Reflective variable beam diameter optical system, laser processing head and laser processing machine

Abstract

The reflective variable beam diameter optical system comprises a first off-axis parabolic mirror (20) onto which incident light (10), which is parallel light, is incident in the same direction as the direction of the main axis of rotation (22) of the first off-axis parabolic mirror (20), a second off-axis parabolic mirror (30) arranged so that the focal point (33) of the second off-axis parabolic mirror (30) coincides with the focal point (23) of the first off-axis parabolic mirror (20), and a movable base (40) that translates the first off-axis parabolic mirror (20) and the second off-axis parabolic mirror (30) in a direction different from the direction of the main axis of rotation (22), and varies the beam diameter of the outgoing light (12) emitted from the second off-axis parabolic mirror (30).

Description

[Technical Field]

[0001] The present disclosure relates to a reflective beam diameter variable optical system that uses a reflective optical element to vary the beam diameter of laser light, a laser processing head, and a laser processing machine. [Background technology]

[0002] The reflective beam diameter variable optical system of Patent Document 1 includes a first off-axis parabolic mirror having a convex surface and a second off-axis parabolic mirror having a concave surface, and is disposed such that, in a basic position, the axis of rotational symmetry of the first off-axis parabolic mirror coincides with the axis of rotational symmetry of the second off-axis parabolic mirror and the focal point of the first off-axis parabolic mirror coincides with the focal point of the second off-axis parabolic mirror. When a laser beam is incident on the first off-axis parabolic mirror parallel to the axis of rotational symmetry of the first off-axis parabolic mirror, the incident laser beam is reflected by the first off-axis parabolic mirror and enters the second off-axis parabolic mirror while diverging. The second off-axis parabolic mirror is moved along the optical axis of the reflected light from the first off-axis parabolic mirror to change the distance between the first off-axis parabolic mirror and the second off-axis parabolic mirror, thereby making it possible to vary the beam diameter of the laser light emitted from the second off-axis parabolic mirror. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2016-502228 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the distance between the first off-axis parabolic mirror and the second off-axis parabolic mirror is changed to vary the beam diameter of the laser light emitted from the second off-axis parabolic mirror, so the focal point of the first off-axis parabolic mirror and the focal point of the second off-axis parabolic mirror cannot always be made to coincide with each other. Therefore, under conditions where the focal points of the first off-axis parabolic mirror and the second off-axis parabolic mirror do not coincide with each other, there is a problem in that significant aberration occurs in the laser light emitted from the second off-axis parabolic mirror.

[0005] Furthermore, under the condition that the focal points of the first off-axis parabolic mirror and the second off-axis parabolic mirror are aligned, the laser light incident on the first off-axis parabolic mirror as parallel light is emitted from the second off-axis parabolic mirror as parallel light. On the other hand, if the distance between the first off-axis parabolic mirror and the second off-axis parabolic mirror is increased, the laser light emitted from the second off-axis parabolic mirror becomes divergent. On the other hand, if the distance between the first off-axis parabolic mirror and the second off-axis parabolic mirror is decreased, the laser light emitted from the second off-axis parabolic mirror becomes convergent. Therefore, there is also the problem that the divergence angle of the laser light emitted from the second off-axis parabolic mirror changes depending on the distance between the first off-axis parabolic mirror and the second off-axis parabolic mirror.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a reflective variable beam diameter optical system that can vary the beam diameter while suppressing the occurrence of aberrations and changes in the beam divergence angle. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the reflective beam diameter variable optical system of the present disclosure comprises a first off-axis parabolic mirror to which parallel light is incident in the same direction as the direction of the main axis of rotation of the first off-axis parabolic mirror, a second off-axis parabolic mirror arranged so that the focus of the second off-axis parabolic mirror coincides with the focus of the first off-axis parabolic mirror, and a first movable base that translates the first off-axis parabolic mirror and the second off-axis parabolic mirror in a direction different from the direction of the main axis of rotation of the first off-axis parabolic mirror, and is characterized in that it varies the beam diameter of the light emitted from the second off-axis parabolic mirror. [Effects of the Invention]

[0008] The reflective variable beam diameter optical system of the present disclosure has the advantage of being able to vary the beam diameter while suppressing the occurrence of aberrations and changes in the beam divergence angle. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram showing the configuration of a reflective variable beam diameter optical system according to the first embodiment. [Figure 2] FIG. 1 is a schematic diagram showing a state in which a movable base is translated in the reflective variable beam diameter optical system according to the first embodiment; [Figure 3] FIG. 10 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a second embodiment. [Figure 4] FIG. 10 is a schematic diagram showing a state in which a movable base is translated in a reflective variable beam diameter optical system according to the second embodiment; [Figure 5] FIG. 10 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a third embodiment. [Figure 6] FIG. 10 is a schematic diagram showing a state in which the movable base is translated in the −z direction in the reflective variable beam diameter optical system according to the third embodiment. [Figure 7] FIG. 10 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a fourth embodiment. [Figure 8] FIG. 10 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a fifth embodiment. [Figure 9]FIG. 13 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a sixth embodiment. [Figure 10] FIG. 13 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to a seventh embodiment. [Figure 11] 13 is a schematic diagram showing the configuration of a laser processing head according to the eighth embodiment. [Figure 12] A processing tolerance table showing the range of focal point positions that can be used when cutting mild steel. [Figure 13] 13 is a schematic diagram showing the configuration of a laser processing head according to a ninth embodiment. [Figure 14] 16 is a schematic diagram showing the configuration of a laser processing head according to a tenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The reflective variable beam diameter optical system, laser processing head, and laser processing machine according to the embodiments will be described in detail below with reference to the drawings. The same or corresponding parts in each drawing will be denoted by the same reference numerals. Furthermore, to clarify the orientation of the reflective variable beam diameter optical system and the laser processing head, arrows indicating the x, y, and z directions are added to each drawing.

[0011] Embodiment 1 1 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to embodiment 1. The reflective beam diameter variable optical system includes a first off-axis concave parabolic mirror 20, a second off-axis concave parabolic mirror 30, and a movable base 40 serving as a first movable base. The first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed on the movable base 40 such that the position of the focal point 23 of the first off-axis parabolic mirror 20 coincides with the position of the focal point 33 of the second off-axis parabolic mirror 30. The movable base 40 has a mechanism that allows it to move freely in the direction indicated by arrow 41, i.e., in the z direction.

[0012] Next, the operation will be described. Incident light 10 entering the reflective variable beam diameter optical system of the first embodiment is collimated in advance. Furthermore, the parallel incident light 10 is incident on the first off-axis parabolic mirror 20 with the direction of the optical axis 11 of the incident light 10 aligned with the direction of the main axis of rotation 22 of the first off-axis parabolic mirror 20. In principle, a light beam incident on the parabolic mirror with its optical axis aligned with the direction of the main axis of rotation of the parabolic mirror is reflected by the surface of the parabolic mirror and passes through the focal point of the parabolic mirror. Therefore, the incident light 10 is focused by the first off-axis parabolic mirror 20 at the focal point 23 of the first off-axis parabolic mirror 20.

[0013] Incident light 10 is focused at focal point 23 of first off-axis parabolic mirror 20, then diverges, and enters second off-axis parabolic mirror 30. After passing through the focal point of the parabolic mirror, the light rays that enter the parabolic mirror itself are reflected by the surface of the parabolic mirror and exit the parabolic mirror with their optical axes aligned with the direction of the parabolic mirror's main axis of rotation. Because first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30 are arranged so that their focal positions are aligned, incident light 10 that enters second off-axis parabolic mirror 30 while diverging is collimated by reflection on second off-axis parabolic mirror 30, and exits second off-axis parabolic mirror 30 with the optical axis 13 of exiting light 12 aligned with the direction of the main axis of rotation 32 of second off-axis parabolic mirror 30.

[0014] Therefore, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, which are arranged with their foci aligned, form an afocal optical system for the incident light 10, which has been collimated by aligning the direction of the optical axis 11 with the main axis of rotation 22 of the first off-axis parabolic mirror 20.

[0015] Here, if the distance from the incident point 21 of the chief ray of the incident light 10 on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20 is f1, and the distance from the focal point 33 of the second off-axis parabolic mirror 30 to the incident point 31 of the chief ray of the incident light on the second off-axis parabolic mirror 30 is f2, then the lateral magnification β of the afocal optical system is given by the following equation (1): β=f2 / f1 (1)

[0016] Therefore, the beam diameter d1 of the incident light 10 and the beam diameter d2 of the outgoing light 12 have the relationship expressed by the following equation (2). d2=β×d1=(f2 / f1)×d1 (2)

[0017] The distance from the incident point 21 of the chief ray of the incident light 10 on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20 corresponds to the focal length f1 of the first off-axis parabolic mirror 20, and the distance from the focal point 33 of the second off-axis parabolic mirror 30 to the incident point 31 of the chief ray of the incident light on the second off-axis parabolic mirror 30 corresponds to the focal length f2 of the second off-axis parabolic mirror 30.

[0018] Next, a method for varying the beam diameter d2 of the output light 12 will be described. Fig. 2 is a schematic diagram showing a state in which the movable base 40 is translated in the reflective variable beam diameter optical system according to embodiment 1. Note that the beam diameter d1 of the incident light 10 and the position and direction of the optical axis 11 of the incident light 10 are the same as those in Fig. 1.

[0019] Because the movable base 40 is translated in the −z direction, the direction of the main axis of rotation 22 of the first off-axis parabolic mirror 20 does not change. Furthermore, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 remain aligned. Therefore, the direction of the optical axis 11 coincides with the direction of the main axis of rotation 22 of the first off-axis parabolic mirror 20, and the optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 remains an afocal optical system for the incident light 10, which is a parallel light beam incident on the first off-axis parabolic mirror 20.

[0020] On the other hand, by translating in the −z direction the movable base 40 to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed, the position of the incident point 21, at which the chief ray of the incident light 10 is incident, changes on the surface of the first off-axis parabolic mirror 20. As a result, the focal length f1 from the incident point 21 on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20, and the focal length f2 from the incident point 31 on the second off-axis parabolic mirror 30 to the focal point 33 of the second off-axis parabolic mirror 30 change.

[0021] As shown in Figure 2, when the movable base 40 is translated in the -z direction, the focal length f1 decreases and the focal length f2 increases compared to the state in Figure 1. Therefore, the lateral magnification β of the afocal optical system given by equation (1) increases, and the beam diameter d2 of the output light 12 can be increased compared to the state in Figure 1.

[0022] On the other hand, if the movable base 40 is translated in the +z direction, the focal length f1 increases and the focal length f2 decreases compared to the state in Figure 1, so the lateral magnification β of the afocal optical system decreases, and the beam diameter d2 of the output light 12 can be reduced compared to the state in Figure 1.

[0023] As described above, according to the first embodiment, a reflective, variable-magnification afocal optical system can be configured using only two optical elements: the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30. Moreover, the beam diameter can be varied simply by translating the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, which are focused together. This not only facilitates adjustment of the beam diameter, but also simplifies the drive mechanism for varying the beam diameter, thereby reducing the manufacturing cost of the variable-beam-diameter optical system, whether it is a reflective or transmissive type, and further improving the reliability of the optical system. The direction in which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are moved by the movable base 40 may be any direction as long as it is different from the direction of the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the direction of the optical axis 11 of the incident light 10 can be aligned with the main axis of rotation 22 of the first off-axis parabolic mirror 20.

[0024] Furthermore, because this is a reflective afocal optical system based on the basic optical principle that light rays incident on a parabolic mirror parallel to the main axis of rotation of the parabolic mirror always pass through the focal point of the parabolic mirror, it is possible to effectively suppress the occurrence of coma and astigmatism and maintain high beam quality even when the magnification of the afocal optical system is changed.

[0025] Furthermore, in the mid-infrared to far-infrared wavelength range typified by CO2 lasers, and in the deep ultraviolet to extreme ultraviolet wavelength range of 200 nm or less, there are few transparent glass materials with low laser light absorption rates, and when a transmission-type variable beam diameter optical system is used, there is the issue that the beam quality also deteriorates significantly due to the occurrence of thermal lensing and thermal distortion associated with laser light absorption.

[0026] By using the reflective beam diameter variable optical system described in the first embodiment, even when a glass material having a high laser beam absorption rate is used for the off-axis parabolic mirror, the influence of thermal lensing that occurs inside the glass material due to laser beam absorption can be effectively suppressed, and it becomes possible to vary the beam diameter while maintaining the beam quality.

[0027] Furthermore, even if minute burns (damage) occur on the surface of the parabolic mirror due to the adhesion of foreign matter or the like, because it is a reflective optical element, the effects of localized thermal lensing that occurs inside the glass material due to laser light absorption are effectively suppressed, and the damage resistance of the optical element is significantly improved compared to transmissive beam diameter variable optical systems that use lenses, etc., which also has the effect of improving the reliability of the beam diameter variable optical system.

[0028] Embodiment 2 3 is a schematic diagram showing the configuration of a reflective variable beam diameter optical system according to embodiment 2. In embodiment 2, a convex off-axis parabolic mirror with a negative focal length is used as second off-axis parabolic mirror 30. Also in embodiment 2, as in embodiment 1, focal point 23 of first off-axis parabolic mirror 20 and focal point 33 of second off-axis parabolic mirror 30 are aligned.

[0029] In the second embodiment as well, the direction of optical axis 11 of incident light 10, which is parallel light, is aligned with the direction of main rotation axis 22 of first off-axis parabolic mirror 20, and the incident light is made incident on first off-axis parabolic mirror 20. In principle, incident light 10, which is incident on the parabolic mirror with the direction of optical axis 11 aligned with the direction of main rotation axis 22 of first off-axis parabolic mirror 20, is reflected on the surface of first off-axis parabolic mirror 20 and is condensed toward focal point 23 of first off-axis parabolic mirror 20.

[0030] However, in the second embodiment, incident light 10 reflected by first off-axis parabolic mirror 20 is incident on second off-axis parabolic mirror 30 which is a convex mirror before reaching focal point 23 of first off-axis parabolic mirror 20, and is reflected by second off-axis parabolic mirror 30. In principle, the convex parabolic mirror reflects the light beam incident toward the focal point of the convex parabolic mirror in a direction that aligns the optical axis with the direction of the main axis of rotation of the convex parabolic mirror.

[0031] In the second embodiment, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are arranged to coincide with each other, and incident light 10 reflected by the first off-axis parabolic mirror 20 is condensed toward the focal point 23 of the first off-axis parabolic mirror 20, which is arranged to coincide with the focal point 33 of the second off-axis parabolic mirror 30. Therefore, the outgoing light 12 reflected by the second off-axis parabolic mirror 30 is collimated by the second off-axis parabolic mirror 30 and reflected in the direction of the main axis of rotation 32 of the second off-axis parabolic mirror 30. In other words, the direction of the optical axis 13 of the outgoing light 12 coincides with the direction of the main axis of rotation 32 of the second off-axis parabolic mirror 30.

[0032] In the reflective variable beam diameter optical system of the second embodiment, similarly to the first embodiment, incident light 10 is parallel to output light 12, and therefore first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30 form an afocal optical system. The afocal optical system of the first embodiment, which uses the concave second off-axis parabolic mirror 30, is a Keplerian afocal optical system that forms a focal point within the optical system, whereas the afocal optical system of the second embodiment, which uses the convex second off-axis parabolic mirror 30, forms a Galilean afocal optical system that does not form a focal point within the optical system.

[0033] Here, if the distance from the incident point 21 of the chief ray on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20 is f1, and the distance from the incident point 31 of the chief ray on the second off-axis parabolic mirror 30 to the focal point 33 of the second off-axis parabolic mirror 30 is f2, the lateral magnification β of the afocal optical system and the relationship between the beam diameter d1 of the incident light 10 and the beam diameter d2 of the exiting light 12 are given by equations (1) and (2), respectively, as in embodiment 1.

[0034] Next, a method for varying the beam diameter d2 of the output light 12 will be described. Fig. 4 is a schematic diagram showing a state in which the movable base 40 is translated in the reflective variable beam diameter optical system according to embodiment 2. Note that the beam diameter d1 of the incident light 10 and the position and direction of the optical axis 11 of the incident light 10 are the same as those in Fig. 3.

[0035] 4, the movable base 40 is translated in the +z direction from the reflective beam diameter variable optical system shown in FIG. 3, so the direction of the rotational axis 22 of the first off-axis parabolic mirror 20 does not change. Furthermore, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are maintained in a coincident state. Therefore, similar to the first embodiment, the optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 remains an afocal system for the incident light 10, which is a parallel light beam that enters the first off-axis parabolic mirror 20 with the direction of the optical axis 11 coinciding with the direction of the rotational axis 22 of the first off-axis parabolic mirror 20.

[0036] On the other hand, by translating in the +z direction the movable base 40 to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed, the position of the incident point 21, at which the chief ray of the incident light 10 is incident, changes on the surface of the first off-axis parabolic mirror 20. As a result, the focal length f1 from the incident point 21 on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20, and the focal length f2 from the incident point 31 on the second off-axis parabolic mirror 30 to the focal point 33 of the second off-axis parabolic mirror 30 change.

[0037] As shown in Figure 4, when the movable base 40 is translated in the +z direction, the focal length f1 increases and the focal length f2 decreases compared to the state in Figure 3. Therefore, the lateral magnification β of the afocal optical system given by equation (1) decreases, and the beam diameter d2 of the output light 12 can be reduced compared to the state in Figure 3. On the other hand, when the movable base 40 is translated in the -z direction, the focal length f1 decreases and the focal length f2 increases compared to the state in Figure 3, so the lateral magnification β of the afocal optical system increases and the beam diameter d2 of the output light 12 can be increased compared to the state in Figure 3.

[0038] As shown in the second embodiment, when a convex parabolic mirror is used for the second off-axis parabolic mirror 30, the value of the focal length f1 from the incident point 21 of the chief ray on the first off-axis parabolic mirror 20 to the focal point 23 of the first off-axis parabolic mirror 20 is geometrically always greater than the value of the focal length f2 from the incident point 31 of the chief ray on the second off-axis parabolic mirror 30 to the focal point 33 of the second off-axis parabolic mirror 30. Therefore, in a configuration such as the second embodiment, in which a concave parabolic mirror is used for the first off-axis parabolic mirror 20 on the incident side and a convex parabolic mirror is used for the second off-axis parabolic mirror 30 on the output side, the lateral magnification β of the afocal optical system is always 1 or less, and the beam diameter d2 of the output light 12 is always smaller than the beam diameter d1 of the input light 10.

[0039] On the other hand, it goes without saying that a variable beam diameter afocal optical system can also be configured by using a convex parabolic mirror for first off-axis parabolic mirror 20 on the incident side and a concave parabolic mirror for second off-axis parabolic mirror 30 on the exit side, and arranging them so that focal point 23 of first off-axis parabolic mirror 20 coincides with focal point 33 of second off-axis parabolic mirror 30. In this case, the lateral magnification β of the afocal optical system is always 1 or more, and the beam diameter d2 of exiting light 12 is always larger than the beam diameter d1 of incident light 10.

[0040] As described above, according to the second embodiment, a concave parabolic mirror is used for one of the off-axis parabolic mirrors and a convex parabolic mirror is used for the other off-axis parabolic mirror. This not only provides the same effects as the first embodiment, but also makes it possible to shorten the distance between the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 compared to when both the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are concave parabolic mirrors, thereby enabling the reflection type variable beam diameter optical system to be miniaturized.

[0041] Embodiment 3 5 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to Embodiment 3. In Embodiment 3, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are arranged so that the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 coincide with each other, and the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 coincide with each other. In Embodiment 3, the optical axis 11 of the incident light 10, which is a parallel light, the optical axis 13 of the emitted light 12, the main axis of rotation 22 of the first off-axis parabolic mirror 20, and the main axis of rotation 32 of the second off-axis parabolic mirror 30 all coincide with the x-axis.

[0042] In the reflective variable beam diameter optical system of embodiment 3, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are aligned, and the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are aligned so that the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 also match. As a result, the optical axis 11 of the incident light 10, which is a parallel light, and the optical axis 13 of the outgoing light 12, which is a parallel light, can be aligned parallel to the x-axis.

[0043] 6 is a schematic diagram showing a state in which the movable base 40 is translated in the −z direction in the reflective beam diameter variable optical system according to Embodiment 3. As in Embodiments 1 and 2, the beam diameter can be varied by translating the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 while maintaining the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 aligned with each other and the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 aligned with each other, thereby changing the position of the incident point 21 at which the incident light 10 is incident on the first off-axis parabolic mirror 20.

[0044] In the third embodiment, a configuration is shown in which concave parabolic mirrors are used as the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, but as in the second embodiment, either the first off-axis parabolic mirror 20 or the second off-axis parabolic mirror 30 may be a convex parabolic mirror.

[0045] As described above, according to the third embodiment, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are aligned, and the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 are aligned. This not only provides the same effects as those of the first and second embodiments, but also makes the optical axis 11 of the incident light 10 and the optical axis 13 of the outgoing light 12 parallel to each other, thereby significantly facilitating the design, installation, and angle adjustment of the reflective variable beam diameter optical system.

[0046] Embodiment 4 7 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to embodiment 4. In embodiment 4, as in embodiment 3, the focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are aligned, and the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are disposed so that the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 are aligned in the x direction.

[0047] In the reflective variable beam diameter optical system of the fourth embodiment, optical axis 15 of incident light 14, which is a parallel light incident in the +z direction, is bent by 90° in the −x direction parallel to main axis of rotation 22 of first off-axis parabolic mirror 20 by first bending mirror 5 made of a plane mirror, and is made incident on first off-axis parabolic mirror 20. Incident light 10, which is a parallel light incident on first off-axis parabolic mirror 20, passes through an afocal optical system made up of first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30, and is emitted as a parallel light in the +x direction parallel to main axis of rotation 32 of second off-axis parabolic mirror 30.

[0048] Emitted light 12, which is a parallel light emitted in the +x direction, is bent by 90° in the +z direction by second bending mirror 6, which is a plane mirror. Here, second bending mirror 6 is fixed on second movable base 70, which is movable in the z direction.

[0049] In the reflective variable beam diameter optical system of the fourth embodiment, incident light 14 is a parallel light that has been collimated in advance, and optical axis 15 of incident light 14 is fixed at a fixed position and direction. In addition, first bending mirror 5, which is a plane mirror, is also fixed at a fixed position and angle on fixed base 8.

[0050] The movable mechanisms of the movable base 40, to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed and which is movable in the z direction, and the second movable base 70, to which the second bending mirror 6 is fixed and which is also movable in the z direction, are both provided on the fixed base 8, and the movable base 40 and the second movable base 70 move in parallel in the z direction relative to the fixed base 8. In the reflective variable beam diameter optical system of the fourth embodiment, the position of the second movable base 70 in the z direction is set so that the optical axis 15 of the incident light 14 and the optical axis 17 of the outgoing light 16 to the optical system coincide with each other.

[0051] When the movable base 40 is translated in the z direction to change the beam diameter d2 of the output light 12 that is output from the second off-axis parabolic mirror 30, the position of the optical axis 13 of the output light 12 that is output from the second off-axis parabolic mirror 30 also shifts in the z direction. If the amount of parallel shift of the optical axis 13 of the output light 12 that is output from the second off-axis parabolic mirror 30 is Δz, then by translating the second movable base 70 in the z direction in conjunction with the amount of parallel shift Δz of the optical axis 13 of the output light 12, the optical axis 17 of the output light 16 from the optical system can always be maintained at a constant position and angle (direction).

[0052] Here, a specific example will be described assuming a configuration in which parabolic mirrors with a main axis focal length of 25 mm are used as the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30.

[0053] When the lateral magnification β of the afocal optical system consisting of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 is 1x, the distance between the optical axis 11 of the incident light 10 entering the first off-axis parabolic mirror 20 and the optical axis 13 of the outgoing light 12 emerging from the second off-axis parabolic mirror 30 is 100 mm.

[0054] To increase the lateral magnification β of the afocal optical system from 1x to 2x, it is sufficient to translate the movable base 40, to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed, by 14.65 mm in the -z direction, in which case the distance between the optical axis 11 of the incident light 10 entering the first off-axis parabolic mirror 20 and the optical axis 13 of the outgoing light 12 emerging from the second off-axis parabolic mirror 30 is 106.07 mm. In other words, when the state in which the lateral magnification β is 1x is taken as the reference, the amount of translation Δz of the optical axis 13 of the outgoing light 12 emerging from the second off-axis parabolic mirror 30 in the +z direction is 6.07 mm. Therefore, by translating the second movable base 70 to which the second folding mirror 6 is fixed by 6.07 mm in the +z direction, the optical axis 17 of the output light 16 from the optical system, whose direction has been folded 90° in the +z direction by the second folding mirror 6, can be maintained at a constant position and angle.

[0055] Note that the movable direction 71 of the second movable base 70 is not limited to the z direction. For example, if the movable direction 71 of the second movable base 70 is the x direction, even if the second movable base 70 is translated by 6.07 mm in the −x direction, the optical axis 17 of the output light 16 output from the second bending mirror 6 can be maintained constant. In other words, as long as the movable direction 71 of the second movable base 70 is in a direction other than a direction parallel to the mirror surface of the second bending mirror 6, it is possible in principle to compensate for the effect of the optical axis shift of the output light 12 output from the second off-axis parabolic mirror 30 due to a change in the magnification of the afocal optical system, and to maintain the optical axis 17 of the output light 16 from the optical system output from the second bending mirror 6 at a constant position and angle.

[0056] Embodiment 5 8 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to embodiment 5. In embodiment 4, the reflective beam diameter variable optical system is shown in which the rotational axis 22 of the first off-axis parabolic mirror 20 and the rotational axis 32 of the second off-axis parabolic mirror 30 are aligned and the optical axis 17 of the output light 16 from the optical system is maintained constant. However, in the reflective beam diameter variable optical system according to embodiment 5, the rotational axis 22 of the first off-axis parabolic mirror 20 and the rotational axis 32 of the second off-axis parabolic mirror 30 do not match, and a second bending mirror 6 fixed on a second movable base 70 is used, and the second bending mirror 6 is installed at an appropriate position depending on the magnification of the afocal optical system. With this configuration, the influence of the optical axis shift of the emitted light 12 exiting the second off-axis parabolic mirror 30 can be compensated for, and the position and direction (angle) of the optical axis 17 of the emitted light 16 from the optical system exiting the second bending mirror 6 can be maintained constant, thereby achieving the same effect as in embodiment 4.

[0057] Furthermore, in cases where oblique incidence at a high angle of incidence is required to ensure the reflectivity of the mirror, such as extreme ultraviolet light with an extremely short wavelength of 100 nm or less, the angle between the main axis of rotation 22 of the first off-axis parabolic mirror 20 and the main axis of rotation 32 of the second off-axis parabolic mirror 30 can be adjusted to an appropriate value to adjust the angle of incidence of the light incident on the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, thereby making it possible to change the beam diameter with low aberration and maintaining a high optical transmission efficiency of the afocal optical system composed of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30.

[0058] Embodiment 6 In the first to fifth embodiments, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed on the same movable base 40, and the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are translated in parallel to change the magnification of the afocal optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, thereby changing the beam diameter d2 of the output light 12. However, the beam diameter changing method is not limited to this.

[0059] 9 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to a sixth embodiment. In the sixth embodiment, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed on a fixed base 8 such that the focal point 23 of the first off-axis parabolic mirror 20 coincides with the focal point 33 of the second off-axis parabolic mirror 30. Meanwhile, the first bending mirror 5 is fixed on a third movable base 80 that is movable in the z direction. The movable mechanism of the third movable base 80 that is movable in the z direction is provided on the fixed base 8, and the third movable base 80 moves in parallel in the z direction relative to the fixed base 8. Furthermore, the second bending mirror 6 is fixed on a second movable base 70 that is movable in the z direction.

[0060] As in the reflective beam diameter variable optical system of embodiment 6, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed on a fixed base 8, and the third movable base 80 to which the first bending mirror 5 is fixed is translated in the movable direction 81 (z direction). By aligning the direction of the optical axis 11 of the incident light 10, which is a parallel light, with the direction of the main rotation axis 22 of the first off-axis parabolic mirror 20, and changing the position of the incident point 21 at which the chief ray of the incident light 10 is incident on the first off-axis parabolic mirror 20, similarly to embodiments 1 to 5, the magnification of the afocal optical system composed of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 can be changed and the beam diameter d2 of the output light 12 can be varied while effectively suppressing the occurrence of coma aberration and astigmatism.

[0061] In the sixth embodiment, the third movable base 80 to which the first bending mirror 5 is fixed is translated in the z direction, but the movable direction 81 of the translation is not limited to the z direction. If the movable direction 81 of the third movable base 80 is a direction other than a direction parallel to the mirror surface of the first bending mirror 5, the position of the incident point 21 on the first off-axis parabolic mirror 20 can be changed by translating the third movable base 80. Therefore, the magnification of the afocal optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 can be changed, and the beam diameter d2 of the output light 12, which is a parallel light, can be varied.

[0062] As shown in the sixth embodiment, the configuration in which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed and arranged with their foci aligned, and the first folding mirror 5 is translated to vary the magnification of the afocal optical system composed of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 is not limited to the configuration of the sixth embodiment shown in FIG. 9, but can be applied to any of the reflective beam diameter variable optical systems shown in the second to fifth embodiments, and in addition to obtaining the same effects as the second to fifth embodiments, there is also the effect of facilitating adjustment of the position of the incident light 10 incident on the first off-axis parabolic mirror 20.

[0063] Embodiment 7 10 is a schematic diagram showing the configuration of a reflective beam diameter variable optical system according to embodiment 7. In the reflective beam diameter variable optical system according to embodiment 7, a fourth movable base 60 for translating the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 includes a movable mechanism that is movable in two directions: a direction indicated by an arrow 61 that is parallel to the rotational axis 32 of the second off-axis parabolic mirror 30; and a direction indicated by an arrow 62 that is parallel to the rotational axis 22 of the first off-axis parabolic mirror 20.

[0064] When the fourth movable base 60 is translated in a direction parallel to the main axis of rotation 32 of the second off-axis parabolic mirror 30 indicated by arrow 61, the incident point 21 at which the optical axis 11 of the incident light 10, which is parallel light, enters the first off-axis parabolic mirror 20 changes, and therefore the focal length f1 of the first off-axis parabolic mirror 20 and the focal length f2 of the second off-axis parabolic mirror 30 change, and the magnification of the afocal optical system composed of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 can be changed.

[0065] Furthermore, when fourth movable base 60 is translated in a direction parallel to main rotation axis 22 of first off-axis parabolic mirror 20 as indicated by arrow 62, incident point 21 at which optical axis 11 of incident light 10 enters first off-axis parabolic mirror 20 does not change, and therefore the magnification of the afocal optical system formed by first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30 is maintained constant. Meanwhile, as fourth movable base 60 translates in the direction of arrow 62, optical axis 13 of output light 12 translates. That is, by translating the fourth movable base 60 in a direction parallel to the main axis of rotation 22 of the first off-axis parabolic mirror 20 indicated by the arrow 62, it becomes possible to adjust the position of the optical axis 13 of the emitted light 12 while maintaining the magnification of the afocal optical system consisting of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 constant.

[0066] As in the reflective beam diameter variable optical system of the seventh embodiment, if a movable mechanism capable of translation in at least two directions is provided on the fourth movable base 60 for translating the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30, which are arranged with their focal points coincident, it becomes possible to adjust the position of the optical axis 13 of the output light 12 in addition to adjusting the magnification of the afocal optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 by translating the fourth movable base 60. As a result, it becomes possible to change the magnification of the afocal optical system while maintaining the optical axis 13 of the output light 12 constant, without using the second bending mirror 6 or the second movable base 70 as in the reflective beam diameter variable optical systems shown in the fourth to sixth embodiments.

[0067] In particular, as shown in the reflective beam diameter variable optical system of embodiment 7, if one of the directions of parallel movement of the fourth movable base 60 is selected to be a direction parallel to the main axis of rotation 22 of the first off-axis parabolic mirror 20, it becomes possible to adjust the position of the optical axis 13 of the emitted light 12 while maintaining the magnification of the afocal optical system constant. Therefore, by independently adjusting the magnification of the afocal optical system and the position of the optical axis 13 of the emitted light 12, it has the effect of making adjustment of the optical system significantly easier.

[0068] The direction in which the fourth movable base 60, to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed while their focal points are aligned, is translated is not limited to this. If a movable mechanism capable of translation in any two different directions is provided within a plane including the main rotation axis 22 of the first off-axis parabolic mirror 20 and the main rotation axis 32 of the second off-axis parabolic mirror 30, it becomes possible to both change the lateral magnification of the afocal optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 and adjust the position of the optical axis 13 of the output light 12 emerging from the second off-axis parabolic mirror 30. The two appropriate directions can be selected depending on the desired optical system configuration and spatial limitations around the optical system.

[0069] Embodiment 8 In the first to seventh embodiments, the configuration of a reflective variable beam diameter optical system that uses a reflective optical element and can vary the beam diameter while effectively suppressing the occurrence of aberration has been described. From the eighth embodiment, the configuration of a laser processing head used for laser processing in a laser processing machine will be described as a specific practical example of the reflective variable beam diameter optical system.

[0070] Figure 11 is a schematic diagram showing the configuration of a laser processing head according to embodiment 8. The laser processing head according to embodiment 8 is equipped with a reflective variable beam diameter optical system having the same configuration as that of embodiment 4 shown in Figure 7. Incident light 14 to the optical system, which is a pre-collimated parallel light that enters first bending mirror 5, which is a plane mirror, in the +z direction, passes through the reflective variable beam diameter optical system, which is made up of first bending mirror 5, first off-axis parabolic mirror 20, second off-axis parabolic mirror 30, and second bending mirror 6, and is emitted as parallel light in the +z direction.

[0071] The collimated light beam 16 emitted from the reflective variable beam diameter optical system in the +z direction enters the third bending mirror 9, which is a flat mirror, bending the optical axis direction of the incident light by 90° in the -x direction, and then enters the collector mirror 100. The collector mirror 100 is a first aspherical mirror that bends the optical axis direction of the incident light incident in the -x direction by 90° in the +z direction and has a focusing performance with a focal length of f3 in the +z direction. Note that in the laser processing head of the eighth embodiment, the collector mirror 100 is a 90° off-axis parabolic mirror with a principal axis focal length of f3 / 2 and a reflection focal length of f3. The irradiated light beam 18 reflected by the collector mirror 100 is focused toward a focusing point 102, which is a focal length of f3 away from the collector mirror 100. By placing a workpiece near the focusing point 102, laser processing such as cutting, drilling, and welding can be performed.

[0072] The third bending mirror 9 and the collecting mirror 100 are fixed on a fifth movable base 110 that is movable in the z direction. A movable mechanism of the fifth movable base 110 that is movable in the z direction indicated by arrow 111 is provided on the fixed base 8, and the fifth movable base 110 moves parallel to the fixed base 8 in the z direction.

[0073] Incident light 14, which is a parallel light beam with a beam diameter d1 incident on the optical system, is converted into emerging light 16, which is a parallel light beam with a beam diameter d2, by a reflective variable beam diameter optical system consisting of a first bending mirror 5, a first off-axis parabolic mirror 20, a second off-axis parabolic mirror 30, and a second bending mirror 6. Here, the second movable base 70 to which the second bending mirror 6 is fixed has its translation amount in the z direction adjusted so that the optical axis 17 of the emerging light from the optical system is always at a constant position, regardless of the magnification of the reflective variable beam diameter optical system, i.e., the translation amount of the movable base 40 in the z direction. Therefore, the chief ray of emerging light 16 from the optical system is always incident on incident point 101 on collector mirror 100, which is always at a constant position on collector mirror 100, and the optical axis 19 of illumination light 18 is also always maintained at a constant position and direction.

[0074] The focused beam diameter d3 at the focusing point 102 is inversely proportional to the beam diameter d2 of the incident light incident on the focusing mirror 100. That is, as the beam diameter d2 of the incident light increases, the focused beam diameter d3 decreases, and as the beam diameter d2 decreases, the focused beam diameter d3 increases. Therefore, by changing the beam diameter d2 of the output light 12 using the reflective beam diameter variable optical system, it is possible to adjust the focused beam diameter d3 to an appropriate value depending on the application.

[0075] Furthermore, the fifth movable base 110 to which the third folding mirror 9 and the focusing mirror 100 are fixed can be freely moved in the z direction indicated by the arrow 111, and by translating the fifth movable base 110 in the z direction, the position of the focusing point 102 can also be freely adjusted in the z direction.

[0076] Generally, when the focused beam diameter d3 of the laser beam used in laser processing changes, the optimal focal point position relative to the workpiece material also changes. Figure 12 is a diagram showing a processing tolerance table indicating the range of focal point positions that are possible when cutting mild steel. Figure 12 shows a processing tolerance table obtained through experiments to determine the range of focal point positions that are possible (good processing) for the focused beam diameter when cutting mild steel with a plate thickness of 9 mm. In Figure 12, the focal point position indicates the distance from the surface of the workpiece material to the focal point. In Figure 12, gray areas other than the white background indicate good processing, indicated by a circle. As is clear from the processing tolerance table in Figure 12, as the focused beam diameter increases, the optimal focal point position shifts away from the non-workpiece material.

[0077] As shown in the eighth embodiment, a fifth movable base 110 is provided to which the third bending mirror 9 and the collecting mirror 100 are fixed, and the fifth movable base 110 is configured to be freely movable in the z direction in which the laser light is collected by the collecting mirror 100. By adjusting the focusing point 102 to an optimal position in conjunction with the magnification of the reflective type variable beam diameter optical system, it is possible to obtain the effect of always maintaining stable and good processing.

[0078] Furthermore, the emitted light 12 that leaves the second off-axis parabolic mirror 30 is collimated parallel light, and the second movable base 70 ensures that the chief ray of the emitted light 16 from the optical system always enters a fixed incident point 101 on the focusing mirror 100 regardless of the magnification of the reflective type variable beam diameter optical system. Therefore, the effect on the beam characteristics of changes in the optical path length from the second off-axis parabolic mirror 30 to the focusing point 102 due to parallel movement of the fifth movable base 110 can be minimized.

[0079] Although conventional reflective beam diameter variable optical systems were able to suppress aberrations for a specific magnification, the occurrence of aberrations became more pronounced as the magnification was changed, making it difficult to achieve both a reflective optical system and variable beam diameter in a laser processing head. The configuration of the laser processing head shown in the eighth embodiment makes it possible to provide a laser processing head that is both a total reflection type and a variable focused beam diameter while effectively suppressing the occurrence of aberrations. In particular, in the eighth embodiment, a 90° off-axis parabolic mirror is also used for the focusing mirror 100, so that the occurrence of aberrations can also be effectively suppressed in the irradiation light 18 that is irradiated onto the non-workpiece.

[0080] Furthermore, in the mid-infrared to far-infrared wavelength range represented by CO2 lasers, and in the deep ultraviolet to extreme ultraviolet wavelength range of 200 nm or less, there are few transparent glass materials with low laser light absorption rates. Therefore, when a laser processing head composed of transmission optical elements such as lenses is used, the absorption of laser light in the transmission optical elements causes thermal lensing and thermal distortion, resulting in a significant focus shift and a significant deterioration in beam quality, making it difficult to maintain the required processing performance.

[0081] On the other hand, if a laser processing head configured with a reflective optical element as shown in embodiment 8 is used, even if a glass material that highly absorbs laser light is used as the reflective optical element, the influence of thermal lensing that occurs inside the optical element due to laser light absorption can be effectively suppressed, and there is an exceptional effect that high processing performance can be stably maintained while suppressing focus shift.

[0082] Furthermore, even if minute burns (damage) occur on the surface of the optical elements that make up the laser processing head due to the adhesion of foreign matter, etc., because they are reflective optical elements, the effects of localized thermal lensing that occurs inside the optical elements due to laser light absorption are effectively suppressed, and compared to laser processing heads that use transmissive optical elements such as lenses, the damage resistance of the optical elements, i.e., light resistance, can be greatly increased while maintaining processing stability, thereby significantly improving the reliability of the laser processing head. Furthermore, the laser output that can be used with the laser processing head is also increased, which has the effect of greatly improving the productivity of the laser processing itself.

[0083] Furthermore, according to the laser processing head of embodiment 8, the occurrence of coma aberration and astigmatism can be effectively suppressed while using a reflective optical element, and the focused beam diameter can also be changed, making it possible to select an appropriate focused beam diameter depending on the application, and effectively expanding the field of application of the laser processing head.

[0084] For example, in cutting applications, the optimal focused beam diameter and focal point position will vary depending on the type and thickness of the material being cut. Generally, when cutting thin materials, a smaller focused beam diameter allows for faster cutting speeds. On the other hand, when cutting thick materials, a larger focused beam diameter will result in higher cutting quality from the perspective of molten material removal. Also, when cutting mild steel using oxygen as the assist gas, the focal point is generally set outside the material, whereas when cutting stainless steel using nitrogen as the assist gas, the focal point is set inside the material.

[0085] In the laser processing head of embodiment 8, the third bending mirror 9 and the focusing mirror 100 are mounted on a fifth movable base 110 that is movable in the z direction. Therefore, by moving the fifth movable base 110 parallel to the z direction, the focusing point 102 can be set to an appropriate position depending on the application or the shape of the material to be processed.

[0086] Furthermore, because the laser processing head of embodiment 8 is configured with mirrors, which are reflective optical elements, as the main optical system, it is possible to use opaque metal mirrors. When a metal mirror is used, a cooling water pipe can be formed inside the mirror, facilitating direct water cooling of the mirror. This effectively improves the mirror's cooling performance, making it possible to improve its light resistance strength, and also reduces the manufacturing cost of the mirror compared to using a dielectric material such as quartz for the mirror's glass material.

[0087] Although the eighth embodiment shows a configuration in which a 90° off-axis parabolic mirror is used as the collector mirror 100, the type of collector mirror 100 is not limited to this, and for example, a toroidal mirror with a focal length f3 designed to bend the optical axis by 90° may be used. Compared to an off-axis parabolic mirror, a toroidal mirror inevitably generates coma aberration, but has the advantages of being easier to manufacture and cheaper to obtain, as well as reducing the adjustment margin required when installing the collector mirror 100.

[0088] 11, it goes without saying that protective glass may be installed between the collector mirror 100 and the focal point 102 to prevent contamination of the optical elements inside the laser processing head due to vaporized matter (fumes) or molten matter (spatters) generated at the processing point. Also, a gas nozzle may be installed between the collector mirror 100 and the focal point 102 to supply assist gas for laser processing or shield gas to prevent oxidation of the workpiece.

[0089] Embodiment 9 Fig. 13 is a schematic diagram showing the configuration of a laser processing head according to embodiment 9. In the laser processing head of embodiment 9, laser light is transmitted from the laser light source to the laser processing head using an optical fiber 130 having a core diameter d0. Although not shown in Fig. 13, the laser processing head of embodiment 9 uses a fiber laser with a wavelength of 1070 nm as the laser light source.

[0090] An optical fiber connector 132 is attached to the end of the optical fiber 130, and the optical fiber connector 132 is fixed on a fixed base 8. Incident light 14 to the optical system, which is laser light emitted from the optical fiber 130, travels in the +z direction while expanding its beam diameter, and is incident on a collimating mirror 120. The collimating mirror 120 is fixed on the fixed base 8, and is a second aspherical mirror that bends the optical axis direction of incident light 14 incident in the +z direction by 90° to the -x direction, and has a focusing performance with a focal length of f0 in the -z direction. Note that the laser processing head of the ninth embodiment uses a 90° off-axis parabolic mirror as the collimating mirror 120, with a principal axis focal length of f0 / 2 and a reflection focal length of f0.

[0091] An output end surface 131 of the optical fiber connector 132 is fixed so as to coincide with the focal point 121 of the collimating mirror 120, and the incident light 10, which is a laser beam reflected by the collimating mirror 120, is collimated so that the beam diameter is constant at d1, and the optical axis direction is bent by 90° in the −x direction, which is the same direction as the main rotation axis 22 of the first off-axis parabolic mirror 20, and then enters the first off-axis parabolic mirror 20. The optical system configuration from the first off-axis parabolic mirror 20 to the collecting mirror 100 is the same as that of the laser processing head of the eighth embodiment.

[0092] Furthermore, the direction of the optical axis (optical axis 11 of incident light) of the laser light (incident light 10) collimated by collimating mirror 120 and turned into parallel light coincides with the direction of main rotation axis 22 of first off-axis parabolic mirror 20, so first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30, which are arranged with their foci coincident, satisfy the conditions of an afocal optical system. Therefore, by translating movable base 40, to which first off-axis parabolic mirror 20 and second off-axis parabolic mirror 30 are fixed, in the z direction indicated by arrow 41, the magnification of the afocal optical system can be changed, and the beam diameter d2 of output light 12 emerging from second off-axis parabolic mirror 30 can be varied.

[0093] The first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 constitute an afocal optical system, and the exit end face 131 of the optical fiber 130 is fixed at the position of the focal point 121 of the collimating mirror. Therefore, the exit end face 131 of the optical fiber 130 and the focusing point 102 that coincides with the focal point of the focusing mirror 100 are optically conjugate, and the relationship between the core diameter d0 of the optical fiber 130 and the focused beam diameter d3 is expressed by the following equation (3). d3=(f3 / f0)×(f1 / f2)×d0 (3)

[0094] The focal length f1 of the first off-axis parabolic mirror 20 and the focal length f2 of the second off-axis parabolic mirror 30 can be changed by translating the movable base 40 to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed, so that the diameter d3 of the focused beam can be made variable.

[0095] It goes without saying that the same effect as the laser processing head shown in embodiment 8 can be obtained by using the laser processing head shown in embodiment 9, and even in a configuration in which laser light is transmitted from the laser light source to the laser processing head using optical fiber 130, the divergent light emitted from optical fiber 130 can be collimated to form parallel light, and the optical axis (optical axis 11 of the incident light) of the parallel laser light (incident light 10) can be made incident on the first off-axis parabolic mirror 20 parallel to the main rotation axis 22 of the first off-axis parabolic mirror 20, thereby making it possible to obtain a laser processing head with low aberration and variable focused beam diameter that uses reflective optical elements in the main optical system.

[0096] Furthermore, in the laser processing head of embodiment 9, a 90° off-axis parabolic mirror is also used as the parallelizing mirror 120, and the output end surface 131 of the optical fiber 130 is located at the focal position of the parallelizing mirror 120, so that the occurrence of aberration can also be effectively suppressed for the incident light 10 entering the first off-axis parabolic mirror 20.

[0097] In the ninth embodiment, a configuration has been described in which a fiber laser is used as the laser light source, but the type of laser light source is not limited to this. It goes without saying that similar effects can be obtained with any laser light source that can be transmitted through an optical fiber, such as a solid-state laser or a semiconductor laser.

[0098] Although not shown, protective glass may be installed between the optical fiber connector 132 and the collimating mirror 120. Installing protective glass between the optical fiber connector 132 and the collimating mirror 120 can effectively prevent dust particles from entering the inside of the laser processing head when the optical fiber 130 is attached or detached.

[0099] Embodiment 10 14 is a schematic diagram showing the configuration of a laser processing head according to a tenth embodiment. As in the ninth embodiment, the laser processing head of the tenth embodiment also employs a configuration in which laser light is transmitted from the laser light source to the laser processing head using an optical fiber 130 having a core diameter d0. Also, as in the ninth embodiment, incident light 14, which is laser light emitted from optical fiber 130, is converted into parallel light using a collimating mirror 120, and the optical axis is bent toward the rotational axis 22 of the first off-axis parabolic mirror 20.

[0100] The laser processing head of the tenth embodiment employs the reflective beam diameter variable optical system described in the seventh embodiment. The focal point 23 of the first off-axis parabolic mirror 20 and the focal point 33 of the second off-axis parabolic mirror 30 are aligned, the direction of the main rotation axis 22 of the first off-axis parabolic mirror 20 is aligned in the x direction, and the direction of the main rotation axis 32 of the second off-axis parabolic mirror 30 is aligned in the z direction. The first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed on a fourth movable base 60 with their focal points aligned and their main rotation axes at an angle of 90°. The fourth movable base 60 of the tenth embodiment is provided on a fixed base 8 and has a mechanism that allows it to move freely in two directions: the z direction indicated by arrow 61 and the x direction indicated by arrow 62.

[0101] In the laser processing head of embodiment 10, the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are also arranged with their foci aligned, and the optical axis 11 of the incident light 10, which is collimated parallel light, is aligned with the direction of the main axis of rotation 22 of the first off-axis parabolic mirror 20 and is incident on the first off-axis parabolic mirror 20, so that the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 form an afocal optical system.

[0102] In the laser processing head of the tenth embodiment, the position at which incident light 10 is incident on first off-axis parabolic mirror 20 is changed by translating fourth movable base 60 in the z direction indicated by arrow 61, thereby varying the magnification of the afocal optical system. Furthermore, when fourth movable base 60 is translated in the z direction indicated by arrow 61 to change the magnification of the afocal optical system, fourth movable base 60 is translated in the x direction indicated by arrow 62 to adjust so that optical axis 13 of output light 12 emerging from second off-axis parabolic mirror 30 is maintained at a constant position.

[0103] Furthermore, since the direction of parallel movement of the fourth movable base 60 indicated by arrow 62 coincides with the direction of the main rotation axis 22 of the first off-axis parabolic mirror 20, when the fourth movable base 60 is translated in the x direction indicated by arrow 62, it is possible to adjust the position of the optical axis 13 of the emitted light 12 while maintaining the magnification of the afocal optical system consisting of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 constant.

[0104] The third folding mirror 9 and the collecting mirror 100 are fixed on a fifth movable base 110 that is movable in the z direction indicated by the arrow 111, which is the same direction as the optical axis 13 of the emitted light 12 that exits the second off-axis parabolic mirror 30. Furthermore, the collecting direction of the collecting mirror 100 also coincides with the direction of the optical axis 13 of the emitted light 12 that exits the second off-axis parabolic mirror 30. Therefore, even if the magnification of the afocal optical system consisting of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 changes, it is possible to adjust the focusing point 102 to an optimal position and height while maintaining the optical axis 19 of the irradiated light 18 constant.

[0105] The configuration of the laser processing head shown in embodiment 10 not only achieves the same effects as those of embodiments 8 to 9, but also eliminates the need for the second bending mirror 6 and second movable base 70 used in the laser processing heads of embodiments 8 and 9 to correct the optical axis shift that occurs when the magnification of the afocal optical system consisting of the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 changes, thereby simplifying the configuration of the laser processing head and reducing the manufacturing costs of the laser processing head.In addition, the reduced number of driving units has the effect of improving the robustness and reliability of the laser processing head.

[0106] In the tenth embodiment, the configuration is shown in which the rotational axis 22 of the first off-axis parabolic mirror 20 and the rotational axis 32 of the second off-axis parabolic mirror 30 are arranged at an angle of 90°, but the angle formed by the rotational axis 22 of the first off-axis parabolic mirror 20 and the rotational axis 32 of the second off-axis parabolic mirror 30 is not limited to this. If the primary axis of rotation 22 of the first off-axis parabolic mirror 20 and the primary axis of rotation 32 of the second off-axis parabolic mirror 30 are arranged so as not to coincide with each other, and if a movable mechanism capable of translation in at least two directions is provided on the fourth movable base 60 to which the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30 are fixed, it is theoretically possible to maintain a constant position of the optical axis 13 of the output light 12 emitted from the second off-axis parabolic mirror 30 while changing the magnification of the afocal optical system formed by the first off-axis parabolic mirror 20 and the second off-axis parabolic mirror 30. The angle formed by the primary axis of rotation 22 of the first off-axis parabolic mirror 20 and the primary axis of rotation 32 of the second off-axis parabolic mirror 30 can be optimally selected taking into consideration the optical system configuration, spatial constraints, etc.

[0107] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, and parts of the configurations may be omitted or modified within the scope of the gist of the present disclosure. [Explanation of symbols]

[0108] 5 first folding mirror, 6 second folding mirror, 8 fixed base, 9 third folding mirror, 10, 14 incident light, 11, 13, 15, 17, 19 optical axis, 12, 16 output light, 18 illumination light, 20 first off-axis parabolic mirror, 21, 31, 101 incident point, 22, 32 main axis of rotation, 23, 33, 121 focus, 30 second off-axis parabolic mirror, 40 movable base (first movable base), 60 fourth movable base, 70 second movable base, 80 third movable base, 100 focusing mirror, 102 focusing point, 110 fifth movable base, 120 collimating mirror, 130 optical fiber, 131 output end face, 132 optical fiber connector.

Claims

1. a first off-axis parabolic mirror on which parallel light is incident in the same direction as a direction of a rotational axis of the first off-axis parabolic mirror; a second off-axis parabolic mirror arranged such that a focal point of the second off-axis parabolic mirror coincides with a focal point of the first off-axis parabolic mirror; a first movable base that translates the first off-axis parabolic mirror and the second off-axis parabolic mirror in a direction different from the direction of the main rotation axis of the first off-axis parabolic mirror, The beam diameter of the light emitted from the second off-axis parabolic mirror is made variable. A reflective type variable beam diameter optical system.

2. a second bending mirror that bends the optical axis of the light emitted from the second off-axis parabolic mirror; a second movable base that translates the second folding mirror in a direction different from a direction parallel to a mirror surface of the second folding mirror, The position and direction of the optical axis of the light emitted from the second folding mirror are maintained constant.

2. The reflective variable beam diameter optical system according to claim 1.

3. Either the first off-axis parabolic mirror or the second off-axis parabolic mirror is a convex off-axis parabolic mirror.

2. The reflective variable beam diameter optical system according to claim 1.

4. a first off-axis parabolic mirror; and a second off-axis parabolic mirror arranged such that a focal point of the second off-axis parabolic mirror coincides with a focal point of the first off-axis parabolic mirror; a first bending mirror that bends an optical axis of the incident parallel light in the same direction as a direction of a main axis of rotation of the first off-axis parabolic mirror and causes the incident parallel light to be incident on the first off-axis parabolic mirror; a third movable base that translates the first folding mirror in a direction different from a direction parallel to a mirror surface of the first folding mirror, The beam diameter of the light emitted from the second off-axis parabolic mirror is made variable. A reflective type variable beam diameter optical system.

5. a second bending mirror that bends the optical axis of the light emitted from the second off-axis parabolic mirror; a second movable base that translates the second folding mirror in a direction different from a direction parallel to a mirror surface of the second folding mirror, The position and direction of the optical axis of the light emitted from the second folding mirror are maintained constant.

5. The reflective variable beam diameter optical system according to claim 4.

6. Either the first off-axis parabolic mirror or the second off-axis parabolic mirror is a convex off-axis parabolic mirror.

5. The reflective variable beam diameter optical system according to claim 4.

7. a first off-axis parabolic mirror on which parallel light is incident in the same direction as a direction of a rotational axis of the first off-axis parabolic mirror; a second off-axis parabolic mirror arranged such that a focal point of the second off-axis parabolic mirror coincides with a focal point of the first off-axis parabolic mirror; The first off-axis parabolic mirror and the second off-axis parabolic mirror are a fourth movable base that translates the first off-axis parabolic mirror and the second off-axis parabolic mirror in at least two different directions within a plane including the main axis of rotation of the first off-axis parabolic mirror and the main axis of rotation of the second off-axis parabolic mirror; The beam diameter of the light emitted from the second off-axis parabolic mirror is made variable. A reflective type variable beam diameter optical system.

8. A reflective type variable beam diameter optical system according to any one of claims 1 to 7, a first aspherical mirror that collects the light emitted from the reflective variable beam diameter optical system; A laser processing head comprising:

9. an optical fiber for transmitting laser light; a second aspheric mirror that collimates the laser light emitted from the optical fiber and causes the laser light to enter the reflective variable beam diameter optical system.

9. The laser processing head according to claim 8.

10. The first aspherical mirror and the second aspherical mirror are off-axis parabolic mirrors.

10. The laser processing head according to claim 9.

11. The laser processing head according to claim 8 is provided. A laser processing machine characterized by:

Images