JPS6217044A - Formation of antireflection film resistant to laser damage and having high wear resistance on optical element surface - Google Patents

Abstract

PURPOSE:To obtain the titled antireflection film resistant to laser damage and having high resistance to wear by mixing a metallic alcoholate into the dispersion of colloidal silica in an org. solvent or water, hydrolyzing and partially condensation-polymerizing a liq. mixture obtained by dissolving the mixture in an org. solvent to obtain a sol soln., coating the sol soln. on the surface of an optical element and heat-treating the element. CONSTITUTION:One or >=2 kinds of metallic alcoholates is mixed into the dispersion of colloidal silica in water or an org. solvent, the mixture is dissolved in an org. solvent and the liq. mixture is hydrolyzed and partially condensation-polymerized to obtain a sol soln. The sol soln. is coated on the surface of an optical element and the element is heat-treated. Consequently, a vitreous coated film contg. silica fine particles is formed on the surface of the optical element. The coated film acts as an antireflection film having high resistance to wear and resistant to laser damage. A substance expressed by the formula, Me(OR)n (Me is a metallic element such as Si, Al, Na and B and R is an alkyl group such as CH3, C2H5, C3H5, C3H7 and C4H9). is preferably used as the metallic alcoholate.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention is a glass coating for optical elements used in laser systems, which is resistant to laser damage and has high abrasion resistance and is made of a glassy coating containing fine silica powder. It relates to forming an anti-reflection coating.

[Conventional technology - Glass is used as many optical elements (windows, lenses) in laser oscillation systems, but anti-reflection coatings are formed on these optical elements to improve the efficiency of laser output. It is designed to be easily removed. As the method, negative air deposition method and surface chemical treatment method are known.

[Problems to be Solved by the Invention] When an antireflection film is formed by multilayer coating using a vacuum evaporation method, the damage value against laser light is low (4 to 5 J/cm2.1.06 μm, pulse Width 1n
s), which limits the output of the laser system. In addition, when a porous antireflection film with a refractive index gradient is formed on the glass surface by selective elution of components from the glass surface using a chemical treatment method, the damage value against laser light is high (15 to 20 J /cm2.1.06μm1
The pulse width is 1 ns), but the surface layer is very weak and easily scratched. Furthermore, if dirt adheres to the surface, it cannot be removed by hand, making it difficult to handle. Another chemical treatment method is to coat the surface of an optical glass element with a sol solution made by hydrolysis of metal alcoholate, heat treat it to create a glassy film, and leaching it to create a porous and refractive film. Even when an anti-reflection film is formed with a gradient in rate, the same problems as in the case of an anti-reflection film based on selective elution from the surface of the glass itself exist.

In order to solve the above-mentioned problems, the present invention aims to produce an antireflection film that has a high laser damage threshold and high wear resistance.

[Means for Solving the Problems] The present invention involves mixing one or more metal alcoholates with colloidal silica dispersed in an organic solvent or water,
It is created by coating an optical glass element by dipping it in a sol solution obtained by diluting it with an organic solvent such as alcohol, stirring and mixing it, and then subjecting it to hydrolysis and partial condensation polymerization, followed by drying and heat treatment. We have discovered that a porous glassy coating containing fine silica particles provides an antireflection coating with high wear resistance and a high laser damage threshold. Here, the silica fine particles are colloidal silica dispersed in water or an organic solvent such as alcohol.
A particle size of 40 μm is used. Metal alcoholates have the general formula Me (OR).

(n is the coordination number of Me) Me is a metal element that forms glass as an oxide, such as Si, Al1, B,
Na, R is CH3, C2H5, C3H7, C4H
9 alkyl group, for example, s i (OC2Ha
)4, Af (OC2H5)3, B (OC4H9
)3 is used. Organic solvents for dilution include methanol, ethanol, isopropyl alcohol, butanol,
Acetylacetone and the like are used.

] 0.0% metal alcoholate per mole of rhoidal silica.
A suitable amount of an organic solvent for dilution is added, and after mixing and stirring, water for hydrolysis is mixed with HCl or HNO31m and metal alcoholate 1
It is added in a range of 1 to 8 moles per mole, and thoroughly mixed and stirred. The sol solution subjected to hydrolysis and partial condensation polymerization in this manner is used as a coating liquid.

When forming an anti-reflection film, the film thickness is determined by the formula nd = π/4 (n: film refractive index, λ
: wavelength at reflectance min, d: film thickness), and the film thickness is controlled by the viscosity of the coating liquid and the pulling speed.

The optical glass element is coated by dipping it in the coating liquid and pulling it up. After drying at 30° C. to 120° C., an antireflection film is formed by heat treatment at 300° C. to 800° C. in an oxygen gas atmosphere.

According to the present invention, the reflection loss of 7 to 10% per optical glass element can be reduced to 0.0 by forming a glass film containing silica fine particles using the simple wet coating method as described above.
The antireflection coating was reduced to 1 to 1.0%, and the result was a durable antireflection film that would not be scratched even when rubbed with steel wool.

The anti-reflection effect achieved by containing colloidal silica is because silica particles shrink less when heated, and the large shrinkage of the gel part made of metal alcoholate allows the spaces held by the silica particles to be uniformly distributed within the film. This is thought to be due to the fact that it becomes porous and has a low refractive index.

By forming an antireflection film according to the present invention on an optical glass element used in a laser system, it has become possible to efficiently extract laser output. Improvements in laser damage threshold and wear resistance will be specifically described in the following examples. Note that the present invention is not limited to the scope of the following examples.

[Example] Example 1 Add 1 mole of tetraethoxysilane to 1 mole of ethanol-dispersed colloidal silica and dilute with 20 moles of ethanol. Add 2 moles of water acidified with hydrochloric acid and thoroughly mix and stir to cause hydrolysis and partial condensation. The quartz glass of the optical element was immersed in a sol solution containing polymerized colloidal silica and then pulled up at a constant speed to coat it. After drying at room temperature and at 120°C, the temperature was gradually raised to 390°C and kept in an oxygen gas atmosphere for 10 hours to form a porous glass film.

The reflectance curve of quartz glass coated with this glassy coating is shown in FIG. 1, and the reflectance has a minimum value of 0.0 at a wavelength of 330 nm.
2χ (single-sided), and is useful as an optical element for 3ω light of Nddope glass lasers. The laser damage threshold is 8 J/cta2, which is 8 J/cta2.
It showed higher yield strength than 5J/Cll12.

In addition, no scratches were observed with the naked eye in a rubbing test with stainless wool.

Example 2 Isopropyl alcohol dispersed colloidal silica 1.25
Mol, salt in a mixture of 1 mole of tetraethoxysilane and 10 moles of isopropyl alcohol! Add 4 moles of u-based water,
After hydrolyzing at 40° C. with stirring, 1 mole of triethoxyboron diluted with 0.5 mole of isopropyl alcohol was added, thoroughly mixed and stirred, and the resulting sol solution was used as a coating liquid.

An optical glass element was coated by dipping and pulling up, and after drying at 120°C, the temperature was slowly raised to 500°C and held in an oxygen gas atmosphere for 15 hours to form a porous glassy coating. By forming this antireflection film, the reflectance decreased to 0.5χ at 350 nm on one side, as shown in FIG. Laser damage threshold is Nd laser 3
It was 10J/Cm2 with ω light. In addition, in a rubbing test with stainless wool, no mouth was observed with the naked eye.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are reflectance curves of the antireflection films described in Example 1 and Example 2, respectively. Applicant Hoya Co., Ltd. Agent Masayuki Asakura Figure 1 χ (nm) '22 illustration (nml) Continued ?t13, +E Yq Showa 6
August 8, 0

Claims (1)

[Scope of Claims] 1. On the surface of an optical element, one or more metal alcoholates are mixed with colloidal silica dispersed in water or an organic solvent, and the mixed solution dissolved in an organic solvent such as alcohol is hydrolyzed. By coating a condensation-polymerized sol solution and heat-treating it, a glassy film containing fine silica particles is formed to form an anti-reflection film that is resistant to laser damage and has high abrasion resistance on the surface of optical elements. Method. 2. The antireflection coating resistant to laser damage and having high abrasion resistance as set forth in claim 1, characterized in that the mixing molar ratio of colloidal silica:metal alcoholate is 1:0.1 to 5, is used in an optical element. How to form on the surface. 3 Metal alcoholate is represented by the general formula Me(OR)_n, where Me is a metal element Si, Al, Na, or B, and R is CH_3, C_2H_5, C_3H_7, C_4
A method for forming an antireflection film on the surface of an optical element that is resistant to laser damage and has high abrasion resistance, as set forth in claim 1, wherein the H_9 alkyl group is a H_9 alkyl group.