JPH0580317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser beam focusing head used in a laser processing device.

[Conventional technology]

Generally, an optical system such as a lens, a concave mirror, or a parabolic mirror is used for a laser beam focusing system in a laser processing device. However, the laser beam profile at the focal point varies widely depending on the laser oscillation mode, but generally has a high center brightness, so it is difficult to perform laser heat treatment, etc. that requires a uniform heat-affected zone in the width direction. It is not preferable in this case.

To address these problems, conventionally, a segmented reflector as shown in "Laser Handbook" published by Ohm Co., Ltd., page 673, and a differential user, as shown in page 690 of the same, have been used.

[Problem that the invention seeks to solve]

Figure 7 shows a configuration diagram of the segmented reflector 5. As shown in the figure, by overlapping the reflected beams from a large number of plane mirror pieces, uniform beam intensity is achieved at the condensing point. It is something to do. Here, the diameter of the focused beam by this mirror is
Since the size almost corresponds to the size of the reflecting mirror segment, if it is desired to change the condensing shape, it is necessary to prepare individual segmented reflecting mirrors 5 corresponding to the shape. However, the segmented reflecting mirror 5 is expensive even as a single unit because it is necessary to strictly set the angle of each reflecting mirror element, and preparing a large number of segmented reflecting mirrors poses a problem in terms of cost.

Next, FIG. 8 shows the configuration of an apparatus used for laser annealing of semiconductors, and the diff user 8 in the figure has a reflective surface on its inner surface.
Uniform distribution of beam intensity is achieved through multiple reflections. The diff user 8 is generally prismatic or cylindrical, and it is necessary to narrow down the laser beam to some extent before it enters the diff user 8, which requires the lens 7 and strict alignment to match the optical axis of the lens with the axis of the diff user. is necessary. There are some problems. this is,
When transmitting a high-power beam exceeding 10Kw over long distances, there are major problems with the light resistance of the lens, cost, and optical axis stability.

The object of the present invention is to provide a laser focusing head that uses an inexpensive optical system and forms a laser focusing spot with a stable and uniform beam intensity at a fixed position even when there are disturbances such as fluctuations in the laser optical axis. Our goal is to provide the following.

[Means for solving problems]

The present invention is characterized in that in the laser beam focusing head, the hollow inner surface is made of a highly reflective material, the aperture area on the beam incidence side is larger than the aperture area on the output side, and all of the incident beam is The slope of the inner surface and the size of the entrance/exit aperture are determined so that the light is guided to the exit aperture.

[Effect]

The operation of the present invention will be explained based on the drawings. FIG. 3 is an explanatory diagram showing the principle of the present invention geometrically and optically. When a parallel laser beam with optical diameter d coaxially enters a groove with an opening angle θ, the outermost portion of the beam travels toward the opening while undergoing multiple reflections as shown by the solid line in Figure 3. do.
Considering similar multiple reflections for the whole beam,
Due to this integral effect, the intensity distribution of the beam emitted from the aperture becomes uniform. Next, considering the situation of multiple reflections, the angle of incidence of the beam on the reflecting surface 3 increases by θ for each reflection, so as the number of multiple reflections increases, the angle of incidence exceeds 90°, and the beam A phenomenon occurs in which the angle of incidence begins to return. Therefore, the maximum number of reflections Nmax for which the angle of incidence does not exceed 90° is given by the maximum integer N that satisfies the following equation (1).

(N-1/2)・θ90゜...(1) Furthermore, if you set the coordinate system as shown in Figure 3,
The coordinate values (Xn, yn) at the Nth reflection are as follows (2),
It is given by equation (3).

Xn=d/tanθ/2 _o П П ⁱ⁼¹ tan(i-1)θ−tanθ/2/tan(i-1)θ+ta
nθ/2 ……(2) yn=−tan(θ/2)Xn (first quadrant) ……(3) Once θ and d are determined from the above formula, the minimum aperture size that allows the entire power to be emitted is determined. yn max is found. In other words, the aperture angle θ that narrows down the laser beam with radius d to the desired exit aperture size is determined.

Note that, hereinafter, the radius of the entrance/exit aperture is defined as half the cross-sectional length of the aperture shown in FIG. For example, when the opening is rectangular, half of the length of the change is defined as the radius.

FIG. 5a summarizes the results of calculations carried out according to the above formula, and also includes the value of the X coordinate (X ₁ ) at the first reflection. Therefore, for example, if a laser beam with a radius of 30 mm is to be condensed to a radius of 1 mm, the divergence angle is 4° or less and the length of the focusing head is 900 mm or more based on the value of _X1 . In the above example, the case where a parallel beam is incident on the condensing head is described. Next, the case where a convergent beam is incident on the condensing head will be explained.

FIG. 4 illustrates the situation of multiple reflections when a laser beam whose convergence half angle at the outermost portion of the beam is α is incident on the condensing head. In this case, the above equations (1) to (3) can be replaced with the following equations (4) to (6).

(N-1/2) θ-α<90° ...(4) Xn=d/tanθ/2・tanθ/2-tanα/tanθ
/2+tanα _o П П ⁱ⁼¹ tan [(i-1)θ-α]-tanθ/2/tan [(i-
1) θ−α〕+tanθ/2……(5) yn=−tan(θ/2)Xn (quadrant)……(6) Figure 5b shows (4) to ( The results calculated using formula 6) are summarized in the same form as Figure 5a. It can be seen from the figure that in this case the length of the condensing head can be made much smaller than in the case of parallel beam incidence.

Next, the configuration of the condensing head when actually used will be explained.

Regarding yn max, expanding equations (5) and (6) gives the following
Obtain equation (7).

yn max=d×tan(θ−α)−tanθ/2/tan(θ−α
)+tanθ/2 ×tan(2θ−α)−tanθ/2/tan(2θ−α)+tan
θ/2×……×tan [(Nmax−1)θ−α]−tanθ/2/tan[(N
max-1) θ-α〕+tanθ/2 ...(7) Here, tanA-tanB/tanA+tanB=sin(A-B)/sin
Since (A+B), equation (7) becomes equation (8) below.

Yn max=d×sin(θ/2−α)/sin(3θ/2−α) ×sin(3θ/2−α)/sin(5θ/2−α)×…×sin[(Nmax−3/ 2) θ−α〕/sin〔(Nmax−1
/2) θ-α] = d sin (θ/2-α)/sin [(Nmax-1/2) θ
−α〕……(8) Here, in order to obtain the integral effect due to multiple reflections, at least 3 to 4 reflections are required, so the maximum value of θ is about 30° (π/6). thing,
In addition, since the angle of incidence is almost 90° (π/2) in the reflection of Nmax, if θ and α are defined in radians, sin(θ/2−α)θ/2−α,
sin [(Nmax-1/2) θ-α] can be set as 1, and Yn maxd (θ/2-α) ...(9). Therefore, the maximum value θmax of θ with respect to the exit-side aperture radius y, which is determined by the desired radius of the output beam, is given by the following equation (10).

θmax=2(y+dα)/2...(10) Note that there is also a lower limit for θ, and in order to cause multiple reflections, θ must be larger than the full beam convergence angle 2α, so 2α<θθmax θ is determined within the range of .

Furthermore, the incident aperture radius qi is determined on the condition that it is larger than the incident beam diameter d.

Note that the homogeneity of the emitted beam is better as θ is smaller, and the larger qi is, the better the margin for optical axis fluctuation is. However, on the other hand, the entire focusing head becomes larger, so the values of θ and qi are It is determined.

Normally, the exit aperture radius y is set to be equal to the diameter of the desired beam size, but since the focused beam of this focusing head is emitted with a divergence angle, the value of y should be set small in advance. Set it to
By changing the distance between the exit aperture and the workpiece, the beam size can be changed continuously over a certain range. Therefore, in practice, it is not necessary to create individual focusing heads for each desired beam size, and a wide range of beam sizes can be covered by a limited number of focusing heads.

Furthermore, in this method, even if the optical axis of the incident beam changes slightly, due to the integral effect of multiple reflections, a homogeneous beam equivalent to that of coaxial incidence can be created.
It is guided to the exit aperture end.

(Embodiment) FIG. 1 shows an embodiment of a laser focusing head according to the present invention. In the figure, a condensing head 1 is composed of an assembly of four metal pieces. The metal piece is
The material is steel or the like which has a high reflectance to the laser beam, and the inner surface 3 is subjected to surface treatment such as gold plating to further improve the reflectance. The cooling pipe 2 is bonded to the outer periphery of the condensing head 1 by brazing or the like, and cools the heat generated by some beam absorption in the condensing head 1 by flowing cooling water inside.

In the above configuration, the aperture on the beam incidence side is 54.4
mm, θ=10°, focusing head current 300mm, beam exit side aperture 2mm, α=3°, d=20mm, output
When a 10Kw CO ₂ laser beam was applied,
A rectangular focused beam with uniform beam intensity distribution was obtained. Furthermore, even when the incident optical axis was intentionally varied, a homogeneous rectangular focused beam could be obtained at the same point.

In FIG. 1, the condensing head 1 is shaped like a square truncated pyramid to obtain a square beam, but the bottom surface may be rectangular or linear to obtain a linear beam.

FIG. 2 shows another embodiment of the present invention,
It has a truncated cone shape and is configured to obtain a circular, homogeneous focused beam.

Furthermore, in this embodiment, the output beam of the condensing head 1 is directly irradiated onto the workpiece, but it is also possible to add an optical system to the output side of the condensing head 1. The condensed beam may be reconfigured using a condensing mirror or a condensing mirror.

FIG. 6 shows an example in which a special optical system is added to the main condensing head. In the figure, the multiple reflection cavity 4 is an optical system that has a spherical reverse slope on its inner surface, and improves laser processing performance by returning the reflected light from the workpiece to the workpiece through multiple reflections. It is something.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to form a condensed beam having a uniform beam intensity and an arbitrary shape with a simple configuration, so that the present invention has the advantage that it can be an inexpensive optical device. Furthermore, even if the beam optical axis fluctuates, a stable light focusing spot can be obtained, so even if the workpiece fluctuates, all you need to do is follow the main focusing head.
This has the advantage of simplifying the tracing control system.

[Brief explanation of the drawing]

1 and 2 are drawings showing an embodiment of a laser condensing head according to the present invention, the upper figure being a front view on the laser incidence side, and the lower figure being a top view. FIGS. 3 and 4 are explanatory diagrams showing the state of multiple reflection of a laser beam in the present invention. Figures 5a and 5b are graphs showing example calculation results for the design of a condensing head based on the effects of the present invention. FIG. 6 is a plan view showing an embodiment of the present invention in which a special optical system is added. FIG. 7 is a cross-sectional view and a front view of a conventional optical system for forming a homogeneous beam, and FIG. 8 is a side view showing the configuration of a conventional optical system for forming a homogeneous beam. 1: Laser focusing head, 2: Cooling tube, 3: Laser reflecting surface, 4: Multiple reflection cavity, 5: Segmented reflector, 6: Laser oscillator, 7: Lens, 8: Diffuser, 9: Workpiece.

Claims (1)

[Scope of Claims] 1. In a hollow-shaped head that focuses a laser beam extracted from a laser generator and irradiates it onto a workpiece, the laser beam of the laser focusing head has an inner surface made of a highly reflective material. The aperture radius on the exit side of the head is set to be larger than the laser beam radius and the exit aperture radius of the head, the aperture radius on the exit side is equal to or smaller than the radius of the desired exit laser beam, and the opening angle θ of the laser focusing head is set. A laser condensing head configured to output the incident laser beam while subjecting it to multiple reflections within the following range: 2α<θ<θmax However, θmax=2(y+dα)/d(red) where α: Half angle of convergence of the incident laser beam ( red) y: Laser beam exit side aperture radius (mm) d: Incident laser beam radius (mm).