Laser oscillation device and laser oscillation method

Abstract

To provide a laser oscillation device and a laser oscillation method that can initiate pulse oscillation of laser light with desired characteristics.SOLUTION: A laser oscillation device 1 includes a pair of mirrors 31, 32, a laser medium 33, an attenuator 34 that puts the laser light L1 in a non-resonant state at a first attenuation rate and puts the laser light L1 in a resonant state at a second attenuation rate, and a control unit 2. The control unit 2 causes the attenuator 34 to maintain the attenuation rate at the second attenuation rate such that the laser light L1 is oscillated as a continuous wave in a first period, and causes the attenuator 34 to switch the attenuation rate such that the first attenuation rate and the second attenuation rate are alternately repeated in a second period that is continuous with the first period. The first period is longer than the time from the timing at which the attenuation rate is switched to the second attenuation rate for the first time to the timing at which the attenuation rate is switched to the second attenuation rate for the second time in the second period.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laser oscillation device and a laser oscillation method. [Background technology]

[0002] Patent Document 1 describes a Q-switched laser device that oscillates laser light as a pulse wave by a Q-switched oscillation method. In the Q-switched laser device described in Patent Document 1, a high-frequency signal is input from a high-frequency generator to an acousto-optical Q-switch, and the oscillation of the laser light is suppressed by the acousto-optical Q-switch, energy is accumulated in the laser medium, and the amplitude of the high-frequency signal is gradually reduced from that state with a predetermined time constant, thereby starting pulsed oscillation of the laser light. For example, if the amplitude of the high-frequency signal is instantly reduced, the peak output of the laser light may become higher than expected at the start of pulsed oscillation of the laser light, but the Q-switched laser device described in Patent Document 1 can prevent such a phenomenon from occurring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-332791 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the pulse oscillation of the laser light starts, not only the peak output of the laser light but also the beam diameter, pulse width, etc. of the laser light are likely to fluctuate, so in the Q-switched laser device described in Patent Document 1, there is a risk that the pulse oscillation of the laser light will start in a state where the beam diameter, pulse width, etc. of the laser light deviate from the desired values.

[0005] An object of the present invention is to provide a laser oscillation device and a laser oscillation method that can start pulse oscillation of laser light with desired characteristics. [Means for solving the problem]

[0006] The laser oscillation device of the present invention is, [1] "a pair of mirrors that causes laser light to travel back and forth along a resonant optical path, a laser medium that is disposed on the resonant optical path and that amplifies the laser light, an attenuator that is disposed on the resonant optical path and that causes the laser light to be in a non-resonant state at a first attenuation rate and in a resonant state at a second attenuation rate, and a control unit that controls the attenuator, wherein the control unit causes the attenuator to maintain an attenuation rate at which the second attenuation rate is maintained so that the laser light is oscillated as a continuous wave in a first period, and causes the attenuator to switch the attenuation rate so that the first attenuation rate and the second attenuation rate are alternately repeated so that the laser light is oscillated as a pulse wave in a second period that is subsequent to the first period, and the first period is longer than a time from a timing at which the attenuation rate is switched to the second attenuation rate for the first time to a timing at which the attenuation rate is switched to the second attenuation rate for the second time in the second period."

[0007] In the laser oscillation device described in [1] above, the laser light is oscillated as a continuous wave in the first period, and the laser light is oscillated as a pulse wave in the second period that is continuous with the first period. Furthermore, the first period in which the laser light is oscillated as a continuous wave is longer than the time from the timing at which the attenuation rate is switched to the second attenuation rate for the first time to the timing at which the attenuation rate is switched to the second attenuation rate for the second time in the second period in which the laser light is oscillated as a pulse wave. As a result, the heat distribution of each component including the laser medium, the pair of mirrors, the attenuator, etc. is less likely to vary between the first period and the second period, compared to the case in which the oscillation of the laser light is stopped by maintaining the attenuation rate of the attenuator at the first attenuation rate in the first period, and as a result, the peak output, beam diameter, pulse width, etc. of the laser light are less likely to vary at the start of the pulse oscillation of the laser light. Therefore, according to the laser oscillation device described in [1] above, the pulse oscillation of the laser light can be started with the desired characteristics.

[0008] The laser oscillation device of the present invention may be [2] "the laser oscillation device described in [1] above, in which one of the pair of mirrors emits the laser light as the continuous wave in the first period and emits the laser light as the pulse wave in the second period." According to the laser oscillation device described in [2], it is possible to simplify the structure without providing a shutter or the like that blocks the laser light emitted as a continuous wave.

[0009] The laser oscillation device of the present invention may be [3] "the laser oscillation device according to the above [1] or [2], in which the difference between the average output of the laser light in the first period and the average output of the laser light in the second period is 30% or less of the average output of the laser light in the second period." According to the laser oscillation device according to [3], the difference between the average output of the laser light in the first period and the average output of the laser light in the second period is suppressed, so that the heat distribution of each component including the laser medium, the pair of mirrors, the attenuator, etc. becomes less likely to fluctuate between the first period and the second period.

[0010] The laser oscillation device of the present invention may be [4] "the laser oscillation device according to any one of the above [1] to [3], in which the average output of the laser light in the first period is 0.5% or less of the peak output of the laser light in the second period." According to the laser oscillation device described in [4], the average output of the laser light oscillated as a continuous wave in the first period is prevented from becoming excessively large, so that the object irradiated with the laser light can be prevented from being thermally affected in the first period.

[0011] The laser oscillation device of the present invention may be [5] "the laser oscillation device according to any one of the above [1] to [4], wherein the first period is 10 seconds or longer." According to the laser oscillation device according to [5], for example, even at the start of the laser oscillation device, the heat distribution of each component including the laser medium, the pair of mirrors, and the attenuator can be made to be in a state in which it is difficult to vary between the first period and the second period.

[0012] The laser oscillation device of the present invention may be [6] "the laser oscillation device according to any one of the above [1] to [5], wherein the control unit controls the attenuator so that the switching of the attenuation rate starts with the implementation of the first attenuation rate in the second period." According to the laser oscillation device described in [6], when the attenuation rate is switched to the second attenuation rate for the first time in the second period, one pulse of laser light having desired characteristics can be emitted.

[0013] The laser oscillation device of the present invention may be [7] "the laser oscillation device according to any one of the above [1] to [6], wherein the control unit controls the attenuator so that the maintenance of the attenuation rate in the first period and the switching of the attenuation rate in the second period are alternately repeated." According to the laser oscillation device described in [7], in any of the repeated second periods, the heat distribution of each component including the laser medium, the pair of mirrors, the attenuator, etc. can be made to be in a state that is unlikely to fluctuate between the first period and the second period.

[0014] The laser oscillation device of the present invention may be the laser oscillation device described in [7] above, in which the control unit causes the attenuator to gradually decrease the attenuation rate to the second attenuation rate during a third period from the end of the second period to the start of the first period. According to the laser oscillation device described in [8], it is possible to suppress fluctuations in the output of the laser light that may occur if the attenuator immediately starts to maintain the second attenuation rate when transitioning from the second period to the first period.

[0015] The laser oscillation device of the present invention may be [9] "the laser oscillation device according to any one of the above [1] to [8], wherein the control unit controls the attenuator so that the switching of the attenuation rate in the second period ends with the implementation of the second attenuation rate." According to the laser oscillation device described in [9], when the attenuation rate is finally switched to the second attenuation rate in the second period, one pulse of laser light having desired characteristics can be emitted.

[0016] The laser oscillator of the present invention may be

[10] "the laser oscillator according to any one of [1] to [9] above, in which the attenuator is an acousto-optical modulator and the control unit includes an RF oscillator." According to the laser oscillator according to

[10] , it is possible to suitably adjust the attenuation rate of the attenuator.

[0017] The laser oscillator of the present invention may be

[11] "the laser oscillator according to any one of [1] to [9] above, in which the attenuator is an opto-electrical modulator and the control unit includes a voltage generator." According to the laser oscillator according to

[11] , it is possible to suitably adjust the attenuation rate of the attenuator.

[0018] The laser oscillation method of the present invention may be

[12] "a laser oscillation method performed in a laser oscillation device including a pair of mirrors that causes a laser beam to travel back and forth along a resonant optical path, a laser medium that is disposed on the resonant optical path and that amplifies the laser beam, and an attenuator that is disposed on the resonant optical path and that causes the laser beam to be in a non-resonant state at a first attenuation rate and in a resonant state at a second attenuation rate, the method including: a step of the attenuator maintaining an attenuation rate at which the second attenuation rate is maintained so that the laser beam is oscillated as a continuous wave in a first period; and a step of the attenuator switching the attenuation rate so that the first attenuation rate and the second attenuation rate are alternately repeated in a second period that is continuous with the first period, the first period being longer than a time from a timing at which the attenuation rate is switched to the second attenuation rate for the first time to a timing at which the attenuation rate is switched to the second attenuation rate for the second time in the second period."

[0019] According to the laser oscillation method described in

[12] above, for the same reason as in the laser oscillation device described in [1] above, it is possible to start pulse oscillation of laser light with desired characteristics. Effect of the Invention

[0020] According to the present invention, it is possible to provide a laser oscillation device and a laser oscillation method that can start pulse oscillation of laser light with desired characteristics. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram showing a configuration of a laser processing apparatus including a laser oscillation apparatus according to one embodiment; [Diagram 2] 2 is a diagram for explaining an example of processing carried out by the laser processing apparatus shown in FIG. 1. [Diagram 3] 2A to 2C are diagrams for explaining a laser oscillation method carried out in the laser oscillation device shown in FIG. [Figure 4] 2 is a diagram showing a control signal, a laser light output, and a processing result in the laser oscillation device shown in FIG. 1. [Diagram 5] 5A to 5C are diagrams illustrating a control signal, a laser light output, and a processing result in a laser oscillation device of a comparative example. [Figure 6] 13A to 13C are diagrams illustrating a control signal, a laser light output, and a processing result in a laser oscillation device of a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted. [Laser processing equipment configuration]

[0023] As shown in FIG. 1, the laser processing apparatus 10 includes a laser oscillator 1, a galvanometer mirror 11, and a control device 12. The laser oscillator 1 oscillates a laser beam L1 as a pulse wave PW. The pulse wave PW is a laser beam for processing. The galvanometer mirror 11 scans an object (not shown) with the pulse wave PW emitted from the laser oscillator 1. The control device 12 controls the laser oscillator 1 and the galvanometer mirror 11. As an example, the laser processing apparatus 10 is used to cut out a plurality of chips from a wafer (object) in a semiconductor manufacturing process. As another example, the laser processing apparatus 10 is used to form holes or grooves on the surface of a wafer for patterning or marking.

[0024] The laser oscillation device 1 includes a control unit 2, a laser resonator 3, and a light source 4. The control unit 2 includes a laser control unit 21 and a signal generating unit 22. The laser resonator 3 includes a pair of mirrors 31, 32, a laser medium 33, and an attenuator 34. The control unit 2 controls the attenuator 34 (details will be described later).

[0025] The laser control unit 21 controls the signal generating unit 22 based on an instruction signal input from the control device 12. The signal generating unit 22 is an RF oscillator that outputs an RF signal. In other words, the control unit 2 includes an RF oscillator. The signal generating unit 22 is controlled by the laser control unit 21 to modulate the RF signal and generate a control signal.

[0026] The pair of mirrors 31, 32 face each other. A resonant optical path A is formed between the pair of mirrors 31, 32. The mirror 31 is a total reflection mirror, and the mirror 32 is a semi-reflection mirror. The laser medium 33 is disposed on the resonant optical path A between the pair of mirrors 31, 32. The laser medium 33 is irradiated with the excitation light L2 emitted from the light source 4. The attenuator 34 is disposed on the resonant optical path A between the laser medium 33 and one of the mirrors 32. The attenuator 34 is an optical acoustic modulator. The attenuator 34 converts a control signal, which is an RF signal, into ultrasonic waves and uses the ultrasonic waves to change the optical characteristics of the laser light L1, thereby switching the attenuation rate.

[0027] In the laser resonator 3, when the attenuator 34 is in a state in which the laser light L1 can pass through, the laser medium 33 is excited by irradiation with the excitation light L2, whereby the laser light L1 is generated in the laser medium 33, and the laser light L is amplified by the laser medium 33 while the pair of mirrors 31 and 32 cause the laser light L to travel back and forth along the resonant optical path A. A portion of the amplified laser light L passes through the mirror 32 and is emitted to the outside, and is scanned by the galvanometer mirror 11. The wavelength of the laser light L1 is, for example, 1.1 μm or more. The laser medium 33 is, for example, a solid-state laser medium. An example of a solid-state laser medium that generates the laser light L1 with a wavelength of 1.1 μm or more is Nd:YVO 4 The heat distribution of the solid-state laser medium generating the laser light L1 with a wavelength of 1.1 μm or more is likely to change (changes relatively quickly and significantly) between when the solid-state laser medium is excited by being irradiated with the excitation light L2 and when the solid-state laser medium is not excited by not being irradiated with the excitation light L2.

[0028] The attenuator 34 switches the attenuation rate between the first attenuation rate and the second attenuation rate based on the control signal input from the signal generating unit 22. The first attenuation rate is greater than the second attenuation rate. The attenuator 34 attenuates the laser light L1 by setting the attenuation rate to the first attenuation rate, and sets the laser light L1 in a non-resonant state. In the non-resonant state, the laser light L1 is not made to go back and forth between the pair of mirrors 31, 32, and the energy of the excitation light L2 is accumulated in the laser medium 33. The attenuator 34 transmits the laser light L1 by setting the attenuation rate to the second attenuation rate, and sets the laser light L1 in a resonant state. In the resonant state, the laser light L1 is made to go back and forth between the pair of mirrors 31, 32, and the laser light L is amplified by the laser medium 33. In this embodiment, when the attenuator 34 maintains the attenuation rate at which the second attenuation rate is maintained, the laser light L1 is emitted from the mirror 32 as a continuous wave CW (see FIG. 3). Also. When the attenuator 34 switches the attenuation rate between the first attenuation rate and the second attenuation rate, the laser light L1 is emitted from the mirror 32 as a pulse wave PW. [Laser oscillation method implemented in a laser oscillation device]

[0029] For the sake of simplicity, the laser oscillation method performed by the laser oscillation device 1 will be described below using as an example a case where the laser processing device 10 prints the alphabet "A" on the surface of an object. Printing by the laser processing device 10 is achieved, for example, by processing (charring or cutting) the surface of the object to a predetermined depth by ablation.

[0030] The control device 12 receives a character ("A") to be printed by the laser light L1, for example, from a user interface. The control device 12 then registers information on the scanning sequence and coordinates of "A" in, for example, an internal memory. Based on the registered information, the control device 12 generates a scanning signal Sg that instructs the scanning procedure for printing "A", as shown in FIG. 2(a). In FIG. 2(a), the horizontal axis indicates time, and the vertical axis indicates the magnitude of the scanning signal Sg (here, a voltage value is used as an example). The scanning signal Sg is a pulse signal whose signal level changes between a low level and a high level at predetermined time intervals. In the example shown in FIG. 2(a), the scanning signal Sg is active when it is at a high level.

[0031] The printing procedure for the letter "A" based on the scanning signal Sg is as follows. First, the control device 12 controls the laser oscillator 1 so that the pulse wave PW is not oscillated from time t1 to time t2, and also controls the optical axis of the pulse wave PW to coincide with the coordinate S 1 Next, the control device 12 controls the laser oscillator 1 so that the pulse wave PW is oscillated from time t3 to time t4, and also controls the laser oscillator 1 so that the pulse wave PW is oscillated at the coordinate S 1 From coordinate E 1 The control unit 12 controls the galvanometer mirror 11 so that the pulse wave PW scans toward the coordinate S. As a result, the first stroke of the letter "A" is printed on the surface of the object. Next, the control unit 12 controls the laser oscillator 1 so that the pulse wave PW is oscillated from time t5 to time t6, and also controls the laser oscillator 1 so that the pulse wave PW is oscillated toward the coordinate S. 2 From coordinate E 2 The galvanometer mirror 11 is controlled so that the pulse wave PW scans toward the target object. As a result, the second stroke of the letter "A" is printed on the surface of the target object.

[0032] Next, from time t7 to time t8, the control device 12 controls the laser oscillator 1 so that the pulse wave PW is not oscillated, and the optical axis of the pulse wave PW is aligned with the coordinate S 3Finally, the control device 12 controls the laser oscillator 1 so that the pulse wave PW is oscillated from time t9 to time t10, and also controls the laser oscillator 1 so that the pulse wave PW is oscillated at the coordinate S 3 From coordinate E 3 The galvanometer mirror 11 is controlled so that the pulse wave PW scans toward the target object. As a result, the third stroke of the letter "A" is printed on the surface of the target object. In this way, the laser processing device 10 prints the letter "A" on the surface of the target object.

[0033] When scanning the surface of the object with the pulse wave PW as described above, the control device 12 generates an instruction signal Sd based on the scanning signal Sg, as shown in (a) and (b) of FIG. 3. The instruction signal Sd is a signal that indicates the period during which the laser oscillation device 1 oscillates the laser light L1 as a pulse wave PW. In (b) of FIG. 3, the horizontal axis indicates time, and the vertical axis indicates the magnitude of the instruction signal Sd (here, as an example, a voltage value). The instruction signal Sd is a pulse signal whose signal level changes between a low level and a high level at predetermined time intervals. In the example shown in (b) of FIG. 3, the instruction signal Sd becomes active when it is at a high level.

[0034] The laser oscillation device 1 oscillates the laser light L1 as a pulse wave PW during a period when the instruction signal Sd is at Hi level. The instruction signal Sd becomes Hi level in synchronization with a period during which "A" is printed in the scanning signal Sg. Specifically, the instruction signal Sd becomes Hi level between time t3 and time t4, between time t5 and time t6, and between time t9 and time t10.

[0035] The laser control unit 21 controls the signal generating unit 22 based on the instruction signal Sd input from the control device 12. The signal generating unit 22 is controlled by the laser control unit 21 to modulate the RF signal and generate a control signal Sc.

[0036] As shown in FIG. 3(c), the control signal Sc includes a first period T1, a second period T2, and a third period T3. The first period T1, the second period T2, and the third period T3 are repeated in the order of the first period T1, the second period T2, and the third period T3. In FIG. 3(c), the horizontal axis indicates time, and the vertical axis indicates the magnitude of the control signal Sc (here, the voltage value is used as an example). The second period T2 corresponds to the period during which the instruction signal Sd is at Hi level. The first period T1 and the third period T3 correspond to the period during which the instruction signal Sd is at Low level. The first period T1 ends and the second period T2 starts when the instruction signal Sd rises from Low level to Hi level as a trigger. The second period T2 ends and the third period T3 starts when the instruction signal Sd falls from Hi level to Low level as a trigger. The timing when the second period T2 starts coincides with the timing when the instruction signal Sd rises from a low level to a high level, and the timing when the second period T2 ends substantially coincides with the timing when the instruction signal Sd falls from a high level to a low level.

[0037] The control unit 2 causes the attenuator 34 to maintain the attenuation rate so that the laser light L1 is oscillated as a continuous wave CW in the first period T1 (step of the attenuator maintaining the attenuation rate). The laser control unit 21 controls the signal generating unit 22 not to output the control signal Sc in the first period T1. The second attenuation rate is a value that does not attenuate the laser light L1, and is substantially zero. However, the second attenuation rate may be greater than zero as long as it is within a range of values ​​that can maintain the resonant state of the laser light L1. The attenuator 34 maintains the attenuation rate at the second attenuation rate in the first period T1. This maintains the resonant state of the laser light L1. As a result, as shown in (d) of FIG. 3, the laser oscillation device 1 oscillates the laser light L1 as a continuous wave CW in the first period T1. In (d) of FIG. 3, the horizontal axis indicates time, and the vertical axis indicates the output of the laser light L1. The unit of the output of the laser light L1 is, for example, watts [W]. The continuous wave CW is a non-processing laser light. That is, the output of the continuous wave CW (the output of the laser light L1 in the first period T1) is smaller than the processing threshold, which is the output threshold at which the target object is processed. As a result, during the first period T1, no marking is performed on the surface of the target object.

[0038] The second period T2 is continuous with the first period T1. The timing at which the second period T2 starts is synchronized with the timing at which the instruction signal Sd switches from a low level to a high level. In the second period T2, the control unit 2 causes the attenuator 34 to switch the attenuation rate so that the first attenuation rate and the second attenuation rate are alternately repeated so that the laser light L1 is oscillated as a pulse wave PW (a step in which the attenuator switches the attenuation rate). In the second period T2, the laser control unit 21 controls the signal generating unit 22 so that a period in which the control signal Sc is output with an amplitude W1 and a period in which the control signal Sc is not output are repeated. In the period in which the control signal Sc is output with an amplitude W1, the attenuator 34 sets the attenuation rate to the first attenuation rate, and in the period in which the control signal Sc is not output, the attenuation rate to the second attenuation rate. As a result, in the second period T2, the non-resonant state of the laser light L1 and the resonant state of the laser light L1 are repeated, and thus the accumulation of energy in the excitation light L2 and the release of energy in the excitation light L2 are repeated. As a result, as shown in (d) of Fig. 3, the laser oscillation device 1 oscillates the laser light L1 as a processing pulse wave PW in the second period T2. As a result, the first stroke of "A" is printed on the surface of the object in the second period T2.

[0039] The pulse wave PW is a pulse group consisting of a plurality of pulses P generated at a constant repetition frequency. The repetition frequency of the plurality of pulses P is, for example, several kHz. The time interval (period) between adjacent pulses P in the plurality of pulses P is, for example, a value between 10 μm and 100 μm. Furthermore, the peak output Pk of each pulse P is substantially the same for all pulses P. Here, substantially the same means that the peak output varies within an allowable error range. The peak output Pk is the maximum value of the output of each pulse P. The peak output Pk is also a value obtained by dividing the pulse energy of the laser light L1 by the pulse width of each pulse P. The unit of the peak output Pk is watts [W].

[0040] The first period T1 is longer than the time T21 from the timing when the attenuation rate is switched to the second attenuation rate for the first time in the second period T2 to the timing when the attenuation rate is switched to the second time. The time T21 is approximately equal to the time from when the first pulse P is output in the pulse wave PW to when the second pulse P is output. The first first period T1 after the laser oscillation device 1 is started is, for example, 10 seconds or more. The second and subsequent first periods may be 10 seconds or less as long as they are longer than the time T21.

[0041] The control unit 2 controls the attenuator 34 so that the switching of the attenuation rate starts with the first attenuation rate in the second period T2. Specifically, when the first period T1 ends and the second period T2 starts, the attenuator 34 switches the attenuation rate from the second attenuation rate to the first attenuation rate. The attenuator 34 starts the switching of the attenuation rate at the first attenuation rate in the second period T2. Then, the attenuator 34 switches the attenuation rate to the second attenuation rate after maintaining the first attenuation rate for a predetermined time. This predetermined time is a time during which the energy of the excitation light L2 can be accumulated in the laser medium 33 so that the first pulse P is appropriately output. By maintaining the first attenuation rate for a predetermined time by the attenuator 34, as shown in (d) of FIG. 3, when switching from the first period T1 to the second period T2, the oscillation of the continuous wave CW and the oscillation of the first pulse P are separated in time.

[0042] In the first period T1, the mirror 32 emits the laser light L1 as a continuous wave CW. In the second period T2, the mirror 32 emits the laser light L1 as a pulse wave PW.

[0043] The difference between the average output of the laser light L1 in the first period T1 oscillated as a continuous wave CW and the average output of the laser light L1 in the second period T2 oscillated as a pulse wave PW is 30% or less of the average output of the laser light L1 in the second period T2 oscillated as a pulse wave PW. The average output is the sum of the outputs of the laser light L1 per unit time. The average output is also a value obtained by multiplying the pulse energy of the laser light L1 by the repetition frequency. The unit of the average output is watts [W]. Moreover, the average output of the laser light L1 in the first period T1 oscillated as a continuous wave CW is 0.5% or less of the peak output Pk of the laser light L1 in the second period T2 oscillated as a pulse wave PW. Here, the peak output Pk is the maximum peak output Pk among the peak outputs Pk of the multiple pulses P constituting the pulse wave PW.

[0044] The control unit 2 controls the attenuator 34 so that the switching of the attenuation rate ends with the implementation of the second attenuation rate in the second period T2. The attenuator 34 ends the switching of the attenuation rate in the second period T2 in a state where the attenuation rate is maintained at the second attenuation rate for a predetermined time based on the control signal Sc. Specifically, when the instruction signal Sd switches from Hi level to Low level, the laser control unit 21 controls the attenuator 34 via the signal generating unit 22 so that the second period T2 ends after a predetermined time has elapsed since the attenuation rate was switched to the second attenuation rate. This predetermined time is a time during which the last pulse P in the second period T2 can be appropriately output. For example, the predetermined time is a time until the output of the last pulse P becomes 0 W and the oscillation of the last pulse P is completed. In other words, the laser control unit 21 does not control the attenuator 34 to end the second period T2 in synchronization with the timing when the instruction signal Sd switches from Hi level to Low level.

[0045] As shown in FIG. 3, at time t4, which is the timing when the instruction signal Sd switches from Hi level to Low level, the attenuation rate is switched to the second attenuation rate, and the last pulse P is oscillated. In this case, the laser control unit 21 controls the attenuator 34 to end the second period T2 after a predetermined time has elapsed since the attenuation rate was switched to the second attenuation rate and the output of the last pulse P becomes 0 W. Also, at time t10, which is another timing when the instruction signal Sd switches from Hi level to Low level, the attenuation rate is switched to the first attenuation rate, and the last pulse P has not yet been oscillated. In this case, the laser control unit 21 controls the attenuator 34 to switch the attenuation rate to the second attenuation rate. Then, the laser control unit 21 controls the attenuator 34 to end the second period T2 after a predetermined time has elapsed since the attenuation rate was switched to the second attenuation rate and the output of the last pulse P becomes 0 W.

[0046] The control unit 2 controls the attenuator 34 so that the attenuation rate in the first period T1 is maintained and the attenuation rate in the second period T2 is switched alternately. Since the first period T1 and the second period T2 are alternately repeated, the attenuator 34 alternately maintains the second attenuation rate in the first period T1 and switches the attenuation rate in the second period T2. As a result, as shown in (d) of FIG. 3, the laser light L1 is alternately oscillated as a continuous wave CW in the first period T1 and the laser light L1 is alternately oscillated as a pulse wave PW in the second period T2.

[0047] The third period T3 is continuous with the second period T2. The third period T3 is a period from the end of the second period T2 to the start of the first period T1. The control unit 2 causes the attenuator 34 to gradually decrease the attenuation rate to the second attenuation rate in the third period T3. As shown in FIG. 3(c), the laser control unit 21 controls the signal generating unit 22 to gradually decrease the control signal Sc from the amplitude W2 to 0 V after gradually increasing the control signal Sc from 0 V to the amplitude W2 in the third period T3. The amplitude W2 is smaller than the amplitude W1. The attenuator 34 gradually increases the attenuation rate from the second attenuation rate to the attenuation rate corresponding to the amplitude W2 in the third period T3 based on the control signal Sc, and then gradually decreases the attenuation rate from the attenuation rate corresponding to the amplitude W2 to the second attenuation rate.

[0048] In the third period T3, since the attenuator 6 does not switch the attenuation rate, the laser light L1 is oscillated as a continuous wave CW. As a result, in the third period T3, no marking is performed on the surface of the object. However, if the attenuator 34 immediately starts to maintain the second attenuation rate when the second period T2 transitions to the first period T1, an unintended pulse wave (hereinafter referred to as a "relaxation oscillation wave") may be generated at the start of the first period T1. This relaxation oscillation wave may cause unintended processing marks on the object. In order to reduce the peak output of the relaxation oscillation wave, it is effective to gradually decrease the attenuation rate. The laser control unit 21 appropriately sets the value of the amplitude W2, the time required to gradually increase the control signal Sc from 0V to the amplitude W2, and the time required to gradually decrease the control signal Sc from the amplitude W2 to 0V, thereby reducing the peak output of the relaxation oscillation wave to a desired value.

[0049] Next, the effect of the laser oscillation device 1 of the embodiment will be described with reference to Figs. 4 and 5. Fig. 4 (a) to (c) show an instruction signal Sd input to the laser oscillation device 1, a control signal Sc generated in the laser oscillation device 1, and the output of the laser light L1 oscillated in the laser oscillation device 1. Fig. 4 (d) shows an example of a processing result by a laser processing device 10 including the laser oscillation device 1. As shown in Fig. 4 (d), the laser processing device 10 prints the character "A" by continuously forming a plurality of processing marks M. Each processing mark M is formed by irradiating the processing target with each pulse P. When the laser oscillation device 1 is used, each of the multiple processing marks M is uniform in size. It can also be seen that the processing marks M are not missing, and processing marks M are not formed in unnecessary places (dents are formed), and good characters are printed.

[0050] 5(a) to (c) show the output of the instruction signal Sd, the control signal Sc, and the laser light L1 in the laser oscillation device of the comparative example. In the laser oscillation device of the comparative example, as shown in FIG. 5(b), the laser control unit 21 outputs the control signal Sc with an amplitude W1 in the first period T1. Also, the control signal Sc does not include the third period T3, and the first period T1 and the second period T2 are repeated alternately. Other than these points, the laser oscillation device is the same as the laser oscillation device 1. In the laser oscillation device of the comparative example, the attenuator 34 sets the attenuation rate to the first attenuation rate in the first period T1, and puts the laser light L1 in a non-resonant state.

[0051] As shown in (c) of FIG. 5, in the second period T2, among the multiple pulses P constituting the pulse wave PW, the peak output Pka of the first pulse P or the second pulse P is smaller than the peak output Pk of the third or subsequent pulse P. This is because the laser light L1 is in a non-resonant state in the first period T1, and it is assumed that the laser resonator 3 is not sufficiently excited in the first period T1, and a deviation occurs between the heat distribution of the laser resonator 3 in the first period T1 and the heat distribution of the laser resonator 3 in the second period T2. As a result, it is assumed that the characteristics of the laser light L1 fluctuate between the first period T1 and the second period T2, causing the peak output to fluctuate. As a result, as shown in (d) of FIG. 5, the size of the processed marks M corresponding to the beginning of each of the first, second, and third strokes of "A" is smaller than the size of the other processed marks M. Therefore, it can be said that the processing accuracy of the laser oscillation device of the comparative example is lower than that of the laser oscillation device 1. [Action and Effects]

[0052] In the laser oscillation device 1, the laser light L1 is oscillated as a continuous wave CW in a first period T1, and the laser light L1 is oscillated as a pulse wave PW in a second period T2 following the first period T1. Furthermore, the first period T1 in which the laser light L1 is oscillated as a continuous wave CW is longer than the time T21 from the timing when the laser light L1 is switched to the second attenuation rate for the first time to the timing when the laser light L1 is switched to the second attenuation rate for the second time in the second period T2 in which the laser light L1 is oscillated as a pulse wave PW. As a result, compared to the case where the oscillation of the laser light L1 is stopped by maintaining the attenuation rate of the attenuator 34 at the first attenuation rate in the first period T1, the heat distribution of each component in the laser resonator 3 (i.e., each component including the pair of mirrors 31, 32, the laser medium 33, and the attenuator 34, etc.) is less likely to vary between the first period T1 and the second period T2, and as a result, the peak output Pk, beam diameter, pulse width, etc. of the laser light L1 are also less likely to vary when the pulse oscillation of the laser light L1 starts. Therefore, according to the laser oscillation device 1, the pulse oscillation of the laser light L1 can be started with desired characteristics.

[0053] One mirror 32 of the pair of mirrors 31, 32 emits the laser light L1 as a continuous wave CW in the first period T1, and emits the laser light L1 as a pulse wave PW in the second period T2. According to the laser oscillation device 1, it is possible to simplify the structure without providing a shutter or the like that blocks the laser light L1 emitted as a continuous wave CW.

[0054] The difference between the average output of the laser light L1 in the first period T1 and the average output of the laser light L1 in the second period T2 is 30% or less of the average output of the laser light L1 in the second period T2. According to the laser oscillation device 1, the difference between the average output of the laser light L1 in the first period T1 and the average output of the laser light L1 in the second period T2 is reduced, so that the heat distribution of each component in the laser resonator 3 becomes even less likely to vary between the first period T1 and the second period T2.

[0055] The average output of the laser light L1 in the first period T1 is 0.5% or less of the peak output Pk of the laser light L1 in the second period T2. According to the laser oscillation device 1, the average output of the laser light L1 oscillated as a continuous wave CW in the first period T1 is prevented from becoming excessively large, so that the object irradiated with the laser light L1 can be prevented from being thermally affected in the first period T1.

[0056] The first period T1 is 10 seconds or more. According to the laser oscillation device 1, even at the start of the laser oscillation device 1, the heat distribution of each component in the laser resonator 3 can be made to be in a state in which it is difficult to vary between the first period T1 and the second period T2.

[0057] The control unit 2 controls the attenuator 34 so that the switching of the attenuation rate starts with the first attenuation rate in the second period T2. According to the laser oscillation device 1, when the attenuation rate is switched to the second attenuation rate for the first time in the second period T2, one pulse of laser light (first pulse P) having desired characteristics can be emitted. The attenuator 34 switches the attenuation rate in the second period T2 to the first attenuation rate and puts the laser light L1 in a non-resonant state, so that the energy of the excitation light L2 can start to be accumulated in the laser medium 33. This makes it possible to prevent the peak output Pk of the first pulse P of the laser light L1 oscillated as a pulse wave PW in the second period T2 from becoming small.

[0058] The control unit 2 controls the attenuator 34 so that the attenuation rate is alternately maintained in the first period T1 and switched in the second period T2. According to the laser oscillation device 1, the heat distribution of each component in the laser resonator 3 can be made to be unlikely to vary between the first period T1 and the second period T2 in any of the repeated second periods T2.

[0059] The control unit 2 causes the attenuator 34 to gradually decrease the attenuation rate to the second attenuation rate in the third period T3 from the end of the second period T2 to the start of the first period T1. According to the laser oscillation device 1, it is possible to suppress fluctuations in the output of the laser light L1 that may occur when the attenuator 34 immediately starts maintaining the second attenuation rate when the second period T2 transitions to the first period T1. When the attenuator 34 immediately starts maintaining the second attenuation rate when the second period T2 transitions to the first period T1, a relaxation oscillation wave may be generated at the start of the first period T1. Such a relaxation oscillation wave has a higher peak output than a continuous wave CW and may be a cause of dents occurring on the target object during laser processing. Therefore, the control unit 2 causes the attenuator 34 to gradually decrease the attenuation rate to the second attenuation rate in the third period T3 until the start of the first period T1. This makes it possible to reduce the peak output of the relaxation oscillation wave to a value that does not affect laser processing, and to suppress dents from occurring on the target object.

[0060] The control unit 2 controls the attenuator 34 so that the switching of the attenuation rate ends with the implementation of the second attenuation rate in the second period T2. According to the laser oscillation device 1, when the attenuation rate is finally switched to the second attenuation rate in the second period T2, one pulse of laser light (the last pulse P) having desired characteristics can be emitted. This makes it possible to prevent the processing of the target object from ending in an insufficient state, as compared with the case where the second period T2 ends when the laser light L1 is in a non-resonant state, for example, and improves the processing accuracy.

[0061] The attenuator is an acousto-optic modulator, and the control unit 2 includes an RF oscillator. According to the laser oscillation device 1, the adjustment of the attenuation rate in the attenuator can be suitably achieved.

[0062] According to the described laser oscillation method using the laser oscillation device 1, for the same reasons as those of the laser oscillation device 1, it is possible to start pulse oscillation of the laser light L1 with desired characteristics. [Variations]

[0063] The present invention is not limited to the above embodiment. For example, the control signal Sc may not include the third period T3, and the first period T1 and the second period T2 may be repeated alternately. (a) to (c) of FIG. 6 show the instruction signal Sd, the control signal Sc, and the output of the laser light L1 in the laser oscillation device of the modified example. In the laser oscillation device of the modified example, as shown in (b) of FIG. 6, the control signal Sc does not include the third period T3, and the first period T1 and the second period T2 are repeated alternately. In addition, the second period T2 ends in synchronization with the timing when the instruction signal Sd switches from Hi level to Low level. Other than these points, it is the same as the laser oscillation device 1 described above.

[0064] As shown in (c) of FIG. 6, in the laser oscillation device of the modified example, the peak output Pk of the multiple pulses P constituting the pulse wave PW is substantially the same for all the pulses P in the second period T2. In the laser oscillation device of the modified example, the laser light L1 is oscillated as a continuous wave CW in the first period T1, and the laser light L1 is oscillated as a pulse wave PW in the second period T2 following the first period T1. This makes it difficult for the heat distribution of each component in the laser resonator 3 to fluctuate between the first period T1 and the second period T2. As a result, as shown in (d) of FIG. 6, it can be seen that "A" is printed without missing the processing mark M. On the other hand, a relaxation oscillation wave PWa is generated at the start of the first period T1 from the second time onwards. The peak output of the relaxation oscillation wave PWa is greater than the peak output of the continuous wave CW. It is assumed that the relaxation oscillation wave PWa is generated by the attenuator 34 abruptly switching the attenuation rate from the first attenuation rate to the second attenuation rate without gradually decreasing the attenuation rate to the second attenuation rate. As a result, as shown in (d) of FIG. 6, a dent Ma is formed after each of the first stroke, the second stroke, and the third stroke of the letter "A."

[0065] The attenuator 34 may be an opto-electrical modulator. The control unit 2 may include a voltage generator. The signal generating unit 22 may be a voltage generator that generates a DC signal. In this case, when the control signal Sc, which is a DC signal, is input, the attenuator 34 changes the optical characteristics of the laser light L1 by the Pockels effect, thereby switching the attenuation rate.

[0066] The oscillation period of the multiple pulses P in the pulse wave PW is not limited to a constant period, and the time interval between adjacent pulses P in the multiple pulses P may vary, for example, randomly. Even in this case, the first period T1 is longer than the time T21 from the timing at which the attenuation rate is switched to the second attenuation rate for the first time in the second period T2 to the timing at which the attenuation rate is switched to the second attenuation rate for the second time.

[0067] The attenuator 34 may be disposed on the resonant optical path A between the laser medium 33 and the mirror 31, which is a total reflection mirror. The difference between the average output of the laser light L1 in the first period T1 and the average output of the laser light L1 in the second period T2 may exceed 30% of the average output of the laser light L1 in the second period T2. The average output of the laser light L1 in the first period T1 may exceed 0.5% of the peak output Pk of the laser light L1 in the second period T2. The first first period T1 after the laser oscillation device 1 is started may be shorter than 10 seconds. The control unit 2 may control the attenuator 34 so that the switching of the attenuation rate starts with the second attenuation rate in the second period T2.

[0068] The control unit 2 may control the attenuator 34 so that the oscillation of the laser light L1 is completed in each of the first period T1 and the second period T2, without the first period T1 and the second period T2 being alternately repeated. Even in this case, the heat distribution in each component of the laser resonator 3 can be made less likely to vary between the first period T1 and the second period T2. The control unit 2 may control the attenuator 34 so that the switching of the attenuation rate is completed at the implementation of the first attenuation rate in the second period T2.

[0069] The laser oscillation device according to the above embodiment and modification is particularly suitable for use in ablation processing. In ablation processing, when processing an object in the second period T2, if the peak output Pk of the pulse wave PW significantly exceeds the processing threshold, the processing may not be performed with high accuracy. Therefore, in ablation processing, it is preferable that the peak output Pk is slightly larger than the processing threshold. However, when the peak output Pk is slightly larger than the processing threshold, a slight change in the laser characteristics is more likely to affect the processing accuracy than when the peak output Pk significantly exceeds the processing threshold. In contrast, in the laser oscillation device according to the above embodiment and modification, the heat distribution of each component in the laser resonator 3 is less likely to change between the first period T1 and the second period T2. As a result, even when the peak output Pk is slightly larger than the processing threshold in ablation processing, high-precision processing can be easily performed. The laser oscillation device according to the above embodiment and modification may be used for laser processing other than ablation processing. [Explanation of symbols]

[0070] 1...laser oscillator, 2...control unit, 31, 32...mirror, 33...laser medium, 34...attenuator.

Claims

1. a pair of mirrors that move the laser light back and forth along a resonant optical path; a laser medium disposed on the resonant optical path and amplifying the laser light; an attenuator disposed on the resonant optical path, the attenuator putting the laser light in a non-resonant state at a first attenuation rate and putting the laser light in a resonant state at a second attenuation rate; A control unit for controlling the attenuator, The control unit is During a first period, the attenuator is caused to maintain an attenuation rate at which the second attenuation rate is maintained so that the laser light is oscillated as a continuous wave; causing the attenuator to perform switching of the attenuation rate such that the first attenuation rate and the second attenuation rate are alternately repeated in a second period that is continuous with the first period, so that the laser light is oscillated as a pulse wave; The first period is longer than a time from a timing when the attenuation rate is switched to the second attenuation rate for a first time to a timing when the attenuation rate is switched to the second attenuation rate for a second time in the second period.

2. 2 . The laser oscillation device according to claim 1 , wherein one of the pair of mirrors emits the laser light as the continuous wave in the first period and emits the laser light as the pulse wave in the second period.

3. 2. The laser oscillation device according to claim 1, wherein a difference between an average output of the laser light in the first period and an average output of the laser light in the second period is 30% or less of the average output of the laser light in the second period.

4. 2 . The laser oscillation device according to claim 1 , wherein an average output of the laser light in the first period is 0.5% or less of a peak output of the laser light in the second period.

5. The laser oscillation device according to claim 1 , wherein the first period is equal to or longer than 10 seconds.

6. The laser oscillation device according to claim 1 , wherein the control unit controls the attenuator such that the switching of the attenuation rate starts with the implementation of the first attenuation rate during the second period.

7. The laser oscillation device according to claim 1 , wherein the control unit controls the attenuator so that the maintenance of the attenuation rate in the first period and the switching of the attenuation rate in the second period are alternately repeated.

8. 8. The laser oscillation device according to claim 7, wherein the control unit causes the attenuator to gradually decrease the attenuation rate to the second attenuation rate during a third period from the end of the second period to the start of the first period.

9. The laser oscillation device according to claim 1 , wherein the control unit controls the attenuator such that the switching of the attenuation rate in the second period ends with the implementation of the second attenuation rate.

10. the attenuator is an acousto-optic modulator; The laser oscillation device according to claim 1 , wherein the control unit includes an RF oscillator.

11. the attenuator is an opto-electrical modulator; The laser oscillation device according to claim 1 , wherein the control unit includes a voltage generator.

12. a pair of mirrors that move the laser light back and forth along a resonant optical path; a laser medium disposed on the resonant optical path and amplifying the laser light; a laser oscillation method implemented in a laser oscillation device including an attenuator disposed on the resonant optical path, the attenuator putting the laser light in a non-resonant state at a first attenuation rate and putting the laser light in a resonant state at a second attenuation rate, the method comprising: a step of maintaining an attenuation rate in a first period by the attenuator so that the second attenuation rate is maintained so that the laser light is oscillated as a continuous wave; and a step of the attenuator switching the attenuation rate such that the first attenuation rate and the second attenuation rate are alternately repeated in a second period that is continuous with the first period, so that the laser light is oscillated as a pulse wave, The laser oscillation method, wherein the first period is longer than a time from a timing when the attenuation rate is switched to the second attenuation rate for a first time to a timing when the attenuation rate is switched to the second attenuation rate for a second time in the second period.

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