Laser oscillation device and laser oscillation method

Abstract

This laser oscillation device is provided with: a pair of mirrors; a laser medium; an attenuator that causes the laser light to be in a non-resonant state at a first attenuation rate and causes the laser light to be in a resonant state at a second attenuation rate; and a control unit. The control unit causes the attenuator to maintain the attenuation rate of the second attenuation rate so that the laser light oscillates as a continuous wave during a first period, and causes the attenuator to switch the attenuation rates of the first attenuation rate and the second attenuation rate so that the laser light oscillates as a pulse wave during a second period that is continuous with the first period. The first period is longer than the time from the time at which the first time is switched to the second attenuation rate to the time at which the second time is switched to the second attenuation rate in the second period.

Description

Technical Field

[0001] This disclosure relates to a laser oscillation device and a laser oscillation method. Background Technology

[0002] Patent Document 1 describes a Q-switched laser device that uses a Q-switched oscillation method to oscillate laser light as a pulse wave. In the Q-switched laser device described in Patent Document 1, a high-frequency signal is input from a high-frequency generation device to an acousto-optic Q-switch. The acousto-optic Q-switch suppresses laser oscillation, accumulating energy in the laser medium. From this state, the amplitude of the high-frequency signal is gradually reduced with a predetermined time constant, thereby initiating laser pulse oscillation. For example, if the amplitude of the high-frequency signal is reduced instantaneously, there is a concern that the peak output of the laser may become excessively high at the beginning of the laser pulse oscillation. However, according to the Q-switched laser device described in Patent Document 1, this phenomenon can be suppressed. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2001-332791 Summary of the Invention The technical problem that the invention aims to solve

[0004] However, at the start of laser pulse oscillation, not only the peak output of the laser, but also the laser beam diameter, pulse width, etc., are prone to change. Therefore, in the Q-switched laser device described in Patent Document 1, there is a concern that the laser pulse oscillation may start when the laser beam diameter, pulse width, etc., deviate from the desired values.

[0005] The purpose of this disclosure is to provide a laser oscillation device and laser oscillation method that can initiate the pulse oscillation of a laser with desired characteristics. Technical means to solve the problem

[0006] A laser oscillation device of one aspect of this disclosure, [1] "comprising: a pair of mirrors that cause a laser to travel back and forth along a resonant optical path; a laser medium disposed on the resonant optical path to amplify the laser; an attenuator disposed on the resonant optical path that sets the laser to a non-resonant state at a first attenuation rate and sets the laser to a resonant state at a second attenuation rate; and a control unit that controls the attenuator, wherein during a first period, the control unit causes the attenuator to maintain the attenuation rate of the second attenuation rate by oscillating the laser as a continuous wave, and during a second period, which is continuous with the first period, the attenuator causes the attenuator to alternately switch between the attenuation rates of the first attenuation rate and the second attenuation rate by oscillating the laser as a pulse wave, wherein the first period is longer than the time from the moment of the first switch to the second attenuation rate to the moment of the second switch to the second attenuation rate during the second period."

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

[0008] One aspect of the laser oscillation device disclosed herein may be [2] "a laser oscillation device as described in [1] above, wherein one of the pair of mirrors emits the laser as a continuous wave during the first period and emits the laser as a pulse wave during the second period." According to this [2] laser oscillation device, a shutter or similar device that blocks the laser emitted as a continuous wave can be omitted, thereby simplifying the structure.

[0009] One aspect of the laser oscillation device disclosed herein may be [3] "a laser oscillation device as described in [1] or [2] above, wherein the difference between the average output of the laser during the first period and the average output of the laser during the second period is less than 30% of the average output of the laser during the second period." According to the laser oscillation device of [3], since the difference between the average output of the laser during the first period and the average output of the laser during the second period is suppressed, the heat distribution of each component including the laser medium, a pair of mirrors, and attenuator is less likely to change between the first period and the second period.

[0010] One aspect of the laser oscillation device disclosed herein may be [4] "a laser oscillation device as described in any one of [1] to [3] above, wherein the average output of the laser during the first period is less than 0.5% of the peak output of the laser during the second period." According to the laser oscillation device of [4], since the average output of the laser oscillating as a continuous wave during the first period is suppressed from becoming too large, the thermal effects on the object irradiated by the laser can be suppressed during the first period.

[0011] One aspect of the laser oscillation device disclosed herein may be [5] "a laser oscillation device as described in any one of [1] to [4] above, wherein the first period is 10 seconds or more." According to the laser oscillation device of [5], even when, for example, the laser oscillation device is started, the heat distribution of each component including the laser medium, a pair of mirrors, and an attenuator can be set to a state that does not change significantly between the first period and the second period.

[0012] One aspect of the laser oscillation device disclosed herein may be [6] "a laser oscillation device as described in any one of [1] to [5] above, wherein the control unit controls the attenuator in such a manner that the switching of the attenuation rate begins with the implementation of the first attenuation rate during the second period." According to the laser oscillation device of [6], when the second attenuation rate is switched to for the first time during the second period, a single pulse of laser with desired characteristics can be emitted.

[0013] One aspect of the laser oscillation device disclosed herein may be [7] "a laser oscillation device as described in any of [1] to [6] above, wherein the control unit controls the attenuator in a manner that alternately repeats the maintenance of the attenuation rate during the first period and the switching of the attenuation rate during the second period." According to the laser oscillation device of [7], during any repeated second period, the heat distribution of each component including the laser medium, a pair of mirrors, and the attenuator can be set to a state that is not easily changed between the first period and the second period.

[0014] One aspect of the laser oscillation device disclosed herein may be [8] "a laser oscillation device as described above [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 beginning of the first period." According to this [8] laser oscillation device, fluctuations in laser output that may occur when the attenuator immediately begins to maintain the second attenuation rate when transitioning from the second period to the first period can be suppressed.

[0015] One aspect of the laser oscillation device disclosed herein may be [9] "a laser oscillation device as described in any of [1] to [8] above, wherein the control unit controls the attenuator in such a manner that the switching of the attenuation rate ends with the implementation of the second attenuation rate during the second period." According to the laser oscillation device of [9], when the second attenuation rate is finally switched to during the second period, a single pulse of laser with desired characteristics can be emitted.

[0016] One aspect of the laser oscillation device disclosed herein may be

[10] "a laser oscillation device as described in any of [1] to [9] above, wherein the attenuator is an acousto-optic modulator and the control unit includes an RF oscillator." According to the laser oscillation device of

[10] , the attenuation rate in the attenuator can be appropriately adjusted.

[0017] One aspect of the laser oscillation device disclosed herein may be

[11] "a laser oscillation device as described in any of [1] to [9] above, wherein the attenuator is a photoelectric modulator and the control unit includes a voltage generator." According to the laser oscillation device of

[11] , the attenuation rate in the attenuator can be appropriately adjusted.

[0018] One aspect of this disclosure is a laser oscillation method,

[12] "which is a laser oscillation method implemented in a laser oscillation device comprising: a pair of mirrors that cause a laser to travel back and forth along a resonant optical path; a laser medium disposed on the resonant optical path to amplify the laser; and an attenuator disposed on the resonant optical path to set the laser to a non-resonant state at a first attenuation rate and to set the laser to a resonant state at a second attenuation rate, the laser oscillation method comprising: during a first period, the attenuator performs a step of maintaining the attenuation rate of the second attenuation rate in a manner in which the laser is oscillated as a continuous wave; and during a second period, which is continuous with the first period, the attenuator performs a step of alternately switching the attenuation rate of the first attenuation rate and the attenuation rate of the second attenuation rate in a manner in which the laser is oscillated as a pulse wave; wherein the first period is longer than the time from the moment of the first switch to the second attenuation rate to the moment of the second switch to the second attenuation rate during the second period.

[0019] According to the laser oscillation method described above

[12] , for the same reasons as the laser oscillation device described above [1], the desired characteristics can be used to start the pulse oscillation of the laser. The effects of the invention

[0020] According to this disclosure, a laser oscillation apparatus and a laser oscillation method can be provided that can initiate the pulse oscillation of a laser with desired characteristics. Attached Figure Description

[0021] Figure 1 This is a diagram showing the configuration of a laser processing apparatus including a laser oscillation device according to one embodiment. Figure 2 It is used to explain in Figure 1 A diagram showing an example of processing performed in the laser processing apparatus. Figure 3 It is used to explain in Figure 1 A diagram showing the laser oscillation method implemented in the laser processing apparatus. Figure 4 It is shown Figure 1 The diagram shows the control signals, laser output, and processing results of the laser oscillation device. Figure 5 This is a diagram showing the control signals, laser output, and processing results in the laser oscillation device of the comparative example. Figure 6 This is a diagram showing the control signals, laser output, and processing results in a modified laser oscillation device. Detailed Implementation

[0022] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, in each drawing, the same or equivalent parts will be labeled with the same reference numerals, and repeated descriptions will be omitted. [Composition of Laser Processing Equipment]

[0023] like Figure 1 As shown, the laser processing apparatus 10 includes: a laser oscillation device 1, a galvanometer reflector 11, and a control device 12. The laser oscillation device 1 oscillates a laser L1 with a pulse wave PW. The pulse wave PW is the laser used for processing. The galvanometer reflector 11 scans the pulse wave PW emitted from the laser oscillation device 1 against the object (not shown). The control device 12 controls the laser oscillation device 1 and the galvanometer reflector 11. As one example, the laser processing apparatus 10 is used in a semiconductor manufacturing process to cut multiple chips from a wafer (object). As another example, the laser processing apparatus 10 is used for patterning or marking to form holes or grooves on the surface of a wafer.

[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 generation unit 22. The laser resonator 3 includes a pair of mirrors 31 and 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 generation unit 22 based on the instruction signal input from the self-control device 12. The signal generation unit 22 is an RF oscillator that outputs an RF signal. That is, the control unit 2 includes an RF oscillator. The signal generation unit 22 modulates the RF signal to generate a control signal by being controlled by the laser control unit 21.

[0026] A pair of reflectors 31 and 32 face each other. A resonant optical path A is formed between the reflectors 31 and 32. Reflector 31 is a total reflection mirror, and reflector 32 is a partial reflection mirror. A laser medium 33 is positioned between the reflectors 31 and 32 on the resonant optical path A. The laser medium 33 is irradiated by excitation light L2 emitted from the light source 4. An attenuator 34 is positioned between the laser medium 33 and a reflector 32 on the resonant optical path A. The attenuator 34 is an acousto-optic modulator. The attenuator 34 switches the attenuation rate by converting the RF signal (i.e., the control signal) into ultrasonic waves, which change the optical properties of the laser L1.

[0027] In the laser resonator 3, when the attenuator 34 is in a state that allows laser L1 to pass through, when the laser medium 33 is excited by the excitation light L2, laser L1 is generated in the laser medium 33. The laser L1 travels back and forth along the resonant optical path A through a pair of reflectors 31 and 32, and is simultaneously amplified by the laser medium 33. A portion of the amplified laser L1 is emitted to the outside through the reflector 32 and scanned by the galvanometer reflector 11. The wavelength of laser L1 is, for example, 1.1 μm or more. The laser medium 33 is, for example, a solid-state laser medium. Examples of solid-state laser media that generate laser L1 with a wavelength of 1.1 μm or more include Nd:YVO4. Furthermore, the thermal distribution of the solid-state laser medium that generates laser L1 with a wavelength of 1.1 μm or more is prone to change (earlier and larger changes) when the solid-state laser medium is excited by the excitation light L2 and when it is not excited by the excitation light L2.

[0028] Attenuator 34 switches the attenuation rate between a first attenuation rate and a second attenuation rate based on the control signal input from the signal generation unit 22. The first attenuation rate is greater than the second attenuation rate. Attenuator 34 attenuates the laser L1 by setting the attenuation rate to the first attenuation rate, thus setting the laser L1 to a non-resonant state. In the non-resonant state, the laser L1 does not travel back and forth between the pair of reflectors 31 and 32, and the energy of the excitation light L2 is stored in the laser medium 33. Attenuator 34 allows the laser L1 to pass through by setting the attenuation rate to the second attenuation rate, thus setting the laser L1 to a resonant state. In the resonant state, the laser L1 travels back and forth between the pair of reflectors 31 and 32, amplifying the laser L through the laser medium 33. In this embodiment, when attenuator 34 maintains the attenuation rate of the second attenuation rate, the reflector 32 transmits the laser L1 in a continuous wave CW (refer to...). Figure 3 Furthermore, when the attenuator 34 alternately switches between the first attenuation rate and the second attenuation rate, the self-reflecting mirror 32 emits the laser L1 as a pulse wave PW. [Laser oscillation method implemented in a laser oscillation device]

[0029] For the sake of simplicity, the following explanation will focus on the case where the laser processing apparatus 10 prints the letter "A" onto the surface of an object, and will describe the laser oscillation method implemented in the laser oscillation apparatus 1. The printing performed by the laser processing apparatus 10 is achieved by, for example, processing (burning or cutting) the surface of the object to a predetermined depth through ablation.

[0030] Control device 12, for example, receives text (“A”) printed via laser L1 through a user interface. Furthermore, control device 12 stores information related to the scanning order and coordinates of “A” in its internal memory. Based on the stored information, control device 12... Figure 2 As shown in (a), a scan signal Sg is generated that indicates the scan order for printing "A". Figure 2 In (a), the horizontal axis represents time, and the vertical axis represents the magnitude of the scan signal Sg (here, as an example, it is set to a voltage value). The scan signal Sg is a pulse signal in which the signal level changes between a low level and a high level at each specified time interval. Figure 2 In the example shown in (a), the scan signal Sg is valid at the high bit.

[0031] The printing sequence of the letter "A" based on the scanning signal Sg is as follows: First, from time t1 to time t2, control device 12 controls laser oscillation device 1 without oscillating the pulse wave PW, and controls galvanometer reflector 11 with the optical axis of the pulse wave PW located at coordinate S1. Next, from time t3 to time t4, control device 12 controls laser oscillation device 1 with pulse wave PW oscillation, and controls galvanometer reflector 11 by scanning the pulse wave PW from coordinate S1 to coordinate E1. Thus, the first stroke of "A" is printed on the surface of the object. Next, from time t5 to time t6, control device 12 controls laser oscillation device 1 with pulse wave PW oscillation, and controls galvanometer reflector 11 by scanning the pulse wave PW from coordinate S2 to coordinate E2. Thus, the second stroke of "A" is printed on the surface of the object.

[0032] Subsequently, from time t7 to time t8, control device 12 controls laser oscillation device 1 without pulse wave PW, and controls galvanometer reflector 11 with the optical axis of pulse wave PW located at coordinate S3. Finally, from time t9 to time t10, control device 12 controls laser oscillation device 1 with pulse wave PW, and controls galvanometer reflector 11 by scanning pulse wave PW from coordinate S3 to coordinate E3. Thus, the third stroke of "A" is printed on the surface of the object. Through the above method, laser processing device 10 prints "A" on the surface of the object.

[0033] In the case of scanning pulse wave PW on the surface of the object as described above, the control device 12, as... Figure 3 As shown in (a) and (b), an indication signal Sd is generated based on the scanning signal Sg. The indication signal Sd is a signal indicating the period during which the laser oscillation device 1 oscillates the laser L1 with a pulse wave PW. Figure 3 In (b), the horizontal axis represents time, and the vertical axis represents the magnitude of the indicator signal Sd (here, as an example, it is set to a voltage value). The indicator signal Sd is a pulse signal in which the signal level changes between a low level and a high level at each specified interval. Figure 3 In the example shown in (b), the indicator signal Sd is valid at the high bit.

[0034] During the period when the indicator signal Sd is at a high level, the laser oscillation device 1 oscillates the laser L1 with a pulse wave PW. The indicator signal Sd becomes a high level synchronously with the period during which "A" is printed in the scanning signal Sg. Specifically, the indicator signal Sd becomes a high 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 generation unit 22 based on the instruction signal Sd input from the self-control device 12. The signal generation unit 22 modulates the RF signal and generates a control signal Sc under the control of the laser control unit 21.

[0036] like Figure 3 As shown in (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. Figure 3 In (c), the horizontal axis represents time, and the vertical axis represents the magnitude of the control signal Sc (here, as an example, it is set to a voltage value). Period 2 T2 corresponds to the period when the indicator signal Sd becomes a high level. Periods 1 T1 and 3 T3 correspond to the periods when the indicator signal Sd becomes a low level. Period 1 T1 ends and Period 2 T2 begins when the indicator signal Sd rises from a low level to a high level. Period 2 T2 ends and Period 3 T3 begins when the indicator signal Sd falls from a high level to a low level. The start time of Period 2 T2 coincides with the time when the indicator signal Sd rises from a low level to a high level. The end time of Period 2 T2 approximately coincides with the time when the indicator signal Sd falls from a high level to a low level.

[0037] During the first period T1, control unit 2 causes attenuator 34 to maintain the attenuation rate of the second attenuation rate by means of continuous wave CW oscillation of laser L1 (the step of attenuator maintaining attenuation rate). During the first period T1, laser control unit 21 controls signal generation unit 22 without outputting control signal Sc. The second attenuation rate is a value that does not attenuate laser L1, which is essentially zero. However, the second attenuation rate can be greater than zero as long as it is within the range of values ​​that can maintain the resonant state of laser L1. During the first period T1, attenuator 34 maintains the attenuation rate at the second attenuation rate. Thus, the resonant state of laser L1 is maintained. As a result, as Figure 3 As shown in (d), the laser oscillation device 1 oscillates the laser L1 with a continuous wave CW during the first period T1. Figure 3 In (d), the horizontal axis represents time, and the vertical axis represents the output of laser L1. The unit of laser L1 output is, for example, watts [W]. Continuous wave CW is a non-processing laser. That is, the output of continuous wave CW (the output of laser L1 during the first period T1) is smaller than the threshold of the output of the object being processed, i.e., the processing threshold. Therefore, during the first period T1, no printing is performed on the surface of the object.

[0038] The second period T2 continues from the first period T1. The start time of the second period T2 is synchronized with the time when the indicator signal Sd switches from a low level to a high level. During the second period T2, the control unit 2 causes the attenuator 34 to alternately switch between the first attenuation rate and the second attenuation rate by means of the laser L1 oscillating with a pulse wave PW (the step of the attenuator switching the attenuation rate). During the second period T2, the laser control unit 21 controls the signal generation unit 22 to repeat the period during which the control signal Sc is output with amplitude W1 and the period during which the control signal Sc is not output. During the period during which the control signal Sc is output with amplitude W1, the attenuator 34 sets the attenuation rate to the first attenuation rate, and during the period during which the control signal Sc is not output, the attenuation rate is set to the second attenuation rate. Thus, during the second period T2, the non-resonant state and the resonant state of the laser L1 are repeated, thereby repeatedly accumulating the energy of the excitation light L2 and releasing the energy of the excitation light L2. As a result, as Figure 3 As shown in (d), the laser oscillation device 1 oscillates the laser L1 as a processing pulse wave PW during the second period T2. Thus, during the second period T2, the first stroke of the "A" on the surface of the object is printed.

[0039] A pulse wave PW is a pulse group consisting of multiple pulses P generated at a certain repetition frequency. The repetition frequency of the multiple pulses P is, for example, several kHz. The time interval (period) between adjacent 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 across all pulses P. Here, "substantially the same" means that the peak output varies within an acceptable error range. The peak output Pk is the maximum value of the output of each pulse P. The peak output Pk can be obtained by dividing the pulse energy from laser L1 by the pulse width of each pulse P. The unit of peak output Pk is watts [W].

[0040] The first period T1 is longer than the second period T2, which is the time from the first switch to the second attenuation rate to the second switch to the second attenuation rate (T21). Time T21 is approximately the same as the time from the first output pulse P to the second output pulse P in the pulse wave PW. After the laser oscillation device 1 is started, the first period T1 is, for example, 10 seconds or more. Subsequent periods can be less than 10 seconds as long as they are longer than T21.

[0041] During the second period T2, control unit 2 controls attenuator 34 in a manner that the switching of attenuation rate begins with the implementation of the first attenuation rate. Specifically, when the second period T2 begins after the end of the first period T1, attenuator 34 switches the attenuation rate from maintaining the second attenuation rate to the first attenuation rate. During the second period T2, attenuator 34 begins the attenuation rate switching with the first attenuation rate. Then, after maintaining the first attenuation rate for a predetermined time, attenuator 34 switches the attenuation rate to the second attenuation rate. This predetermined time is the time during which the energy of the excitation light L2 can be stored in the laser medium 33 to appropriately output the first pulse P. By maintaining the first attenuation rate for the predetermined time by attenuator 34, as... Figure 3 As shown in (d), when switching from the first period T1 to the second period T2, the oscillation of the continuous wave CW is time-separated from the oscillation of the first pulse P.

[0042] During the first period T1, the reflector 32 emits laser L1 as a continuous wave CW. During the second period T2, the reflector 32 emits laser L1 as a pulsed wave PW.

[0043] The difference between the average output of laser L1 during the first period T1 of continuous wave (CW) oscillation and the average output of laser L1 during the second period T2 of pulsed wave (PW) oscillation is less than 30% of the average output of laser L1 during the second period T2 of pulsed wave (PW) oscillation. The average output is the sum of the outputs of laser L1 per unit time. The average output is also the value obtained by multiplying the pulse energy of laser L1 by the repetition frequency. The unit of average output is watts (W). Furthermore, the average output of laser L1 during the first period T1 of continuous wave (CW) oscillation is less than 0.5% of the peak output Pk of laser L1 during the second period T2 of pulsed wave (PW) oscillation. Here, the peak output Pk is the largest peak output Pk among the multiple pulses P constituting the pulsed wave PW.

[0044] During the second period T2, the control unit 2 controls the attenuator 34 to end the switching of the attenuation rate by implementing the second attenuation rate. Based on the control signal Sc, the attenuator 34 ends the switching of the attenuation rate during the second period T2 while maintaining the attenuation rate at the second attenuation rate for a predetermined time. Specifically, when the indicator signal Sd switches from a high level to a low level, the laser control unit 21 controls the attenuator 34 via the signal generation unit 22 to end the second period T2 by waiting for the attenuation rate to switch to the second attenuation rate for a predetermined time. This predetermined time is the time during which the last pulse P within the second period T2 can be appropriately output. For example, the predetermined time is the time until the output of the last pulse P becomes 0W and the oscillation of the last pulse P is complete. That is, the laser control unit 21 does not control the attenuator 34 to end the second period T2 synchronously with the moment when the indicator signal Sd switches from a high level to a low level.

[0045] like Figure 3 As shown, at time t4, when the indicator signal Sd switches from a high level to a low level, the attenuation rate has switched to the second attenuation rate, and the final pulse P oscillates. In this case, the laser control unit 21 waits for a predetermined time for the attenuation rate to switch to the second attenuation rate, and the output of the final pulse P becomes 0W, thus ending the second period T2, and controls the attenuator 34. Conversely, at time t10, when the indicator signal Sd switches from a high level to a low level, the attenuation rate has switched to the first attenuation rate, and the final pulse P has not yet 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 waits for a predetermined time for the attenuation rate to switch to the second attenuation rate, and the output of the final pulse P becomes 0W, thus ending the second period T2, and controls the attenuator 34.

[0046] Control unit 2 controls attenuator 34 by alternately maintaining the attenuation rate during the first period T1 and switching the attenuation rate during the second period T2. Because the first period T1 and the second period T2 alternately repeat, attenuator 34 alternately maintains the second attenuation rate during the first period T1 and switches the attenuation rate during the second period T2. Thus, as... Figure 3 As shown in (d), the laser L1 is oscillated with a continuous wave CW during the first period T1 and with a pulsed wave PW during the second period T2.

[0047] The third period T3 is continuous with the second period T2. The third period T3 is the period from the end of the second period T2 to the beginning of the first period T1. During the third period T3, the control unit 2 causes the attenuator 34 to gradually decrease the attenuation rate to the second attenuation rate. Figure 3 As shown in (c), during the third period T3, the laser control unit 21 controls the signal generation unit 22 in a manner that after gradually increasing the control signal Sc from 0V to the amplitude W2, the control signal Sc is gradually decreased from the amplitude W2 back to 0V. The amplitude W2 is smaller than the amplitude W1. Based on the control signal Sc, during the third period T3, the attenuator 34 gradually decreases the attenuation rate from the second attenuation rate to the attenuation rate corresponding to the amplitude W2, and then gradually decreases the attenuation rate from the attenuation rate corresponding to the amplitude W2 back to the second attenuation rate.

[0048] During the third period T3, since the attenuator 6 does not switch the attenuation rate, the laser L1 oscillates with a continuous wave CW. Therefore, no marking is applied to the surface of the object during the third period T3. However, assuming that the attenuator 34 immediately begins maintaining the second attenuation rate when transitioning from the second period T2 to the first period T1, an unintended pulse wave (hereinafter referred to as a "mild vibration wave") may be generated at the beginning of the first period T1. This mild vibration wave may cause unintended machining marks on the object. Gradually decreasing the attenuation rate is effective in reducing the peak output of the mild vibration wave. The laser control unit 21 reduces the peak output of the mild vibration wave to the desired value by appropriately setting the value of the amplitude W2, the time required for the control signal Sc to gradually increase from 0V to the amplitude W2, and the time required for the control signal Sc to gradually decrease from the amplitude W2 to 0V.

[0049] Furthermore, while referring to Figure 4 and Figure 5 The effects of the laser oscillation device 1 in the embodiment will be explained. Figure 4 (a) to (c) show the indicator signal Sd input to the laser oscillator 1, the control signal Sc generated in the laser oscillator 1, and the output of the laser L1 oscillating in the laser oscillator 1. Figure 4 (d) shows an example of the processing result of the laser processing apparatus 10 including the laser oscillation device 1. For example... Figure 4 As shown in (d), the laser processing apparatus 10 prints the letter "A" by continuously forming multiple processing marks M. Each processing mark M is formed by irradiating the workpiece with each pulse P. When using the laser oscillation device 1, the multiple processing marks M are all of equal size. Furthermore, it is known that the printed text is well-formed when the processing marks M are not damaged or are not formed in unnecessary areas (no scratches are formed).

[0050] Figure 5 Images (a) through (c) show the indicator signal Sd, control signal Sc, and laser L1 output in the comparative example's laser oscillation device. In the comparative example's laser oscillation device, as... Figure 5 As shown in (b), the laser control unit 21 outputs a control signal Sc with an amplitude W1 during the first period T1. Furthermore, the control signal Sc does not include the third period T3, and alternates between the first period T1 and the second period T2. Except for these points, it is the same as the laser oscillation device 1. In the comparative example's laser oscillation device, the attenuator 34 sets the attenuation rate to the first attenuation rate during the first period T1, setting the laser L1 to a non-resonant state.

[0051] like Figure 5As shown in (c), during the second period T2, the peak output Pka of the first pulse P to the second pulse P among the multiple pulses P constituting the pulse wave PW is smaller than the peak output Pk of the third and subsequent pulses P. This is because during the first period T1, the laser L1 is in a non-resonant state, and it is assumed that the laser resonator 3 is not fully excited during the first period T1, resulting in a divergence between the thermal distribution of the laser resonator 3 during the first period T1 and the thermal distribution of the laser resonator 3 during the second period T2. Therefore, the characteristics of the laser L1 vary between the first period T1 and the second period T2, thus assuming a variation in peak output. As a result, as... Figure 5 As shown in (d), the size of the machining marks M corresponding to the starting strokes of the first, second, and third strokes of "A" is smaller than the size of the other machining marks M. Therefore, the laser oscillation device of the comparative example has a lower machining accuracy compared to laser oscillation device 1. [Functions and Effects]

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

[0053] One of the pair of reflectors 31 and 32 emits laser L1 as a continuous wave (CW) during the first period T1 and as a pulsed wave (PW) during the second period T2. According to the laser oscillation device 1, it is possible to simplify the structure by not installing a shutter or other means to block the continuous wave (CW) emitted laser L1.

[0054] The difference between the average output of laser L1 during the first period T1 and the average output of laser L1 during the second period T2 is less than 30% of the average output of laser L1 during the second period T2. According to the laser oscillation device 1, since the difference between the average output of laser L1 during the first period T1 and the average output of laser L1 during the second period T2 is suppressed, 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.

[0055] The average output of laser L1 during the first period T1 is less than 0.5% of the peak output Pk of laser L1 during the second period T2. According to the laser oscillation device 1, since the average output of laser L1 oscillating with continuous wave CW during the first period T1 is suppressed from becoming too large, the thermal effects on the object irradiated by laser L1 during the first period T1 can be suppressed.

[0056] The first period T1 is 10 seconds or more. According to the laser oscillation device 1, even when the laser oscillation device 1 is started, for example, the heat distribution of each component in the laser resonator 3 can be set to a state that does not change much between the first period T1 and the second period T2.

[0057] During the second period T2, the control unit 2 controls the attenuator 34 to switch the attenuation rate to the first attenuation rate. According to the laser oscillation device 1, when the attenuation rate is switched to the second time during the second period T2, a laser pulse with the desired characteristics (the first pulse P) can be emitted. By switching the attenuation rate to the first attenuation rate during the second period T2 through the attenuator 34, the laser L1 is set to a non-resonant state, and the energy of the excitation light L2 is stored in the laser medium 33. As a result, the peak output Pk of the initial pulse P of the laser L1 oscillating with pulse wave PW during the second period T2 can be prevented from becoming smaller.

[0058] The control unit 2 controls the attenuator 34 by alternately maintaining the attenuation rate during the first period T1 and switching the attenuation rate during the second period T2. According to the laser oscillation device 1, during any of the repeated second periods T2, the heat distribution of each component in the laser resonator 3 can be set to a state that does not change significantly between the first period T1 and the second period T2.

[0059] During the third period T3, from the end of the second period T2 to the beginning of the first period T1, the control unit 2 causes the attenuator 34 to gradually decrease its attenuation rate to a second attenuation rate. According to the laser oscillation device 1, fluctuations in the output of the laser L1 that may occur when the attenuator 34 immediately begins maintaining the second attenuation rate upon transition from the second period T2 to the first period T1 can be suppressed. When the attenuator 34 immediately begins maintaining the second attenuation rate upon transition from the second period T2 to the first period T1, a mild vibration wave may be generated at the beginning of the first period T1. The peak output of this mild vibration wave is larger than the continuous wave CW, which may cause scratches on the object during laser processing. Therefore, during the third period T3 before the beginning of the first period T1, the control unit 2 causes the attenuator 34 to gradually decrease its attenuation rate to a second attenuation rate. This reduces the peak output of the mild vibration wave to a value that does not affect laser processing, thus suppressing scratches on the object.

[0060] During the second period T2, the control unit 2 controls the attenuator 34 to switch attenuation rates and terminate the process by implementing the second attenuation rate. According to the laser oscillation device 1, when the second attenuation rate is finally switched to during the second period T2, a single-pulse laser with the desired characteristics (the last pulse P) can be emitted. Thus, for example, compared to the case where the second period T2 ends when the laser L1 is in a non-resonant state, the process can be prevented from ending in a state of insufficient processing of the object, thereby improving processing accuracy.

[0061] The attenuator 34 is an acousto-optic modulator, and the control unit 2 includes an RF oscillator. The attenuation rate in the attenuator 34 can be appropriately adjusted according to the laser oscillation device 1.

[0062] According to the laser oscillation method described using laser oscillation device 1, the pulse oscillation of laser L1 can be started with the desired characteristics based on the laser oscillation device 1. [Variation Example]

[0063] This disclosure is not limited to the above-described embodiments. 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. Figure 6 Images (a) through (c) show the indicator signal Sd, the control signal Sc, and the output of the laser L1 in the modified laser oscillation apparatus. In the modified laser oscillation apparatus, as shown... Figure 6 As shown in (b), the control signal Sc does not include the third period T3, and alternates between the first period T1 and the second period T2. Furthermore, the second period T2 ends synchronously with the moment when the indicator signal Sd switches from a high level to a low level. Apart from these points, it is the same as the laser oscillation device 1 described above.

[0064] like Figure 6 As shown in (c), in the modified laser oscillation device, also during the second period T2, the peak output Pk of the multiple pulses P constituting the pulse wave PW is substantially the same in all pulses P. In the modified laser oscillation device, the laser L1 is oscillated with a continuous wave CW during the first period T1, and then oscillated with a pulse wave PW during the second period T2, which is continuous with the first period T1. As a result, the heat distribution of each component in the laser resonator 3 does not easily change between the first period T1 and the second period T2. Figure 6 As shown in (d), the machining mark M is not defective, while the "A" is printed. On the other hand, at the beginning of the first period T1 after the second time, a mild vibration wave PWa is generated. The peak output of the mild vibration wave PWa is larger than the peak output of the continuous wave CW. It is assumed that the mild vibration wave PWa is generated because the attenuator 34 abruptly switches from the first attenuation rate to the second attenuation rate, rather than gradually decreasing the attenuation rate to the second attenuation rate. As a result, as Figure 6 As shown in (d), scratches Ma are formed after the first, second, and third strokes of “A”.

[0065] The attenuator 34 can be an optoelectronic modulator. The control unit 2 can include a voltage generator. The signal generation unit 22 can be a voltage generator that generates a DC signal. In this case, when the attenuator 34 is input with a DC signal, i.e., the control signal Sc, the optical characteristics of the laser L1 change due to the Pockels effect, thus switching the attenuation rate.

[0066] The oscillation period of multiple pulses P in the pulse wave PW is not limited to a certain period, and the time interval between adjacent pulses P can vary randomly, for example. In this case, the first period T1 is also longer than the time T21 from the moment of the first switch to the second decay rate to the moment of the second switch to the second decay rate in the second period T2.

[0067] The attenuator 34 is disposed on the resonant optical path A between the laser medium 33 and the total reflection mirror, i.e., the reflector 31. The difference between the average output of laser L1 during the first period T1 and the average output of laser L1 during the second period T2 can exceed 30% of the average output of laser L1 during the second period T2. The average output of laser L1 during the first period T1 can exceed 0.5% of the peak output Pk of laser L1 during the second period T2. After the laser oscillation device 1 is started, the first period T1 can be less than 10 seconds. During the second period T2, the control unit 2 can control the attenuator 34 in a manner that the switching of the attenuation rate begins with the implementation of the second attenuation rate.

[0068] Control unit 2 can control attenuator 34 in a manner that the oscillation of laser L1 is completed once in each of the first period T1 and the second period T2 without alternating between them. In this case, the heat distribution in each component of laser resonator 3 can also be set to a state that does not change significantly between the first period T1 and the second period T2. During the second period T2, control unit 2 can control attenuator 34 in a manner that the switching of attenuation rate ends with the implementation of the first attenuation rate.

[0069] The laser oscillation apparatus described in the above embodiments and modifications is particularly suitable for ablation processing. In ablation processing, when processing the object during the second period T2, if the peak output Pk of the pulse wave PW significantly exceeds the processing threshold, high-precision processing may sometimes be impossible. 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, slight variations in laser characteristics can easily affect processing accuracy compared to when the peak output Pk significantly exceeds the processing threshold. To address this, in the laser oscillation apparatus described in the above embodiments and modifications, the heat distribution of each component in the laser resonator 3 does not easily change between the first period T1 and the second period T2. Therefore, even when the peak output Pk is slightly larger than the processing threshold in ablation processing, high-precision processing is still easily achieved. Furthermore, the laser oscillation apparatus described in the above embodiments and modifications can be used for laser processing other than ablation. Symbol Explanation

[0070] 1…Laser oscillation device; 2…Control unit; 31, 32…Reflector; 33…Laser medium; 34…Attenuator.

Claims

1. A laser oscillation device, wherein, have: A pair of mirrors cause the laser to travel back and forth along the resonant optical path; A laser medium, which is disposed in the resonant optical path, amplifies the laser beam; An attenuator, disposed in the resonant optical path, sets the laser to a non-resonant state at a first attenuation rate and sets the laser to a resonant state at a second attenuation rate; and The control unit controls the attenuator. The control unit: During the first period, the attenuator maintains the attenuation rate of the second attenuation rate by using the laser as a continuous wave oscillation. During the second period, which is continuous with the first period, the attenuator alternately switches between the first attenuation rate and the second attenuation rate by using the laser as a pulse wave oscillation. The first period is longer than the second period from the moment of the first switch to the second decay rate to the moment of the second switch to the second decay rate.

2. The laser oscillation device as described in claim 1, wherein, One of the pair of reflectors emits the laser as a continuous wave during the first period and as a pulsed wave during the second period.

3. The laser oscillation device as described in claim 1 or 2, wherein, The difference between the average output of the laser during the first period and the average output of the laser during the second period is less than 30% of the average output of the laser during the second period.

4. The laser oscillation device according to any one of claims 1 to 3, wherein, The average output of the laser during the first period is less than 0.5% of the peak output of the laser during the second period.

5. The laser oscillation device according to any one of claims 1 to 4, wherein, The first period is 10 seconds or more.

6. The laser oscillation device according to any one of claims 1 to 5, wherein, During the second period, the control unit controls the attenuator in such a manner that the switching of the attenuation rate begins with the implementation of the first attenuation rate.

7. The laser oscillation device according to any one of claims 1 to 6, wherein, The control unit controls the attenuator by alternately repeating the maintenance of the attenuation rate during the first period and the switching of the attenuation rate during the second period.

8. The laser oscillation device as described in claim 7, wherein, During the third period, from the end of the second period to the beginning of the first period, the control unit causes the attenuator to gradually reduce the attenuation rate to the second attenuation rate.

9. The laser oscillation device according to any one of claims 1 to 8, wherein, The control unit controls the attenuator during the second period in such a way that the switching of the attenuation rate ends with the implementation of the second attenuation rate.

10. The laser oscillation device according to any one of claims 1 to 9, wherein, The attenuator is an acousto-optic modulator. The control unit includes an RF oscillator.

11. The laser oscillation device according to any one of claims 1 to 9, wherein, The attenuator is a photoelectric modulator. The control unit includes a voltage generator.

12. A laser oscillation method, wherein, This is a laser oscillation method implemented in a laser oscillation device, which includes: A pair of mirrors cause the laser to travel back and forth along the resonant optical path; A laser medium, disposed in the resonant optical path, amplifies the laser beam; and An attenuator, configured in the resonant optical path, sets the laser beam to a non-resonant state at a first attenuation rate and sets it to a resonant state at a second attenuation rate. This laser oscillation method has the following characteristics: During the first period, the attenuator performs the step of maintaining the attenuation rate of the second attenuation rate, using the laser as a continuous wave oscillation; and During the second period, which is continuous with the first period, the attenuator performs the step of alternately switching the attenuation rate between the first attenuation rate and the second attenuation rate in a manner that uses the laser as a pulse wave oscillation. The first period is longer than the second period from the moment of the first switch to the second decay rate to the moment of the second switch to the second decay rate.

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