JP2001317995A - Power damper for high power laser, laser power meter and laser power measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent laser energy from concentrating locally in a conical laser beam receiving part. SOLUTION: In the power damper for absorbing laser energy at a laser beam receiving part 11 as thermal energy, by having a conical beam receiving surface irradiated with a laser beam and the laser power meter for measuring the laser power, a laser beam LB is inclined with respect to the cone center axis 1 and incident off the cone center axis 1 toward a direction perpendicular thereto, after passing the cone vertex 3 and two laser beams on a plane involving the cone center axis 1 and the laser beam center axis 5 reflect and advance at reflecting regions in the conical beam-receiving surface, where among the reflecting regions the second and third reflecting regions do not mutually overlap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power damper for a high-power laser, a laser power meter, and a laser power measuring method.

[0002]

2. Description of the Related Art In recent years, with the advance of laser oscillators, kW
High-power lasers of a class are used in a wide range of industrial fields mainly for cutting and welding of metals. Laser processing is 1mm
The laser beam is focused on an area as small as the diameter, and the processing is completed instantaneously with an extremely high energy density. Processing quality is greatly affected by processing parameters such as laser output, laser focus diameter determined by the optical system, and processing assist gas.
In particular, setting the laser output appropriately is an essential element in performing good laser processing.

FIG. 8 shows an example of a conventional water-cooled power dump type laser power meter. In the laser power meter 10, a helical cooling water passage 15 is mainly formed by a conical laser receiving section 11 (inner cone), a casing (outer cone) 12, and a guide plate 14 provided therebetween. I have. Cooling water is supplied from the water supply device 20 to the cooling water passage 15 via the pipe 21. For laser power meter
A cooling water flow meter 23 and a water temperature meter 24 such as a thermocouple are provided on the inlet 16 side.
However, a water temperature gauge 26 is provided on the outlet 17 side. The measured values of the flow rate Q of the cooling water, the inlet temperature T _1, and the outlet temperature T ₀ measured by these instruments are output to the controller 28.

When the laser LB is irradiated toward the conical laser receiving section 11 of the laser power meter 10, the laser LB is absorbed while repeating multiple reflections on the conical light receiving surface of the laser receiving section 11, and the energy of the laser LB is absorbed. Is transmitted to the conical laser receiving unit 11 as thermal energy. By flowing the cooling water through the cooling water passage 15, the heat of the conical laser light receiving unit 11 is transmitted to the cooling water. The controller 28 calculates the amount of heat transmitted to the cooling water from the flow rate of the cooling water and the amount of temperature rise in this manner, converts the amount of energy, converts the control signal as necessary to a laser oscillator ( (Not shown).

A water-cooled power dump type laser power meter is
When measuring the total laser output, the accuracy is good,
It is said that the output can be measured even with a high output laser of up to kW, and is widely used as an output meter of a carbon dioxide laser.

[0006]

However, conventionally,
When measuring the laser output by the water-cooled power dump method, the laser beam BL was irradiated toward the conical vertex 3 in parallel with the conical center axis 1 of the laser power meter 10. For this reason, the energy density near the conical apex 3 becomes extremely high, and there is a possibility that erosion may occur near the conical apex 3 depending on the output of the laser to be measured.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the gist of the invention is as follows.
It is as follows. (1) In a power damper that irradiates a laser beam having a ring-shaped cross section onto a conical light receiving surface and absorbs laser energy as heat energy in a laser light receiving unit, the laser beam is inclined with respect to the central axis of the cone and the vertex of the cone is formed. A power damper for a high-power laser, which has a function of adjusting a position of a light receiving portion for making light incident in a direction orthogonal to a central axis of a through cone. (2) A power meter for a high-power laser, wherein a heat energy measuring means for measuring the heat energy absorbed by the power damper according to (1) is added. As the thermal energy measuring means, a cooling water flow meter, an inlet water temperature meter of the power damper, an outlet water temperature meter, or the like is used. (3) In a laser output measuring method for irradiating a laser beam having a ring-shaped cross section to a conical light receiving surface and causing the laser light receiving portion to absorb laser energy as thermal energy and measure laser output, the laser beam is focused on a conical central axis. The two laser beams which are inclined with respect to each other and are shifted in the direction perpendicular to the conical central axis through the conical apex, and two laser beams existing on a plane including the conical central axis and the laser beam central axis are within the conical light receiving surface. A laser output measuring method, wherein a second reflection region and a third reflection region are not overlapped with each other among reflection regions which are reflected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A conventional laser measurement method using a water-cooled power damper and a power dump method irradiates a laser beam horizontally to a central axis of a conical laser light receiving portion toward the center of the laser light receiving portion. On the other hand, the power damper, the laser power meter, and the measuring method of the present invention are most characterized in that the laser beam is applied to a position inclined and shifted with respect to the center axis of the conical laser receiving unit.

FIG. 1 shows a power meter 30 of the present invention. The same members as those shown in FIG. 8 described above are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG.
The conical power meter main body 31 is supported on a gantry 32 via two arms 34 and 35. The lower ends of the arms 34 and 35 are screw portions 36, which are fitted to nuts 38 fixed to the gantry 32. The height and the inclination of the incident laser beam with respect to the power meter main body 31 are adjusted by rotating the arms 34 and 35 to adjust the length.

FIG. 9 shows how the laser beam is reflected multiple times on the conical light receiving surface 11a when the laser beam LB is irradiated toward the center 3 of the laser light receiving portion 11 in parallel with the central axis 1 of the laser light receiving portion. . At this time, the angle of incidence of the laser beam LB on the conical light receiving surface 11a is reduced while performing multiple reflections. As a result, the absorptance also increases as shown in FIG. 6, and is greatly absorbed in the second and third reflection areas. At this time, as shown in the figure, the upper second reflection area and the lower third reflection area, the lower second reflection area and the upper third reflection area overlap, and at the same time, the absorption energy is reduced. Superimposed and very large. FIG. 10 shows a simulation result of the laser energy density distribution absorbed by the conical light receiving surface 11a. As the simulation conditions, the laser output is 33 kW, the laser beam is a ring-shaped, conical light-receiving surface having an outer diameter of 100 mm and an inner diameter of 60 mm as shown in FIG. 7, and the apex angle is 30 degrees. The conical light-receiving surface has been subjected to a black dyeing treatment with copper oxide or the like in order to increase the absorption efficiency, and the resulting absorption rate has an angle dependence as shown in FIG. As shown in FIG. 10, the absorption power density becomes extremely high in the vicinity of 25 mm to 45 mm from the apex of the cone.

FIG. 2 shows a state in which the laser beam is irradiated at a position shifted by 10 degrees with respect to the central axis 1 of the laser receiving portion and by 20 mm with respect to the vertex 3 of the cone. As the simulation conditions, the laser output is 33 kW, the laser beam is a ring-shaped, conical light-receiving surface having an outer diameter of 100 mm and an inner diameter of 60 mm as shown in FIG. 7, and the apex angle is 30 degrees. The conical light receiving surface 11a of the laser light receiving unit 11 has been subjected to blackening treatment such as copper oxide to increase absorption efficiency,
The resulting absorptance is angle dependent, as shown in FIG. At this time, as shown in FIG. 2, the upper second reflection area and the lower third reflection area, the lower second reflection area and the upper third reflection area do not overlap, and the laser beam LB does not overlap.
Are dispersed and absorbed, and as shown in FIGS. 3 and 4 on L ₁ and L ₂ , the absorption power is reduced by about 30% compared to the condition (FIG. 10) when the laser beam LB is parallel even at the maximum position. I knew it was there.

FIG. 5 shows a specific method for determining these conditions.
In the laser beam outer diameter Do, the beam inner diameter Din, the cone apex angle 2α, the beam inclination angle β, and the beam shift amount Dp, the following two expressions need to be satisfied. Equation (1) is a condition that the upper second reflection area is deeper than the lower third reflection area, and equation (2) is that the upper first reflection area is in the upper part of the conical light receiving surface. It is a condition to fit in.

(Equation 1)

According to the present invention, by irradiating the laser beam in this manner, it is possible to prevent the absorption energy density from being partially concentrated on the conical light receiving surface and to prevent the erosion generated in the conical laser light receiving portion. .

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Example of the present invention] The conical light receiving surface opening diameter is 170.
A laser power meter having a mm and a cone apex angle of 30 degrees was manufactured.
The conical light-receiving surface was subjected to a blackening treatment of copper oxide in order to increase the absorption efficiency, and the resulting absorption was as shown in FIG. The laser output is 33.0 kW, and the laser beam is a ring-shaped high-power carbon dioxide laser having an outer diameter Do = 100 mm and an inner diameter Din = 60 mm. Dp = 2
A laser beam was irradiated to a position shifted by 0 mm, and the output was measured. In the cooling unit, 40.0 L of cooling water at a water temperature of 10 degrees per minute
Supplied with At this time, the inlet water temperature was 10 degrees, the outlet water temperature was 24 degrees, and the indicated value of the output meter was 33.0 kW. Irradiation was continued for 8000 hours under these conditions, but no deformation or erosion occurred in the conical laser receiving portion.

COMPARATIVE EXAMPLE As a comparative example, a laser beam was irradiated in parallel with the central axis of the cone with the laser inclination β = 0 and the shift amount Dp = 0 without changing other conditions. At about 25 mm from the apex of the cone, erosion occurred.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an example of a water-cooled power dump laser output meter according to the present invention.

FIG. 2 is a schematic diagram showing a state of laser reflection on a conical light receiving surface in the present invention.

FIG. 3 is a perspective view of a conical light receiving surface according to the present invention;
FIG. 4 is a diagram showing a simulation result of an absorption power density on ₁ .

FIG. 4 is a sectional view of the conical light receiving surface according to the present invention;
Is a graph showing the simulation result of the absorption power density on _2.

FIG. 5 is a view for explaining necessary parameters for determining conditions in the present invention.

FIG. 6 is a diagram showing an example of a measurement result of an inner surface absorptance of a generally used water-cooled power dump system.

FIG. 7 is a schematic diagram illustrating an example of a beam shape of a general high-power laser.

FIG. 8 is a device configuration diagram showing an example of a conventionally used water-cooled power dump type laser power meter.

FIG. 9 is a schematic diagram showing a state of laser reflection on a conical light receiving surface in a conventional method.

FIG. 10 is a diagram showing a simulation result of an absorption power density on a conical light receiving surface in a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conical center axis 3 Conical vertex 5 Laser beam axis 10 Laser power meter 11 Conical laser light receiving part 11a Conical light receiving surface 12 Casing 15 Cooling water channel 20 Water supply device 23 Cooling water flow meter 24 Inlet water temperature meter 26 Outlet water temperature meter 28 Controller 30 Laser output meter 31 Output meter main body 32 Mount 34, 35 Arm (Light receiving part position adjusting function) 38 Nut (Light receiving part position adjusting function)

Continued on the front page F term (reference) 2G065 AA04 AB09 BA11 BB24 BB41 BC13 DA05 5F072 AA05 HH02 JJ05 TT01 TT11 YY11

Claims (3)

[Claims] 1. A power damper for irradiating a conical light receiving surface with a laser beam having a ring-shaped cross section to absorb laser energy as heat energy in a laser light receiving section, wherein the laser beam is inclined with respect to a central axis of the cone and conical. A power damper for a high-power laser, which has a function of adjusting the position of a light-receiving portion for causing light to enter while being shifted in a direction perpendicular to a central axis of a cone passing through a vertex. 2. A power meter for a high-power laser, further comprising a thermal energy measuring means for measuring thermal energy absorbed by the power damper according to claim 1. 3. A laser power measuring method for irradiating a conical light receiving surface with a laser beam having a ring-shaped cross section and absorbing laser energy as heat energy in a laser light receiving section to measure a laser output. Two laser beams present on a plane including the conical central axis and the laser beam central axis are tilted with respect to the axis and shifted in a direction perpendicular to the conical central axis through the conical apex. A second reflection area and a third reflection area of the reflection areas which are reflected and propagated in the step (a), do not overlap each other.