JP2018085469A - Laser device, ignition device and internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser device which enables the increase in oscillation efficiency.SOLUTION: A laser device comprises: a light-source device including a surface emitting laser array and a first condensing optical system; an optical fiber for transmitting light from the light-source device; a second condensing optical system for condensing light from the optical fiber; and a laser resonator including a laser medium and excited by light from the second condensing optical system. The laser medium has a length of 5 mm in a Z axial direction. The volume fraction Rv corresponding to the value of "a volume of a column part of which the diameter is equal to a beam waist size of the light" to "a volume of light in the laser medium" is 45% or more. The relation between an Mvalue of light launched from the optical fiber and the beam waist size (diameter) D of light from the second condensing optical system is set to satisfy the following requirement: Mvalue≤769.1×D-53.166×D.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a laser device, an ignition device, and an internal combustion engine, and more particularly to a laser device having a laser resonator, an ignition device having the laser device, and an internal combustion engine including the ignition device.

  A laser device having a laser resonator that oscillates by optical excitation is expected to be applied to various fields such as an ignition device, a laser processing machine, and a medical device.

  For example, Patent Document 1 discloses a laser ignition device for an internal combustion engine that includes a laser device having a laser active solid and a Q switch circuit, and a pump light source for optically pumping the laser device.

  Further, Patent Document 2 discloses an in-vehicle ignition device including a semiconductor laser light source and a solid-state laser medium that emits a pulse laser light for fuel ignition excited by the semiconductor laser light emitted from the semiconductor laser light source. Has been.

  However, the conventional laser device has room for improvement in terms of improving the oscillation efficiency.

The present invention includes a light source device, a light transmission member that transmits light from the light source device, an optical system that collects light from the light transmission member, and a laser medium, and is excited by light from the optical system. And is emitted from the optical transmission member based on the size of “the volume of the cylindrical portion whose diameter is the beam waist diameter of the light” with respect to “the volume of the light in the laser medium” This is a laser device in which the relationship between the M ² value of the emitted light and the beam waist diameter of the light from the optical system has been determined.

  According to the laser device of the present invention, the oscillation efficiency can be improved.

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 a 2nd condensing optical system. FIG. 6 is a first diagram for explaining the size of a region that does not contribute to oscillation; FIG. 6 is a second diagram for explaining the size of a region that does not contribute to oscillation; It is a figure for demonstrating a volume ratio. It is a figure for demonstrating the area | region in which the several light emission part is provided in a surface emitting laser array. When the volume ratio is 45%, which is a diagram for explaining a relationship between the M ² value and the light beam waist diameter D of the light emitted from the optical fiber. It is a figure for demonstrating the case where the light which injected into the laser medium hits the side surface of a laser medium when passing in the laser medium. It is a figure for demonstrating the case where the light which injected into the laser medium does not hit the side surface of a laser medium when passing in the laser medium. It is a figure for demonstrating the case where the beam diameter of excitation light is larger than the incident end surface of a laser resonator. It is a figure for demonstrating the case where the incident end surface of a laser resonator is larger than the beam diameter of excitation light. FIG. 14A and FIG. 14B are diagrams for explaining a schematic configuration of a laser annealing apparatus, respectively. It is a figure for demonstrating schematic structure of a laser beam machine.

"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"
The adjustment of the condensing position of the light emitted from the laser device 200 in the Z-axis direction can be 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. .

  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. 4 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.

  Specifically, the laser resonator 206 has a quadrangular prism shape whose longitudinal direction is the Z-axis direction, and the length in the X-axis direction and the length in the Y-axis direction are 5 mm. The laser medium 206a has a length in the Z-axis direction of 5 mm and a refractive index of 1.829. The saturable absorber 206b is adjusted so that the initial transmittance is 0.50 (50%).

  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”.

  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.

The optical fiber 204 is an optical fiber having a core diameter of 1.5 mm and an NA of 0.39. The M ² value indicating the beam quality of light emitted from the optical fiber 204 is about 1400.

  At this time, when the beam waist diameter is about 1 mm, as shown in FIG. 5 as an example, the excitation light diverges in the laser oscillator, and the region that does not contribute to oscillation becomes large. That is, the oscillation efficiency is poor.

  Therefore, when the beam waist diameter is about 1.5 mm, as shown in FIG. 6 as an example, the excitation light is less likely to diverge in the laser oscillator, and the region that does not contribute to oscillation is reduced. That is, the oscillation efficiency is improved.

In this embodiment, M ^{2 of the} light emitted from the optical fiber is based on the “volume of the cylindrical portion having the beam waist diameter in the light as a diameter” with respect to “the volume of the light in the laser medium”. The relationship between the value and the beam waist diameter of the light from the second condensing optical system is determined.

Here, the light emitted from the optical fiber is stopped using an arbitrary lens in the atmosphere (refractive index = 1.0), and, as shown in FIG. Then, a 5 mm range centering on the beam waist position is extracted. And the volume of the extracted light is set to Vt. Further, the volume of the cylindrical portion having the beam waist diameter in the extracted light as a diameter is defined as Vb. Then, as indicated by the following equation (1), the magnitude of Vb with respect to Vt is defined as a volume ratio Rv (%).
Rv = Vb ÷ Vt × 100 (1)

  In the present embodiment, as shown in FIG. 8, the diameter of the region where the plurality of light emitting units is provided in the surface emitting laser array 201 is about 9 mm. The power of light emitted from the surface emitting laser array 201 is about 300 W. However, the power of the light emitted from the optical fiber 204 is about 200 W due to the position error and shape error of each optical member.

  The inventors obtained new knowledge that, in this embodiment, if the volume ratio Rv is 45% or more, the output of the laser resonator necessary for engine ignition can be obtained. At this time, the laser resonator was able to output four pulses of 2.5 mJ pulsed light within 500 μsec when heated to about 100 ° C., assuming that the engine was in operation. If 4 pulses of 2.5 mJ pulsed light can be output, it is possible to operate the engine stably (Masaki Tokibu, five others, “Engine Ignition with Microlasers”, Laser Research, Vol. 37, Vol. 4, p283-p289, April 2009).

FIG. 9 shows the relationship between the M ² value of the light emitted from the optical fiber 204 and the beam waist diameter (diameter) D of the light from the second condensing optical system 205 when the volume ratio Rv is 45%. It is shown. It was found that this relationship is expressed by the following equation (2).
M ² value = 769.1 × D ² −53.166 × D (2)

When the following expression (3) is satisfied, the volume ratio Rv is 45% or more.
M ² value ≦ 769.1 × D ² −53.166 × D (3)

That is, when the above expression (3) is satisfied, the output of the laser resonator necessary for engine ignition can be obtained. In the present embodiment, since M ² value of 1400 is set as follows: (4) is satisfied.
769.1 × D ² −53.166 × D ≧ 1400 (4)

When the above equation (4) is solved, D ≧ 1.385 mm. In this embodiment, the beam waist diameter D is set to 1.60 mm (1 / e ² ).

  As an example, as shown in FIG. 10, when light incident on the laser medium 206a passes through the laser medium 206a and hits the side surface of the laser medium 206a, excitation light returns to the laser medium 206a, and the laser medium Heat may be generated in 206a, which may adversely affect the characteristics of the laser medium 206a. In some cases, the excitation light reflected by the side surface of the laser medium 206a is amplified in the laser medium 206a, and unwanted parasitic oscillation may occur. This parasitic oscillation is an unnecessary oscillation and consumes excitation energy that should be used for amplification of the original light, resulting in a decrease in the output of the laser resonator.

  Therefore, in the present embodiment, it is set so that the light incident on the laser medium 206a does not hit the side surface of the laser medium 206a when passing through the laser medium 206a (see FIG. 11).

  As an example, as shown in FIG. 12, when the beam diameter of the excitation light is larger than the incident end face (first surface) of the laser medium 206a, a part of the excitation light hits the side surface of the laser medium 206a. The excitation light is reflected there. In this case, the energy of the excitation light is not converted to the Q-switched laser, and the oscillation efficiency is reduced.

  Therefore, in the present embodiment, the size of the incident end surface (first surface) of the laser medium 206a is set to be larger than the beam diameter of the excitation light (see FIG. 13).

  As is apparent from the above description, in the laser device 200 according to the present embodiment, the surface emitting laser array 201 and the first condensing optical system 203 constitute a light source device in the laser device of the present invention. In the laser apparatus 200 according to the present embodiment, the second condensing optical system 205 constitutes an optical system in the laser apparatus of the present invention, and the optical fiber 204 constitutes a transmission member in the laser apparatus of the present invention. Yes.

  In the ignition device 301 according to this embodiment, the emission optical system 210 constitutes the “optical system for condensing light from the laser device” in the ignition device of the present invention.

  As described above, the laser apparatus 200 according to this embodiment includes the surface emitting laser array 201, the first condensing optical system 203, the optical fiber 204, the second condensing optical system 205, the laser resonator 206, and the like. ing.

  The surface emitting laser array 201 is an excitation light source, and light emitted from the surface emitting laser array 201 is excited via the first condensing optical system 203, the optical fiber 204, and the second condensing optical system 205. The light enters the laser resonator 206 as light.

  The laser resonator 206 is a Q-switched laser, and includes a laser medium 206a and a saturable absorber 206b.

Based on the volume ratio Rv, the relationship between the M ² value of the light emitted from the optical fiber 204 and the beam waist diameter of the light from the second condensing optical system 205 is determined. That is, the length of the laser medium 206a in the Z-axis direction is 5 mm, and corresponds to the size of “the volume of the cylindrical portion having the beam waist diameter in the light as a diameter” with respect to the “volume of light in the laser medium 206a”. The volume ratio Rv is 45% or more, and the relationship between the M ² value of the light emitted from the optical fiber 204 and the beam waist diameter D of the light from the second condensing optical system 205 satisfies the above expression (3). It is set to be. Further, the light passing through the laser medium 206a is set so as not to hit the side surface of the laser medium 206a. Furthermore, the size of the incident end surface (first surface) of the laser medium 206a is set to be larger than the beam diameter of the excitation light. In this case, the oscillation efficiency can be improved.

  Since the ignition device 301 includes the laser device 200, stable ignition can be performed efficiently.

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

  In the above embodiment, the emission optical system 210 may be composed of a single optical element or a plurality of optical elements.

  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.

  Moreover, although the said embodiment demonstrated the case where the power of the light inject | emitted from the optical fiber 204 was 200 W, it is not limited to this. The power of light emitted from the optical fiber 204 is preferably 200 W or more.

Further, in the above embodiment, the M ² value of the light emitted from the optical fiber 204 has been described for the case of 1400, but is not limited thereto. By determining the beam waist diameter of the light from the second condensing optical system 205 according to the M ² value of the light emitted from the optical fiber 204, the same effect as in the above embodiment can be obtained.

  Moreover, although the said embodiment demonstrated the case where the length regarding the Z-axis direction of the laser medium 206a was 5 mm, it is not limited to this. If the length of the laser medium 206a in the Z-axis direction is too small, the quality of the laser light emitted from the laser resonator 206 is degraded. Therefore, the length of the laser medium 206a in the Z-axis direction is preferably 5 mm or more.

  The laser device 200 can be used in a laser annealing device or a laser processing machine.

<Laser annealing equipment>
As an example, FIG. 14A and FIG. 14B show a schematic configuration of a laser annealing apparatus 1000 having a laser apparatus 200. The laser annealing apparatus 1000 includes a light source 1010, an optical system 1020, a table apparatus 1030, a control apparatus, and the like.

  The light source 1010 includes the laser device 200 described above and can emit laser light. The optical system 1020 guides the laser light emitted from the light source 1010 to the surface of the object P. The table device 1030 has a table on which the object P is placed. The table can move at least along the Y-axis direction.

  For example, in the case where the object P is amorphous silicon (a-Si), when irradiated with laser light, the amorphous silicon (a-Si) is crystallized by increasing the temperature and then gradually cooling, It becomes polysilicon (p-Si).

  In this laser annealing apparatus 1000, since the light source 1010 has the laser apparatus 200, the processing efficiency can be improved.

<Laser processing machine>
As an example, FIG. 15 shows a schematic configuration of a laser processing machine 3000 having the laser device 200 described above. The laser processing machine 3000 includes a light source 3010, an optical system 3100, a table 3150 on which an object P is placed, a table driving device 3160, an operation panel 3180, a control device 3200, and the like.

  The light source 3010 has a laser device 200 and emits laser light based on an instruction from the control device 3200. The optical system 3100 focuses the laser light emitted from the light source 3010 in the vicinity of the surface of the object P. The table driving device 3160 moves the table 3150 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on instructions from the control device 3200.

  The operation panel 3180 has a plurality of keys for the operator to make various settings and a display for displaying various information. The control device 3200 controls the light source 3010 and the table driving device 3160 based on various setting information from the operation panel 3180.

  In the laser processing machine 3000, since the light source 3010 has the laser device 200, the processing efficiency of processing (for example, cutting and welding) can be improved.

  Note that the laser processing machine 3000 may include a plurality of light sources 3010.

  Further, the laser apparatus 200 described above is also suitable for an apparatus using laser light other than a laser annealing apparatus and a laser processing machine. For example, the laser device 200 may be used as a light source for a display device.

  DESCRIPTION OF SYMBOLS 200 ... Laser apparatus, 201 ... Surface emitting laser array (a part of light source device), 203 ... 1st condensing optical system (a part of light source device), 204 ... Optical fiber (transmission member), 205 ... 2nd condensing Optical system (optical system for condensing light from the optical transmission member), 205a ... first lens, 205b ... second lens, 206 ... laser resonator, 206a ... laser medium, 206b ... saturable absorber, 210 ... eject Optical system (optical system for condensing light from the laser device), 212... Protection member, 220... Drive device, 222... Engine control device, 300 ... engine (internal combustion engine), 301 ... ignition device, 302. , 303 ... exhaust mechanism, 304 ... combustion chamber, 305 ... piston, 1000 ... laser annealing device, 1010 ... light source, 1020 ... optical system, 1030 ... table device, 3000 ... laser processing machine 3010 ... light source, 3100 ... optical system, 3150 ... table, 3160 ... table drive apparatus, 3180 ... control panel, 3200 ... control unit, P ... object.

Special table 2013-545280 gazette JP 2014-192166 A

Claims (15)

A light source device;
An optical transmission member for transmitting light from the light source device;
An optical system for collecting light from the light transmission member;
A laser resonator including a laser medium and excited by light from the optical system,
Based on the size of “the volume of the cylindrical portion whose diameter is the beam waist diameter in the light” relative to “the volume of light in the laser medium”, the M ² value of the light emitted from the optical transmission member and the A laser apparatus in which a relationship with a beam waist diameter of light from an optical system is determined. The relationship between the M ² value of light emitted from the light transmission member and the beam waist diameter of light from the optical system is as follows:
For the light from the optical system, in the atmosphere, the range corresponding to the length of the laser medium is extracted with the beam waist position as the center with respect to the traveling direction of the light, the volume of the extracted light is Vt, The volume is determined based on a volume ratio (%) obtained by Vb ÷ Vt × 100, where Vb is a volume of a cylindrical portion having a beam waist diameter in the extracted light as a diameter. 2. The laser device according to 1. The length of the laser medium is 5 mm, and the M ² value of the light emitted from the optical transmission member and the beam waist diameter of the light from the optical system so that the volume ratio (%) is 45% or more. The laser device according to claim 2, wherein the relationship is determined. The relationship between the M ² value of the light emitted from the optical transmission member and the beam waist diameter (diameter) D of the light from the optical system is M ² value ≦ 769.1 × D ² −53.166 × D, The laser device according to claim 3, wherein:   The laser apparatus according to claim 1, wherein the light incident on the laser medium passes through the laser medium without hitting a side surface of the laser medium.   The laser apparatus according to claim 1, wherein a beam diameter of light incident on the laser resonator is smaller than a size of an incident end face of the laser resonator.   The laser device according to claim 1, wherein the optical transmission member is an optical fiber.   The laser device according to claim 1, wherein the light source device includes a vertical cavity surface emitting laser.   The laser device according to claim 1, wherein the laser resonator is a Q-switched laser.   The laser device according to claim 9, wherein the laser resonator includes a saturable absorber.   11. The laser device according to claim 10, wherein the laser medium is a YAG crystal doped with Nd, and the saturable absorber is a YAG crystal doped with Cr.   The laser device according to claim 1, wherein the power of light emitted from the optical transmission member is 200 W or more.   The laser device according to claim 1, wherein the length of the laser medium is 5 mm or more. A laser device according to any one of claims 1 to 13,
And an optical system that collects light from the laser device. 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.

Images