JPH031104A - Laser light transmission device for processing machine - Google Patents

Abstract

PURPOSE:To greatly improving processing performance, such as cutting by providing >=1 points of parts where there are no dielectric thin films near the end of a hollow metallic optical waveguide coated with the dielectric thin film on the inside surface. CONSTITUTION:The dielectric thin film 2 of a low loss is applied on the inside surface of a hollow metallic tube 3 and the dielectric thin film 2 of the hollow metallic optical waveguide internally contg. the dielectrics is partially substd. with metal, by which the substd. parts are functioned as mode filter parts 6a, 6b to absorb only the mode of higher order into the metal walls and to attenu ate the same with substantially no influence on the mode of lower order. The flexible introduction of the output of a CO2 laser to the work is possible in this way and the control mechanism of the processing device is simplified. Particularly the microfocusing of the output laser beam is possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser beam transmission device for a processing machine, and particularly to a laser beam transmission device using a flexible hollow optical waveguide for transmitting a high-power carbon dioxide laser beam. It is.

[Prior Art] Carbon dioxide lasers, which have high efficiency and high output, have already been introduced into the industrial field for laser processing such as welding, cutting, and heat treatment of metals. However, these industrial laser processing machines use a spatial beam transmission method that combines a reflector and a lens to guide the output light from the laser oscillator to the workpiece, which requires complex and precise control R.
Not only does this require a horizontal space, making the device large and expensive, but it is also not easy to maintain.

If a flexible optical waveguide capable of flexibly transmitting high-power laser light could be realized, all of these inconveniences would be solved, so its practical use has been long awaited.

So far, candidates include infrared optical fibers made of materials such as chalcogenide, fluoride glass, metal halides, and KH2-5, rectangular metal hollow optical waveguides with a square-shaped cross section, and dielectric thin films on the inner walls of the hollow. Coated circular metal hollow optical waveguides have been proposed and studied;
The metal hollow optical waveguide type is considered to be the most promising for industrial processing. In particular, the dielectric interior metal hollow type has zero transmission loss.
．． 05 dB/m or less, and it has already been demonstrated that power transmission of 500 W or more is possible by further cooling the optical waveguide, making it the shortest path to practical use for industrial processing. .

[Problems to be solved by the invention] Dielectric-incorporated metal hollow optical waveguides have advantages for high power energy transmission, such as high cooling efficiency and no reflection, thermal breakdown, or dielectric breakdown at the input and output ends. However, the diameter of the hollow portion, which is the optical energy propagation region, is about two orders of magnitude larger than the wavelength of carbon dioxide laser light, which is 10.6 μl. Therefore, there are many modes propagating inside.
This is a so-called oversized multimode transmission line. Therefore, higher-order modes are generated due to ■ mismatch between the spot size of the incident beam and the inner diameter of the optical waveguide, ■ surface roughness of the inner wall of the optical waveguide, ■ sudden bending of the optical waveguide, etc. propagate. Since these higher-order modes have a larger diffusion angle when radiated from the output end of the optical waveguide than the fundamental mode of the optical waveguide, the diameter of the condensed light when condensed by a lens is increased.

Therefore, when applied to cutting, the cutting width becomes wide, and if there is a higher-order mode in which the intensity distribution is asymmetric with respect to the center, the cutting performance changes depending on the direction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser beam transmission device for a carbon dioxide laser processing machine that can eliminate the drawbacks of the prior art described above and significantly improve processing performance such as cutting.

[Means for Solving the Problems] A laser beam transmission device for a processing machine of the present invention includes a flexible hollow optical waveguide for guiding a high-power carbon dioxide laser beam to a laser beam irradiation part, and a laser beam transmission device in the hollow optical waveguide. and a processing head that focuses the output of the hollow guided waveguide and irradiates it onto the workpiece together with an assist gas, the hollow optical waveguide has an inner surface coated with a dielectric thin film. It is a metal hollow optical waveguide,
Near at least one end of the output side and the input side,
The structure has at least one portion without dielectric thin film coating.

In this case, it is preferable that the hollow guide waveguide is an optical waveguide whose inner surface is air-cooled and whose outer surface is water-cooled, and the input coupling section has an iris-type optical waveguide between the coupling lens and the hollow guide waveguide. It is preferable that the processing head includes one of a hollow metal type or a tapered metal hollow type excitation guide waveguide, and further, the processing head includes one or more lenses that focus the diffused light emitted from the hollow guide waveguide. It is preferable to have a configuration including the following.

By converting a portion of the hollow optical waveguide whose inner wall is coated with a dielectric thin film into a metal hollow optical waveguide without dielectric thin film coating, the transmission loss for higher-order modes within the optical waveguide is reduced in those portions. It is larger than the fundamental mode and operates as a so-called mode filter that absorbs higher-order modes.

Since the higher-order modes are absorbed, the condensing diameter when the light emitted from the leading waveguide is condensed by a lens becomes smaller.
Therefore, when applied to cutting, the cutting width becomes narrower, and the processing performance is greatly improved.

[Example] The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a longitudinal sectional view of the optical waveguide of the present invention.

The inner wall of the hollow metal tube 3 is coated with a low-loss dielectric weight H2 at a wavelength of 10.6 μl. For this purpose, select the water thin film 2 appropriately (for details, refer to the following literature: Shinji Technical Report 0QE82).
-120 (1983)), the CO2 laser beam propagates while repeating complete reflection inside the hollow metal tube 3.

The hollow waveguide region 1 of this optical waveguide is a so-called oversized optical waveguide whose inner diameter is sufficiently larger than the wavelength, so there are a large number of propagating modes. Among these modes, low-order modes are The number of reflections on the wall surface per unit length is small, and the number of reflections in higher-order modes is large. Therefore, by partially replacing the dielectric weight JiA2 of the dielectric-incorporated metal hollow optical waveguide with metal, as shown in Fig. A mode filter section 6a that absorbs and attenuates only higher-order modes into the metal wall while having almost no effect on the modes.

6b.

The structure shown in FIG. 1 can also be realized by connecting a dielectric-incorporated metal hollow optical waveguide and a metal hollow optical waveguide. However, because higher-order modes are generated due to slight axis misalignment or angular bending between the two, not only does it not function adequately as a mode filter, but the mechanical strength of the connection becomes a problem.
The advantages of a flexible optical waveguide cannot be utilized.

Therefore, sputtering and plating as shown in FIG.

It is fabricated by making slight modifications to the basic process of etching, which is the basic process for making hollow metal optical waveguides with a dielectric interior. That is, a dielectric thin film 2 is formed by sputtering on the outer surface of the base material aluminum bar 4.
Prior to forming the dielectric weight 1i2, the portions (6a, 6b) from which the dielectric weight 1i2 is to be removed are masked with thin aluminum or Teflon tape. After the sputtering is finished, this masking is removed, and plating and etching are then carried out as usual.The dielectric thin film 2 is not formed in the masked part and remains as a metal part due to plating, so the inside of the dielectric shown in FIG. Mode filter sections 6a and 6b in the metal-plated hollow optical waveguide 5 can be obtained.

Since the dielectric thin film 2 is extremely thin, usually less than 1 .mu.m, there is no problem at all in the manufacturing process, and this has been confirmed in prototype production.

Next, we will discuss the operation and merits of this optical waveguide in Part 3.
This will be explained with reference to the diagram.

The output light from the CO2 laser is converted using a coupling lens 7 and input into the dielectric-incorporated metal hollow optical waveguide 5 having the mode filter sections 6a and 6b near both ends thereof, so as to obtain an optimum light condition. The output light from the C02 laser generally does not have a perfect Gaussian power distribution, but includes higher-order modes (distribution 5a in Figure 3).Furthermore, the laser output light,
Higher-order modes are also generated within the optical waveguide due to mutual positional deviation between the coupling lens 7, the optical waveguide 5, and the like.

However, this higher-order mode is absorbed by passing through the mode filter section 6a, and the power distribution within the optical waveguide 5 becomes Gaussian (distribution 5b in FIG. 3).
When the optical waveguide 5 is bent, the internal power distribution shifts somewhat to the outside of the bend (distribution 5C in Figure 3).Furthermore, the presence of irregularities on the inner wall surface of the optical waveguide 5 also causes higher-order modes to occur. However, these are absorbed by the mode filter section 6b on the output end side. Therefore, the power distribution of the light emitted from the optical waveguide 5 becomes a Gaussian power distribution (distribution 5d in FIG. 3) that is symmetrical about the center.

As a result, a Gaussian output is almost always obtained, almost unaffected by the unique output characteristics of the CO laser and the bending direction of the optical waveguide, making it possible to cut thin metal sheets, plastics, cloth, etc. using CO laser light. This is an extremely effective feature.

FIG. 4 shows the structure of the input coupling part of the optical waveguide 5. The structure of this input coupling part is such that the inside of the hollow waveguide region 1 of the optical waveguide 5 is air-cooled, the outer surface is water-cooled, and the laser beam is The structure allows the light to enter the optical waveguide efficiently.

That is, the cooling water flowing in from the cooling water inlet 10 cools the coupling lens 7, passes through the input section mount 8, and flows toward the output end side while cooling the outer surface of the optical waveguide 5. Further, a cooling gas that also serves as an assist gas is flowed into the hollow waveguide region 1 of the optical waveguide 5, and after cooling the inner wall of the optical waveguide 5,
The coupling lens 7 is cooled, and the cooling gas flows out through the cooling gas outlet 11.

The optical waveguide #I5 is fixed to the input section mount 8 by a holder 9. The focal length of the coupling lens 7 is the same as that of the optical waveguide 5.
The spot size diameter at the incident end is selected to be 0.4 to 0.6 times the optical waveguide aperture diameter, and the distance between the lens and the optical waveguide is approximately equal to the focal length.

FIG. 5 shows the structure of a processing head connected to the optical waveguide 5. As shown in FIG.

The cooling water that cooled the outer surface of the optical waveguide 5 is supplied to the processing head 1
The cooling water passes through the cooling water outlet 15, cools the lenses 13 and 14, and flows out from the cooling water outlet 15. For assist gas, use gas inlet port 16.
Processing head nozzle 1 coaxial with the output laser beam
7 and reaches the workpiece. A part of it is branched and used for the purpose of air cooling the hollow region 1 of the optical waveguide 5.

The light emitted from the optical waveguide 5 is focused by lenses 13 and 14 and irradiated onto the workpiece. In this embodiment, the light guide A lens 13 that converts the diffused light emitted from the wave path into approximately parallel light, and a lens 14 that focuses the parallel light into a minute spot diameter and irradiates it onto the workpiece are used.

FIG. 6 shows the structure of an input coupling section in which an iris-type optical waveguide 19 is installed between the coupling lens and the optical waveguide 5.

In order to prevent the input end of the optical waveguide from being burnt out due to higher-order mode components contained in the laser output light, an iris-type optical waveguide 19 is used to remove unnecessary higher-order mode components and increase the power transmission capacity. It was planned. The diameter 2a of the aperture 18 of this iris-type optical waveguide 19 changes depending on the distance NZ from the input end of the optical waveguide 5, and if the inner diameter of the optical waveguide 2ao is set, a2 = a, 2 (1 + [λ2 / (πr2
ao')])...(1) However, λ is the wavelength r of the laser light, and the range is approximately 0.4 to 0.6, and the distance d between the apertures 18 is the Fresnel number N of the apertures. =
The value of a2/λd is selected to be 1115 or more.

FIG. 7 shows a metal hollow space between the coupling lens 7 and the optical waveguide 5, which has an inner diameter equal to or slightly smaller than the inner diameter of the optical waveguide 5, in order to remove unnecessary higher-order mode components contained in the laser beam. An optical waveguide 20 is installed.

Figure 8 shows that the inner diameter of the optical waveguide end is gradually changed by hand.
This is a so-called tapered optical waveguide 21. The laser output light is gradually converted into an optical waveguide mode at the tapered portion. Therefore, the number of higher-order modes excited within the optical waveguide 5 is reduced. Correspondingly, the heat generation near the input end of the optical waveguide is also reduced, making it possible to increase the power transmission capacity.

[Effects of the Invention] According to the present invention, it is possible to fully guide the output of the CO2 laser to the workpiece, which makes it possible to extremely simplify the control of conventional processing equipment, and to reduce the cost. is also possible. In particular, by being able to focus the output laser beam minutely, processing can be performed with less power than before, and W! II! Application fields such as II processing will also open up.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of a dielectric-incorporated metal hollow optical waveguide with a both-end mode filter according to the present invention, Fig. 2 is a diagram showing the basic manufacturing process of the dielectric-incorporated metal hollow optical waveguide, and Fig. 3 Figure 1 shows the operation of the dielectric interior metal hollow optical waveguide with a mode filter at both ends, Figure 4 shows the structure of the manual coupling part with air/water cooling, and Figure 5 shows the structure of the processing head with air/water cooling. 6 is a diagram showing the structure of the input coupling section including the iris type waveguide for excitation, FIG. 7 is a diagram showing the structure of the input coupling section including the hollow metal waveguide for excitation, and FIG. FIG. 3 is a diagram illustrating an input coupling section using a waveguide. In the figure, 1 is a hollow waveguide region, 2 is a dielectric thin film, 3 is a metal tube, 4 is an aluminum tube as a base material, 5 is a dielectric-incorporated metal hollow optical waveguide with mode filters at both ends, and 5a to 5d are waveguides. Inner power distribution, 6a and 6b indicate mode filter sections. a b Diagram C b

Claims (1)

[Claims] 1. A flexible hollow optical waveguide for guiding a high-power carbon dioxide laser beam to a laser beam irradiation section, an input coupling section for coupling the laser beam to the hollow optical waveguide, and an output of the hollow optical waveguide. In a laser beam transmission device consisting of a processing head that focuses and irradiates the workpiece together with an assist gas, the hollow optical waveguide is a metal hollow optical waveguide whose inner surface is coated with a dielectric thin film, and the output side and the input side thereof are 1. A laser beam transmission device for a processing machine, having at least one portion without a dielectric thin film coating near at least one end of the device. 2. The laser beam transmission device for a processing machine according to claim 1, wherein the hollow optical waveguide is an optical waveguide whose inner surface is air-cooled and whose outer surface is water-cooled. 3. Claim 1 or 2, wherein the input coupling section includes an iris type, metal hollow type, or tapered metal hollow type excitation optical waveguide between the coupling lens and the hollow optical waveguide. The laser beam transmission device for processing machines described above. 4. The laser beam transmission device for a processing machine according to claim 1, 2 or 3, wherein the processing head includes one or more lenses that focus the diffused light emitted from the hollow optical waveguide.