WO2006092949A1 - Optical element with laser damage suppression film - Google Patents

Abstract

An optical element having a laser damage suppression film which is capable of withstanding high power blue laser and formed on a plastic substrate. Specifically disclosed is an antireflection optical element wherein a multilayer film, which is composed of low refractive index material layers (105) and high refractive index material layers (107) arranged alternately, is formed on a plastic substrate. In this antireflection optical element, the oxygen permeability coefficient is decreased such that variation in laser permeability is 2% or less after being continuously irradiated with blue laser having an energy density of 120 mW/mm2 for 1000 hours at an ambient temperature of 25°C. In one embodiment, the oxygen permeability coefficient is set at 30 cm3·mm/(m2·24hr·atm) or less.

Description

 Specification

 Optical element having laser damage suppressing film

 Technical field

The present invention relates to an optical element having a damage suppression film on a substrate made of a blue laser compatible plastic material. In particular, the present invention relates to an optical element having a laser damage suppression film used for a blue laser with a short wavelength and a pi power (30 mWZmm ² or more).

 Background art

 [0002] Short wavelength, high power blue lasers are expected to be used more and more widely in optical pickups and the like. Plastics are generally susceptible to laser damage. Therefore, some of the optical components in devices that use short-wavelength, high-power blue lasers use glass rather than plastic to avoid laser damage. For this reason, the price of the device is relatively high, which is an obstacle to expanding the plant.

 [0003] At present, plastic materials that can handle a relatively low-power blue laser have the power of each material manufacturer. There is no plastic material that can withstand a high-power blue laser.

 [0004] On the other hand, an antireflection film is often formed on the surface of a plastic lens used in a video camera, a still camera, glasses, or the like. Such an antireflection film is formed of a multilayer film in which low refractive index layers and high refractive index layers are alternately laminated. Such multilayer films are disclosed in JP-A-11-30703, JP-A-11-171596, JP-A-11 326634, JP-A-2002-71903, JP-A-2003-98308 and JP-A-2003-.

This is described in, for example, 248102. However, conventional anti-reflection coatings cannot prevent damage from high-power blue lasers.

[0005] Since there is no plastic material that can withstand high-power blue lasers, if an optical element that can withstand high-power blue lasers is to be realized with plastic materials, a laser damage suppression film such as an anti-reflective film is required. A method of forming on the surface of a substrate that also has plastic material strength can be considered. Disclosure of the invention

 [0006] Under the above background art, there is a need for an optical element provided with a laser damage suppression film on a plastic substrate that can withstand a high-power blue laser.

[0007] An optical element according to the present invention is an antireflection optical element comprising a multilayer film in which a layer made of a low refractive material and a layer having a high refractive material force are alternately laminated on a plastic substrate. The oxygen transmission coefficient is reduced so that the laser transmittance change after continuous irradiation with a blue laser with an energy density of 120 mWZmm ² at an ambient temperature of 25 ° C is 2% or less.

 [0008] Since the optical element according to the present invention has a small oxygen transmission coefficient, it is not easily damaged by blue laser irradiation.

 Brief Description of Drawings

 FIG. 1 is a diagram showing a configuration of an optical element provided with a laser damage suppressing film according to one embodiment of the present invention.

 FIG. 2 is a diagram showing the result of measuring the light intensity change rate of an optical element after irradiating the optical element with a blue laser for 1000 hours.

 FIG. 3 is a diagram showing the result of measuring the total wavefront aberration (RMS) of the optical element before and after irradiating the optical element with a blue laser for 1000 hours.

 FIG. 4 is a diagram showing a configuration of an ion plating apparatus for performing an ion plating method.

 FIG. 5 is a diagram showing the amount of change in light transmittance of an optical element in which a conventional film is formed on a conventional substrate and an optical element in which improvement films 1 and 2 are formed on a conventional substrate.

 FIG. 6 is a diagram showing oxygen transmission coefficients of an optical element in which a conventional film is formed on a conventional substrate and an optical element in which improvement films 1 and 2 are formed on a conventional substrate.

 [Fig. 7] A diagram showing the change in the amount of chemiluminescence after irradiation with a blue laser on an optical element in which a conventional film is formed on a conventional substrate and an optical element in which an improvement film 1 is formed on a conventional substrate, and then stopped. is there.

 FIG. 8 is an enlarged view of a part of the time axis in FIG.

 FIG. 9 is a view showing a change in light transmittance between a conventional substrate and a nitrogen molded substrate.

[Figure 10] A conventional substrate and a nitrogen-molded substrate with a wavelength of about 280 nm when excited at a wavelength of 280 nm. It is a figure which shows the light emission amount.

 FIG. 11 is a diagram showing a change in light transmittance between an optical element in which the improvement film 1 is formed on a conventional substrate and an optical element in which the improvement film 1 is formed on a nitrogen-molded substrate.

 BEST MODE FOR CARRYING OUT THE INVENTION

 FIG. 1 is a diagram showing a configuration of an optical element provided with a laser damage suppressing film according to one embodiment of the present invention. In FIG. 1, a layer 103 made of monoacidic silicon (SiO) is formed on a substrate 101 that also has a plastic material strength for blue laser. The layer 103 made of silicon monoxide fulfills a function of improving the adhesion between the substrate 101 having plastic material strength and the layer formed thereon. On the layer 103 made of an oxide layer, layers 105 made of a low refractive material and layers 107 made of a high refractive material cover are alternately laminated. In this embodiment, three layers 105 made of a low refractive material cover and three layers 107 made of a high refractive material cover are formed.

 Here, the blue laser compatible plastic material is an olefin-based material. More specifically, it is a thermoplastic transparent olefin cycloolefin polymer having a function of preventing acidification.

 The layer 103 made of silicon monoxide is formed on the substrate 101 by a vacuum deposition method. In the vacuum evaporation method, a material to be formed into a thin film (in this case, silicon monoxide) is heated with a resistance wire, or the material is irradiated with an electron beam and evaporated by heating. The evaporated material is deposited (deposited) on the substrate to form a thin film. The thickness of the layer 103 made of silicon monoxide is about several hundred nanometers.

 [0013] The low refractive index material is silicon dioxide (SiO 2) in the present embodiment. From silicon dioxide

 2

 The refractive index of the layer 105 is 1.4-1.5. The layer 105, which is also composed of diacid oxide, is formed by vacuum evaporation. The thickness of the layer 105, which is also a diacid key, is several tens to several hundreds of nanometers.

In the present embodiment, the high refractive index material is made of tantalum pentoxide (Ta 2 O 3) and titanium dioxide (TiO 2).

 2 5 2

). The refractive index of the layer 107, which mainly consists of tantalum pentoxide, is 2.0-2.3. The layer 107 mainly composed of tantalum pentoxide force is formed by an ion plating method. The ion plating method uses gas plasma to ionize a part of evaporated particles and deposit it on a substrate biased at a negative high voltage. Since the vapor deposition material is accelerated by the electric field and adheres to the substrate, a film having a strong adhesion can be obtained. Mainly tantalum pentoxide The thickness of the layer 107 made of aluminum is several tens of nanometers to several hundreds of nanometers.

[0015] As the material of the layer 107, a material in which the values of x and y of TaO are appropriately determined can be used.

[0016] As the high refractive index material, an acid titanium-based material can also be used.

 [0017] By alternately laminating layers having different refractive indexes, a large number of reflection surfaces are formed, and external light reflected by the large number of reflection surfaces interferes with each other to cancel each other, thereby obtaining an antireflection effect. It may be. In addition, the optical path length (= layer thickness / refractive index) of each layer is made different so that interference occurs in a wide wavelength range so that an antireflection effect can be obtained in a wide and wavelength range of outside light. Good. In this way, the multilayer film may have an antireflection function in addition to the laser damage suppressing function.

 FIG. 4 is a diagram showing a configuration of an ion plating apparatus for performing the ion plating method. An ion plating apparatus is disclosed in, for example, Japanese Patent Publication No. 1-48347. In the vacuum chamber 412, a capacitor 406 is formed by a base material holder 407, which is a conductive member supporting the base material 408, and a support member, which is a conductive member supporting the base material holder via an insulating member. Is configured.

 A high-frequency power source 401 is connected between the vacuum chamber 412 and the base material holder 407 via a blocking capacitor 403 and a matching box 402 to supply a high-frequency voltage. A DC power supply 404 is connected between the vacuum chamber 412 and the substrate holder 407 via a choke coil 405 so that the substrate holder 407 side becomes a cathode, and a DC noise voltage is supplied. The output of the high frequency power supply 401 is 500 W, and the voltage of the DC power supply 404 is 10 OV.

 [0020] The output of the high frequency power supply 401 is preferably a power S of 300-900W. By adjusting the output value within this range, the denseness of the film can be increased.

[0021] Capacitor 406 force By operating together with a matching box 402 connected to a high-frequency power source 401 that supplies a high-frequency voltage into the chamber 412 to perform matching, the evaporation material 409 on the resistance heating board 410 and the base A stable electric field can be formed and maintained with the material 408. As a result, a high-purity 'high density' and high adhesion thin film can be formed on the surface of the substrate 408. [0022] At the bottom of the crucible including the resistance heating board 410, there is an electron gun 4 for electron beam heating.

101 is installed.

The outline of the film forming method is shown in the following table.

 [table 1]

“No plasma generation” refers to the case where the high frequency power supply 401 and the DC power supply 404 are not used. In this case, the film is formed by a vacuum deposition method.

[0025] Here, RH is resistance heating, and EB is electron beam heating.

[0026] During film formation, oxygen is introduced into the vacuum chamber 412 by a valve (not shown).

 The oxygen introduction pressure setting is a setting of the oxygen pressure of the chamber. Oxygen partial pressure is 3.0 X 10

A it is preferably in the range of ~5.0 X 10- ² Pa. By adjusting the oxygen partial pressure value within the above range, the light intensity change rate of the optical element described later can be set to an appropriate value. The gas in the vacuum chamber 412 is exhausted from the exhaust port 411.

In order to compare with the optical element of the embodiment shown in FIG. 1, two types of optical elements (Comparative Examples 1 and 2) shown in Table 2 below were prepared.

[Table 2] This embodiment Comparative example 1 Comparative example 2 Substrate material Blue laser vs. J core Blue laser vs. J core

 PM MA plastic

 Plastic Plastic High refractive index material layer

 Ion plating method Ion plating method Vacuum deposition method

[0028] Furthermore, as Comparative Example 3, an optical element including a blue laser compatible plasticizer having no surface coated was also prepared.

[0029] FIG. 2 is a diagram showing the results of measuring the light intensity change rate of the optical element after irradiating the optical element with a blue laser for 1000 hours at an ambient temperature of 25 ° C. Energy density of the blue laser radiation is about 120mWZmm ^2. Here, the light intensity change rate of the optical element can be expressed by the following equation.

 [0030] Light intensity change rate = ((transmission after irradiation Z transmission before irradiation) 1) · 100%

 As an example, if the transmittance before irradiation is 90% and the transmittance after irradiation is 80%, the rate of change in light intensity is

 ((0. 80/0. 90)-1) 100 = —11. 1%

 It becomes.

 FIG. 2B shows the measurement result of the light intensity change rate of the optical element of the present embodiment. A in FIG. 2 shows the measurement result of the light intensity change rate of Comparative Example 1. C in FIG. 2 shows the measurement result of the light intensity change rate of Comparative Example 2. D of FIG. 2 shows the measurement result of the light intensity change rate of the optical element of Comparative Example 3. The optical element of Comparative Example 3 was irradiated with a blue laser in a nitrogen atmosphere.

[0032] FIG. 3 is a diagram showing the results of measuring the total wavefront aberration (RMS) of the optical element before and after irradiating the optical element with a blue laser for 1000 hours at an ambient temperature of 25 ° C. The energy density of the blue laser radiation is about 120mWZmm ^2.

 [0033] The total wavefront aberration is a deviation of the wavefront from the reference spherical surface expressed as a standard deviation.

Here, the reference spherical surface refers to a spherical surface that takes the principal ray as the center and intersects the optical axis at the center of the entrance and exit pupils. The total wavefront aberration is measured by generating an interference fringe with an interferometer. Map force of fringes Calculates wavefront aberration.

 In FIG. 3, Β1 and Β2 show the measurement results of the total wavefront aberration of the optical element of the present embodiment.

 Α1 and Α2 in Fig. 3 show the measurement results of total wavefront aberration in Comparative Example 1. C1′C2 in FIG. 3 shows the measurement result of the total wavefront aberration of Comparative Example 2. D1 'D2 in Fig. 3 shows the measurement result of the total wavefront aberration of the optical element of Comparative Example 3. The optical element of Comparative Example 3 was irradiated with a blue laser in a nitrogen atmosphere. Al, Bl, Cl, and D1 show the measurement results of total wavefront aberration before blue laser irradiation, and A2, B2, C2, and D2 show the measurement results of total wavefront aberration after blue laser irradiation.

 [0035] The following points become clear from the measurement results of FIGS. In the case of the present embodiment, the light intensity hardly changes even when irradiated with a high-power blue laser for 1000 hours. Also, the total wavefront aberration hardly changes before and after irradiation.

 [0036] The light intensity change rate is about 10% in Comparative Example 1 (A in FIG. 2), about 20% in Comparative Example 2 (C in FIG. 2), and about 20% in Comparative Example 3 (D in FIG. 2). Decrease by about 5%. The light intensity change is large in the case of Comparative Example 2 (C in Fig. 2) without using the ion plating method to form the high refractive index material layer! That is, the light transmission intensity of the optical element is greatly reduced. The reason why the light transmission intensity of the optical element decreases is that, when a high-power blue laser is irradiated for a long time, the chemical bond of the polymer plastic is broken (damaged) and the bonding state changes. it is conceivable that. If ion plating is used to form the high refractive index material layer, the above damage can be suppressed.

 [0037] When the uncoated optical element of Comparative Example 3 is placed in a nitrogen atmosphere, the decrease in light transmission intensity is relatively small. This suggests that substances other than nitrogen present in the air accelerate the damage to the optical element. Therefore, it is considered that the rate at which substances in the air that accelerate damage to the optical element are mixed into the optical element can be reduced by using the ion plating method for forming the high refractive index material layer.

[0038] The total wavefront aberration after irradiation with the high-power blue laser is about 2.5 times in the case of Comparative Example 1 (Α1 and Α2 in Fig. 3) using PMMA plastic for the substrate. In the case of Comparative Examples 2 and 3, the total wavefront aberration after irradiating the same blue laser is almost unchanged. Because of this, optical elements using blue laser plastic In this case, it is considered that the shape of the surface of the optical element hardly changes. On the other hand, in the case of an optical element using PMMA plastic, the shape of the optical element surface changes, so the total wavefront aberration is thought to increase.

 [0039] In the above embodiment, the film is formed by the ion plating method! /, And the plasma state is generated by the 1S plasma CVD method, the ion beam assisted vapor deposition method, the sputtering method, or the like. Do film formation.

 [0040] The present invention is characterized in that a film is formed on a blue laser plastic material substrate by a method of generating plasma such as an ion plating method.

 [0041] Due to this feature, the above-described remarkable effect is produced in suppressing damage to the optical element by the laser. The mechanism that produces this effect is considered as follows.

 [0042] A catalytic action that creates a function having an oxidative decomposition ability from moisture and oxygen uses a substrate that is a thermoplastic transparent olefin cycloolefin polymer having an antioxidant function, and is based on an ion plating method. It is thought to be suppressed by improving the film density by forming a film (forming an oxygen-impermeable film). Therefore, it can be estimated that substrate damage due to blue laser light is suppressed. The grounds for this estimation are also expected from the measurement results of the rate of change of light intensity when laser irradiation experiments are performed in a nitrogen atmosphere (D in Fig. 2). In addition, it is considered that the use of an acid-italic tantalum material further improves the film density in the film formation by the ion plating method.

 [0043] As another embodiment, a multilayer film formed by the following film forming method will be described. A multilayer film formed by this film forming method is referred to as an improvement film 1.

[Table 3]

02 Introduction Ar introduction Deposition time

 Deposition rate Plasma Film configuration Pressure setting Pressure setting Film thickness (guideline) (min) Evaporation source

 Setting occurrence

(Pa) (Pa) (approximate)

 1st layer SiO 2.80E-02 3.0 A / S 2440 A 13.5 RH None

Second layer Si02 6.00E-03 10A / S 1650 A 2.8 With EB Tan oxide

 3rd layer Tal system 3.00E-02 3.0 A / S 125A 1.7 With EB Material

 4th layer Si02 6.00E-03 10A / S 300 A 0.6 EB Yes Tan oxide

 5th layer Tal system 3.00E-02 3.0 A / S 330 A 1.8 With EB Material

 6th layer Si02 6.00E-03 10A / S 630 A 1.0 With EB Total film thickness 5475 A

[0044] The film forming method shown in Table 3 is different from the film forming method shown in Table 1 in that a low refractive material layer made of diacidic silicon is formed while generating a plasma state in an argon atmosphere. Argon partial at the time of forming the low refractive index material layer pressure value ^{3.0 X 10- 3 ~5.0 X 10- ¥} a in the range and even not preferable for. When a low refractive material layer is formed while generating a plasma state in an argon atmosphere, the substrate is exposed to a high temperature environment (e.g. 85 ° C) or a high temperature and high humidity environment (e.g. 60 ° C 90%) for a long time. In any case, this is more advantageous than an oxygen plasma atmosphere in which there is almost no change in transmittance.

 As still another embodiment, a multilayer film formed by the following film forming method will be described. A multilayer film formed by this film forming method is referred to as an improvement film 2.

 [Table 4]

改善膜 2は、ー酸ィ匕ケィ素からなる密着層を含まず、基板上の 1層目に酸化タンタ ル系材料力 なる層を備えている。改善膜 1の合計膜厚は、 547. 5nmであるが、改 善膜 2の合計膜厚は、 182. Onmである。表面に微細構造が形成されている回折光 学素子では、膜厚が厚いと微細構造の形状への影響が大きくなる。改善膜 2は、膜 厚が薄いので、微細構造の形状への影響が小さい。

The improvement film 2 does not include an adhesion layer made of oxy-enzyme, and has a layer made of tantalum oxide-based material as the first layer on the substrate. The total film thickness of improvement film 1 is 547.5 nm. The total film thickness of good film 2 is 182. Onm. In a diffractive optical element having a fine structure formed on the surface, if the film thickness is thick, the influence on the shape of the fine structure increases. The improvement film 2 has a small film thickness and thus has little influence on the shape of the microstructure.

[0047] A multilayer film having a structure similar to that of the improvement film 1 formed by a vacuum deposition method that does not generate plasma is referred to as a conventional film.

[0048] A substrate made of a thermoplastic transparent olefin cycloolefin polymer, which is not a nitrogen-molded substrate described later, is referred to as a conventional substrate.

FIG. 5 is a diagram showing the light transmittance change amount of the optical element in which the conventional film is formed on the conventional substrate and the optical element in which the improvement films 1 and 2 are formed on the conventional substrate. The optical transmittance change amount of the optical element formed with the improvement films 1 and 2 is greatly improved compared to the optical transmittance change amount of the optical element formed with the conventional film.

 FIG. 6 is a diagram showing oxygen transmission coefficients of an optical element in which a conventional film is formed on a conventional substrate and an optical element in which improvement films 1 and 2 are formed on a conventional substrate. In general, the gas permeability coefficient can be expressed by the following equation.

 [0051] Gas permeation coefficient = Gas permeation (standard volume) X thickness

 Z (pressure difference X permeation area X hours)

In FIG. 6, the unit of the oxygen transmission coefficient is cm ³ 'mmZ (m ² '24hr'atm).

[0052] The oxygen transmission coefficient of the optical element in which the improved films 1 and 2 are formed on the conventional substrate is lower than the oxygen transmission coefficient of the optical element in which the conventional film is formed on the conventional substrate. An optical element in which the improvement films 1 and 2 are formed on the substrate is difficult to transmit oxygen.

As a result, it is assumed that when the optical element is irradiated with a blue laser, the deterioration of the substrate material is accelerated by a chemical reaction mediated by oxygen, and the amount of change in light transmittance is increased. In FIG. 2, this assumption is consistent with the fact that when the uncoated optical element of Comparative Example 3 is placed in a nitrogen atmosphere, the decrease in light transmission intensity is relatively small.

That is, by forming a multilayer film having a low oxygen permeability coefficient, it is possible to suppress the amount of change in light transmittance of the optical element.

[0055] Fig. 7 shows the change in the amount of chemiluminescence after the blue laser was irradiated to the optical element in which the conventional film was formed on the conventional substrate and the optical element in which the improvement film 1 was formed on the conventional substrate. In the figure shown is there. FIG. 8 is an enlarged view of a part of the time axis of FIG. In FIGS. 7 and 8, the amount of chemiluminescence shows the relative magnitude. For up to 20 seconds after the irradiation is stopped, the chemiluminescence amount of the optical element in which the conventional film is formed on the conventional substrate is larger than the chemiluminescence amount of the optical element in which the improvement film 1 is formed on the conventional substrate. Chemiluminescence is believed to be caused by oxygen-mediated reactions. The optical element with the improved film 1 formed on the conventional substrate has a smaller oxygen transmission coefficient than the optical element with the conventional film formed on the conventional substrate, and is less likely to transmit oxygen. It is thought that the chemical reaction is suppressed.

 [0056] FIG. 9 is a diagram showing the amount of fluorescence emission between a conventional substrate and a nitrogen-molded substrate at a wavelength of about 320 nm when excited at a wavelength of 280 nm. The nitrogen-molded substrate is a substrate obtained by drying a thermoplastic transparent olefin cycloolefin polymer in nitrogen, transporting it in a nitrogen atmosphere, and molding it in the nitrogen atmosphere. In FIG. 9, the amount of fluorescent light emission is an arbitrary unit and indicates a relative size. Since the fluorescence emission is considered to be oxygen-mediated, the reason why the amount of fluorescence emission of the nitrogen-molded substrate is small is considered to be because the amount of oxygen absorbed is smaller than that of the conventional substrate.

 FIG. 10 is a diagram showing the amount of change in light transmittance between the conventional substrate and the nitrogen molded substrate. The amount of change in light transmittance of the nitrogen-shaped substrate is significantly smaller than the amount of change in light transmittance of the conventional substrate. Thus, the nitrogen molded substrate is less susceptible to damage from the blue laser irradiation than the conventional substrate.

 [0058] It is considered that damage caused by irradiation with a blue laser proceeds by an oxygen-mediated chemical reaction. Therefore, it is considered that a nitrogen-molded substrate is less susceptible to damage due to blue laser irradiation because it absorbs less oxygen than a conventional substrate.

 FIG. 11 is a diagram showing a change in light transmittance between an optical element in which the improvement film 1 is formed on a conventional substrate and an optical element in which the improvement film 1 is formed on a nitrogen-molded substrate. The amount of change in light transmittance can be kept very small by combining a low-oxygen absorption substrate with a nitrogen-molded substrate and an improved film 1 that hardly transmits oxygen.

Claims

The scope of the claims [1] An anti-reflective optical element comprising a multilayer film in which a layer having a low refractive material force and a layer having a high refractive material force are alternately laminated on a plastic substrate, for 1000 hours at an ambient temperature of 25 ° C. An optical element with a small oxygen transmission coefficient so that the change in laser transmittance after continuous irradiation with a blue laser with an energy density of 120 mWZmm ² is 2% or less. 2. The optical element according to claim 1, wherein the oxygen transmission coefficient is 30 cm ³ 'mmZ (m ² '24hr'atm) or less.  [3] The optical element according to [1] or [2], wherein the plastic substrate is molded in a nitrogen environment.  [4] The optical element according to any one of [1] to [3], wherein the highly refractive material is an acid-tantalum-based material.  [5] The optical element according to any one of [1] to [4], wherein the low-refractive-index material is nickel silicate. 6. The optical element according to any one of claims 1 to 5, wherein the layer made of a high refractive index material is formed under conditions that generate a plasma state. 7. The optical element according to any one of claims 1 to 6, wherein the layer made of a high refractive index material is the first layer on the substrate.