JP2018152539A - Laser device, ignition device and internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a laser device which enables the achievement of remarkably good and stable laser characteristics and which is improved in the property of dissipating heat generated in a laser resonator; an ignition device; and an internal combustion engine.SOLUTION: A laser device comprises: a light source 101 for excitation, which includes a surface emitting laser 121 and emits excitation light; a laser resonator 114 which performs a Q switch laser operation in such a way that a laser medium is excited by excitation light emitted from the light source 101 for excitation; a metal film 115 formed on at least part of a side face in the laser resonator 114, except a first face on an incident side of the laser resonator, which is perpendicular to an optical axis of the excitation light, and a second face on an outgoing side, which is perpendicular to the optical axis of the excitation light; and a fixing member 113 serving to fix the laser resonator 114 with the metal film 115 formed therein by pressing it with good adhesion.SELECTED DRAWING: Figure 2

Description

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

  A solid-state laser device using a laser crystal that oscillates by photoexcitation is expected to be applied to various fields such as a laser ignition device, a laser processing device, and a medical device, and has been put into practical use. Among them, in particular, a Q-switched laser in which a medium called a saturable absorber is provided at the tip of a laser crystal has a laser output with a very high peak value, and thus requires a high spatial energy density such as laser ignition. Very promising for application.

  As a light source for exciting the laser crystal, a semiconductor laser is generally used. A VCSEL (Vertical Cavity Surface Emitting Laser) is a semiconductor laser that oscillates in a direction perpendicular to a substrate, has a very high wavelength stability with respect to temperature, and has a high two-dimensional array. It has the feature that output is easy. From these characteristics, it is desirable to use a surface emitting laser as a light source for exciting a solid-state laser.

  However, when a surface emitting laser is used as a light source for excitation, the VCSEL has a large light emitting area of each light emitting element, so that the quality of the excitation light tends to be deteriorated. In such a case, the pumping efficiency of the laser medium of the laser resonator decreases, and heat generation increases, causing problems that the characteristics are deteriorated or varied due to the heat generation.

  Therefore, conventionally, a technique for providing a cooling mechanism and cooling the heat generated in the laser resonator has been disclosed (for example, Patent Document 1).

  However, since the holding member for holding the laser resonator is machined with mechanical accuracy, the contact area between the laser resonator and the fixing member of the laser resonator is smaller than the surface area of the laser resonator. The thermal resistance of the part tends to be high. That is, there arises a problem that even if the cooling mechanism is provided, the cooling effect cannot be sufficiently obtained. For this reason, the conventional technology has a problem that the cooling mechanism provided to obtain a desired cooling effect is large in size and is likely to be expensive, or even if a cooling mechanism is provided, the desired cooling effect cannot be obtained. There is.

  Therefore, Patent Document 2 discloses a technique of providing an elastic body between a laser resonator and a fixing member of the laser resonator.

  However, in the technique disclosed in Patent Document 2, it is necessary to press the elastic body with good adhesion to the laser resonator, which is practically difficult. For example, if a force in a direction parallel to the contact surface is applied to the elastic body when the elastic body is pressed, the elastic body may be deformed and a gap may be formed between the elastic body and the laser resonator. Even if the contact is made without such deformation, a certain amount of gap or non-uniformity is inevitably generated between the elastic body manufactured within the range of mechanical error and the laser resonator.

  The present invention has been made in view of the above, and has improved a heat dissipation property of heat generated in a laser resonator, and can realize extremely good and stable laser characteristics. An object is to provide an internal combustion engine.

  In order to solve the above-described problems and achieve the object, the present invention includes an excitation light source that includes a surface emitting laser and emits excitation light, and an excitation medium that is excited by the excitation light emitted from the excitation light source. A laser resonator performing Q-switched laser operation, a first surface on the incident side perpendicular to the optical axis of the excitation light in the laser resonator, and an emission side perpendicular to the optical axis of the excitation light A metal film formed on at least a part of the side surface excluding the second surface; and a fixing member that presses and fixes the laser resonator on which the metal film is formed. To do.

  According to the present invention, it is possible to improve the heat dissipation of the heat generated in the laser resonator, and to realize extremely good and stable laser characteristics.

FIG. 1 is a diagram illustrating a schematic configuration of an engine according to an embodiment. FIG. 2 is a schematic diagram schematically showing the configuration of the ignition device. FIG. 3A is a perspective view schematically showing the configuration of the laser resonator, and FIG. 3B is a front view. FIG. 4 is a front view schematically showing a modification of the configuration of the laser resonator.

  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.

  FIG. 1 is a diagram illustrating a schematic configuration of an engine 300 according to the embodiment. As shown in FIG. 1, an engine 300 that is an internal combustion engine includes an ignition device 301, a fuel injection mechanism 302, an exhaust mechanism 303, a combustion chamber 304, a piston 305, and the like.

Here, the operation of the 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.

  The engine 300 performs the above operation based on an instruction of an engine control device 220 (see FIG. 2) provided outside the engine 300 and electrically connected to the engine 300.

  Next, the ignition device 301 will be described.

  Here, FIG. 2 is a schematic diagram schematically showing the configuration of the ignition device 301. As shown in FIG. 2, the ignition device 301 includes a laser device 100, a driving device 200, an emission optical system 210, a protection member 212, and the like.

  The laser device 100 includes a surface emitting laser light source 101, an optical fiber 102, an excitation optical system 112, a laser crystal holding / fixing member 113, and a laser resonator 114. A surface emitting laser light source 101, an optical fiber 102, an excitation optical system 112, a laser crystal holding / fixing member 113, and a laser resonator 114 are accommodated in a housing 111.

  The surface emitting laser light source 101 includes a surface emitting laser array 121 and a condensing optical system 122. In the present embodiment, an explanation will be given using the XYZ three-dimensional orthogonal coordinate system and assuming that the light emission direction from the surface emitting laser light source 101 (surface emitting laser array 121) is the + Z direction.

  The surface emitting laser array 121 is a light source for excitation, and has a plurality of light emitting units. Each light emitting unit is a vertical cavity surface emitting laser (VCSEL). When the laser light is emitted from the surface emitting laser array 121, the plurality of light emitting units emit light simultaneously. The wavelength of light emitted from the surface emitting laser array 121 is 808 nm. The surface emitting laser array 121 is driven by the driving device 200.

  The surface-emitting laser array 121 is a light source that is advantageous for exciting a Q-switched laser (laser resonator 114) whose characteristics change greatly due to a shift in pumping wavelength because the wavelength shift due to temperature is very small. Therefore, when the surface emitting laser array 121 is used as an excitation light source, there is an advantage that environmental temperature control can be simplified.

  The condensing optical system 122 is a condensing lens, and condenses the light emitted from the surface emitting laser array 121.

  The condensing optical system 122 may be composed of a plurality of optical elements. The condensing optical system 122 has a microlens array and a condensing lens as an example here. The microlens array is disposed on the optical path of the light emitted from the surface emitting laser array 121. This microlens array has a plurality of lens portions corresponding to the plurality of light emitting portions of the surface emitting laser array 121. And each lens part makes the light radiate | emitted from the corresponding light emission part into substantially parallel light. That is, the microlens array collimates the light emitted from the surface emitting laser array 121. The distance between the surface emitting laser array 121 and the microlens array in the Z-axis direction is determined according to the focal length of the microlens array. The condensing lens condenses light through the microlens array. An appropriate condensing lens is selected according to the cross-sectional area of the light passing through the microlens array, the core diameter of the optical fiber 102 and the NA.

  The optical fiber 102 connects a surface-emitting laser light source 101 that is an excitation light source and a laser resonator 114. The optical fiber 102 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 condensing optical system 122. Here, an optical fiber having a core diameter of 1.5 mm is used as the optical fiber 102. As described above, by using the optical fiber 102 having a core diameter of 1.0 mm or more and less than 2.0 mm, the excitation light can be efficiently transmitted even in the surface emitting laser light source 101 in which the condensing spot diameter tends to be large. . That is, a more efficient laser device 100 can be provided.

  Further, by providing the optical fiber 102, the surface emitting laser light source 101 can be placed at a position away from the laser resonator 114, so that the surface emitting laser light source 101 is separated from the influence of heat generated by the laser resonator 114. be able to. Thereby, the freedom degree of arrangement design can be increased and the laser apparatus 100 with higher reliability can be provided. Further, when the laser device 100 is used for the ignition device 301, the surface emitting laser light source 101 can be moved away from the heat source, so that the range of methods for cooling the engine 300 can be widened. Furthermore, since the surface emitting laser light source 101 can be moved away from the engine 300 as a vibration source, the reliability of the surface emitting laser light source 101 can be improved.

  The light incident on the optical fiber 102 propagates in the core and is emitted from the + Z side end face of the core. The excitation optical system 112 is disposed on the optical path of the light emitted from the optical fiber 102 and collects the light. Note that a plurality of optical elements may be used as the excitation optical system 112. The light condensed by the excitation optical system 112 enters the laser resonator 114.

  In the present embodiment, the form in which the excitation light emitted from the surface emitting laser light source 101 is transmitted to the laser resonator 114 using the optical fiber 102 has been described. However, the present invention is not limited to this. For example, a method may be used in which a surface emitting laser array 121 is provided immediately before the laser resonator 114 and the laser resonator 114 is directly excited by laser light emitted from the surface emitting laser array 121.

  Here, the excitation optical system 112 includes a first lens 112a and a second lens 112b. The excitation optical system 112 may have three or more lenses. The first lens 112a is a collimating lens, and makes light emitted from the optical fiber 102 substantially parallel light. The 2nd lens 112b is a condensing lens, and condenses the light made into the substantially parallel light by the 1st lens 112a.

  The laser resonator 114 is a Q switch laser. The Q-switched laser is characterized by increasing the inversion distribution by irradiating light from the excitation light source in advance and taking out energy by releasing the Q-switch element, so that high peak energy can be obtained. . Because of such characteristics, the Q switch laser is applied to an ignition device for a combustible air-fuel mixture in a combustion chamber in an internal combustion engine.

  The laser resonator 114 includes a laser medium 114a and a saturable absorber 114b. The laser medium 114a is an Nd: YAG ceramic crystal, and Nd is doped by 1.1%. The saturable absorber 114b is a Cr: YAG ceramic crystal and has an initial transmittance of about 50%.

  Here, the Nd: YAG crystal and the Cr: YAG crystal are both ceramics. The laser resonator 114 is a so-called composite crystal in which a laser medium 114a and a saturable absorber 114b are joined.

  The light from the excitation optical system 112 is incident on the laser medium 114a. That is, the laser medium 114 a is excited by the light from the excitation optical system 112. The wavelength of light emitted from the surface emitting laser array 121 (here, 808 nm) is the wavelength with the highest absorption efficiency in the YAG crystal. The saturable absorber 114b performs a Q switch laser operation.

  The surface on the incident side (−Z side) of the laser medium 114a and the surface on the emission side (+ Z side) of the saturable absorber 114b are subjected to an optical polishing process and serve as a mirror. Hereinafter, for convenience, a surface perpendicular to the optical axis on the incident side of the laser medium 114a is also referred to as a “first surface”, and a surface perpendicular to the optical axis on the output side of the saturable absorber 114b is referred to as “first surface”. Also referred to as “second surface”.

  The first surface and the second surface have a wavelength of light emitted from the surface emitting laser array 121 (here, 808 nm) and a wavelength of light emitted from the laser resonator 114 (here, 1064 nm). A corresponding dielectric multilayer film is coated. 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. Thereby, the light resonates and is amplified in the laser resonator 114.

  3A is a perspective view schematically showing the configuration of the laser resonator 114, and FIG. 3B is a front view. As shown in FIG. 3, a metal film 115 is formed on the side surface of the laser resonator 114 excluding the first surface and the second surface. In other words, the metal film 115 is formed in all regions on the surface in contact with the laser crystal holding / fixing member 113. Here, the metal film 115 is formed by depositing silver (Ag) having a thickness of 50 μm by a metallization method. The material of the laser crystal holding / fixing member 113 is copper (Cu).

  In the present embodiment, the metal film 115 is formed on all sides of the laser resonator 114 except for the first and second surfaces, that is, the surface in contact with the laser crystal holding / fixing member 113. The film is formed but is not limited to this. For example, even when the metal film 115 is formed on at least a part of the side surface of the laser resonator 114 excluding the first surface and the second surface, heat dissipation of the heat generated in the laser resonator 114 is achieved. It is possible to improve.

  As shown in FIG. 3, the laser resonator 114 on which the metal film 115 is formed is pressed and fixed to the laser crystal holding / fixing member 113 with good adhesion, and is held at a predetermined position in the laser device 100. .

  The material of the metal film 115 is a material having a Young's modulus (longitudinal elastic modulus) smaller than that of the laser crystal holding / fixing member 113. Thereby, the metal film 115 is deformed, the contact area tends to be large, and the heat dissipation effect can be enhanced.

  That is, in the laser apparatus 100, the metal film 115 provided between the laser resonator 114 and the laser crystal holding / fixing member 113 is deformed, so that the laser resonator 114 and the laser crystal holding / fixing member 113 are The contact area can be increased. Thereby, it is possible to provide the laser device 100 with higher heat dissipation and uniformity.

  In the present embodiment, as a method for forming the metal film 115 on the laser resonator 114, a method of metallizing silver on the side surface of the laser resonator 114 has been described, but the present invention is not limited to this. For example, the metal film 115 may be formed by plating or vapor deposition. The material is not limited to silver, and may be nickel, silver copper titanium, or the like. However, since the YAG ceramic crystal may be deteriorated at a high temperature, when using a method of providing metallization on the side surface of the laser resonator 114, a material capable of providing the metal film 115 at about 1000 ° C. or less. It is desirable to use Further, as in the present embodiment, it is desirable to use a material having a Young's modulus smaller than that of the laser crystal holding / fixing member 113 as the material of the metal film 115, but the present invention is not limited to this.

  In the present embodiment, the case where the laser crystal holding / fixing member 113 is an independent member has been described. However, the present invention is not limited to this. For example, the laser crystal holding / fixing member 113 and the housing 111 may be integrated.

  By the way, as shown in FIG.3 (b), the shape of the 1st surface and 2nd surface of the laser resonator 114 is a rectangle. Thus, by making the shape of the first surface and the second surface of the laser resonator 114 rectangular, the processing of the laser resonator 114 and the laser crystal holding / fixing member 113 can be simplified. Therefore, these processing costs can be reduced and the surface accuracy of the processing can be increased, so that the contact area between the laser resonator 114 and the laser crystal holding / fixing member 113 can be easily increased. That is, a more efficient and stable laser device 100 can be realized at low cost.

  The emission optical system 210 is disposed on the optical path of the light emitted from the laser device 100 (laser resonator 114). The emission optical system 210 is composed of, for example, at least one lens. In this case, the condensing position of the light emitted from the laser device 100 (laser resonator 114) can be adjusted by the position of the lens in the optical axis direction and the combination of the lenses. As an example, the exit optical system 210 uses a condensing lens here. Light is condensed by the emission optical system 210, and a high energy density can be obtained at the focal point.

  The protection member 212 is made of a transparent or translucent member disposed on the optical path of the light emitted from the emission optical system 210. The protection member 212 is attached to the periphery of the opening formed on the surface facing the combustion chamber 304 so as to cover the opening. As a material of the protection member 212, sapphire glass having excellent durability under a high temperature and high pressure environment is used.

  Returning to FIG. 2, the driving device 200 drives the surface emitting laser array 121 based on an instruction from the engine control device 220. That is, drive device 200 drives surface-emitting laser array 121 so that light is emitted from ignition device 301 at the timing of ignition in the operation of engine 300. In addition, the several light emission part in the surface emitting laser array 121 is lighted on and off simultaneously.

  As described above, according to the present embodiment, the metal film 115 is directly formed on the entire area of the surface of the laser resonator 114 that contacts the laser crystal holding / fixing member 113, so that the laser resonator 114 and the metal film are formed. It is possible to ensure adhesion at the atomic level with 115 and provide a very high heat conduction effect. As a result, the heat dissipation of the heat generated by the laser resonator 114 can be improved, and laser characteristics that are extremely good and stable can be realized. In addition, the laser device 100 with high efficiency and stability, and the engine 300 that is an internal combustion engine that has the same size and cost as the conventional one, and is more efficient and stable than the conventional one, or the smaller size than the conventional one with the same characteristics as the conventional one. An engine 300 that is a low-cost internal combustion engine can be provided.

  Further, even when the cooling mechanism for cooling the heat generated by the laser resonator 114 is provided in the ignition device 301 as in the prior art, the cooling effect can be obtained with high efficiency. Can be.

  Further, by directly forming the metal film 115 on the entire region of the surface of the laser resonator 114 that is in contact with the laser crystal holding / fixing member 113, the excitation light that tries to escape to the outside of the laser resonator 114 is reflected on the side surface. It is reflected by the metal film 115, returned to the laser resonator 114, and can be used as excitation light. Therefore, the utilization efficiency of excitation light can be improved simultaneously with enhancing the heat dissipation effect. That is, the highly efficient and stable laser device 100 can be realized at a small size and at a low cost.

  In the present embodiment, the shape of the first surface and the second surface of the laser resonator 114 is rectangular, but the present invention is not limited to this. Here, FIG. 4 is a front view schematically showing a modified example of the configuration of the laser resonator 114. As shown in FIG. 4, the shape of the first surface and the second surface of the laser resonator 114 may be circular. In this case, when viewed from the optical axis direction, heat generation in the laser resonator 114 occurs concentrically. Thereby, the heat generated by the laser resonator 114 can be efficiently radiated.

  In the present embodiment, the case of an engine (piston engine) 300 that moves a piston with 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 100 is used for the ignition device 301 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.

DESCRIPTION OF SYMBOLS 100 Laser apparatus 101 Light source for excitation 102 Optical fiber 113 Fixing member 114 Laser resonator 115 Metal film 121 Surface emitting laser 200 Drive apparatus 210 Output optical system 300 Internal combustion engine 301 Ignition apparatus

Japanese Patent No. 581224 JP2013-016678A

Claims (10)

An excitation light source that emits excitation light with a surface emitting laser; and
A laser resonator that performs Q-switched laser operation by exciting a laser medium with excitation light emitted from the excitation light source;
At least one of the side surfaces of the laser resonator except for the first surface on the incident side perpendicular to the optical axis of the excitation light and the second surface on the emission side perpendicular to the optical axis of the excitation light. A metal film formed on the part,
A fixing member that presses and fixes the laser resonator on which the metal film is formed;
A laser device comprising: The shapes of the first surface and the second surface of the laser resonator are rectangular.
The laser apparatus according to claim 1. The shapes of the first surface and the second surface of the laser resonator are circular,
The laser apparatus according to claim 1. The metal film is formed on all sides of the side surface that is in contact with the fixing member except for the first surface and the second surface of the laser resonator.
The laser apparatus according to claim 1, wherein the laser apparatus is characterized in that Comprising an optical fiber connecting the excitation light source and the laser resonator;
The optical fiber transmits excitation light emitted from the excitation light source to the laser resonator.
The laser apparatus according to claim 1, wherein The diameter of the core of the optical fiber is 1.0 mm or more and less than 2.0 mm,
The laser device according to claim 5, wherein: The material of the metal film is a material having a Young's modulus smaller than the material of the fixing member.
The laser apparatus according to claim 1, wherein A laser device according to any one of claims 1 to 7,
A driving device for driving a surface emitting laser included in the laser device;
An emission optical system arranged on an optical path of light emitted from the laser device by driving the drive device, and condensing the light;
An ignition device comprising: A cooling mechanism for cooling the heat generated in the laser resonator;
The ignition device according to claim 8. In an internal combustion engine that generates combustion gas by burning fuel,
The igniter according to claim 8 or 9 for igniting the fuel,
An internal combustion engine characterized by that.

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