Laser processing device and laser processing method

Abstract

To provide a laser processing apparatus capable of suppressing decrease in processing quality even when power of the laser beam output from the laser oscillator fluctuates.SOLUTION: An optical switching element cuts out a portion of a laser beam from the laser beam output from the laser oscillator on a time axis and directs the portion toward an object. A controller changes transmittance of the optical switching element according to power of the laser beam output from the laser oscillator.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a laser processing apparatus and a laser processing method. [Background technology]

[0002] There is known a laser processing device that performs hole drilling using a laser beam (see Patent Document 1). In the laser processing device disclosed in Patent Document 1, a part is cut out from a pulse laser beam output from a laser oscillator by using an acousto-optic deflector (AOD), and the cut-out laser pulse is made to enter an object to be processed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-186822 A Summary of the Invention [Problem to be solved by the invention]

[0004] The peak power of a pulsed laser beam output from a laser oscillator may change depending on the oscillation conditions. For example, depending on the laser oscillator, the peak power may tend to decrease according to the time elapsed from the start of oscillation. In addition, the peak power may tend to decrease as the pulse repetition frequency increases. Fluctuations in peak power result in variations in processing quality.

[0006] An object of the present invention is to provide a laser processing apparatus and a laser processing method that are capable of suppressing deterioration in processing quality even if the power of a laser beam output from a laser oscillator fluctuates. [Means for solving the problem]

[0007] According to one aspect of the present invention, A laser oscillator; The laser oscillator outputsPulse an optical switching element for extracting a portion of the laser beam on a time axis and directing the portion toward a target; The laser oscillator outputs Pulse Laser beam Peaks of each of the multiple laser pulses a control device that changes the transmittance of the optical switching element in response to power; A laser processing apparatus comprising:

[0008] According to another aspect of the invention, Pulse A laser beam is made incident on an optical switching element, and a portion of the laser beam is cut out on the time axis and directed toward a target object. The light is incident on the optical switching element. Pulse Laser beam Peaks of each of the multiple laser pulses A laser processing method in which the power of the laser beam incident on the object is adjusted by changing the transmittance of the optical switching element in response to the power. Effect of the Invention

[0009] The power of the laser beam incident on the target object can be adjusted by changing the transmittance of the optical switching element in accordance with the power of the laser beam output from the laser oscillator. By adjusting the transmittance, it is possible to compensate for fluctuations in the power of the laser beam output from the laser oscillator. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a laser processing apparatus according to one embodiment. [Diagram 2] FIG. 2 is a graph showing an example of the waveform of a pulse laser beam on the input side of an optical switching element, the diffraction efficiency value commanded by an analog signal, the cut-out timing commanded by a digital signal, and the waveform of a pulse laser beam on the output side of an optical switching element. [Diagram 3]FIG. 3 is a graph showing an example of the change over time in the pulse energy of the input pulse laser beam and the output pulse laser beam of the optical switching element, and in the diffraction efficiency of the optical switching element. [Figure 4] 4A and 4B are graphs showing an example of basic information for the control device to change the diffraction efficiency. [Diagram 5] FIG. 5A is a graph showing an example of the relationship between the pulse repetition frequency and peak power of a laser processing device according to another embodiment, and FIG. 5B is a graph showing basic information for a control device to control the diffraction efficiency of an optical switching element. [Figure 6] FIG. 6 is a graph showing a schematic waveform of the input pulse laser beam of the optical switching element, the diffraction efficiency of the optical switching element commanded by an analog signal (FIG. 1), and a schematic waveform of the output pulse laser beam. [Figure 7] FIG. 7 is a table showing basic information used by a control device of a laser processing device according to still another embodiment for controlling the diffraction efficiency of an optical switching element. [Figure 8] FIG. 8A is a diagram showing an example of the distribution of a plurality of work points defined on the surface of an object, and FIG. 8B is a diagram showing an example of the machining order of the plurality of work points. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A laser processing device according to one embodiment of the present invention will be described with reference to FIGS. 1 to 4. 1 is a schematic diagram of a laser processing device according to one embodiment. A laser oscillator 10 outputs a pulsed laser beam in response to a command from a control device 30. For example, a carbon dioxide gas laser is used as the laser oscillator 10. The pulsed laser beam output from the laser oscillator 10 is input to an aperture 12 via a beam shaping optical system 11. The beam shaping optical system 11 is, for example, a beam expander, and adjusts the beam diameter and spread angle of the pulsed laser beam.

[0012] The pulsed laser beam that has passed through the aperture 12 is incident on the optical switching element 13. For example, an acousto-optical deflection element is used as the optical switching element 13. A driver 14 drives the optical switching element 13 in response to a command from the control device 30. The optical switching element 13 extracts a part of the laser beam on the time axis from the input pulsed laser beam P1, and directs the extracted pulsed laser beam P2 toward the target 50. The part of the pulsed laser beam P1 that is not extracted and incident on the optical switching element 13 is incident on a beam dumper 21.

[0013] As an example, the control device 30 provides the driver 14 with an analog signal AM instructing the diffraction efficiency and a digital signal DM instructing the timing of cutting out the laser beam. During the period when the digital signal DM instructing the timing of cutting out is at a high level, the pulsed laser beam is directed to a path toward the object 50, and during the other period, the pulsed laser beam is input to the beam damper 21. The diffraction efficiency of the optical switching element 13 is set by the analog signal AM instructing the diffraction efficiency. The diffraction efficiency corresponds to the ratio of the power of the pulsed laser beam P2 on the output side to the power of the pulsed laser beam P1 on the input side of the optical switching element 13. Therefore, the diffraction efficiency can be considered as the transmittance of the pulsed laser beam toward the object 50.

[0014] The pulsed laser beam P2 extracted by the optical switching element 13 is incident on the object 50 via the mirror 22, the beam scanner 25, and the condenser lens 26. A galvano scanner including a pair of oscillating mirrors 25X and 25Y is used as the beam scanner 25. The beam scanner 25 is controlled by the control device 30 to move the incidence position of the pulsed laser beam on the surface of the object 50 within a two-dimensional plane. The condenser lens 26 condenses the pulsed laser beam on the surface of the object 50. An fθ lens, for example, is used as the condenser lens 26.

[0015] The object 50 is, for example, a printed circuit board on which holes are to be drilled, and is held on the horizontal support surface of the stage 27. In response to a command from the control device 30, the stage 27 moves the object 50 in two directions that are parallel to the support surface and perpendicular to each other.

[0016] A measuring instrument 28 is attached to the stage 27. By moving the stage 27 and irradiating a pulsed laser beam on the measuring instrument 28, the measuring instrument 28 can measure the energy per pulse of the pulsed laser beam (hereinafter referred to as "pulse energy") or the peak power. The measurement results of the measuring instrument 28 are input to the control device 30.

[0017] 2 is a graph showing an example of the waveform of the pulse laser beam P1 on the input side of the optical switching element 13, the value of the diffraction efficiency commanded by the analog signal AM, the cut-out timing commanded by the digital signal DM, and the waveform of the pulse laser beam P2 on the output side of the optical switching element 13. Note that the waveforms of the two laser pulses 41 and 42 of the pulse laser beam P1 shown in FIG. 2 are simplified representations of the actual waveforms.

[0018] The peak power of the pulsed laser beam output from the laser oscillator 10 varies due to various factors. Fig. 2 shows an example in which the peak power of the laser pulse 41 is greater than the peak power of the laser pulse 42. The diffraction efficiency M1 commanded by the analog signal AM during the period from the rising edge (t1) to the falling edge (t4) of the laser pulse 41 is lower than the diffraction efficiency M2 commanded during the period from the rising edge (t5) to the falling edge (t8) of the laser pulse 42.

[0019] The digital signal DM goes high during a portion (t2 to t3) of the period from the rising edge to the falling edge of the laser pulse 41 and during a portion (t6 to t7) of the period from the rising edge to the falling edge of the laser pulse 42. During the period when the digital signal DM is at high level, a pulsed laser beam P2 directed toward the target 50 (FIG. 1) is output. The pulsed laser beam P2 includes laser pulses 43 and 44 extracted from the laser pulses 41 and 42, respectively.

[0020] The peak power of the extracted laser pulses 43 and 44 is equal to the peak power of the original laser pulses 41 and 42 multiplied by the diffraction efficiencies M1 and M2. By appropriately setting the diffraction efficiencies M1 and M2, the peak power of the extracted laser pulses 43 and 44 can be made almost the same.

[0021] The area of ​​the waveforms of the laser pulses 41, 42, 43, and 44 corresponds to the pulse energy. When the pulse widths of the laser pulses 41 and 42 are equal, the pulse energy of the laser pulse 41 is greater than the pulse energy of the laser pulse 42. Since the peak powers of the extracted laser pulses 43 and 44 are approximately equal, when the pulse widths of the two are equal, the pulse energies of the two are also approximately equal. In this way, by changing the diffraction efficiency according to the peak power of the input pulse laser beam P1, the pulse energy of the extracted pulse laser beam P2 can be made uniform.

[0022] Next, with reference to FIG. 3, a method of controlling the optical switching element 13 in the case where a pulse laser beam is output for a certain period with the pulse repetition frequency kept constant will be described.

[0023] FIG. 3 is a graph showing an example of the change over time in the pulse energy of the input pulse laser beam P1 and the output pulse laser beam P2 of the optical switching element 13 (FIG. 1), and in the diffraction efficiency of the optical switching element 13. In FIG.

[0024] In the period from time t11 to t12 and in the period from time t13 to t14, the pulse laser beam P1 is output at a constant frequency. In the period from time t12 to t13, the pulse laser beam is not output. The laser oscillator 10 (FIG. 1) has a characteristic that the pulse energy varies according to the elapsed time from the output start time t11, t13 of the pulse laser beam P1. For example, the pulse energy decreases as time passes from the output start time of the pulse laser beam P1.

[0025] The control device 30 (FIG. 1) issues a command to the driver 14 (FIG. 1) to increase the diffraction efficiency of the optical switching element 13 as time passes from the start time (t11, t13) of outputting the pulsed laser beam P1. More specifically, the control device 30 changes the diffraction efficiency so that the pulse energy of the extracted pulsed laser beam P2 becomes approximately constant. Basic information for changing the diffraction efficiency is stored in advance in the memory of the control device 30. As a result, the pulse energy of the pulsed laser beam P2 becomes approximately constant during the period from time t11 to t12 and the period from time t13 to t14.

[0026] FIG. 4A is a graph showing an example of basic information for the control device 30 to change the diffraction efficiency. The basic information shown in FIG. 4A defines the relationship between the time elapsed from the start of output of the pulsed laser beam P1 and the diffraction efficiency. The horizontal axis of FIG. 4A represents the time elapsed from the start of output of the pulsed laser beam P1, and the vertical axis represents the diffraction efficiency. If the laser oscillator 10 (FIG. 1) has a characteristic in which the peak power decreases with increasing elapsed time, the basic information increases the diffraction efficiency with increasing elapsed time so as to compensate for the decrease in peak power. For example, the diffraction efficiency asymptotically approaches the maximum diffraction efficiency Dmax of the optical switching element 13 (FIG. 1) from the initial value Dini as the elapsed time increases.

[0027] FIG. 4B is a graph showing another example of basic information for the control device 30 to change the diffraction efficiency. The basic information shown in FIG. 4B defines the relationship between the serial numbers given to the laser pulses outputted sequentially from the start of output of the pulsed laser beam P1 and the diffraction efficiency. The horizontal axis of FIG. 4B represents the serial numbers given to the laser pulses, and the vertical axis represents the diffraction efficiency. In the basic information, the diffraction efficiency is increased with an increase in the serial number so as to compensate for the decrease in peak power. For example, the diffraction efficiency asymptotically approaches the maximum diffraction efficiency Dmax of the optical switching element 13 from the initial value Dini as the serial numbers given to the laser pulses increase.

[0028] Although the basic information is shown in graphs in Figures 4A and 4B, in practice information defining the relationship between elapsed time or laser pulse serial number and diffraction efficiency is stored in the memory of the control device 30 in table format.

[0029] Next, a method for defining the basic information shown in Figures 4A and 4B will be described. First, the diffraction efficiency of the optical switching element 13 is fixed to a certain value, a pulse laser beam is output from the laser oscillator 10 (Figure 1), and the pulse energy is measured by the measuring instrument 28 (Figure 1). From this measurement result, the characteristics of the laser oscillator 10 regarding fluctuations in the pulse energy can be known. The basic information can be defined so as to compensate for this fluctuation in the pulse energy.

[0030] Next, the excellent effects of the above embodiment will be described. In the above embodiment, the temporal fluctuation of the pulse energy of the pulse laser beam output from the laser oscillator 10 is compensated for by adjusting the diffraction efficiency of the optical switching element 13. This makes it possible to suppress the fluctuation of the pulse energy on the surface of the object 50 and suppress the deterioration of the processing quality.

[0031] Furthermore, in the above embodiment, the fluctuation in pulse energy is compensated for by using the optical switching element 13 that cuts out the laser pulse for processing from the pulse laser beam, so there is no need to add a new optical element for compensating for the fluctuation in pulse energy.

[0032] Next, a modification of the embodiment shown in Figs. 1 to 4B will be described. In the above embodiment, the laser oscillator 10 outputs a pulsed laser beam, but in this modified example, the laser oscillator 10 outputs a continuous wave (CW) laser beam. The laser oscillator 10 has a characteristic that the power of the continuous wave laser beam varies depending on the time elapsed from the start of output. The control device 30 compensates for the variation in the power of the continuous wave laser beam by changing the diffraction efficiency of the optical switching element 13 depending on the time elapsed from the start of output of the continuous wave laser beam. In this way, by adjusting the diffraction efficiency of the optical switching element 13, it is possible to suppress the time variation in the power of the continuous wave laser beam.

[0033] Next, a laser processing apparatus according to another embodiment will be described with reference to Figures 5A to 6. Below, a description of the configuration common to the laser processing apparatus according to the embodiment shown in Figures 1 to 4B will be omitted.

[0034] The laser oscillator 10 used in the laser processing apparatus of this embodiment has a characteristic that the peak power of the pulse laser beam varies depending on the pulse repetition frequency.

[0035] 5A is a graph showing an example of the relationship between the pulse repetition frequency and the peak power. As the pulse repetition frequency increases, the peak power decreases. The control device 30 adjusts the diffraction efficiency of the optical switching element 13 so as to compensate for the fluctuation in the peak power according to the pulse repetition frequency.

[0036] 5B is a graph showing basic information for the control device 30 to control the diffraction efficiency of the optical switching element 13. The horizontal axis represents the pulse repetition frequency, and the vertical axis represents the diffraction efficiency. As the pulse repetition frequency increases, the diffraction efficiency increases and approaches the maximum diffraction efficiency Dmax of the optical switching element 13. By controlling the diffraction efficiency in this manner, fluctuations in the peak power and pulse energy of the pulse laser beam P1 are compensated for.

[0037] 6 is a graph showing a schematic waveform of the input pulse laser beam P1 of the optical switching element 13, the diffraction efficiency of the optical switching element 13 commanded by the analog signal AM (FIG. 1), and a schematic waveform of the output pulse laser beam P2. In FIG. 6, one laser pulse of the pulse laser beams P1 and P2 is represented by one straight line.

[0038] During the period from time t21 to t24, the laser oscillator 10 (FIG. 1) outputs a pulsed laser beam. The pulse repetition frequencies during the periods from time t11 to t22, from time t22 to t23, and from time t23 to t24 are f1, f2, and f3, respectively. Frequency f1 is the highest, and frequency f3 is the lowest. Since the laser oscillator 10 has the characteristics shown in FIG. 5A, the peak power of the pulsed laser beam P1 during the period from time t11 to t22 is the lowest, and the peak power of the pulsed laser beam P1 during the period from time t23 to t24 is the highest.

[0039] The control device 30 changes the diffraction efficiency of the optical switching element 13 based on the basic information shown in Fig. 5B. That is, the diffraction efficiency is made highest in the period from time t11 to t22, and is made lowest in the period from time t23 to t24.

[0040] The peak power of the output pulse laser beam P2 extracted by the optical switching element 13 becomes almost constant over the period from time t21 to t24. As a result, the pulse energy of the pulse laser beam P2 incident on the target 50 becomes almost constant regardless of the pulse repetition frequency.

[0041] Next, a laser processing apparatus according to still another embodiment will be described with reference to Fig. 7. Below, a description of the configuration common to the laser processing apparatus according to the embodiment shown in Figs. 1 to 6 will be omitted.

[0042] Fig. 7 is a table showing basic information used by the control device 30 of the laser processing device according to this embodiment to control the diffraction efficiency of the optical switching element 13. In the embodiment shown in Figs. 1 to 4B, the relationship between the elapsed time from the start of output or the serial number given to the laser pulse and the diffraction efficiency (Figs. 4A and 4B) is defined as the basic information for controlling the diffraction efficiency of the optical switching element 13. In the embodiment shown in Figs. 5A to 6, the relationship between the pulse repetition frequency and the diffraction efficiency (Fig. 5B) is defined as the basic information for controlling the diffraction efficiency of the optical switching element 13.

[0043] In contrast to this, in this embodiment, the relationship between the diffraction efficiency and both the pulse repetition frequency and the serial number given to the laser pulse is defined as basic information. One diffraction efficiency is defined for each combination of one serial number and one frequency. When focusing on one frequency, the diffraction efficiency is increased as the laser pulse serial number increases, similar to the basic information shown in FIG. 4B. When focusing on one serial number, the diffraction efficiency is increased as the pulse repetition frequency increases, similar to the basic information shown in FIG. 5B.

[0044] Next, the excellent effects of the embodiment shown in FIG. 7 will be described. In this embodiment, both the fluctuation in peak power according to the elapsed time from the start of output of the pulse laser beam from the laser oscillator 10 (FIG. 1) and the fluctuation in peak power caused by the pulse repetition frequency can be compensated for, thereby suppressing the fluctuation in pulse energy of the pulse laser beam incident on the target 50.

[0045] Next, a laser processing apparatus according to still another embodiment will be described with reference to Figures 8A and 8B. Below, a description of the configuration common to the laser processing apparatus according to the embodiment shown in Figures 1 to 7 will be omitted.

[0046] Fig. 8A is a diagram showing an example of the distribution of a plurality of work points 53 defined on the surface of an object 50. Fig. 8A shows only a portion of the plurality of work points 53. The object 50 is a printed circuit board, and the work points 53 indicate positions where holes should be drilled. The shape of the object 50 is rectangular.

[0047] Alignment marks 51 are provided at each of the four corners of the target object 50. A plurality of processing points 53 are defined on the surface of the target object 50. In Fig. 8A, the processing points 53 are shown by circular symbols, but in reality, no marks are provided on the surface of the target object 50, and position data defining the positions of the plurality of processing points 53 is stored in the control device 30.

[0048] A plurality of scan areas 52 are defined on the surface of the object 50. The shape of each of the scan areas 52 is square, and the size is approximately equal to the size of the range in which the incident position of the pulse laser beam can be moved by operating the beam scanner 25 (FIG. 1). The plurality of scan areas 52 are arranged so that all the workpiece points 53 on the object 50 are included within any one of the scan areas 52. The plurality of scan areas 52 may partially overlap, and a scan area 52 may not be arranged in an area where the workpiece points 53 are not distributed. A workpiece point 53 located in an area where the plurality of scan areas 52 overlap belongs to any one of the scan areas 52, and the workpiece point 53 is processed when the scan area 52 to which the workpiece point 53 belongs is processed.

[0049] When processing the object 50, one scan area 52 of the object 50 is moved directly below the condenser lens 26 (FIG. 1). The scan area 52 is processed by sequentially positioning the incident position of the pulse laser beam on a plurality of processing points 53 in the scan area 52 arranged directly below the condenser lens 26. When the processing of one scan area 52 is completed, the stage 27 (FIG. 1) is operated to move the next scan area 52 to be processed directly below the condenser lens 26. During the processing of one scan area 52, the stage 27 remains stationary. In FIG. 8A, the processing order of the scan areas 52 is indicated by arrows.

[0050] Fig. 8B is a diagram showing an example of the order of machining a plurality of work points 53. A serial number is assigned to the plurality of work points 53. The beam scanner 25 (Fig. 1) is operated to cause a pulse laser beam to be incident on the plurality of work points 53 in the order of the serial numbers, thereby machining one scan area 52. In Fig. 8B, the order of machining a plurality of work points 53 is indicated by arrows. The order of machining the work points 53 is determined, for example, so that the movement path of the incident position of the pulse laser beam is the shortest.

[0051] The time required to move the incident position of the pulsed laser beam from processing one work point 53 to the next work point 53 depends on the distance between the two work points 53. When the distance between the two work points 53 is long, the time interval between the laser pulses becomes long. In other words, the pulse repetition frequency becomes low. For this reason, when processing a scan area 52 in which the work points 53 are densely distributed, the pulse repetition frequency can be made higher than when processing a scan area 52 in which the work points 53 are sparsely distributed. In this way, the preferable pulse repetition frequency of the pulsed laser beam used for processing differs for each scan area 52.

[0052] 8A, the points to be processed 53 are distributed more densely in the scan area 52 to be processed second than in the scan area 52 to be processed first. For this reason, the pulse repetition frequency f1 of the pulse laser beam used to process the scan area 52 to be processed second is made higher than the pulse repetition frequency f2 of the pulse laser beam used to process the scan area 52 to be processed first.

[0053] In this way, processing is performed by setting the pulse repetition frequency of the pulse laser beam to an optimal value for each scan area 52. At this time, as in the embodiment shown in Fig. 5B or Fig. 7, the diffraction efficiency of the optical switching element 13 is adjusted according to the pulse repetition frequency.

[0054] Next, the excellent effects of the embodiment shown in Figures 8A and 8B will be described. In this embodiment, even if the pulse repetition frequency is made different for each scan area 52, processing can be performed with almost constant pulse energy. Therefore, it is possible to suppress the deterioration of processing quality caused by the variation in pulse energy.

[0055] Next, a modification of the above embodiment will be described. 1 to 8, the laser beam is extracted by the optical switching element 13 and propagates along one path toward the target 50, but the pulsed laser beam may be propagated along two paths having different diffraction angles by the optical switching element 13. For example, a laser pulse propagating along one path and a laser pulse propagating along the other path may be extracted from one laser pulse of the input pulsed laser beam P1. In this case as well, the peak power and pulse energy of the extracted laser pulse can be made substantially constant by controlling the diffraction efficiency.

[0056] In the above embodiment, an acousto-optic deflector is used as the optical switching element 13, but other optical elements may be used, for example, an electro-optic modulator (EOM) and a polarizing beam splitter may be used.

[0057] The above-mentioned embodiments are merely examples, and it goes without saying that partial replacement or combination of the configurations shown in different embodiments is possible. Similar effects due to similar configurations of multiple embodiments are not mentioned in each embodiment. Furthermore, the present invention is not limited to the above-mentioned embodiments. For example, it will be obvious to those skilled in the art that various modifications, improvements, combinations, etc. are possible. [Explanation of symbols]

[0058] 10 Laser Oscillator 11 Beam shaping optics 12 Aperture 13 Optical switching element 14 Drivers 21 Beam dumper 22. Mirror 25 Beam Scanner 25X, 25Y oscillating mirror 26 Condenser Lens 27 Stages 28 Measuring Instruments 30 Control device 41, 42 Laser pulse at the input of the optical switching element 43, 44 Laser pulses extracted by optical switching elements 50 Objects 51 Alignment Mark 52 Scan Area 53 Processing point

Claims

1. A laser oscillator; an optical switching element for cutting out a part of the pulsed laser beam output from the laser oscillator on a time axis and directing the part of the laser beam toward an object; a control device that changes the transmittance of the optical switching element in response to peak power of each of a plurality of laser pulses of the pulse laser beam output from the laser oscillator; A laser processing device equipped with the above-mentioned.

2. The peak power of the pulsed laser beam output from the laser oscillator varies according to the elapsed time from the start of output of the pulsed laser beam, 2. The laser processing apparatus according to claim 1, wherein the control device changes the transmittance of the optical switching element in accordance with the elapsed time from the start of output of the pulse laser beam from the laser oscillator.

3. The peak power of the pulsed laser beam output from the laser oscillator varies according to the elapsed time from the start of output of the pulsed laser beam, 2. The laser processing apparatus according to claim 1, wherein the control device changes the transmittance of the optical switching element in accordance with a serial number given to laser pulses outputted sequentially from a point in time when output of the pulse laser beam from the laser oscillator is started.

4. The peak power of the pulsed laser beam output from the laser oscillator varies depending on the pulse repetition frequency, 2. The laser processing apparatus according to claim 1, wherein the control device changes the transmittance of the optical switching element in response to a pulse repetition frequency.

5. A pulsed laser beam is incident on an optical switching element, a portion of the laser beam is cut out on the time axis, and directed toward a target object; A laser processing method in which the power of the laser beam incident on the object is adjusted by changing the transmittance of the optical switching element in accordance with the peak power of each of a plurality of laser pulses of the pulsed laser beam incident on the optical switching element.

6. A laser processing method as described in claim 5, in which, when adjusting the power of the laser beam incident on the object, the transmittance of the optical switching element is changed, thereby making the peak power of the pulsed laser beam incident on the object closer to a constant value.

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