Laser irradiation device and mirror device

Abstract

A laser head is provided with: a mirror (331) that reflects a laser beam emitted from a laser oscillator and changes the direction of the laser beam; a holding part (335) that holds the mirror (331); and a drive unit that rotationally drives the holding part (335) in a state in which the normal direction to a front surface of the mirror (331) held by the holding part (335) is inclined with respect to the axial direction of the rotation axis, thereby causing an irradiation spot of the laser beam reflected by the mirror (331) to rotationally move circularly on a surface of an object. The front surface of the mirror (331) has a first reflectance in a first angle range and has a second reflectance lower than the first reflectance in a second angle range different from the first angle range. A back surface of the mirror (331) has a third reflectance higher than the second reflectance in the first angle range and the second angle range.

Description

Laser Irradiation Device and Mirror Device

[0001] The present invention relates to a laser irradiation device and a mirror device.

[0002] Patent Document 1 describes cooling a mirror by flowing cooling water through a cooling water path. Patent Document 2 describes cooling a lens held by a lens frame by allowing a cooling gas to flow while touching a lens frame having a plurality of slits.

[0003] Japanese Patent Application Laid-Open No. 2000-334592 Japanese Patent Application Laid-Open No. 2001-30199

[0004] However, in the technologies described in Patent Documents 1 and 2, although it is possible to lower the temperature of the optical component by cooling, it is not possible to suppress the heat generation itself. Especially when the laser light has a high output, the temperature rise of the optical component due to heat generation becomes large, so more energy and resources are required to cool it.

[0005] An object of the present invention is to suppress heat generation in the holding portion of the mirror.

[0006] One aspect of the present invention includes a mirror that reflects laser light emitted from a laser oscillator and changes the direction of the laser light, a holding portion that holds the mirror, and a driving portion that rotationally drives the holding portion in a state where the normal direction of the surface of the mirror held by the holding portion is inclined with respect to the axial direction of the rotation axis, so that the irradiation spot of the laser light reflected by the mirror rotates circularly on the surface of the object. The surface of the mirror has a first reflectivity in a first angle range and has a second reflectivity lower than the first reflectivity in a second angle range different from the first angle range. A surface having a third reflectivity higher than the second reflectivity in the first angle range and the second angle range is provided between the holding portion and the surface of the mirror. A laser irradiation device is provided.

[0007] The mirror may include a wedge prism.

[0008] The end portion of the mirror may have a fourth reflectivity lower than the first reflectivity in the first angle range and the second angle range.

[0009] The holding portion has a first opening that exposes the surface of the mirror, a pressing portion that presses a part of the end of the mirror from the side of the first opening, and a second opening that exposes the portion of the end of the mirror that is not covered by the pressing portion to the outside, and the laser light that has passed through the surface of the mirror may be radiated to the outside from the end of the mirror through the second opening.

[0010] The pressing portion has an optical passage that communicates with the second opening, and the laser light that has passed through the surface of the mirror may be radiated from the end of the mirror into the optical passage and radiated to the outside from the second opening through the optical passage.

[0011] Another aspect of the present invention provides a mirror device comprising a mirror that reflects laser light emitted from a laser oscillator and changes the direction of the laser light, and a holding part that holds the mirror, wherein the surface of the mirror has a first reflectance in a first angular range and a second reflectance lower than the first reflectance in a second angular range different from the first angular range, and a surface having a third reflectance higher than the second reflectance in the first and second angular ranges is provided between the holding part and the surface of the mirror.

[0012] According to the present invention, heat generation in the mirror holder can be suppressed.

[0013] A diagram showing an example configuration of a laser irradiation system according to the embodiment. A diagram illustrating a laser head according to a comparative example. A diagram showing an example of using the laser head according to the embodiment. A diagram showing an example of the internal configuration of the laser head. An enlarged view of part A in Figure 4. A graph illustrating the spectral characteristics of the coatings on the front and back surfaces of the mirror. A graph illustrating the change in angle of the laser light emitted from the mirror to the outside due to multiple reflections within the mirror. A graph illustrating the change in angle of the laser light emitted from the mirror to the outside due to multiple reflections within the mirror. A graph illustrating the spectral characteristics of the uncoated portion. A front view of the mirror holder portion. A graph illustrating the heat generation suppression effect of the holding portion according to the embodiment. A diagram showing combinations of the configurations of each example shown in Figure 10A. A front view of the mirror holder portion according to a modified example. An enlarged view of part A in Figure 4 according to a modified example. A graph illustrating the reflection characteristics of the mirror surface and holding portion according to a modified example.

[0014] Embodiments of the present invention will be described below with reference to the drawings. Note that the dimensions, shapes, and proportions in the drawings may differ from those of the actual invention in order to facilitate understanding.

[0015] Figure 1 shows an example of the configuration of a laser irradiation system 1 according to an embodiment. The laser irradiation system 1 removes rust, paint films, harmful substances, and other deposits from the surface of an object W using laser light L. This object W includes, for example, road and railway bridges, transmission towers, plants, storage tanks, pipes, ships, and aircraft.

[0016] The laser irradiation system 1 comprises a laser oscillator 10, a fiber 20, and a laser head 30. The laser oscillator 10 and the laser head 30 are connected via the fiber 20. The laser irradiation system 1 is transportable by vehicle. The laser oscillator 10 may be used while mounted on this vehicle. The laser head 30 is small and lightweight and can be carried by an operator. The operator holds the laser head 30 by hand at the work site and moves it along the surface of the target object W.

[0017] The laser oscillator 10 generates laser light L. The laser oscillator 10 is, for example, a solid-state laser or a semiconductor laser, and is preferably a fiber laser. However, the laser oscillator 10 is not limited to a solid-state laser or a semiconductor laser, and may also be a gas laser or a liquid laser. The output of the laser light L is high, for example, 6 kW.

[0018] Fiber 20 is an optical fiber cable that transmits the laser light L emitted from the laser oscillator 10 to the laser head 30. One end of fiber 20 is connected to the laser oscillator 10, and the other end is connected to the laser head 30.

[0019] The laser head 30 changes the direction of the laser beam L emitted from the fiber 20 by a predetermined angle and irradiates the surface of the object W. The predetermined angle is any angle set in advance, for example, 90 degrees. The laser head 30 is an example of a laser irradiation device according to the present invention.

[0020] Figure 2 illustrates a laser head according to the comparative example. Here, the object W is assumed to have a narrow section N. As shown in Figure 2, the laser head according to the comparative example irradiates the surface of the object W without changing the direction of the laser beam L, so the laser beam L is irradiated along the longitudinal direction of the laser head. However, because the narrow section N is narrow, it is not possible to insert the laser head into the narrow section N in a direction that allows the laser beam L to be irradiated onto the bottom surface of the narrow section N. Therefore, in the comparative example, it is not possible to remove deposits on the bottom surface of the narrow section N with the laser beam L.

[0021] Figure 3 shows an example of the use of the laser head 30 according to this embodiment. As described above, the laser head 30 according to this embodiment changes the direction of the laser beam L and irradiates the surface of the object W. As shown in Figure 3, when the laser head 30 changes the direction of the laser beam L by 90 degrees, the laser beam L will be irradiated along the shorter side of the laser head 30. In this case, the laser head 30 can be placed inside the narrow part N in a direction that allows the laser beam L to be irradiated onto the bottom surface of the narrow part N. Therefore, in this embodiment, it is possible to remove deposits on the bottom surface of the narrow part N using the laser beam L.

[0022] Figure 4 shows an example of the internal configuration of the laser head 30. In Figure 4, the internal configuration of the laser head 30 is shown as a cross-sectional view obtained by cutting it through the center along its longitudinal direction. The laser head 30 comprises a fiber connector 31, a collimator 32, a mirror holder 33, a drive unit 34, a focusing lens 35, a nozzle 36, and a protective window 37.

[0023] The fiber connector 31 holds the other end of the fiber 20 and transmits the laser light L. The fiber 20 is inserted inside the fiber connector 31, and the exit end face of the fiber 20 is positioned at its tip. The laser light L is emitted from this exit end face and incident on the collimator 32.

[0024] The collimator 32 makes the laser light L, which is emitted from the exit end face of the fiber 20 while spreading out, into parallel light. The collimator 32 has multiple lenses built in to focus the incident light and make it into parallel light.

[0025] The mirror holder portion 33 reflects the laser beam L that has passed through the collimator 32 and changes its direction. The mirror holder portion 33 comprises a mirror 331 and a holding portion 335. The mirror 331 reflects the laser beam L on its surface. The mirror 331 is positioned so that the direction of the normal of its surface is inclined with respect to the incident direction of the laser beam L in order to change the direction of the laser beam L. For example, the mirror 331 is positioned at an angle such that the laser beam L is incident on the mirror 331 at an incident angle of approximately 45 degrees. The laser beam L is reflected off the surface of the mirror 331 and reflected at a reflection angle of 45 degrees, which is equal to the incident angle. As a result, the direction of the laser beam L is changed by approximately 90 degrees. The holding portion 335 holds the mirror 331 so that the direction of the normal of the surface of the mirror 331 is inclined with respect to the incident direction of the laser beam L. The holding portion 335 is made of a lightweight material that does not easily absorb heat, such as aluminum, in order to suppress heat generation and reduce the load on the drive unit 34.

[0026] The drive unit 34 has a rotating shaft and rotates the holding unit 335. The drive unit 34 is, for example, a small solid motor. The drive unit 34 is capable of high-speed rotation, for example, 20,000 revolutions per minute. The drive unit 34 rotates the holding unit 335 in such a state that the normal direction of the surface of the mirror 331 held by the holding unit 335 is inclined with respect to the axial direction of the rotation shaft in order to rotate the irradiation spot of the laser beam L in an elliptical shape on the surface of the object W. More specifically, the rotating shaft of the drive unit 34 is connected to the back surface of the holding unit 335 at an angle such that the normal direction of the surface of the mirror 331 is inclined with respect to the axial direction of the rotation shaft. The axial direction of the rotation shaft of the drive unit 34 and the normal direction of the surface of the mirror 331 form an inclination angle α. The inclination angle α is an angle greater than 0, for example, 5 degrees. By rotating the holding unit 335 with the drive unit 34, the irradiation spot of the laser beam L rotates in an elliptical shape on the surface of the object W.

[0027] The focusing lens 35 concentrates the laser beam L reflected by the mirror 331 onto the surface of the object W. The focusing lens 35 may consist of one lens or multiple lenses.

[0028] The nozzle 36 is the exit point for the laser beam L. The laser beam L that has passed through the focusing lens 35 is emitted from the nozzle 36 towards the target object W.

[0029] The protective window 37 protects the optical system inside the laser head 30 from dust particles flying from the object W as a result of the irradiation of the laser beam L. The protective window 37 is provided between the focusing lens 35 and the nozzle 36. The protective window 37 is made of a transparent material that transmits the laser beam L.

[0030] The irradiation spot of the laser beam L emitted from the laser head 30 rotates in an elliptical shape on the surface of the object W. By moving the laser head 30 along the surface of the object W, the laser beam L rotates in a spiral shape and is irradiated onto the surface of the object W. This removes rust, paint films, harmful substances, and other deposits from the surface of the object W. Note that the shape of the trajectory of the irradiation spot of the laser beam L is not necessarily limited to an ellipse, and may be a perfect circle.

[0031] Figure 5 is an enlarged view of section A in Figure 4. Mirror 331 is composed of a wedge prism 332 and a parallel mirror 333. The wedge prism 332 is a prism in which one surface is inclined relative to the other surface, and bends the laser beam L. The wedge prism 332 has the shape of a cylinder that has been cut at an angle. In plan view, the wedge prism 332 is circular, and its cross-sectional shape is wedge-shaped. The parallel mirror 333 has two parallel surfaces and reflects the laser beam L at a reflection angle equal to the incidence angle when reflecting the laser beam L. The parallel mirror 333 is cylindrical. In plan view, the parallel mirror 333 is circular, and its cross-sectional shape is rectangular. The wedge prism 332 is positioned on the parallel mirror 333 so that their centers overlap. However, since the diameter of the wedge prism 332 is smaller than the diameter of the parallel mirror 333, the wedge prism 332 does not overlap the ends of the parallel mirror 333.

[0032] The wedge prism 332 has a first surface 332a and a second surface 332b. The first surface 332a is the surface of the mirror 331 and reflects the laser light L. Also, since the first surface 332a is inclined with respect to the second surface 332b, the wedge prism 332 can change the reflection angle of the laser light L that has passed through the first surface 332a. The parallel mirror 333 has a first surface 333a and a second surface 333b that are parallel to each other. The first surface 333a is in contact with the second surface 332b of the wedge prism 332. The second surface 333b is the back surface of the mirror 331.

[0033] The surface of the mirror 331 is designed to reflect most of the incident laser light L. However, even if the reflectivity of the surface of the mirror 331 is 99.9%, if the output of the laser light L is 6 kW, then 0.1% of 6 kW, or 6 W of laser light L, will pass through the surface of the mirror 331. When the holding part 335 is heated by the transmitted laser light L, that heat is transferred to the drive part 34 via the rotating shaft, causing the drive part 34 to heat up. This heating can cause malfunctions in the drive part 34. Therefore, the mirror holder part 33 according to this embodiment has features related to the coating of the mirror 331 and features related to the structure of the holding part 335 in order to suppress the heat generation of the holding part 335.

[0034] Figure 6 is a graph illustrating the spectral characteristics of the coatings on the front and back surfaces of the mirror 331. The horizontal axis of this graph represents the angle on the air side [deg], and the vertical axis represents the reflectance [%]. Line R1 in this graph represents the reflectance of the first surface 332a of the wedge prism 332, which is the front surface of the mirror 331. Line R2 represents the reflectance of the second surface 333b of the parallel mirror 333, which is the back surface of the mirror 331. The first surface 332a of the wedge prism 332 and the second surface 333b of the parallel mirror 333 are coated to adjust their reflectance. The reflectance of the coating depends on the angle of the laser beam L on the air side. This angle on the air side represents the angle of incidence of the laser beam L when the laser beam L is incident on the interface between the mirror 331 and the air from the air side. The angle of incidence is the angle formed by the light ray incident on the interface and the normal perpendicular to the interface. On the other hand, this angle on the air side indicates the emission angle of the laser beam L when the laser beam L is incident on this interface from the mirror 331 side. The emission angle, also called the refraction angle, is the angle formed between the light ray after it has passed through the interface and the normal perpendicular to the interface. Therefore, for example, the reflectance when the angle on the air side is 45 degrees applies to both cases where the laser beam L is incident on the interface between air and mirror 331 from the air side at an incident angle of 45 degrees, and where the laser beam L incident from the mirror 331 side passes through the interface and is emitted at an emission angle of 45 degrees. This coating is realized, for example, by stacking multiple dielectric thin films. Note that the second surface 332b of the wedge prism 332, the side surface of the wedge prism 332, the first surface 333a of the parallel mirror 333, and the side surface of the parallel mirror 333 are not coated. Furthermore, the reflectance characteristics are measured at the oscillation wavelength of the laser oscillator 10 used in the laser irradiation system 1. If the laser oscillator 10 is a fiber laser, its oscillation wavelength is, for example, 1070 nm. Furthermore, the reflectance is calculated as the average value of the reflectance of p-polarized light and the reflectance of s-polarized light.

[0035] The first surface 332a of the wedge prism 332 is coated to have different reflectivity depending on the angle of the laser beam L to the air, in order to efficiently reflect the incident laser beam L and allow the transmitted laser beam L to escape to the outside. As described above, the mirror 331 rotates with the normal direction of its surface tilted by an inclination angle α with respect to the axis of rotation. Therefore, the laser beam L is incident on the mirror 331 at an angle of reference angle ± inclination angle α. Here, we assume that the reference angle is 45 degrees and the inclination angle α is 5 degrees. In this case, in order to efficiently reflect the laser beam L incident on the mirror 331 at an angle of 45 degrees ± 5 degrees, the first surface 332a is coated to have a high reflectivity in the target angle range including 45 degrees ± 5 degrees. Furthermore, in order to allow the laser light L that has passed through the first surface 332a of the wedge prism 332 to escape to the outside from this first surface 332a, the first surface 332a is coated such that it has a low reflectivity in the non-asymmetrical angle range excluding the symmetrical angle range.

[0036] In the example shown in Figure 6, the target angle range is the range of 35 degrees to 55 degrees, and the non-target angle range is the range other than the target angle range, i.e., the range of 0 degrees to less than 35 degrees and greater than 55 degrees and less than or equal to 90 degrees. The target angle range and the non-target angle range are examples of the first angle range and the second angle range according to the present invention, respectively. As shown by line R1, the reflectance of the first surface 332a of the wedge prism 332 in the target angle range is approximately 99.9%. On the other hand, the reflectance of the first surface 332a of the wedge prism 332 in the non-target angle range is lower than approximately 99.9%. For example, the reflectance of the first surface 332a at 15 degrees is approximately 53%, the reflectance at 30 degrees is approximately 58%, the reflectance at 60 degrees is approximately 96%, and the reflectance at 75 degrees is approximately 64%. The reflectance of the first surface 332a in the target angle range and the reflectance in the non-target angle range are examples of the first reflectance and the second reflectance according to the present invention, respectively.

[0037] The second surface 333b of the parallel mirror 333 is coated to have a high reflectivity over the entire angular range in order to efficiently reflect the laser light L that has passed through the first surface 332a of the wedge prism 332. This suppresses the laser light L that has passed through the first surface 332a of the wedge prism 332 from further passing through the second surface 333b of the parallel mirror 333 and irradiating the holding part 335. In the example shown in Figure 6, the entire angular range is from 0 degrees to 90 degrees. As shown by line R2, the reflectivity of the second surface 333b of the parallel mirror 333 over the entire angular range is approximately 99.0%. The reflectivity of the second surface 333b of the parallel mirror 333 is higher than the reflectivity of the first surface 332a of the wedge prism 332 over the asymmetrical angular range. The reflectivity of the second surface 333b is an example of the third reflectivity according to the present invention. The second surface 333b of the parallel mirror 333 is provided between the first surface 332a of the wedge prism 332 and the mirror holder portion 33, and is therefore an example of a surface having a third reflectivity provided between the holding portion and the surface of the mirror according to the present invention.

[0038] Furthermore, the reflectivity of the first surface 332a of the wedge prism 332 in the target angle range is not limited to approximately 99.9%, but may be higher than 99.9% or lower than 99.9%. Also, the reflectivity of the first surface 332a of the wedge prism 332 in the non-target angle range is not limited to the reflectivity mentioned above, but may be lower than the reflectivity in the target angle range. Moreover, the reflectivity of the second surface 333b of the parallel mirror 333 is not limited to approximately 99.0%, but may be higher than 99.0% or lower than 99.0%.

[0039] As shown in Figure 5, the direction of the normal to the first surface 332a of the wedge prism 332 and the direction of the normal to the second surface 333b of the parallel mirror 333 are not parallel. Therefore, when the laser light L that has passed through the first surface 332a of the wedge prism 332 is reflected by the second surface 333b of the parallel mirror 333 and the first surface 332a of the wedge prism 332, the reflection angle changes.

[0040] Figures 7A and 7B are graphs illustrating the change in angle of the laser beam L emitted from the mirror 331 to the outside due to multiple reflections within the mirror 331. In the examples shown in Figures 7A and 7B, the reflectance of the first surface 332a of the wedge prism 332 and the reflectance of the second surface 333b of the parallel mirror 333 are both approximately 10% across the entire angular range, so that the change in angle of the laser beam L due to multiple reflections is easily understood. Figure 7A shows the change in angle of the laser beam L at the first surface 332a of the wedge prism 332, which is the surface of the mirror 331. Figure 7B shows the change in angle of the laser beam L at the second surface 333b of the parallel mirror 333, which is the back surface of the mirror 331. The horizontal axis of each graph represents the emission angle [deg] of the laser beam L on the air side, and the vertical axis represents the radiance. This emission angle on the air side represents the emission angle of the laser beam L incident from the mirror 331 side at the interface between the mirror 331 and the air. Radiance indicates the intensity of a light ray. Figure 5 shows refracted light L1 that enters the interface between the first surface 332a of the wedge prism 332 and the air from the mirror 331 side, passes through the interface, and exits. In the graph shown in Figure 7A, the horizontal axis represents the exit angle θ1 of the refracted light L1 shown in Figure 5, and the vertical axis represents the intensity of the refracted light L1 shown in Figure 5. Also in Figure 5, refracted light L2 that enters the interface between the second surface 333b of the parallel mirror 333 and the air from the mirror 331 side, passes through the interface, and exits. In the graph shown in Figure 7B, the horizontal axis represents the exit angle θ2 of the refracted light L2 shown in Figure 5, and the vertical axis represents the intensity of the refracted light L2 shown in Figure 5. The lines Z0, Z90, Z180, and Z270 that make up each graph show the change in the angle of the laser beam L when the rotation position of the mirror holder 33 is at 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively.

[0041] As shown by line Z0 in Figure 7A, when the rotation position of the mirror holder 33 is at 0 degrees, the angle of the laser beam L on the first surface 332a of the wedge prism 332 gradually decreases from 45 degrees ± 5 degrees and moves out of the target angle range including 45 degrees ± 5 degrees. Also, as shown by lines Z90, Z180, and Z270 in Figure 7A, when the rotation position of the mirror holder 33 is at 90 degrees, 180 degrees, and 270 degrees, the angle of the laser beam L on the first surface 332a of the wedge prism 332 gradually increases from 45 degrees ± 5 degrees and moves out of the target angle range including 45 degrees ± 5 degrees.

[0042] As shown in Figure 7B, on the second surface 333b of the parallel mirror 333, the angle of the laser beam L changes in accordance with the change in the angle of the laser beam L on the first surface 332a of the wedge prism 332. As shown by line Z0 in Figure 7B, when the rotation position of the mirror holder 33 is at 0 degrees, the angle of the laser beam L on the second surface 333b of the parallel mirror 333 gradually decreases from 45 degrees ± 5 degrees and changes over the entire angular range from 0 degrees to 90 degrees. Also, as shown by lines Z90, Z180, and Z270 in Figure 7B, when the rotation position of the mirror holder 33 is at 90 degrees, 180 degrees, and 270 degrees, the angle of the laser beam L on the second surface 333b of the parallel mirror 333 gradually increases from 45 degrees ± 5 degrees and changes over the entire angular range from 0 degrees to 90 degrees.

[0043] As shown in FIG. 5, the laser beam L transmitted through the first surface 332a of the wedge prism 332 is sequentially reflected by the second surface 333b of the parallel mirror 333 and the first surface 332a of the wedge prism 332, and propagates inside while changing its angle. At this time, the angle of the laser beam L changes over the entire angular range. However, when the reflectance in the entire angular range of the second surface 333b of the parallel mirror 333 is about 99.0% as in the example shown in FIG. 6, the laser beam L is unlikely to be emitted from the second surface 333b of the parallel mirror 333. And when the reflectance in the target angular range of the first surface 332a of the wedge prism 332 is about 99.9% and the reflectance in the non-target angular range is lower than about 99.0%, which is the reflectance in the entire angular range of the second surface 333b, this laser beam L is emitted to the outside from the first surface 332a of the wedge prism 332 when the angle deviates from the target angular range including 45 degrees ± 5 degrees.

[0044] Also, as shown in FIG. 5, a non-coated no-coat portion 333c is provided at the end of the parallel mirror 333. The no-coat portion 333c includes the inner edge of the circumference of the first surface 333a of the parallel mirror 333. Also, the no-coat portion 333c may include at least a part of the side surface of the parallel mirror 333. The wedge prism 332 is not overlapped on the no-coat portion 333c. The reflectance of the no-coat portion 333c is lower than the reflectance in the target angular range of the first surface 332a of the wedge prism 332 having a coating in the entire angular range.

[0045] Figure 8 is a graph illustrating the spectral characteristics of the uncoated portion 333c. The horizontal axis of this graph represents the angle on the air side [deg], and the vertical axis represents the reflectance [%]. Similar to the angle on the air side shown in Figure 6, this angle on the air side indicates the angle of incidence of the laser beam L when the laser beam L is incident on the interface between the mirror 331 and the air from the air side, and the angle of emission of the laser beam L when the laser beam L is incident on this interface from the mirror 331 side. As shown by line R3, when the reflectance of the first surface 332a of the wedge prism 332 in the target angle range is approximately 99.9%, the reflectance of the uncoated portion 333c is lower than approximately 99.9% across the entire angle range. For example, the reflectance of the uncoated portion 333c at 15 degrees is approximately 3%, at 30 degrees it is approximately 3%, at 56 degrees it is approximately 7%, at 81 degrees it is approximately 42%, and at 90 degrees it is approximately 98%. The reflectance of the uncoated portion 333c is an example of the fourth reflectance according to the present invention. As described above, the laser light L that has passed through the first surface 332a of the wedge prism 332 propagates through the interior while being sequentially reflected by the second surface 333b of the parallel mirror 333 and the first surface 332a of the wedge prism 332. When this laser light L reaches the uncoated portion 333c, it is radiated from the uncoated portion 333c to the outside of the parallel mirror 333. In particular, when the rotation position of the mirror holder portion 33 is 90 degrees or 270 degrees, as shown in Figures 7A and 7B, the angle of the laser light L changes little, so the laser light L is less likely to be radiated to the outside from the first surface 332a of the wedge prism 332, and is mainly radiated to the outside from the uncoated portion 333c.

[0046] Figure 9 is a front view of the mirror holder portion 33. The holding portion 335 has a main body portion 336 and a plurality of pressing portions 337. In the example shown in Figure 9, there are six pressing portions 337, but the number of pressing portions 337 is not limited to six; it may be five or fewer, or seven or more. The main body portion 336 has a hollow cylindrical shape. As shown in Figure 5, the main body portion 336 has a bottom portion 336a, an opening 336b, and a recess 336c.

[0047] The bottom 336a is provided at one end of the main body 336. The opening 336b is formed at the other end of the main body 336 (hereinafter referred to as the "open end"). The opening 336b exposes the first surface 332a of the wedge prism 332, which is the surface of the mirror 331, to the outside. The opening 336b is an example of the first opening according to the present invention. The recess 336c is provided inside the main body 336 and houses the mirror 331. In the recess 336c, the parallel mirror 333 is arranged on the bottom 336a side, and the wedge prism 332 is arranged on the opening 336b side, and they are fixed in a superimposed state so that their centers overlap.

[0048] A plurality of pressing portions 337 press a part of the end of the parallel mirror 333 from the opening 336b side. As shown in FIG. 5, each pressing portion 337 has a substantially U-shaped cross section. One end of each pressing portion 337 is connected to the open end of the main body 336. Each pressing portion 337 protrudes from the open end of the main body 336 toward the inside of the opening 336b. The other end of each pressing portion 337 contacts the end of the parallel mirror 333 from the opening 336b side. Thereby, the mirror 331 is fixed within the holding portion 335.

[0049] In addition, in the present embodiment, the configuration in which the pressing portion 337 presses the end of the parallel mirror 333 instead of the end of the wedge prism 332 is adopted because the end of the parallel mirror 333 has a uniform thickness, so that it is easier to design the holding structure than the configuration in which the end of the wedge prism 332 with different thicknesses on one side and the other side is pressed.

[0050] As shown in Figure 9, the multiple retaining portions 337 are arranged at approximately equal intervals at the open end of the main body portion 336. A radiation opening 338 is formed between adjacent retaining portions 337 and other retaining portions 337. The radiation opening 338 exposes the uncoated portion 333c of the parallel mirror 333 to the outside. The radiation opening 338 is an example of a second opening according to the present invention. A portion of the uncoated portion 333c of the parallel mirror 333 is covered by the multiple retaining portions 337. On the other hand, the remaining portion of the uncoated portion 333c of the parallel mirror 333 that is not covered by the multiple retaining portions 337 is exposed to the outside by the radiation opening 338. Therefore, when the laser light L that has passed through the first surface 333a propagates through the interior and reaches the uncoated portion 333c, it is radiated to the outside from this uncoated portion 333c through the radiation opening 338.

[0051] Furthermore, as shown in Figure 5, an optical passage 339 is formed in each retaining portion 337. The optical passage 339 is used to radiate the laser light L emitted from the uncoated portion 333c of the parallel mirror 333 to the outside through the radiating aperture 338. Since each retaining portion 337 is positioned so that its opening faces the uncoated portion 333c of the parallel mirror 333, a space is formed between the inside of each retaining portion 337 and the parallel mirror 333. This space becomes the optical passage 339. The optical passage 339 is in communication with the radiating aperture 338. Therefore, the laser light L that has passed through the first surface 332a of the wedge prism 332 and propagated through the interior is radiated from the uncoated portion 333c of the parallel mirror 333 to the optical passage 339, and then radiated to the outside through the radiating aperture 338 via the optical passage 339.

[0052] Figure 10A is a graph illustrating the heat generation suppression effect of the holding portion 335 according to this embodiment. The vertical axis in this graph represents the amount of heat absorbed by the holding portion 335 [W]. This graph was generated by simulation. In this simulation, the reflectance of the holding portion 335 in the comparative example, Examples 1 and 2 (hereinafter referred to as "holder reflectance") was set to 20% across the entire angular range, while the holder reflectance in Examples 3 to 6 was set to 90% across the entire angular range. All other simulation conditions were the same.

[0053] Figure 10B is a diagram showing the combination of configurations for each example shown in Figure 10A. Each example is defined by a combination of "mirror back surface coating," "holder relief structure," and "holder reflectivity." "Mirror back surface coating" also refers to the characteristics of the coating of the mirror 331, and refers to the presence or absence of a coating that provides high reflectivity over the entire angular range to the second surface 333b of the parallel mirror 333. "Present" indicates that this coating is applied, and "absent" indicates that it is not applied. "Holder relief structure" also refers to the characteristics of the structure of the holding part 335, and refers to the presence or absence of a radiation opening 338 and an optical path 339. "Present" indicates that these are formed, and "absent" indicates that they are not formed. "Holder reflectivity" refers to the reflectivity of the holding part 335. "High" indicates that the reflectivity of the holding part 335, including the surface facing the second surface 333b of the parallel mirror 333 in the main body 336, is high over the entire angular range (90% in this example), as in Modification Example 1 described later, and "Low" indicates that this reflectivity is low over the entire angular range (20% in this example).

[0054] In the comparative example, the mirror holder portion 33 lacks both a "mirror back surface coating" and a "holder relief structure," resulting in a low "holder reflectivity." In Example 1, the mirror holder portion 33 has a "mirror back surface coating," but lacks a "holder relief structure" and has a low "holder reflectivity." In Example 2, the mirror holder portion 33 has both a "mirror back surface coating" and a "holder relief structure," but has a low "holder reflectivity." In Example 3, the mirror holder portion 33 has a high "holder reflectivity," but lacks both a "mirror back surface coating" and a "holder relief structure." In Example 4, the mirror holder portion 33 has a "holder relief structure" and a high "holder reflectivity," but lacks a "mirror back surface coating." The mirror holder portion 33 in Example 5 has a "mirror back surface coating" and a "high holder reflectivity," but lacks a "holder relief structure." The mirror holder portion 33 in Example 6 has both a "mirror back surface coating" and a "holder relief structure," and also has a "high holder reflectivity."

[0055] In Figure 10A, bar B1 shows the amount of heat absorbed by the holding portion 335 in the comparative example. As described above, in the comparative example, the "mirror back surface coating" is "none" and the "holder reflectivity" is "low". In this case, the reflectivity of the second surface 333b of the parallel mirror 333 is low across the entire angular range, and the reflectivity of the surface of the holding portion 335 facing the second surface 333b is also low. Therefore, the laser light L passes through the second surface 333b of the parallel mirror 333 and irradiates the holding portion 335, making it easier for heat to be absorbed. In addition, the "holder relief structure" is also "none" in the comparative example. In this case, the radiation opening 338 is not formed, and the uncoated portion 333c of the parallel mirror 333 is entirely covered by the pressing portion 337. Furthermore, no optical path 339 is formed in the pressing portion 337, and the uncoated portion 333c of the parallel mirror 333 is in contact with the inner surface of the pressing portion 337. Therefore, the laser light L that passes through the first surface 332a of the wedge prism 332 is confined inside and less likely to be emitted to the outside.

[0056] Bars B2 to B7 represent the amount of heat absorbed by the holding portion 335 in Examples 1 to 6, respectively. As shown by bar B1, the amount of heat absorbed by the holding portion 335 in the comparative example is approximately 5.5 W. In contrast, as shown by bars B2 to B7, the amount of heat absorbed by the holding portion 335 in each example is approximately 2.5 W in Example 1, approximately 1.4 W in Example 2, approximately 3.7 W in Example 3, approximately 2.6 W in Example 4, approximately 1.6 W in Example 5, and approximately 0.6 W in Example 6. From these simulation results, it can be seen that the amount of heat absorbed by the holding portion 335 in Examples 1 to 6 is less than that in the comparative example.

[0057] Furthermore, comparing the comparative examples with each of Examples 1, 3, and 5, these examples all share the characteristic of not employing a holder relief structure. However, as shown by bars B1, B2, B4, and B6, Examples 1, 3, and 5, which employ at least one of the mirror back surface coating or high holder reflectivity, absorb less heat than the comparative examples that do not employ either. From this, it can be seen that heat generation in the holding portion 335 can be suppressed by employing the mirror back surface coating or high holder reflectivity.

[0058] Furthermore, comparing Example 1 with Example 2, Example 3 with Example 4, and Example 5 with Example 6, the mirror back surface coating and holder reflectivity configurations are common to both pairs of these examples. However, as shown by bars B2 to B7, in each of the comparison examples, the latter Examples 2, 4, and 6, which employ a holder relief structure, absorb less heat than the former Examples 1, 3, and 5, which do not employ a holder relief structure. From this, it can be seen that the heat generation suppression effect of the holding portion 335 is further improved by adopting a holder relief structure.

[0059] As shown by bars B1 to B7, Example 6, which employs a mirror back surface coating, a holder relief structure, and high holder reflectivity, absorbs less heat than Comparative Examples and Examples 1 to 5, which do not employ at least one of these features. Therefore, it can be seen that Example 6 achieves the highest heat suppression effect among Comparative Examples and Examples 1 to 6.

[0060] According to the above-described embodiment, the coating on the second surface 333b of the parallel mirror 333 suppresses the transmission of laser light L through this second surface 333b to the holding portion 335, thereby suppressing heat generation in the holding portion 335. Furthermore, since the first surface 332a of the wedge prism 332 has a lower reflectivity in the non-asymmetrical angle range than in the symmetrical angle range, laser light L transmitted through the first surface 332a is more easily radiated to the outside from the first surface 332a. In addition, since the mirror 331 includes the wedge prism 332, the reflection angle of the laser light L within the mirror 331 can be changed. This makes it easier for laser light L transmitted through the first surface 332a of the wedge prism 332 to be radiated to the outside from the first surface 332a. Furthermore, since the parallel mirror 333 has an uncoated portion 333c, laser light L transmitted through the surface of the mirror 331 is more easily radiated to the outside from the uncoated portion 333c. Furthermore, since a radiation opening 338 is formed between one adjacent pressing portion 337 and the other pressing portion 337 that press the end of the parallel mirror 333, the laser light L that has passed through the surface of the mirror 331 is more easily radiated to the outside from the uncoated portion 333c. Furthermore, since an optical path 339 is formed in the pressing portion 337, the laser light L that has passed through the surface of the mirror 331 is more easily radiated to the outside from the uncoated portion 333c.

[0061] (Modifications) The present invention is not limited to the embodiments described above and may be modified as follows. The following modifications may be used individually or in combination.

[0062] (1) Modification 1 In the above-described embodiment, instead of or in addition to the coating of the second surface 333b of the parallel mirror 333, the surface of the main body portion 336 of the holding portion 335 that faces the second surface 333b of the parallel mirror 333 may have a high reflectivity over the entire angular range, for example, about 99.0%. Since this surface of the holding portion 335 is provided between the first surface 332a of the wedge prism 332 and the mirror holder portion 33, it is an example of a surface having a third reflectivity provided between the holding portion and the surface of the mirror according to the present invention. In one example, the inner surface of the bottom portion 336a that faces the second surface 333b of the parallel mirror 333 may be formed of a material with high reflectivity. The inner surface of the bottom portion 336a may be formed of aluminum, for example. Furthermore, the inner surface of the bottom portion 336a may be further coated with silver to increase reflectivity. According to the reflection spectra of metal surfaces, the reflectivity of metals such as aluminum and silver gradually increases with increasing wavelength, and in the long-wavelength and infrared regions, the reflectivity of silver is approximately 99%, while that of other metals is approximately 98%. In another example, a plate-shaped member with high reflectivity may be inserted between the second surface 333b and the bottom portion 336a of the parallel mirror 333. With this modification, the absorption of the laser light L transmitted through the mirror 331 by the holding portion 335 is suppressed, and thus the heat generation of the holding portion 335 can be suppressed.

[0063] (2) Modification 2 In the embodiments described above, the mirror 331 is not limited to a combination of a wedge prism 332 and a parallel mirror 333. In one example, the mirror 331 may consist only of a wedge prism 332. However, in this modification, the end of the first surface 332a of the wedge prism 332 is not coated. Therefore, the reflectance of the end of the first surface 332a of the wedge prism 332 is lower than the reflectance in the target angle range of the central part over the entire angular range. Even with this configuration, the reflection angle of the laser light L transmitted through the first surface 332a of the wedge prism 332 can be changed, so that the laser light L can be radiated to the outside from the end of the first surface 332a of the wedge prism 332.

[0064] In another example, the mirror 331 may consist only of parallel mirrors 333. However, in this modification, the edges of the first surface 333a of the parallel mirrors 333 are not coated. Therefore, the reflectivity of the edges of the first surface 333a of the parallel mirrors 333 is lower than that of the central part in the target angle range across the entire angular range. With this configuration, the reflection angle of the laser light L transmitted through the first surface 333a of the parallel mirrors 333 does not change much, but the laser light L can be emitted to the outside from the uncoated edges of the parallel mirrors 333.

[0065] (3) Modification 3 In the embodiments described above, the mirror holder portion 33 does not necessarily have to have all the features for suppressing heat generation of the holding portion 335. The mirror holder portion 33 may have only some of the features relating to the coating of the mirror 331 and the features relating to the structure of the holding portion 335. In one example, an uncoated portion 333c is not provided at the end of the mirror 331. In this case, the end of the mirror 331 is also coated. In another example, the surface of the mirror 331 may have high reflectivity in the central part over the entire angular range and low reflectivity at the ends over the entire angular range. This can be achieved, for example, by coating the central part of the surface of the mirror 331 to have high reflectivity over the entire angular range, and not coating the ends of the surface of the mirror 331. In yet another example, a radiating aperture 338 is not formed. In this case, the uncoated portion 333c of the parallel mirror 333 is entirely covered by the retaining portion 337. In yet another example, an optical passage 339 is not formed in the retaining portion 337. In this case, the uncoated portion 333c of the parallel mirror 333 comes into contact with the inner surface of the pressing portion 337. Even with this modified configuration, heat generation in the holding portion 335 can be suppressed compared to the case where all the features for suppressing heat generation in the holding portion 335 are not present.

[0066] (4) Modification 4 The configuration, function, and operation of the laser head 30 described in the above-described embodiment are illustrative and not limited thereto. The shape, structure, material, arrangement, and number of each part constituting the laser head 30 may be appropriately changed from those described in the above-described embodiment. The laser head 30 may have functions different from those described in the above-described embodiment, or it may be configured without some functions. The operation procedure of the laser head 30 may be rearranged or some operation procedures may be omitted, as long as they are not contradictory.

[0067] (5) Modification 5 The configuration, functions, and operation of the laser irradiation system 1 described in the above embodiments are illustrative and not limited thereto. The laser irradiation system 1 may be configured to include one or more of the above-described devices or parts, to include additional devices or parts, or to omit some of the devices or parts. For example, the laser irradiation system 1 may further include a compressor, a power supply, an operating terminal, and a dust collector. The compressor supplies gas to the laser head 30. The gas supplied from the compressor is ejected from the nozzle 36. This gas ejection pushes back dust and other particles flying from the object W in conjunction with the irradiation of the laser beam L, protecting the optical system inside the laser head 30. The power supply supplies power to each part of the laser irradiation system 1. The operating terminal is used to operate the laser irradiation system 1. The dust collector sucks up and collects the removed material removed from the object W by the irradiation of the laser beam L by the laser head 30. In addition, at least part of the function of one device included in the laser irradiation system 1 may be performed by another device. Furthermore, the operating procedure of the laser irradiation system 1 may be rearranged or some operating procedures may be omitted, as long as there is no contradiction.

[0068] (6) Modification 6 Another embodiment of the present invention may be provided as a combination of the mirror holder 33 and the drive unit 34, as the mirror holder 33 alone, or as the mirror 331 alone. The mirror holder 33 is an example of a mirror device according to the present invention. When provided as a combination of the mirror holder 33 and the drive unit 34, as the mirror holder 33 alone, or as the mirror 331 alone, these components do not necessarily have to be used in a laser irradiation system 1 for removing deposits from the surface of an object W. For example, these components may be used in a system or device that utilizes a laser for purposes other than removing deposits from the surface of an object W. Also, when provided as the mirror holder 33 alone or the mirror 331 alone, the mirror holder 33 or the mirror 331 does not necessarily have to be rotationally driven by the drive unit 34.

[0069] (7) Modification 7 In the above-described embodiment, the relationship between the reflectance of the surface of the mirror 331 in the target angle range, the reflectance of the surface of the mirror 331 in the non-target angle range, the reflectance of the back surface of the mirror 331 in the entire angle range, and the reflectance of the uncoated portion 333c in the entire angle range does not necessarily have to hold true for all angles. The reflectance of the surface of the mirror 331 in a part of the angle range other than the target angle range does not have to satisfy the relationship that the reflectance of the back surface of the mirror 331 in the entire angle range is higher than the reflectance in that angle range. For example, the target angle range may be set to a range of 35 degrees or more and 55 degrees or less, the non-target angle range may be set to a range of 0 degrees or more and 30 degrees or less, and 60 degrees or more and 90 degrees or less, and the range between the target angle range and the non-target angle range, which is between 30 degrees and less than 35 degrees and between 55 degrees and less than 60 degrees, may be set as the boundary range. The reflectance of this boundary range may be about 99.0% or more, which is the reflectance of the second surface 333b of the parallel mirror 333 in the entire angle range, or it may be less than about 99.0%. In short, the angular ranges other than the target angular range within the total angular range of the reflectance of the surface of the mirror 331 may include angular ranges that satisfy the relationship that the reflectance of the back surface of the mirror 331 over the entire angular range is higher than the reflectance in that angular range, as well as other angular ranges. The reflectance of the other angular ranges may be any reflectance.

[0070] Furthermore, the reflectance of the first surface 332a of the wedge prism 332, which forms the surface of the mirror 331, in the target angular range may be the average reflectance in the target angular range. Similarly, the reflectance of the first surface 332a of the wedge prism 332 in the non-asymmetric angular range, the reflectance of the second surface 333b of the parallel mirror 333, which forms the back surface of the mirror 331, in the entire angular range, and the reflectance of the uncoated portion 333c in the entire angular range may be the average reflectance of the first surface 332a of the wedge prism 332 in the non-asymmetric angular range, the average reflectance of the second surface 333b of the parallel mirror 333, and the average reflectance of the uncoated portion 333c in the entire angular range, respectively.

[0071] (8) Modification 8 In the embodiment described above, an opening 340 may be formed in the bottom 336a of the holding portion 335 that faces the second surface 333b of the parallel mirror 333 which forms the back surface of the mirror 331. Figure 11 is a front view of the mirror holder portion 33 according to this modification. Figure 12 is an enlarged view of portion A in Figure 4 according to this modification. In this modification, the holding portion 335 may be made of stainless steel, which has lower reflectivity than aluminum but higher rigidity. Also, the second surface 333b of the parallel mirror 333 which forms the back surface of the mirror 331 does not need to be coated. In the example shown in Figures 11 and 12, six openings 340 are formed in the bottom 336a of the holding portion 335. These openings 340 are arranged at equal intervals along the inner circumference of the bottom 336a. Each opening 340 is circular in plan view. Note that the number, arrangement, and shape of the openings 340 shown in Figure 11 are illustrative and not limited thereto. By providing an opening 340 at the bottom 336a of the holding portion 335, as shown in Figure 12, refracted light L2 that enters the interface between the second surface 333b of the parallel mirror 333 and the air from the mirror 331 side and exits through the interface is radiated to the outside through the opening 340. This reduces the amount of light received by the holding portion 335 and suppresses heat generation in the holding portion 335.

[0072] Furthermore, when adopting the configuration according to this modified example, it is not necessary to adopt the structural features of the holding portion 335. If the structural features of the holding portion 335 are not adopted, the entire uncoated portion 333c of the parallel mirror 333 is covered by the pressing portion 337. In addition, no optical path 339 is formed in the pressing portion 337, and the uncoated portion 333c of the parallel mirror 333 comes into contact with the inner surface of the pressing portion 337. Even with this configuration, the laser light L transmitted through the first surface 332a of the wedge prism 332 is radiated to the outside through the opening 340, so that heat generation of the holding portion 335 can be suppressed.

[0073] (9) Modification 9 In the embodiment described above, the reference angle of the laser beam L is not limited to 45 degrees. This reference angle may be less than 45 degrees or greater than 45 degrees. The target angle range may also be defined by the formula reference angle ± kα (where k is a coefficient and α is the inclination angle). In this case, the first surface 332a of the wedge prism 332 is coated such that the reflectivity is high in the target angle range of reference angle ± kα. For example, 2 is used as the coefficient k. This is because the reflection spectrum may shift in the angular direction due to manufacturing variations in the coating, and considering variations in the light ray due to errors and aberrations of optical components, it is preferable to design the reflectivity to be high in the range of reference angle ± 2α. However, the coefficient k is not limited to 2, and should be determined to an appropriate value considering these factors.

[0074] (10) Modification 10 In the embodiments described above, the surface of the mirror 331 has a high reflectivity in the target angle range including 45 degrees ± 5 degrees and a low reflectivity in the other non-target angle range, and the back surface of the mirror 331 has a high reflectivity over the entire angle range. However, the reflectivity of the surface and back surface of the mirror 331 is not limited to this example.

[0075] Figure 13 is a graph illustrating the reflective properties of the surface of the mirror 331 and the holding portion 335 according to this modified example. Similar to the graph shown in Figure 6, the horizontal axis of this graph represents the angle [deg] on the air side, and the vertical axis represents the reflectance [%]. Line R11 in this graph represents the reflectance of the first surface 332a of the wedge prism 332, which is the surface of the mirror 331. Line R12 represents the reflectance of the holding portion 335. In this modified example, the first surface 332a of the wedge prism 332 is coated such that the reflectance is 99.9% or higher in the target angle range of 0 degrees to approximately 60 degrees, and lower than 99.9% in the non-target angle range of more than approximately 60 degrees to 90 degrees. For example, the reflectance of the first surface 332a of the wedge prism 332 at 61 degrees is approximately 99.8%, at 70 degrees it is approximately 52.6%, at 77 degrees it is approximately 80.8%, and at 84 degrees it is approximately 75.7%. This target angle range of 0 degrees to approximately 60 degrees is an example of the "first angle range" according to the present invention, and the non-target angle range of more than approximately 60 degrees to 90 degrees is an example of the "second angle range" according to the present invention. The reflectance in this target angle range and the reflectance in the non-target angle range are examples of the "first reflectance" and "second reflectance" according to the present invention, respectively.

[0076] Furthermore, in this modified example, the second surface 333b of the parallel mirror 333, which forms the back surface of the mirror 331, is not coated. Therefore, the reflectivity of the second surface 333b of the parallel mirror 333 is generally lower than the reflectivity of the first surface 332a of the wedge prism 332 across the entire angular range. However, in this modified example, instead of coating the back surface of the mirror 331 to increase its reflectivity, the holding portion 335 is formed of highly reflective aluminum. As a result, the inner surface of the bottom portion 336a of the holding portion 335, which faces the second surface 333b of the parallel mirror 333, has a reflectivity of approximately 90% across the entire angular range. This reflectivity is higher than at least a portion of the reflectivity of the surface of the mirror 331 in the asymmetrical angular range. The inner surface of the bottom portion 336a is positioned between the surface of the mirror 331 and the main body of the holding portion 335 in the optical path of the laser beam. Therefore, the inner surface of the bottom portion 336a is an example of a surface provided "between the holding portion and the surface of the mirror" according to the present invention. The reflectance of the inner surface of the bottom portion 336a over the entire angular range is an example of the "third reflectance" according to the present invention.

[0077] With this configuration, the laser light that passes through the mirror 331 is reflected by the inner surface of the bottom portion 336a of the holding portion 335, making it less likely to be absorbed by the holding portion 335 itself. This suppresses heat generation in the holding portion 335.

[0078] In this modified example, the relationship between the reflectance of the mirror 331 surface in the target angular range, the reflectance of the mirror 331 surface in the non-target angular range, and the reflectance of the holding portion 335 in the entire angular range does not necessarily have to hold true for all angles, but only for some angles. For example, the reflectance of the mirror 331 surface in the non-target angular range should be lower than the reflectance of the mirror 331 surface in the target angular range for at least some angles. Similarly, the reflectance of the holding portion 335 in the entire angular range should be higher than the reflectance of the mirror 331 surface in at least some angles within the non-target angular range. Alternatively, these relationships may be defined based on the average reflectance in each angular range. For example, the average reflectance of the mirror 331 surface in the non-target angular range may be lower than the average reflectance of the mirror 331 surface in the target angular range. Similarly, the average reflectance of the holding portion 335 in the entire angular range may be higher than the average reflectance of the mirror 331 surface in the non-target angular range.

[0079] 1: Laser irradiation system, 10: Laser oscillator, 20: Fiber, 30: Laser head, 31: Fiber connector, 32: Collimator, 33: Mirror holder section, 34: Drive section, 35: Focusing lens, 36: Nozzle, 37: Protective window, 331: Mirror, 332: Wedge prism, 332a: First surface, 332b: Second surface, 333: Parallel mirror, 333a: First surface, 333b: Second surface, 333c: Uncoated section, 335: Holding section, 336: Main body section, 336a: Bottom section, 336b: Opening, 336c: Recess, 337: Pressing section, 338: Radiation opening, 339: Optical path

Claims

1. A laser irradiation device comprising: a mirror that reflects laser light emitted from a laser oscillator and changes the direction of the laser light; a holding part that holds the mirror; and a drive part that rotates the holding part while the normal direction of the surface of the mirror held by the holding part is inclined with respect to the axis of rotation, thereby causing the irradiation spot of the laser light reflected by the mirror to rotate in a circular manner on the surface of an object, wherein the surface of the mirror has a first reflectance in a first angular range and a second reflectance lower than the first reflectance in a second angular range different from the first angular range, and a surface having a third reflectance higher than the second reflectance in the first and second angular ranges is provided between the holding part and the surface of the mirror.

2. The laser irradiation apparatus according to claim 1, wherein the mirror includes a wedge prism.

3. The laser irradiation device according to claim 1, wherein the end of the mirror has a fourth reflectance lower than the first reflectance in the first and second angular ranges.

4. The laser irradiation device according to claim 3, wherein the holding portion has a first opening that exposes the surface of the mirror, a pressing portion that presses a part of the end of the mirror from the side of the first opening, and a second opening that exposes to the outside the portion of the end of the mirror that is not covered by the pressing portion, and the laser light that has passed through the surface of the mirror is radiated to the outside from the end of the mirror through the second opening.

5. The laser irradiation device according to claim 4, wherein an optical passage communicating with the second opening is formed in the pressing portion, and the laser light transmitted through the surface of the mirror is radiated from the end of the mirror into the optical passage and radiated to the outside from the second opening through the optical passage.

6. A mirror device comprising: a mirror that reflects laser light emitted from a laser oscillator and changes the direction of the laser light; and a holding part that holds the mirror, wherein the surface of the mirror has a first reflectance in a first angular range and a second reflectance lower than the first reflectance in a second angular range different from the first angular range, and a surface having a third reflectance higher than the second reflectance in the first and second angular ranges is provided between the holding part and the surface of the mirror.

Images