Laser system

Abstract

Provided is a laser system including: a first measurement device (104) that measures the intensity of return light of second laser light reflected on a processing target surface (152); a second measurement device (105) that calculates the distance between a reference position and the processing target surface (152) from the return light of the second laser light reflected on the processing target surface (152); and a controller (106) that enables a first laser device (101) to emit first laser light in the case where the intensity measured by the first measurement device (104) is larger than an intensity threshold, and the distance calculated by the second measurement device (105) falls within a distance range.

Description

[Technical Field]

[0001] This invention relates to a laser system for purposes such as removing rust from metals. [Background technology]

[0002] For rust removal from metal components, metal brushes, power tools, or blasters—devices that blast sand or fine iron balls at high speed—are commonly used. However, power tools have problems such as difficulty in rusting uneven surfaces of steel, the time required to acquire the necessary skills, and significant noise and physical strain on the worker. Furthermore, when using blasters, it is necessary to surround the structure with sheets to prevent the scattering of blasted sand or iron balls, and there are also problems such as high noise levels and time-consuming cleanup after the work is completed.

[0003] Laser devices are a technology that can solve these problems. Laser devices have many advantages, such as noise reduction, easier rust removal from uneven metal surfaces, and easier collection of scattered debris. In this type of laser device, there is a mechanism to protect the optical gain medium from being damaged (Non-Patent Literature 1). In this technology, for example, if there is no optical input for a while, the optical gain is observed to prevent damage caused by parasitic laser oscillation or Q switching that occurs when the optical gain of the gain medium increases. Non-Patent Literature 1 describes observing "amplified spontaneous emission (ASE)" light and turning off the pump light source before the gain reaches a level that causes parasitic laser oscillation or Q switching (assumed to be 30 dB in Non-Patent Literature 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] P. BOOKER et al., "Experimental and numerical study of interlock requirements for high-power EYDFAs", Optics Express, vol. 28, no. 21, pp. 31480-31486, 2020. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the aforementioned technology protects the optical gain medium, and does not describe any technology to prevent the laser output light from affecting people or objects that are not being rusted.

[0006] This invention was made to solve the above-mentioned problems and aims to prevent the influence of laser output light on areas other than those being rusted. [Means for solving the problem]

[0007] The laser system according to the present invention comprises a first laser device that emits a first laser beam for rust removal, a second laser device that emits a second laser beam for observation, an optical system that irradiates the surface of a structure to be treated with the first and second laser beams, a first measuring device that measures the intensity of the reflected light of the second laser beam reflected from the surface to be treated, a second measuring device that determines the distance between a reference position and the surface to be treated from the reflected light of the second laser beam reflected from the surface to be treated, and a controller that enables the emission of the first laser beam by the first laser device when the intensity measured by the first measuring device is greater than an intensity threshold and the distance determined by the second measuring device is within a distance range. [Effects of the Invention]

[0008] As explained above, according to the present invention, the emission of the first laser beam by the first laser device is made possible based on the intensity of the reflected light of the second laser beam and the distance to the surface to be treated determined from the reflected light, thereby preventing the laser output light from affecting areas other than the rust removal target. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a configuration diagram showing the configuration of a laser system according to an embodiment of the present invention. [Figure 2] Figure 2 is a configuration diagram showing a more detailed configuration of the laser system according to an embodiment of the present invention. [Figure 3] Figure 3 is an explanatory diagram illustrating the arrangement of the first light spot 131a at the irradiation position of the first laser beam 131, and the second light spot 132a at the irradiation position of the second laser beam 132. [Figure 4] Figure 4 is an explanatory diagram illustrating the arrangement of the first light spot 131a at the irradiation position of the first laser beam 131, and the second light spot 132a at the irradiation position of the second laser beam 132. [Figure 5] Figure 5 is a configuration diagram showing a more detailed configuration of the LiDAR 110 and controller 106. [Figure 6A] Figure 6A is a configuration diagram showing a more detailed configuration of the LiDAR 110 and controller 106. [Figure 6B] Figure 6B is a configuration diagram showing a more detailed configuration of the LiDAR 110 and controller 106. [Figure 7A] Figure 7A is a configuration diagram showing a more detailed configuration of the controller 106. [Figure 7B] Figure 7B is a configuration diagram showing a more detailed configuration of the controller 106. [Figure 8] Figure 8 is an explanatory diagram illustrating the exit surface of the diffraction optical element (DOE), which acts as a beam shaper BS to form the beam shape of the second laser beam, and the main lobe of the second laser beam. [Figure 9] Figure 9 is an explanatory diagram for explaining φ shown in equation (1). [Figure 10]Figure 10 is an explanatory diagram illustrating the thickness of the DOE, which acts as a beam shaper BS to form the beam shape of the second laser beam, and the equiphase surface of the emitted light. [Figure 11] Figure 11 is an explanatory diagram illustrating the DOE emission surface and the light focusing range, which act as a beam shaper BS that forms the beam shape of the second laser beam. [Figure 12A] Figure 12A is a characteristic diagram showing the simulation results of the maximum power density and beam diameter of the spherical wave-integrated beam of the second laser beam that has passed through the DOE, with respect to a position z in the z-axis direction perpendicular to the DOE exit surface. [Figure 12B] Figure 12B is a characteristic diagram showing the simulation results of the maximum power density and beam diameter of the Bessel beam of the second laser light that has passed through the DOE, with respect to a position z in the z-axis direction perpendicular to the DOE exit surface. [Modes for carrying out the invention]

[0010] Hereinafter, a laser system according to an embodiment of the present invention will be described with reference to Figure 1. This laser system first comprises a first laser device 101 that emits a first laser beam for rust removal, a second laser device 102 that emits a second laser beam for observation, and an optical system 103 that irradiates the surface 152 of a structure 151 to be processed with the first and second laser beams. The optical system 103 aligns the principal ray of the first laser beam with the center line of the light beam of the second laser beam. The structure 151 is made of, for example, steel.

[0011] Furthermore, this laser system includes a first measuring device 104 that measures the intensity of the reflected light of the second laser beam reflected from the surface 152 to be processed, a second measuring device 105 that determines the distance between a reference position and the surface 152 to be processed from the reflected light of the second laser beam reflected from the surface 152 to be processed, and a controller 106 that enables the emission of the first laser beam by the first laser device 101 when the intensity measured by the first measuring device 104 is greater than an intensity threshold and the distance determined by the second measuring device 105 is within a distance range. The reference position, intensity threshold, and distance range can be set in advance. The reference position can be, for example, a predetermined position in the optical path of the optical system 103.

[0012] According to this laser system, the first laser beam is emitted only when it is detected that the structure 151 to be treated is within a predetermined distance range set by the user on the main beam of the first laser beam used for rust removal; otherwise, the first laser beam is not emitted. By setting the thresholds of the controller 106 so that the range in which the structure 151 exists is within the distance range set by the user, it is possible to prevent the first laser beam from irradiating and affecting objects or people other than the structure 151.

[0013] Furthermore, since it becomes unnecessary to install a screen to prevent the first laser beam from irradiating outside the user-defined range (for example, the first laser beam passing through the gaps in the steel tower being treated), the labor involved in rust removal work and the purchase of screens are eliminated.

[0014] The details will be explained below with reference to Figure 2. The optical system 103 of the laser system can consist of a first fiber collimator lens (FC1) 121, a focusing optical system (CO) 122, a second fiber collimator lens (FC2) 123, a beam shaper (BS) 124, a dichroic mirror (DM) 125, an optical deflector (OD) 126, and the like.

[0015] The first fiber collimator lens 121 makes the first laser beam 131 output from the first laser device 101 into parallel light. The focusing optical system 122 focuses the first laser beam 131, which has been made into parallel light. The second fiber collimator lens 123 makes the second laser beam 132 output from the second laser device 102 into parallel light. The beam shaper 124 changes the beam shape of the second laser beam 132, which has been made into parallel light.

[0016] The first laser beam emitted from the first laser device 101 is guided through the first optical fiber 127 to the first fiber collimator lens 121. The second laser beam emitted from the second laser device 102 is guided through the second optical fiber 128 to the second fiber collimator lens 123.

[0017] The dichroic mirror 125 reflects the second laser beam 132 and transmits the first laser beam 131. For example, the dichroic mirror 125 transmits the first laser beam 131 with a wavelength of 1070 nm and reflects the second laser beam 132 with a wavelength of 1310 nm or 1550 nm. The optical deflector 126 deflects both the first laser beam 131 and the second laser beam 132.

[0018] The first laser beam 131 and the second laser beam 132, incident on the dichroic mirror 125, are combined at the dichroic mirror 125. In addition, the optical axes of the first fiber collimator lens 121, the focusing optical system 122, the second fiber collimator lens 123, and the beam shaper 124 are adjusted so that the principal ray 141 of the first laser beam 131 and the beam center line 142 passing through the center of the beam of the second laser beam 132 coincide.

[0019] The fiber collimator lens 121, focusing optical system 122, fiber collimator lens 123, beam shaper 124, dichroic mirror 125, and optical deflector 126 can be housed in the laser head 129. In the optical system 103 comprising these components, the principal ray 141 of the first laser beam 131 and the beam center line 142 passing through the center of the beam of the second laser beam 132 are aligned, and the first laser beam 131 and the second laser beam 132 are emitted simultaneously toward the structure 151.

[0020] Furthermore, the second laser beam, deflected by the optical deflector 126 and irradiated onto the structure 151, and the reflected light from the structure 151, is guided through the optical deflector 126, dichroic mirror 125, beam shaper 124, and second fiber collimator lens 123, through the second optical fiber 128, and led to the first measuring device 104 and the second measuring device 105. The second laser device 102 and the second measuring device 105 can be well-known LiDAR (light detection and ranging) 110. The first measuring device 104 can also be integrated into the LiDAR 110 or the controller 106.

[0021] Here, the arrangement (relative arrangement) of the first light spot 131a at the irradiation position of the first laser beam 131 emitted from the optical system 103 (laser head 129), and the second light spot 132a at the irradiation position of the second laser beam 132, will be explained with reference to Figures 3 and 4. As shown in Figures 3 and 4, the second light spot 132a of the second laser beam 132 is irradiated so as not to overlap with the first light spot 131a of the first laser beam 131. Furthermore, the second light spot 132a is irradiated in the vicinity of the first light spot 131a.

[0022] This arrangement takes into account the possibility that the reflected light of the second laser beam 132 may not return to the LiDAR 110 because, in the area irradiated by the first laser beam 131, the surface 152 to be treated for rust removal is scraped or melted, resulting in significant light scattering and attenuation, or because specularly reflected light due to the smoothing of the surface 152 does not return to the optical system 103. Because the area irradiated by the first laser beam 131 is in an unstable state, the second laser beam 132 is irradiated near the area irradiated by the first laser beam 131 to enable stable distance measurement to the target.

[0023] The aforementioned "nearby" means, for example, the area outside the range (rust removal effect range) in which the surface 152 to be treated by the first laser beam 131 undergoes physical changes such as melting or abrasion, or chemical changes such as oxidation (changes such as oxidation caused by high heat). To achieve this, the irradiation position of the second laser beam 132 can be positioned so as to be adjacent to the rust removal effect range. The rust removal effect range can be calculated (predicted) using the light intensity density distribution within the light spot at the irradiation position of the first laser beam 131, obtained by measurement or calculation, and the physical and chemical properties of the structure 151 to be irradiated.

[0024] The light spot at the irradiation position of the second laser beam 132 can be positioned so as to be in contact with the rust removal effect area. Positioning so as to be in contact means, for example, a region where the intensity of the light spot of the second laser beam 132 is half or more, or 1 / e 2 The area described above is designated as the rust removal effect area, and the equipment is positioned to be adjacent to that area.

[0025] In the examples of the first light spot 131a and the second light spot 132a shown in Figures 3(b), (c), (d), and (e), the center of the rust removal effect area by the first laser beam 131 (the centroid of the rust removal effect area) coincides with the center of the beam (light flux = bundle of light rays) of the second laser beam 132 (the centroid of the light intensity). Figure 3(e) shows the case where the light spot 132 is ring-shaped. In these cases, the second light spot 132a is arranged surrounding the first light spot 131a, and the second light spot 132a is in contact with the first light spot 131a. With this arrangement, even if there is variation in the attenuation of reflected light due to light scattering and absorption on the surface to be rusted depending on the position where the second laser beam 132 is irradiated (dependence on the irradiation position of the second laser beam 132), the reflected light from each point is averaged out, thus providing resistance to positional variation in reflected light attenuation.

[0026] On the other hand, in the spot configuration shown in Figure 3(a), one second optical spot 132a is positioned so as to be adjacent to the affected area. If the total power of the second laser beam 132 is the same in all spot configurations from Figure 3(a) to (e), then the power density increases as the area of ​​the optical spot (total area) decreases. Therefore, if we assume that there is no positional variation in reflected light attenuation (no positional dependence of reflected light attenuation), the resistance to reflected light attenuation of the spot configuration shown in Figure 3(a) will be the highest compared to the others.

[0027] Figure 4 shows an example where the second light spot 132a is separated from the first light spot 131a without touching it. Regarding the distance between the center of the rust removal effect area (first light spot 131a) and the center of the second light spot 132a, for example, if the spot shapes of both the first light spot 131a and the second light spot 132a are circular, and the spot radius of the first light spot 131a is r R The spot radius of the second light spot 132a is r L When the distance between the center of the first light spot 131a and the center of the second light spot 132a is d, r R +r L Make sure that ≤ d.

[0028] r R +rL When it is = d, it is when the first light spot 131a and the second light spot 132a are in contact. The upper limit of d is r R ≥ r L In the case of, for example, 2r R is also acceptable. That is, r R + r L ≤ d ≤ 2r R is also acceptable. Similarly, r R < r L In the case of, for example, 2r L is also acceptable. That is, r R + r L ≤ d ≤ 2r L is also acceptable.

[0029] In the above, the spot shapes of the first light spot 131a and the second light spot 132a are circles and circular rings, but it is not limited to this. For example, it can be an ellipse or a rectangle including a square. In the case of an ellipse, the semi-minor axis or semi-major axis of the first light spot 131a and the second light spot 132a is r R or r L is replaced, and the second light spot 132a is arranged with respect to the first light spot 131a so that the distance d follows the above formula. Also, in the case of a rectangle, similarly, half of the long side or the short side is r R or r L is replaced, and the second light spot 132a is arranged with respect to the first light spot 131a so that the distance d follows the above formula. In the case of a square, similarly, half of one side is r R or r L is replaced, and the second light spot 132a is arranged with respect to the first light spot 131a so that the distance d follows the above formula. Also, not limited to the above examples, the second light spot 132a may be arranged in the vicinity of the first light spot 131a.

[0030] The spot shape of the second light spot 132a can be set by the beam shaper 124. The beam shaper 124 transforms the Gaussian beam emitted from the second fiber collimator lens 123 into a beam having the spot shape of the second light spot 132a described above. The design method of the beam shaper 124 will be described later.

[0031] LiDAR 110 captures the second laser light 132 returned from the processing target surface 152 via the optical system 103 (laser head 129), measures and outputs the intensity of the return light with the first measuring device 104, and measures (distance measurement) the distance to the processing target surface 152 with the second measuring device 105 and outputs the measured distance. This distance measurement can be carried out, for example, by a "time of flight: (TOF)" method or a "frequency modulated continuous wave: (FMCW)" method.

[0032] When all of several conditions are satisfied (true), the controller 106 outputs a control signal to set the state in which the first laser light 131 is output from the first laser device 101 (laser light ON), and when not, outputs a control signal to set the state in which the first laser light 131 is not output from the first laser device 101 (laser light OFF).

[0033] The above conditions include at least two conditions. First, it is a condition of whether or not a structure 151 exists within the distance range set by the user, and second, assuming that the structure 151 is not on the principal ray of the second laser light 132, it is a condition of whether or not the light intensity received by LiDAR 110 (measured by the first measuring device 104) is below the intensity set by the user.

[0034] First, the first condition will be described. When the distance range set by the user is represented as S, S can specify two distances dmin, dmax (dmin < dmax) and set these ranges to be dmin or more and dmax or less. As the set distance range, a plurality of ranges S of two or more iWhen (i is an index representing a range, for example, when representing N ranges, i can be represented by an integer where 0 < i < N - 1), each S i is d imin , d imax (i is an index specifying a range, d imin < d imax ), as such, multiple ranges d imin or more, d imax or less can be specified.

[0035] Compare the set distance range with the distance z S ’ obtained from LiDAR110 (measured by the second measuring device 105), and the condition that z S ’ is included in S, or is included in any of S i (i = 0,..., N - 1) is one of the conditions for outputting the first laser light 131 from the first laser device 101.

[0036] Next, the second condition will be described. When the threshold value of the light intensity set by the user is I Th and the light intensity received by LiDAR110 (measured by the first measuring device 104) is I, the condition I > I Th is also one of the conditions for outputting the first laser light 131 from the first laser device 101. When this condition is true, it is considered that the structure 151 exists on the optical beam center line of the second laser light 132 emitted from the laser head 129.

[0037] When both of the above two conditions are satisfied (true), the controller 106 outputs a signal (laser ON / OFF control signal for rust removal) for performing an operation of outputting the first laser light 131 from the first laser device 101 (laser ON) and not outputting the first laser light 131 from the first laser device 101 (laser OFF) in other conditions.

[0038] The first laser device 101 includes a laser light source for rust removal, and turns ON / OFF the first laser light 131 output from the laser light source for rust removal according to the output of the controller 106 (laser ON / OFF control signal for rust removal).

[0039] To control the ON / OFF output of the first laser device 101, if the laser light source has an interlock terminal, it can be used. However, some rust removal laser light sources require several seconds to receive output light from the first laser device 101 after the OFF operation (laser OFF, operation that does not output laser light) is performed using the interlock terminal, or a physical switch operation is required to turn it ON again after turning it OFF. In such cases, it is not possible to turn the laser light output ON / OFF in a short time.

[0040] When using the first laser device 101 which includes such a rust removal laser light source, if the laser light source has a mechanism for modulating the laser light intensity output by a command from an external terminal voltage or from a terminal such as a computer connected externally via a digital I / F, then a voltage can be applied to such a terminal capable of optical output modulation, or a command can be sent from the terminal.

[0041] Next, the LiDAR 110 and controller 106 will be described in more detail with reference to Figure 5. In this configuration, the LiDAR 110 uses the FMCW method.

[0042] The LiDAR 110 comprises a wavelength-swept light source 201, part of a target interferometer 202, a reference interferometer 203, an analog-to-digital converter (ADC) 204, and a LiDAR signal processing unit 205. The target interferometer 202 includes a laser head 129 and a structure 151 (more specifically, a processing target surface 152). The LiDAR signal processing unit 205 is located within the signal processing unit 206 and is implemented in software or hardware. For example, if the signal processing unit 206 is a computer, the LiDAR signal processing unit 205 is implemented by a program. Alternatively, if the signal processing unit 206 is implemented as a gate array such as an FPGA, the LiDAR signal processing unit 205 is implemented in hardware by connecting wires of a logic circuit.

[0043] Refer to Figure 5 to explain the operation of LiDAR 110 in detail. The wavelength-swept light output from the wavelength-swept light source 201 is split by the optical coupler C1 to the target interferometer 202 and the reference interferometer 203. The target interferometer 202 emits the wavelength-swept light source (second laser light) towards the structure 151 via the optical coupler C2, circulator Cir1, and laser head 129. If there is reflected light, the reflected light via the laser head 129, circulator Cir1, and optical coupler C3 is combined with the light propagating directly from optical coupler C2 to optical coupler C3 in the target interferometer 202, and is incident on the balanced photodetector BPD1, where it is photoelectrically converted and acquired as a target interference signal by the signal processing device 206 via Ch1 of the ADC 204.

[0044] Furthermore, the reference plane 221 is the virtual reflection point where the optical path length directly connecting optical coupler C2 and optical coupler C3 is equal to the optical path length between optical coupler C2 and optical coupler C3 that is reflected back from the virtual reflection point of the target interferometer 202 via circulator Cir1. The distance from the reference plane 221 of the target interferometer 202 to the surface to be processed 152 is z S Therefore, the difference between the optical path length between optical couplers C2 and C3 that are reflected back from the surface 152 to be processed via circulator Cir1 and the optical path length directly connecting optical coupler C2 and optical coupler C3 is 2z S This is the result.

[0045] The reference interferometer 203 is the same as the target interferometer 202 but with the structure 151 replaced by a mirror 223, and the distance from the reference plane 222 to the mirror 223 in the reference interferometer 203 is known as z R Therefore, the difference in optical path length between the optical path length directly connecting optical coupler C4 and optical coupler C5 and the optical path length between optical coupler C4 and optical coupler C5 reflected by mirror 223 via circulator Cir2 is 2z. R Therefore, BPD2 has an optical path length difference of 2z. R Interfering light is incident on the signal and is captured as a reference interference signal by the signal processing device 206 via Ch2 of the ADC204.

[0046] Within the signal processing device 206, the reference interference signal is first Fourier transformed in the FFT0 section. Next, the Fourier transformed reference interference signal has its zero-frequency components (DC components) and negative frequency components replaced with zero in the negative frequency zero section, and is then inversely Fourier transformed in the inverse FFT section to obtain a complex signal. Subsequently, the deviation angle of the complex signal reference interference signal is calculated in the deviation angle calculation section for each time interval (range: -π to π, or 0 to 2π).

[0047] Next, the phase merging section merges the discontinuities in the argument angles (for example, arranging the argument angles in time t order (where t is 0, 1, ..., M-1, and M is the number of data samples obtained by ADC204), and merging the argument angles only if the absolute value of the difference between adjacent argument angles ("argument angle at t before phase merging" - "argument angle at t+1 before phase merging") is π or greater ("argument angle at t+1 after phase merging" = "argument angle at t+1 before phase merging" + "sign of the difference in the argument angle" × 2π × "number of times merged so far + 1").

[0048] This phase merging process is sometimes called unwrapping. The phase angle obtained after phase merging in this way will be called the phase change curve (time-angle curve). The phase change curve represents the temporal phase change of the reference interference signal and, according to the sign of the angle difference, increases approximately monotonically with respect to time (when the sign of the angle difference is > 0) or decreases approximately monotonically (when the sign of the angle difference is < 0). The reason for using the expression "approximately" is that if a small amount of noise is superimposed on the angle before phase merging, it may not strictly increase or decrease monotonically depending on the fluctuations of that noise.

[0049] The phase change curve θ(t) obtained in this way becomes data for acquiring equally phased time intervals (resampling timing) according to the number of samples N when the target interference signal and the reference interference signal are sampled again (resampling) in the resampling part 1 and resampling part 2 described later. The resampling timing calculation unit calculates the resampling timing.

[0050] As an example of the operation of the resampling timing calculation unit, if the user specifies the number of data after resampling as N, the unit calculates δθ = Δθ / (N-1) from the phase change width Δθ (maximum phase - minimum phase) in the phase change curve, and calculates the time τ of the phase where θ'(n) = θ(0) + nδθ (n=0 to N-1, θ(0) = "phase at t=0", t=0,1,...,M-1). n (n=0 to N-1) is defined as the resampling timing.

[0051] If θ(t) < θ'(n) < θ(t+1), then interpolation can be performed to obtain θ(τ n τ such that ) = θ'(n) n Calculate τ. If linear interpolation is used as the interpolation method, n We calculate this as =t|θ(t+1)-θ'(n)|+(t+1)|θ'(n)-θ(t)|. Here, |x| (where x is a real number) is the absolute value of x.

[0052] Resampling 1 and Resampling 2 use the resampling timing τ calculated by the resampling timing calculation unit. n At this timing, the target interference signal and the reference interference signal are resampled, respectively. n Many of them can be real numbers, but τ n If the result is a real number, resampling is performed using interpolation such as linear interpolation.

[0053] Through resampling, the target interference signal and the reference interference signal are separated by time τ. n As the phase changes linearly with respect to the reference interference signal, the reference interference signal after resampling is approximately a sine wave (because there is only one reflection point due to reflection by the mirror, and therefore the optical path length round trip between the reference surface 222, the mirror 223, and the reference surface 222 is fixed to one). Similarly, the target interference signal after resampling is also approximately a sine wave if the surface to be processed 152 is planar, the center line of the light beam of the second laser emitted from the laser head 129 intersects the surface to be processed 152 perpendicularly, and the reflected light contributes to the interference as backlight. In all other cases, multiple sine waves are generated depending on the distance from the reference surface 221, and these are combined to form a signal.

[0054] FFT1 and FFT2 perform Fourier transforms on the resampled target interference signal and the reference interference signal, respectively. As described above, when the interference signal is approximately sinusoidal, the signal after the Fourier transform is calculated as a spectrum with a peak. This signal with a peak is called the "point spread function (PSF)". The frequency at which the intensity of this PSF peaks is the surface position z of the processing target surface 152 of the target interferometer 202 and the mirror of the reference interferometer 203. S , z R It corresponds (is proportional to).

[0055] The intensity peak frequency acquisition parts 1 and 2 acquire the frequency at which the intensity of the PSF obtained in FFT part 1 and FFT part 2 peaks. The frequency at which the intensity peaks obtained from the PSF originating from the target interference signal is f S f R Let's assume that.

[0056] The distance calculation unit calculates z, which is half the optical path length difference within the reference interferometer 203. R And the f obtained from parts 1 and 2 of the intensity peak frequency acquisition, respectively. S and f R From there, the distance z from the reference plane (reference position) 221 of the target interferometer 202 to the structure 151 (surface to be processed 152) S Measured value z S ' to z S '=z R f S / f R It is calculated using the following formula.

[0057] The controller 106 includes a first laser ON / OFF control signal processing unit 207 and a digital-to-analog converter (DAC) 208. This is based on the premise that the ON / OFF output of the first laser beam output from the first laser device 101 is controlled by an analog signal. The first laser ON / OFF control signal processing unit 207, like the LiDAR signal processing unit 205, is implemented using software and hardware, or hardware alone.

[0058] As shown in Figure 5, when the LiDAR signal processing unit 205 and part of the controller 106 (first laser ON / OFF control signal processing unit 207) are implemented on the signal processing unit 206, the distance z from the reference position calculated from the LiDAR signal processing unit 205 to the structure 151 (processing target surface 152) is S This can be passed to the first laser ON / OFF control signal processing unit 207 of the controller 106 via the memory provided by the signal processing unit 206.

[0059] The DAC208 and the signal processing unit 206 are connected via a digital interface (I / F). This digital interface can be, for example, USB (Universal Serial Bus).

[0060] The controller 106 detects the intensity threshold I set by the user. Th The distance range S, the intensity I of the reflected light received by the LiDAR 110, and the distance z from the reference position to the structure 151 (surface to be processed 152). S Using this, the ON / OFF state of the first laser output from the first laser device 101 is controlled as shown below.

[0061] [When the distance range is 1 (S)] If "z S ' is included in S and I > I Th When this happens, the first laser beam is output from the first laser device 101 (laser ON). Otherwise, the first laser beam from the first laser device 101 is not output (laser OFF).

[0062] [Multiple distance ranges (S i [In the case of (i=0,1,…,N-1)] If "z S ' is S i "Included in any of (i=0, ..., N-1)" and "I>I Th When this happens, the first laser beam is output from the first laser device 101 (laser ON). Otherwise, the first laser beam from the first laser device 101 is not output (laser OFF).

[0063] This section describes how to measure the intensity I of the reflected light received by the LiDAR 110. Below, we will explain how the first measuring device 104 calculates the intensity I of the reflected light of the second laser beam when the first measuring device 104 is built into the controller 106. For example, I can be calculated from the target interference signal by the first laser ON / OFF control signal processing unit 207 (Figure 6A). As shown in Figure 6A, first, the target interference signal (one sweep time or half sweep time of the wavelength-swept light source 201) acquired through channel 1 (Ch1) of the ADC 204 is processed in the following order: Fourier transform (FFT), processing to make the zero-frequency component (DC component) and negative frequency components zero, and inverse Fourier transform (inverse FFT). The intensity of the resulting signal (complex signal) at each time is calculated by multiplying the sum of the squares of the real part and the imaginary part by 4, and the time average of these intensities is taken as I.

[0064] For reference, the time waveform obtained by taking the square root of the sum of the squares of the real and imaginary parts of the signal (complex signal) obtained by processing the signal in the order of Fourier transform (FFT), processing the zero-frequency component (DC component) and negative frequency components to zero, and then the inverse Fourier transform (inverse FFT) represents half of the amplitude waveform (envelope waveform) of the target interference signal. Since this amplitude waveform is proportional to the electric field strength of the reflected light, doubling the calculated waveform and squaring it (equivalent to squaring it and multiplying by 4) gives the energy time waveform. Therefore, the intensity I of the reflected light is obtained by time averaging this energy time waveform.

[0065] Other methods for measuring the reflected light intensity I are described. For example, as shown in Figure 6B, the result of FFT processing of I through resampling of the target interference signal in the FMCW LiDAR signal processing unit 205, and the peak position frequency f obtained therefrom are described. R Therefore, there is a method to determine it by calculation in the first laser ON / OFF control signal processing unit 207.

[0066] The result of FFT processing via resampling of the target interference signal in the FMCW LiDAR signal processing unit 205 is a PSF signal with a peak at a frequency corresponding to the distance from the reference position included in the target interferometer 202 to the processing target surface 152. Its peak intensity is proportional to the electric field of the reflected light from the structure 151 (proportional to the square root of the power).

[0067] Therefore, the first laser ON / OFF control signal processing unit 207 processes the peak position frequency f of the PSF acquired from the LiDAR signal processing unit 205. R The intensity of the PSF is obtained, and I is obtained by squaring that intensity.

[0068] Note that while Figures 6A and 6B only show the target interferometer 202, ADC 204 and its Ch1 and Ch2, and the signal processing device 206 and the LiDAR signal processing unit 205 and the first laser ON / OFF control signal processing unit 207 that are configured within it, the other parts shown in Figures 2 and 5 are assumed to be configured in the same way as in Figures 2 and 5.

[0069] Furthermore, in the first and second examples of obtaining I above, I is obtained by squaring the electric field strength after acquiring it, but it is possible to determine the strength of the electric field strength directly without squaring it.

[0070] In the two examples above, the signal was obtained from the target interference signal through signal processing (calculation). However, the following example describes a case in which a portion of the reflected light from the laser head 129 is measured by a photodetector, and the measurement result is input as I to the signal processing device 206 via a new channel 3 (Ch3) of the ADC204 of the LiDAR 110.

[0071] One method for acquiring (sampling) a portion of this reflected light is to insert a new optical coupler C6 as an optical sampler in the middle of the optical fiber between the circulator Cir1 and the laser head 129 in the interferometer 202 of the LiDAR 110, as shown in Figure 7A, or in the middle of the optical fiber connecting the circulator Cir1 and the optical coupler C3, as shown in Figure 7B. In this case, by pre-measuring the branching ratio of the newly inserted optical coupler C6 and converting the optical power output from the newly inserted optical coupler C6, the absolute value of the reflected light intensity can be obtained.

[0072] Note that while Figures 7A and 7B only show the target interferometer 202, ADC 204 and its Ch1 and Ch3, the signal processing device 206 and the first laser ON / OFF control signal processing unit 207 configured within it, the other parts shown in Figures 2 and 5 are assumed to be configured in the same way as in Figures 2 and 5.

[0073] The first laser device 101 shown in Figure 5 includes a first laser light source, similar to that in Figure 2. The output of the first laser beam emitted from the device can be controlled (ON / OFF) by the voltage of an external terminal. Using this mechanism, the first laser device 101 controls (ON / OFF) the output of the first laser beam by an analog voltage signal from the controller 106.

[0074] The operation of each device is described below. However, LiDAR110 is assumed to use the FMCW method. As preparation, the controller 106 is pre-configured with distance range S or S i (i=0,…,N-1) and intensity threshold I Th Set it up.

[0075] The LiDAR 110 emits light from the wavelength-swept light source 201, which then exits the LiDAR 110 and is subsequently emitted outside the device via the laser head 129. The LiDAR 110 also acquires the reflected light via the laser head 129 and obtains the target interference signal via the target interferometer 202 and ADC 204. After this, the LiDAR 110 uses the acquired target interference signal and a reference interference signal separately acquired from the reference interferometer 203 via the ADC 204 to perform distance measurement calculations in the LiDAR signal processing unit 205, determining the distance z to the structure 151 (processing target surface 152). S Calculate and output '.

[0076] In the controller 106, the first laser ON / OFF control signal processing unit 207 calculates the reflected light intensity I of the second laser beam from the target interference signal. Furthermore, the first laser ON / OFF control signal processing unit 207 calculates the distance z of the structure 151 (processing target surface 152) calculated by the LiDAR 110. S Using ' and I, a first laser ON / OFF signal is generated according to the conditional expression shown in the description of controller 106 above and output to DAC208 of controller 106. DAC208 applies an analog voltage to the first laser device 101 according to the acquired laser ON / OFF signal.

[0077] The first laser device 101 controls the output power of the first laser beam emitted from the first laser light source included in the first laser device 101 according to the voltage applied by the DAC 208 (output: ON, do not output: OFF).

[0078] The principal beam of the first laser light output from the first laser device 101 is positioned in the laser head 129 to coincide with the center line of the second laser beam. Although not explicitly shown in Figure 5, it is deflected by the optical deflector OD in the laser head 129, focused by the focusing optical system CO, and output from the laser head 129.

[0079] Next, we will discuss the beam shaper BS that forms the beam shape of the second laser beam, as mentioned above. The beam shaper BS described here can be a diffraction optical element (DOE).

[0080] It is desirable that the beam shape of the second laser beam remains constant with respect to the propagation distance of the second laser beam. Therefore, the final electric field distribution on the beam shaper BS is obtained by convolution and integral of the electric field on the beam shaper BS surface that forms a first-order zero-order Bessel beam, which is a type of non-diffracted light, and the intensity distribution of the desired shape.

[0081] In this regard, we will describe a specific example of a DOE where the exit surface is a plane. Figure 8 shows the plane P0 representing the DOE exit surface and its coordinate system. Assume that the z-axis is perpendicular to P0, and the x-axis and y-axis are parallel to P0. This coordinate system represented by the x-axis, y-axis, and z-axis is a Cartesian coordinate system, with the coordinate origin 0 on P0.

[0082] First, let's describe a first-order zero-order Bessel beam where the center of the main lobe is located on the z-axis. Let the wavenumber of the second laser beam be k and the wavelength be λ, and the beam power, diameter, and full width at half maximum (FWHM) of the main lobe be... of 2r B and When this is done, if we use φ such that equation (1) below holds, the electric field distribution on P0 that generates such a first-kind zero-order Bessel beam u B,0 This can be expressed as shown in equation (2) below.

[0083]

number

[0084] However, r xy This can be expressed by the following equation (3).

number

[0085] Also, A(r xy) is a function that represents the electric field strength.

[0086] A desired electric field distribution on a plane parallel to the xy-plane (for example, Figure 3 ,figure 4 If (a) to (e) are the electric field strength distributions, i.e., the distribution of electric field strengths, then let h(x, y) be the electric field distribution u0 on the DOE emission surface (plane P0) where h(x, y) is generated, then the electric field distribution u0 is expressed by the following convolution integral equation.

[0087]

number

[0088] In equation (4), S represents the light emission range of the DOE emission surface.

[0089] The meaning of φ in equation (1) will be explained with reference to Figure 9. In Figure 9, the propagation of incident and outgoing light to the DOE exit surface (plane P0) is indicated by arrows. As shown in Figure 9, the Bessel beam is formed in the overlapping portion of the beam when light is incident from all points on P0 at the same angle φ along the z-axis. The diameter of the main lobe of the Bessel beam (FWHM) is calculated by equation (1).

[0090] The design method for DOE using equation (4) is described below. The DOE designed here is a transmissive type, roughly a dielectric in the form of parallel plates, with irregularities on the surface of the parallel plates.

[0091] Figure 10 shows the thickness of a transmissive DOE and the equiphase surface of the emitted light. Light is assumed to enter from the left and exit to the right in Figure 10. There are two optical paths, A and B, with lengths Ld for optical path A and L for optical path B within the DOE. Let n be the refractive index inside the DOE and n0 be the refractive index outside the DOE. Let λ and k be the wavelength and wavenumber of the light entering and exiting the DOE in a vacuum. If points a and b are the intersections of the exit surface P0 (where the maximum DOE thickness L is) and optical paths A and B, respectively, then the phase θ of point a is given by the phase of point b. d It can be expressed by the following formula.

[0092]

number

[0093] In equation (5), θ a and θ b These are the phases at points a and b, respectively. According to equation (5), the larger d is, that is, the thinner the thickness Ld of the DOE, the more the phase of the DOE at the DOE exit surface P0 advances by θ(d) = 2πd(n-n0) / λ.

[0094] By the way, from the electric field distribution obtained by equation (4), the phase θ(x,y) of a point (x,y) on P0 can be expressed by the following equation.

[0095]

number

[0096] In equation (6), arg(u0(x,y)) is the argument when u0(x,y) is expressed as a complex number. This represents the angle between the line connecting the origin on the complex plane and (Re(u0(x,y))) and Im(u0(x,y))) and the real axis, when "u0(x,y) = Re(u0(x,y)) + j·Im(u0(x,y))". Here, Re(u0(x,y)) and Im(u0(x,y)) are the real and imaginary parts, respectively, and j is the imaginary unit.

[0097] θ in equation (5) d Substituting θ(x,y) into equation (6) and solving for d, we get the following expression for d.

[0098]

number

[0099] Therefore, d can be calculated from arg(u0(x,y)) according to Equation (7), and a DOE with the position of the coordinate (x, y) recessed (cut) by that amount of d can be fabricated. That is, the thickness of the DOE at the position of the coordinate (x, y) where the phase is arg(u0(x,y)) may be processed so as to be L - d.

[0100] By the way, in Equation (4), for calculating the electric field distribution on the DOE exit surface (on the plane P0), the convolution integral of the electric field distribution u B (x,y) on P0 that generates the zero-order Bessel beam of the first kind and h(x,y) was performed, but instead of u B (x,y), the electric field distribution on the plane P0 that forms an optical beam that converges within a certain range on the z-axis may be used. FIG. 11 is an example of the light convergence range formed from such an electric field distribution, and it shows a state where light is converging within the range indicated by z α ≦z≦z β on the z-axis. An example of the electric field distribution u IS (x,y) on the plane P0 that forms such a convergence state on the z-axis is shown below.

[0101]

Number

[0102] However, r is expressed by the following equation.

[0103]

Number

[0104] u IS (x,y) regards the bright line segment (the range where light is converging) within the range of z α ≦z≦z β on the z-axis as a set of bright spots, and for each spherical wave e jkrIt corresponds to (spherical wave integration) the sum (integration) of the electric field distributions on the plane P0 for all the bright spots. kzcosφ is the phase corresponding to the position on the z-axis of each spherical wave, and it has the same phase as the phase of the center of the main lobe of the Bessel beam formed on the z-axis described above. φ is a parameter related to the full width at half maximum (FWHM) 2r of the main lobe of the optical beam formed on the z-axis. Similar to Equation (1), the following equation holds. IS It is a parameter related to IS , and the following equation holds as in Equation (1).

[0105] [Number]

[0106] u IS The calculation formula of u0(x, y) using (x, y) is described below.

[0107] [Number]

[0108] The advantage of the beam by spherical wave integration (spherical wave integration beam) over the Bessel beam is that the range in which the power of the main lobe is maintained in the z-axis direction is long. When the power holding range in the z-axis direction is wide, the range in which the reflected light intensity of the second laser light can be maintained becomes wide according to the width of the power holding range, so the ranging range of LiDAR expands, which is desirable as an application of LiDAR.

[0109] Figures 12A and 12B are graphs of the simulation results of the maximum power density and beam diameter (FWHM) of the second laser light passing through the DOE with respect to the position z in the z-axis direction perpendicular to the DOE exit surface. Figure 12A plots the data of the spherical wave integration beam, and Figure 12B plots the data of the Bessel beam. In both cases, a Gaussian beam with a diameter of 5.1 mm and a wavelength of 1.07 μm is incident on the DOE. It is assumed that the DOE is processed according to d at 5 μm × 5 μm on the exit surface (on the plane P0).

[0110] According to Figures 12A and 12B, the range in which the variation in the maximum beam power in the z direction can be suppressed to about 2.45 times is about 750 mm for the spherical wave integral beam and about 650 mm for the Bessel beam, indicating that the spherical wave integral beam can be extended about 100 mm longer. However, the variation in beam diameter relative to the average diameter is -10% to +13% for the spherical wave integral beam, while it is -2.5% to 1.2% for the Bessel beam, so the variation is larger for the spherical wave integral beam.

[0111] While the electric field distribution of a Bessel beam is inherently constant on a plane parallel to the xy-plane with respect to the z-direction, a pseudo-Bessel beam (pseudo-Bessel beam) formed by passing a Gaussian beam through a DOE exhibits power fluctuations as described above. Therefore, caution is required regarding its applicability in applications where power fluctuations are problematic.

[0112] The above is about the method for calculating the electric field distribution u0(x,y) on the DOE emission surface (on plane P0). different An example of this is explained below.

[0113] When h(x,y) is the desired electric field distribution on a plane parallel to the xy-plane at position z on the z-axis, generally, u0(x,y) and h(x,y) have the following relationship.

[0114]

number

[0115] In equation (12), g z (x,y) is a function that represents the propagation of light and can be expressed by the following equation.

[0116]

number

[0117] In equation (13), cosψ = ​​z / r, which depends on the direction of light emission. ((1+cosψ)) / 2 represents the variation in electric field strength with respect to the direction of light emission (directivity of light) and is called the "inclination factor". Since equation (12) is a convolution integral, a two-dimensional Fourier transform of both sides yields the following:

[0118]

number

[0119] However, ν and υ are the spatial frequencies in the x-axis and y-axis directions, respectively, H(ν,υ), U0(ν,υ), and G z (ν,υ) are h(x,y), u0(x,y), g z This is the 2D Fourier transform result of (x,y). Solving equation (14) for U0(ν,υ) yields the following:

[0120]

number

[0121] Taking the inverse Fourier transform of both sides of equation (15) yields u0(x, y) as follows.

[0122]

number

[0123] Therefore, h(x,y) and g z The Fourier transforms are applied to (x,y), and the resulting values ​​are H(ν,υ) and G. z Using (ν,υ), H(ν,υ) / G z We calculate (ν,υ) and then perform an inverse Fourier transform on the result to calculate u0(x,y).

[0124] Equation (16) can also be transformed as follows:

[0125]

number

[0126] Here, g z -1 (x,y) is the backpropagation function of light, and is expressed by the following equation.

[0127]

number

[0128] If g z (-1) (x,y) ≈ e jkr If so, equation (17) can be expressed as follows:

[0129]

number

[0130] As described above, according to the present invention, the emission of the first laser beam by the first laser device is made possible based on the intensity of the reflected light of the second laser beam and the distance to the surface to be treated determined from the reflected light, thereby preventing the laser output light from affecting areas other than those to be rusted.

[0131] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art. [Explanation of symbols]

[0132] 101...First laser device, 102...Second laser device, 103...Optical system, 104...First measuring device, 105...Second measuring device, 106...Controller, 151...Structure, 152...Surface to be processed.

Claims

1. A first laser device that emits a first laser beam for rust removal, A second laser device that emits a second laser beam for observation, An optical system that irradiates the surface of a structure to be processed with the first laser beam and the second laser beam by aligning the principal ray of the first laser beam with the center line of the light beam of the second laser beam, and arranging the second light spot of the second laser beam at the irradiation position surrounding the first light spot at the irradiation position of the first laser beam, A first measuring device for measuring the intensity of the reflected light of the second laser beam reflected from the surface to be processed, A second measuring device that determines the distance between a reference position and the surface to be processed from the reflected light of the second laser beam reflected from the surface to be processed, A controller that enables the emission of the first laser beam by the first laser device only when the intensity measured by the first measuring device is greater than an intensity threshold and the distance determined by the second measuring device is within a set distance range. A laser system equipped with [the following features].

2. In the laser system according to claim 1, The second light spot is a laser system positioned in contact with the first light spot.

3. In the laser system according to Claim 1, The second light spot is positioned in non-contact with the first light spot. A laser system in which the spot radius of the first light spot is rR, the spot radius of the second light spot is rL, and the distance between the center of the first light spot and the center of the second light spot is d, such that when rR ≥ rL, rR + rL ≤ d ≤ 2rR, and when rR < rL, rR + rL ≤ d ≤ 2rL.

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