.pm or less.

[Table] As is clear from this table, conventional glass that does not contain _F2 (sample No. 1) has a higher wavelength than BK-7.
The glasses according to the present invention (Samples Nos. 2 to 8) have higher light transmittance at a wavelength of 0.35 μm than the glass of Sample No. 1. Next, a method for forming an antireflection film will be described according to examples. Example 1 Glass of sample No. 4 in the above table was 5mm thick and 50mm×
Optically polished to 50mm and mixed with 0.05M Na ₂ CO ₃ .
After immersing for 16 hours in a solution at 60°C mixed with 0.1M NaHCO ₃ solution at a volume ratio of 1:9, it was washed with warm water at 60°C, further immersed in ethanol at room temperature, and then dried at room temperature. This was used as a reflectance measurement sample. The measurement results of the reflectance are shown in a in the figure. Similar to the light transmittance measurement, the Shimadzu multi-purpose self-recording spectrophotometer model MPS-5000 manufactured by Shimadzu Corporation was used for the reflectance measurement. Note that the pH at the time of preparing this mixed solution was 8.7, and did not change even after the glass sample was immersed for 16 hours. Example 2 The same glass as Example 1 was treated with 0.03M Na ₂ HPO ₄
After being immersed in the solution at 60° C. for 16 hours, the glass was washed and dried in the same manner as in Example 1 to obtain a glass with an antireflection film. The measurement results of the reflectance are shown in b in the figure. The pH of this solution at the time of preparation was 9.8, and did not change even after the glass sample was immersed for 16 hours. Example 3 The same glass as Example 1 was used at 0.03M.
After immersing in a solution of Na ₂ HAsO ₄ at 60° C. for 16 hours, a glass with an antireflection film was obtained in the same manner as in Example 1. The measurement results of the reflectance are shown in C in the figure. The pH of this solution at the time of preparation was 9.2, and did not change even after immersing the glass in the solution for 16 hours. Note that d in the figure is the measurement result of the reflectance of the conventional glass sample No. 1 treated by the method of Example 3. As is clear from the figure, the F ₂ -containing glass according to the present invention has an antireflection coating formed thereon, and as a result has a lower reflectance than the conventional glass. Furthermore, the treatment liquid used to form the anti-reflection film is an acid salt of a weakly acidic liquid, and even after glass treatment,
It can be seen that there is no change in pH and that it has a buffering effect. Since this invention is configured as described above, the wavelength
It has a high light transmittance at 0.35 μm, so in laser fusion experiments, for example, it has a shorter wavelength than the conventional wavelength of 1.05 μm and causes implosion with less energy.
It has excellent effects such as being suitable as an optical element glass in a 0.35 μm laser system. In addition to the above-mentioned effects, the ultraviolet transmitting glass of the present invention, which has a porous anti-reflection coating formed on its surface, has a higher damage threshold against laser light than the conventional multilayer anti-reflection coating made by vacuum evaporation. Therefore, the output can be extracted efficiently in the laser system, and the output can be improved.

[Brief explanation of drawings]

Figures a, b, and c show the results of measuring the reflectance when glass according to the present invention was treated with each treatment liquid.For reference, the reflectance of conventional glass treated with the same treatment liquid is shown. The measurement results are shown in d.

Claims (1)

[Claims] 1% by weight SiO ₂ 60-70 Al ₂ O ₃ 1-5 B ₂ O ₃ 15-25 R ₂ O (R=K, Na, Li) 10-15 R'O (R' = Mg, Ca, Sr, Ba, Zn, Pb) 0 to 5 Ultraviolet transmitting glass having a composition consisting of F ₂ 0.1 to 6 in terms of outer division. 2% by weight SiO ₂ 60-70 Al ₂ O ₃ 1-5 B ₂ O ₃ 15-25 R ₂ O (R = K, Na, Li) 10-15 R'O (R' = Mg, Ca, Sr , Ba, Zn, Pb) 0 to 5 F ₂ 0.1 to 6 in terms of outer fraction, and has a porous antireflection film formed on its surface. 3 The antireflection film is made of glass having the above composition.
The ultraviolet transmitting glass according to claim 2, which is formed by surface treatment with a solution having a pH of 8.7 to 10.0. 4. The ultraviolet transmitting glass according to claim 3, wherein the solution has a buffering effect at pH 8.7 to 10.0.