Laser beam dimming device

Abstract

The objective is to provide a laser beam attenuation device that can reduce the intensity of a laser beam to a predetermined level and separate the observed light from stray light, even when observing observation light with a large numerical aperture. [Solution] To achieve this objective, a laser beam attenuation device is employed that includes a beam splitter 1 in which the reflected light is used as observation light, the beam splitter 1 reflects 10% or less of the incident light, the beam splitter 1 is positioned such that when the origin of the beam splitter 1 on a plane perpendicular to the optical axis is the optical axis and the X and Y axes are arbitrary orthogonal coordinate axes on the optical axis, the incident angle of the incident light at the position of the optical axis is 45° with the X axis as the axis of rotation, and the cross-sectional shape of the beam splitter 1 in the plane determined by the incident light and reflected light of the beam splitter 1 is a wedge shape in which the incident light side of the beam splitter 1 is thin and the reflected light side of the beam splitter 1 is thick.

Description

Technical Field

[0001] The present invention relates to a laser beam dimming device for dimming a laser beam provided in a laser beam profiler used when profiling a laser beam irradiated from a laser beam irradiation optical system for laser processing by forming and irradiating spots of the laser beam on a processing object.

Background Art

[0002] In recent years, laser beams have been widely used in the processing of various products. By condensing a laser beam at a single point and irradiating the workpiece, the surface temperature of the workpiece is rapidly increased, and the irradiated surface of the workpiece is melted or evaporated. A laser processing apparatus using such a laser beam is a device that performs processing such as cutting, drilling, and welding on the workpiece in this way. And, since the laser beam is condensed at a single point, pinpoint precision and fine processing are possible. Also, by using a laser beam with higher energy, the processing time can be shortened, and it is also possible to process workpieces with high hardness that are difficult to process with a cutting tool.

[0003] Here, a laser processing apparatus includes a laser beam irradiation optical system. This laser beam irradiation optical system has functions of condensing a laser beam at a single spot and irradiating the laser beam at the spot with a circular image shape and a Gaussian or top-hat energy intensity distribution. However, in this conventional laser processing that adopts the image shape of the spot, there is a problem that when cutting, welding, or drilling the workpiece, the workpiece melted by the laser beam remains on the cutting surface or the hole, deteriorating the processing quality. Therefore, in recent years, laser processing has been proposed in which the image shape of the laser beam at the spot is made annular to appropriately blow off the melted workpiece and prevent it from remaining on the cutting surface or the hole.

[0004] Furthermore, before performing laser processing, a laser beam profiler is used to confirm that the image shape of the laser beam at the spot and the energy intensity distribution in that image shape meet the desired specifications. Known methods for attenuating the laser beam in this laser beam profiler include: attenuating the laser beam with a filter and observing it with an image sensor such as a CCD or CMOS; measuring the transmitted light intensity while partially blocking the laser beam with a pinhole, slit, or knife edge, and calculating the intensity from the correlation between the blocking position and the transmitted light intensity; secondarily scanning the laser beam with a rod with a small mirror at the tip or a light guide rod with a small hole at the tip to measure the intensity distribution; and irradiating a plate that scatters the laser beam with the laser beam and capturing an image of the scattered light from behind with a camera.

[0005] However, the above methods have problems such as the filter deforming due to the heat of the laser beam, the image shape of the laser beam being impaired by pinholes, slits, or knife edges, difficulty in measuring minute image shapes with small mirrors, and blurring of the image when scattered light is used. Therefore, a method has been proposed in which the laser beam is attenuated by separating the laser beam into transmitted and reflected light using a beam splitter, and the image shape of the laser beam and the energy intensity distribution in that image shape are measured by observing the attenuated transmitted or reflected light.

[0006] When using beam splitters to attenuate a beam, stray light can become a problem. For example, when using the reflected light from a parallel plate beam splitter as attenuating light, there is not only a surface reflection path where the light is reflected off the surface of the beam splitter, but also a back reflection path where the light passes through the surface of the beam splitter, is reflected off the back surface of the beam splitter, and then passes through the surface of the beam splitter again. Furthermore, there is a back reflection path where the light is repeatedly reflected inside the beam splitter, passes through the surface, and is emitted. This light from the back reflection path is stray light. Since the stray light from the back reflection path is parallel to the reflected light from the surface reflection path, if stray light enters an observation device such as an image sensor, it can cause problems in correctly observing the image of the laser beam.

[0007] Therefore, Patent Document 1 proposes a nanotexture attenuator that uses reflected light from a beam splitter with a wedge-shaped cross-section, rather than a parallel plate, to attenuate the laser beam. Although a back-surface reflected light path exists even with a wedge-shaped beam splitter, because the cross-section of the beam splitter is wedge-shaped, the stray light from the back-surface reflected light path of the wedge-shaped beam splitter becomes non-parallel to the reflected light from the front-surface reflected light path, and it is expected that this will suppress the incidence of stray light on the image sensor. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special table number 2022-537450 [Overview of the project] [Problems that the invention aims to solve]

[0009] Since laser processing equipment processes a workpiece by focusing a laser beam to a single spot and rapidly increasing its surface temperature, the observation light observed by a laser beam profiler is generally focused light. In such cases, observation light with a large numerical aperture (NA) is observed. However, the inventors have found that when observing observation light with a large numerical aperture, the nanotexture attenuator employing a wedge-shaped beam splitter disclosed in Patent Document 1 does not adequately address stray light.

[0010] The present invention has been made in view of these circumstances. The purpose of the present invention is to provide a laser beam attenuation device that can reduce the intensity of a laser beam to a predetermined level and separate the observed light from stray light, even when observing observation light with a large numerical aperture. [Means for solving the problem]

[0011] In order to solve the aforementioned problems, we conducted intensive research and arrived at the following laser beam dimming device.

[0012] The laser beam attenuation device according to the present invention is a laser beam attenuation device for attenuating a laser beam provided in a laser beam profiler, and comprises a beam splitter 1 whose reflected light is used as observation light, the beam splitter 1 reflects 10% or less of the incident light, the beam splitter 1 is positioned such that when the origin of an arbitrary orthogonal coordinate axis on a plane perpendicular to the optical axis is the optical axis and the X and Y axes are defined as such, the incident angle of the incident light at the position of the optical axis is 45° with the X axis as the axis of rotation, and the cross-sectional shape of the beam splitter 1 in the plane determined by the incident light and the reflected light of the beam splitter 1 is a wedge shape in which the incident light side of the beam splitter 1 is thin and the reflected light side of the beam splitter 1 is thick.

[0013] The laser beam profiler according to the present invention employs a laser beam profiler that comprises the above-mentioned laser beam attenuation device and an observation device for observing the observation light attenuated by the laser beam attenuation device. [Effects of the Invention]

[0014] The laser beam attenuation device according to the present invention can attenuate the laser beam to a predetermined intensity and separate the observed light from stray light, even when observing observation light with a large numerical aperture. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view of the beam splitter 1 in the first embodiment and a schematic diagram showing the trajectories of the incident and reflected light. [Figure 2] This is a schematic diagram showing the relationship between reflected light and stray light in the first embodiment. [Figure 3] This shows a cross-sectional view of beam splitter 1 and beam splitter 2 in the second embodiment, and a schematic diagram showing the trajectories of incident and reflected light. [Figure 4] Cross-sectional view of the beam splitter 1 in the third embodiment, a view of the beam splitter 2' as seen from the incident direction of the laser beam, and a schematic diagram showing the trajectories of the incident light and the reflected light to each of them. [Figure 5] Cross-sectional view of the beam splitter 1 in the third embodiment, a view of the beam splitter 2' as seen from the incident direction of the laser beam, and a schematic diagram showing the trajectories of the incident light and the reflected light to each of them. [Figure 6] Schematic diagram showing the portion of the beam splitter 2' in FIG. 4 in a direction where the Y-axis is perpendicular to the drawing plane. [Figure 7] Schematic diagram showing the portion of the beam splitter 2' in FIG. 5 in a direction where the Y-axis is perpendicular to the drawing plane. [Figure 8] Results of simulating the reflected light and stray light in Example 1. [Figure 9] Results of simulating the reflected light and stray light in Example 2. [Figure 10] Results of simulating the reflected light and stray light in Example 3. [Figure 11] Results of simulating the reflected light and stray light in Example 4. [Figure 12] Results of simulating the reflected light and stray light in Example 5. [Figure 13] Results of simulating the reflected light and stray light in Example 6. [Figure 14] Results of simulating the reflected light and stray light in Comparative Example 1. [Figure 15] Results of simulating the reflected light and stray light in Comparative Example 2. [Figure 16] Results of simulating the reflected light and stray light in Comparative Example 3. [Figure 17] Overall configuration diagram of the laser beam attenuation device of the second embodiment attached to the optical system of the laser processing device. [Figure 18] Overall configuration diagram of the laser beam attenuation device of the third embodiment attached to the optical system of the laser processing device. [Modes for carrying out the invention]

[0016] The following describes embodiments of the laser beam attenuation device according to the present invention and a laser beam profiler equipped with the laser beam attenuation device. It should be noted that the following description merely illustrates one aspect and should not be interpreted as limiting the scope of the description below.

[0017] 1. Embodiment of a laser beam dimming device The laser beam attenuation device according to the present invention is a laser beam attenuation device for reducing the energy of a laser beam provided in a laser beam profiler. A laser beam profiler is used to confirm that the image shape of the laser beam at a spot and the energy intensity distribution in that image shape meet the desired specifications before performing laser processing. The laser beam attenuation device is a laser beam attenuation (decay) device used to prevent damage to observation devices such as image sensors provided in the laser beam profiler due to the high energy of the laser beam.

[0018] A laser beam profiler is installed between the laser beam irradiation optical system, which focuses the laser beam onto a spot by shaping the laser beam's image shape and energy intensity distribution at the spot to a desired form, and the spot itself. The laser beam profiler observes the laser beam's image shape and energy intensity distribution at the spot. After observing these, and if necessary, adjusting the laser beam's image shape and energy intensity distribution at the spot and observing them again, the laser beam profiler can be removed from the laser beam irradiation optical system. Subsequently, the workpiece can be placed at the spot's position, and laser processing can be performed.

[0019] The laser beam incident on the laser beam attenuation device according to the present invention via an optical fiber from a laser oscillator can be any laser beam that can be used for laser processing. In particular, near-infrared laser beams with an oscillation wavelength of 920 nm to 1090 nm are preferred, such as YAG lasers (wavelength 1064 nm), fiber lasers (wavelength 1070 nm), disk lasers (wavelength 1030 nm), and semiconductor lasers (wavelengths 935 nm, 940 nm, 980 nm, 940-980 nm, 940-1025 nm). Furthermore, laser beams in the blue, green, and ultraviolet regions are also acceptable, as long as they can be used for laser processing.

[0020] [First embodiment of a laser beam attenuation device] Figure 1 shows a cross-sectional view of the beam splitter 1 in the laser beam attenuation device according to the present invention, and a schematic diagram showing the trajectories of the incident and reflected light on the beam splitter 1. The cross-section of the beam splitter 1 shows the portion cut out in the plane determined by the incident and reflected light on the beam splitter 1. Only the incident and reflected light on the optical axis 10 portion are shown. The incident light is actually the focused light of the laser beam, but it is not shown in the illustration. In the specification of the present invention, when simply referred to as incident light and reflected light, it refers to the incident light on the surface of the beam splitter 1 and the reflected light reflected from the surface. Similarly, the same meaning applies to other beam splitters.

[0021] In Figure 1, the laser beam attenuation device according to the present invention includes a beam splitter 1 in which reflected light is used as observation light. The beam splitter 1 is positioned such that, when the origin of an arbitrary orthogonal coordinate axis on a plane perpendicular to the optical axis 10 is the optical axis 10, the incident angle of the incident light at the position of the optical axis 10 is 45° with the X axis as the axis of rotation. The cross-sectional shape of the beam splitter 1 in the plane determined by the incident light and reflected light of the beam splitter 1 is a wedge shape, with the incident light side of the beam splitter 1 being thin and the reflected light side being thick. As is clear from Figure 1, "incident light side of the beam splitter 1" refers to the side of the cross-sectional shape of the beam splitter 1 where the incident light has an incident angle of 45°, and "reflected light side of the beam splitter 1" refers to the side of the cross-sectional shape of the beam splitter 1 where the reflected light has an emission angle of 45°. In the specification of the present invention, the same expression applies to other beam splitters. Also, Figure 1(b) shows the relationship between the X and Y axes in Figure 1, where the X axis is perpendicular to the plane of Figure 1.

[0022] This beam splitter 1 has reflectivity characteristics that reflect less than 10% of the incident light. This is so that the reflected light can be used as attenuated observation light. Note that "reflecting less than 10% of the incident light" means that less than 10% of the energy of the incident light is reflected, and the reflection in this specification is due to reflection at the surface of beam splitter 1 and does not include stray light components. The same applies to other beam splitters thereafter.

[0023] Furthermore, it is preferable that the angle α of the wedge shape of the beam splitter 1 is 0.5° or greater. This is because, in the configuration of the laser beam attenuation device according to the present invention shown in Figure 1, even when observing observation light with a large numerical aperture, the observation light and stray light can be separated. For this reason, it is even more preferable that the angle α of the wedge shape of the beam splitter 1 is 1° or greater.

[0024] Figure 1 illustrates only the laser beam at the optical axis position, but the actual incident laser beam is focused light. In this case, the incident angle of the laser beam to the beam splitter 1 changes continuously from 45° at the optical axis position as it moves away from the optical axis position. Therefore, in the first embodiment, it is preferable to use a beam splitter 1 in which the reflectance over the incident angle range of the beam splitter 1 is approximately constant (for example, the variation in reflectance with respect to the average value of the reflectance over the incident angle range is within 5%). This is because even if the incident light to the beam splitter 1 is focused light with a continuously changing incident angle, the energy intensity distribution can be accurately measured using the reflected light. On the other hand, if a beam splitter with a continuously changing reflectance over the incident angle range is used, the energy intensity distribution of the reflected light will be affected by different reflectances depending on the incident position to the beam splitter 1, making it impossible to accurately measure the energy intensity distribution.

[0025] Figure 2 shows a schematic diagram illustrating the relationship between reflected light and stray light. The laser beam attenuation device of the first embodiment employs a wedge shape in the cross-sectional shape of the beam splitter 1 in the plane determined by the incident light and reflected light of the beam splitter 1, where the incident light side of the beam splitter 1 is thin and the reflected light side is thick. This shows that, on a plane 11 perpendicular to the optical axis at a distance T1=(mm) along the optical axis from the position of the optical axis on the surface of the beam splitter 1 where the reflected light is used as observation light, the distance of stray light from the optical axis due to the incident light at the position of the optical axis of the beam splitter 1 can be set to T2(mm) or more. For example, if the angle α of the wedge shape of the beam splitter 1 is 3°, T1=40mm and T2=10mm or more can be achieved. This makes it possible to suppress stray light from entering observation devices such as image sensors. Note that the stray light in Figure 2 represents the laser beam that passes through the surface of the beam splitter 1, is reflected off the back surface of the beam splitter 1, and passes through the surface of the beam splitter 1 again. The stray light that repeatedly reflects inside the beam splitter 1 and passes through the surface before being emitted is not shown in the figure.

[0026] Furthermore, the laser beam attenuation device according to the present invention uses reflected light from a beam splitter as the observation light. While it is conceivable to use transmitted light from a beam splitter as the observation light, if the incident light is focused light, astigmatism occurs in the transmitted light, causing distortion of the image shape. Although it is possible to correct the distortion of the image shape due to astigmatism by using three or more beam splitters, using transmitted light as the observation light is undesirable for reasons such as the increased number of optical elements used in the laser beam attenuation device compared to when reflected light is used, and the difficulty in arranging beam splitters in optical systems with short focal lengths.

[0027] [Second embodiment of the laser beam dimming device] Figure 3 shows a cross-sectional view of beam splitter 1 and beam splitter 2 in the laser beam attenuation device according to the present invention, as a second embodiment, and a schematic diagram showing the trajectories of the incident and reflected light to each. The cross-section of beam splitter 2 shows the portion cut out in the plane determined by the incident and reflected light of beam splitter 2. Only the incident and reflected light from the optical axis 10 portion are shown. In reality, it is the focused light of the laser beam, but it is omitted from the illustration. Beam splitter 1 is the same as in the first embodiment.

[0028] In Figure 3, the second embodiment of the laser beam attenuation device according to the present invention includes a beam splitter 2 in addition to a beam splitter 1 whose reflected light is used as observation light. The beam splitter 2 is positioned such that the incident angle of the incident light at the position of the optical axis 10 is parallel to the X axis and rotates at 45° with respect to the X' axis passing through the optical axis 10. The beam splitter 2 is positioned so that the reflected light from the beam splitter 2 is incident on the beam splitter 1. In this case, the orientation of the reflective surface of the beam splitter 2 is such that the plane containing the reflective surface of the beam splitter 1 and the plane containing the reflective surface of the beam splitter 2 are orthogonal. The cross-sectional shape of the beam splitter 2 in the plane determined by the incident and reflected light of the beam splitter 2 is a wedge shape, with the incident light side of the beam splitter 2 being thicker and the reflected light side being thinner. Figure 3(b) shows the relationship between the X axis and the Y axis in Figure 3, where the X axis is perpendicular to the plane of Figure 3.

[0029] This beam splitter 2 has reflectivity characteristics that reflect less than 10% of the incident light. This is so that the reflected light can be used as attenuated observation light.

[0030] Furthermore, it is preferable that the angle α of the wedge shape of the beam splitter 2 is 0.5° or greater. This is because, in the configuration of the laser beam attenuation device according to the present invention shown in Figure 3, even when observing observation light with a large numerical aperture, the observed light and stray light can be separated.

[0031] Figure 3 illustrates only the laser beam at the optical axis position, but the actual incident laser beam is focused light. In this case, the incident angle of the laser beam to the beam splitter changes continuously from 45° at the optical axis position as it moves away from the optical axis position. In the first embodiment, it was preferred to use a beam splitter 1 in which the reflectivity is substantially constant within the range of incident angles, but in the second embodiment, it is not necessarily required to use a beam splitter in which the reflectivity is substantially constant within the range of incident angles, and beam splitters 1 and 2 can be used in which the reflectivity changes continuously within the range of incident angles.

[0032] Let me explain the above. In the second embodiment shown in Figure 3, the reflected light reflected by beam splitter 2 is incident on beam splitter 1. In this configuration, even if focused light is incident on beam splitter 2, a laser beam incident on beam splitter 2 at an angle smaller than 45° is incident on beam splitter 1 at an angle greater than 45°, and a laser beam incident on beam splitter 2 at an angle greater than 45° is incident on beam splitter 1 at an angle smaller than 45°. In this case, even if the reflectivity of the beam splitter surface has the characteristic of continuously changing in accordance with the change in incident angle, the reflected light reflected by beam splitter 2 and then reflected by beam splitter 1 can cancel out the change in reflectivity due to the incident angle. Therefore, the reflected light from beam splitter 1 in the second embodiment can be accurately measured for its energy intensity distribution. In this case, it is preferable to adopt beam splitter 1 and beam splitter 2 with the same incident angle characteristics for reflectivity.

[0033] Furthermore, regarding the orientation of the reflective surface of beam splitter 2, in an arrangement where the plane containing the reflective surface of beam splitter 1 and the plane containing the reflective surface of beam splitter 2 are parallel, the change in reflectivity due to the angle of incidence cannot be canceled out. This is because a laser beam incident on beam splitter 2 at an angle less than 45° will be incident on beam splitter 1 at an angle less than 45°, and a laser beam incident on beam splitter 2 at an angle greater than 45° will be incident on beam splitter 1 at an angle greater than 45°.

[0034] Figure 17 shows an overall configuration diagram of the laser beam attenuation device of the second embodiment attached to the optical system of a laser processing apparatus. Figure 17 shows how a laser beam emitted radially from the output end of a fiber laser (not shown at the top of the figure) enters the beam splitter 2 via a collimating lens, a focusing lens, and protective glass, and how the laser beam reflected from the surface of beam splitter 2 is reflected and focused from the surface of beam splitter 1. Note that in Figure 17, only the reflective surfaces of beam splitter 1 and beam splitter 2 are shown. Also, stray light is not shown.

[0035] In the second embodiment of the laser beam attenuation device, the cross-sectional shape of beam splitter 1 in the plane determined by the incident and reflected light of beam splitter 1 is a wedge shape in which the incident light side of beam splitter 1 is thin and the reflected light side of beam splitter 1 is thick, and the cross-sectional shape of beam splitter 2 in the plane determined by the incident and reflected light of beam splitter 2 is a wedge shape in which the incident light side of beam splitter 2 is thick and the reflected light side of beam splitter 2 is thin. As a result, on a plane 11 perpendicular to the optical axis at a distance T1 (mm) along the optical axis from the position of the optical axis on the surface of beam splitter 1 towards the reflected light side, the distance from the optical axis of the stray light closest to the optical axis among all the stray light generated by beam splitter 1 and beam splitter 2 can be set to T2 (mm) or more. For example, if the angle α of the wedge shape of beam splitter 1 and beam splitter 2 is 1°, T1 = 90 mm and T2 = 3.5 mm or more can be set. This makes it possible to suppress stray light from entering observation devices such as image sensors. In the second embodiment, stray light also includes light generated by the beam splitter 2. Specifically, this includes surface-to-back surface reflection stray light that is reflected by the surface of the beam splitter 2, transmitted through the surface of the beam splitter 1, reflected by the back surface, and transmitted through the surface again; back-to-surface reflection stray light that is transmitted through the surface of the beam splitter 2, reflected by the back surface, transmitted through the surface, and reflected by the surface of the beam splitter 1 again; and back-to-back surface reflection stray light that is transmitted through the surface of the beam splitter 2, reflected by the back surface, transmitted through the surface, transmitted through the surface of the beam splitter 1, reflected by the back surface, and transmitted through the surface again.

[0036] As described above, the second embodiment uses two beam splitters, allowing for a greater reduction in the laser beam's intensity (attenuation) compared to the first embodiment, which uses only one beam splitter. In this case, it can handle laser beams with high energy intensity.

[0037] Furthermore, in the cross-sectional shape of the beam splitter 2 in the plane determined by the incident and reflected light of the beam splitter 2, if a wedge-shaped configuration is used in which the incident light side of the beam splitter 2 is thin and the reflected light side is thick, it is undesirable because it is not possible to sufficiently suppress stray light generated by the beam splitter 2 from entering observation devices such as image sensors.

[0038] [Third embodiment of the laser beam attenuation device] Figures 4 and 5 show a cross-sectional view of beam splitter 1 and a view of beam splitter 2' from the direction of laser beam incidence, as well as schematic diagrams showing the trajectories of incident and reflected light in each, as a third embodiment of the laser beam attenuation device according to the present invention. In Figure 4, the incident light to beam splitter 2' is incident from the front to the back of the drawing in a direction perpendicular to the drawing, and in Figure 5, the incident light to beam splitter 2' is incident from the back to the front of the drawing in a direction perpendicular to the drawing. Only the incident and reflected light from the optical axis 10 portion are shown. In reality, it is the focused light of the laser beam, but it is omitted from the illustration. The beam splitter 1 is the same as in the first embodiment.

[0039] In Figures 4 and 5, the third embodiment of the laser beam attenuation device according to the present invention includes, in addition to a beam splitter 1 whose reflected light is used as observation light, a beam splitter 2' which is positioned such that the incident angle of the incident light at the position of the optical axis 10 is parallel to the Y axis and rotates at 45° with respect to the Y' axis passing through the optical axis 10. This beam splitter 2' is positioned so that the reflected light from beam splitter 2' is incident on beam splitter 1. Schematic diagrams showing the beam splitter 2' portion of Figures 4 and 5 in the direction where the Y axis is perpendicular to the drawing are shown in Figures 6 and 7. As shown in Figures 6 and 7, the cross-sectional shape of beam splitter 2' in the plane determined by the incident light and reflected light of beam splitter 2' is a wedge shape, with the incident light side of beam splitter 2' being thin and the reflected light side being thick. Furthermore, Figures 4(b) and 5(b) show the relationship between the X and Y axes in Figures 4 and 5, where the X axis represents the direction perpendicular to the planes in Figures 4 and 5. Figures 6(b) and 7(b) show the relationship between the X and Y axes in Figures 6 and 6, where the Y axis represents the direction perpendicular to the planes in Figures 6 and 7.

[0040] This beam splitter 2' has reflectivity characteristics that reflect less than 10% of the incident light. This is so that the reflected light can be used as attenuated observation light.

[0041] Furthermore, it is preferable that the angle α of the wedge shape of the beam splitter 2' is 0.5° or greater. This is because, in the configuration of the laser beam attenuation device according to the present invention shown in Figures 4 and 5, even when observing observation light with a large numerical aperture, the observed light and stray light can be separated.

[0042] Figures 4 and 5 illustrate only the laser beam at the optical axis position, but the actual incident laser beam is focused light. In this case, the incident angle of the laser beam to the beam splitter changes continuously from 45° at the optical axis position as it moves away from the optical axis position. In the third embodiment, it is preferable to use beam splitters 1 and 2' that have substantially constant reflectivity within the same incident angle range as described in the first embodiment. This is because even if the incident light to beam splitter 1 is focused light with a continuously changing incident angle, the energy intensity distribution can be accurately measured using the reflected light. On the other hand, if a beam splitter with continuously changing reflectivity within the incident angle range is used, the energy intensity distribution of the reflected light will be affected by different reflectivity depending on the incident position to beam splitter 1 and beam splitter 2', making it impossible to accurately measure the energy intensity distribution.

[0043] Figure 18 shows an overall configuration diagram of the laser beam attenuation device of the third embodiment attached to the optical system of a laser processing apparatus. Figure 18 shows how a laser beam emitted radially from the output end of a fiber laser (not shown at the top of the figure) enters the beam splitter 2' via a collimating lens, a focusing lens, and protective glass, and how the laser beam reflected from the surface of beam splitter 2' is reflected and focused from the surface of beam splitter 1. Note that in Figure 18, only the reflective surfaces of beam splitter 1 and beam splitter 2' are shown. Also, stray light is not shown.

[0044] In the third embodiment of the laser beam attenuation device, the cross-sectional shape of beam splitter 1 in the plane determined by the incident and reflected light of beam splitter 1 is a wedge shape in which the incident light side of beam splitter 1 is thin and the reflected light side of beam splitter 1 is thick, and the cross-sectional shape of beam splitter 2' in the plane determined by the incident and reflected light of beam splitter 2' is a wedge shape in which the incident light side of beam splitter 2' is thin and the reflected light side of beam splitter 2 is thick, so that on a plane 11 perpendicular to the optical axis at a distance T1 (mm) along the optical axis from the position of the optical axis on the surface of beam splitter 1 towards the reflected light side, the distance from the optical axis of the stray light closest to the optical axis among all the stray light generated by beam splitter 1 and beam splitter 2' can be set to T2 (mm) or more. For example, if the angle α of the wedge shape of beam splitter 1 and beam splitter 2' is 0.5°, then T1 = 40 mm and T2 = 4.5 mm or more can be set. This makes it possible to suppress stray light from entering observation devices such as image sensors. In addition, the stray light in the third embodiment also includes that generated by the beam splitter 2'. Specifically, this includes surface-back reflection type stray light that is reflected by the surface of beam splitter 2', transmitted through the surface of beam splitter 1, reflected by the back surface, and transmitted through the surface again before being emitted; back-surface reflection type stray light that is transmitted through the surface of beam splitter 2', reflected by the back surface, transmitted through the surface, and reflected by the surface of beam splitter 1 again before being emitted; and back-back reflection type stray light that is transmitted through the surface of beam splitter 2', reflected by the back surface, transmitted through the surface, transmitted through the surface of beam splitter 1, reflected by the back surface, and transmitted through the surface again before being emitted.

[0045] As described above, the third embodiment uses two beam splitters, allowing for greater attenuation (dimming) of the laser beam than the first embodiment, which uses one beam splitter. In this case, it can also handle laser beams with high energy intensity. Furthermore, in the second embodiment, the direction of emission of the observation light is such that it returns to the side of the incident light to the laser beam attenuation device in the second embodiment, which restricts the arrangement of the laser beam attenuation device and observation device in the second embodiment. However, in the third embodiment, the direction of emission of the observation light is different from the side of the incident light to the laser beam attenuation device in the third embodiment, thus providing greater flexibility in the arrangement of the laser beam attenuation device and observation device in the third embodiment.

[0046] Furthermore, in the cross-sectional shape of the beam splitter 2' in the plane determined by the incident and reflected light of the beam splitter 2', if a wedge-shaped configuration is used in which the incident light side of the beam splitter 2' is thicker and the reflected light side is thinner, it is undesirable because it is not possible to sufficiently suppress stray light generated by the beam splitter 2' from entering observation devices such as image sensors.

[0047] [Beam Splitter] For the optical materials of beam splitter 1, beam splitter 2, and beam splitter 2', quartz with a refractive index of 1.449 at a wavelength of 1070 nm is preferred. This is because quartz has high transmittance at a wavelength of 1070 nm and a low coefficient of thermal expansion, making it less susceptible to damage even when a laser beam is incident on it.

[0048] 2. Embodiment of a laser beam profiler The laser beam profiler according to the present invention comprises the above-described laser beam attenuation device and an observation device for observing the observation light attenuated by the laser beam attenuation device. Because the laser beam profiler according to the present invention is equipped with the above-described laser beam attenuation device, even when observing observation light with a large numerical aperture, the laser beam can be attenuated to a predetermined intensity and the observation light can be separated from stray light. As a result, the image shape and energy intensity distribution of the laser beam at the spot can be accurately observed and measured.

[0049] [Observation equipment] The observation device is not particularly limited as long as it can observe the irradiation position and image shape of the laser beam at the spot, as well as the energy intensity distribution of the laser beam. Any observation device, such as an image sensor like a CCD or CMOS, can be used.

[0050] The embodiments of the present invention described above are one aspect of the present invention and can be modified as appropriate without departing from the spirit of the present invention. Furthermore, the dimming device of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. [Examples]

[0051] Example 1 describes the configuration of the first embodiment of a laser beam attenuation device. The beam splitter 1 has a refractive index of 1.449 at a wavelength of 1070 nm, a wedge-shaped angle α of 3°, and a thickness of 7 mm at the optical axis. The reflected light and stray light when a focused laser beam of 1070 nm, which has a point shape at the spot and a uniform energy intensity distribution, is incident on the beam splitter 1 were simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). In the simulation, only the laser beam that passes through the surface of the beam splitter 1, is reflected on the back surface of the beam splitter 1, and passes through the surface of the beam splitter 1 is considered as stray light, and the laser beam that repeatedly reflects inside the beam splitter 1 and passes through the surface before being emitted is omitted. This is because the position of the image on the imaging plane of the laser beam that repeatedly reflects inside the beam splitter 1 and passes through the surface before being emitted is farther away than that of the laser beam that reflects once on the back surface of the beam splitter 1 and passes through the surface before being emitted.

[0052] The distance T1 from the optical axis of beam splitter 1 to the imaging plane on the reflected light side is set to 40 mm. Figure 8(a) shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. The black dot image in the center of Figure 8(a) is the reflected light. A vertically distorted image of stray light is shown at a position T2 = 10 mm away from the black dot image. That is, it was confirmed that stray light can be separated from reflected light at a distance of T2 = 10 mm at the imaging plane. Note that Figure 8(b) shows the trajectories of incident light and stray light at beam splitter 1 in the simulation of Example 1, but does not show the trajectory of reflected light. [Examples]

[0053] Example 2 describes the configuration of a second embodiment of the laser beam attenuation device. The refractive index of beam splitter 1 and beam splitter 2 at a wavelength of 1070 nm is 1.449, the angle α of the wedge shape is 1°, and the thickness at the optical axis is 7 mm. The reflected light and stray light of beam splitter 1 when focused light of a 1070 nm laser beam, which has a point shape at the spot and a uniform energy intensity distribution, is incident on beam splitter 2 was simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). In the simulation, only surface-back reflection type stray light (reflected by the surface of beam splitter 2, transmitted through the surface of beam splitter 1, reflected on the back surface, transmitted through the surface again, and exited) is considered. Surface-back reflection type stray light (transmitted through the surface of beam splitter 2, reflected on the back surface, transmitted through the surface, reflected on the surface of beam splitter 1, and exited) is also considered. Laser beams that repeatedly reflect inside beam splitter 2 and beam splitter 1 and exit through the surface are omitted. This is because the image position of laser beams that repeatedly reflect inside beam splitter 2 and beam splitter 1 and exit through the surface is further away from the image plane than the stray light targeted in the simulation.

[0054] With T1 = 90 mm, Figure 9 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 9, from left to right, the cases of surface-to-backside reflection stray light, surface-to-frontside reflection stray light, and surface-to-backside reflection stray light are shown. The black dot images in the center of each are reflected light. Distorted stray light images are shown at positions T2 = 8.5 mm, 3.5 mm, and 14.5 mm away from the black dot images, respectively. That is, it was confirmed that stray light can be separated from reflected light at a distance of at least T2 = 3.5 mm at the imaging plane. [Examples]

[0055] Example 3 is a configuration of the second embodiment of the laser beam attenuation device. The refractive index of beam splitter 1 and beam splitter 2 at a wavelength of 1070 nm is 1.449, the angle α of the wedge shape is 3°, and the thickness at the optical axis is 7 mm. Then, similar to Example 2, the reflected light and stray light of beam splitter 1 when focused light of a 1070 nm laser beam, in which the spot shape is point-like and the energy intensity distribution is uniform, is incident on beam splitter 2 was simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.).

[0056] With T1 = 40 mm, Figure 10 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 10, from left to right, the cases of surface-back reflection stray light, surface-back reflection stray light, and surface-back reflection stray light are shown. The black dot images in the center of each are reflected light. Distorted stray light images are shown at positions T2 = 10 mm, 10 mm, and 24 mm away from the black dot images, respectively. That is, it was confirmed that stray light can be separated from reflected light at a distance of at least T2 = 10 mm at the imaging plane. Furthermore, in Example 2, where the angle α of the wedge shape is 1°, the distance T2 of the stray light closest to the reflected light was 3.5 mm at T1 = 90 mm. On the other hand, in Example 3, since the angle α of the wedge shape is 3°, even though T1 = 40 mm is close, the distance T2 of the closest stray light was 10 mm. [Examples]

[0057] Example 4 is a third embodiment of the laser beam attenuation device, using the configuration shown in Figure 4. The refractive index of beam splitter 1 and beam splitter 2' at a wavelength of 1070 nm was 1.449, the angle α of the wedge shape was 0.5°, and the thickness at the optical axis was 7 mm. The reflected light and stray light from beam splitter 1 when focused light from a 1070 nm laser beam, which has a point shape at the spot and a uniform energy intensity distribution, is incident on beam splitter 2' was simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). In the simulation, only surface-back reflection type stray light (reflected by the surface of beam splitter 2, transmitted through the surface of beam splitter 1, reflected on the back surface, and transmitted through the surface again) is considered; back-surface reflection type stray light (transmitted through the surface of beam splitter 2', reflected on the back surface, transmitted through the surface, reflected on the surface of beam splitter 1, and emitted); and back-back reflection type stray light (transmitted through the surface of beam splitter 2', reflected on the back surface, transmitted through the surface, transmitted through the surface of beam splitter 1, reflected on the back surface, and emitted) is considered; laser beams that repeatedly reflect inside beam splitter 2' and beam splitter 1 and are emitted through the surface are omitted. This is because the position of the image on the imaging plane of laser beams that repeatedly reflect inside beam splitter 2' and beam splitter 1 and are emitted through the surface is further away than the stray light targeted in the simulation.

[0058] With T1 = 40 mm, Figure 11 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 11, from left to right, the cases of surface-to-backside reflection stray light, surface-to-frontside reflection stray light, and surface-to-backside reflection stray light are shown. The black dot images in the center of each are reflected light. Distorted stray light images are shown at positions T2 = 4.5 mm, 6 mm, and 7.5 mm away from the black dot images, respectively. That is, it was confirmed that stray light can be separated from reflected light at a distance of at least T2 = 4.5 mm at the imaging plane. [Examples]

[0059] Example 5 used the same configuration as Example 4. Similar to Example 4, the reflected and stray light from beam splitter 1 were simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.) when a focused laser beam with a point-like spot shape and uniform energy intensity distribution was incident on beam splitter 2'.

[0060] With T1 = 90 mm, Figure 12 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 12, from left to right, the cases of surface-to-backside reflection stray light, surface-to-frontside reflection stray light, and surface-to-backside reflection stray light are shown. The black dot images in the center of each are reflected light. Distorted stray light images are shown at positions T2 = 6 mm, 7 mm, and 10 mm away from the black dot images, respectively. That is, it was confirmed that stray light can be separated from reflected light at a distance of at least T2 = 6 mm at the imaging plane. [Examples]

[0061] Example 6 is a third embodiment of the laser beam attenuation device, using the configuration shown in Figure 4. The refractive index of beam splitter 1 and beam splitter 2' at a wavelength of 1070 nm was 1.449, the angle α of the wedge shape was 3°, and the thickness at the optical axis was 7 mm. Then, similar to Example 4, the reflected light and stray light of beam splitter 1 when focused light of a 1070 nm laser beam, which has a point shape at the spot and a uniform energy intensity distribution, is incident on beam splitter 2' was simulated using the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.).

[0062] With T1 = 40 mm, Figure 13 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 13, from left to right, the cases of surface-to-backside reflection stray light, surface-to-frontside reflection stray light, and surface-to-backside reflection stray light are shown. The black dot images in the center of each represent reflected light. Distorted stray light images are shown at positions T2 = 10 mm, 18 mm, and 22.5 mm away from the black dot images, respectively. That is, it was confirmed that stray light can be separated from reflected light at a distance of at least T2 = 10 mm at the imaging plane. Comparative Example

[0063] [Comparative Example 1] Comparative Example 1 is a comparative example of Example 1. Unlike Example 1, the cross-sectional shape of the beam splitter 1 in the plane determined by the incident and reflected light of the beam splitter 1 is a wedge shape, with the incident light side of the beam splitter 1 being thicker and the reflected light side being thinner. The other configurations are the same as in Example 1. The simulation was then performed in the same manner as in Example 1.

[0064] With T1 = 40 mm, Figure 14(a) shows the images of reflected and stray light in a plane perpendicular to the optical axis at the imaging plane. The black dot image in the center of Figure 14(a) is the reflected light. The image of stray light is shown at a position T2 = 3 mm away from the black dot image. In other words, it is clear that the stray light separation ability of Comparative Example 1 is inferior to that of Example 1. Note that Figure 14(b) shows the trajectories of incident light and stray light at beam splitter 1 in the simulation of Comparative Example 1, but does not show the trajectory of reflected light.

[0065] [Comparative Example 2] Comparative Example 2 is a comparative example of Example 3. Unlike Example 3, the cross-sectional shape of the beam splitter 2 in the plane determined by the incident and reflected light of the beam splitter 2 is a wedge shape, with the incident light side of the beam splitter 2 being thin and the reflected light side being thick. The other configurations are the same as in Example 3. Then, a simulation was performed in the same manner as in Example 3.

[0066] With T1 = 40 mm, Figure 15 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 15, from left to right, the cases of surface-back reflection stray light, surface-back reflection stray light, and surface-back reflection stray light are shown. The black dot image in the center of each is the reflected light. Distorted stray light images are shown at positions T2 = 10 mm, 19 mm, and 6 mm away from the black dot image, respectively. In Example 3, the distance T2 of the stray light closest to the reflected light is 10 mm, while in Comparative Example 2, T2 = 6 mm. In other words, it is clear that the stray light separation ability of Comparative Example 2 is inferior to that of Example 3.

[0067] [Comparative Example 3] Comparative Example 3 is a comparative example of Example 6. Unlike Example 6, the cross-sectional shape of the beam splitter 2' in the plane determined by the incident and reflected light of the beam splitter 2' is a wedge shape, with the incident light side of the beam splitter 2' being thicker and the reflected light side being thinner. The other configurations are the same as in Example 6. The simulation was then performed in the same manner as in Example 6.

[0068] With T1 = 40 mm, Figure 16 shows the images of reflected and stray light on a plane perpendicular to the optical axis at the imaging plane. In Figure 16, from left to right, the cases of surface-to-backside reflection stray light, surface-to-frontside reflection stray light, and surface-to-backside reflection stray light are shown. The black dot image in the center of each is the reflected light. Distorted stray light images are shown at positions T2 = 10 mm, 10 mm, and 14.5 mm away from the black dot image, respectively. For surface-to-backside reflection stray light, T2 = 10 mm in both Example 6 and Comparative Example 3, but for surface-to-backside reflection stray light and surface-to-backside reflection stray light, the stray light distance T2 in Comparative Example 3 was shorter than in Example 6. In other words, it became clear that the stray light separation ability of Comparative Example 3 was inferior to that of Example 6. [Industrial applicability]

[0069] The laser beam attenuation device according to the present invention can attenuate the laser beam to a predetermined intensity and separate the observed light from stray light, even when observing observation light with a large numerical aperture. The laser beam profiler according to the present invention, equipped with the above-described laser beam attenuation device, can accurately observe and measure the image shape and energy intensity distribution of the laser beam at the spot. In other words, the laser beam attenuation device and laser beam profiler according to the present invention are suitable for use in laser processing equipment that processes objects by irradiating them with a laser beam, when observing and measuring the image shape and energy intensity distribution of the laser beam at the spot using an observation device. [Explanation of Symbols]

[0070] 1 Beam Splitter 2 Beam Splitter 2' Beam Splitter 10 Optical axis 11. A plane perpendicular to the optical axis

Claims

1. A laser beam attenuation device for reducing the intensity of a laser beam, which is provided in a laser beam profiler, It is equipped with a beam splitter 1 in which the reflected light is used as observation light, The beam splitter 1 reflects less than 10% of the incident light. The beam splitter 1 is positioned such that, when the origin of an arbitrary orthogonal coordinate axis on a plane perpendicular to the optical axis is located on the optical axis, the X-axis and Y-axis are defined as such, the angle of incidence of the incident light at the position of the optical axis is 45° with the X-axis as the axis of rotation. A laser beam attenuation device characterized in that the cross-sectional shape of the beam splitter 1 in the plane determined by the incident light and the reflected light of the beam splitter 1 is a wedge shape, with the incident light side of the beam splitter 1 being thin and the reflected light side being thick.

2. The laser beam attenuation device according to claim 1, wherein the angle of the wedge shape of the beam splitter 1 is 0.5° or more.

3. The beam splitter 2 is provided such that the angle of incidence of the incident light at the position of the optical axis is parallel to the X axis and rotates at 45° with respect to the X' axis passing through the optical axis. The beam splitter 2 reflects less than 10% of the incident light. The beam splitter 2 is positioned such that the reflected light from the beam splitter 2 is incident on the beam splitter 1. The orientation of the reflective surface of the beam splitter 2 is such that the plane containing the reflective surface of the beam splitter 1 and the plane containing the reflective surface of the beam splitter 2 are orthogonal to each other. The laser beam attenuation device according to claim 1 or claim 2, wherein the cross-sectional shape of the beam splitter 2 in the plane determined by the incident light and the reflected light of the beam splitter 2 is a wedge shape in which the incident light side of the beam splitter 2 is thicker and the reflected light side of the beam splitter 2 is thinner.

4. The laser beam attenuation device according to claim 3, wherein the angle of the wedge shape of the beam splitter 2 is 0.5° or more.

5. The beam splitter 2' is provided such that the angle of incidence of the incident light at the position of the optical axis is parallel to the Y axis and rotates 45° with respect to the Y' axis passing through the optical axis. The beam splitter 2' reflects less than 10% of the incident light. The beam splitter 2' is positioned such that the reflected light from the beam splitter 2' is incident on the beam splitter 1. The laser beam attenuation device according to claim 1 or claim 2, wherein the cross-sectional shape of the beam splitter 2' in the plane determined by the incident light and the reflected light of the beam splitter 2' is a wedge shape in which the incident light side of the beam splitter 2' is thin and the reflected light side of the beam splitter 2' is thick.

6. The laser beam attenuation device according to claim 5, wherein the angle of the wedge shape of the beam splitter 2' is 0.5° or more.

7. A laser beam profiler comprising a laser beam attenuation device as described in claim 1, and an observation device for observing the observation light attenuated by the laser beam attenuation device.

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