JP6739748B2 - Laser device, ignition device and internal combustion engine - Google Patents

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 provided with the ignition device.

A laser device using a laser medium 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 that optically pumps the laser device.

Patent Document 2 discloses a vehicle-mounted ignition device that includes a semiconductor laser light source and a solid-state laser medium that is excited by the semiconductor laser light emitted from the semiconductor laser light source and emits a pulsed laser light for fuel ignition. Has been done.

However, in the conventional laser device, the energy per pulse has not been taken into consideration.

The present invention relates to an optical system including a light source device including a surface emitting laser array having a plurality of light emitting parts, an optical fiber for transmitting light from the light source device, and a lens system for condensing light through the optical fiber. System and a laser resonator irradiated with light through the optical system and emitting laser light, and with respect to the traveling direction of the light through the optical system, the light through the optical system in the laser resonator. Is a laser device in which the position of the incident surface is on the downstream side of the beam waist position of the light.

According to the laser device of the present invention, the energy per pulse can be increased.

It is a figure for explaining the outline of engine 300 concerning one embodiment of the present invention. It is a figure for demonstrating the ignition device 301. It is a figure for demonstrating the laser resonator 206. It is a figure for demonstrating a surface emitting laser array. It is a figure for demonstrating a 2nd condensing optical system. It is a figure for explaining excitation light. It is a figure for demonstrating the Rayleigh length. It is a figure for demonstrating the relationship between the energy per 1 pulse, and the position of the 1st surface regarding a Z-axis direction. FIGS. 9A and 9B are diagrams for explaining regions that do not contribute to oscillation. FIG. 10A and FIG. 10B are each a diagram for explaining the schematic configuration of the laser annealing apparatus. It is a figure for explaining a schematic structure of a laser beam machine.

"Overview"
An embodiment of the present invention will be described below 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 injection mechanism 302, an exhaust mechanism 303, a combustion chamber 304, a piston 305, and the like.

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. As a result, 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).

In this way, a series of processes including intake, compression, ignition, combustion, and exhaust are repeated. Then, the piston 305 moves in response to the 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 from an engine control device that is provided outside the engine 300 and that is electrically connected to the engine 300.

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

The emission optical system 210 collects 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 facing the combustion chamber 304. Here, as an example, sapphire glass is used as the material of the protective 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 this specification, the XYZ three-dimensional orthogonal coordinate system is used, and the emission direction of light from the surface emitting laser array 201 is described as the +Z direction.

The surface emitting laser array 201 is a pumping light source and has a plurality of light emitting units. Each light emitting portion 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 advantageous for pumping a Q-switched laser whose characteristics largely change due to the shift of the pumping wavelength, because the wavelength shift of the emitted light due to the temperature is very small. Therefore, when the surface emitting laser array is used as the excitation light source, there is an advantage that the temperature control of the environment 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 such that the center of the −Z side end face of the core is located at a position where the light is condensed 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. As a result, the degree of freedom in layout design can be increased. Further, when the laser device 200 is used as an ignition device, the surface emitting laser array 201 can be kept away from the heat source, so that the range of methods for cooling the engine 300 can be expanded.

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

The second condensing optical system 205 is arranged 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 passive Q-switched laser, and has 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 is doped with 1.1% of Nd. The saturable absorber 206b is a rectangular parallelepiped Cr:YAG crystal, and the initial transmittance thereof is appropriately adjusted within a range of 0.15 (15%) to 0.70 (70%).

Note that, here, the Nd:YAG crystal and the Cr:YAG crystal are joined to each other to form a so-called composite crystal. Both Nd:YAG crystal and 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 having the highest absorption efficiency in the YAG crystal. Then, the saturable absorber 206b operates as a Q switch.

The surface of the laser medium 206a on the incident side (-Z side) and the surface of the saturable absorber 206b on the emitting side (+Z side) are optically polished and serve as mirrors. Note that, hereinafter, for convenience, the surface of the laser medium 206a on the incident side is also referred to as a "first surface", and the surface of the saturable absorber 206b on the exit side is also referred to as a "second surface" (see FIG. 3).

Then, the first surface and the second surface are coated with a dielectric film according to the wavelength of light emitted from the surface-emission 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 with a wavelength of 808 nm and a high reflectance for light with a wavelength of 1064 nm. The second surface is provided with a coating having a reflectance of about 50% with respect to light having a wavelength of 1064 nm.

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

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

In the above embodiment, if 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.

Further, here, the case of an engine (piston engine) in which a piston is moved by combustion gas is described as the internal combustion engine, but the invention is not limited to this. For example, it may be a rotary engine, a gas turbine engine, or a jet engine. In short, any material can be used as long as it burns fuel to generate combustion gas.

In addition, the ignition device 301 may be used for cogeneration, which is a system that takes out power, warm heat, and cold heat by utilizing exhaust heat and enhances energy efficiency comprehensively.

Further, although the case where the ignition device 301 is used in the 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 for the 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 device, a terahertz generating device, and the like.

"Details"
The focus position of the light emitted from the laser device 200 in the Z-axis direction can be adjusted 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. ..

Since the surface-emission laser array 201 has a plurality of light-emitting portions, it is possible to increase the light output. Here, the light output of the surface emitting laser array 201 is about 400 W.

Further, the plurality of light emitting portions in the surface emitting laser array 201 are arranged in a region having a diameter of 9 mm (see FIG. 4). The distance between the two most distant light emitting portions in the surface emitting laser array 201 is 7.0 mm or more.

The first condensing optical system 203 has at least one condensing lens. The first condensing optical system 203 may be composed of a plurality of optical elements.

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 for the ignition device of the engine, the surface emitting laser array 201 can be kept away from the high temperature region and the vibration region around the engine, and the reliability of the ignition device can be improved.

Here, the M ² value of the light emitted from the optical fiber 204 is about 1200. The M ² value of the light emitted from the optical fiber 204 may be 1500 or less.

Details of the second condensing optical system 205 will be described.

The second condensing optical system 205 has a plurality of optical elements. Here, the second condensing optical system 205 is composed of a first lens 205a and a second lens 205b (see FIG. 5). The second condensing optical system 205 may be composed of three or more optical elements.

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

The second lens 205b is a condensing lens and condenses the light made into the substantially parallel light by the first lens 205a.

The second condensing optical system 205 has a magnification of 1.
The magnification of the second condensing optical system 205 may be 0.7 or more.

The light that has passed through the second lens 205b is incident on the laser resonator 206. In the following, the light incident on the laser resonator 206 via the second lens 205b is also referred to as “excitation light” (see FIG. 6).

Here, the beam waist diameter (diameter) of the excitation light is about 1.5 mm (1/e ² ).

By the way, the range until the beam diameter becomes √2 times the beam waist is called Rayleigh length (see FIG. 7).

Details of the laser resonator 206 will be described.

Here, since the Nd:YAG crystal and the Cr:YAG crystal are both ceramics, the productivity is better than that of the single crystal.

Further, since the boundary between the Nd:YAG crystal and the Cr:YAG crystal is not separated, the same characteristics as a single crystal can be obtained, which is mechanically and optically advantageous.

The light (excitation light) that has passed through the second lens 205b is incident on the laser medium 206a. That is, the laser medium 206a is excited by the light (excitation light) that has passed through the second lens 205b.

FIG. 8 shows a part of the result of measuring the energy per pulse of the laser light emitted from the laser resonator 206 by changing the position of the first surface of the laser resonator 206 in the Z-axis direction. ing.

According to this, as the position of the first surface of the laser resonator 206 is moved from the −Z side (upstream side) of the beam waist position to the +Z side, one pulse of the laser light emitted from the laser resonator 206 Energy tends to increase.

For example, when the first surface of the laser resonator 206 is located on the -Z side (upstream side) of the beam waist position at 0.5 mm, the energy per pulse of the laser light emitted from the laser resonator 206 is about. It is 3.3 mJ.

Further, when the first surface of the laser resonator 206 is at the beam waist position, the energy per pulse of the laser light emitted from the laser resonator 206 is about 3.65 mJ.

Further, when the first surface of the laser resonator 206 is at a position of 0.5 mm on the +Z side (downstream side) of the beam waist position, the energy per pulse of the laser light emitted from the laser resonator 206 is about 3. It is 0.75 mJ.

The energy per pulse of the laser light emitted from the laser resonator 206 is saturated at about 3.75 mJ.

If the position of the first surface of the laser resonator 206 is on the +Z side (downstream side) of the beam waist position, the energy per pulse of the laser light emitted from the laser resonator 206 is about 3. A value larger than 65 mJ is maintained.

Therefore, the laser resonator 206 is arranged so that the position of the first surface is on the downstream side (+Z side) of the beam waist position of the excitation light in the traveling direction of the excitation light (Z-axis direction). good.

In the present embodiment, in the laser resonator 206, the position of the first surface is 0.5 mm downstream (+Z side) from the beam waist position of the excitation light in the traveling direction of the excitation light (Z-axis direction). It is arranged as in.

In the conventional laser device, the energy per pulse is not taken into consideration, and the laser resonator is arranged so that the first surface is located at the beam waist position.

By the way, the wavelength of the light emitted from the edge-emitting laser varies greatly with temperature. Therefore, in the ignition device which is supposed to be used in a high temperature environment, when the edge-emitting laser is used as the excitation light source, a precise temperature control mechanism for keeping the temperature of the edge-emitting laser constant is required. This leads to larger size and higher cost.

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

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

As is clear from the above description, in the laser device 200 according to the present embodiment, the optical fiber 204 constitutes the “transmission member” in the laser device of the present invention. Then, in the ignition device 301 according to the present embodiment, the emission optical system 210 constitutes the “optical system for condensing the laser light emitted from the laser device” in the ignition device of the present invention.

As described above, the laser device 200 according to the present embodiment includes the surface emitting laser array 201, the first condensing optical system 203, the optical fiber 204, the second condensing optical system 205, and the laser resonator 206. There is.

The surface-emission laser array 201 is an excitation light source, and the light emitted from the surface-emission laser array 201 is excited through the first condensing optical system 203, the optical fiber 204, and the second condensing optical system 205. It is incident on the laser resonator 206 as light.

Then, with respect to the traveling direction (Z-axis direction) of the light passing through the second condensing optical system 205, the position of the surface of the laser resonator 206 on which the light passing through the second condensing optical system 205 is incident is It is set to be on the downstream side (+Z side) of the beam waist position.

In this case, the laser device 200 can increase the energy per pulse as compared with the conventional case.

When the oscillation efficiency is taken into consideration, the first surface of the laser resonator 206 is preferably placed within the Rayleigh length range. When the first surface of the laser resonator 206 is located outside the Rayleigh length range, the converging angle and divergence angle of the excitation light (see FIG. 6) are larger than those within the Rayleigh length range, and the laser A region that does not contribute to oscillation may increase in the resonator (see FIGS. 9A and 9B).

The M ² value of the light emitted from the optical fiber 204 is 1500 or less. If the M ² value of the light emitted from the optical fiber 204 is larger than 1500, the divergence angle of the light incident on the laser resonator 206 is the same even if the second focusing optical system and the laser resonator are the same. Will grow. In this case, the Rayleigh length becomes short, and the distance between the beam waist position and the position where the energy per pulse of the laser light emitted from the laser resonator 206 is saturated becomes short.

The second condensing optical system 205 has a magnification of 0.7 or more. If the magnification of the second condensing optical system 205 is smaller than 0.7, the divergence angle of the light incident on the laser resonator 206 becomes large. In this case, the Rayleigh length becomes short, and the distance between the beam waist position and the position where the energy per pulse of the laser light emitted from the laser resonator 206 is saturated becomes short.

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

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

It should be noted that in the above embodiment, both the first condensing optical system 203 and the emission optical system 210 may be composed of a single optical element, or may be composed of a plurality of optical elements.

Further, the laser device 200 can be used in a laser annealing device or a laser processing machine.

<Laser annealing device>
As an example, FIGS. 10A and 10B show a schematic configuration of a laser annealing apparatus 1000 having the laser apparatus 200 described above. The laser annealing apparatus 1000 includes a light source 1010, an optical system 1020, a table device 1030, and a control device (not shown).

The light source 1010 has a laser device 200 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, when the object P is amorphous silicon (a-Si), when the laser light is irradiated, the temperature of the amorphous silicon (a-Si) rises, and then the amorphous silicon (a-Si) is crystallized by being gradually cooled, It becomes polysilicon (p-Si).

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

<Laser processing machine>
As an example, FIG. 11 shows a schematic configuration of a laser processing machine 3000 having the laser device 200 described above. The laser beam machine 3000 includes a light source 3010, an optical system 3100, a table 3150 on which an object P is placed, a table drive 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 near the surface of the object P. The table drive device 3160 moves the table 3150 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on an instruction from the control device 3200.

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

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

The laser beam machine 3000 may include a plurality of light sources 3010.

Further, the laser device 200 is also suitable for a device that uses laser light other than the laser annealing device and the laser processing machine. For example, the laser device 200 may be used as the light source of the display device.

Reference numeral 200... Laser device, 201... Surface emitting laser array, 203... First condensing optical system (part of optical system), 204... Optical fiber (part of optical system, transmission member), 205... Second condensing optics System (part of optical system, lens system), 205a... First lens, 205b... Second lens, 206... Laser resonator, 206a... Laser medium, 206b... Saturable absorber, 210... Ejection optical system (laser device) Optical system for condensing light from the), 212... Protective member, 220... Drive device, 222... Engine control device, 300... Engine (internal combustion engine), 301... Ignition device, 302... Fuel injection mechanism, 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 device, 3180... operation panel, 3200... control device, P... object.

Japanese Patent Publication No. 2013-545280 JP, 2014-192166, A

Claims (13)

A light source device including a surface emitting laser array having a plurality of light emitting parts ;
An optical system that includes an optical fiber that transmits the light from the light source device and a lens system that collects the light through the optical fiber ;
It is provided with a laser resonator that is irradiated with light through the optical system and emits laser light,
A laser device in which a position of a surface of the laser resonator on which light through the optical system is incident is downstream of a beam waist position of the light in a traveling direction of the light through the optical system. The laser device according to claim 1, wherein a position of a surface of the laser resonator on which light is incident through the optical system is within a Rayleigh length of the light. The laser device according to claim 1, wherein the optical fiber has a core diameter of 1.5 mm . Wherein the optical system, the laser apparatus according to claim 1, characterized in that it comprises at least one optical element disposed on an optical path between the optical fiber and the light source device. Wherein M ² value of the light through the optical system, the laser apparatus according to any one of claims 1 to 4, characterized in that it is 1500 or less. Wherein the optical system, the magnification laser device according to any one of claims 1 to 5, characterized in that at least 0.7 times. The laser resonator, the laser device according to any one of claims 1 to 6, characterized in that a Q-switched laser. The laser device according to claim 7 , wherein the laser resonator includes a laser medium and a saturable absorber. 9. The laser device according to claim 8 , wherein the laser medium is a Nd-doped YAG crystal, and the saturable absorber is a Cr-doped YAG crystal. The laser device according to claim 8 or 9 , wherein the laser resonator is a composite crystal. The laser resonator, the laser device according to any one of claims 1 to 10, characterized in that a ceramic. A laser device according to any one of claims 1 to 11
An ignition system comprising: an optical system that collects light from the laser device. In an internal combustion engine that burns fuel to produce combustion gas,
An internal combustion engine comprising the ignition device according to claim 12 for igniting the fuel.

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