JP5657246B2 - Optical components for machining - Google Patents

Description

  The present invention relates to an antireflection film, and more particularly to an antireflection film suitable for a high-power laser.

  Light entering and exiting an optical component that transmits light, such as glass or plastic, has a light transmittance that is reduced because part of the light is reflected on the surface. Therefore, conventionally, in order to increase the light transmittance, an antireflection film is provided on the light incident surface and the light exit surface of many optical components. In forming the antireflection film, it is necessary to satisfy predetermined conditions in order to ensure low reflectivity.

  For example, when a single layer (single layer) antireflection film is formed on a substrate of an optical component existing in air (medium), the following conditions must be satisfied.

N _f ² = N ₀ · N _S
(N _f : refractive index of antireflection film, N ₀ : refractive index of medium, N _S : refractive index of substrate)
If the base material is quartz glass or optical fiber whose main component is silicon dioxide (SiO ₂ , refractive index: about 1.44), the refractive index of air is about 1.00. The refractive index of the film needs to be about 1.20.

  However, no suitable material satisfying this condition is recognized among the general materials used for the antireflection film, including silicon dioxide. Therefore, in such a case, a multilayer antireflection film that satisfies the condition is often formed by laminating a plurality of materials.

In the present invention, for example, an antireflection film having a three-layer structure in which an intermediate layer made of Al ₂ O ₃ , Ta ₂ O ₅ or the like is provided between inner and outer layers made of SiO _{2 with} respect to a substrate made of Nd: YAG Is disclosed (Patent Document 1).

An antireflection film having a multilayer structure using SiO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ or the like is also disclosed (Patent Document 2). However, this antireflection film is provided with a layer mainly composed of YAG (yttrium, aluminum, garnet) in order to improve laser resistance and the like.

JP-A-4-38885 JP 2004-287274 A

  In recent years, there has been an increasing demand for improving the performance of high-power lasers in various fields. As the performance of high-power lasers improves, the output energy becomes even higher, so the antireflection film used in the optical component is easily damaged by heat, etc., and not only has high light transmittance but also high Laser resistance is also required. In particular, when a high-power laser is output at a high frequency, the antireflection film is exposed to a high temperature, and thus countermeasures are necessary.

Examples of the antireflection film material having high laser resistance include silicon dioxide and aluminum oxide (Al ₂ O ₃ ). In Patent Document 1, an antireflection film having a three-layer structure is formed using only these, but this is because an Nd: YAG substrate (refractive index: about 1.82) having a high refractive index is used as a base material. Because.

  When quartz glass or the like mainly composed of silicon dioxide is a base material, the refractive index is low. Therefore, in such a configuration, for example, a low-reflection antireflection film having a reflectance of 0.25% or less. Cannot be designed. In order to form a low-reflective antireflection film on quartz glass or the like using only silicon dioxide and aluminum oxide, a multilayer structure of four or more layers is usually required.

  However, when the antireflection film has a multilayer structure, there is a problem that the laser resistance decreases as the number of layers increases. If the number of layers increases, the number of interfaces between each layer increases, and the overall film thickness increases, making it easier to be affected by impurities, which makes it easier for laser energy to act on the antireflection film. It is guessed.

Therefore, the present applicant has previously proposed an antireflection film having a two-layer structure formed of a predetermined material based on this viewpoint in order to improve laser resistance (Japanese Patent Application No. 2008-123808). Specifically, an antireflection film is formed of a high refractive index layer such as Ta ₂ O ₅ and a low refractive index layer of SiO ₂ formed thereon.

  Even with this two-layer antireflection film, it is possible to improve laser resistance while ensuring low reflectivity. However, since combinations of antireflection film materials are limited, it is difficult to satisfy the requirements when higher laser resistance is required.

  Therefore, an object of the present invention is to provide an antireflection film that can improve laser resistance to a higher level while ensuring low reflectivity.

  In order to achieve the above object, in the present invention, the antireflection film has a three-layer structure, and an intermediate layer having excellent thermal conductivity is provided therebetween.

Specifically, the antireflection film of the present invention is a three-layered antireflection film formed on an optical substrate mainly composed of SiO ₂ , and is formed on the optical substrate. It has a lower layer, an intermediate layer formed on the lower layer, and an upper layer formed on the intermediate layer, and the intermediate layer is formed using Al ₂ O ₃ .

According to the antireflection film having such a configuration, since Al ₂ O ₃ having excellent thermal conductivity is provided in the intermediate layer, a high output laser acts on the antireflection film and heat is concentrated on a part thereof. However, the heat can be efficiently dispersed around. In particular, when a high-power laser is continuously irradiated, the concentration of heat can be effectively reduced, so that high laser resistance can be realized.

Specifically, the lower layer can be formed using Ta ₂ O ₅ and the upper layer can be formed using SiO ₂ . In particular, the thickness of the intermediate layer is preferably set to 100 nm or less.

By doing so, it is possible to realize an antireflection film having low reflectivity and excellent laser resistance. Since SiO ₂ having high hardness is used for the upper layer, the durability of the antireflection film can be improved.

  According to the antireflection film of the present invention, the laser resistance can be improved to a higher level while ensuring low reflectivity.

It is a schematic sectional drawing which shows the optical component to which the antireflection film of this embodiment is applied. It is a schematic sectional drawing of an antireflection film. It is a figure for demonstrating a laser tolerance test. It is a graph which shows the laser tolerance test result of an Example and a comparative example. It is a graph which shows the laser tolerance test result of an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following description is merely illustrative in nature and does not limit the present invention, its application, or its use. The name “laser guide” of the optical component of the present embodiment is a registered trademark.

  FIG. 1 shows a laser guide 1 (optical component) to which the antireflection film 4 of this embodiment is applied. The laser guide 1 is a laser guide for an Nd: YAG laser system used for machining such as welding and cutting, and is used to transmit a high-power laser beam (basic wavelength 1064 nm) output from a light source. It is done. The figure shows the end of the laser guide 1, and a laser beam enters or exits from this end.

  The laser guide 1 includes a cable 2 and connectors 3 provided at both ends of the cable 2.

  The cable 2 includes an optical fiber 2a (optical base material) that is a core wire and a tube 2b that covers the optical fiber 2a. Each end of the cable 2 is processed so that the tube 2b is peeled off for a predetermined length and the optical fiber 2a is exposed.

  The connector 3 includes a substantially cylindrical connector body 31 and a cap 32 provided so as to cover one end (also referred to as a connection end) of the connector body 31. The connector main body 31 has a mounting hole 31a penetrating in the axial direction. At the other end of the connector body 31, a receiving port 31b for receiving the end of the cable 2 is formed, and this receiving port 31b communicates with the mounting hole 31a. A cylindrical sapphire chip 33 is provided coaxially with the connector main body 31 at the opening on the connection end side of the mounting hole 31a. A highly reflective film 34 is provided on the end face of the sapphire chip 33 on the connection end side.

  The end of the cable 2 is inserted into the mounting hole 31a of the connector main body 31 from the receiving port 31b, and the end of the cable 2 is embedded and fixed in the connector main body 31 with resin. The exposed optical fiber 2 a is inserted into the sapphire chip 33, and is held in a state where the tip protrudes toward the connection end side of the sapphire chip 33.

  The cap 32 has a cylindrical cover 32a and a quartz glass 32b (optical substrate) that closes an opening at one end of the cover 32a, and has a bottomed cylindrical appearance. The cap 32 is attached to the connection end of the connector main body 31 from the opening side, and covers the tip of the bare optical fiber 2a. A laser beam is transmitted from the tip of the optical fiber 2a by entering or exiting through the quartz glass 32b.

  Antireflection films 4 are provided on both surfaces of the quartz glass 32b and the tip of the optical fiber 2a, on which the high energy laser beam is incident or emitted, so as to cover the respective surfaces.

Since the quartz glass 32b and the optical fiber 2a on which the antireflection film 4 is provided are mainly composed of silicon dioxide (SiO ₂ ), the refractive index thereof is about 1.44. In general, the refractive index of the quartz glass 32b or the like is lower than that of the material used for the antireflection film 4. Thus, when the refractive index of a base material is low, when designing the low-reflective antireflection film 4 having a reflectance of 0.25% or less, the material and structure are limited, so that the film design is difficult. .

  In addition, when the output of the laser used is high, it is easily damaged by heat or the like, and high laser resistance is required. In particular, when a laser is continuously output at a high frequency, it is easily affected by heat and countermeasures are required.

  For this reason, no suitable material is found in the single-layer structure, and when the low-reflective antireflection film 4 is formed using only silicon dioxide or aluminum oxide, which is an antireflective film material that is relatively excellent in laser resistance, four layers are formed. The above multilayer structure is required. However, when the antireflection film 4 has a multi-layer structure, the laser resistance is lowered, so that the characteristics of these materials cannot be utilized.

  Therefore, in the present embodiment, the intermediate layer 42 having excellent thermal conductivity is provided between the high refractive index lower layer 41 and the low refractive index upper layer 43 to form the antireflection film 4 having a three-layer structure. By doing so, a high level of laser resistance can be achieved while ensuring low reflectivity.

FIG. 2 shows a cross-sectional structure of the antireflection film 4. The antireflection film 4 has a three-layer structure, and includes a lower layer 41 formed on the quartz glass 32b and the optical fiber 2a, an intermediate layer 42 formed thereon, and an upper layer 43 formed thereon. Have. The lower layer 41 is formed using tantalum oxide (Ta ₂ O ₅ ), the intermediate layer 42 is formed using aluminum oxide (Al ₂ O ₃ ), and the upper layer 43 is formed using silicon dioxide (SiO ₂ ).

The lower layer 41 is not limited to tantalum oxide, but other highly flexible materials such as titanium oxide (TiO ₂ ), hafnium oxide (HfO ₂ ), niobium oxide (Nb ₂ O ₅ ), zirconium oxide (ZrO ₂ ), Scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), or the like may be used. The upper layer 43 is not limited to silicon dioxide, and other low-flexibility materials such as magnesium fluoride (MgF ₂ ) may be used.

  By using aluminum oxide for the intermediate layer 42, laser resistance, particularly heat resistance, can be improved. In other words, since aluminum oxide has excellent thermal conductivity, even if a high-power laser acts on the antireflection film 4 and heat is concentrated on a part of the aluminum oxide, the heat is efficiently dispersed around. Can do. Especially, when high-power laser is continuously irradiated, it is effective for continuous use of high-power laser because it can effectively relieve the concentration of heat in part, and realizes high laser resistance. it can.

  By using silicon dioxide for the upper layer 43, the manufacture becomes easy and the productivity is excellent. Further, since silicon dioxide has a high hardness and an excellent protective function, the durability of the antireflection film 4 is also improved.

  The lower layer 41 can be designed to have a thickness of, for example, about 30 to 50 nm, the intermediate layer 42 can have a thickness of, for example, about 10 to 100 nm, and the upper layer 43 can have a thickness of, for example, about 150 to 250 nm. What is necessary is just to design the combination of the film thickness of each layer suitably according to the reflectance to obtain | require, the wavelength of the laser beam to be used, etc. For example, in the present embodiment, the reflectance may be designed to be 0.25% or less in accordance with the laser beam (basic wavelength of 1064 nm).

  However, the total film thickness is preferably designed not to exceed 310 nm. If it is 310 nm or less, the influence of impurities can be reduced and high laser resistance can be obtained. Further, the film thickness of the intermediate layer 42 is preferably at least 100 nm or less, and more preferably thinner. By doing so, high laser resistance can be obtained while ensuring low reflectivity.

A portion of the quartz glass 32b or the like on which the antireflection film 4 is provided has, for example, an area of 0.008 to 8000 mm ² and is processed into a flat surface or a curved surface. In addition, this portion may be subjected to processing such as etching by a method such as sputtering or ion cleaning. The surface roughness when etching is performed is, for example, 5 to 10 Årms.

  Such an antireflection film 4 can be formed by using a conventional method such as a vacuum vapor deposition method, an ion assist vapor deposition method, a sputter vapor deposition method, an ion plating vapor deposition method, or a sol-gel method.

(Example)
The antireflection film 4 of the present embodiment was subjected to an evaluation test for laser resistance.

[sample]
In producing each sample used for the evaluation test, quartz glass was used as a base material, and a film design capable of obtaining a reflectance of 0.25% with respect to a laser beam having a fundamental wavelength of 1064 nm was set as a basic condition. While adjusting the film thicknesses so as to satisfy this basic condition, the film thickness of the intermediate layer 42 was changed to produce five types of antireflection films (Examples 1 to 5). Table 1 shows the film configurations of Examples 1 to 5.

  For comparison, an antireflection film having a four-layer structure was produced using only silicon dioxide and aluminum oxide under the same basic conditions as in Examples (Comparative Example 1). The antireflection film of Comparative Example 1 is composed of a first layer of aluminum oxide, a second layer of silicon dioxide, a third layer of aluminum oxide, and a fourth layer of silicon dioxide in this order from the substrate side. The film configuration of Comparative Example 1 is shown in Table 2.

[Laser endurance test]
As a laser resistance test method for this type of optical thin film, a test (1-on-1 test) for obtaining the minimum energy value at which damage is caused by irradiating a laser beam once on a sample, or a plurality of samples. There is a test (ISO 11254) in which each of the locations is irradiated with a laser a plurality of times to check the presence or absence of damage, and an energy value at which damage is not generated stochastically is obtained. For example, when it irradiates 100 times, it is called a 100-on-1 test.

  When the laser works continuously as in the laser guide 1 described above, the latter test is closer to the actual situation. Therefore, in this test, the laser was irradiated 6000 times on each of the 10 locations of each sample. Then, a test for examining the presence or absence of damage was performed (6000-on-1 test).

Specifically, as shown in FIG. 3, the same energy value (J / cm ²⁾ is obtained 6000 times in about 10 minutes in each of the 10 irradiation sites 50 a on the antireflection film forming surface 50 of each sample. ) Was irradiated. A plurality of similar laser irradiations were continuously performed while changing the energy value. A Q-switched YAG laser having a pulse width of about 20 ns was used as the light source of the laser L to be irradiated.

FIG. 4 shows a graph representing the test results. In the figure, the vertical axis represents the damage probability (%), and the horizontal axis represents the laser energy value (J / cm ² ). As shown in the figure, Examples 1-5 all showed higher laser resistance than Comparative Example 1.

For example, in Comparative Example 1, the damage probability is 10% at an energy value of about 25 J / cm ² , and the damage probability reaches 100% when the energy value exceeds 40 J / cm ^2. Then, no damage is observed even at 40 J / cm ² , and the damage probability is 100% when the speed reaches 60 J / cm ² . Even in comparison with Example 5 where the laser resistance was the lowest among the examples, in Example 5, the damage reached about 30 J / cm ² and about 10% was observed, whereas in Comparative Example 1, Over 70% of damage was already observed at the same energy level. Differences in these results are presumed to be due to the fact that each example had a smaller number of layers than the comparative example 1, and the number of interfaces and the total film thickness were reduced.

  Based on this result, judging from the film thickness configurations of Examples 1 to 5, it is found that the intermediate layer 42 is preferably designed to be 100 nm or less, and the total film thickness is preferably designed to be 310 nm or less. If it does so, laser resistance can be improved, ensuring low reflectivity.

  In particular, Examples 1 and 2 showed higher laser resistance than Examples 3-5. This is presumed to be due to the fact that Examples 1 and 2 have a smaller total film thickness than Examples 3-5. Further, even if the intermediate layer 42 is thin, the intermediate layer 42 can sufficiently exhibit its thermal conductivity, so that it may be 30 nm or less, and the total thickness of the antireflection film is more preferably designed to be 295 nm or less.

  FIG. 5 shows the result of comparing the laser resistance of Example 1 with a two-layer antireflection film (antireflection film previously proposed by the present applicant, Comparative Example 2). Comparative example 2 was also produced under the same basic conditions as in each example, and the same material as in the example was used for lower layer 41 and upper layer 43 thereof. Comparative Example 2 is significantly different from Example 1 in that the intermediate layer 42 is not provided. Table 3 shows the film configuration of the antireflection film of Comparative Example 2.

As shown in the figure, the damage threshold at which the damage probability is 0% was the same (40 J / cm ² ) in Example 1 and Comparative Example 2. However, when the energy value of the irradiated laser beam was increased, the damage probability of Example 1 was smaller than that of Comparative Example 2. In particular, when the energy value was high, it was confirmed that Example 1 was superior in laser resistance. This is presumably because the heat concentration of the antireflection film was alleviated by providing the aluminum oxide intermediate layer 42 excellent in thermal conductivity.

  In this test, a laser that irradiates intermittently was used as the light source of the high-power laser. Therefore, the above results are obtained when the thermal effect is relatively small among high-power lasers, and the antireflection film of the present invention is applied to a type of laser that is continuously irradiated, such as a CW laser. When applied, it is presumed to be even more effective.

2a Optical fiber (optical substrate)
4 Antireflection film 32b Quartz glass (optical substrate)
41 Lower layer 42 Middle layer 43 Upper layer

Claims (2)

A cable whose core is made of optical fiber;
A connector provided at an end of the cable;
With
Inside the connector, held in a state where the tip of the optical fiber protrudes,
The tip of the optical fiber is covered by the glass installed in the connector,
An optical component for machining in which a high-power laser enters or exits the tip of the optical fiber through the glass,
An antireflection film having a three-layer structure is provided on the surface of at least one of the glass and the tip of the optical fiber,
The antireflection film is
A lower layer having a film thickness of 30 to 50 nm formed using Ta ₂ O ₅ on the optical substrate;
An intermediate layer having a thickness of 10 to 100 nm formed using Al ₂ O ₃ on the lower layer;
An upper layer having a thickness of 150 to 250 nm formed using SiO ₂ on the intermediate layer;
Have
The total film thickness of the antireflection film is designed to be 295 nm or less,
Energy value of the high output laser, optical components for machining at least 20 J / cm ² or more. In the optical component for machining according to claim 1,
Optics for machining the thickness of the intermediate layer is set below 30 nm.

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