JP2018084140A - Window member, ignition device, and internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a window member that can reduce reflected light.SOLUTION: A protective member 212 serving as a window member comprises: a plate-like member 212a comprising a surface A on which light is incident, and a surface B from which the light incident on the surface A is emitted; and a dielectric film 213 provided on at least one of the surface A and the surface B of the plate-like member 212a. The dielectric film 213 includes a fine structure part 213b comprising a plurality of fine convex structures or fine concave structures. In this case, a reflectivity is gradually changed at an interface between the protective member 212 and a combustion chamber, and reflected light can be reduced.SELECTED DRAWING: Figure 17

Description

  The present invention relates to a window member, an ignition device, and an internal combustion engine, and more particularly to a window member disposed on an optical path of light, an ignition device having the window member, and an internal combustion engine including the ignition device.

  In recent years, various ignition devices using laser light have been studied as ignition devices in internal combustion engines such as engines.

  In Patent Document 1, laser light emitted from a laser device that generates laser light is transmitted through a condensing lens provided in a laser light path of a cylinder head and an incident transparent window into a combustion chamber, There has been disclosed a laser ignition engine configured to ignite fuel injected into the fuel chamber by generating plasma in the combustion chamber.

  Patent Document 2 discloses a laser ignition device in which a superhydrophilic film containing superhydrophilic particles and thermally excited catalyst particles is provided on the surface of a constituent member of an ignition plug facing a combustion chamber.

  In Patent Document 3, a protection optical window having a parallel plate shape is provided at a position facing the combustion chamber so that the pulse laser focusing optical element is isolated from the combustion chamber to protect the optical element. A laser igniter is disclosed in which the material is sapphire.

  Patent Document 4 discloses a laser ignition device having an optical system that condenses laser light emitted from a laser unit in a combustion chamber, and a plate of a translucent spinel sintered body is provided on an optical element constituting the optical system. A laser ignition device characterized by being used is disclosed.

  However, the conventional window member has room for improvement with respect to reduction of reflected light.

  The present invention is a window member disposed on an optical path of light, the plate member having an A surface on which the light is incident, and a B surface on which light incident on the A surface is emitted, and the plate And a dielectric film provided on at least one of the A surface and the B surface, and the dielectric film includes a microstructure having a plurality of convex or concave microstructures. It is a window member.

  According to the window member of the present invention, it is possible to reduce the reflected light.

It is a figure for explaining an outline of an engine concerning one embodiment of the present invention. It is a figure for demonstrating an ignition device. It is a figure for demonstrating a laser resonator. It is a figure for demonstrating the housing | casing of an ignition device. It is a figure for demonstrating the Example of a protection member. FIG. 6A is a diagram for explaining a plate-shaped member coated with a single-layer AR film, and FIG. 6B is a diagram for explaining a plate-shaped member coated with a two-layer AR film. FIG. It is a figure for demonstrating the thermal stress which arises in two-layer AR film. FIG. 8A and FIG. 8B are diagrams for explaining calculation models for obtaining the influence of the structure width on the reflectance, respectively. FIG. 9A and FIG. 9B are diagrams for explaining changes in the structure width. It is a figure for demonstrating the calculation result regarding the influence of the structure width on a reflectance. FIG. 11A and FIG. 11B are diagrams for explaining calculation models for obtaining the influence of the structure height on the reflectance, respectively. FIG. 12A and FIG. 12B are diagrams for explaining changes in the structural height. It is a figure for demonstrating the calculation result regarding the influence of the structure height on a reflectance. FIG. 14A and FIG. 14B are diagrams for explaining calculation models for obtaining the insertion effect of the Si ₃ N ₄ layer on the reflectance, respectively. FIGS. 15A and 15B are diagrams for explaining changes in the thickness of the inserted Si ₃ N ₄ layer. FIGS. 16A and 16B are diagrams for explaining calculation results regarding the insertion effect of the Si ₃ N ₄ layer on the reflectance, respectively. It is a figure for demonstrating the Example of a dielectric film. FIG. 18A and FIG. 18B are diagrams for explaining a procedure for forming a dielectric film. It is a figure for demonstrating the specific example 1 of a fine structure part. It is a figure for demonstrating the specific example 2 of a microstructure part. It is a figure for demonstrating the specific example 3 of a microstructure part. It is a figure for demonstrating reflection of the light in the protection member (only plate-shaped member) of a comparative example. It is a figure for demonstrating reflection of the light in the protection member of an Example. FIG. 24A and FIG. 24B are diagrams for explaining the effect of reducing reflected light in the protection member of the example. FIG. 25A is a schematic diagram for explaining the adhesion of dirt on the protective member (only the plate-like member) of the comparative example, and FIG. 25B shows the suppression of dirt adhesion on the protective member of the example. It is a schematic diagram for demonstrating. It is a figure for demonstrating the modification 1 of a fine structure part. It is a figure for demonstrating the modification 2 of a fine structure part. It is a figure for demonstrating Gaussian distribution. It is a figure for demonstrating the example 1 of a fine structure part area | region. It is a figure for demonstrating the example 2 of a fine structure part area | region. It is a figure for demonstrating the example 3 of a fine structure area | region. It is a figure for demonstrating an effective beam diameter. It is a figure for demonstrating the example 4 of a fine structure area | region. It is a figure for demonstrating the example 5 of a fine structure part area | region. FIG. 35A and FIG. 35B are diagrams for explaining the relationship between the length in the convex direction of the fine convex structure and the gradient of the refractive index change, respectively. It is a figure for demonstrating a 2nd condensing optical system. It is a figure for demonstrating the modification 1 of a protection member. FIG. 38A and FIG. 38B are diagrams for explaining a procedure for forming a dielectric film in the protection member of Modification Example 1, respectively. It is a figure for demonstrating the modification 2 of a protection member. It is a figure for demonstrating the modification 3 of a protection member. It is a figure for demonstrating the modification 4 of a protection member. It is a figure for demonstrating the modification 5 of a protection member. It is a figure for demonstrating the modification 6 of a protection member. It is a figure for demonstrating the case where a fine structure is a column shape. It is a figure for demonstrating the case where the flat part is not provided. It is a figure for demonstrating the case where a dielectric film is a multilayer film.

"Overview"
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a main part of an engine 300 as an internal combustion engine according to an embodiment.

  The engine 300 includes an ignition device 301, a fuel ejection mechanism 302, an exhaust mechanism 303, a combustion chamber 304, a piston 305, and the like.

The operation of engine 300 will be briefly described.
(1) The fuel ejection mechanism 302 ejects a combustible mixture of fuel and air into the combustion chamber 304 (intake).
(2) The piston 305 rises and compresses the combustible air-fuel mixture (compression).
(3) The ignition device 301 emits laser light into the combustion chamber 304. Thereby, the fuel is ignited (ignition).
(4) Combustion gas is generated and the piston 305 descends (combustion).
(5) The exhaust mechanism 303 exhausts the combustion gas to the outside of the combustion chamber 304 (exhaust).

  Thus, a series of processes consisting of intake, compression, ignition, combustion, and exhaust are repeated. Then, the piston 305 moves in response to a change in the volume of the gas in the combustion chamber 304 to generate kinetic energy. For example, natural gas or gasoline is used as the fuel.

  Engine 300 performs the above operation based on an instruction of an engine control device that is provided outside engine 300 and is electrically connected to engine 300.

  As shown in FIG. 2 as an example, the ignition device 301 includes a laser device 200, an emission optical system 210, a protection member 212, and the like.

  The emission optical system 210 condenses the light emitted from the laser device 200. Thereby, a high energy density can be obtained at the condensing point.

  The protection member 212 is a transparent window provided facing the combustion chamber 304. Here, as an example, sapphire glass is used as the material of the protection member 212.

  The laser device 200 includes a surface emitting laser array 201, a first condensing optical system 203, an optical fiber 204, a second condensing optical system 205, and a laser resonator 206. In the present specification, description will be made using the XYZ three-dimensional orthogonal coordinate system and assuming that the light emission direction from the surface emitting laser array 201 is the + Z direction.

  The surface emitting laser array 201 is an excitation light source and has a plurality of light emitting units. Each of the light emitting units is a vertical cavity surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser). The wavelength of light emitted from the surface emitting laser array 201 is 808 nm.

  The surface-emitting laser array is a light source that is advantageous for exciting a Q-switched laser whose characteristics change greatly due to a shift in excitation wavelength because the wavelength shift of emitted light due to temperature is very small. Therefore, when a surface emitting laser array is used as an excitation light source, there is an advantage that environmental temperature control can be simplified.

  The first condensing optical system 203 condenses the light emitted from the surface emitting laser array 201.

  The optical fiber 204 is arranged so that the center of the end face on the −Z side of the core is located at a position where the light is collected by the first condensing optical system 203. Here, as the optical fiber 204, an optical fiber having a core diameter of 1.5 mm and an NA of 0.39 is used.

  By providing the optical fiber 204, the surface emitting laser array 201 can be placed at a position away from the laser resonator 206. Thereby, the freedom degree of arrangement design can be increased. Further, when the laser device 200 is used as an ignition device, the surface emitting laser array 201 can be moved away from the heat source, so that the range of methods for cooling the engine 300 can be increased.

  The light incident on the optical fiber 204 propagates through the core and is emitted from the + Z side end face of the core.

  The second condensing optical system 205 is disposed on the optical path of the light emitted from the optical fiber 204 and condenses the light. The light condensed by the second condensing optical system 205 enters the laser resonator 206.

  The laser resonator 206 is a Q-switched laser and includes a laser medium 206a and a saturable absorber 206b as shown in FIG. 3 as an example.

  The laser medium 206a is a rectangular parallelepiped Nd: YAG crystal, and Nd is doped by 1.1%. The saturable absorber 206b is a rectangular parallelepiped Cr: YAG crystal, and the initial transmittance is appropriately adjusted between 0.15 (15%) and 0.70 (70%).

  Here, the Nd: YAG crystal and the Cr: YAG crystal are joined to form a so-called composite crystal. Both the Nd: YAG crystal and the Cr: YAG crystal are ceramics.

  The light from the second condensing optical system 205 is incident on the laser medium 206a. That is, the laser medium 206a is excited by the light from the second condensing optical system 205. The wavelength of the light emitted from the surface emitting laser array 201 is the wavelength with the highest absorption efficiency in the YAG crystal. The saturable absorber 206b operates as a Q switch.

  The surface on the incident side (−Z side) of the laser medium 206a and the surface on the exit side (+ Z side) of the saturable absorber 206b are subjected to an optical polishing process and serve as a mirror. Hereinafter, for convenience, the incident-side surface of the laser medium 206a is also referred to as a “first surface”, and the exit-side surface of the saturable absorber 206b is also referred to as a “second surface” (see FIG. 3).

  The first surface and the second surface are coated with a dielectric film corresponding to the wavelength of light emitted from the surface emitting laser array 201 and the wavelength of light emitted from the laser resonator 206. .

  Specifically, the first surface is coated with a high transmittance for light having a wavelength of 808 nm and a high reflectance for light having a wavelength of 1064 nm. The second surface is coated with a reflectance of about 50% for light having a wavelength of 1064 nm.

  As a result, the light resonates and is amplified in the laser resonator 206.

  Returning to FIG. 2, the driving device 220 drives the surface emitting laser array 201 based on an instruction from the engine control device 222. That is, drive device 220 drives surface emitting laser array 201 so that light is emitted from ignition device 301 at the timing of ignition in the operation of engine 300. The plurality of light emitting units in the surface emitting laser array 201 are turned on and off simultaneously.

  In the above embodiment, when it is not necessary to place the surface emitting laser array 201 at a position away from the laser resonator 206, the optical fiber 204 may not be provided.

  Here, the case of an engine (piston engine) in which a piston is moved by combustion gas as an internal combustion engine has been described. However, the present invention is not limited to this. For example, a rotary engine, a gas turbine engine, or a jet engine may be used. In short, what is necessary is just to burn the fuel and generate the combustion gas.

  In addition, the ignition device 301 may be used for cogeneration, which is a system that uses exhaust heat to extract power, heat, and cold to improve energy efficiency comprehensively.

  Although the case where the ignition device 301 is used in an internal combustion engine has been described here, the present invention is not limited to this.

  Although the case where the laser device 200 is used in an ignition device has been described here, the present invention is not limited to this. For example, it can be used for a laser processing machine, a laser peening apparatus, a terahertz generator, and the like.

"Details"
At present, ignition of a combustible air-fuel mixture introduced into a combustion chamber in an internal combustion engine is mainly performed by an ignition plug, that is, spark ignition by a discharge method. However, in spark ignition, due to the configuration of the spark plug, the electrode is exposed in the combustion chamber, so that the electrode is inevitably consumed.

  On the other hand, in laser ignition in which ignition is performed by condensing laser light, no electrode is required and the electrode is not exposed in the combustion chamber of the internal combustion engine. Therefore, it is not necessary to consider the consumption of the electrodes, and the life of the ignition device can be expected to be extended.

  As shown in FIG. 4 as an example, the ignition device 301 has a casing 214 in which the laser device 200 and the emission optical system 210 are accommodated. The casing 214 protects the laser device 200 and the injection optical system 210 from high temperature and high pressure in the combustion chamber and contamination due to fuel, soot, and the like.

  A protective member 212 as a window member is provided in the housing 214 at a position that does not obstruct the path of the laser light emitted from the laser device 200 and collected by the emission optical system 210. In other words, the protection member 212 is provided on the housing 214 on the optical path of the laser light via the emission optical system 210.

  As shown in FIG. 5 as an example, the protection member 212 is a plate-like member 212a on which light from the emission optical system 210 is incident, and the surface of the plate-like member 212a on the combustion chamber 304 side (here, + Z side). It has a dielectric layer 213 provided thereon.

  In the following, for convenience, the surface on the emission optical system 210 side (here, −Z side) of the plate-like member 212a is also referred to as “A surface”, and the surface on the combustion chamber 304 side (here, + Z side) is “ Also referred to as “B side”.

  Generally, in an engine, engine oil is used to reduce friction of a piston and the like, and an oil mist that is atomized in the combustion chamber floats. For this reason, if the protective member is only a plate-like member, oil mist adheres to the -Z side surface of the plate-like member. And when the ash, soot, etc. accumulate and form a deposit, the light quantity of the laser beam inject | emitted from an ignition device may fall, and there exists a possibility that ignition stability may be impaired.

  As the material of the plate member, optical glass, heat-resistant glass, quartz glass, sapphire glass, etc. are generally used. In particular, the plate-like member needs to have sufficient pressure resistance in order to protect the optical member and the like inside the housing from the combustion pressure generated in the combustion chamber. Therefore, it is conceivable to increase the thickness of the plate-like member. However, when the thickness of the plate-like member is increased, the laser beam reflected by the emission end face of the plate-like member is easily collected inside the plate-like member. . In order to suppress light condensing inside the plate member, it is necessary to increase the focal length of the emission optical system.

  When the focal length of the emission optical system is increased, the numerical aperture (NA) of the lens is reduced. And electric field intensity | strength (light collection intensity | strength) falls and ignitability falls. Therefore, the thickness of the plate member is preferably as thin as possible. Therefore, it is conceivable to use sapphire glass having a high pressure resistance as the material of the plate member.

  However, since the refractive index of sapphire glass is 1.74, which is higher than that of optical glass, heat-resistant glass, and quartz glass (refractive index = 1.46), the amount of reflected light generated in sapphire glass is that of other glasses. Doubled. Therefore, even if the thickness is reduced by using sapphire glass as the plate-like member, the laser light reflected by the surface on the + Z side of the plate-like member is easily condensed inside the emission optical system or the plate-like member. .

  If there is a plate-like member or emission optical system in the vicinity of the reflected light condensing position, the energy of the reflected light concentrates on that part, generating plasma or shock waves, and cracking occurs in the plate-like member or emission optical system. Or the AR coating film applied to the surface of the emission optical system may be peeled off.

  Further, when dirt is attached to the surface of the plate-like member, the dirt-attached portion becomes a pseudo mirror, and a part or all of the laser light from the laser device is reflected by the pseudo mirror to be in the ignition device. In the same way, there is a risk of damaging the optical member.

  Further, the laser light reflected by the plate-like member may affect the optical member that is coaxial with the surface emitting laser array as return light, and may change the light intensity of the laser light.

  In order to solve these disadvantages, it is conceivable to coat the plate-like member with an anti-reflection (AR) film made of an optical multilayer film.

  Here, the coating of the antireflection film on the surface on the + Z side of the plate-like member will be described. Hereinafter, for convenience, the light reflection preventing film is also referred to as an “AR film”.

6A shows a plate-like member 212a coated with a single-layer AR film 215, and FIG. 6B shows a plate-like member coated with two-layer AR films (215a, 215b). Member 212a is shown. Here, the refractive index of the plate-like member 212a and _{n 2.} The refractive index of the AR film 215 is n _AR and the film thickness is d _AR . The refractive index of the AR film 215a is n _AR1 and the film thickness is d _AR1 . The refractive index of the AR film 215b is n _AR2 and the film thickness is d _AR2 . N ₀ is the refractive index of air, and n ₀ = 1.

The refractive index n _AR of the single-layer AR film 215 calculated so as to minimize the reflectance is expressed by the following equation (1).
n _AR = √ (n ₀ · n ₂ ) (1)

The film thickness d _AR of the single-layer AR film 215 at that time is expressed by the following equation (2). Here, λ is the wavelength of the laser beam.
d _AR = λ / (4 · n _AR ) (2)

If the material of the plate-like member 212a is sapphire glass, the refractive index n ₂ = 1.74. Here, λ = 1064 nm. Therefore, the refractive index n _AR is 1.32 and the film thickness d _AR is 201.5 nm, whereby the antireflection function can be realized by the single-layer AR film 215.

Examples of the material having a refractive index close to 1.32 include MgF having a refractive index of 1.38 and NaAlF ₆ having a refractive index of 1.34. However, these materials all have low heat resistance, and it is difficult to withstand the heat in the combustion chamber.

On the other hand, there is an oxide silicon-based material such as SiO ₂ as a heat resistant material. However, since this material has a high refractive index of 1.46, it is difficult to realize a good antireflection function with a single-layer film made of this material.

  Next, a multilayer film using a silicon-based material is considered.

The reflectance R of the two-layer AR film shown in FIG. 6B is expressed by the following equation (3).
R = [(n ₀ · (n _AR ² ) ² −n ₂ · (n _{AR 1} ) ² ) / (n ₀ · (n _AR ² ) ² + n ₂ · (n _{AR 1} ) ² )] ² (3)

The film thickness d _AR1 of the AR film 215a is expressed by the following equation (4), and the film thickness d _AR2 of the AR film 215b is expressed by the following equation (5).
d _AR1 = λ / (4 · n _AR1 ) (4)
d _AR2 = λ / (4 · n _AR2 ) (5)

As can be seen from the above equation (3), in order to reduce the reflectivity R and obtain a good antireflection function, it is necessary to increase the refractive index difference between the two AR films. Examples of silicon-based materials include SiO ₂ and Si ₃ N ₄ . Therefore, for example, when the material of the AR film 215a is SiO ₂ and the material of the AR film 215b is Si ₃ N ₄ , n _AR1 = 1.46 and n _AR2 = 1.99, and therefore, the above equation (3) is applied. Then, the reflectance R is about 0.001, and a high antireflection function can be realized.

However, each of the thermal expansion coefficient of the SiO ₂ and _Si 3 _{N 4} is ^{0.55 × 10 -6 /℃,3.5×10 -6 / ℃} , there is a difference in thermal expansion coefficient as about 6 times. The temperature in the combustion chamber is very high. If the thermal expansion coefficient of the AR film 215a and the thermal expansion coefficient of the AR film 215b are greatly different, thermal stress is applied to each AR film, the AR film is destroyed, and the optical characteristics are reduced. There is a risk of significant change (see FIG. 7).

  For the above reasons, it is difficult to realize an antireflection function that can withstand high temperatures only by coating the AR film.

  In view of this, the inventors have devised forming a fine structure having a plurality of convex fine structures or concave fine structures in a single-layer AR film. Hereinafter, for the sake of convenience, the convex microstructure is also referred to as a “fine convex structure”, and the concave microstructure is also referred to as a “fine concave structure”. And when they are not distinguished, they are also simply referred to as “fine structures”.

Then, as an example, the surface of the sapphire substrate was subjected to numerical calculation of reflectance when applied to the Si ₃ N ₄ film having a fine structure having a plurality of fine convex structure is formed. Here, in order to simplify the calculation by using an xyz three-dimensional orthogonal coordinate system, a model in which a quadrangular columnar Si ₃ N ₄ fine convex structure is provided on the + z side of the sapphire substrate is used. Note that reflection on the surface of the sapphire substrate on the −z side is ignored.

  The wavelength of the laser light incident on the −z side surface of the sapphire substrate is 1064 nm. The reflectance of the surface of the sapphire substrate on the + z side with respect to the laser beam having a wavelength of 1064 nm is about 0.074.

(I) The calculation result about the influence of the structure width on the reflectance will be described.

  8A and 8B show one fine convex structure 217 on the sapphire substrate 216. FIG. One fine convex structure 217 is provided for each 250 nm × 250 nm region on the sapphire substrate 216. The length of the fine convex structure 217 in the z-axis direction is 250 nm, and the length in the x-axis direction and the length in the y-axis direction are w. This length w is the “structure width”.

  Then, as shown in FIGS. 9A and 9B, the relationship between the reflectance and the wavelength was obtained while changing the value of the structure width w. The result is shown in FIG. Here, for each structure width, the wavelength at which the reflectance in the relationship between reflectance and wavelength takes the minimum value is referred to as “dip wavelength”.

  In this embodiment, the wavelength of the laser beam is 1064 nm. However, this wavelength is an example, and the main purpose is to reduce the reflectance. Therefore, here, the value of the reflectance at the dip wavelength is focused. Note that the dip wavelength can be set to 1064 nm by adjusting the shape of the fine structure.

  According to FIG. 10, even if the structure width w changes, the change in the position of the dip wavelength is small. In particular, when the structure width w is 150 nm to 180 nm, it is found that a reflectance of 0.01 or less can be obtained at the dip wavelength. . Moreover, it turned out that a reflectance rises as the structure width w becomes large, and when the structure width w is 240 nm, it is larger than the reflectance (about 0.074) when only the sapphire substrate is used.

(Ii) The calculation result about the influence of the structure height on the reflectance will be described.

  11A and 11B show one fine convex structure 217 on the sapphire substrate 216. FIG. One fine convex structure 217 is provided for each 250 nm × 250 nm region on the sapphire substrate 216. The length in the x-axis direction and the length in the y-axis direction of the fine convex structure 217 is 170 nm, and the length in the z-axis direction is h. This length h is the “structure height”.

  Then, as shown in FIGS. 12A and 12B, the relationship between the reflectance and the wavelength was obtained while changing the value of the structural height h. The result is shown in FIG.

  According to FIG. 13, it has been found that the dip wavelength continuously changes corresponding to the structural height h.

(Iii) The calculation result of the reflectance when the Si ₃ N ₄ layer is inserted between the sapphire substrate and the fine structure will be described.

Here, as shown in FIGS. 14A and 14B, a model in which a Si ₃ N ₄ layer 218 is inserted between the sapphire substrate 216 and the fine convex structure 217 is used.

One fine convex structure 217 is provided for each 250 nm × 250 nm region on the Si ₃ N ₄ layer 218. The length in the x-axis direction and the length in the y-axis direction of the fine convex structure 217 is 170 nm, and the length in the z-axis direction is 215 nm. Further, the length of the Si ₃ N ₄ film 218 in the z-axis direction is h _b .

Then, as shown in FIG. 15 (A) and FIG. 15 (B), the while changing the value of h _b, obtained relation between the reflectance and the wavelength. The results are shown in FIGS. 16 (A) and 16 (B).

According to FIG. 16 (A) and FIG. 16 (B), the corresponds to the thickness _{h b} the _Si 3 _{N 4} layer, a change in reflectance at the dip wavelength was observed, the thickness of the _Si 3 _{N 4} layers When the thickness was 30 nm, the reflectance was reduced more than when there was no Si ₃ N ₄ layer, and a reflectance of 0.003 was obtained. That is, it has been found that the same effect as that of the two-layer AR coating can be expected by inserting a Si ₃ N ₄ layer between the microstructure and the sapphire substrate.

  In this embodiment, the structure width and the structure height are set so that the reflectance at the dip wavelength is minimized. In addition, the shape of the fine structure is adjusted so that the dip wavelength is about 1064 nm.

  Here, the material of the dielectric film 213 will be described.

  The material of the dielectric film 213 includes Si, Al, Ca, Mg, B, C, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Zr, Nb, and Ru. , Pd, Ag, In, Sn, Hf, Ta, W, Ot, Au, Bi, or any of the main component fluoride, nitride, oxide, and carbide A material including at least one can be used.

Specifically, for example, Si ₃ N ₄ or SiO ₂ can be used. In addition, the smaller the refractive index difference between the dielectric film 213 and the plate-like member 212a, the better the antireflection characteristics. Therefore, the gas component during the dielectric film formation is adjusted, and the refractive index of sapphire is adjusted. it may be a yelling match _Si x _{N y.} In addition, when adjusting the gas component, if there is a concern about variations in the characteristics of the dielectric after film formation, a mixture of SiO ₂ and Si ₃ N ₄ may be used.

Here, the dielectric film 213 in the present embodiment will be described. In the present embodiment, the material of the plate-like member 212a is sapphire glass, and the material of the dielectric film 213 is Si ₃ N ₄ .

  FIG. 17 shows an example (example) of the dielectric film 213 provided on the B surface of the plate-like member 212a. The dielectric film 213 includes a base portion 213a and a fine structure portion 213b. Here, the fine structure portion 213b has a plurality of fine convex structures, and is provided on the + Z side of the base portion 213a. The pitch P (vertex interval) of the fine convex structures in the fine structure portion 213b is set to be shorter than the wavelength of incident light (here, 1064 nm).

  The fine convex structure has a conical shape in which the cross-sectional area continuously decreases in the + Z direction. Note that the cone shape may be any of a circular shape, an elliptical cone shape, a quadrangular pyramid shape, and a polygonal pyramid shape.

  Here, as shown in FIG. 18 (A), first, the base portion 213a is formed on the B surface of the plate-like member 212a, and then, as shown in FIG. 18 (B), the base portion 213a is formed. A dielectric film 213 is provided by forming a plurality of fine convex structures.

  Specific examples of the fine structure portion 213b are shown in FIGS. The fine structure shown in FIG. 19 (referred to as “fine structure A”) is a cone-shaped fine convex structure (referred to as “fine convex structure A”) having a height of 300 nm and a bottom diameter of 300 nm. Are arranged in a shape.

  The fine structure portion (referred to as “fine structure portion B”) shown in FIG. 20 has a conical fine convex structure (referred to as “fine convex structure B”) having a height of 500 nm and a bottom diameter of 300 nm being 300 nm. Are arranged in a honeycomb shape at a pitch of. The fine convex structure B is a fine convex structure having a high aspect ratio in which the ratio of the height to the maximum diameter is higher than that of the fine convex structure A.

  The fine structure portion (referred to as “fine structure portion C”) shown in FIG. 21 is a square quadrangular pyramid-shaped fine convex structure (referred to as “fine convex structure C”) having a height of 500 nm and a bottom surface of 300 nm on one side. Are arranged in a grid pattern.

  In this embodiment, the dielectric film is composed of a base portion and a fine structure portion, thereby realizing an optical antireflection characteristic equivalent to that of a two-layer antireflection coating. Therefore, it is preferable that there is a flat portion between two adjacent fine convex structures. Specifically, the area of the flat part is preferably 30% to 60% of the area of the fine structure part.

The length (thickness) in the Z-axis direction of the base portion 213a is λ / (4 · n _p ) or λ / (2 ··, where n _p is the refractive index of the dielectric film in order to reduce the reflectance. n _p ). This corresponds to the thickness d _AR1 of the first layer in the above-described AR film having a two-layer structure (see FIG. 6B). Specifically, the length (thickness) in the Z-axis direction of the base portion 213a is 30 nm.

FIG. 22 shows a case where a fine structure portion is not given to the plate-like member 212a as a comparative example. Hereinafter, cities refractive index n ₂ of the plate-like member 212a, the refractive index n ₁ of the atmosphere in the combustion chamber. In this comparative example, since the refractive index change (n ₂ → n ₁ ) at the interface between the plate-like member 212a and the combustion chamber is abrupt, the reflectance at the interface increases.

  For this reason, in the comparative example, the reflected light from the interface is condensed in the plate-like member 212a, the plate-like member 212a is altered, or the reflected light returns to the laser medium 206a or the surface emitting laser array 201. The light intensity of the laser light emitted from the laser device 200 may vary. In addition, particles generated in the combustion chamber may adhere to the plate-like member 212a and reduce the amount of laser light emitted from the ignition device 302.

  FIG. 23 shows the case of this embodiment. In this embodiment, as schematically shown in FIGS. 24B and 24B, since the change in the refractive index at the interface between the protective member 212 and the combustion chamber is small, the light at the interface is reduced. The reflectance can be lowered. Therefore, in this embodiment, the deterioration of the plate-like member 212a and the return light to the surface emitting laser array 201 can be suppressed.

  By the way, in the combustion chamber 304, liquids such as engine oil and water, fine particles such as calcium oxide added to maintain the quality of the engine oil, or fine metal particles from engine parts are mixed.

  Then, as shown in FIG. 25A, in the case of the comparative example in which the fine structure portion is not provided on the surface of the plate-like member 212a, the liquid 501 and the fine particles 502 adhere to the surface of the plate-like member 212a. The light intensity of the laser beam is reduced.

  On the other hand, as shown in FIG. 25B, the present embodiment has an effect of repelling the liquid 501. Further, the fine particles 502 can also reduce the contact area with the particles by the fine structure portion, so that adhesion of particles to the protective member 212 can be suppressed. That is, contamination of the protection member 212 can be prevented. As a result, it is possible to suppress a decrease in the light intensity of the laser light emitted from the laser device 200.

  Further, even if it is contaminated, it is possible to reuse the laser device without replacing it by forming the dielectric film 213 again after forming the dielectric film 213 and forming the fine structure portion. It becomes possible, and cost reduction can be aimed at.

  In addition, although the present Example demonstrated the case where the shape of the fine convex structure was a cone shape, it is not limited to this. For example, the shape of the fine convex structure may be a truncated cone shape, an elliptical truncated cone shape, or a polygonal truncated cone shape.

  Further, the shape of the fine convex structure may be a bell shape as shown in FIG. 26 as an example. As an example, as shown in FIG. 27, the interval between two adjacent fine convex structures may not be uniform.

  In addition, when the space | interval of two adjacent fine convex structures is not uniform, it is preferable that the average space | interval of the two adjacent fine convex structures in a fine structure part is below half of the wavelength of incident light. Moreover, it is preferable that the space | interval of two adjacent fine convex structures in a fine structure part is a random space | interval according to Gaussian distribution. As shown in FIG. 28, the 2σ value of the Gaussian distribution is preferably 1 / √2 times or less of the wavelength.

  Here, for convenience, the fine structure shown in FIG. 26 is referred to as “fine structure D”, and the fine convex structure is referred to as “fine convex structure D”. 27 is referred to as “fine structure E”, and the fine convex structure is referred to as “fine convex structure E”.

  The fine structure portion A to the fine structure portion C are mainly produced by using electron beam lithography and etching, and the fine structure portion D and the fine structure portion E are mainly produced by etching using metal nanoparticles as a mask. . In addition, X-ray lithography, photolithography, or the like may be used.

  Further, the fine convex structure may be curved at the side of the longitudinal section (cross section parallel to the Z axis). In addition, the fine convex structure may have a shape in which the cross-sectional area decreases stepwise in the + Z direction.

  Further, the plurality of fine convex structures may be structures having a pitch shorter than the wavelength of incident light, and may be different in shape and size from each other. For example, the diameter of the plurality of fine convex structures may be random between 5 nm and 1000 nm. The pitch of the plurality of fine convex structures may be random between 10 nm and 2000 nm. Further, the arrangement form of the plurality of fine convex structures may not have regularity.

  Next, the area | region of the fine structure part provided in the dielectric material film 213 is demonstrated. Hereinafter, the region of the fine structure portion is abbreviated as “fine structure portion region”.

  FIG. 29 shows an example 1 in which the fine structure region is a region inside a flat portion of a rectangular frame shape joined to the casing 214 on the B surface and includes a beam passing region. Yes. In this case, all the light passing through the B surface enters the fine structure region, and the reflectance of all the light is reduced. Further, even if the light passing position with respect to the B surface is slightly shifted, the reflectance of all the light is lowered.

  FIG. 30 shows an example 2 in which the fine structure region is a region that coincides with the beam passage region on the B-plane. In this case, all the light passing through the B surface enters the fine structure region, and the reflectance of all the light is reduced. In addition, since the fine convex structure only needs to be formed in the region on the B surface where light passes, the processing range of the dielectric film 213 can be narrowed.

FIG. 31 shows an example 3 in which the fine structure region is included in the beam passing region on the B surface and includes a region having the maximum effective beam diameter on the B surface. “Effective beam diameter” means the beam diameter of the portion where the relative intensity with respect to the maximum intensity (100%) is 1 / e ² (13.5%) in the Gaussian distribution of the light intensity (see FIG. 32).

  In this case, all the light within the region having the maximum effective beam diameter that substantially affects the intensity fluctuation of the light emitted from the laser device 200 out of the light passing through the B surface is incident on the fine structure region. , The reflectance of all the light decreases. Further, even if the light passing position with respect to the B surface is slightly shifted, the reflectance of all the light in the region where the effective beam diameter is the maximum diameter is lowered. Further, since it is only necessary to form the fine convex structure only in the region through which the light that substantially affects the intensity variation passes, the processing range in the dielectric film 213 can be further narrowed.

  FIG. 33 shows Example 4 in which the fine structure region is a region that coincides with a region having the maximum effective beam diameter on the B surface. In this case, all the light within the effective beam diameter that substantially affects the intensity fluctuation of the light emitted from the laser device 200 out of the light passing through the B surface enters the fine structure region, and Reflectivity decreases. In addition, since the fine convex structure only needs to be formed in the region having the maximum effective beam diameter, the processing range of the dielectric film 213 can be further narrowed.

  FIG. 34 shows an example 5 in which the fine structure region is a region included in the region having the maximum effective beam diameter on the B surface. In this case, the intensity variation of the light emitted from the laser device 200, which is a part of the light that passes through the B surface and has a large intensity including the light having the maximum intensity in the region having the effective beam diameter as the maximum diameter. A part of the light that greatly affects the light enters the fine structure region, and the reflectance of the part of the light is lowered. In addition, since the fine convex structure need only be formed in a region smaller than the region where the effective beam diameter is the maximum diameter, the processing range in the dielectric film 213 can be further narrowed.

  In the present embodiment, the fine structure region is set to be one of Examples 1 to 5.

  By the way, usually, at the boundary between air and the window member, there is a sudden change in the refractive index, so that part of the light is reflected (see FIG. 24A). In this embodiment, since the fine structure portion 213b having a plurality of conical fine convex structures is formed on the surface of the dielectric film 213 on the + Z side, a region between the air and the dielectric film 213 is formed. The apparent refractive index can be continuously changed (see FIG. 24B), and reflection of light can be suppressed.

  As a result, it is possible to suppress the laser light from being condensed inside the window member, the window member being altered and the transmittance being lowered, and the laser light from being returned to the laser medium or the excitation light source. Moreover, it can suppress that the intensity | strength of the laser beam inject | emitted from an ignition device falls.

  Conventionally, in order to reduce reflection at the window member, a method of coating the window member with an antireflection film is used. However, in the ignition device, the window member is provided facing the combustion chamber and has a temperature of about 600 ° C. Many of the coating materials are altered by exposure to high temperatures.

  In this embodiment, the window member has a dielectric film that can withstand about 600 ° C., and a plurality of fine convex structures are formed on the exit end face of the dielectric film. The reflection at the exit end face can be suppressed as compared with the case where it is not. In addition, in this embodiment, the contact area between the injection end face of the dielectric film and the particles generated in the combustion chamber is smaller than in the case where there is no fine convex structure, thereby suppressing the adhesion of particles to the dielectric film. Can do. That is, contamination of the window member can be prevented.

  In this embodiment, the fine convex structure has a tapered shape in which the cross section (transverse cross section) gradually decreases in the direction from the incident side to the exit side, so that the refractive index change can be moderated and the reflectivity is sufficient. Can be lowered. Then, as shown in FIGS. 35 (A) and 35 (B), as the length (height) in the convex direction of the fine convex structure is longer, the refractive index change can be made more gradual, and the reflectance Can be further reduced.

  In addition, when the center interval between the plurality of fine convex structures is substantially constant, a substantially uniform reflectance reduction effect can be obtained over the entire area where the fine convex structures are formed. And, in a plurality of fine convex structures, the diameter of each fine convex structure is 5 nm to 1000 nm, and the reflectance is sufficiently lowered even if the interval between two adjacent fine convex structures is 10 nm to 2000 nm. Can do.

  Returning to FIG. 2, the adjustment of the condensing position of the light emitted from the laser device 200 in the Z-axis direction is performed by adjusting the focal length of the emission optical system 210 and the arrangement position of the emission optical system 210 in the Z-axis direction. ,It can be carried out.

  The first condensing optical system 203 has at least one condensing lens. Here, the configuration of the optical element in the first condensing optical system 203 is not limited. In short, the light emitted from the surface emitting laser array 201 may be collected at the central portion of the end face on the −Z side of the optical fiber 204.

  In the present embodiment, by using the optical fiber 204, the distance between the surface emitting laser array 201 and the laser resonator 206 can be increased by the length of the optical fiber 204.

  Therefore, when the laser device 200 is used as an ignition device for an internal combustion engine, the surface emitting laser array 201 can be moved away from a high temperature region or a vibration region around the internal combustion engine, thereby improving the reliability of the ignition device. it can.

  Here, as shown in FIG. 36 as an example, the second condensing optical system 205 includes a first lens 205a and a second lens 205b.

  The first lens 205a is a collimating lens, and makes light emitted from the optical fiber 204 substantially parallel light.

  The second lens 205b is a condensing lens, and condenses the light that has been made substantially parallel by the first lens 205a.

  The second condensing optical system 205 may be composed of three or more optical elements. Further, the second condensing optical system 205 may be composed of one optical element. In this case, the one optical element is a condenser lens.

  In the present embodiment, since the Nd: YAG crystal and the Cr: YAG crystal are both ceramics, the laser resonator 206 is lower in production cost and cheaper than a single crystal. Further, since the boundary between the Nd: YAG crystal and the Cr: YAG crystal is not separated, characteristics equivalent to those of a single crystal can be obtained, which is advantageous in terms of mechanical strength and optical properties.

  The light condensed by the second lens 205b is incident on the laser medium 206a. That is, the laser medium 206a is excited by the light condensed by the second lens 205b. Hereinafter, the light incident on the laser medium 206a is also referred to as “excitation light”.

  The emission optical system 210 may be composed of a single optical element or a plurality of optical elements.

  By the way, an edge emitting laser is widely known as a semiconductor laser. However, the light emitted from the edge emitting laser has a large variation in wavelength with respect to temperature. Therefore, in an ignition device that is assumed to be used in a high temperature environment, when an edge emitting laser is used as an excitation light source, a precise temperature control mechanism is required to keep the temperature of the edge emitting laser constant. This increases the size and cost of the device.

  On the other hand, the light emitted from the surface emitting laser array has a wavelength variation with respect to temperature of about 1/10 that of the edge emitting laser. Therefore, an ignition device that uses a surface emitting laser array as an excitation light source does not require a precise temperature control mechanism. Therefore, a small and low-cost ignition device can be realized.

  In addition, since the surface emitting laser array has a light emitting region inside the semiconductor, there is no fear of end face destruction, and the reliability of the ignition device can be improved.

  As is clear from the above description, in the ignition device 301 according to this embodiment, the protective member 212 constitutes the window member in the ignition device of the present invention.

  In the ignition device 301 according to this embodiment, the laser device 200 constitutes the light source in the ignition device of the present invention, and the emission optical system 210 constitutes the optical system in the ignition device of the present invention.

  As described above, the protection member 212 according to the present embodiment includes the plate-like member 212a having the A surface on which light is incident and the B surface on which the light incident on the A surface is emitted, and the plate-like member. And a dielectric film 213 provided on the B surface of 212a. The dielectric film 213 includes a fine structure having a plurality of fine convex structures.

  The shape of the fine convex structure is a cone shape whose cross-sectional area continuously decreases in the light traveling direction. The diameter of the fine convex structure is ½ or less of the wavelength of light, and the interval between the plurality of fine convex structures in the fine structure is ½ or less of the wavelength of light.

The plate-like member 212a is sapphire glass, and the dielectric film 213 is made of Si ₃ N ₄ .

  According to this protective member 212, it is possible to achieve both improvement in heat resistance and reduction in reflected light, and to suppress the adhesion of dirt.

  The protective member 212 is particularly effective for a window member used in a high temperature environment where a reflective coating is difficult when used in a low temperature environment or a normal temperature environment. That is, the protection member 212 can be widely applied as a window member under any temperature environment.

  And since the ignition device 301 has the protection member 212, stable ignition can be performed efficiently.

  Further, since engine 300 includes ignition device 301, efficiency can be improved as a result.

  In the above-described embodiment, the case where the plate-like member 212a has a rectangular plate shape has been described. However, the present invention is not limited thereto. For example, the plate-like member 212a has a circular plate shape, an elliptical plate shape, a rectangular plate shape, or a polygonal plate shape. There may be.

  Moreover, although the said embodiment demonstrated the case where the protection member 212 was used for an ignition device, it is not limited to this. For example, it can be used as a window member in an image forming apparatus (for example, a laser copying machine or a laser printer) or an image projection apparatus (for example, a projector).

  Further, the protective member 212 may be used as a window member of an apparatus that does not require heat resistance.

  Moreover, in the said embodiment, although the case where a surface emitting laser array was used as a light source for excitation was demonstrated, it is not limited to this.

  Next, modified examples (modified examples 1 to 6) of the protection member 212 will be described.

  In the protection member 212 of Modification 1, as shown in FIG. 37 as an example, a dielectric film 213 is provided on the B surface of the plate member 212a. The fine structure portion 213b has a plurality of fine concave structures, and the fine structure portion 213b is provided on the + Z side of the base portion 213a.

  Here, as shown in FIG. 38 (A), first, the base portion 213a is formed on the B surface of the plate-like member 212a, and then the base portion 213a is shaved as shown in FIG. 38 (B). A dielectric film 213 is provided by forming a plurality of fine concave structures. The protection member 212 of the first modification can obtain the same effects as in the above embodiment.

  In the protection member 212 of Modification 2, as shown in FIG. 39 as an example, a dielectric film 213 is provided on the A surface of the plate member 212a. The fine structure portion 213b has a plurality of fine convex structures, and the fine structure portion 213b is provided on the −Z side of the base portion 213a. The fine convex structure has a shape in which the cross-sectional area continuously increases in the + Z direction. The fine convex structure may have a shape in which the cross-sectional area increases stepwise in the + Z direction.

  In this case, reflection on the surface on the −Z side of the dielectric film 213 can be suppressed. Therefore, according to the protection member 212 of the second modification, both improvement in heat resistance and reduction in reflected light can be achieved.

  In the protection member 212 of Modification 3, as shown in FIG. 40 as an example, a dielectric film 213 is provided on the A surface of the plate member 212a. The fine structure portion 213b has a plurality of fine concave structures, and the fine structure portion 213b is provided on the −Z side of the base portion 213a.

  In this case, reflection on the surface on the −Z side of the dielectric film 213 can be suppressed. Therefore, according to the protection member 212 of the third modification, both improvement in heat resistance and reduction in reflected light can be achieved.

  In the protection member 212 of Modification 4, as shown in FIG. 41 as an example, a dielectric film 213 is provided on the A surface and the B surface of the plate member 212a. The fine structure portion of each dielectric film 213 has a plurality of fine convex structures. The protection member 212 of the modification 4 can obtain the same effect as that of the above embodiment.

  In the protective member 212 of Modification 5, as shown in FIG. 42 as an example, a dielectric film 213 is provided on the A surface and the B surface of the plate member 212a. The fine structure portion of each dielectric film 213 has a plurality of fine concave structures. The protection member 212 of the modification 5 can obtain the same effect as the above embodiment.

  In the protection member 212 of Modification 4, the positions of the fine convex structures on the A surface side and the fine convex structures on the B surface side may be aligned or may be shifted from each other. Similarly, in the protection member 212 of Modification 5, the positions of the fine concave structure on the A surface side and the fine concave structure on the B surface side may be aligned or may be shifted from each other.

  Further, the A surface side may be a fine convex structure, the B surface side may be a fine concave structure, the A surface side may be a fine concave structure, and the B surface side may be a fine convex structure.

  As shown in FIG. 43 as an example, the protection member 212 of Modification 6 is configured by only a fine structure portion without a base portion. Also in this case, substantially the same effect as in the above embodiment can be obtained.

  Moreover, in the said Example and modification, as FIG. 44 shows as an example, the shape of a fine convex structure and a fine concave structure may be column shape. Even in this case, the reflected light can be reduced as compared with the conventional case. Therefore, both improvement in heat resistance and reduction in reflected light can be achieved. Note that the columnar shape includes a columnar shape, an elliptical columnar shape, a quadrangular columnar shape, a polygonal columnar shape, and the like.

  Further, in the above embodiment and modification, as shown in FIG. 45 as an example, the interval between two adjacent fine structures may be substantially zero. That is, the flat part in the said Example does not need to be provided. Even in this case, the reflected light can be reduced as compared with the conventional case. Therefore, both improvement in heat resistance and reduction in reflected light can be achieved.

  Further, in the above embodiments and modifications, the dielectric film 213 may be a multilayer film. For example, as shown in FIG. 46, the fine structure portion 213b may be coated with a dielectric 213c. In this case, a reflectance smaller than or equal to that of the conventional multilayer film can be realized with a smaller number of layers than the conventional multilayer film. And since the number of layers may be smaller than the conventional multilayer film, generation | occurrence | production of a crack can be suppressed.

Further, in the above embodiment, the material of the dielectric film 213 has been described for the case of Si ₃ N _4, but is not limited thereto. In short, any material having heat resistance corresponding to the use environment may be used. In this case, not only the nitride, oxide, and carbide described above, but also, for example, Si, Al, Ca, Mg, B, C, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn , Ga, Sr, Zr, Nb, Ru, Pd, Ag, In, Sn, Hf, Ta, W, Ot, Au, Bi, or a main component fluoride or the main component fluoride is used. You can also.

  Moreover, although the said Example demonstrated the case where the material of the plate-shaped member 212a was sapphire glass, it is not limited to this.

DESCRIPTION OF SYMBOLS 200 ... Laser apparatus (light source), 201 ... Surface emitting laser array, 203 ... 1st condensing optical system, 204 ... Optical fiber (transmission member), 205 ... 2nd condensing optical system, 205a ... 1st lens, 205b ... Second lens 206... Laser resonator 206 a. Laser medium 206 b Saturable absorber 210 Ejection optical system (optical system) 212 Protection member (window member) 212 a Plate member 213 Dielectric Body film, 213a ... underlying part, 213b ... fine structure part, 213c ... dielectric, 214 ... housing, 215 ... AR film, 215a ... AR film, 215b ... AR film, 216 ... sapphire substrate, 217 ... fine convex structure , 218 ... _Si 3 _{N 4} layer, 220 ... driving apparatus, 222 ... engine control unit, 300 ... engine (internal combustion engine), 301 ... igniter 302 ... fuel injection mechanism, 303 ... exhaust machine , 304 ... combustion chamber, 305 ... piston 501 ... liquid, 502 ... microparticles.

Japanese Patent No. 4021954 JP, 2006-109128, A Japanese Patent No. 5892804 JP 2010-19150 A

Claims (15)

A window member disposed on an optical path of light,
A plate-like member having an A surface on which the light is incident and a B surface on which the light incident on the A surface is emitted;
A dielectric film provided on at least one of the A surface and the B surface of the plate-like member,
The dielectric film is a window member including a microstructure part having a plurality of convex or concave microstructures. The dielectric film is provided on the B surface,
2. The window member according to claim 1, wherein the fine structure has a cross-sectional area that decreases continuously or stepwise in the light traveling direction. The dielectric film is provided on the A surface,
3. The window member according to claim 1, wherein the fine structure has a cross-sectional area that increases continuously or stepwise in the traveling direction of the light.   The window member according to claim 1, wherein the fine structure has a conical shape.   The window member according to claim 1, wherein the fine structure has a column shape. The diameter of the microstructure is not more than 1/2 of the wavelength of the light,
The window member according to any one of claims 1 to 5, wherein the diameters of the plurality of fine structures in the fine structure portion are not uniform.   The window according to any one of claims 1 to 6, wherein an interval between the plurality of fine structures in the fine structure portion is 1/2 or less of the wavelength of the light and is not uniform. Element.   The optical window member according to any one of claims 1 to 7, wherein a plurality of microstructures in the microstructure section are formed in a region including an effective beam diameter of the light.   The window member according to any one of claims 1 to 7, wherein a plurality of microstructures in the microstructure section are formed in a region including the light passage region.   The window member according to claim 1, wherein the dielectric film is a single-layer film.   The window member according to claim 1, wherein the dielectric film is a multilayer film.   The said plate-shaped member is a sapphire glass, The window member as described in any one of Claims 1-11 characterized by the above-mentioned.   The dielectric film includes Si, Al, Ca, Mg, B, C, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Zr, Nb, Ru, Pd, At least one of a material mainly containing any one of Ag, In, Sn, Hf, Ta, W, Ot, Au, and Bi, or a fluoride, nitride, oxide, and carbide of the main component. The window member according to any one of claims 1 to 12, wherein the window member is made of a material containing the window member. A light source;
An optical system for collecting the light emitted from the light source;
A housing that houses the light source and the optical system;
An ignition device comprising: the window member according to any one of claims 1 to 13 provided on the housing on an optical path of light through the optical system. In an internal combustion engine that generates combustion gas by burning fuel,
An internal combustion engine comprising the ignition device according to claim 14 for igniting the fuel.

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