JP2019165087A - Laser device, ignition device, and internal combustion engine - Google Patents

Abstract

To allow easy replacement of optical windows.SOLUTION: The laser device includes: a light source that emits a laser beam; an optical element through which the laser beam passes; a first housing that houses the optical element; and an optical window, held in a second housing, through which light that has passed through the optical element passes.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a laser device, an ignition device, and an internal combustion engine.

  A laser device using a semiconductor laser as an excitation light source is expected to be applied to various fields such as an ignition device, a laser processing machine, and a medical device. In particular, a method of using such a laser device as an ignition device in an internal combustion engine such as an automobile has been studied.

  In such an ignition device, a laser beam (excitation light) oscillated from a semiconductor laser is irradiated to a Q-switch type laser resonator to oscillate a pulsed laser beam having a high energy density. The oscillated pulse laser beam is condensed into the air-fuel mixture introduced into the combustion chamber through a condensing lens and an incident transparent combustion chamber window (optical window). Thereby, plasma is generated in the combustion chamber, and the fuel injected into the combustion chamber is ignited (see, for example, Patent Document 1).

  However, in the conventional ignition device, the contamination of the optical window has been a problem. Thus, for example, Patent Document 1 discloses a method of providing a superhydrophilic film containing superhydrophilic particles and thermally excited catalyst particles on the surface of an optical window.

  However, it is very difficult to completely prevent the dust and impurities generated in the internal combustion engine from adhering to the optical window, and it will eventually become dirty during use, resulting in a decrease in the power of the laser light and combustion. There is a problem that performance deteriorates.

  The present invention has been made in view of the above, and an object of the present invention is to provide a laser apparatus that enables easy replacement of an optical window.

  In order to solve the above-described problems and achieve the object, a laser apparatus according to the present invention includes a light source that emits laser light, an optical element through which the laser light passes, and a first element that houses the optical element. A housing and an optical window that is held by the second housing and through which the light that has passed through the optical element passes.

  ADVANTAGE OF THE INVENTION According to this invention, the laser apparatus which makes it possible to replace | exchange an optical window easily is realizable.

FIG. 1 is a diagram schematically illustrating a main part of an internal combustion engine including a laser device as an ignition device according to a first embodiment. FIG. 2 is a diagram illustrating a schematic configuration example of the laser apparatus according to the first embodiment. FIG. 3 is a partially enlarged view of the laser apparatus shown in FIG. FIG. 4 is a diagram illustrating a schematic configuration example of the laser apparatus according to the second embodiment. FIG. 5 is a diagram illustrating a schematic configuration example of a laser apparatus according to the third embodiment.

  Hereinafter, embodiments of a laser device, an ignition device, and an internal combustion engine will be described in detail with reference to the accompanying drawings.

[First Embodiment]
A laser device, an ignition device, and an internal combustion engine according to a first embodiment will be described with reference to the drawings. In this embodiment, a case where an engine is used as the internal combustion engine will be described.

<Internal combustion engine>
FIG. 1 is a diagram schematically illustrating a main part of an internal combustion engine including a laser device as an ignition device according to a first embodiment. As shown in FIG. 1, the engine 10 includes a laser device 11, a fuel ejection mechanism 12, an exhaust mechanism 13, a combustion chamber 14, and a piston 15.

  The operation of the engine 10 will be briefly described. The fuel ejection mechanism 12 ejects a combustible air-fuel mixture containing fuel and air into the combustion chamber 14 (intake air). Thereafter, the piston 15 rises and the combustible air-fuel mixture is compressed (compression). The laser device 11 condenses laser light in the compressed air-fuel mixture in the combustion chamber 14 to generate plasma. The generated plasma ignites the fuel in the mixture (ignition). When the air-fuel mixture burns by ignition, the combustion gas expands in the combustion chamber 14. As a result, the piston 15 descends (combustion). Thereafter, the exhaust mechanism 13 exhausts the combustion gas to the outside of the combustion chamber 14 (exhaust).

  Thus, in the engine 10, a series of steps consisting of intake, compression, ignition, combustion, and exhaust are repeated. Then, the piston 15 moves corresponding to the volume change of the gas in the combustion chamber 14 to generate kinetic energy. For example, natural gas or gasoline is used as the fuel.

  The laser device 11 is electrically connected to a driving device 16 provided outside the engine 10, and the laser device 11 emits laser light based on an instruction from the engine control device 17. Controlled by

<Laser device>
The laser device 11 will be described. An example of the configuration of the laser device 11 is shown in FIG. As shown in FIG. 2, the laser device 11 includes a surface emitting laser (light source) 21, a first condensing optical system 22, an optical fiber (transmission member) 23, a second condensing optical system 24, a laser resonator 25, a first 3 has a condensing optical system 26, a window member 27 </ b> A, and a housing (housing) 28. In FIG. 2, the laser beam is indicated by a two-dot chain line. In this specification, a three-dimensional orthogonal coordinate system in the three-axis directions (X-axis direction, Y-axis direction, and Z-axis direction) is used, and the emission direction of the laser light from the surface-emitting laser 21 is defined as the + Z direction. In the plane orthogonal to the axis, one of the two directions orthogonal to each other will be described as the X-axis direction and the other as the Y-axis direction.

  The surface emitting laser 21 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 the laser light emitted from the surface emitting laser 21 is, for example, about 808 nm.

  The surface emitting laser 21 is electrically connected to the driving device 16, and the driving device 16 drives the surface emitting laser 21 and emits laser light from the surface emitting laser 21 based on an instruction from the engine control device 17. Is done. In this embodiment, since the temperature dependence of the wavelength of the emitted laser light is low, the surface emitting laser is used as the light source. However, when the temperature dependence of the laser is not a problem, the edge emitting laser is used as the light source. It can also be used.

  The first condensing optical system 22 condenses the laser beam emitted from the surface emitting laser 21 at the center of the −Z side end surface of the optical fiber 23. The first condensing optical system 22 has at least one condensing lens. In the present embodiment, the first condensing optical system 22 includes a microlens 221 and a condensing lens system 222.

  The microlens 221 is disposed on the optical path of the laser light emitted from the surface emitting laser 21. The microlens 221 has a plurality of lenses corresponding to a plurality of light emitting units of the surface emitting laser 21. Each lens makes the laser light emitted from the corresponding light emitting portion substantially parallel light. In other words, the microlens 221 collimates the laser light emitted from the surface emitting laser 21.

  The condensing lens system 222 condenses the laser light via the microlens 221.

  In addition, the 1st condensing optical system 22 should just have at least 1 condensing lens, and may be comprised by the some optical element.

  The optical fiber 23 is disposed so that the center of the end surface on the −Z side of the core is located at a position where the laser light is condensed by the first condensing optical system 22. The laser light incident on the optical fiber 23 propagates through the core and exits from the + Z side end face of the core.

  The second condensing optical system 24 is disposed on the optical path of the laser light emitted from the optical fiber 23 and condenses the light emitted from the optical fiber 23. The laser beam condensed by the second condensing optical system 24 enters the laser resonator 25. In the present embodiment, the second condensing optical system 24 includes a first lens 241 and a second lens 242.

  The first lens 241 is a collimating lens, and makes the laser light emitted from the optical fiber 23 substantially parallel light.

  The second lens 242 is a condensing lens, and condenses the laser light that has been made substantially parallel light by the first lens 241.

  As long as the second condensing optical system 24 has a condensing lens, the second condensing optical system 24 may be constituted by one optical element or may have three or more lenses.

  The laser resonator 25 is a Q-switch type laser resonator. In the present embodiment, the laser resonator 25 includes a laser medium 251 and a saturable absorber 252. In the laser resonator 25, the energy density of incident laser light is increased, and laser light having a wavelength of, for example, about 1064 nm is emitted with a short pulse width.

  The laser medium 251 is a substantially rectangular parallelepiped Nd: YAG crystal, and Nd is doped by 1.1%.

  The saturable absorber 252 is a substantially rectangular parallelepiped Cr: YAG crystal. The saturable absorber 252 has a transmittance that varies depending on the amount of laser light absorbed, and the initial transmittance is approximately 0.50 (50%). When the amount of absorption of laser light is small, it functions as an absorber, and becomes transparent when the amount of absorption of laser light is saturated. When the saturable absorber 252 becomes transparent, Q-switch oscillation occurs.

  When the laser light condensed by the second condensing optical system 24 enters the laser resonator 25, the laser light resonates and is amplified in the laser resonator 25. Further, the laser medium 251 is excited by the laser light incident on the laser medium 251. The wavelength of the laser light emitted from the surface emitting laser 21 (for example, 808 nm) is the wavelength with the highest absorption efficiency in the YAG crystal.

  Laser light is resonated and amplified in the laser resonator 25. When the amount of laser light absorption is saturated in the saturable absorber 252, Q-switch oscillation occurs in the saturable absorber 252. As a result, laser light having a high energy density is emitted from the laser resonator 25 while concentrating energy with a short pulse width. When Nd: YAG is used as the laser medium 251, the wavelength of the emitted laser light is about 1064 nm.

  The laser light emitted from the laser resonator 25 is incident on the third condensing optical system 26.

  The third condensing optical system 26 is disposed on the optical path of the laser light emitted from the laser resonator 25. The third condensing optical system 26 condenses the laser light emitted from the laser resonator 25 and obtains a high energy density at the condensing point. When the condensed laser light exceeds a certain energy density, the molecules constituting the gas contained in the combustible gas mixture in the combustion chamber 14 are ionized, separated into cations and electrons, and converted into plasma (break). Down).

  In the present embodiment, the third condensing optical system 26 includes a third lens 261, a fourth lens 262, and a fifth lens 263.

  The third lens 261 is an optical element for increasing the divergence angle of the laser light emitted from the laser resonator 25, and a concave lens is used in this embodiment.

  The fourth lens 262 is an optical element for collimating the diverging light from the third lens 261, and a collimating lens is used in this embodiment.

  The fifth lens 263 is an optical element for condensing the laser light from the fourth lens 262, and a condensing lens is used in the present embodiment.

  Note that the third condensing optical system 26 is configured by three lenses, but may be configured by at least one lens, and may be configured by one optical element or a plurality of optical elements. It may be comprised.

  The laser light emitted from the third condensing optical system 26 passes through the optical window (second optical window) 271 and is condensed in the combustion chamber 14.

  Before describing the configuration of the window member 27A, the housing 28 will be described. The housing 28 includes a first housing 28-1 that houses optical elements such as the second condensing optical system 24, a laser resonator 25, and a third condensing optical system 26, and a second housing 28- that houses a window member 27A. 2 and.

  A window member 27A is provided at the tip (combustion chamber side) of the second housing 28-2 in order to ensure optical continuity between the second housing 28-2 and the combustion chamber. The window member 27 </ b> A includes a second optical window 271 and an optical window holding member 272, and the optical window holding member 272 holds the second optical window 271. The second optical window 271 is disposed on the optical path of the laser light emitted from the third condensing optical system 26 and is made of a material that is transparent to the incident laser light. The second optical window 271 is disposed so as to be positioned at an opening formed on the surface of the second housing 28-2 on the combustion chamber 14 side.

  Since the second optical window 271 is provided facing the combustion chamber, dirt adheres to the emission surface of the second optical window 271 as the laser device is used. In the present embodiment, the second housing 28-2 is removed from the first housing 28-1 that houses the optical element, and only the second optical window 271 that is contaminated can be replaced with the first housing 28-1. Two housings 28-2 are formed as separate bodies. As a result, the optical window can be easily replaced.

  Furthermore, a first optical window 208 for ensuring optical continuity between the first housing 28-1 and the second housing 28-2 is provided at the tip (combustion chamber side) of the first housing 28-1. It may be provided.

  The first optical window 208 is disposed on the optical path of the laser light emitted from the third condensing optical system 26 and is made of a material that is transparent to the incident laser light. The first optical window 208 seals optical elements such as the second condensing optical system 24, the laser resonator 25, and the third condensing optical system 26 in the first housing 28-1. Thereby, even if the second housing 28-2 is removed when the window member 27A is replaced, the optical element in the first housing 28-1 is not exposed to the outside air. The first optical window 208 can protect the optical elements in the first housing 28-1 from dust, impurities, etc. floating in the air. As described above, the first housing 28-1 is separated from the window member 27A and can be kept in a sealed state, thereby contaminating optical elements such as a lens used in the laser device 11. The second optical window 271 can be replaced without any change.

  In a conventional ignition device (for example, Patent Document 1), an optical element such as a condenser lens or a laser resonator and an optical window are attached to the same casing. Therefore, the optical window cannot be easily replaced. In the prior art, when dirt is attached to the optical window, it is necessary to remove and clean the housing or replace the entire housing including the optical element, which increases the cost.

  For fixing the second housing 28-2 to the first housing 28-1, brazing, laser welding, screwing, shrink fitting, adhesion, or the like can be used. For example, a screw part that fits to each other is provided at a contact point between the second housing 28-2 and the first housing 28-1, and the second housing 28-2 is fixed to the first housing 28-1 by the screw part. May be.

  In addition to the first optical window 208, the first housing 28-1 has an O-ring, brazing, welding, gasket, shrink fitting, It is necessary to seal with adhesion or the like. For example, in FIG. 2, the sealing material provided in two places, the joint part of the 1st housing 28-1 and the 2nd housing 28-2, and the attachment part of the optical fiber 23 with respect to the 1st housing 28-1. 291 and 292 prevent impurities from entering from the outside.

  The first optical window 208 is fixed to the first housing 28-1. Brazing, laser welding, screwing, shrink fitting, adhesion, or the like can be used as the fixing method. When bonding is used as a fixing method, it is better to use an adhesive material that does not easily generate gas at high temperatures. This is because when the gas is generated, it adheres to the optical element and may cause a problem such as burning when irradiated with a high-intensity laser beam.

  It is preferable to use a metal having high heat resistance for at least the second housing 28-2 of the housing 28. For example, heat-resistant metals such as iron, Ni—Fe alloy, Ni—Cr—Fe alloy, Ni—Co—Fe alloy, and stainless steel are used. Examples of the Ni—Cr—Fe alloy include inconel. Examples of the Ni—Co—Fe alloy include kovar. Moreover, you may form the 1st housing 28-1 and the 2nd housing 28-2 with the same material.

  Since the window member 27 </ b> A is exposed to combustion, it is preferable to use brazing at the joint portion from the viewpoint of heat resistance and pressure resistance. In the present embodiment, the second optical window 271 is brazed to the inner surface of the optical window holding member 272 using a brazing material (bonding material). Brazing is also used when fixing the window member 27A to the second housing 28-2.

  The shape of the second optical window 271 in plan view is not particularly limited, and may be, for example, a rectangular shape, a circular shape, an elliptical shape, a rectangular shape, or a polygonal shape.

  As a material of the second optical window 271, for example, optical glass, heat-resistant glass, quartz glass, sapphire glass, or the like can be used. In particular, it is desirable that the second optical window 271 has sufficient pressure resistance to protect optical members such as the first optical window 208 on the housing 28 side from the combustion pressure generated in the combustion chamber 14. For example, the second optical window 271 may have a heat resistance of 600 ° C. or higher and a pressure resistance of 50 MPa (megapascal) or higher. Therefore, it is conceivable to increase the thickness of the second optical window 271. However, when the thickness of the second optical window 271 is increased, a part of the laser light incident on the emission surface of the second optical window 271 is reflected and is easily collected inside the second optical window 271. Therefore, in order to suppress the condensing inside the second optical window 271, it is necessary to increase the focal length of the third condensing optical system 26.

  As a material for forming the optical window holding member 272, for example, a heat-resistant metal material such as iron, nickel, a Ni—Fe alloy, a Ni—Cr—Fe alloy, a Ni—Co—Fe alloy, or stainless steel is used. Can do. Examples of the Ni—Cr—Fe alloy include inconel. Examples of the Ni—Co—Fe alloy include kovar. Especially, in this embodiment, since the 2nd optical window 271 is preferably formed with sapphire, it is preferable that the material forming the optical window holding member 272 uses sapphire having a thermal expansion coefficient close to that of sapphire. .

  As described above, according to the present embodiment, the second optical window 271 can be easily replaced. Furthermore, by providing the first optical window, it is possible to protect the optical element such as the second condensing optical system 24 from dust and impurities in the air when the second optical window is replaced.

  In the above configuration, the area of the first optical window 208 is determined in consideration of the beam diameter of the laser beam because the laser beam passes when the laser beam starts to be collected by the fifth lens 263. Further, the second optical window 271 is located closer to the combustion chamber than the first optical window 208. Therefore, as shown in FIG. 3, the area S <b> 2 of the second optical window 271 may be smaller than the area S <b> 1 of the first optical window 208. Thereby, the material cost can be reduced, and the pressure applied to the second optical window 271 can also be reduced. As a result, reliability can be improved.

  The first optical window 208 may be made of sapphire, glass, resin, or the like as long as the laser beam passes therethrough.

  Since the first optical window 208 is protected by being shielded from the outside air by the second housing 28-2, the pressure is not as high as that of the second optical window 271. Therefore, the thickness may be thinner than the second optical window 271.

  The laser light is condensed by the fifth lens 263 where it has passed through the second optical window 271, and breakdown (ignition) occurs. At this time, it is possible to grow the formed flame more efficiently by igniting near the center of the combustion chamber than when igniting near the wall of the combustion chamber. Therefore, it is preferable that the fifth lens 263 is closer to the combustion chamber side. Therefore, it is preferable that the thickness of the first optical window 208 is as thin as possible as long as airtightness is maintained. However, when the first optical window 208 is attached to the first housing 28-1, it is necessary to set the thickness so that damage or leakage does not occur when force is applied to the first optical window 208 such as shrink fitting.

  On the other hand, the window member 27A is exposed to a high temperature and high pressure environment. For this reason, it is preferable to use a highly durable material such as sapphire for the second optical window 271, and the thickness needs to be set so as not to break or leak. The second optical window 271 is preferably formed to be at least thicker than the first optical window 208.

  In addition, it is necessary to prevent the light reflected from the second optical window 271 from being focused in the optical elements such as various lenses, the laser resonator 25, and the first optical window 208. Therefore, an antireflection (AR) film (AR film) or an antireflection structure may be provided on the incident surface 271a and the exit surface 271b through which the laser light of the second optical window 271 passes. The antireflection structure is, for example, a structure in which a plurality of convex fine structures as disclosed in Japanese Patent Application Laid-Open No. 2017-111278 are formed with a pitch (vertical interval) shorter than the wavelength of incident light. The exit surface of the second optical window 271 faces the combustion chamber and is exposed to high temperature and pressure. For this reason, the antireflection structure is preferably provided on the exit surface of the second optical window rather than the antireflection film. On the other hand, since the first optical window 208 is protected by the second optical window 271, an antireflection film can be provided on the entrance surface 208 a and the exit surface 208 b of the first optical window 208. The incident surface 208a / 271a is the surface of the optical window 208/271 on the third condensing optical system 26 side, and the exit surface 208b / 271b is the surface of the optical window 208/271 on the combustion chamber 14 side.

Furthermore, a catalyst layer that exhibits a catalytic function by light or heat may be provided on the emission surface of the second optical window 271. For example, TiO ₂ can be used as the catalyst layer.

[Second Embodiment]
Next, a laser device, an ignition device, and an internal combustion engine according to a second embodiment will be described with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description thereof is omitted.

  The internal combustion engine according to the present embodiment may be the same as the internal combustion engine described with reference to FIG. 1 in the first embodiment. However, in this embodiment, the laser apparatus 11 is replaced with a laser apparatus 11A shown in FIG.

<Laser device>
As shown in FIG. 4, the laser device 11A according to the present embodiment has a configuration in which the housing 28 is replaced with a housing 28A in the same configuration as the laser device 11 shown in FIG.

  In the housing 28A, the first housing 28-1 in the first embodiment is divided into an excitation side housing 28-1a that excites crystals and a condensing side housing 28-1b that condenses laser light. ing. For example, the excitation side housing 28-1a and the condensing side housing 28-1b may be sealed with a sealing material 293 so that impurities do not enter from the connecting portion. Similar to the first embodiment, a first optical window 208 is provided at the tip (combustion chamber side) of the condensing side housing 28-1b. And the 2nd housing 28-2 provided with the window member 27A is fixed with respect to the 1st housing comprised by the excitation side housing 28-1a and the condensing side housing 28-1b similarly to 1st Embodiment. . Thereby, for example, the condensing side housing 28-1b is covered by the second housing 28-2.

  By providing the above configuration, as in the first embodiment, the optical elements such as the second condensing optical system 24 are protected from dust and impurities floating in the atmosphere when the window member 27A is replaced. Therefore, the dirty second optical window 271 can be easily replaced without being contaminated when the optical element such as a lens used in the laser device 11 is exposed to the air. .

  Since other configurations, operations, and effects are the same as those of the first embodiment described above, detailed description thereof is omitted here.

[Third Embodiment]
Next, a laser device, an ignition device, and an internal combustion engine according to a third embodiment will be described with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant description thereof is omitted.

  The internal combustion engine according to the present embodiment may be the same as the internal combustion engine described with reference to FIG. 1 in the first embodiment. However, in this embodiment, the laser apparatus 11 is replaced with a laser apparatus 11B shown in FIG.

<Laser device>
As shown in FIG. 5, the laser device 11 </ b> B according to this embodiment has the same configuration as the laser device 11 shown in FIG. 2, and the second housing 28-2 is a first optical window in the first housing 28-1. The second housing 28-2a that covers only the surface to which 208 is attached is provided. The junction between the first housing 28-1 and the second housing 28-2a is sealed with, for example, a sealing material 294, thereby preventing impurities from entering from the outside.

  As described above, the second housing 28-2a including the window member 27A covers only the surface to which the first optical window 208 is attached, thereby facilitating the removal of the second housing 28-2a. It is possible to improve the workability. Further, since the replacement part 28-2a can be reduced in size and shape, the manufacturing cost can be reduced. Note that the attachment of the second housing 28-2a to the first housing 28-1 is preferably, for example, screw fastening, but is not limited thereto.

  Since other configurations, operations, and effects are the same as those of the first embodiment described above, detailed description thereof is omitted here.

  In the above-described embodiment, the second optical window 271 is attached to the second housing 28-2 / 28-2a via the optical window holding member 272, but the second optical window holding member 272 is omitted. The housing 28-2 / 28-2a may be configured to hold the second optical window 271.

  In the above-described embodiment, the case where the second housing 28-2 / 28-2a is a member different from the members constituting the engine 10, such as the housing of the combustion chamber 14, is illustrated, but the present invention is not limited thereto. It is not something. For example, the housing of the combustion chamber 14 is used instead of the second housing 28-2 / 28-2a, the window member 27A is attached to the housing of the combustion chamber 14, and the housing of the combustion chamber 14 to which the window member 27A is attached. The first housing 28-1 (28-1a and 28-1b) may be attached to the body.

  As described above, the embodiment has been described. However, the embodiment is presented as an example, and the present invention is not limited to the embodiment. The above-described embodiment can be implemented in various other forms, and various combinations, omissions, replacements, changes, and the like can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 Engine (Internal combustion engine)
DESCRIPTION OF SYMBOLS 11, 11A, 11B Laser apparatus 12 Fuel injection mechanism 13 Exhaust mechanism 14 Combustion chamber 15 Piston 16 Drive apparatus 17 Engine control apparatus 21 Surface emitting laser 22 1st condensing optical system 221 Microlens 222 Condensing lens system 23 Optical fiber 24 1st 2 condensing optical system 241 first lens 242 second lens 25 laser resonator 251 laser medium 252 saturable absorber 26 third condensing optical system 261 third lens 262 fourth lens 263 fifth lens 27A window member 208 first Optical window 271 Second optical window 272 Optical window holding member 28 Housing 28-1 First housing 28-1a Excitation side housing 28-1b Condensing side housing 28-2, 28-2a Second housing 291, 292, 293, 294 Sealing material

JP, 2006-109128, A Japanese Patent Laying-Open No. 2015-1158 Japanese Patent No. 5766280

Claims (11)

A light source that emits laser light;
An optical element through which the laser beam passes;
A first housing that houses the optical element;
An optical window held by the second housing and through which the light having passed through the optical element passes;
A laser device. The laser device according to claim 1, wherein the first housing and the second housing are combined and integrated.   The laser device according to claim 1, wherein the second housing covers at least a part of the first housing.   4. The laser device according to claim 1, wherein the first housing and the second housing each have a threaded portion that fits into each other. 5.   5. The laser device according to claim 1, wherein a coupling portion between the first housing and the second housing is sealed with a sealing material.   The laser apparatus according to claim 1, further comprising an optical window held by the first housing.   The laser apparatus according to claim 6, wherein the optical window of the second casing is thicker than the optical window of the first casing.   The laser device according to claim 6, wherein an area of a light passage surface of the optical window of the second casing is smaller than an area of a light passage surface of the optical window of the first casing.   The antireflection film according to any one of claims 6 to 8, wherein an antireflection film is provided on an entrance surface and an exit surface of the optical window of the first housing and an entrance surface of the optical window of the second housing. Laser device.   An ignition device characterized in that fuel is ignited by the laser device according to any one of claims 1 to 9.   An internal combustion engine comprising the ignition device according to claim 10.

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