JPH0455084A - Optical system for energy transmission path - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an energy transmission path optical system, particularly for cutting metal,
The present invention relates to a high-power energy transmission path optical system useful for laser processing such as drilling.

[Prior Art] COx lasers have a high oscillation effect and can provide high output, so they have come to be widely used as medical laser scalpels and for industrial processing such as cutting and welding. However, because its oscillation wavelength is in the infrared region of 10.6 μm, conventional silica-based optical fibers cannot be used as transmission lines.Currently, only a few fibers are used as energy transmission line optical systems for guiding CO2 laser light. The main method is spatial transmission using mirrors, which is extremely disadvantageous in terms of operability and high speed.

For the above reasons, development of visible waveguides that can easily transmit C02 laser light has become active.

Currently, hollow metal waveguides with internal dielectric thin films such as germanium are being developed for application to laser processing. Transmission loss so far is 0.05dB
/11. It has been confirmed that a transmission capacity of IKv can be achieved and sufficient energy can be transmitted for cutting metal.

[Problem B to be solved by the invention] By the way, in conventional energy transmission path optical systems, the main focus is on energy transmission efficiency, and no consideration is given to processing accuracy such as the surface roughness of the cut surface. , the characteristics of the beam emitted from the transmission path have a large effect on processing accuracy. The characteristics of this emitted beam depend on the excitation conditions on the incident side, the curvature of the transmission path, and imperfections such as the roughness of the waveguide wall surface.

When cutting or drilling with a laser beam, the part where the irradiation power is highest is processed instantly. The dielectric-incorporated metal hollow waveguide currently under development has relatively low loss even in higher-order modes, so higher-order mode components are also present to some extent on the output side. The intensity distribution of higher-order modes is
Around the outer periphery of the maximum peak, there is a peak with lower intensity.

The maximum peak contributes to cutting when it exceeds a certain threshold, but low-intensity peaks that generally exist around the periphery of the maximum peak do not effectively contribute to cutting and increase the surface roughness of the cut surface. This adversely affects machining accuracy, such as dross adhesion.

Up until now, cutting experiments using hollow waveguides have had the problem that the surface roughness of the cut surface is two to three times greater than in the case of spatial propagation, and that the range of processing conditions that give a good machined surface is narrow. there were.

An object of the present invention is to solve the problems of the prior art described above in a laser machining system using a flexible waveguide, and to provide an energy transmission line optical system with higher machining accuracy.

5. Means for Solving Problems] The energy transmission path optical system of the present invention basically has a configuration in which at least one circular aperture is provided on the output side of a hollow waveguide.

In this case, it is preferable that at least two lenses are arranged on the output side of the hollow waveguide, and that at least one circular aperture is inserted between these two lenses.

In terms of processing accuracy, a suitable energy transmission path optical system is such that the beam radius W of the laser beam between the lenses is as follows: λ: wavelength T of the laser beam; waveguide radius 2 of the hollow waveguide: from the output end of the waveguide. When the distance dT to the aperture, the distance fl from the waveguide output end to the first lens; the focal length u of the first lens from the waveguide output end; 2.405 or 5.52, the above aperture This can be obtained by setting the diameter to a value that satisfies 2w<D<3.4w.

[Operation] Theoretically, when there is no lateral axis deviation (the center of the laser beam coincides with the center of the waveguide) and the transmission line is excited by the beam waist of the incident beam, the excited modes are HE,
, mode only. However, here m=1.2, 3.・
It is...

FIG. 4 shows the coupling efficiency η1 of 6 modes.
Here, T is the waveguide radius.

W is the spot size at the beam waist.

As can be seen from Fig. 4, in order to excite the lowest order HE mode with maximum efficiency, it is sufficient to satisfy w/T -0,64=-(1), and in this case, the HE mode The excitation frequency is 98.1%. The HE mode is the mode with the lowest loss, and its intensity distribution is close to a Gaussian distribution, so it can be said to be the mode most suitable for processing.

On the other hand, the condition for maximum transmittance does not necessarily match Equation (1). In other words, in a transmission line where even higher-order modes have relatively low loss, the amount of loss that can be absorbed into the transmission line is smaller than the amount of loss in higher-order modes. If the power is zero, it cannot be ignored, and transmittance may be increased if the beam is narrowed down a little more.

FIG. 5 shows theoretical values of transmittance of various hollow waveguides when the spot size of the incident beam is changed.

However, here, the radius T of the waveguide is 0.75 mm, and the length is 1
It is set as 1. As can be seen from Figure 5, for example, the conditions for maximum transmittance in the case of a germanium-included silver hollow waveguide are as follows:
w/T=0.3 to 0.5. It can be seen from FIG. 4 that at this time, not only the HE mode but also the HE+x mode is excited relatively frequently.

A C02 laser beam was propagated in a hollow waveguide with a waveguide diameter of 1.5 I'll and a waveguide length of 11, and the acrylic block was irradiated with the laser beam. Full width 2θ is 30~351r
It was ad. From this beam spread, it is thought that the number of propagating modes is at most about 1041 as shown in FIG.

FIG. 6 also shows the loss of each mode in the germanium-included silver hollow waveguide with a waveguide diameter of 1.5u and a waveguide length I11.

The T E o l mode has a loss comparable to that of the HE mode, but its electric field has only a component parallel to the waveguide wall surface, and its intensity distribution is donut-shaped, which is different from that of a normal laser. When a laser beam from an oscillator is incident, the excitation efficiency is extremely small.The TM mode is a mode in which the magnetic field has only a component parallel to the waveguide wall surface, and like the TE mode, the excitation efficiency is very low. Since it is small and the loss is somewhat large compared to other modes, it is considered that almost no propagation occurs.

Theoretically, as described above, when there is no axis shift in the lateral direction and the waveguide is excited by the beam waist of the incident beam, only the HE mode is excited in the waveguide. In reality, it is thought that other modes are also excited due to higher-order mode components of the laser light source, misalignment with the optical axis, waveguide curvature, surface roughness, etc., but in most cases HE ,.

mode, and then the HE 1x mode is excited.

The present invention provides at least one circular aperture on the output side of the transmission line in order to effectively utilize only the HE + l mode, or only the center energy of the HE, l mode and HE, 2 modes. , which prioritizes processing accuracy over energy transmission efficiency and improves processing accuracy in cutting and drilling.

In the case of a configuration in which at least two lenses are arranged on the output side of the hollow waveguide, the circular aperture can be inserted before the first lens or after the second lens.
When the aperture is inserted between these two lenses, damage to the aperture can be reduced and fluctuations in the beam system can be reduced.

In terms of processing accuracy, the optimum energy transmission path optical system is such that when the beam radius W of the laser beam between the lenses is not expressed by the above formula, the diameter of the aperture is 2w<D<3.4w.
It can be obtained by taking a value that satisfies .

[Example] Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the distance from the output end of the hollow waveguide 11 is 2, and a lens 12 with a focal length f1 is placed at z=di.
However, a lens 13 with a focal pressure Mf2 is further placed at z=dl+d2.

At this time, when focusing only on the maximum peak at the center of the HE mode and the HE2 mode, the beam radius with respect to the distance Hz from the output end of the waveguide is as shown in FIG. Second
The figure shows dl = f1. This is a case of a so-called confocal lens system where d2 = flf2. However, the waveguide diameter is φ1.
5 am, the focal length of lens 12°13 is fl = 1
27 mm, f2 = 38.11111. In the case of a confocal lens system, the focal point I does not depend on the mode, and all light is focused at z=2 (fl-f2), that is, at a distance f2 from the second lens 13. The center maximum peaks of the HE, , mode and HE, □ mode overlap at the focal point, and the workpiece is irradiated with high power density.

In Figure 2, we focus only on the maximum peaks at the center of the HE 1+ mode and HE 12 mode, but in reality, as mentioned above, there are peaks around the HE r□□ mode and other modes. , which has a negative effect on machining accuracy.

In FIG. 1, a circular aperture 14 is inserted between the lens 12 and the lens 1 in order to cut the power that does not contribute to these cuts.
It is inserted between 3. If the aperture 14 is slightly larger than the beam diameter shown in FIG. The effects of the present invention can be seen even if the lens 13 is present.

However, as can be seen from FIG. 2, when d1=f1, the laser beam after passing through the lens 12 becomes almost parallel light, and the power density is low.

Therefore, if the aperture 14 is placed between the lenses 12 and 13, not only can the damage to the aperture 14 be minimized, but also the beam diameter will not fluctuate and high positional accuracy will not be required, resulting in a more practical arrangement. Become.

By the way, in FIG. 2, the beam radius W of the laser beam between the lens 12 and the lens 13 is vr4 < (1
"7%">' + <% >' [Z-9yo and 1.
．． 1/! ...Q] is expressed as. Here, λ is the wavelength of the laser beam, T is the waveguide radius of the hollow waveguide, Z is the distance from the waveguide output end to the aperture, dl is the distance from the waveguide output end to the first lens, and fl is the This is the focal length of the first lens from the waveguide output end. Mana U is 2.40j for HE11 mode
, 5.52 for HE +t mode.

Now, with respect to W in equation (2) where u = 5.52, if the aperture 14, which is slightly larger than 2W, is placed between the lenses 12 and 13, the center of the HE l 1 mode and the HE l 2 mode will be Only the energy of that part contributes to the processing of the irradiated object, making it possible to cut with small surface roughness.

By the way, the beam diameter expressed by formula (2) is approximated by a Gaussian distribution near the largest peak, and the beam diameter of the peak is calculated by e −
It is theoretically defined within the range of 1.

According to this definition, when there is a perfect Gaussian distribution, Equation (2)
The power within the beam diameter range expressed by is only 86.5% of the total power.If the power of the laser light source is insufficient and the power cut by the aperture cannot be ignored, The power can be tolerated up to 3.4W. At this time, the adverse effects of unnecessary modes on machining accuracy can be suppressed, and the HE lomodes can make maximum use of the energy of only the central portion of the HE I 2 mode.

In other words, the diameter of the opening is 2w<D<3.4w (3)
must be satisfied.

FIG. 2 shows the case of a confocal lens system, and since the distance between lenses 12 and 13 is equal to the sum of the focal lengths of the two lenses, the length of the optical system is relatively long.

In Figure 3, d1 = f1, d2 = 5ni, HE1
1 mode and HE, beam radius versus distance 2 from the waveguide output end when focusing only on the maximum peak at the center of the mode. However, fl and f2 are the same as in Fig. 2, f1=127in, f2=
381 +u. At this time, lens 12 and lens 1
3 and the aperture 14 can be mounted on one holder, and the length of the optical system can be reduced.

However, as can be seen from FIG. 3, the number of focal points is 1 for each mode. As a result, the surface roughness may become non-uniform across the thickness of the cut surface. If this non-uniformity is a problem, it is necessary to perform cutting only in HE, + + mode, and for W in equation (2) where u = 2.405, an aperture slightly larger than 2W is set. It must be inserted between the lenses 12 and 13. In this case as well, the permissible range of the aperture size must satisfy equation (3).

Furthermore, for W in equation (2) where u=5.52, 2W
It has been confirmed that even when a slightly larger opening is inserted, the surface roughness of the machined surface is smaller than when no opening is inserted at all.

The above is the case where one aperture 14 is inserted, but in the case of high power, to avoid damage to the aperture 14, several apertures 14 are inserted in order from the largest one, and finally HE +
It is also possible to utilize only the energy of the central portion of the + mode or HE I 2 mode. Furthermore, the number of lenses in the output side optical system is not limited to two, and a compound lens system may be used in order to further reduce the condensing system or obtain an arbitrary beam diameter.

[Effects of the Invention] As explained above, according to the present invention, in a laser annealing system using a flexible waveguide, an energy transmission path optical system with small surface roughness of the cut surface and high processing accuracy is formed. be able to.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an energy transmission path optical system showing an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing the results when focusing only on the HE mode and the maximum peak at the center of the HE mode, respectively. Figure 4 is a diagram showing the beam radius versus distance 2 from the waveguide exit end; Figure 4 is a diagram showing the calculation results of the coupling efficiency of modes HE, ~HE, when changing the incident beam diameter with respect to the waveguide diameter; Figure 5 is a diagram showing the theoretical transmittance values of various aerial waveguides when the incident beam diameter is varied with respect to the waveguide diameter, and Figure 6 is a diagram showing the modes thought to be propagating in the hollow waveguide and their transmission losses. It is a figure which shows in the form of a table. In the figure, 11 is a hollow waveguide, 12 and 13 are lenses, and 14 is an aperture. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinuya Beam radius (mm) Figure 1 #PJ4 Figure

Claims (1)

[Scope of Claims] 1. An energy transmission path optical system characterized in that at least one circular aperture is provided on the output side of a hollow waveguide. 2. An energy transmission path optical system characterized in that at least two lenses are arranged on the output side of a hollow waveguide, and at least one circular aperture is inserted between these two lenses. 3. In the energy transmission path optical system according to claim 2,
The beam radius w of the laser beam between the above lenses is ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ However, λ; wavelength T of the laser beam; waveguide radius Z of the hollow waveguide; distance from the waveguide output end to the aperture When d1; distance f1 from the waveguide output end to the first lens; focal length u of the first lens from the waveguide output end; 2.405 or 5.52, the diameter D of the above aperture is 2w An energy transmission path optical system characterized by having a value satisfying <D<3.4w.