Measurement method and device

Abstract

In a scheme for scanning laser light by using a scattering body, in order to make it possible to accurately measure a beam profile regardless of the size of the scattering body: laser light which is a measurement target for a beam profile is scanned in a scanning direction that is a direction perpendicular to the irradiation direction of the laser light by using a linear scattering body in which the edge on the side thereof irradiated with the laser light and a cross section parallel to a plane stretching in the irradiation direction of the laser light and in the scanning direction is bilaterally symmetrical with respect to an axis, serving as an axis of symmetry, that is parallel to the irradiation direction of the laser light; and reflected light from the linear scattering body are detected. Removed from the center of a waveform representing the temporal changes in the detected reflected light are waveform portions before and after the period required for moving the distance from the axis of symmetry to the right end part or the left end part in the cross section of the scattering body at the moving speed of the scattering body during the scanning, the remaining waveforms are connected, and information related to the beam profile of the laser light is generated on the basis of the connected remaining waveforms.

Description

Measurement method and apparatus

[0001] This invention relates to a beam profile measurement technique.

[0002] High-power laser processing technology enables advanced processing that is difficult with conventional machining, such as cutting steel plates and sintering metal powders, and has become one of the fundamental technologies supporting manufacturing. In laser processing, the laser light functions as a "tool" for the workpiece, so the shape of the focused spot, or "beam profile," which is equivalent to the cutting edge shape of an end mill, has an essential influence on the processing result. For this reason, beam profile measurement devices using CCD (Charge-Coupled Device) image sensors (i.e., methods using image sensors) and slits (i.e., methods that scan a light-shielding material in relation to the laser) have been commercialized and are widely used.

[0003] In addition to these methods, another technique for measuring beam profiles involves scanning a scatterer in relation to the laser. This method of scanning a scatterer has many advantages, such as being easily adaptable to multidimensional and real-time operation through equipment modifications, and having excellent laser tolerance, and several examples have been reported. However, it has the problem that the measurement accuracy is limited by the size of the scatterer.

[0004] When a scatterer is scanned in relation to a laser, the resulting signal is a convolution of the spatial light intensity distribution (i.e., the beam profile) and the optical properties of the scatterer (i.e., the window function). As schematically shown in Figure 1, when a beam profile P with a Gaussian distribution is measured with a scatterer having a window function V, the resulting signal S will be broader than the Gaussian distribution because the window function V has a finite width.

[0005] To improve measurement accuracy, conventional approaches involve reducing the size of the scatterer. The ISO (International Organization for Standardization) standard document (ISO / TR 11146-3), while not specifying the size of the scatterer, requires a slit width of 1 / 20 or less of the beam diameter to be measured for the method of scanning the light shield. However, there are limits to how small the scatterer can be, and it is difficult to ensure scattering efficiency (affecting the measurement S / N ratio) and mechanical strength (affecting positional accuracy) with a small scatterer.

[0006] As an ideal window function that does not change the beam profile or affect the measured signal-to-noise ratio even when convolution occurs, the delta function can be cited as shown in Figure 2. However, the corresponding scatterer must be infinitesimally small in size and have infinite scattering efficiency, making its realization difficult. Therefore, as a physical scatterer, it is preferable to use one that is as small as possible to improve spatial resolution and has the highest possible reflectivity to ensure the measured signal-to-noise ratio. Since the reflectivity corresponding to the scattering efficiency is at most 1, it is preferable for the physical scatterer to have a height of 1 and an infinitesimally small width, exhibiting pulse-like reflectivity characteristics that approximate a discrete-time unit impulse signal.

[0007] On the other hand, a scattering material that can be realistically used is a thin metal wire. Here, as shown in Figure 3(a), when a laser beam, represented by a thick arrow, is incident from above the plane of the paper, and the incident laser beam is scanned by a wire W with a circular cross-section and radius r, the laser incident position on the surface of the wire W, corresponding to the incident angle θ of the laser beam, is denoted as X. For normalization of the position, X / r is used. On the other hand, as shown in Figure 3(b), the reflected laser beam on the surface of the wire W is represented by a thick arrow, and the reflection angle is 2θ with respect to the incident angle θ. Although it is common to define the reflection angle as the angle θ between the normal to the reflective surface and the reflected light, in this application, the angle 2θ between the incident light and the reflected light is treated as the reflection angle.

[0008] Figure 4(a) shows the distribution of the reflectivity with respect to the incident position (X / r) of a laser beam (wavelength 633 nm) when an Au wire is used. The dashed-dotted line represents the reflectivity R of the laser beam with P polarization ave , p , s and the dotted line represents the reflectivity R of the laser beam with S polarization s and the solid line represents the reflectivity R of the laser beam with unpolarized light. ave Thus, in the case of an Au wire, regardless of the incident position, the reflectivity is almost 1 for any polarization, and a window function corresponding to the diameter of the Au wire is formed.

[0009] Note that Figure 4(b) shows the reflection angle distribution of the reflectivity when an Au wire is used. Although there are some slightly different parts, it is almost the same for any polarization, and the reflection angle dependence of the reflectivity is low.

[0010] On the other hand, Figure 5(a) shows the distribution of the reflectivity with respect to the incident position (X / r) of a laser beam (wavelength 633 nm) when a SUS (Steel Use Stainless) 304 wire, which is a type of stainless steel, is used. Similar to Figures 4(a) and (b), the dashed-dotted line represents the reflectivity R of the laser beam with P polarization p and the dotted line represents the reflectivity R of the laser beam with S polarization s and the solid line represents the reflectivity R of the laser beam with unpolarized light. ave The SUS304 wire is different from the Au wire in that there is a large difference in the distribution of the reflectivity depending on the polarization. Also, if it is the reflectivity R p of P polarization, the reflectivity once decreases in front of both ends of the wire but becomes almost "1" at both ends. If it is the reflectivity R [[ID=​​​​​Figure 5(b) shows the reflection angle distribution of reflectance when SUS304 wire is used. Here again, the reflection angle distribution of reflectance differs greatly depending on the polarization, and the reflectance is highly dependent on the reflection angle.

[0012] Furthermore, when we simulated the detection signal (where the intensity of the detection signal represents the sum of the reflected light from the scatterer; the same applies in the following description) when scanning a 10 μm diameter laser beam (wavelength 633 nm) with a 100 μm diameter Au wire, we obtained the results shown in Figure 6(a). In Figure 6(a), the fine dotted line shows the detection signal obtained when scanning the laser beam with an ideal delta function, the dashed line shows the detection signal for P-polarized laser light, the dotted line shows the detection signal for S-polarized laser light, and the solid line shows the detection signal for unpolarized laser light. Thus, it can be seen that when the wire diameter:beam diameter of the object being measured is about 10:1, the beam shape does not appear in the detection signal, making measurement impossible.

[0013] On the other hand, when we simulated the detection signal when scanning a 1 mm diameter laser beam with a 100 μm diameter Au wire, we obtained the results shown in Figure 6(b). In Figure 6(b), the fine dotted line, dashed line, dotted line, and solid line all represent the same detection signals as in Figure 6(a), but they all overlap. Thus, it can be seen that when the wire diameter:beam diameter of the object being measured is about 1:10, the Au wire acquires desirable scattering characteristics, and results close to an ideal delta function can be obtained.

[0014] Furthermore, Figure 7 shows the simulation results for the beam radius of laser light obtained by scanning laser light of various beam diameters (wavelength 633 nm) with a 100 μm diameter Au wire, in relation to the beam diameter / wire diameter. In Figure 7, the dotted line represents the wire radius, which is a fixed value (50 μm for a diameter of 100 μm) and therefore does not depend on the beam diameter / wire diameter on the horizontal axis. The solid line represents the relationship between the beam diameter / wire diameter and the beam radius of the laser light being measured when the radius of the laser light being measured is changed, and it is a straight line sloping upwards to the right. On the other hand, the circles plotted represent the results of a simulation of the beam radius of laser light obtained by scanning unpolarized laser light with a 100 μm diameter Au wire. When beam diameter / wire diameter > 1, the result is almost on the solid line, suggesting that it can be measured with a 100 μm diameter Au wire. However, when beam diameter / wire diameter becomes less than 1, the radius of the obtained laser light becomes the same as the radius of the wire, deviating significantly from the solid line, indicating that it cannot be measured with a 100 μm diameter Au wire.

[0015] For example, Patent Document 1 discloses a technique for determining the characteristics of a sample light beam by passing the beam through a needle or wire, which is a reflector, and receiving the reflected sample light beam. This publication discloses that the reflector is formed from a reflective material or by covering the surface of a non-reflective material with a reflective coating, and further states that it is preferable for the reflector to be substantially narrower than the light beam. Therefore, no solution to the problems described above is disclosed or suggested.

[0016] Furthermore, for example, Patent Document 2 discloses a technique for detecting the intensity of a laser beam, in which an integrating sphere and a laser beam scatterer composed of at least two wires that cross the center of the laser beam point-symmetrically are used, and the energy of the laser beam, which has been reflected and homogenized by the laser beam scatterer and the integrating sphere, is detected by a laser detector. However, the problems described above are neither disclosed nor suggested.

[0017] Furthermore, for example, Patent Document 3 discloses a technique for scanning a light-shielding material with respect to a laser. Specifically, it involves rotating a blade assembly in which multiple blades are arranged to sequentially cross the laser as it rotates along the optical axis of the laser, detecting the laser light with a detector positioned on the optical axis, and obtaining a beam profile by processing the detected signal. However, it neither discloses nor suggests the above-mentioned problems regarding the technique for scanning a scatterer.

[0018] Special Table of Contents No. 2005-516208 Publication of Japanese Unexamined Patent Publication No. 1983-100334 Publication of Special Publication No. 2015-535596

[0019] Therefore, in one aspect, the object of the present invention is to provide a technique for accurately measuring the beam profile regardless of the size of the scatterer in a method of scanning laser light with a scatterer.

[0020] A measurement method according to a first aspect of the present invention involves (A) scanning the laser light to be measured for beam profile using a linear scatterer in a scanning direction perpendicular to the irradiation direction of the laser light, with the edge on the side irradiated by the laser light being symmetrical with respect to an axis parallel to the irradiation direction of the laser light in a cross-section parallel to the plane stretched in the irradiation direction and scanning direction; (B) detecting reflected light from the linear scatterer; (C) removing the waveform from the point immediately after the time when the center of the waveform is moved backward by the time when the distance from the axis of symmetry to the right end or left end in the cross-section of the scatterer is moved at the speed of movement of the scatterer in the above scanning, and then removing the waveform from the point immediately after the point when the time when the center of the waveform is moved forward by the same amount of time from the center of the waveform, and concatenating the remaining waveforms; and (D) generating information regarding the beam profile of the laser light based on the concatenated remaining waveforms.

[0021] A measurement system according to a second aspect of the present invention includes: (A) a linear scatterer whose edge on the side irradiated by the laser light is symmetrical with respect to an axis parallel to the irradiation direction of the laser light, in a cross-section parallel to a plane stretched in the direction of irradiation of the laser light that is the target of beam profile measurement and in a scanning direction perpendicular to the irradiation direction; (B) a mechanism for scanning the laser light in the scanning direction using the linear scatterer; (C) a photodetector for detecting reflected light from the linear scatterer; and (D) a processing unit that removes the waveform from the point immediately after the time taken to move the scatterer forward by

[0022] A measurement method according to a third aspect of the present invention involves (A) scanning the laser beam perpendicular to the irradiation direction of the laser beam using a linear scatterer having a first surface portion on the surface irradiated with the laser beam, which is the target of beam profile measurement, where the incident angle of the laser beam is in the vicinity of 90° and 90°, and which has pulsed reflectance characteristics in the vicinity of 90° and 90°, and in the vicinity of 90°, the reflectance decreases by a predetermined rate or more from the peak in the vicinity of 90° and 90°, and a second surface portion on the surface irradiated with the laser beam, other than the first surface portion, in which the reflectance to the laser beam is suppressed to (1 - predetermined rate) or less, (B) detecting the reflected light from the linear scatterer, and (C) generating information regarding the beam profile of the laser beam based on a waveform representing the time change of the detected reflected light.

[0023] A measurement system according to a fourth aspect of the present invention includes: (A) a linear scatterer having a first surface portion of the surface irradiated with laser light, which is the target of beam profile measurement, where the incident angle of the laser light is in the vicinity of 90° and 90°, and which has pulsed reflectance characteristics in the vicinity of 90° and 90°, and in the vicinity of 90°, the reflectance decreases by a predetermined rate or more from the peak in the vicinity of 90°; and a second surface portion of the surface irradiated with laser light other than the first surface, where the reflectance to the laser light is suppressed to (1 - predetermined rate) or less; (B) a mechanism for scanning the laser light with the linear scatterer in a direction perpendicular to the irradiation direction of the laser light; (C) a photodetector for detecting reflected light from the linear scatterer; and (D) a processing unit for generating information regarding the beam profile of the laser light based on a waveform representing the time change of the detected reflected light.

[0024] Figure 1 is a diagram illustrating the problems of the prior art. Figure 2 is a diagram illustrating an ideal delta function-shaped window function. Figures 3(a) and (b) are diagrams illustrating the relationship between a cylindrical wire and laser light. Figures 4(a) and (b) are diagrams illustrating the characteristics of the Au wire. Figures 5(a) and (b) are diagrams illustrating the characteristics of the SUS304 wire. Figures 6(a) and (b) are diagrams illustrating the simulation results of the signal detected when using the Au wire. Figure 7 is a diagram illustrating the simulation results of the beam radius relative to the beam diameter / wire diameter obtained when using the Au wire. Figure 8 is a diagram illustrating the cross-section of the cylindrical wire used in the first embodiment. Figure 9 is a diagram illustrating the time change of the detected signal of reflected light when the laser light is scanned with the SUS304 wire for several cases with different ratios between the beam diameter of the laser light and the wire diameter of the SUS304 wire. Figure 10 is a diagram illustrating the range removed in the removal process in the first embodiment. Figure 11 is a diagram illustrating the state in which the remaining waveform portion after the removal process in the first embodiment is connected. Figure 12 is a diagram illustrating the measurement of the beam diameter. Figure 13 is a diagram showing the simulation results of the beam radius as a ratio of beam diameter / wire diameter obtained when using a SUS304 wire in the first embodiment. Figure 14 is a diagram showing an overview of the measurement system according to the first and second embodiments. Figure 15 is a diagram showing an example of a mechanism for translating the wire. Figure 16 is a diagram showing the experimental results (signal waveform) and processing results for the first embodiment. Figures 17(a) and (b) are diagrams illustrating the effectiveness of the first embodiment. Figure 18 is a diagram showing the simulation results of the beam radius as a ratio of beam diameter / wire diameter for several cases with different ratios between the beam diameter of the laser light and the wire diameter of wires of various materials. Figure 19 is a diagram illustrating the reflectivity characteristics of graphite. Figure 20 is a diagram illustrating the reflectivity characteristics of blackened stainless steel (Fe3O4). Figure 21 is a diagram illustrating the reflectivity characteristics of SUS304. Figure 22 is a diagram illustrating the reflectivity characteristics of Au. Figure 23 is a diagram illustrating a wire with an elliptical cross-sectional shape.Figure 24 is a diagram illustrating a wire with an oval cross-section. Figure 25 is a diagram illustrating a wire with a flat oval cross-section. Figure 26 is a diagram illustrating a wire with a triangular cross-section. Figure 27 is a diagram showing the reflectivity characteristics of a graphite wire with a flat oval cross-section. Figure 28 is a diagram showing the reflectivity characteristics of a graphite wire with a triangular cross-section. Figure 29 is a diagram showing the reflectivity characteristics of a stainless steel (Fe3O4) wire with a flat oval cross-section and black oxide treatment. Figure 30 is a diagram showing the reflectivity characteristics of a stainless steel (Fe3O4) wire with a triangular cross-section and black oxide treatment. Figure 31 is a diagram showing the reflectivity characteristics of a SUS304 wire with a triangular cross-section. Figure 32 is a diagram showing the reflectivity characteristics of an Au wire with a triangular cross-section. Figures 33(a) and (b) show the characteristics of a graphite wire. Figure 34 shows the reflectivity characteristics of a graphite wire. Figure 35 illustrates the scanning of a Gaussian beam with a wire having a circular cross-section. Figure 36 shows an example of the time waveform when the beam diameter:wire diameter of P-polarized laser light is varied. Figure 37 shows an example of the time waveform when the beam diameter:wire diameter of S-polarized laser light is varied. Figure 38 shows an example of the time waveform when the beam diameter:wire diameter of unpolarized laser light is varied. Figure 39 illustrates the range of reflection angles to be masked when a graphite wire is used. Figure 40 schematically shows the reflectance distribution of the inner wall (cross-section) of the integrating sphere when a graphite wire is used. Figure 41 illustrates an example of a configuration when the wire is rotated. Figure 42 shows an example of the time waveform of reflected light obtained when the wire is rotated. Figure 43 illustrates an embodiment when the wire is in reciprocating motion. Figure 44 is a multimode TEM. 10 This figure shows the beam shape. Figures 45(a) to (c) show the relationship between signal intensity and position for laser light and the relationship between reflectance and position of the window function formed by the wire for P-polarized, S-polarized, and unpolarized laser light, respectively. Figures 46(a) to (c) show the TEM10 This figure shows the time waveform of the reflected light obtained when the laser beam is scanned with a wire for each of the P-polarized, S-polarized, and unpolarized modes. Figures 47(a) to (c) are TEM 10 This figure shows the time waveform and rejection range of the reflected light obtained when the laser beam is scanned with a wire for each of the P-polarized, S-polarized, and unpolarized modes. Figures 48(a) to (c) are TEM 10 This figure shows the relationship between signal intensity and position obtained from the shaped time waveform and the relationship between signal intensity and position of the measured object for each of the P-polarized, S-polarized, and unpolarized modes. Figure 49 is a multimode TEM. 20 This figure shows the beam shape. Figures 50(a) to (c) show the TEM 20 This figure shows the relationship between signal intensity and position for the laser light and the relationship between reflectance and position of the window function formed by the wire, for each of the P-polarized, S-polarized, and unpolarized modes. Figures 51(a) to (c) are TEM 20 This figure shows the time waveform of the reflected light obtained when the laser beam is scanned with a wire for each of the P-polarized, S-polarized, and unpolarized modes. Figures 52(a) to (c) are TEM 20 This figure shows the time waveform and rejection range of the reflected light obtained when the laser beam is scanned with a wire for each of the P-polarized, S-polarized, and unpolarized modes. Figures 53(a) to (c) are TEM 20 This figure shows the relationship between signal intensity and position obtained from the shaped time waveform and the relationship between signal intensity and position of the measurement target for each of the P-polarized, S-polarized, and unpolarized modes. Figure 54 is a diagram illustrating the scanning of laser light with a wire having a semicircular cross-section. Figure 55 is a diagram illustrating the scanning of laser light with a wire having a sector-shaped cross-section smaller than a semicircle. Figure 56 is a diagram showing an example of the cross-sectional shape in Modification 3 of the second embodiment. Figure 57 is a diagram showing an overview of the measurement system according to Modification 4 of the second embodiment. Figure 58 is a diagram showing the arrangement of wires in a spiral wire scanner from above. Figure 59 is a diagram showing an example of the time waveform of reflected light obtained in Modification 4 of the second embodiment. Figure 60 is a multimode TEM 11This figure shows the beam shape. Figure 61 is a top view showing the arrangement of two spiral wire scanners and the arrangement of their wires. Figure 62 is a diagram showing an overview of the measurement system according to Modification 6 of the second embodiment. Figure 63 is a top view of the measurement system according to Modification 6 of the second embodiment. Figure 64 is a diagram showing an overview of the measurement system according to Modification 7 of the second embodiment. Figure 65 is a diagram illustrating the measurement system according to Modification 8 of the second embodiment. Figure 66 is a diagram showing an example of an integrating enclosure according to the third embodiment. Figure 67 is a diagram illustrating the direction of reflected light generated from a scatterer. Figure 68 is a diagram illustrating an example of the reflectance distribution on the inner wall of the integrating enclosure. Figure 69 is a diagram illustrating another example of the reflectance distribution on the inner wall of the integrating enclosure. Figure 70 is a diagram illustrating another example of the reflectance distribution on the inner wall of the integrating enclosure. Figure 71 is a diagram showing the relationship between the angle of incidence and reflectance when blackened stainless steel is used as the scatterer, and the range that can be utilized by an integrating enclosure with a distributed reflectance. Figure 72 shows the relationship between the angle of incidence of the laser light to be measured onto the scatterer and the intensity of the reflected light obtained by using an integrating enclosure with a distributed reflectivity. Figure 73 shows an example of an integrating enclosure according to Modification 1 of the third embodiment. Figure 74 shows an example of an integrating enclosure according to Modification 2 of the third embodiment. Figure 75 shows another example of an integrating enclosure according to Modification 2 of the third embodiment.

[0025] [Outline of Embodiments of the Invention] Below, in the first embodiment, a configuration for solving the above-mentioned problems will be described by performing predetermined signal processing on the detection signal of reflected light from a scatterer scanning a laser beam. In the second embodiment, a configuration for solving the above-mentioned problems will be described by using a scatterer with a height of 1 and an infinitesimal width that exhibits pulse-like reflectivity characteristics approximating a unit impulse signal in a discrete-time system. Furthermore, in the third embodiment, a configuration will be described in which an integrating enclosure having a cylindrical or rectangular parallelepiped shape is used instead of a spherical integrating sphere.

[0026] [Embodiment 1] In this embodiment, we will describe a case in which a cylindrical wire is used to scan a laser beam perpendicular to its irradiation direction (also called the direction of propagation).

[0027] Furthermore, if the scanning direction of the cylindrical wire is the X-axis direction and the propagation direction of the laser beam is the Z-axis direction, the cross-section of the cylindrical wire when cut in the XZ plane is a circular shape that is symmetrical with respect to the axis of symmetry shown by the dashed line, as shown in Figure 8. Here, the radius of the circle is r. e Furthermore, the angle θ of incidence of the laser beam, indicated by the thick arrow, onto the cylindrical wire is 0° on the axis of symmetry and 90° at either the right or left end of the cylindrical wire in Figure 8.

[0028] Next, we will explain in more detail the case where a SUS304 wire having the reflectivity characteristics shown in Figure 5 is used as the scatterer.

[0029] First, Figure 9 shows the time evolution (i.e., time waveform) of the detected signal of reflected light obtained by simulation for each case of a laser beam diameter:wire diameter ratio of 1:1 (thin dotted line), 1:2 (normal dotted line), 1:5 (single dashed line), 1:10 (long dotted line), 1:20 (double dashed line), and 1:100 (solid line) of a laser beam with a wavelength of 633 nm, unpolarized, and a Gaussian distribution of laser light intensity. In Figure 9, time and signal intensity are normalized to compare each case, with the horizontal axis representing arbitrary time [a.u.] (Arbitrary Unit) and the vertical axis representing signal intensity [a.u.]. The time at which the center of the wire and the center of the laser beam intersect is set to 0.

[0030] In the case of beam diameter:wire diameter = 1:1, represented by a thin dotted line, the waveform is close to a Gaussian distribution. However, in the case of beam diameter:wire diameter = 1:2, represented by a regular dotted line, the rise and fall of the waveform are steeper than in the 1:1 case, and the waveform saturates at a signal intensity of 1 around time 0. Similarly, in the case of beam diameter:wire diameter = 1:5, represented by a dashed line, the rise and fall of the waveform are steeper than in the 1:2 case, and the time during which the signal intensity saturates at 1 around time 0 is longer. Furthermore, in the case of beam diameter:wire diameter = 1:10, represented by a long dotted line, this tendency is even stronger than in the 1:5 case.

[0031] Furthermore, in the case of beam diameter:wire diameter = 1:20, shown by the dashed line, the rise and fall are steeper than in the 1:10 case. In addition, after the rise reaches a signal strength of 1, the signal strength decreases slightly and then immediately saturates at a signal strength of 1, creating a dip. A similar dip occurs in the falling portion, although it is reversed on the left and right. Furthermore, in the case of beam diameter:wire diameter = 1:100, shown by the solid line, the rise and fall are steeper than in the 1:20 case. In addition, after the rise reaches a signal strength of 1, the signal strength decreases sharply, then increases slightly and is maintained at a signal strength of approximately 0.61, creating a rapid change. A similar rapid change occurs in the falling portion, although it is reversed on the left and right.

[0032] This is because, as shown in Figure 5(a), the reflectivity is 1 near position X / r = 1, which corresponds to an incident angle of 90°, but decreases sharply as the incident angle moves away from 90°, reaching a minimum reflectivity. However, as it approaches position X / r = 0, which corresponds to an incident angle of 0°, the reflectivity increases slightly and settles at around 0.61.

[0033] When such a reflected light detection signal is obtained, let v be the scanning speed of the wire relative to the laser light, and let r be the radius of the circle which is the cross-section. e Therefore, -Δt = -r e / v < t < +Δt = re Remove waveforms within the / v range.

[0034] The value of Δt is determined by considering the extreme characteristics of Fresnel reflection on the scattering surface, that is, the characteristic that any optical material has a reflectivity of 1 at an incident angle of 90°, and the symmetry of the wire's cross-section. That is, as shown in Figure 8, the cross-section has radius r e If it is a circle, then the distance r e The time required to pass through at velocity v is Δt = r e The value is / v, and at exactly time ±Δt, the incident angle becomes 90° and the reflectivity is 1, so the intention is to extract only the detection signal of the reflected light at that time.

[0035] Figure 10 shows the range S to be removed. The beam diameter and wire diameter are the same as in Figure 9. Also, since it is normalized, Δt is the same in all cases. The waveform portion that falls within the gray-shaded range S is removed. Then, as shown in Figure 11, the remaining waveform portions are concatenated. In Figure 11 as well, the beam diameter and wire diameter are the same as in Figure 9. In this way, a pulsed waveform with one peak is obtained for all beam diameter and wire diameter cases.

[0036] Then, the beam diameter is measured from the concatenated waveforms. As schematically shown in Figure 12, when the pulse height is set to 1, the height is 1 / e 2 The time interval t is such that (e is Napier's number, or sometimes 1 / 2) w Let's assume that the beam width 2ω is calculated using the following formula: 2ω = t w ×v

[0037] Figure 13 shows the relationship between beam diameter / wire diameter and beam radius, obtained by simulating the scanning of unpolarized laser light (wavelength 633 nm) with various beam diameters using a SUS304 wire with a diameter of 100 μm. The laser light is a single-mode laser. Similar to Figure 7, in Figure 13, the dotted line represents the wire radius and is independent of the beam diameter / wire diameter, while the solid line represents the relationship between the beam diameter / wire diameter and the radius of the laser light being measured, and is a straight line sloping upwards to the right. The black triangles plotted indicate the radius of the laser light obtained based on the signal waveform shown in Figure 9 without performing the removal process described above, and when the beam diameter / wire diameter is less than 1, it is plotted along the dotted line. In other words, it cannot be said that the laser profile is being measured with high accuracy. On the other hand, the white triangles plotted indicate the radius of the laser light obtained after performing the removal process described above, and are plotted along the solid line. In other words, it shows that the beam diameter can be measured even when the beam diameter is small, without being limited by the wire diameter. Although only unpolarized laser light is shown in the illustration, similar results were obtained for P-polarized and S-polarized laser light.

[0038] Figure 14 shows an overview of an actual measurement system utilizing the main principles of this embodiment as described above. In this embodiment, the laser light 10 output from the light source 100 is focused by the focusing lens 110 to become laser light 11, which is input to the integrating sphere 200 from the input port 210 and output from the output port 220. At this time, as shown by the dotted line 12, the laser light 11 converges within the integrating sphere 200, so the beam diameter decreases, and the beam diameter becomes minimum at the beam waist. After passing the beam waist, the laser light 11 begins to diverge again, and the beam diameter increases.

[0039] The measurement system according to this embodiment includes an integrating sphere 200, a wire 310 for scanning the laser beam 11 between an input port 210 and an output port 220, a mechanism 300 for moving the wire 310 to scan the laser beam 11 perpendicularly, a photodetector 400 for detecting reflected light 13 from the wire 310 inside the integrating sphere 200, an oscilloscope 500 for forming a time waveform of the reflected light 13 detected by the photodetector 400, and an information processing device 600 for generating information regarding the beam profile of the laser beam 11 from the output of the oscilloscope 500.

[0040] As shown in Figure 8, the wire 310 has a cross-section in a plane stretched between the scanning direction of the wire 310 (X-axis direction) and the propagation direction of the laser beam 11 (Z-axis direction), which is a symmetrical circle with the Z-axis direction as the axis of symmetry. The mechanism 300, for example, translates the wire 310, and will be explained together with the processing details of the information processing device 600.

[0041] The inner wall of the integrating sphere 200 is designed to uniformly reflect the light reflected from the wire 310 across its entire surface.

[0042] Here, an example of a configuration in which the mechanism 300 translates the wire 310 will be explained using Figure 15. Figure 15 is a top view of the inside of the integrating sphere 200, that is, a view from above in the direction of propagation of the laser beam 11 (Z-axis direction). As shown in Figure 15, the mechanism 300 includes a translation stage that holds one end of the wire 310 and translates the wire 310. Here, the mechanism 300 moves the wire 310 at a velocity v so that the wire 310 scans the cross section 11c of the laser beam 11 that is traveling from the top to the bottom of the paper.

[0043] In such cases, the information processing device 600 obtains a time waveform as shown in Figure 9. For example, by using the symmetry of the time waveform, the intersection time between the center of the wire 310 and the center of the laser beam 11 is determined, and when that intersection time is set to 0, -Δt = -r e / v < t < +Δt = r e The / v waveform portion is removed (Figure 10), and the remaining waveform portions are concatenated (Figure 11). Then, the information processing device 600 sets the height to 1 / e when the peak height in the concatenated time waveform is set to 1. 2The time width t is (in some cases 1 / 2). w Measure (Figure 12). Then, t w The beam diameter is calculated by multiplying by v.

[0044] By adopting this configuration, it is possible to scan a cross-section of any position of the laser beam 11 inside the integrating sphere 200 and obtain the beam diameter at that position.

[0045] In addition, since the area of ​​a single pulsed waveform shown in Figure 12 is proportional to the power of the laser light 11, the power of the laser light can also be determined by calculating the area of ​​a single pulsed waveform.

[0046] Alternatively, an information processing device 600 equipped with the functions of an oscilloscope 500 may be used. Furthermore, the time width t w For this, for example, the pulsed waveform may be approximated to a Gaussian function using the least squares method, and then calculated.

[0047] [Experimental Example of Embodiment 1] Figure 16 shows the signal waveform obtained when scanning a laser beam (single-mode in this case) with a beam diameter of approximately 50 μm and a wavelength of 633 nm using a SUS304 wire with a diameter of 80 μm. In Figure 16, the dotted line represents the waveform of the detected signal, the fine dotted line represents the waveform obtained by removing the waveform portion -Δt < t < +Δt and concatenating the remaining waveform portions, and the solid line represents the waveform approximated by a Gaussian function relative to the fine dotted line. The height of the waveform after this Gaussian function approximation is 1 / e 2 You may also measure the time interval in this case.

[0048] Reflecting the results of these experiments, Figure 17(a) shows the measured beam diameter at various positions of the laser beam 11, which has a beam waist of approximately 50 μm in diameter and a wavelength of 633 nm. The Z-axis is set parallel to the irradiation direction of the laser beam 11, and the beam waist position of the laser beam 11 is set to z=0, with the input port 210 side being negative and the output port 220 side being positive. In Figure 17(a), the horizontal axis represents position, the vertical axis represents beam radius, the dotted line represents the analytical beam radius, and the plotted figures represent experimental results. Figure 17(a) shows the beam radius obtained when processing is performed to remove the waveform portion -Δt < t < +Δt, and it is in close agreement with the analytical beam radius, indicating that this method is effective. On the other hand, Figure 17(b) shows the results when processing is not performed to remove the waveform portion -Δt < t < +Δt, and the plot near position "0" deviates from the analytical beam radius represented by the dotted line. Thus, the effectiveness of the method according to the first embodiment was confirmed.

[0049] [Modification 1 of Embodiment 1] In the first embodiment, an example was shown in which a SUS304 wire is used as the scatterer. However, as long as the cross-section of the wire in the plane stretched between the direction of laser light propagation (Z-axis direction) and the scanning direction of the wire (X-axis direction) is circular, wires of various materials can be used.

[0050] Figure 18 shows the relationship between beam diameter / wire diameter and beam radius, obtained by simulating the scanning of unpolarized laser light (wavelength 633 nm) with various beam diameters using graphite (circles), blackened stainless steel (Fe3O4) (X marks), SUS304 (triangle marks), and Au (square marks) wires with a diameter of 100 μm. The laser light is single-mode. For reference, the convolution results using a rectangular window function with a reflectivity of 1 across the entire width are also shown with a + mark.

[0051] Similar to Figure 13, in Figure 18, the dotted line represents the wire radius and is independent of the beam diameter / wire diameter ratio, while the solid line represents the relationship between the beam diameter / wire diameter and the radius of the laser beam being measured, and is a straight line sloping upwards to the right. In Figure 18, for all materials and even when using a rectangular window function with a reflectivity of 1 across the entire width, the data is plotted along the solid line. This indicates that the beam diameter can be measured even when the beam diameter is small, without being limited by the wire diameter. Although only unpolarized laser light is shown, similar results were obtained for P-polarized and S-polarized laser light.

[0052] [Modification 2 of Embodiment 1] In the first embodiment, an example of a configuration in which the wire 310 is translated by the mechanism 300 was shown, but the wire 310 may be rotated to scan the laser beam 11. Alternatively, the laser beam 11 may be scanned by vibrating the wire 310.

[0053] In either case, if the velocity v of the wire 310 is known, then Δt = r e Since / v can be calculated, the removal process described above can be performed on the time waveform of the detected reflected light.

[0054] [Modification 3 of Embodiment 1] Above, we described the case where the cross-section of the wire in the plane stretched between the direction of laser light propagation (Z-axis direction) and the scanning direction of the wire (X-axis direction), that is, the case in which a cylindrical wire is used as the scatterer. However, the scatterer is not limited to a cylindrical wire.

[0055] Specifically, since the symmetry of the time waveform, which is the result of detecting reflected light, is utilized, it is sufficient that the XZ cross-section is symmetrical with respect to the direction of laser beam propagation (Z-axis direction). More precisely, it is sufficient that the edge on the side struck by the laser beam is symmetrical. In addition, shapes such as those described later may be adopted to improve the mechanical strength of the wire and to obtain more appropriate reflectivity characteristics.

[0056] Furthermore, by utilizing the ultimate characteristic of Fresnel reflection on the surface of a scattering material, that is, the characteristic that any optical material has a reflectivity of 1 at an incident angle of 90°, if a pulsed reflectivity characteristic approximating a discrete-time unit impulse signal can be obtained, it becomes possible to handle not only single-mode but also multi-mode laser light. Therefore, the incident angle θ that is closest to an incident angle of 90° and has the minimum reflectivity other than an incident angle of 0° is determined. Rmin Let's focus on that.

[0057] For example, in the case of graphite, the relationship between the incident angle θ [°] and reflectance for laser light with a wavelength of 633 nm is as shown in Figure 19. In Figure 19, the dashed line represents the reflectance R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows the change. In the case of graphite, for unpolarized and S-polarized light, the reflectivity follows a curve where it decreases from an incident angle of 90° to 0°, but for P-polarized light, although the reflectivity decreases from an incident angle of 90°, it reaches its lowest point (almost 0) at an incident angle of 56.3°, and then at smaller incident angles, the reflectivity is higher than that lowest point. Thus, when the reflectivity is lowest at a specific angle rather than an incident angle of 0°, the incident angle θ at which the reflectivity is lowest is determined. Rmin This can be utilized.

[0058] Furthermore, for a stainless steel (Fe3O4) wire that has undergone blackening treatment, the relationship between the incident angle θ [°] and reflectance for laser light with a wavelength of 633 nm is as shown in Figure 20. In Figure 20, the dashed line also represents the reflectance R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. aveThis shows the changes. For blackened stainless steel (Fe3O4), the reflectivity curve decreases from 90° to 0° of incidence for unpolarized and S-polarized light, but for P-polarized light, although the reflectivity decreases from 90° of incidence, it reaches its lowest point (almost 0) at 67° of incidence, and then becomes higher than that lowest point at smaller angles of incidence. Furthermore, the reflectivity near 0° of incidence is higher than that of graphite, and in the case of S-polarized light, the rate of decrease in reflectivity from 90° to 0° of incidence becomes gentler.

[0059] Furthermore, for a wire made of SUS304, a type of stainless steel, the relationship between the incident angle θ [°] and reflectance for laser light with a wavelength of 633 nm is as shown in Figure 21. In Figure 21, the dashed line represents the reflectance R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows the change. For SUS304, the reflectivity for S-polarized light follows a curve where it decreases from an incident angle of 90° to 0°, but for unpolarized and P-polarized light, the reflectivity decreases from an incident angle of 90°, but it shows a minimum reflectivity at a specific incident angle, and at smaller incident angles, the reflectivity is higher than that minimum reflectivity. Since the reflectivity for P-polarized light is lower than for unpolarized light, the incident angle at which the reflectivity for P-polarized light is minimum is θ. Rmin Here, the angle is approximately 77°. Furthermore, the reflectance near the incident angle of 0° is higher than that of blackened stainless steel (Fe3O4), and the reflectance is generally higher for both unpolarized and S-polarized light.

[0060] Furthermore, for an Au wire, the relationship between the incident angle θ [°] and reflectance for a laser beam with a wavelength of 633 nm is as shown in Figure 22. In Figure 22, the dashed line represents the reflectance R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. aveThis shows the changes. For Au, the reflectivity is generally high, and the reflectivity does not change much even when the angle of incidence changes. For unpolarized and S-polarized light, the reflectivity follows a curve where it decreases from an angle of incidence of 90° to 0°, but for P-polarized light, the reflectivity decreases from an angle of incidence of 90°, but once it reaches a minimum at a specific angle of incidence, the reflectivity is higher than that minimum at angles of incidence smaller than that. Therefore, the angle of incidence at which the reflectivity is minimum for P-polarized light is θ. Rmin Here, the angle is approximately 72°.

[0061] Next, Figure 23 shows an example of an elliptical wire cross-sectional shape that can be used in the first embodiment. By making the cross-sectional shape thicker than that of a wire with a circular cross-section, the mechanical strength can be increased and deflection and deformation during scanning can be suppressed. In Figure 23, the cross-sectional shape of the wire is shown in the XZ plane, with the scanning direction as the X axis and the laser beam incidence direction as the Z axis. In this example, the cross-section has a radius r e The arc of the circle appears at the right and left ends, and half the length of the major axis of the ellipse is r. e It is +L. Also, the incident angle θ is the one where the reflectivity is minimal. Rmin The length in the X-axis direction Δx is as follows: Rmin This is also shown. This length Δx Rmin The shorter the angle of incidence, the smaller the range near 90° (for example, θ). Rmin Sharp, pulsed reflectivity characteristics can be obtained in the range of 90° or less.

[0062] When measuring using a wire with such an elliptical cross-section, Δt = (r e The formula becomes (+L) / v, where v is the wire's speed.

[0063] As is the case with the other cross-sectional shapes shown below, the laser beam only hits the edge of the part above the dashed line, so it is sufficient that only the upper part of the edge is symmetrical with respect to the axis of symmetry.

[0064] Furthermore, if there are many areas with high reflectivity outside the vicinity of the incident angle of 90°, the effect may become significant, so a shape like the one shown in Figure 24 can also be considered. That is, as shown in Figure 24, the cross-section of the wire may be shaped like a rectangle connecting the semicircles at both ends. In Figure 24, the scanning direction is the X-axis and the direction of incidence of the laser light is the Z-axis, and the cross-sectional shape of the wire is shown in the XZ plane. In this example, in the cross-section, the radius r e Semicircles appear at the right and left ends, with a height of 2r. e A rectangle with a length of 2L is connected to it. It is preferable to apply an anti-reflection coating (i.e., AR (Anti-Reflection) coating) to at least the 2L portion of the rectangle that is struck by the laser light. This cross-sectional shape will be referred to as oval.

[0065] Even when measuring using a wire with a cross-section of this shape, Δt = (r e It becomes (+L) / v.

[0066] Figure 25 shows an improved oval cross-sectional shape, which is the same as the cross-sectional shape shown in Figure 24. In Figure 25, the scanning direction is the X-axis and the laser beam incidence direction is the Z-axis, showing the cross-sectional shape of the wire in the XZ plane. The cross-sectional shape shown in Figure 25 is for when the laser beam incidence angle is 0° and θ Rmin The shape is deformed so that the angle is 90° or less. Specifically, in Figure 24, the wire has a cross-section that is a rectangle with length 2L and radius r. e It had a shape with semicircles connected at both ends, but the plane where the angle of incidence of the laser light is 0° was of length r e × (1 - cosθ) Rmin By machining by ) in the Z-axis direction, the length at which the incident angle of the laser beam becomes 0° is 2L + 2r e ×sinθ Rmin This is the case. Furthermore, the angle of incidence θ Rmin The length in the X-axis direction Δx is greater than or equal to 90°. Rmin is, r e × (1 - sinθ) Rmin This results in the following cross-sectional shape, which we will refer to as a flat oval.

[0067] With this cross-sectional shape, the incident angle θ is from the plane where the incident angle of the laser beam is 0°. Rmin Since the portion of the cross-section that is 90° or less will be affected by the laser beam striking the arc-shaped surface, if an optical reflection reduction process is applied to the surface where the incident angle of the laser beam is 0°, a sharp, pulsed reflectivity characteristic can be obtained in the range near the incident angle of 90°.

[0068] Even when measuring using a wire with such a cross-sectional shape, Δt = (r e It becomes (+L) / v.

[0069] Alternatively, a wire having a cross-sectional shape as shown in Figure 26 may be used. In Figure 26, the scanning direction is the X-axis and the direction of incidence of the laser beam is the Z-axis, and the cross-sectional shape of the wire in the XZ plane is shown. The cross-sectional shape shown in Figure 26 is roughly triangular, but circular arcs appear at the left and right ends. The hypotenuse of the triangle is the angle of incidence of the laser beam at θ. Rmin It is set up so that the angle between the axis of symmetry and the hypotenuse is 90° - θ Rmin And the angle of incidence of the arc portion is θ. Rmin The angle is limited to 90° or less. The radius of the circle is r. e That is the case.

[0070] Furthermore, the width Δx of the front end portion where reflected light from the laser beam 11 is generated. Rmin is, r e (1 - sinθ) Rmin ) becomes. width Δx Rmin is the radius r e Shortening the value results in a small value, and θ is in the range where reflectance is high. Rmin ≦Incidence angle θ in Width Δx in the X-axis direction for which the angle is ≤90° Rmin Because the field narrows, a sharp, pulsed reflectivity characteristic can be obtained.

[0071] Even when measuring using a wire with such a triangular cross-section, Δt = (r e It becomes (+L) / v.

[0072] Here, as shown in Fig. 25, the reflectance characteristics of a graphite wire with a flat oval cross-section are shown in Fig. 27. Note that for the part with an incident angle of 0°, it is the reflectance characteristics when reflectance reduction processing is performed. In Fig. 27, the horizontal axis represents the incident position of the laser beam, and the vertical axis represents the reflectance. Also, the dashed-dotted line indicates the change in the reflectance R p for P-polarized light, the dotted line indicates the change in the reflectance R s for S-polarized light, and the solid line indicates the change in the reflectance R ave for unpolarized light. Here, the sharp pulse-like reflectance characteristics mean that when the incident angle of the laser beam on the surface of the scatterer is 90°, the reflectance peaks, and in the vicinity of 90°, the reflectance decreases by a predetermined ratio (for example, 0.85 (= 85%)), and outside the vicinity range of 90°, the reflectance is suppressed within (1 - the predetermined ratio) (for example, 0.15 (= 15%)). It is preferable that this is the case.

[0073] In Fig. 27, for the portions of length L + r e ×sinθ Rmin on the right and left sides of the symmetry axis, the reflectance is suppressed to 0 by the reflectance reduction processing, and for the width Δx Rmin corresponding to the arc portion, the reflectance characteristics with an incident angle of θ Rmin or more appear in Fig. 19. Such reflectance characteristics show that the reflectance is reduced by 85% or more (here 100%) from an incident angle of 90° to its vicinity range, and the reflectance is also suppressed to 15% or less (here 0%) outside the vicinity range. Therefore, it can be said that it is a pulse-like reflectance characteristic similar to a discrete-time unit impulse signal that can also be used in the second embodiment.

[0074] ​​​​​​​​​Thus, the lengths L+r on the right and left sides of the axis of symmetry are as follows: e ×sinθ Rmin Regarding the part, θ Rmin The reflectivity is suppressed to the width Δx corresponding to the arc portion. Rmin Regarding this, in Figure 19, the angle of incidence θ Rmin The above reflectivity characteristics are observed. Such reflectivity characteristics show that the reflectivity is reduced by more than 85% in the range from the incident angle of 90° to its vicinity, and even outside this range, the reflectivity is suppressed to 15% or less. Therefore, it can be said that these are pulse-like reflectivity characteristics similar to a discrete-time unit impulse signal, which can also be used in the second embodiment.

[0076] Furthermore, Figure 29 shows the reflectivity characteristics of a stainless steel (Fe3O4) wire that has been processed into a flat oval cross-section and blackened, as shown in Figure 25. Note that the portion with an incident angle of 0° represents the reflectivity characteristics when reflection reduction processing has been performed. In Figure 29, the horizontal axis represents the incident position of the laser beam, and the vertical axis represents the reflectivity. The dashed line represents the reflectivity R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows a change.

[0077] Thus, the lengths L+r on the right and left sides of the axis of symmetry are as follows: e ×sinθ Rmin In this section, the reflectivity is suppressed to 0 by reflection reduction processing, and the width Δx corresponds to the arc portion. Rmin Regarding this, in Figure 20, the angle of incidence θ Rmin The above reflectivity characteristics are observed. Furthermore, Δx is compared to a graphite wire. Rmin The width can be shortened. Such reflectivity characteristics show that the reflectivity is reduced by 85% or more (100% in this case) from the incident angle of 90° and in the vicinity of it, and even outside the vicinity, the reflectivity is suppressed to 15% or less (0% in this case). Therefore, it can be said that this is a pulsed reflectivity characteristic similar to a discrete-time unit impulse signal, which can also be used in the second embodiment.

[0078] Furthermore, Figure 30 shows the reflectivity characteristics of a stainless steel (Fe3O4) wire that has been processed into a triangular cross-section and blackened, as shown in Figure 26. In Figure 30, the horizontal axis represents the incident position of the laser beam, and the vertical axis represents the reflectivity. The dashed line represents the reflectivity R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows a change.

[0079] Thus, the lengths L+r on the right and left sides of the axis of symmetry are as follows: e ×sinθ Rmin Regarding the part, θ Rmin The reflectivity is suppressed to the width Δx corresponding to the arc portion. Rmin Regarding this, in Figure 20, the angle of incidence θ Rmin The above reflectivity characteristics are observed. As can be seen from Figure 30, for P-polarized light, the reflectivity is reduced by more than 85% (100% in this case) in the range from the incident angle of 90° to its vicinity, and even outside this range, the reflectivity is suppressed to 15% or less (0% in this case). Therefore, it can be said that this is a pulsed reflectivity characteristic similar to a discrete-time unit impulse signal, which can also be used in the second embodiment.

[0080] Furthermore, Figure 31 shows the reflectivity characteristics of a SUS304 wire with a triangular cross-section, as shown in Figure 26. In Figure 31, the horizontal axis represents the incident position of the laser beam, and the vertical axis represents the reflectivity. The dashed line represents the reflectivity R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows a change.

[0081] Thus, the lengths L+r on the right and left sides of the axis of symmetry are as follows: e ×sinθ Rmin Regarding the part, θ Rmin The reflectivity is suppressed to the width Δx corresponding to the arc portion. Rmin Regarding this, in Figure 21, the angle of incidence θ Rmin The above reflectivity characteristics are observed. Note that ΔxRmin This can be made shorter than a stainless steel wire that has been treated with blackening. However, as can be seen from Figure 31, the reflectivity characteristics for any of the polarizations cannot be said to be pulse-like, similar to a discrete-time unit impulse signal.

[0082] Furthermore, Figure 32 shows the reflectivity characteristics of an Au wire processed into a triangular cross-section, as shown in Figure 26. In Figure 32, the horizontal axis represents the incident position of the laser light, and the vertical axis represents the reflectivity. The dashed line represents the reflectivity R for P-polarized light. p This shows the change, and the dotted line represents the reflectance R for S-polarized light. s This shows the change, and the solid line represents the unpolarized reflectance R. ave This shows a change.

[0083] Thus, the lengths L+r on the right and left sides of the axis of symmetry are as follows: e ×sinθ Rmin Regarding the part, θ Rmin The reflectivity is suppressed to the width Δx corresponding to the arc portion. Rmin Regarding this, in Figure 22, the angle of incidence θ Rmin The above reflectivity characteristics are observed. Note that Δx Rmin This can be made shorter than a stainless steel wire that has been treated with blackening. However, as can be seen from Figure 32, the pulsed reflectivity characteristics of any of the polarizations cannot be said to be similar to a discrete-time unit impulse signal.

[0084] Even with a wire having the cross-sectional shape described above, the beam profile can be measured accurately regardless of the size of the scatterer, as explained in the first embodiment.

[0085] Furthermore, even if a single-mode laser beam does not have pulsed reflectivity characteristics that approximate a discrete-time unit impulse signal, its beam profile can be measured accurately regardless of the size of the scatterer.

[0086] [Embodiment 2] As described above, the ideal window function is the delta function, and as a physical scatterer, it is preferable to have a height of 1 and an infinitesimally small width, exhibiting pulsed reflectivity characteristics that approximate a unit impulse signal in a discrete-time system. In the second embodiment, the limiting characteristic of Fresnel reflection on the surface of the scatterer, that is, the characteristic that any optical material has a reflectivity of 1 at an incident angle of 90°, is utilized to make use of a scatterer that exhibits pulsed (i.e., steeply convex) reflectivity characteristics that approximate a unit impulse signal around an incident angle of 90°.

[0087] In other words, a scattering material having pulsed reflectivity characteristics that peak at an incident angle of 90° of laser light on the surface is preferred. To put it another way, a scattering material having pulsed reflectivity characteristics such that the reflectivity peaks at an incident angle of 90° of laser light on the surface and decreases sharply (i.e., rapidly) as the incident angle moves away from 90° is preferred.

[0088] More specifically, a scattering material having pulsed reflectivity characteristics is preferred, such that the reflectivity peaks at an incident angle of 90° of laser light to the surface, and decreases by a predetermined percentage (e.g., 0.85 (=85%)) or more in the vicinity of 90°. Here, the vicinity range is, for example, an angle θ other than the incident angle of 0° that is closest to 90° and where the reflectivity is minimal. Rmin This is within the range up to 90°. Furthermore, it is preferable that the reflectance is suppressed to within (1 - predetermined percentage) (for example, 0.15 (=15%)) in ranges other than the vicinity of 90°.

[0089] From another perspective, a linear scatterer is preferred, which has a first surface portion on which the laser beam is irradiated, where the incident angle of the laser beam is within the range of 90° and near 90°, and the reflectivity decreases by a first predetermined percentage (for example, 0.85 = (85%)) or more from the peak, and a second surface portion other than the first surface portion, where the reflectivity to the laser beam is suppressed to a second predetermined percentage (for example, (1 - first predetermined percentage) = 15%) or less.

[0090] The preferred scatterer is not limited to a specific material, but may be a material that exhibits pulsed reflectivity characteristics approximating a unit impulse signal at an incident angle of around 90°, or a material that has been processed to exhibit such reflectivity characteristics. Specific examples are shown below.

[0091] Figure 33(a) shows the relationship between the incident position (X / r) and reflectance when a graphite wire with a circular cross-section of radius r is used. In Figure 33(a), as in Figures 4(a) and (b), the dashed line represents the reflectance R of P-polarized laser light. p The dotted line represents the reflectance R of S-polarized laser light. s This represents the reflectance R of unpolarized laser light, with the solid line showing the reflectance R. ave This represents the following: In the case of graphite, the reflectivity distribution differs slightly depending on the polarization, but the reflectivity is 1 at both ends of the wire (at the incident position ±1), and the reflectivity decreases sharply as you move away from the ends of the wire towards the center. Also, although it differs slightly depending on the polarization, the reflectivity is not completely 0 except near the ends of the wire, but it is sufficiently low.

[0092] In the case of P-polarized light, the reflectivity initially becomes almost zero as you move away from both ends of the wire, but then slightly increases as you move further towards the center. In the case of S-polarized light, the reflectivity continues to decrease as you move away from both ends of the wire, reaching a minimum value at the center of the wire (X / r = 0). In the case of unpolarized light, an intermediate reflectivity between P-polarized and S-polarized light is obtained.

[0093] Unlike the characteristics of the Au wire and SUS304 wire shown in Figures 4(a) and 5(a), the graphite wire exhibits pulsed reflectivity characteristics near both ends that approximate a unit impulse signal.

[0094] Figure 33(b) shows the reflection angle distribution of reflectance when a graphite wire is used. As can be seen from Figure 33(b), a reflection angle of ±180° corresponds to an incident angle of ±90°, and the reflectance is 1 at a reflection angle of ±180°. It can also be seen that, although it differs slightly depending on the polarization, the reflectance decreases sharply when moving to the left or right of a reflection angle of ±180°.

[0095] Figure 34 again shows the relationship between the incident position (X / r) and reflectance when a graphite wire is used, but for P-polarized light, the incident position ±x Rmin The reflectivity is almost zero at / r. This occurs at the incident position ±x Rmin / r is the incident position where the reflectivity is minimal, being closest to the incident position ±1 among P-polarized, S-polarized, and unpolarized light. Here, x is located near the incident position 1. Rmin The neighboring range Δx up to / r Rmin Let / r. In the case of graphite, the neighboring range Δx Rmin At / r, the reflectance is 0.15 even for S-polarized light, and it decreases by 85% from the incident position ±1, in the nearby range Δx Rmin Outside the range of / r, the reflectivity is kept within the range of 0 to 0.15 or less. Note that the incident position x Rmin / r is the angle of incidence θ Rmin Corresponding to the neighborhood range Δx Rmin If we express / r as an angle, then θ Rmin This means it's between 56.3° and 90°.

[0096] Next, as schematically shown in Figure 35, we simulated the signal waveform detected when a laser beam with a Gaussian distribution of laser light intensity in its cross-section is scanned at a constant speed using a graphite wire with a circular cross-section, by varying the laser beam diameter 2ω. The wire diameter was fixed at 100 μm.

[0097] Figure 36 shows the signal waveforms (in this case, time waveforms) obtained when a P-polarized laser beam is irradiated for beam diameter:wire diameter ratios of 1:1 (thin dotted line), 1:2 (dotted line), 1:5 (single dashed line), 1:10 (long dotted line), 1:20 (double dashed line), and solid line (1:100). In Figure 36, the horizontal axis represents arbitrary time [a.u. (Arbitrary Unit)], and the vertical axis represents signal intensity [a.u.].

[0098] As can be seen in Figure 36, regardless of the beam diameter:wire diameter values, a waveform with approximately three peaks is obtained. The peaks other than the one in the central part at time "0" are due to reflections at the incident angle of 90° and its vicinity, corresponding to both ends of the wire. The peak in the central part at time "0" is a peak that occurs because the reflectivity is not zero at an incident angle of 0°.

[0099] Figure 37 shows the signal waveforms obtained for various beam diameter:wire diameter variations shown in Figure 36 when S-polarized laser light is irradiated. In Figure 37, the horizontal axis also represents an arbitrary time [a.u.], and the vertical axis represents the signal intensity [a.u.].

[0100] As can be seen in Figure 37, regardless of the beam diameter:wire diameter values, a waveform with two peaks is obtained, which are peaks due to reflections at the incident angle of 90° and its vicinity, corresponding to both ends of the wire.

[0101] Figure 38 shows the signal waveforms obtained for various beam diameter:wire diameter variations shown in Figure 36 when unpolarized laser light is irradiated. In Figure 38, the horizontal axis also represents an arbitrary time [a.u.], and the vertical axis represents the signal intensity [a.u.].

[0102] As can be seen in Figure 38, regardless of the beam diameter:wire diameter values, a waveform with two peaks is obtained, which are peaks due to reflections at the incident angle of 90° and its vicinity, corresponding to both ends of the wire.

[0103] By utilizing the extreme characteristics of Fresnel reflection in this way, it was found that even with a laser beam having a beam diameter of 1 / 100th of the wire diameter, scanning the laser beam with a scatterer having the reflectivity characteristics described above makes it possible to obtain a time waveform that exhibits the characteristics of the beam profile.

[0104] However, if a wire with a circular cross-section is used, two peaks are generated at the front and back ends of the wire in each scan, and the coexistence of these two peaks becomes a limiting factor in resolution.

[0105] In this embodiment, the cross-section of the linear scatterer is circular, and the reflected light from the scatterer is detected using an integrating sphere with a distribution of reflectivity on its inner wall.

[0106] The outline of the measurement system according to the second embodiment is the same as that shown in Figure 14 in the first embodiment. However, the wire 310 is a scatterer having the desirable reflectivity characteristics described above, and there are differences in the reflectivity distribution of the inner wall of the integrating sphere 200 and the data processing of the information processing device 600. These points will be explained below.

[0107] For example, if wire 310 is made of graphite, the reflectance angle distribution will be as shown in Figure 33(b). With a graphite wire, the reflectance attenuates quickly when moving to the right or left of the reflection angle ±180°, which corresponds to the incident angle ±90°. Therefore, as shown in gray in Figure 39, if the reflected light from the reflection angle 0° to -180° (excluding -180°) can be masked, the photodetector 400 can detect pulsed reflected light having only one peak occurring near the front or rear end of wire 310.

[0108] Specifically, as schematically shown in Figure 40, the cross-section of the integrating sphere 200 is made black on the inner surface 260 of the left hemisphere of the integrating sphere 200 to absorb or severely attenuate the reflected light so that the reflected light cannot be detected by the photodetector 400. On the other hand, the inner surface 250 of the right hemisphere of the integrating sphere 200 is made to reflect and scatter the reflected light 13 so that the reflected light 13 can be detected by the photodetector 400. The left and right hemispheres may also be reversed.

[0109] Furthermore, to further reduce unwanted reflected light, a portion of the inner surface of the right hemisphere may also be made to absorb reflected light. For example, at a reflection angle of 0°, the angle 2θ at which the reflectance of P-polarized light becomes 0. Rmin You can also set it to black out up to (for example, 112.6°).

[0110] By using such an integrating sphere 200, it becomes possible to obtain only one of the peaks at either end of the time waveform of the reflected light shown in Figures 36 to 38.

[0111] When forming wires from materials other than graphite, it may be preferable to adjust the area to be blackened according to the characteristics of that material.

[0112] In the first embodiment, a process was performed to remove the waveform portion included in the range -Δt < t < +Δt, but in this embodiment, the removal process is omitted by using a wire 310 which is a scatterer having the desirable reflectivity characteristics described above. That is, as shown in Figure 12, the information processing device 600 has a height of 1 / e when the peak height is 1. 2 The time width t is (in some cases 1 / 2). w The beam width 2ω is calculated using the following formula, where v is the speed of movement of the wire 310. 2ω = t w ×v

[0113] In the first embodiment, the mechanism 300 was shown as one that translates the wire 310, and the same is true in this embodiment.

[0114] In addition, since the area of ​​a single pulsed waveform shown in Figure 12 is proportional to the power of the laser light 11, the laser power can also be determined by calculating the area of ​​a single pulsed waveform.

[0115] Alternatively, an information processing device 600 equipped with the functions of an oscilloscope 500 may be used. Furthermore, the time width t w For example, the pulsed waveform may be approximated by a Gaussian function using the least squares method before calculation.

[0116] [Modification 1 of Embodiment 2] Above, the mechanism 300 was mainly described in a configuration in which the wire 310 is translated. However, it may also be configured to rotate or reciprocate in addition to translation.

[0117] First, an example configuration in which the mechanism 300 rotates the wire 310 will be explained using Figure 41. Figure 41 is a top view of the inside of the integrating sphere 200. As shown in Figure 41, the wire 310 is installed perpendicular to the rotation axis 301 of the mechanism 300, and in accordance with the rotation of the rotation axis 301, the wire 310 moves in single mode (TEM) from top to bottom of the paper. 00 The cross-section 11c of the laser beam 11 is scanned. Here, the distance between the center of the rotation axis 301 and the center of the cross-section 11c of the laser beam 11 is R, and the circumference of a circle with radius R is 2πR.

[0118] When the wire 310 is rotated in this manner, the reflected light detected by the photodetector 400 is observed on the oscilloscope 500 to produce a time waveform as shown in Figure 42. As schematically shown in Figure 42, a pulse-like waveform is generated periodically in accordance with the rotation of the wire 310. The period of the pulse is t i Assuming the pulse height is 1, the height is 1 / e 2 The time interval that becomes (in some cases 1 / 2) is t w Let's assume that.

[0119] Then, the beam width 2ω is calculated using the following formula: 2ω = t w ×v v = 2πR / t i

[0120] period t i and time width t w Once the measurement is taken, the information processing device 600 calculates and outputs the beam diameter according to the above formula.

[0121] Furthermore, since a pulse-like waveform is periodically generated in the light intensity, the period t i and time width t w For this, it is also acceptable to calculate the average value and use that value.

[0122] Next, an example of a configuration in which the mechanism 300 causes the wire 310 to reciprocate will be explained using Figure 43. Figure 43 is also a top view of the inside of the integrating sphere 200. As shown in Figure 43, the mechanism 300 holds one end of the wire 310 (also called the fixed end), and causes the other end of the wire 310 (also called the free end) to reciprocate at an oscillation frequency f and a deflection angle 2γ, so as to periodically scan the cross-section 11c of the laser beam 11 that is traveling from the top of the paper downwards. This reciprocating motion is achieved by providing the mechanism 300 with a mechanism that oscillates periodically in response to signals from a quartz crystal oscillator or piezoelectric element.

[0123] Even when the wire 310 is moved back and forth in this manner, a time waveform like the one shown in Figure 42 can be obtained. Note that the pulse period t i This becomes 1 / f / 2.

[0124] Then, the beam width 2ω can be calculated using, for example, the following formula: 2ω = t w ×v v=πRγ / 90 / t i

[0125] period t i and time width t w Once the measurement is taken, the information processing device 600 calculates and outputs the beam diameter according to the above formula.

[0126] [Modification 2 of Embodiment 2] In the second embodiment, the reflectivity was distributed on the inner wall of the integrating sphere 200 so that only one of the peaks at both ends of the time waveform of the reflected light, as shown in Figures 36 to 38, could be detected.

[0127] However, the method shown in the first embodiment may be used as a means to detect only one of the peaks at both ends that occur in the time waveform of the reflected light. That is, instead of having a distribution of reflectivity on the inner wall of the integrating sphere 200, a method is employed in which the entire inner wall reflects the reflected light from the scatterer. The information processing device 600 also performs the waveform removal process for -Δt < t < +Δt described in the first embodiment.

[0128] Furthermore, when the wire 310 is rotated as shown in Figure 41, Δt is expressed as follows.e Δt = r e / v v = 2πR / t i

[0129] Furthermore, when the wire 310 is moved back and forth as shown in Figure 43, Δt is expressed as follows: Δt = r e / v v=πRγ / 90 / t i

[0130] Furthermore, when the wire 310 is translated as shown in Figure 15, Δt is expressed as follows: Δt = r e / v v = movement speed of the translation stage

[0131] [Application Example 1 of Modification 2 of Embodiment 2] In Modification 2 of the second embodiment, single mode (TEM) 00 We have explained the processing of laser light, but here we will describe the multimode (TEM) laser light shown in Figure 44. 10 Let's consider the case where it is applied to laser light. As shown in Figure 44, TEM 10 The mode beam contains two peaks, with a peak spacing Δx of 50 μm. We consider scanning this laser beam with a graphite wire with a diameter of 100 μm. The simulation results are shown below.

[0132] Figure 45(a) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for P-polarized laser light, Figure 45(b) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for S-polarized laser light, and Figure 45(c) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for unpolarized laser light. Position 0 is defined as the position where the central axis of the wire and the central axis of the laser beam 11 intersect. There are two peaks in the laser beam and two peaks in the reflectance.

[0133] When such laser light is scanned with the wire described above, a signal waveform like the one shown in Figure 46 is obtained. Figure 46(a) shows the time waveform detected in the case of P-polarized laser light, Figure 46(b) shows the time waveform detected in the case of S-polarized laser light, and Figure 46(c) shows the time waveform detected in the case of unpolarized laser light. Time 0 is the time when the central axis of the wire and the central axis of the laser light 11 intersect. In this way, it can be seen that in all cases, a time waveform containing four large peaks is obtained for each of the two peaks of the laser light.

[0134] In the second modification of the second embodiment, the time waveform in the range of -Δt < t < +Δt is removed. The method for calculating Δt remains the same even in multimode. The range to be removed in the case of Figure 44 is shown in Figure 47. Figure 47(a) shows the time waveform detected and the gray removal range in the case of P-polarized laser light, Figure 47(b) shows the time waveform detected and the gray removal range in the case of S-polarized laser light, and Figure 47(c) shows the time waveform detected and the gray removal range in the case of unpolarized laser light. In all cases, the range including the two peaks in the central part is removed.

[0135] Figure 48 shows the result of removing the time waveform in the range -Δt < t < +Δt and concatenating the remaining waveform portion. In Figure 48(a), the relationship between signal intensity and position obtained from the shaped time waveform in the case of P-polarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). Similarly, in Figure 48(b), the relationship between signal intensity and position obtained from the shaped time waveform in the case of S-polarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). In Figure 48(c), the relationship between signal intensity and position obtained from the shaped time waveform in the case of unpolarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). In all cases, the signal detected as a time waveform is converted to units of position according to the scanning speed of the wire. Furthermore, in all cases, the peak position obtained from the shaped time waveform matches the peak position of the measured object, and the peak heights are also similar.

[0136] Therefore, TEM 10 Good results can be obtained even when applied to modes.

[0137] [Application Example 2 of Modification 2 of Embodiment 2] In the above application example 1, TEM having two peaks 10 An example of application to modes is shown, but TEM has three peaks. 20 Let's consider the case where Modification 2 of the second embodiment is applied to the laser light of the mode. As shown in Figure 49, TEM 20 The beam of the mode contains three peaks, with a peak spacing Δx of 50 μm. We consider scanning this laser beam with a graphite wire with a diameter of 100 μm. The simulation results are shown below.

[0138] Figure 50(a) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for P-polarized laser light, Figure 50(b) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for S-polarized laser light, and Figure 50(c) shows the relationship between signal intensity and position and the relationship between wire reflectance and position (window function shape) for unpolarized laser light. Position 0 is defined as the position where the central axis of the wire and the central axis of the laser beam 11 intersect. There are three peaks in the laser beam and two peaks in the window function.

[0139] When such laser light is scanned with the wire described above, a signal waveform like the one shown in Figure 51 is obtained. Figure 51(a) shows the time waveform detected in the case of P-polarized laser light, Figure 51(b) shows the time waveform detected in the case of S-polarized laser light, and Figure 51(c) shows the time waveform detected in the case of unpolarized laser light. Time 0 is the time when the central axis of the wire and the central axis of the laser light 11 intersect. In this way, it can be seen that in all cases, a time waveform containing six large peaks is obtained for each of the three peaks of the laser light.

[0140] TEM 20 In this mode, as in the second embodiment, the time waveform in the range of -Δt < t < +Δt is removed. The method for calculating Δt remains the same in this mode as well. The range to be removed in the case of Figure 34 is shown in Figure 52. Figure 52(a) shows the time waveform detected and the gray removal range in the case of P-polarized laser light, Figure 52(b) shows the time waveform detected and the gray removal range in the case of S-polarized laser light, and Figure 52(c) shows the time waveform detected and the gray removal range in the case of unpolarized laser light. In all cases, the range including the two peaks in the central part and half of the second peak from each end is removed.

[0141] For example, Figure 53 shows the result of removing the time waveform in the range -Δt < t < +Δt and concatenating the remaining waveform portion. In Figure 53(a), the relationship between signal intensity and position obtained from the shaped time waveform in the case of P-polarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). Similarly, in Figure 53(b), the relationship between signal intensity and position obtained from the shaped time waveform in the case of S-polarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). In Figure 53(c), the relationship between signal intensity and position obtained from the shaped time waveform in the case of unpolarized laser light is represented by a solid line (detection signal), and the relationship between the signal intensity and position of the original laser light is represented by a dotted line (measurement target). In all cases, the signal detected as a time waveform is converted to units of position according to the scanning speed of the wire. Furthermore, in all cases, the peak position obtained from the shaped time waveform matches the peak position of the measured object, and the peak heights are also similar.

[0142] Therefore, TEM 20 Good results can be obtained even when applied to modes.

[0143] [Modification 3 of Embodiment 2] In the second embodiment, an integrating sphere with a distributed reflectivity on its inner wall was used to limit the reflected light from the scatterer detected by the photodetector 400, thereby obtaining a time waveform with a single peak. This is because a scatterer with a circular cross-section was used. In other words, reflected light is generated at the time when the right or left end of the scatterer begins to come into contact with the laser beam 11, and at the time when the left or right end of the scatterer begins to move away from the laser beam 11.

[0144] In this modified example, the cross-sectional shape of the scattering body is modified so that reflected light is generated only at one of two times: when the edge of the scattering body begins to come into contact with the laser beam 11, or when the edge of the scattering body begins to move away from the laser beam 11. When modifying the cross-sectional shape of the scattering body, as in the first embodiment and Modification 2 of the second embodiment, the inner wall of the integrating sphere may be designed to reflect all light without any distribution of reflectivity.

[0145] Specifically, if the cross-sectional shape of the scatterer is a circle as shown in Figure 8, then it is sufficient to make it a semicircle, either to the right or left of the axis of symmetry. In this case, if the wire is made of graphite, only the right or left characteristic of the reflectivity characteristics shown in Figure 34 will be present, so that a time waveform with only one peak can be obtained for each time the laser beam is scanned by the wire.

[0146] Furthermore, when the cross-sectional shape is semicircular, it is preferable to slightly tilt the upper part of the wire 310b to the left, for example, as shown in Figure 54, in order to avoid the laser beam hitting the straight portion corresponding to the diameter of the semicircle at an incident angle of approximately 90°.

[0147] Furthermore, the cross-section does not have to be a semicircle. For example, as shown in Figure 55, a wire 310c with a sector-shaped cross-section smaller than a semicircle may be used. In this case as well, in order to avoid the laser beam 11 hitting the straight portion of the cross-section other than the arc at an incident angle of approximately 90°, it is preferable to scan the laser beam in such an arrangement that the arc portion of the cross-section hides the straight portion from the laser beam, as shown in Figure 55.

[0148] Furthermore, the cross-section may have other shapes, particularly those that include an arc in part of the cross-section, especially at the ends. Specifically, the cross-sectional shapes of each wire shown in Figures 23 to 26 may be further cut along the axis of symmetry.

[0149] As also mentioned in Figures 23 to 26, the area irradiated with laser light is affected by the reflected light, but the area not irradiated with laser light may be deformed into various shapes considering strength and manufacturing considerations.

[0150] As mentioned in the cases where the cross-sectional shape is semicircular or sectoral, when the cross-section is cut along the axis of symmetry, if the laser beam is incident on the cut surface at an incident angle of 90°, the reflected light from that cut surface will also be detected, so it is preferable to avoid this. For this reason, for example, in the case of the triangular cross-section shown in Figure 26, it is possible to consider using the cross-sectional shape shown in Figure 56.

[0151] Figure 56 shows an XZ cross-section, where the wire 310d scans the laser beam 11 in the X-axis direction. The outer edge of the cross-section of this wire 310d is composed of a straight line jk, a circular arc km, a straight line mn, and a straight line nj.

[0152] When compared to the right side of the axis of symmetry in the cross-sectional shape shown in Figure 26, the straight line jk and the circular arc km are the same, but the straight line mn and the straight line nj are different. That is, the slope of the straight line nj is the angle of incidence θ in In relation to θ in By setting the angle to >90°, unwanted reflections at the rear end of wire 310d can be avoided.

[0153] Note that the line nm does not have to be a straight line, and points n and m may coincide.

[0154] Since a wire is a linear object, a plane is formed by straight lines in the cross-section as shown in the diagram, and a curved surface is formed by arcs.

[0155] [Modification 4 of Embodiment 2] Up to this point, as shown in Figure 14, a configuration has been shown in which laser light 11 is incident into the integrating sphere 200 from the incident port 210 via the focusing lens 110, and information regarding the beam profile is obtained within the integrating sphere 200 using a single wire 310. However, as shown by the dotted line 12 in Figure 14, the beam diameter of the laser light 11 decreases up to the beam waist, and then increases again after the beam waist. With a single wire 310, changes in beam diameter and other information are obtained by repeatedly shifting its scanning position and taking measurements.

[0156] Therefore, in this modified example, by using multiple wires, it is possible to obtain information about the beam profile for each position in the irradiation direction of the laser beam 11.

[0157] A schematic example of the configuration relating to this modified example is shown in Figure 57. In this embodiment as well, the laser light from the omitted light source is focused by the focusing lens 110 to become laser light 11, which is input to the integrating sphere 200 from the input port 210 and output from the output port 220. At this time, as shown by the dotted line 12, the laser light 11 converges within the integrating sphere 200, so the beam diameter decreases, and the beam diameter becomes minimum at the beam waist. After passing the beam waist, the laser light 11 begins to diverge again, and the beam diameter increases.

[0158] The measurement system according to this modified example includes an integrating sphere 200, a spiral wire scanner 320 for scanning the laser beam 11 with a plurality of wires 311 to 318 between an input port 210 and an output port 220, a mechanism 300b for rotating the rod 321 of the spiral wire scanner 320, a photodetector 400 for detecting reflected light from each wire in the integrating sphere 200, an oscilloscope 500 for forming a time waveform of the reflected light detected by the photodetector 400, and an information processing device 600b for generating information regarding the beam profile of the laser beam 11 from the output of the oscilloscope 500.

[0159] The integrating sphere 200 is provided with a reflectivity distribution on its inner wall according to the characteristics of the wires 311 to 318, similar to the second embodiment. However, since reflected light is generated at multiple positions in the Z-axis direction, the range to be masked on the inner wall of the integrating sphere 200 is adjusted.

[0160] The spiral wire scanner 320 has a rod 321 that is arranged parallel to the irradiation direction (Z-axis direction) of the laser beam 11 and serves as the axis of rotation in the rotation by the mechanism 300b, and wires 311 to 318 that are installed perpendicular to the rod 321. The wires 311 to 318 are installed at predetermined intervals from each other in the longitudinal direction of the rod 321. However, as shown in Figure 58, when viewed from above, the wires 311 to 318 are arranged at equal angles such that the angle between them and other adjacent wires is the same with respect to the rod 321 as the center point. That is, the angular spacing between the wires 311 to 318 is 360° / 8 = 45°. In this way, the free ends of the wires 311 to 318 are arranged to form a spiral. However, the number of wires is not limited to 8.

[0161] By rotating the rod 321 around the axis of rotation in this way, information regarding the beam profile can be obtained at eight locations in the irradiation direction of the laser beam 11, as schematically shown in Figure 57.

[0162] More specifically, when the reflected light from wires 311 to 318 detected by the photodetector 400 is viewed on the oscilloscope 500, it produces a time waveform as shown in Figure 59. Since the scan is performed using eight wires 311 to 318, eight pulse-like waveforms are considered as one set, and waveforms are obtained for the number of rotations of the rod 321, with two sets shown in Figure 59. Here, the period of one rotation of the rod 321 is t. i And when the height of the largest peak among the peaks of the pulsed waveform is set to 1, the height 1 / e 2 The intensity was reduced to half (in some cases) over a time interval t. w Measure the time width of the fourth pulsed waveform here, but you can measure the time width of any of the eight pulsed waveforms in the same way.

[0163] Then, the beam width 2ω can be expressed as follows: 2ω = t w ×v v = 2πR / t i

[0164] R is the length from the center of the rod 321 to the center of the laser beam 11. The form of the equation itself is the same as when the wire 310 is rotated in Modification 1 of the second embodiment.

[0165] In the information processing device 600b, the time width t is determined for each pulse-like waveform. w The beam width is calculated using the above formula after measuring the beam width.

[0166] In this embodiment as well, since the area of ​​each pulsed waveform is proportional to the power of the laser light, the area of ​​each pulsed waveform may be calculated, and the power of the laser light may be calculated according to that area.

[0167] Furthermore, when using a wire having a cross-sectional shape as shown in Modification 3 of the second embodiment, the spiral wire scanner 320 may be used with a uniform reflectivity across the entire inner wall of the integrating sphere 200.

[0168] Furthermore, in the first embodiment as well, a spiral wire scanner 320 may be used. In this case, if a time waveform of reflected light as shown in Figure 59 is obtained, the period t of one rotation i After measuring the parameters, a removal process is performed on each peak to remove the values ​​between -Δt < t < +Δt.

[0169] [Modification 5 of Embodiment 2] In Application Example 1 of Modification 2 of the Second Embodiment, an application to multimode was shown, but it is also possible to modify Modification 4 of the Second Embodiment to accommodate multimode.

[0170] Note that the TEM shown in Figure 44 10 Modes and TEM shown in Figure 49 20 In this mode, scanning in one direction is sufficient, so the spiral wire scanner 320 according to modification 4 of the second embodiment can be used.

[0171] On the other hand, TEM as shown in Figure 60 11 Unlike modes where the beams are aligned in one direction, if the beams are aligned in two directions, a single spiral wire scanner 320 cannot handle the situation.

[0172] Therefore, TEM 11In cases where the beams are aligned in two directions, such as in a mode, two spiral wire scanners 320 are used.

[0173] Figure 61 shows a view from the top of the paper of a scene in which laser light 11 is irradiated from the top of the paper downwards. For example, the spiral wire scanner 320 shown in Modification 4 of the second embodiment is used as a scanner in the Y-axis direction, and the rod 321 is rotated clockwise by mechanism 300b. In addition to this, a spiral wire scanner 340 is installed as a scanner in the X-axis direction. The spiral wire scanner 340 includes a rod 331 and wires 341 to 348. The relationship between the rod 331 and wires 341 to 348 is the same as in the spiral wire scanner 320, and another mechanism 300c (not shown) is used to rotate the rod 331 counterclockwise.

[0174] If either wire of the spiral wire scanner 320 and either wire of the spiral wire scanner 340 scan the laser beam 11 simultaneously, the reflected light will overlap. Therefore, the laser beam 11 is scanned alternately. Furthermore, in order to scan in the Y-axis and X-axis directions while their positions on the Z-axis are on the same plane, either wire of the spiral wire scanner 320 and the corresponding wire of the spiral wire scanner 340 are positioned on the same plane on the Z-axis.

[0175] This approach allows us to handle multimode ray emission, where the beams are aligned in two directions.

[0176] This configuration using the spiral wire scanner 340 can also be applied to the first embodiment.

[0177] [Modification 6 of Embodiment 2] Modification 4 of the second embodiment showed an example in which an integrating sphere 200 is used. However, the reflected light from wires 311 to 318 may be detected without using the integrating sphere 200.

[0178] In this modified example, as schematically shown in Figure 62, the integrating sphere 200 and the photodetector 400 are removed, and a semicircular photodetector 410 is used. The semicircular photodetector 410 is positioned to detect reflected light from one end of the wires 311 to 318 when scanning the laser beam 11.

[0179] More specifically, Figure 63 illustrates the case where the laser beam 11 is irradiated from the top of the paper downwards, as seen from the top of the paper.

[0180] As can be seen in Figure 63, a semicircular photodetector 410 is positioned in front of the wires 311 to 318 in the direction of travel, surrounding the cross-section of the laser beam 11. This allows for the detection of reflected light generated at the front ends of the wires 311 to 318. This reflected light is detected as a time waveform having only one peak. By rotating the rod 321, each wire 311 to 318 scans the laser beam 11 in the manner shown in Figure 63. However, since the position on the Z-axis differs for each wire, the shape and position of the semicircular photodetector 410 are adjusted.

[0181] Furthermore, if the goal is to detect reflected light generated at the rear ends of the wires 311 to 318, a semicircular-shaped photodetector 410 can be placed behind the wires 311 to 318 in the direction of travel, so as to surround the cross-section of the laser beam 11.

[0182] [Modification 7 of Embodiment 2] As in Modification 6 of the second embodiment, other methods may be employed to detect the reflected light from the wires 311 to 318 without using the integrating sphere 200.

[0183] In this modified example, as schematically shown in Figure 64, when scanning the laser beam 11, the reflected light generated from the front ends of each of the wires 311 to 318 is reflected by a reflective lens 700 and then detected by a photodetector 420.

[0184] As shown in Figure 64, in order to focus the reflected light from wires 311 to 318 so that it can be detected by a single photodetector 420, the position and shape of the reflective lens 700 are adjusted from the optical path of each reflected light (shown as solid and dotted lines from each wire in Figure 64).

[0185] Alternatively, the system may be modified so that the reflected light generated from the rear ends of the wires 311 to 318 is reflected by the reflective lens 700 and then detected by the photodetector 420. In this case, the position and shape of the reflective lens 700 should be adjusted accordingly.

[0186] [Modification 8 of Embodiment 2] Even when using a single wire 310 as in the second embodiment, the reflected light can be detected as a time waveform having only one peak by using a semi-circular-shaped photodetector 410 or a set of a reflective lens 700 and a photodetector 420, without using an integrating sphere 200 as in Modifications 6 and 7 of the second embodiment.

[0187] [Modification 9 of Embodiment 2] As can be seen from the reflectivity characteristics of the graphite wire shown in Figure 33 and the reflectivity characteristics of wires made of various materials shown in Figures 19 to 22, the way in which reflectivity attenuates from an incident angle of 90°, i.e., the shape of the window function, differs depending on the polarization. Therefore, when the laser light to be measured is polarized in a specific direction, the measurement results will differ depending on the orientation from which the scatterer is crossed.

[0188] When scanning a graphite wire with the laser beam being measured incident on its surface as P-polarized light, there is an angle near the edge of the incident angle of 90° where the reflectivity is minimal. Therefore, the reflectivity characteristics approximated by the unit impulse signal are pulsed. However, outside the incident angle range of 90°, there are areas where the reflectivity increases, and this may affect the reflected light.

[0189] On the other hand, in the case of S-polarized light, the reflectivity does not become minimal at the edge in the vicinity of an incident angle of 90°, and exhibits a broader tail than the reflectivity characteristics of P-polarized light. This broadening of the tail can cause errors in beam diameter measurement.

[0190] Therefore, when the laser light being measured is polarized, the accuracy of beam diameter measurement can be improved by appropriately setting the scanning direction of the wire.

[0191] Therefore, a second mechanism is introduced to change the scanning direction of the laser beam using the wire. Figure 65 shows an example in which a second mechanism 800 is introduced to change the scanning direction of the laser beam using the wire by moving the mechanism 300 that translates the wire 310 shown in Figure 15.

[0192] Figure 65 shows a scenario in which the laser beam 11 is incident on the paper from top to bottom along the Z-axis direction, and a cross-section 11c of the laser beam 11 is shown, with the paper representing the XY plane. In this example, as shown in the magnified view on the right, the polarization direction of the laser beam 11 is parallel to the Y-axis.

[0193] In this state, when the mechanism 300 is positioned at the mechanism 300y position and the wire 310 is translated, the wire 310 is in the direction parallel to the Y axis Y s The laser beam 11 will cross in this direction Y. s This is the scanning direction in which the window function for P-polarization is obtained.

[0194] On the other hand, when mechanism 300 is positioned at mechanism 300x and the wire 310 is translated, the wire 310 is in the direction parallel to the X axis X s The laser beam 11 will cross in this direction X. s This is the scanning direction in which the window function for S-polarization is obtained.

[0195] Thus, if the polarization direction of the laser light 11 to be measured, as measured from the laser light source and the optical system along the way to the wire 310, is known, the position of the mechanism 300 can be changed by the second mechanism 800 to match that polarization direction, thereby achieving a scanning direction that matches the polarization direction.

[0196] On the other hand, if the polarization direction of the laser light to be measured is unknown, for example, if P polarization is the most desirable reflectivity characteristic, the second mechanism 800 may be used to move the mechanism 300 to various positions and repeatedly scan the wire 310 with respect to the laser light 11 at various angles, and the measurement result at the position where the beam diameter is narrowest may be adopted. The movement of the second mechanism 800 and the control of the mechanism 300 may be performed by the information processing device 600.

[0197] The configuration in this modified example is also applicable to the first embodiment.

[0198] [Embodiment 3] In the first and second embodiments, examples using a spherical integrating sphere were shown, but the shape is not limited to a sphere. That is, it may be any other shape as long as it has the function of reflecting the light reflected from the scattering material by the inner wall and detecting it with a photodetector, which is generated when the laser light to be measured is irradiated onto the scattering material.

[0199] In other words, while maintaining measurement performance, various shapes can be adopted from the standpoint of making the entire device compact by spatially efficiently integrating the scatterers and the mechanism for scanning them, depending on the scanning method of the scatterers (translation, vibration, rotation, etc.) and the number of scatterers (spiral scanner, etc.), as well as from the standpoint of making it easy to attach the mechanism for scanning the scatterers and equipment such as photodetectors, as well as the ease of processing the laser beam's entrance and exit apertures and manufacturing the entire device, and controlling the detection characteristics of the reflected light signal.

[0200] In this embodiment, an integral enclosure having a shape other than a sphere and possessing the above-described function is referred to as an integral enclosure. In this embodiment, a horizontally oriented cylindrical integral enclosure 2000 as shown in Figure 66 is used. That is, the upper and lower surfaces, which are discs, face left and right, and the curved side surfaces are arranged to face the front, top, back, and bottom.

[0201] As shown in Figure 66, an aperture 2100 is provided at the upper part of the curved surface of the integrating housing 2000 for injecting the laser beam 11 to be measured, and an aperture 2200 is also provided at the lower part of the curved surface of the integrating housing 2000 for emitting the laser beam 11 to be measured. The scattering body, wire 3100, is placed inside the integrating housing 2000 and moves by mechanism 3000 to scan the laser beam 11. A photodetector 4000 for detecting reflected light from the wire 3100 is also placed inside the integrating housing 2000.

[0202] As shown in the example in Figure 66, when measuring the beam cross-section of the laser light 11 to be measured at only one location, if the scattering body is a single cylindrical shape like the wire 3100, then, as shown in Figure 67, the reflected light (13a to 13c in Figure 67) is generated within a plane P stretched perpendicular to the axis 3100a of the wire 3100. In other words, the portion of the inner wall of the integrating housing 2000 to which the reflected light does not travel does not contribute to signal detection and therefore does not need to be given special consideration. When using a horizontally oriented cylindrical integrating housing 2000 as shown in Figure 66, it is sufficient to consider the reflectivity only for the curved inner surface of the cylinder.

[0203] The horizontally oriented cylindrical integrating enclosure 2000 has several advantages, including its simple structure, the fact that the shape and arrangement of the inner wall of the integrating enclosure 2000 allows reflected light from the scatterer to be incident perpendicularly on at least the curved portion, making it easy to set the reflectivity, simplifying the design and fabrication of the measurement system, and making it easy to obtain a signal faithful to theory, simplifying analysis and improving measurement accuracy. Depending on the embodiment described above, the reflectivity of the inner wall of the integrating enclosure 2000 may be uniform.

[0204] Next, Figure 68 shows an example of a case where the reflectivity of the inner wall of the integrating enclosure 2000 is distributed. Figure 68 is a view from the direction of arrow A in Figure 66, i.e., from the right side of the cylinder. Here, the laser beam 11 irradiated from the top to the bottom of the paper is scanned from left to right by a cylindrical wire 3100. In order to detect reflected light only from one side of the circular arc in the cross-section of the cylinder, the right portion 2300 of the inner curved surface of the integrating enclosure 2000 is configured to diffusely reflect the reflected light from the wire 3100 with high reflectivity, while the left portion 2400 is configured to absorb and extinguish the reflected light from the wire 3100. The inner surfaces of the top and bottom of the cylinder are also configured to diffusely reflect the reflected light from the wire 3100 with high reflectivity. This makes it possible to obtain an effect similar to that of a spherical integrating sphere schematically shown in Figure 40. The same effect can be obtained by swapping the left and right sides of portions 2300 and 2400.

[0205] Furthermore, in order to further reduce unwanted reflected light, the portion that diffusely reflects the reflected light with high reflectivity may be reduced. That is, as shown in Figure 69, the left portion 2400 of the curved inner surface of the integrating housing 2000 is configured to absorb and extinguish the reflected light from the wire 3100, similar to Figure 68. On the other hand, the right side is divided into a portion 2310 that absorbs and extinguishes the reflected light from the wire 3100, and a portion 2320 that is close to the aperture 2200 for emitting the laser beam 11 and diffusely reflects the reflected light with high reflectivity. The inner surfaces of the upper and lower surfaces of the cylinder are also configured to diffusely reflect the reflected light from the wire 3100 with high reflectivity.

[0206] The details will be explained using Figure 70. In Figure 70, the direction of propagation of the laser beam 11 is defined as the Z-axis, the scanning direction of the wire 3100 as the X-axis, the direction perpendicular to the plane of the paper as the Y-axis, and the point where the cylindrical wire 3100 and the laser beam 11 touch is defined as the origin. At this time, if the direction in which the laser beam 11 is incident (negative Z-axis direction) is defined as 0° and the direction in which the laser beam 11 is emitted (positive Z-axis direction) is defined as 180° around the Y-axis, then from 0°, the incident angle θ is the angle closest to 90° (excluding 0°) at which the reflectivity is minimized. Rmin Twice that, i.e., 2θ Rmin Up to this point, the portion 2310 is designed to absorb reflected light and extinguish it, and 2θ Rmin From 180° to 180° (180°-2θ) Rmin The area within the specified range is designated as portion 2320, which diffusely reflects reflected light with high reflectivity. Note that portion 2400 and portions 2310 and 2320 may be swapped left and right.

[0207] By creating a reflectivity distribution on the inner wall of the integrating housing 2000 in this way, it becomes possible to selectively detect reflected light within the range of an incident angle of 90° and its vicinity for the laser beam 11 on the wire 3100, as shown in Figure 71. Figure 71, similar to Figure 20, shows the relationship between the incident angle θ [°] for a 633 nm wavelength laser beam and the reflectivity for a blackened stainless steel wire. θ Rmin Since reflected light for incident angles less than θ is not used, by adopting the configuration described above, RminThis allows for the selective use of reflected light for the above incidence angles. Rmin It is also acceptable to limit the incidence angle to larger angles only. In that case, (180° - 2θ) Rmin This will result in a narrower range than )°.

[0208] By using such an integrating enclosure 2000, the relationship between the incident position (X / r) on the cylindrical wire 3100 and the signal intensity of the reflected light [a.u.] can be obtained, as shown in Figure 72. In this way, the incident angle θ from the incident position 1 can be obtained. Rmin The corresponding incident position x Rmin Since the signal is only detected up to / r, it becomes possible to detect reflected light corresponding to a single pulse-like reflectivity characteristic that approximates a unit impulse signal in a discrete-time system.

[0209] [Modification 1 of Embodiment 3] In the third embodiment, a horizontally oriented cylindrical integrating housing was shown, but the shape of the integrating housing is not limited to this, and a rectangular parallelepiped integrating housing 2000b may be used as shown in Figure 73. The basic arrangement of the wire 3100, the mechanism 3000 for translating the wire 3100, and the photodetector 4000, as well as the incident direction of the laser beam 11 to be measured, are the same as in the horizontally oriented cylindrical integrating housing 2000. That is, the laser beam 11 is incident from the top to the bottom of the paper through the opening 2100b of the rectangular parallelepiped integrating housing 2000b, the laser beam 11 is scanned vertically by the wire 3100 inside the integrating housing 2000b, and the reflected light generated at that time is detected by the photodetector 4000. The laser beam 11 is then emitted to the outside of the integrating housing 2000b through the opening 2200b.

[0210] Even with such a rectangular parallelepiped-shaped integrating enclosure 2000b, its inner wall may be made to have a uniform reflectivity, depending on the embodiment described above. Alternatively, as described above, the reflectivity may be distributed so that only the desirable reflected light can be detected by the photodetector 4000.

[0211] The rectangular integrating enclosure 2000b has the advantage of being easy to manufacture.

[0212] [Modification 2 of Embodiment 3] Alternatively, as shown in Figure 74, a vertically oriented cylindrical integrating housing 2000c may be used. When using a mechanism 3000c that scans the laser beam 11 by rotating the wire 3100, for example, by arranging the rotation axis of the mechanism 3000c on a central axis connecting the center of the upper surface and the center of the lower surface of the cylinder, the rotation of the wire 3100 can be more easily contained within the integrating housing 2000c. In this case, an opening 2100c for injecting the laser beam 11 is provided on the upper surface of the cylinder, and an opening 2200c for emitting the laser beam 11 is provided on the lower surface. The openings 2100c and 2200c are provided relatively close to the edges of the upper and lower surfaces of the cylinder, rather than in the center, so that the laser beam 11 is scanned with an appropriate portion of the wire 3100. It is preferable to position the photodetector 4000 in such a position that reflected light generated by the wire 3100 does not directly enter it.

[0213] In the case of a vertically oriented cylindrical shape, by extending the height in the central axis direction as described above, it is easy to enclose a spiral scanner 3400 equipped with multiple wires 3100, as shown in Figure 75. As shown in Figure 75, the spiral scanner 3400 is rotated by the mechanism 3000d, and the laser light 11 incident from the opening 2100d on the upper surface of the vertically oriented cylindrical integrating housing 2000d is sequentially scanned by each wire 3100, and the reflected light is detected by the photodetector 4000. The laser light 11 is emitted from the opening 2200d on the lower surface of the integrating housing 2000d.

[0214] Even with such vertically oriented cylindrical integrating housings 2000c and 2000d, their inner walls may be made to have a uniform reflectivity, depending on the embodiment described above. Alternatively, as described above, the reflectivity may be distributed so that only the desirable reflected light can be detected by the photodetector 4000.

[0215] Although embodiments of the present invention have been described above, the present invention is not limited thereto. For example, depending on the purpose, any technical features in each embodiment or modification described above may be deleted, or any technical features described in other embodiments or modifications may be added. Furthermore, any technical features in any embodiment or modification may be combined.

[0216] For example, regarding the cross-section of a wire used to detect the time waveform of reflected light having only one peak, the shape described above is just one example, and other shapes that are in line with the purpose can also be adopted.

[0217] The information processing devices 600 and 600b described above are computer devices in which memory, a CPU (Central Processing Unit), a hard disk drive (HDD; it may also be an SSD (Solid State Drive)), a display control unit connected to a display device, a drive unit for removable disks, an input device, and a communication control unit for connecting to a network are connected by a bus. The operating system (OS) and the application program for performing the processing in this embodiment are stored in the HDD and are read from the HDD into memory when executed by the CPU. The CPU controls the display control unit, communication control unit, and drive unit according to the processing content of the application program to perform predetermined operations. Data in the process of processing is mainly stored in memory, but may also be stored in the HDD. In the embodiment of the present invention, the application program for performing the processing described above is stored in a computer-readable removable disk and distributed, and installed from the drive unit to the HDD. In some cases, it may also be installed on the HDD via a network such as the Internet and the communication control unit. Such computer devices achieve the various functions described above through the organic cooperation of hardware such as the CPU and memory mentioned above, and programs such as the OS and application programs.

[0218] To summarize the embodiment described above, it is as follows:

[0219] The measurement method according to the first aspect of this embodiment involves (A) scanning the laser light to be measured for beam profile using a linear scatterer in a scanning direction perpendicular to the irradiation direction of the laser light, with the edge on the side irradiated by the laser light being symmetrical with respect to an axis parallel to the irradiation direction of the laser light in a cross-section parallel to the plane stretched in the irradiation direction and scanning direction; (B) detecting reflected light from the linear scatterer; (C) removing the waveform from the point immediately after the time taken when the scatterer moves a distance from the axis of symmetry to the right end or left end in the cross-section of the scatterer at the speed of movement of the scatterer in the above scanning (e.g., -Δt = distance / movement speed v) to the point immediately after the time taken when the scatterer moves a distance equal to

[0220] With this measurement method, as described in the first embodiment, for example, the beam profile can be measured with high accuracy regardless of the size of the scatterer. This is achieved by utilizing the extreme characteristics of Fresnel reflection on the surface of the scatterer, that is, the characteristic that any optical material has a reflectivity of 1 at an incident angle of 90°, and the symmetry of the time waveform of reflected light according to the symmetry of the cross-section of the scatterer, to remove time waveforms other than the characteristic portion.

[0221] Furthermore, the cross-section of the linear scatterer may include arcs at the right and left ends when viewed from the axis of symmetry. This is because the arc portion makes it easier to create a situation where the angle of incidence to the laser light is 90°.

[0222] Furthermore, the linear scatterer described above may have a first surface portion on the surface irradiated with laser light where the incident angle of the laser light is within 90° and the vicinity of 90°, and within that vicinity, the reflectivity decreases by 85% or more from the peak; and a second surface portion on the surface irradiated with laser light other than the first surface portion, where the reflectivity to the laser light is suppressed to 0.15 or less. If the scatterer has pulsed reflectivity characteristics that approximate a unit impulse signal in a discrete-time system, it will be able to handle not only single-mode laser light but also multi-mode laser light. Note that the cross-section of the scatterer is symmetrical with respect to the axis of symmetry, so the first surface portion is included in two locations.

[0223] The measurement system according to the second aspect of this embodiment includes: (A) a linear scatterer whose edge on the side irradiated by the laser light is symmetrical with respect to an axis parallel to the irradiation direction of the laser light, in a cross-section parallel to a plane stretched in the direction of irradiation of the laser light that is the target of beam profile measurement; (B) a mechanism for scanning the laser light in the scanning direction using the linear scatterer; (C) a photodetector for detecting reflected light from the linear scatterer; and (D) a processing unit that removes the waveform from the point immediately after the time taken to move the scatterer forward by the time taken to move the scatterer forward by the time taken to move the scatterer forward by the time taken to move the scatterer forward by the time taken to move the scatterer forward by the time taken to move the scatterer for the distance from the center of the waveform that represents the time change of the detected reflected light, concatenates the remaining waveforms, and generates information regarding the beam profile of the laser light based on the concatenated remaining waveforms.

[0224] Similar to the measurement method according to the first embodiment, the beam profile can be measured with high accuracy regardless of the size of the scatterer, as described in the first embodiment, for example.

[0225] Furthermore, the cross-section of the linear scattering body described above may include arcs at the right and left ends when viewed from the axis of symmetry.

[0226] Furthermore, the light detection unit described above may be housed within an integrating sphere or integrating enclosure that reflects light from a linear scatterer off its inner wall. This is to facilitate the reception of the reflected light. The shape of the integrating enclosure may be cylindrical, rectangular, or other shapes.

[0227] Furthermore, multiple linear scatterers, as described above, may be provided at intervals in the direction of laser irradiation and sequentially scanned perpendicular to the direction of laser irradiation. Since the beam diameter changes with the direction of laser irradiation, information regarding the beam profile at each position in the irradiation direction can be obtained. Moreover, if the scatterers are scanned sequentially at time intervals, the reflected light will also be generated sequentially at time intervals, allowing for separate analysis.

[0228] The measurement system according to the second embodiment may have a structure in which a plurality of scatterers are installed so as to extend vertically and outward from a rod parallel to the direction of laser irradiation, at intervals in the direction of laser irradiation and at intervals in terms of angles when viewed from the front side of the direction of laser irradiation. In this case, the mechanism described above rotates the rod of the structure. This adopts a configuration such as the spiral wire scanner shown in the embodiment.

[0229] Furthermore, the measurement system according to the second embodiment may further include a second mechanism for moving the mechanism to change the scanning direction. For example, if the reflectivity characteristics differ depending on the polarization, it may be preferable to move the mechanism in accordance with the polarization of the laser light to change the scanning direction of the linear scatterer.

[0230] Furthermore, the linear scatterer described above may have a first surface portion on the surface irradiated with laser light where the incident angle of the laser light is within 90° and the vicinity of 90°, and within that vicinity, the reflectivity decreases by 85% or more from the peak; and a second surface portion on the surface irradiated with laser light other than the first surface portion, where the reflectivity to the laser light is suppressed to 0.15 or less. This is to accommodate multimode laser light.

[0231] Furthermore, the measurement system according to the second embodiment may have multiple structures in which multiple scatterers are installed so as to extend vertically and outward with respect to a rod parallel to the irradiation direction of the laser beam, at intervals in the irradiation direction of the laser beam and at intervals in terms of the angle when viewed from the front side of the irradiation direction of the laser beam. In this case, it is preferable that the mechanism described above rotates the rod of the above structures independently, so that the multiple structures are arranged in a plane perpendicular to the irradiation direction of the laser beam, such that the scatterers in each of the multiple structures cross the laser beam from different directions. 11 This allows for the generation of beam profile information even for multimode lasers like the one described. It is preferable that scatterers from different structures cross the laser beam at different times within the same plane.

[0232] A measurement method according to a third aspect of this embodiment involves (A) scanning the laser beam perpendicular to the irradiation direction of the laser beam using a linear scatterer having a first surface portion on the surface irradiated with the laser beam, which is the target of beam profile measurement, where the incident angle of the laser beam is in the vicinity of 90° and 90°, and which has pulsed reflectance characteristics in the vicinity of 90° and 90°, and in the vicinity of 90°, the reflectance decreases by a predetermined rate or more from the peak in the vicinity of 90° and 90°, and a second surface portion on the surface irradiated with the laser beam, other than the first surface portion, in which the reflectance to the laser beam is suppressed to (1 - predetermined rate) or less, (B) detecting the reflected light from the linear scatterer, and (C) generating information regarding the beam profile of the laser beam based on a waveform representing the time change of the detected reflected light.

[0233] With this measurement method, as described in the first embodiment, for example, the beam profile can be measured with high accuracy regardless of the size of the scatterer. This is based on the extreme characteristics of Fresnel reflection on the surface of the scatterer, that is, the characteristic that any optical material has a reflectivity of 1 at an incident angle of 90°, and uses an appropriate scatterer having pulsed reflectivity characteristics that approximate a discrete-time unit impulse signal. The vicinity range is, for example, the range up to the angle where the reflectivity is minimal as the incident angle is closest to 90°. The predetermined ratio is, for example, 0.85.

[0234] Furthermore, the shape of the linear scatterer described above may include an arc at the end perpendicular to the direction of laser beam irradiation in a cross-section perpendicular to its longitudinal direction. The arc creates the first surface portion. Although various shapes are possible for the cross-sectional shape of the linear scatterer, adopting a shape that results in a single first surface portion simplifies the processing of the detected reflected light.

[0235] Furthermore, the shape of the linear scatterer may be such that, in a cross-section parallel to the plane formed by the laser beam irradiation direction and the scanning direction perpendicular to the irradiation direction, the edge on the side irradiated by the laser beam is symmetrical with respect to an axis parallel to the laser beam irradiation direction. This also includes cases where the cross-sectional shape is circular, which simplifies manufacturing. However, it is not limited to a circular shape. In such cases, there will be two first surface portions.

[0236] Furthermore, in generating information about the beam profile, the waveform representing the time evolution of the detected reflected light may be modified by removing the waveform from the point immediately preceding the point immediately preceding the point immediately preceding the point immediately preceding the point by the same amount of time it takes to move the scattering material's movement speed over the distance from the axis of symmetry to the right or left end of the cross-section of the scattering material at the same time as when the scattering material moves in the scanning motion, starting from the point immediately preceding the point immediately preceding the point. The remaining waveforms are then concatenated, and information about the beam profile of the laser light is generated based on the concatenated remaining waveforms. Even when there are two first surface portions, the same results can be obtained as when there is only one of them. This also makes it possible to handle multimode laser light.

[0237] On the other hand, in the measurement method according to the third embodiment, the reflectance distribution of the inner wall is set to reflect only one of the first reflected light generated when the scanning of the laser light is started or the second reflected light generated when the scanning of the laser light is finished, and an integrating sphere or integrating enclosure is used that is equipped with a photodetector that detects either the first reflected light or the second reflected light reflected by the inner wall. By using such an integrating sphere or integrating enclosure, the time waveform of the first or second reflected light can be processed as is. The shape of the integrating enclosure may be cylindrical or rectangular, etc.

[0238] A measurement system according to a fourth aspect of this embodiment includes: (A) a linear scatterer having a first surface portion of the surface irradiated with laser light, which is the target of beam profile measurement, where the incident angle of the laser light is in the vicinity of 90° and 90°, and which has pulsed reflectance characteristics in the vicinity of 90° and 90°, and in the vicinity of 90°, the reflectance decreases by a predetermined rate or more from the peak in the vicinity of 90°; and a second surface portion of the surface irradiated with laser light other than the first surface, where the reflectance to the laser light is suppressed to (1 - predetermined rate) or less; (B) a mechanism for scanning the laser light with the linear scatterer in a direction perpendicular to the irradiation direction of the laser light; (C) a photodetector for detecting reflected light from the linear scatterer; and (D) a processing unit for generating information regarding the beam profile of the laser light based on a waveform representing the time change of the detected reflected light.

[0239] Similar to the measurement method according to the third embodiment, the beam profile can be measured with high accuracy regardless of the size of the scatterer, as described in the second embodiment, for example.

[0240] Furthermore, the shape of the linear scatterer may be such that a circular arc is included at the end facing the vertical direction in a cross-section perpendicular to the longitudinal direction of the linear scatterer.

[0241] Furthermore, the shape of the linear scatterer described above may also be such that, in a cross-section parallel to the plane formed by the laser beam irradiation direction and the scanning direction perpendicular to the irradiation direction, the edge on the side irradiated by the laser beam is symmetrical with respect to an axis parallel to the laser beam irradiation direction.

[0242] Furthermore, the processing unit described above may remove the waveform from the point immediately after the time when the scattering body moves forward by the time taken to move the scattering body's movement speed in the scan, starting from the center of the waveform representing the time change of the detected reflected light, and then remove the waveform from the point immediately after the time when the scattering body moves forward by the same time, concatenate the remaining waveforms, and generate information regarding the beam profile of the laser light based on the concatenated remaining waveforms.

[0243] Furthermore, the measurement system according to the fourth embodiment may further include an integrating sphere or integrating enclosure in which the reflectance distribution of the inner wall is set to reflect only one of the first reflected light generated when the scanning of the laser light is started or the second reflected light generated when the scanning of the laser light is finished. In this case, the light detection unit described above will detect the reflected light reflected by the inner wall of the integrating sphere or integrating enclosure. The shape of the integrating enclosure may be cylindrical or rectangular, etc.

[0244] Alternatively, multiple linear scatterers, as described above, may be provided at intervals in the direction of laser beam irradiation and sequentially scanned perpendicular to the direction of laser beam irradiation.

[0245] Furthermore, the measurement system according to the fourth embodiment may have a structure in which a plurality of scatterers are installed with respect to a rod parallel to the direction of laser beam irradiation, spaced apart in the direction of laser beam irradiation and spaced apart in terms of the angle when viewed from the front side of the direction of laser beam irradiation, so as to extend vertically and outward. In this case, the mechanism described above rotates the rod of the structure.

[0246] Furthermore, the measurement system according to the fourth embodiment may have multiple structures as described above. In this case, it is preferable that the multiple structures are arranged in a plane perpendicular to the direction of laser beam irradiation, such that the scatterers in each of the multiple structures cross the laser beam from different directions.

[0247] Furthermore, the measurement system according to the fourth embodiment may further include a second mechanism for moving the mechanism to change the scanning direction.

[0248] Furthermore, a program can be created to cause a processor to perform at least the process of generating information related to the beam profile. This program is stored in a computer-readable storage medium or device such as a flexible disk, a CD-ROM (Read Only Memory) or other optical disk, a magneto-optical disk, a semiconductor memory (e.g., ROM), or a hard disk. Data in the process of being processed is temporarily stored in a storage device such as RAM (Random Access Memory).

Claims

1. A measurement method for which the beam profile of a laser beam to be measured is scanned by a linear scatterer in a scanning direction perpendicular to the irradiation direction of the laser beam, in a cross section parallel to the irradiation direction of the laser beam and the plane stretched in the scanning direction, the edge on the side irradiated by the laser beam being scanned is symmetrical with respect to an axis parallel to the irradiation direction of the laser beam as the axis of symmetry; reflected light from the linear scatterer is detected; the waveform representing the time change of the detected reflected light is removed from the point immediately after the time taken to move the scatterer forward by from the center of the waveform representing the time change of the detected reflected light; and information on the beam profile of the laser beam is generated based on the connected remaining waveform.

2. The measurement method according to claim 1, wherein the cross-section of the linear scattering body includes arcs at the right end and the left end when viewed from the axis of symmetry.

3. The measurement method according to claim 1, wherein the linear scatterer comprises a first surface portion of the surface irradiated with the laser light, within a range of 90° and a vicinity of 90° where the incident angle of the laser light is 90°, and within that vicinity range, the reflectance decreases by 85% or more from the peak; and a second surface portion of the surface irradiated with the laser light, other than the first surface portion, where the reflectance to the laser light is suppressed to 0.15 or less.

4. A measurement system comprising: a linear scatterer in a cross-section parallel to a plane stretched in the direction of irradiation of the laser light to be measured and in a scanning direction perpendicular to the irradiation direction, the edge on the side irradiated by the laser light is symmetrical with respect to an axis parallel to the irradiation direction of the laser light as the axis of symmetry; a mechanism for scanning the laser light in the scanning direction using the linear scatterer; a photodetector for detecting reflected light from the linear scatterer; and a processing unit that removes the waveform from the point immediately after the time taken to move the distance from the center of the waveform to the right end or left end of the cross-section of the scatterer at the scanning speed of the scatterer, and then removes the waveform from the point immediately after the point immediately after the time taken to move the distance 5. The measurement system according to claim 4, wherein the cross-section of the linear scattering body includes arcs at the right end and the left end when viewed from the axis of symmetry.

6. The measurement system according to claim 4, wherein the light detection unit is provided in an integrating sphere or integrating housing that reflects reflected light from the linear scatterer off its inner wall.

7. The measurement system according to claim 4, characterized in that a plurality of linear scatterers are provided at intervals in the direction of irradiation of the laser light and sequentially scanned in a direction perpendicular to the direction of irradiation of the laser light.

8. The measurement system according to claim 7, comprising a structure having a plurality of scattering bodies installed with respect to a rod parallel to the irradiation direction of the laser light, spaced apart in the irradiation direction of the laser light and spaced apart in terms of the angle as viewed from the front side of the irradiation direction of the laser light, wherein the mechanism rotates the rod of the structure.

9. The measurement system according to claim 4, further comprising a second mechanism for moving the mechanism to change the scanning direction.

10. The measurement system according to claim 4, wherein the linear scatterer comprises a first surface portion of the surface irradiated with the laser light, within a range of 90° and a vicinity of 90° where the incident angle of the laser light is 90° and within that vicinity range where the reflectance decreases by 85% or more from the peak, and a second surface portion of the surface irradiated with the laser light, other than the first surface portion, where the reflectance to the laser light is suppressed to 0.15 or less.

11. The measurement system according to claim 10, comprising a plurality of structures installed with respect to a rod parallel to the irradiation direction of the laser beam, spaced apart in the irradiation direction of the laser beam and spaced apart in terms of the angle as viewed from the front side of the irradiation direction of the laser beam, wherein the mechanism rotates the rod of the structures independently, and the plurality of structures are arranged such that the scatterers in each of the plurality of structures cross the laser beam from different directions in a plane perpendicular to the irradiation direction of the laser beam.

12. A measurement method comprising: a linear scatterer having a first surface portion of the surface irradiated with laser light, which is the target of beam profile measurement, where the incident angle of the laser light is in the range of 90° and near 90°, and which has pulsed reflectance characteristics in the range of 90° and near 90°, and in the range of near 90°, the reflectance decreases by a predetermined rate or more from the peak in the range of near 90°; and a second surface portion of the surface irradiated with laser light, other than the first surface portion, in which the reflectance to the laser light is suppressed to (1 - predetermined rate) or less; scanning the laser light in a direction perpendicular to the irradiation direction of the laser light; detecting reflected light from the linear scatterer; and generating information regarding the beam profile of the laser light based on a waveform representing the time change of the detected reflected light.

13. The measurement method according to claim 12, wherein the end of the linear scattering body facing the vertical direction in a cross section perpendicular to the longitudinal direction includes an arc.

14. The measurement method according to claim 12, wherein the shape of the linear scatterer is such that, in a cross-section parallel to a plane stretched between the irradiation direction of the laser light and the scanning direction which is perpendicular to the irradiation direction, the edge on the side irradiated by the laser light is symmetrical with respect to an axis parallel to the irradiation direction of the laser light.

15. The measurement method according to claim 14, wherein, in generating information regarding the beam profile, the waveform from immediately after the time taken to advance by the time taken to move the distance from the center of the waveform to the right end or left end of the cross-section of the scatterer at the scanning speed of the scatterer, starting from the center of the waveform representing the time change of the detected reflected light, is removed, and the remaining waveforms are concatenated, and information regarding the beam profile of the laser light is generated based on the concatenated remaining waveforms.

16. The measurement method according to claim 12, wherein the reflectance distribution of the inner wall is set to reflect only one of either a first reflected light generated at the time the scanning with respect to the laser light is started or a second reflected light generated at the time the scanning with respect to the laser light is ended, and an integrating sphere or integrating housing is used which is equipped with a photodetector that detects either the first reflected light or the second reflected light reflected by the inner wall.

17. The measurement method according to claim 12, wherein the predetermined rate is 0.

85.

18. A linear scatterer having a first surface portion of a surface irradiated with laser light, which is the target of beam profile measurement, where the incident angle of the laser light is in the range of 90° and near 90°, and which has pulsed reflectance characteristics in the range of 90° and near 90°, and in the range of near 90°, the reflectance decreases by a predetermined rate or more from the peak in the range of near 90°; and a second surface portion of the surface irradiated with the laser light, other than the first surface, in which the reflectance to the laser light is suppressed to (1 - predetermined rate) or less; a mechanism for scanning the laser light with the linear scatterer in a direction perpendicular to the irradiation direction of the laser light; a photodetector for detecting reflected light from the linear scatterer; and a processing unit for generating information regarding the beam profile of the laser light based on a waveform representing the time change of the detected reflected light.

19. The measurement system according to claim 18, wherein the end of the linear scattering body facing the vertical direction in a cross section perpendicular to the longitudinal direction includes an arc.

20. The measurement system according to claim 18, wherein the shape of the linear scatterer is such that, in a cross-section parallel to a plane stretched between the irradiation direction of the laser light and the scanning direction which is perpendicular to the irradiation direction, the edge on the side irradiated by the laser light is symmetrical with respect to an axis parallel to the irradiation direction of the laser light.

21. The measurement system according to claim 20, wherein the processing unit removes the waveform from the time taken to move the distance from the center of the waveform to the right end or left end of the cross-section of the scattering body at the scanning speed of the scattering body, by a time taken to move the distance from the center of the waveform to the right end or left end of the cross-section of the scattering body by the time taken to move the distance from the center of the waveform by a time, and from the time taken to move the distance from the center of the waveform to the center of the waveform by a time, and from the time, and from the time, and from the time, and from the 22. The measurement system according to claim 18, further comprising an integrating sphere or integrating housing whose inner wall reflectance distribution is set to reflect only one of a first reflected light generated when scanning with respect to the laser light is started and a second reflected light generated when scanning with respect to the laser light is ended, wherein the light detection unit detects the reflected light reflected by the inner wall of the integrating sphere or integrating housing.

23. The measurement system according to claim 18, wherein the predetermined rate is 0.

85.

24. The measurement system according to claim 18, characterized in that a plurality of linear scatterers are provided at intervals in the direction of irradiation of the laser light and sequentially scanned in a direction perpendicular to the direction of irradiation of the laser light.

25. The measurement system according to claim 24, comprising a structure having a plurality of scattering bodies installed with respect to a rod parallel to the irradiation direction of the laser light, spaced apart in the irradiation direction of the laser light and spaced apart in terms of the angle as viewed from the front side of the irradiation direction of the laser light, wherein the mechanism rotates the rod of the structure.

26. The measurement system according to claim 25, wherein the system has a plurality of the structures, and the plurality of structures are arranged such that the scattering bodies in each of the plurality of structures cross the laser light from different directions in a plane perpendicular to the irradiation direction of the laser light.

27. The measurement system according to claim 18, further comprising a second mechanism for moving the mechanism to change the scanning direction.

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