JP2000091670A - Solid-state laser generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state laser generating device wherein burning and breakage due to heat impact of an aperture are prevented by separating a laser light main beam from an undesired stray light. SOLUTION: An aperture 1 of transparent material which is provided with a hole for transmission of laser beam 11 is provided, and the aperture 1 has a total reflection surface 2 tilted by at least the critical angle for a laser wavelength on the rear surface in the irradiation direction of the laser beam 11 and has a surface 3 coated for non-reflection on the front surface. The aperture 1 is held by a cooled holder 4, and a cooled heat sink 6a is provided in front of the aperture 1 in laser irradiation direction while a cooled heat sink 6b in the rear of it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser generator of a high output such as a YAG laser, and more particularly to a solid-state laser generator of a non-absorption type aperture system.

[0002]

2. Description of the Related Art Conventionally, in a high-power solid-state laser generator having an average output of several kW class, the power that can be taken out from one laser crystal is generally limited by the crystal breakdown input limit. Since the beam quality of the laser beam is degraded due to the increase in input power, a cascade connection that arranges multiple concentrators including a laser crystal in series and increases the output while maintaining the beam quality determined by the performance of the concentrator The mold is adopted. The cascade connection type includes a system including only an oscillator including a plurality of concentrators and a system in which a plurality of amplifiers are added to further increase the output (generally referred to as a MOPA system).

FIG. 5 is a schematic diagram showing a conventional MOPA type solid-state laser generator. As shown in FIG. 5, the conventional MOPA type solid-state laser generator includes two oscillation rods 143 for oscillating laser light, two amplifier rods 144 for amplifying the laser light, and laser light 142. Three apertures 141 for separating stray light, which is unnecessary light from the laser light 142, and the laser light 142
And an optical fiber 145 that propagates to the optical fiber 46.

In the conventional solid-state laser generator configured as described above, the laser light 142 oscillated from the oscillation rod 143 is amplified by the amplification rod 144, and the stray light is separated by the aperture 141 provided at an appropriate position. After being collected by a lens or the like, the optical fiber 1
The light is propagated to the processing surface 146 through 45.

In recent years, a solid-state laser generator mainly using a YAG laser has a large average output by connecting a plurality of laser crystals in multiple stages.
W solid-state laser generators have been developed. In such a laser generator of several kW class, it is an issue to be able to generate a laser beam of high beam quality while maintaining a large output. Therefore, it is necessary to improve the performance of the condenser itself and the configuration of the resonator. Have been. As a general technique for improving the beam quality once more and shaping the beam, the higher-order spatial mode light appearing in the peripheral portion due to the spread of the beam is separated, and the lower-order spatial mode light is separated. There is a method of installing an aperture having an opening through which only the light passes.

In a high-power laser generator having an output exceeding 2 to 3 kW, an MOP in which an amplifier is added to an oscillator is used.
The configuration A may be used, but when amplifiers having high gain are connected in multiple stages, ASE light that amplifies the spontaneous emission light generated from the amplifier is generated, which deteriorates the beam quality of the amplified light, To reduce the gain, an aperture similar to that described above for separating the ASE light from the main beam between the amplifiers is required.

Further, since the above-mentioned solid-state laser generator has a structure in which a plurality of optical parts are arranged, scattered light from the end face and diffracted light from the edge of each optical part are generated, and it is necessary to separate them. There is.

Furthermore, when an optical fiber is connected to a high-power laser device, the non-reflection processing is not usually performed on the optical fiber 33, so that 3 to 4% of the end face reflected light returns to the amplifier or oscillator. come. Most of the reflected light from the end face returns coaxially with the main beam, so there is no practical problem.However, when the light slightly deviates from the optical axis of the main beam, for example, it is irradiated near the holder of the laser crystal to heat it. In the worst case, the laser crystal may be damaged. An aperture is also effective to separate such end face reflected light deviated from the optical axis.

Furthermore, when the object to be laser-processed is a material having a high reflectance, the light scattered by the object to be processed propagates through the optical fiber, so that the problem of return light occurs as described above.

As described above, in the high-power laser generator, high-order spatial mode light, ASE light, scattered light from the end face of the optical component, and light from the edge, which have a high output at the periphery of the main beam. Stray light, which is unnecessary light such as diffracted light, reflected light from the end face of the optical fiber, or return light from the object to be processed, occurs, causing problems such as a decrease in the quality of the main beam, a decrease in the amplifier gain, or heat generation of peripheral components. An aperture is installed to separate the main beam and stray light to prevent this. However, in a high-power laser generator, it is necessary to remove stray light having a high power density of several tens to several hundreds of watts. Therefore, it is necessary to provide an aperture which has a high light intensity and can be cooled efficiently.

FIG. 6 is a schematic view showing a peripheral portion of an aperture of a conventional solid-state laser generator. As shown in FIG. 6, the aperture 101 is held by the holder 104 cooled by the flow of the cooling water 105 therein, and the stray light 112 emitted from the oscillator 131 or the amplifier 132 and the aperture 1
The stray light 113 returning to 01 is blocked.

[0012]

However, the material of the above-mentioned aperture 101 is, for example, gold-plated metal or ceramics having a high reflectivity, but the portion in contact with the laser beam is a locally high power density light beam. Irradiation may cause burn-in or damage due to thermal shock, and there is a problem that light intensity is unreliable.

The present invention has been made in view of such a problem, and can separate a laser beam main beam from stray light, which is unnecessary light, to prevent burn-in of an aperture and damage due to thermal shock. It is an object to provide a solid-state laser generator.

[0014]

A solid-state laser generator according to the present invention has an aperture made of a transparent material provided with a hole for transmitting a laser beam, and the aperture is provided on a rear surface of the laser beam irradiation direction. It has a total reflection surface inclined at a critical angle or more with respect to the wavelength.

The aperture has a surface coated with anti-reflection on the front surface in the irradiation direction of the laser beam,
Or, it has an inclined surface inclined with respect to the optical axis.

The aperture is preferably held by a cooled holder, and a heat sink is preferably provided in front and / or rear of the aperture in a laser irradiation direction.

Further, the aperture according to the present invention can be arranged as a spatial filter that removes higher-order spatial mode light and ASE light in the middle of a lens pair that forms a 1: 1 image.

According to the present invention, the generated laser light is not absorbed by the aperture, but is reflected or emitted and absorbed and processed by the holder and the heat sink. Therefore, even for a high-power laser beam, it is possible to prevent the aperture from being damaged or deteriorated due to the absorption of the laser beam.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a solid-state laser generator according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a solid-state laser generator according to a first embodiment of the present invention, and FIG. 2 is a schematic diagram showing an aperture opening thereof.

As shown in FIG. 1, in the solid-state laser generator of the present embodiment, an oscillator rod 31 for oscillating laser light (wavelength 1.06 μm) and amplifying the laser light oscillated from the oscillator rod 31. An amplifier rod 32 is provided, and the amplifier rod 32 outputs a main beam 11, which is a portion containing most power, and stray light 12, which is unnecessary light, around the main beam. Further, an aperture 1 provided with a hole having an appropriate opening diameter through which the main beam 11 passes, and an aperture 1
A lens for condensing the main beam 11 passing through the hole of
An optical fiber 33 for transmitting the main beam condensed by the lens to the processing surface is provided.

The aperture 1 has low absorption and heat resistance.
Suitable for transparent optical material with high power, for example, high power laser
Main bead in aperture 1
The front of the irradiation direction of the beam 11 is orthogonal to the optical axis, and
Is applied. Also, in aperture 1
The rear surface of the main beam 11 in the irradiation direction is tapered.
And have been optically polished. Front (anti-reflective coating surface
The angle 21 formed between 3) and the rear surface (tapered surface 2) is flat with the optical axis.
The incident angle 22 of the stray light 12 of the row to the tapered surface 2 is critical.
The stray light 1
2 is totally reflected by the tapered surface 2. In this embodiment,
The wavelength of the output laser light is 1.06 μm and the aperture is
Since the refractive index n of the synthetic quartz of the material No. 1 is 1.45,
Critical angle θ _cIs sin θ_cFrom the relationship = 1 / n, θ_c= 4
3.6 °. Therefore, angles 21 and 22 are 45 °
Is set to

When the stray light 12 irradiates the non-reflective surface 3 of the aperture 1 configured as described above, the stray light 12 passes through the non-reflective surface 3 and is totally reflected by the tapered surface 2 to obtain the light of the main beam 11. The laser beam advances in a direction perpendicular to the axis and enters the grained surface 1 a of the aperture 1. The grained surface 1a is grained, and the stray light 12 incident on this surface is diffused and emitted.

The aperture 1 is held by the holder 4 on the end face opposite to the optical axis of the main beam 11. The holder 4 is provided with an irradiation surface 4a on which stray light 12 diffused and emitted by the grained surface 1a is incident, and the irradiation surface 4a is an uneven surface.
2 is completely absorbed. Although the stray light 12 changes into heat, cooling water 5 for cooling the holder 4 flows through the holder 4, and the heat generated when the stray light 12 enters the irradiation surface 4a is cooled. You.

The aperture 1 and the holder 4 are provided as a pair with the optical axis of the main beam 11 as a symmetric axis.

When the main beam 11 that has passed through the aperture 1 passes through another optical component, it is reflected to generate return light 13, which is incident on the tapered surface 2 in a direction opposite to the irradiation direction of the main beam 11. The return light 13 is incident from the side of air having a low refractive index. Since the surface reflection loss at 45 ° incidence is about 8%, slight reflected light 14 is generated, but most of the reflected light 14 is refracted and enters the substrate of the aperture 1. At this time, since the incident angle 23 of the return light 13 with respect to the tapered surface 2 is 45 °, it is refracted at an angle 24 = 29.2 ° according to Snell's law n · sin θ (24) = sin θ (23). The refracted return light 13 enters the non-reflection surface 3 and exits the aperture 1 again at an exit angle 25 = 23.3 ° with respect to the non-reflection surface 3. The return light 13 emitted in this manner spreads in a ring shape at an angle far away from the optical axis of the main beam 11. The return light 13 spread in a ring shape is the aperture 1
Is incident on the heat sink 6a on the non-reflection surface 3 side. The cooling water 5 flows inside the heat sink 6a, and the heat generated by the heat sink 6a due to the incidence of the return light 13 is released and cooled.

The diameter of the hole of the aperture 1 is determined in order to select an effective portion of the main beam 11. However, if the diameter of the hole is reduced to reduce the beam quality of the main beam 11, the diameter of the aperture 1 is reduced. The diffracted light 15 may be generated at the edge of the hole. For this reason, a heat sink 6b is provided on the tapered surface 2 side of the aperture 1 so that the diffracted light 15 enters. Cooling water 5 flows through the inside of the heat sink 6b.
The heat generated by the heat sink 6a due to the incident light 3 is released, and the heat sink 6b is cooled.

In the solid-state laser generator according to the present embodiment thus configured, the main beam 1 oscillated from the oscillator lot 31 and amplified by the amplifier rod 32.
1 passes through the opening of the aperture 1, but the stray light 12 from the oscillator rod side present around the main beam 11 does not pass through the opening, and the non-reflection-processed orthogonal surface 3 is substantially parallel to the main beam 11. And is totally reflected from the tapered surface 2 set so as to have an incident angle (45 °) greater than the critical angle. And the stray light 12 is the main beam 11
And enters the grained surface 1 a of the grained aperture 1. This causes the stray light 12 to diffuse and irradiate the irradiation wall 4 a of the holder 4. Since the irradiation surface 4a is uneven, the optical energy of the stray light 12 is completely absorbed, and the holder 4 generates heat, but is cooled by the cooling water 5.

Return light 13 generated by reflection of the main beam 11 passing through the aperture when passing through another optical component is incident on the tapered surface 2 in a direction opposite to the irradiation direction of the main beam 11. Since the light is incident from the air side having a low refractive index, most of the light except the slight reflected light 14 (which is incident on the other aperture 1 and processed) is refracted and enters the aperture 1. At this time, the tapered surface 2,
Next, the light is refracted by the non-reflection surface 3 and emitted from the aperture 1.
The return light 13 emitted in this manner spreads in a ring shape at a sufficiently large angle of 20 ° or more with respect to the optical axis of the main beam, so that the optical energy can be easily transferred by the heat sinks 6 a and 6 b provided separately from the aperture 1. Can be absorbed.

Also, since the diffracted light 15 generated at the edge of the hole of the aperture 1 irradiates the heat sink 6a provided on the tapered surface 2 side, diffusion of the diffracted light 15 can be prevented, and the diffracted light 15 can be separated from other optical elements. It is possible to prevent heat from being incident on the component and easily absorb optical energy.

As described above, in this embodiment, the stray light 1
2. Heat generated by the return light 13 and the diffracted light 15 can be processed not by the aperture 1 but by the holder 4 and the heat sinks 6a and 6b. Therefore, it is possible to prevent the aperture 1 from being damaged and deteriorated due to the absorption of the laser beam.

In the aperture of this embodiment, stray light 1
2 is totally reflected, refracted by the return light 13 and separated from the main beam 11, but is refracted by the stray light 12 and totally reflected by the return light 13. It may be configured as follows. In this case, the powers of the stray light 12 and the return light 13 are compared, and the heat sinks 6a, 6
b) Select an efficient configuration.

The stray light includes higher-order spatial mode light, AS
E light, scattered light from the end face of the optical component, diffracted light from the edge, reflected light from the end face of the optical fiber, return light from the object to be processed, and the like are light generated in the vicinity of the main beam 11. It is particularly effective to install the aperture 1 having an appropriate aperture diameter at an appropriate position in the laser light path in accordance with the nature of the stray light to be targeted. For example, for high-order spatial mode light, installation in an oscillator is effective, for ASE light, installation in an amplifier is effective. For the return light from the object, it is effective to install the optical fiber at the coupling portion of the optical fiber.

As described above, since the high-order spatial mode light can be reduced, the beam quality of the laser light can be improved. Further, by arranging the aperture 1 between the multistage amplifier rows, it is possible to suppress the deterioration of the beam quality due to the ASE light (spontaneous emission amplification light) and the decrease of the gain of the amplifier. Furthermore, by installing the aperture 1 before the optical fiber is incident on the optical fiber processing system, it is possible to remove the reflected light from the end face of the optical fiber or the return light from the processed surface, thereby preventing the parts near the laser crystal holder and the seal material from deteriorating. Can be.

In the first embodiment, a heat sink is indispensable. However, the present invention is not limited to this, and the heat sink may be omitted. A solid-state laser generator according to a second embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 3 is a schematic diagram showing the periphery of the aperture of the solid-state laser generator according to the second embodiment of the present invention, and shows only one side with the optical axis of the main beam 61 as the axis of symmetry. This embodiment is different from the shape of the opening of the aperture shown in FIG.
2a and 52b are provided symmetrically on both the oscillator rod side and the optical fiber side.

As shown in FIG. 3, when the stray light 63 from the optical fiber enters the tapered surface 52b as in the first embodiment, most of the light is refracted by the tapered surface 52b. At this time, although a slight reflected light 64 is generated, the reflected light 64 enters the aperture 91 from the tapered surface 52a of the other aperture and is processed. Further, the refracted stray light 63 is totally reflected by the tapered surface 52a provided so that the incident angle 72 of the refracted stray light 63 is equal to or larger than the critical angle and travels in a direction substantially orthogonal to the optical axis of the main beam 11,
It is incident on a holder (not shown). The stray light 63 enters a cooled block such as a holder and is trapped in the holder for processing. Stray light 62 from the holder oscillator rod side
Similarly, the light is refracted by the tapered surface 52a and further totally reflected by the tapered surface 52b to irradiate a holder (not shown).

In the solid-state laser generator according to the second embodiment of the present invention, stray light can be separated without providing a heat sink, and the configuration of the device can be made compact. So, for example,
It is suitable for an aperture or the like arranged in a resonator.

The present invention can also be applied to a laser generator as a spatial filter for positively removing higher-order spatial mode light and ASE light. FIG. 4 is a schematic diagram showing a solid-state laser generator according to a third embodiment of the present invention, in which the aperture of the present invention is arranged in the middle of a lens pair that forms a 1: 1 image.

In the third embodiment according to the present invention having the above-described structure, since the light condensing portion is in the far field region, the high-order spatial mode light and the ASE light can be easily separated from the low-order spatial mode light. And high-power laser light with high beam quality can be obtained.

[0039]

As described in detail above, according to the present invention,
The generated laser light is not absorbed by the aperture, but is absorbed and processed by the holder and the heat sink. For this reason,
Even for a high-power laser beam, it is possible to prevent damage and deterioration due to absorption of the laser beam by the aperture.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a solid-state laser generator according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing an aperture opening of the solid-state laser generator according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing the periphery of an aperture of a solid-state laser generator according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a solid-state laser generator according to a third embodiment of the present invention.

FIG. 5 is a schematic diagram showing a conventional MOPA type solid-state laser generator.

FIG. 6 is a schematic view showing a peripheral portion of an aperture of a conventional solid-state laser generator.

[Explanation of symbols]

 1, 51, 91, 101, 141; aperture 1a; grained surface 2, 52a, 52b; tapered surface 3; orthogonal surface 4, 104; holder 4a; irradiation surface 5, 105; cooling water 6a, 6b; Main beam 12, 62, 63, 112, 113; stray light 13; return light 14, 64; reflected light 15; diffracted light 21; corner 21 22; corner 22 23; corner 23 24; 25; angles 25 31, 131, 143; oscillator rods 32, 132, 144; amplifier rods 33, 133, 145; optical fiber 72; angle 72 92; lens pair 142; laser light 146;

Claims (7)

[Claims] An aperture made of a transparent material provided with a hole for transmitting laser light, and the aperture has a total reflection surface inclined at a critical angle with respect to a laser wavelength or more on a rear surface of the laser light irradiation direction. A solid-state laser generator. 2. The solid-state laser generator according to claim 1, wherein the aperture has a surface coated with an anti-reflection coating on a front surface in an irradiation direction of the laser light. 3. The solid-state laser generator according to claim 1, wherein the aperture is held by a cooled holder. 4. The solid-state laser generator according to claim 1, wherein a heat sink is provided in front of the aperture in a laser irradiation direction. 5. The solid-state laser generator according to claim 1, wherein a heat sink is provided behind the aperture in a laser irradiation direction. 6. The solid-state laser generator according to claim 1, wherein said aperture has an inclined surface inclined with respect to an optical axis on a front surface in an irradiation direction of said laser light. 7. An aperture according to claim 1 or 6, wherein an aperture according to claim 1 or 6 is arranged as a spatial filter for removing high-order spatial mode light and ASE light in the middle of a lens pair imaged 1: 1. Solid-state laser generator.