JP2001244533A - Laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-power laser device for stably preventing a laser beam from directly hitting an electrode for a long time irrespective of a change in excitation intensity or thermal disturbance, and maintaining a laser output. To provide. SOLUTION: The shape of an opening and / or its central axis can be controlled, and the temperature of an opening plate heated by the outer periphery of a laser beam contacting the opening end is measured, and the temperature and / or temperature distribution is determined by a predetermined value. By changing the opening shape and / or the center axis position of the opening so as to obtain the value,
A high-power laser device having an aperture plate for maintaining a laser output while preventing a laser beam from directly hitting an electrode stably irrespective of a change in excitation intensity or thermal disturbance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high output power, especially 10 kW.
It belongs to a laser device that performs the above high-power oscillation.

[0002]

2. Description of the Related Art In recent years, high power laser devices have been used for welding, cutting,
It is frequently used in drilling and other processing applications, and ultra-high-power laser devices with an average output of 5 kW for YAG lasers and 50 kW for CO ₂ lasers are also in practical use. Above all, since the CO ₂ laser is a gas medium, it can be relatively easily increased in size, and further higher output can be expected in the future.

[0003] Discharge is used to excite a CO ₂ laser, which is a gas laser, and a high frequency discharge performed through a dielectric such as glass or a direct current discharge in which an electrode directly contacts a laser gas is used as a discharge method. In any method, the gas temperature near the electrode is high, and the gas temperature distribution is not constant in a cross section orthogonal to the laser beam optical axis. In a laser device with a relatively low output, the discharge cross section is small, and this temperature distribution can be almost neglected. However, in a laser device having an average output exceeding 10 kW, this temperature distribution is ignored because the discharge cross section becomes large. become unable.

[0004] The refractive index for laser light depends on the temperature of the laser medium. Therefore, the temperature distribution leads to the generation of a refractive index distribution, and when the laser light propagates in a medium having the refractive index distribution, the light is partially refracted, and the divergence characteristics of the beam change.

In the case of a high-output CO ₂ laser, if the temperature rise near the electrode becomes remarkable, the oscillated laser light inside the resonator is refracted when passing near the electrode, and is reflected on the electrode itself or on the glass which is a dielectric. May hit directly. As a result, local heating occurs, damaging the electrodes and glass,
There has been a problem leading to instability of discharge or damage to the device. Such refraction of the laser beam cannot be completely suppressed by the alignment of the resonator mirror.

In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 58-21892 discloses a method in which a fixed aperture plate for regulating the laser beam diameter is provided in a laser resonator to prevent the laser beam from directly hitting an electrode. A workaround is disclosed. Such an aperture plate having a fixed aperture diameter is effective when the beam refraction condition is always constant. However, in actual laser oscillation, when the discharge power is changed to change the output, or when the alignment state of the laser resonator mirror changes due to thermal distortion of the laser housing, the optical axis of the beam changes. This tendency is particularly remarkable in a high-power laser exceeding 10 kW, and it has been difficult to stably avoid direct laser beam impact for a long time with a fixed aperture plate.

[0007]

Therefore, it is conceivable to make the opening diameter variable. However, the aperture diameter determines the effective diameter of the oscillating laser beam. Unnecessary reduction of the diameter to partially block the laser beam leads to a significant decrease in laser output. Therefore, it is necessary to determine the optimal aperture diameter that can maintain the output while avoiding direct beam hits in accordance with the discharge intensity and oscillation conditions. However, the optimal aperture diameter of the variable aperture plate placed inside the resonator, or the optimal aperture diameter There was no clear indicator to determine the center position. In particular, in the case of an unstable resonator that is frequently used in a resonator configuration of a high-power laser, when such an aperture plate is inserted, the outer diameter of the output beam is almost determined by the aperture diameter and position, and the effect on the output is also reduced. Since it is large, it is important to control the opening diameter to an optimum value.

Accordingly, an object of the present invention is to provide an aperture plate that prevents a laser beam from directly hitting an electrode stably for a long period of time irrespective of a change in excitation intensity or thermal disturbance, and that maintains a laser output. An object of the present invention is to provide a high-power laser device in which the laser device is installed inside a resonator.

[0009]

According to the present invention, an aperture plate provided in an optical path of a laser resonator for regulating the diameter of a laser beam can change the shape of the aperture and / or the position of the central axis of the aperture. A laser device comprising a temperature detector for detecting a surface temperature of the aperture plate. Further, the present invention is a laser device provided with an aperture plate control device that controls an aperture shape and / or an aperture center axis position so as to maintain a surface temperature of the aperture plate at a predetermined temperature. The laser resonator is an unstable resonator, and the laser medium is a gas.

That is, according to the present invention, the shape of the aperture and / or the relative position between the central axis of the aperture and the laser optical axis can be controlled, and the temperature of the aperture plate heated by contacting the outer periphery of the laser beam with the edge of the aperture is measured. Opening diameter or opening area so that the temperature and / or temperature distribution becomes a predetermined value,
And / or by changing the position of the opening central axis,
This is an aperture plate that always and stably avoids direct impact of the laser beam on the electrode irrespective of a change in excitation intensity or thermal disturbance, and maintains a laser output. Further, it is a high-power laser device in which it is installed inside a resonator.

[0011]

FIG. 1 is an explanatory view of an embodiment of an aperture plate according to the present invention, and FIG. 2 is an explanatory view of an embodiment of a laser device of the present invention in which the aperture plate is installed in a resonator. . FIG. 3 shows the distance from the opening end of the upper plate and the surface temperature distribution in the present embodiment.

The laser device is a three-axis orthogonal type DC discharge pumped CO ₂ laser, and performs glow discharge pumping in the Z direction between the cathode electrode 10 and the anode electrode 11. The laser gas is circulated at a high speed in the Y direction by a blower (not shown). The laser resonator is a confocal unstable resonator, oscillates between the concave mirror 12 and the convex mirror 13 in the X direction, and an output is extracted as an annular beam 17 from the outer periphery of the convex mirror 13. Here, the distance between the discharge electrodes is 50 mm and the diameter of the concave mirror is 50 mm, so that the diameter of the laser beam is 50 mm or less. The resonator length is about 10 m. The maximum average output of this laser device is about 45 kW.

The aperture plate 9 according to the present invention includes a concave mirror 12.
It is placed in the vicinity and is supported from the mirror support base 15 via the Y-direction movable rail 5, so that the center of the opening can move relative to the center axis 16 of the laser light in the YZ plane. It is. The opening plate for changing the opening diameter or the opening area includes a side plate 3 fixed to the Z-direction rail 4 and an upper plate 1 and a lower plate 2 which can move up and down with respect to the side plate. All of these movable parts are electrically operated by the aperture plate controller 18 from outside the laser housing by a small motor (not shown). The substrate of the aperture plate is made of copper, and is provided with a water cooling tube 6 for water cooling. The cooling water temperature is 25 ° C. The surface is coated with a ceramic coating for absorbing laser light and suppressing reflection. Further, a plurality of thermocouples 7 are installed from the water cooling tube 6 toward the opening end 8, and the surface temperature distribution of the plate from the opening end 8 to the water cooling tube 6 can be measured. The temperature measurement signal is input to the aperture plate controller 18 and becomes a movement amount control signal for the movable aperture plate.

Laser oscillation was performed under various output conditions with the above-described apparatus configuration, and discharge stability and output fluctuation were examined by controlling the aperture diameter using the aperture plate of the present invention. FIG. 3 is a temperature distribution diagram of the upper plate of the aperture plate. First, the diameter of the aperture plate was fixed at 50 mm, which is the mirror diameter in the Y direction. The diameter in the Z direction was set to 50 mm in the initial state. Under these conditions, a relatively low output 3
Oscillation was performed at 0 kW for about 8 hours. As a result, both the discharge and the output were stabilized, and a beam having a beam diameter of 45 mm was obtained. At this time, the temperature distribution of the upper plate of the aperture plate was the distribution shown by line A in FIG. 3, and the temperature near the opening end was about 35 ° C. Therefore, it is assumed that the contact of the beam end portion of the opening end 8 is slight, so that the direct impact of the beam on the electrode is avoided.

Next, while maintaining the same aperture diameter, the discharge intensity was increased to increase the laser output to 45 kW. As a result, in about 3 hours, arc discharge presumed to be caused by direct impact of the beam on the electrode occurred frequently, and the discharge became unstable. This is due to a change in the refractive index due to a remarkable rise in the gas temperature near the electrode, and a change in the beam refraction. At that time, the temperature distribution of the upper plate of the opening was line B in FIG. Then, when the upper plate 1 was moved by 1.5 mm in the -Z direction by controlling the opening diameter, the temperature distribution of the opening plate rose as shown by the line C in FIG. This is because the amount of shielding of the oscillation beam by the aperture plate has increased. As a result, the beam direct hit on the electrode was reduced, and the discharge was stabilized. At this time, the laser output was 44 kW, and the decrease in the output was 3% or less. 0.5 more top plate
When it was moved in the −Z direction by mm, the discharge stability did not change, but the temperature distribution further increased as shown by the line D in FIG. Further, the laser output was 40 kW, and the output was reduced by 10% or more. This is the result of excessively reducing the opening diameter. Under this laser operating condition, the temperature distribution at the opening end is shown in FIG.
It was found that C was desirable in terms of discharge stability and output.

Therefore, the position of the opening plate was adjusted so that the temperature distribution was maintained at the line C in FIG. 3, and continuous operation was performed for 50 hours. On the way, a deviation of the beam center axis, which is considered to be caused by thermal expansion of the laser housing, was observed. As a result, several arc discharges caused by the direct beam hit on the cathode electrode were observed. Then, when the movement of the central axis of the opening was moved by 0.3 mm in the -Z direction, the discharge was stabilized and the output fluctuation was within ± 3%.

Further, in the structure of the laser device of this embodiment, the beam directly hits and the discharge becomes unstable or damage occurs only in the discharge electrode. Is a movable structure, but a structure in which the aperture diameter in the YZ plane is movable by using a diaphragm mechanism may be used. Further, a structure in which the side plates can be independently moved in the Y direction may be adopted. When a plurality of aperture plates can be placed inside the laser resonator, they may be used together with an aperture plate having a fixed aperture diameter.

[0018]

According to the present invention, it is possible to stably prevent a discharge from becoming unstable due to a laser beam directly hitting an electrode inside a resonator in a high-power laser oscillation. Reduction can be minimized. The present invention is particularly effective for a high-output unstable resonator CO ₂ laser in which the beam diameter in the laser resonator passes very close to the discharge electrode.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of an aperture plate installed in a laser device according to the present invention.

FIG. 2 is an explanatory view of an embodiment of an unstable laser resonator in which an aperture plate according to the present invention is installed in a resonator.

FIG. 3 is a surface temperature distribution of an aperture plate (upper plate).

[Explanation of symbols]

 1: Upper plate 2: Lower plate 3: Side plate 4: Z-direction movable rail 5: Y-direction movable rail 6: Water cooling tube 7: Thermocouple 8: Open end 9: Opening plate 10: Cathode electrode 11: Anode electrode 12 : Laser cavity mirror (concave surface) 13: laser cavity mirror (convex surface) 14: mirror holder 15: mirror support 16: laser optical axis (mirror central axis) 17: laser output beam 18: aperture plate controller

Continued on the front page (72) Inventor Naoya Hamada 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division, Nippon Steel Corporation (reference) 5F072 AA05 JJ04 JJ05 KK04 MM20 YY06

Claims (4)

[Claims] An aperture plate provided in an optical path of a laser resonator for restricting a diameter of a laser beam enables a shape of an aperture and / or a central axis position of an aperture to be changed, and a surface temperature of the aperture plate to be reduced. A laser device comprising a temperature detector for detecting. 2. An opening plate control device for controlling an opening shape and / or an opening center axis position so as to maintain a surface temperature of the opening plate at a predetermined temperature.
3. The laser device according to claim 1. 3. The high-power laser device according to claim 1, wherein the laser resonator is an unstable resonator. 4. The high power laser device according to claim 3, wherein the laser medium is a gas.