JPH1076385A - Optical system for laser processing - Google Patents

Abstract

(57) [Summary] [Problem] An optical system for laser processing capable of sufficiently concentrating the power density even if a laser beam with a large divergence angle, which has become multi-mode by increasing the output, is focused. I will provide a. A cone lens (10) is disposed on a light path of a laser beam (5) before a condenser lens (3) as a light beam changing optical unit. As a result, the power density distribution P ₂ in the cross section of the laser beam 5 emitted from the cone lens 10 is large at the central portion and small at the outermost peripheral portion. The laser beam 5 having such a power density distribution is condensed by the condenser lens 3, and a power density distribution in which the power density is sufficiently concentrated at the condensing position is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for laser processing for irradiating a workpiece with a laser beam emitted from a laser oscillator to perform processing such as welding, drilling, and cutting.

[0002]

2. Description of the Related Art Processing using laser light (hereinafter referred to as appropriate)
As laser processing, processing methods such as cutting, drilling, and welding are used in manufacturing processes in various fields such as machines, electronics, and semiconductor devices. FIG. 3 shows an example of an optical system for laser processing in a conventional general laser processing apparatus. The laser beam 5 emitted from the laser oscillator 1 is bent by, for example, 90 ° by the bending mirror 2, is condensed by the condenser lens 3, and is irradiated on the surface of the workpiece 4 placed near the focal point. The laser beam 5 is condensed by the condensing lens 3 to generate a high power density portion in the spot, thereby melting or evaporating the workpiece 4 to realize processing such as cutting, drilling, and welding. doing.

[0003]

Generally, in laser processing, it is first necessary to obtain a high power density by the condensing lens 3 as described above. At that time, the condensing property of the laser beam 5 becomes important. The parameters related to the condensing property and power density of the laser beam 5 emitted from the laser oscillator 1 include the divergence angle θ of the laser beam 5 emitted from the laser oscillator 1 as shown in FIG. FIG.
There is a beam mode of the laser beam 5 as shown in FIG. The divergence angle θ shown in FIG. 4A directly relates to the light collecting property. The light collecting diameter d at the light collecting position when the light is collected by the light collecting lens 3 is determined by the focal point of the light collecting lens 3. Assuming that the distance is f, the distance is represented by the following equation (1). d = 2fθ (1) Therefore, the laser beam 5 emitted from the laser oscillator 1
Is the same, the smaller the spread angle θ, the smaller the converging diameter d, and a higher power density can be obtained at the converging position.

[0004] The beam mode of the laser beam 5 includes a single mode and a multimode. When viewed in the cross-sectional direction of the laser beam 5, the single mode has a sharp peak at the center as shown in FIG. And the multimode has a distribution having several peaks. The aforementioned divergence angle θ is different between the single mode and the multi mode.
In the multi mode, θ is large. In other words, the single mode is superior in terms of light collecting property, and the single mode laser beam is often used for fine cutting and the like.

In order to obtain a high energy density, it is conceivable to increase the output of a laser beam emitted from the laser oscillator 1. However, when the output of the laser oscillator 1 is increased, it becomes difficult to obtain a single-mode laser beam, resulting in a multi-mode. for that reason,
The divergence angle θ also becomes large and the light-gathering property deteriorates, and despite the increase in the output of the laser oscillator 1, the concentration of the power density is insufficient and does not lead to an increase in the power density.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser processing optical system capable of sufficiently concentrating a power density even if a laser beam having a large divergence angle, which is multi-mode by increasing the output, is condensed. It is to provide.

[0007]

According to the present invention, there is provided, in accordance with the present invention, a laser oscillator for emitting a laser beam having a multimode power density in a cross section perpendicular to an optical axis; In a laser processing optical system having a condensing lens for condensing, the light beam changing optical means for changing the position of each parallel light beam constituting the laser beam inside and outside with respect to the optical axis of the laser beam, There is provided an optical system for laser processing, wherein the optical system is arranged on an optical path of the laser beam before entering a condenser lens.

[0008] In the present invention configured as described above,
A beam changing optical unit is arranged on the optical path of the laser beam before entering the condenser lens, thereby changing the power density distribution in the cross section of the laser beam with respect to the optical axis of the laser beam. Specifically, for example, a cone lens can be used as the light beam replacing optical unit. Thus, the energy of the laser beam existing in the annular portion having a certain radial width in the cross section of the laser beam before being incident on the light beam changing optical means is changed in the laser beam cross section after passing through the light beam changing optical means. Will be transferred to another annulus region of the same width in.

However, as compared with the area of the annular portion near the outer peripheral side before entering the above-mentioned light beam replacing optical means, the area of the annular area of the same width near the center where the light rays converge after being emitted from the light beam replacing optical means. Obviously it is smaller. Therefore, the power density (power per unit area) of the annular region near the center in the power density distribution after emission from the light beam changing optical means increases as compared with the case where no light beam changing optical means is provided.

On the other hand, the light beam existing near the center in the section of the laser beam before being incident on the beam changing optical means is transferred to the annular portion near the outer periphery in the section of the laser beam after passing through the beam changing optical means. Therefore, the power density (power per unit area) of the annulus portion near the outer peripheral side in the power density distribution after the light is emitted from the light beam changing optical unit is reduced.

From the above, the power density distribution in the cross section of the laser beam emitted from the light beam replacing optical means is large at the central portion and small at the outer peripheral portion, and looks like a distribution like a single mode. By condensing the laser beam having such a power density distribution by the condensing lens, it becomes possible to sufficiently concentrate the power density at the condensing position.

Further, even if the above-mentioned light beam changing optical means is arranged on the optical path of the laser beam, the divergence angle of the laser beam does not change at all. There is no change, and there is no concern about a decrease in power density due to an increase in the condensing diameter.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a view showing an optical system for laser processing according to the present embodiment. On the optical path of the laser beam 5 (diameter D ₁ ) in front of the condenser lens 3 in FIG. 1, a cone lens 10 as a light beam changing optical unit is disposed. The laser beam 5 emitted in the same manner as in FIG. 1 enters the cone lens 10. FIG. 1 shows a laser beam 5 at a point A before the light enters the cone lens 10 and a point B after the light is emitted to the cone lens 10, and at a point C at the condensing position of the condensing lens 3.
The power density distribution in the cross section of the power density distribution is added to the corresponding position, and the radial distance in this power density distribution is represented by y.
And

The cone lens 10 is disclosed in, for example,
This cone lens is similar to the cone lens disclosed in, for example, JP-A-191689 and JP-A-62-201416. According to the cone lens 10, as shown by an arrow in FIG. The position of the light beam is switched inside and outside with respect to its optical axis. Here, the cone lens 10
Assuming that the power density distribution in the cross section of the laser beam 5 at the point A before being incident on the laser beam 5 is a multimode distribution close to a flat distribution as indicated by P ₁ , the distance y ₁ from the center of the cross section of the laser beam 5 the bundle of light rays radial width is present in HanawaTamaki portion near the outer peripheral side is dy ₁ in place of, dy ₂ at a distance y ₂ from the outer periphery at the point B after passing through the cone lens 10 Laser beam 5 having a width of
Is moved to an annular region near the center in the cross section. Here, naturally, y ₁ = y ₂ and dy ₁ = dy ₂ .

However, compared with the area of the annulus portion near the outer periphery of the width dy ₁ at point A before entering the cone lens 10, the radius d after exiting from the cone lens 10 is
It is clear that the area of the annular region of y ₂ (dy ₂ = dy ₁ ) is smaller. Thus, the power density of the central portion in the power density distribution P ₂ at point B after the exit from the cone lens 10 will be increased as compared with the case without the cone lens 10.

On the other hand, A before entering the cone lens 10
Power that existed near the center of the power density distribution P ₁ is at point, since that will be transferred to HanawaTamaki portion near the outer peripheral side of the power density distribution P ₂ at point B after passing through the cone lens 10, a cone power density of HanawaTamaki portion near the outer peripheral side of the power density distribution P ₂ at point B after emitted from the lens 10 (power per unit area) becomes small.

As a matter of course, the total amount of power (the amount integrated over the entire cross-sectional area) of the power density distribution P ₁ at point A before the light enters the cone lens 10 and the light emitted from the cone lens 10 Power density distribution P at point B
The total amount of power of ₂ (the amount integrated over the entire cross-sectional area) is equal.

From the above, the laser beam 5 at the point B after being emitted from the cone lens 10 has a large power density distribution P ₂ in the cross section at the center (this maximum value is P
_3max ), the distribution becomes smaller at the outermost periphery, and the distribution looks like a single mode at first glance. Such a power density distribution P ₂
By condensing the laser beam 5 from the diameter D ₁ to the diameter D ₂ by the condenser lens 3, it is possible to obtain a power density distribution P _{3 in} which the power density is sufficiently concentrated at the condensing position C.

Even if the above-described cone lens 10 is arranged on the optical path of the laser beam 5, its divergence angle θ (FIG.
Since the reference) does not in any way change, the laser beam 5 is not changed even in the condenser lens 3 condensing diameter D ₂ which is focused by a condensing diameter no fear of reduction in the power density due to spread.

Here, a conventional case in which the multi-mode laser beam 5 is focused without using the cone lens 10 will be described in comparison with this embodiment. FIG. 2 is a diagram showing a laser optical system that does not use the cone lens 10. Similar to FIG. 1, the laser beam at a point K before entering the condenser lens 3 and a point L at the focal position of the condenser lens 3 are shown. The power density distribution in the cross section of No. 5 is added to the corresponding position, and the radial distance from the center in this power density distribution is defined as y.

As shown in FIG. 2, when the power density distribution in the section of the laser beam 5 is a multi-mode distribution as indicated by P ₄ , the condensing lens 3 At point K before focusing, the diameter was D ₃ , but at point L of the focusing lens 3 the diameter was D ₄ determined according to the divergence angle θ of the laser beam 5. Increases. At this time, the power density distribution P ₅ in the section of the laser beam 5 at the point L is represented by the condensing lens 3
, A relationship substantially similar to the power density distribution P ₄ at the point K before the light is incident on the light source is maintained. Of course, also at this time, the power density distribution P at the point K before being incident on the condenser lens 3
It goes without saying equal to the amount of power in the power density distribution P ₅ (the amount obtained by integrating over the entire cross-sectional area) at the focusing position L points to the total amount of ₄ power (amount obtained by integrating over the entire cross-sectional area) . Accordingly, the relatively high power densities to near the outermost peripheral portion in the power density distribution P ₅ at the condensing position L point, the maximum value P _5max is the value of that for consideration of power density conditions that constant amount of power above Stay.

On the other hand, in the power density distribution P ₃ according to the present embodiment shown in FIG. 1, the condition that the power density at the outermost periphery is substantially zero and becomes larger toward the center, and the condition that the total amount of power is constant is considered. Then the direction of the maximum value P _3max becomes much larger at the center of the power density distribution of Fig. 1 than the maximum value P _5max at the center of the power density distribution of Fig. 2 it is clear.

According to the present embodiment as described above, the cone lens 10 as the light beam changing optical means is disposed on the optical path of the laser beam 5 before the condenser lens 3, so that the laser beam emitted from the cone lens 10 The power density distribution P ₂ in the cross section of the beam 5 can be increased at the center and reduced at the outermost periphery, and the laser beam 5 having such a power density distribution is condensed by the condensing lens 3 to collect the laser beam 5. A power density distribution in which the power density is sufficiently concentrated at the light position can be obtained. Therefore, even if the laser beam 5 becomes a multimode with a large divergence angle by increasing the output,
It is possible to sufficiently concentrate the power density. For example, the penetration depth can be increased in welding, and the applicable plate thickness can be increased in cutting and drilling.

[0024]

According to the present invention, since the light-replacement optical means is disposed on the optical path of the laser beam before the condensing lens, the power density distribution in which the power density is sufficiently concentrated at the laser beam condensing position is provided. Can be obtained. Therefore, even if the laser beam is multi-mode having a large divergence angle by increasing the output, it is possible to sufficiently concentrate the power density, and for example, it is possible to increase the penetration depth in welding, Further, in cutting or drilling, the applicable plate thickness can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system for laser processing according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a conventional case of condensing a multi-mode laser beam without using a cone lens.

FIG. 3 is a diagram illustrating an example of an optical system for laser processing in a conventional general laser processing apparatus.

4A is a diagram illustrating a divergence angle of a laser beam, and FIG. 4B is a diagram illustrating a beam mode of the laser beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Bending mirror 3 Condensing lens 4 Workpiece 5 Laser beam 10 Cone lens

Claims (2)

[Claims] 1. A laser processing optical system comprising: a laser oscillator for emitting a laser beam having a multimode power density in a cross section perpendicular to an optical axis; and a condenser lens for condensing the laser beam. A light beam changing optical means for changing the position of each parallel light beam constituting the laser beam inside and outside with respect to the optical axis of the laser beam, is arranged on the optical path of the laser beam before entering the condenser lens. Characteristic optical system for laser processing. 2. The laser processing optical system according to claim 1, wherein said light beam changing optical means is a cone lens.