JP5546119B2 - Fiber laser processing apparatus and fiber laser processing method - Google Patents

Description

  The present invention relates to a fiber laser processing apparatus and a fiber laser processing method for performing desired laser processing by irradiating a workpiece with laser light of a Q switch pulse.

  Recently, fiber laser processing apparatuses that perform desired laser processing by irradiating a workpiece with laser light generated by a fiber laser have been put into practical use. Among them, a fiber laser processing apparatus of a fiber MOPA (Master Oscillator_Power Amplifier) system is also attracting attention.

  In the fiber MOPA system, as disclosed in Patent Document 1, an optical fiber having a core containing a predetermined rare earth element is used for laser amplification, and a low-power seed laser beam generated by a seed (seed) laser oscillator is used. The seed laser beam is amplified or converted into a high-power processing laser beam in the core by exciting the core while propagating from one end to the optical fiber core and propagating to the other end. It has features such as high light conversion efficiency and stable beam mode.

  A Q-switch type fiber laser processing apparatus adopting a fiber MOPA system uses a Q-switch type solid-state laser, for example, a YAG laser, as a seed laser oscillator, and uses a Q-pulse pulse seed laser light with a relatively low peak power at a constant repetition frequency. The Q-switched pulse processing laser beam having a sufficiently high peak output is obtained through the amplification optical fiber.

A normal acousto-optic or electro-optic Q switch is used as the Q switch of the seed laser oscillator. As the excitation light source for optically exciting the active medium (YAG rod) in the seed laser oscillator, a semiconductor laser, that is, a laser diode (LD) is mainly used. Also, a laser diode (LD) is often used as an excitation light source for optically exciting the core of the amplification optical fiber.
JP2007-253189

  In the Q-switch type fiber laser processing apparatus employing the fiber MOPA system as described above, the amplification light is used so that the processing laser light has a desired laser output from the first when the Q-switch pulse is repeatedly oscillated. As long as the device power supply is turned on for the purpose of keeping the fiber on standby, regardless of the on / off status of the seed laser oscillator, that is, regardless of whether the seed laser beam of the Q switch pulse is oscillated or output. The fiber core pumping unit keeps the pumping LD constantly lit to pump the core of the amplification optical fiber. However, during the standby period, the seed laser beam that should absorb the energy of the excitation LD light introduced into the amplification optical fiber and the fluorescence energy of a specific wavelength (for example, 1040 nm) generated in the fiber is contained in the core. In the processing field, it is hated that the excitation LD light and fluorescence do not sufficiently attenuate and leak as unnecessary noise light from the end face of the amplification optical fiber.

  Further, this type of conventional fiber laser processing apparatus has the following more serious problems. That is, if the output of the seed laser beam is too low compared with the output of the core excitation LD, for example, the output of the core excitation LD is 75 W and the output of the seed laser beam is 0.1 W (1 / 750th output). In some cases, even when the seed laser light is being amplified, the pumping LD light is not consumed sufficiently in the amplification optical fiber, and the peak energy is abnormally high (several times normal) due to the remaining energy. Pulse laser light is generated. Therefore, it is considered that the output of the seed laser light is set to a certain high value for better light-to-light conversion efficiency and stability of laser amplification, and is usually set to about 1 W or more.

  On the other hand, in a seed laser oscillator composed of a Q-switch type solid-state laser, when the inversion distribution, which has been saturated until then, is suddenly lowered when Q-switch pulse repetition oscillation is started, the first pulse (fast first) (Pulse) has an undesired characteristic that oscillation is output as a giant pulse, which is a seed laser having an abnormally high peak power. As a method for avoiding this (a so-called one method of the first pulse killer), a method in which the Q value in the oscillator is raised not with a step but with an up slope with a constant gradient is routinely adopted.

  According to this method, it is possible to prevent a giant pulse from being generated by suppressing a rapid decrease in the inversion distribution and oscillating and outputting the first pulse at a low output.

  Actually, it is very difficult to control the peak power of the first pulse to the set value by the first pulse killer method. Usually, the first pulse oscillates at a very low peak power with emphasis on preventing the generation of the giant pulse. In this way, the up slope of the Q value rise is controlled so that the peak output as set is obtained from the second pulse.

  However, when a first pulse with extremely low peak power is introduced or administered from the seed laser oscillator to the amplification optical fiber, the output of the seed laser light in the amplification optical fiber is higher than the output of the core excitation LD light. A remarkably low relationship (condition) is established, and as a result, a processing laser beam with an abnormally high peak power is emitted from the amplifying optical fiber, and the end face of the amplifying optical fiber is burned, or laser processing characteristics・ There were problems such as quality loss.

  Further, as described above, since the amplification optical fiber in the standby state continues to be pumped by the excitation LD, it is overflowing with excitation LD light and fluorescence energy, and the amplification factor immediately after the start of repeated oscillation is constant. Higher than the amplification factor (set value). For this reason, even if the peak power of the first pulse emitted from the seed laser oscillator can be controlled to the set value by the first pulse killer method, the output of the processing laser light overshoots immediately after the start of repeated oscillation and the set value is set. This has also caused the end face of the amplification optical fiber to burn and the laser processing characteristics and quality to deteriorate.

The present invention has been made in view of the above-described problems of the prior art, and prevents the generation of abnormal amplification pulses immediately after the start or restart of repetitive oscillation, thereby protecting the optical fiber for amplification and laser processing. It is an object of the present invention to provide a fiber laser processing apparatus and a fiber laser processing method that realize improvement in characteristics and quality.

The fiber laser processing apparatus of the present invention includes an optical resonator composed of a pair of optically disposed mirrors, a solid active medium disposed on an optical path in the optical resonator, and the active medium. An active medium excitation unit that continuously excites, a Q switch disposed on the same optical path as the active medium in the optical resonator, and a Q switch drive unit for driving the Q switch; A seed laser oscillation unit that oscillates and outputs a seed laser beam having a Q-switch pulse at a predetermined repetition frequency; and a core that includes a predetermined rare earth element, and the seed laser beam from the seed laser oscillation unit is An amplification optical fiber that amplifies the seed laser light and emits it from the other end; and a first optical fiber for amplifying the seed laser light incident on the core from one end of the amplification optical fiber. A fiber core pumping unit that outputs the pumping laser beam of continuous oscillation, a laser emitting unit that emits laser light emitted from the other end of the amplification optical fiber as a processing laser beam, and the seed laser oscillation unit When starting or resuming the repetitive oscillation of the Q switch pulse, the Q value in the optical resonator has a constant gradient for the seed laser light of the first to several shots of the Q switch pulse. The Q switch drive unit is controlled to rise with an up slope waveform, the output of the first excitation laser beam rises with a second up slope waveform having a constant gradient, and the second up slope waveform So that the rise of the pulse is completed after the seed laser beam of the Q-switch pulse from the first to several shots is oscillated and output. And a control unit for controlling the core exciting unit.

In the fiber laser processing method of the present invention, a seed laser oscillation unit having a Q switch type optical resonator oscillates and outputs a seed laser beam of a Q switch pulse at a predetermined repetition frequency, and continuously oscillates the core of an optical fiber for amplification. A processing laser beam that propagates the seed laser beam from one end of the core to the other end while being excited by the first pumping laser beam, and is extracted as a seed laser beam amplified from the other end of the amplification optical fiber the irradiated toward the workpiece, said a fiber laser processing method of applying a desired laser processing on a workpiece, when starting or resuming repeated oscillation of the Q-switched pulse, one shot eyes to several For the seed laser beam of the Q switch pulse until the start , the Q value in the optical resonator rises with a first upslope waveform having a constant gradient. At the same time, the output of the first excitation laser beam is raised with a second upslope waveform having a constant gradient, and the second upslope waveform rises from the first to several times. This is completed after the seed laser beam of the Q switch pulse is oscillated and output.

In the above apparatus configuration or method, in order to perform desired laser processing on the workpiece, when the seed laser oscillation unit starts or restarts repeated oscillation of the Q switch pulse, the first to several shots are performed. With respect to the seed laser beam of the Q switch pulse, the control unit raises the Q value in the optical resonator with the first up-slope waveform having a constant gradient through the control of the Q switch driving unit, so that a so-called first pulse killer is applied. Thus, the first (or first to several) Q switch pulse is oscillated and output at a very low peak power from the seed laser oscillation unit. On the other hand, under the control of the control unit, the fiber core pumping unit sets the output of the first pumping laser beam for pumping the amplification optical fiber with a second continuous up-slope waveform having a constant gradient. And the second up-slope waveform rises and is completed after the first to several Q seed pulse light of the Q switch pulse is oscillated and output. The first seed laser beam propagates in the optical fiber for amplification without much amplification. As a result, no abnormal amplification pulse is generated in the amplification optical fiber, that is, no abnormal amplification pulse is emitted from the amplification optical fiber. Therefore, the end face of the amplification optical fiber is not burned, and the laser processing characteristics and quality are not impaired.

  In a preferred aspect of the present invention, the fiber core pumping unit supplies a first LD driving current to the first laser diode that oscillates and outputs the first pumping laser beam. And a first LD power source. In this case, the control unit controls the first LD drive current through the first LD power source in order to control the output of the first excitation laser beam. The active medium excitation unit oscillates and outputs a second excitation laser beam for exciting the active medium, and a second LD driving current for supplying the second laser diode to the second laser diode. 2 LD power supplies. In a preferred embodiment, the first and second laser diodes are optically coupled to the amplification optical fiber via the first and second transmission optical fibers.

  In a preferred aspect of the present invention, when the Q switch pulse is repeatedly oscillated, the output of the first excitation laser beam is controlled to an amplification laser output value suitable for desired laser processing, When repetitive oscillation of the Q switch pulse is paused or interrupted, the output of the first excitation laser beam is set lower than the amplification laser output value to a standby laser output value suitable for a desired rise characteristic. Control. In this case, when changing the laser output value for amplification, the laser output value for standby is also changed to an optimum value accordingly. Thereby, when laser processing is started, the output of the processing laser beam does not overshoot.

  According to the fiber laser processing apparatus or the fiber laser processing method of the present invention, an amplification optical fiber is irradiated with a laser beam of a Q switch pulse having a laser output as set immediately after the start or restart of repetitive oscillation. Can be protected and the characteristics and quality of laser processing can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  In FIG. 1, the structure of the laser processing apparatus in one Embodiment of this invention is shown. This laser processing apparatus is configured as a fiber MOPA type fiber laser processing apparatus, and includes an amplification optical fiber (hereinafter referred to as “amplifier fiber”) 10, a seed laser oscillation unit 12, a fiber core excitation unit 14, and a laser. The light emission part 16, the process table 18, and the control part 20 are provided.

  Although not shown, the amplifier fiber 10 has a core made of, for example, quartz doped with ions of a rare earth element such as ytterbium (Yb), and a clad made of, for example, quartz surrounding the core coaxially. The seed laser beam SB is a propagation optical path, and the cladding is a propagation optical path of a core excitation LD light FB, which will be described later. The length of the amplifier fiber 10 may be arbitrarily selected, for example, several meters.

  The seed laser oscillation unit 12 includes a Q-switch type YAG laser oscillator (optical resonator) 22 that oscillates and outputs a Q-switch pulse YAG laser beam (wavelength: 1064 nm). This YAG laser oscillator 22 has a YAG rod (active medium) 28 and a Q switch 30 arranged in a linear arrangement between a pair of optically opposed resonator mirrors 24 and 26. The Q switch 30 is composed of an acousto-optic switch, for example, and is switched at a predetermined repetition frequency by the Q switch driver 32 under the control of the control unit 20.

The seed laser oscillating unit 12 includes an end face excitation type electro-optic excitation unit 34 for exciting the YAG rod 28. The electro-optic excitation unit 34 includes a fiber coupling LD 36 and an LD power source 38. The fiber coupling LD 36 is injected with an LD drive current I ₁ from the LD power source 38 under the control of the control unit 20 and outputs, for example, a YAG rod excitation laser beam or LD beam EB having a wavelength of 808 nm in a continuous oscillation. .

  The pumping LD light EB generated by the fiber coupling LD 36 passes through a converging lens (not shown) to one end face (incident end face) of a transmission optical fiber (hereinafter referred to as “transmission fiber”) 40. Incident, propagates through the transmission fiber 40, exits radially from the other end face (outgoing end face), passes through a collimating lens and a converging lens (not shown), enters the YAG laser oscillator 22, and enters the total reflection mirror. 24 is transmitted from the back side (opposite side of the reflecting surface) and is incident on one end surface of the YAG rod 28 to pump the YAG rod 28 continuously or continuously. When the Q switch 30 is switched so that energy is accumulated in the laser resonator 22 by this continuous pumping (inversion distribution is increased) and the Q value in the resonator is increased (inversion distribution is lowered), Giant pulse oscillation occurs and a Q switch pulse YAG laser beam having a high peak power is output from the output mirror 26 of the laser resonator 22. The transmission fiber 40 may be an SI (step index) type fiber, for example.

  The Y switch laser beam of the Q switch pulse oscillated and output from the seed laser oscillator 12 as described above is introduced into the amplifier fiber 10 as the seed laser beam SB. Although not shown, a beam expander and a converging lens of the incident optical system are disposed between the laser exit of the seed laser oscillation unit 12 and the incident end face 10a of the amplifier fiber 10. The seed laser beam SB of the Q switch pulse from the seed laser oscillating unit 12 expands the beam diameter by the beam expander, passes through the converging lens, and enters the incident end face 10a of the amplifier fiber 10 (more precisely, the incident end face of the core). ) Is focused and incident.

  In this fiber laser processing apparatus, as will be described later, the seed laser beam SB is amplified in the amplifier fiber 10 to generate the processing laser beam MB for the workpiece W, so that the laser output (effective) of the seed laser beam SB is effective. Value) can be set to a low value (for example, 1 to 5 W), and the seed laser oscillation unit 12 is configured as a low-power solid-state laser in connection with the low-value fiber. A coupling LD can be used. In this way, the seed laser oscillation unit 12 is a low-power YAG laser and employs an end face excitation method, so that the single mode seed laser beam SB can be easily obtained.

The fiber core excitation unit 14 includes a fiber coupling LD 42, an LD power supply 44, a transmission fiber 46, and the like. The fiber coupling LD 42 is injected with an LD drive current I ₂ from the LD power supply 44 under the control of the control unit 20 and outputs, for example, a laser beam or LD light FB for core excitation having a wavelength of 980 nm in continuous oscillation. The fiber coupling LD 42 has a relatively large array structure in which a large number of LD elements are arranged in one or two dimensions so that the core of the amplifier fiber 10 can be excited with a relatively high power of about 50 to 80 W, for example. It is preferable to adopt a stack structure.

  The core excitation LD light FB emitted from the fiber coupling LD 42 is condensed and incident on one end face (incident end face) of the transmission fiber 46 through a converging lens (not shown). The transmission fiber 46 is made of, for example, an SI-type fiber, and transmits the core excitation LD light FB taken from the LD 42 to the vicinity of the incident surface 10 a of the amplifier fiber 10.

  The other end surface (outgoing end surface) of the transmission fiber 46 is optically coupled to the incident surface 10 a of the amplifier fiber 10 via a collimating lens, a converging lens (not shown), and a folding mirror 48. The folding mirror 48 is disposed at a predetermined angle or orientation at a position where the optical axis on the output side of the transmission fiber 46 and the optical axis on the incident side of the amplifier fiber 10 intersect, and has the wavelength of the core excitation LD light FB. On the other hand, a reflective film and a non-reflective film with respect to the wavelength of the processing laser beam MB are coated. The core excitation LD light FB emitted from the emission end face of the transmission fiber 46 is collimated into parallel light by the collimating lens, condensed by the converging lens, and bent by the folding mirror 48 at a right angle so that the amplifier fiber 10 is bent. Is incident on the incident end face 10a.

  In the amplifier fiber 10, as described above, on the incident end face 10a, the seed laser beam SB of the Q switch pulse from the seed laser oscillation unit 12 and the LD light FB for core excitation of the continuous oscillation from the fiber core excitation unit 14 are provided. Is incident. The seed laser beam SB propagates in the core in the axial direction toward the other end face of the fiber (outgoing end face 10b) while being confined by total reflection at the interface between the core and the clad. On the other hand, the core excitation LD light FB propagates in the axial direction in the amplifier fiber 10 while being confined by the total reflection at the cladding outer peripheral interface, and crosses the core many times during the propagation, so that the Yb ions in the core are absorbed. Photoexcitation. Thus, the seed laser beam SB is amplified until it has a laser output of a set value (for example, 30 W) in the active core while propagating through the amplifier fiber 10, and is amplified as a high-power processing laser beam MB. 10 exits from the exit end face 10b. This processing laser beam MB is a YAG laser beam having the same wavelength (1064 nm) as that of the seed laser beam SB.

  Since the amplifier fiber 10 amplifies the seed laser beam SB by confining the seed laser beam SB in an elongated core having a diameter of about 50 μm and a length of about several meters, the processing laser beam MB with a small beam diameter and a small beam spread angle can be taken out. it can. In addition, since the core excitation LD light FB incident on the incident end face 10a of the amplifier fiber 10 travels through the long optical path in the amplifier fiber 10 and exhausts the excitation energy many times, the efficiency is very high. The low output (for example, 1 W) seed laser beam SB can be amplified to the high output (30 W) processing laser beam MB.

  In addition, since the core of the amplifier fiber 10 does not cause a thermal lens effect, the beam mode is stable and no special cooling is required.

  Note that the core excitation LD light FB is almost exhausted from the laser energy in the amplifier fiber 10 and exits from the emission end face 10b of the amplifier fiber 10 in a state where the light intensity is considerably attenuated. A folding mirror (not shown) for removing the used light FB passing through the amplifier fiber 10 to the side may be arranged.

  As described above, the Q-switched pulse processing laser beam MB emitted on the optical axis from the emission end face 10b of the amplifier fiber 10 enters the emission unit 16 while changing the optical path by the vent mirror 50, for example.

  The emission unit 16 accommodates a galvanometer scanner, an fθ lens, and the like. The galvanometer scanner has a pair of movable mirrors capable of swinging in two orthogonal directions. Both movable mirrors are synchronized with the Q switching operation of the seed laser oscillation unit 12 under the control of the control unit 20. Is controlled to a predetermined angle so that the processing laser beam MB of the Q switch pulse from the amplifier fiber 10 is condensed and irradiated to a desired position on the surface of the workpiece W on the processing table 18. The processing to be performed on the surface of the workpiece W is typically drawing (marking) characters or figures, but surface removal processing such as trimming is also possible.

  The control unit 20 may be composed of a microcomputer, and a person (worker, maintenance worker, etc.) is provided via a man-machine interface including an input unit (not shown) such as a keyboard and a display unit 52 such as a liquid crystal display. Data and information are exchanged with each other, and the entire apparatus or each part is controlled according to a predetermined program.

In particular, the control unit 20 supplies the LD drive current I ₁ to the LD power source 38 so that the YAG rod excitation LD light EB is oscillated and output from the fiber coupling LD 36 to the seed laser oscillation unit 12 at a desired constant power. It gives a command value AI ₁ related with, the seed laser beam SB in the Q-switched pulse from YAG laser oscillator 22 is desired timing and duration, and a desired repetition frequency Q-switched modulation Q switch driver 32 as oscillation output Signal AQ _SW is applied. The Q switch driver 32 has, for example, an oscillation circuit that generates a high frequency of 24 MHz, and amplitude-modulates the high frequency by the Q switch modulation signal AQ _SW from the control unit 20, and the Q switch 30 uses the amplitude-modulated high frequency. Drive. In this embodiment, in order to prevent the so-called giant pulse described above, the control unit 20 applies a first pulse killer through waveform control on the Q switch modulation signal AQ _SW .

In addition, the control unit 20 causes the output of the core excitation LD light FB generated from the fiber coupling LD 42 to the fiber core excitation unit 14 to repeatedly oscillate the Q switch pulse in the seed laser oscillation unit 22. Switch to the desired value (time of laser output value for machining when repeating oscillation, laser output value for standby when paused or interrupted) and repeat Immediately after the start or restart of oscillation, the current switching control signal CH, the standby current command value I _W , and the amplification current are set so as to rise from the standby laser output value to the amplification laser output value with a desired or optimum upslope characteristic. The command value I _S and the rise time (or rise speed, inclination, etc.) command value J _up are given to the LD power source 44.

  Next, with reference to the waveform diagram of FIG. 2, the main operation of the fiber laser processing apparatus of this embodiment will be described.

During standby before irradiating the workpiece W on the processing table 18 with the processing laser beam MB, the seed laser oscillation unit 22 does not repeatedly oscillate the Q switch pulse. During this standby period, the electro-optic excitation unit 34 continues to output the YAG rod excitation LD light EB from the fiber coupling LD 36 in a continuous oscillation. Further, the Q switch driver 32 does not receive the Q switch modulation signal AQ _SW from the control unit 20, and the Q switch driver 32 applies an unmodulated high frequency to the Q switch 30 in the YAG laser oscillator 22 as a Q switch drive signal. ing. Thereby, in the YAG laser oscillator 22, the inversion distribution is the maximum value or the saturated state, and the Q value is kept at the lowest value.

On the other hand, the fiber core pumping unit 14 continues to emit the core pumping LD light FB from the fiber coupling LD 42 during the standby period. However, the LD power supply 44 adjusts the LD drive current I ₂ supplied (injected) to the fiber coupling LD 42 to the standby current value I _W.

Here, the standby current value I _W is set so as to optimize the rising characteristic to the amplification current value I _S , that is, immediately after the start of laser irradiation (repetitive oscillation of the Q switch pulse) to the workpiece W. An appropriate current value corresponding to the amplification current command value I _S is selected so that the switch pulse processing laser light MB has a processing laser output value as set from the first without causing overshoot. .

In this embodiment, for example, a standby current value I _W corresponding (proportional) to the amplification current value I _S is set as a table as shown in FIG. 3 or a function as shown in FIG. There is a table. According to this example, when the amplification current value I _S is selected to be 40 A (ampere), the standby current value I _W is selected to be 16 A (ampere). Therefore, during the standby period, 16 A (ampere) of LD drive current I ₂ is supplied from the LD power source 44 to the fiber coupling LD 42.

  In this way, during the standby period, the core excitation LB light FB supplied from the fiber core excitation unit 14 to the amplifier fiber 10 is suppressed to a standby laser output value lower than the laser output value at the time of laser processing. Therefore, the amplifier fiber 10 does not overflow with excitation LD light or fluorescence energy, and the amount of LD light FB and fluorescence leaking from the end face of the amplifier fiber 10 as unnecessary noise light is small.

All the laser irradiation sequences for the workpiece W are performed under the control of the control unit 20. In order to start the laser irradiation, the control unit 20 starts supplying the Q switch modulation signal AQ _SW to the Q switch driver 32 as shown in FIG. 2, and at the same time, the LD power supply 44 of the fiber core excitation unit 14 is started. The current switching control signal CH is raised from the previous L level to the H level.

The Q switch modulation signal AQ _SW supplied from the control unit 20 rises with an up slope waveform having a desired gradient as shown in FIG. 2 in accordance with the first pulse killer technique. The Q switch driver 32 amplitude-modulates the high frequency with the modulation pulse having the up-slope waveform, and attenuates the amplitude of the output signal, that is, the Q switch drive signal with the down-slope gradient corresponding to the up-slope gradient of the modulation pulse. As a result, the inversion distribution in the YAG laser oscillator 22 decreases from the maximum value until then gradually (with a constant gradient) instead of abruptly (stepwise), that is, the Q value in the YAG laser oscillator 22 is reduced. Instead of abruptly (stepwise) from the base value up to gradual (with a constant gradient), Q switch pulse oscillation is performed with a small energy loss. Thus, the first seed laser beam SB (1) is oscillated and output with a peak power much lower than that of the YAG laser oscillator 22.

On the other hand, the LD power supply 44 of the fiber core excitation unit 14 changes the LD drive current I ₂ from the standby current value I _W to a predetermined gradient according to the switching of the current switching control signal CH from the L level to the H level. And, it rises up to the amplification current value I _S with an up-slope waveform having time characteristics.

  In the amplifier fiber 10, when the first seed laser beam SB (1) from the YAG laser oscillator 22 enters the core, it is not filled with core excitation LD light or fluorescent energy. Since the excitation unit 14 raises the output of the core excitation LD light FB from the standby laser output value to the amplification laser output value not in a stepwise manner but in an upslope waveform, the peak power of the peak power as shown by a virtual line in FIG. The abnormally high pulse laser beam MB (1) ′ is not generated, but rather the first processing laser is emitted from the exit end face 10b of the amplifier fiber 10 while the first seed laser beam SB (1) is hardly amplified. Extracted as light MB (1).

  The first processing laser beam MB (1) having an extremely low peak output is irradiated to the workpiece W through the vent mirror 50 and the laser emitting unit 16, but hardly contributes to the laser processing. Laser processing characteristics and quality are not impaired.

The seed laser oscillating unit 12 oscillates and outputs the first seed laser beam SB (1) by the first pulse killer method as described above to prevent the generation of the giant pulse, and normal from the second one. The seed laser beams SB (2), SB (3), SB (4),... Having a stable and constant peak power are sequentially oscillated and output at a predetermined repetition frequency by the pulse Q switch modulation signal AQ _SW . On the other hand, when the first seed laser beam SB (1) propagates through the core of the amplifier fiber 10 as described above, the fiber core excitation unit 14 suppresses the excitation energy of the amplifier fiber 10 and lowers the amplification factor. Preventing the generation of abnormal amplification pulses. From the second shot, the amplifier fiber 10 is held in a normal excitation state, and the seed laser beams SB (2), SB (3), SB (4),... Are amplified with a set amplification factor, A series of processing laser beams MB (2), MB (3), MB (4)... With uniform peak power can be extracted from the exit end face 10b of the amplifier fiber 10.

  Thus, the second and subsequent machining laser beams MB (2), MB (3), MB (4)... With the same peak power are irradiated to each machining point of the workpiece W, and the workpiece W A desired marking process or surface removal process is performed on the top.

  As described above, in the fiber laser processing apparatus of this embodiment, an abnormal amplification pulse is not generated from the amplifier fiber 10, so that the end surface 10b of the amplifier fiber 10 is not burned, and the laser processing characteristics and quality are impaired. Nor.

Further, the fiber core excitation unit 14 holds the LD drive current I ₂ at a standby current value I _S that is moderately lower than the amplification current value I _W during the standby period, and further according to the amplification current value I _W. Since the standby current value I _S is adjusted to an optimum value, the output of the processing laser beam MB does not overshoot, and the laser processing characteristics and quality can be improved in this respect as well.

In the above example, immediately after starting or restarting the repetitive oscillation of the Q switch pulse, the seed laser oscillation unit 12 applies the first pulse killer to the first pulse, and the first seed laser beam SB (1). While propagating through the amplifier fiber 10, the fiber core excitation unit 14 raises the LD drive current I ₂ from the standby current value I _W to the amplification current value I _S. However, if necessary, it is possible to apply the same pulse killer as the first pulse killer to the second to third pulses in the seed laser oscillation unit 12, or the LD drive current in the fiber core excitation unit 14. It is also possible to extend the time point when I ₂ has been started up to the second and subsequent pulses.

  In the above-described embodiment, the YAG laser is used for the seed laser oscillation unit 12. However, other Q-switched solid-state lasers such as a YVO4 laser can be used, and the wavelengths of the seed laser light and the excitation laser light are also arbitrary. You can choose. It is also possible to omit the transmission fibers 40 and 46 and replace the fiber coupling LDs 36 and 42 with ordinary LDs or LD arrays.

It is a block diagram which shows the structure of the fiber laser processing apparatus of the fiber MOPA system in one Embodiment of this invention. It is a wave form diagram which shows the waveform of each part for demonstrating the main effects in the fiber laser processing apparatus of embodiment. It is a table | surface which shows an example of the electric current value for amplification-current value for standby used with the fiber laser processing apparatus of embodiment. FIG. 4 is a graph showing a function of an approximate expression corresponding to the amplification current value-standby current value table of FIG. 3.

Explanation of symbols

10 Amplifying optical fiber (amplifier fiber)
DESCRIPTION OF SYMBOLS 12 Seed laser oscillation part 14 Fiber core excitation part 16 Output unit 20 Control part 22 YAG laser oscillator 28 YAG rod 30 Q switch 32 Q switch driver 34 Electro-optic excitation part 36 Fiber coupling LD for YAG rod excitation
38 LD power supply 40 Optical fiber for transmission (transmission fiber)
42 Fiber coupling LD for fiber core excitation
44 LD power supply 46 Optical fiber for transmission (transmission fiber)

Claims (10)

An optical resonator comprising a pair of optically disposed mirrors, a solid active medium disposed on an optical path in the optical resonator, and an active medium excitation unit for continuously exciting the active medium And a Q switch disposed on the same optical path as the active medium in the optical resonator, and a Q switch driving unit for driving the Q switch, wherein the Q switch pulse is transmitted at a predetermined repetition rate. A seed laser oscillation unit that oscillates and outputs seed laser light;
An amplification optical fiber having a core containing a predetermined rare earth element, putting the seed laser light from the seed laser oscillation unit into the core from one end, amplifying the seed laser light, and emitting from the other end; ,
A fiber core pumping unit that outputs a first pumping laser beam that is incident on the core from one end of the optical fiber for amplification and amplifies the seed laser beam by continuous oscillation;
A laser emitting portion for emitting laser light emitted from the other end of the amplification optical fiber as processing laser light;
When the seed laser oscillation unit starts or restarts repetitive oscillation of the Q switch pulse, the Q value in the optical resonator is constant for the seed laser light of the first to several shots of the Q switch pulse. Controlling the Q switch drive unit so as to rise with a first upslope waveform having a slope, and the output of the first excitation laser light rises with a second upslope waveform having a constant slope, and A control unit that controls the fiber core excitation unit so that the rise of the second up-slope waveform is completed after the seed laser beam of the Q switch pulse from the first to several is oscillated and output. Fiber laser processing equipment.   When the seed laser oscillating unit repeatedly oscillates the Q switch pulse, the control unit causes the first excitation laser beam to have a laser output value for processing suitable for desired laser processing. When the seed laser oscillation unit pauses or interrupts the repetitive oscillation of the Q switch pulse, the first excitation laser beam is controlled based on the first laser output value. The fiber laser processing apparatus according to claim 1, wherein the fiber core excitation unit is controlled to have a standby laser output value that is low and suitable for a desired rise characteristic. The fiber core excitation unit includes a first laser diode that oscillates and outputs the first excitation laser light, and a first LD power source that supplies a first LD drive current to the first laser diode. And
The control unit controls the first LD driving current through the first LD power source in order to control the output of the first excitation laser beam;
The fiber laser processing apparatus according to claim 2.   When the control unit controls the output of the first excitation laser beam to the laser output value for processing, the control unit controls the first LD drive current to an amplification current value, and When controlling the output of the laser beam to the standby laser output value, the first LD drive current is controlled to the standby current value, and the standby current value is associated with the amplification current value. The fiber laser processing apparatus according to claim 3, wherein a table is stored in a memory, or a function for associating the standby current value with the amplification current value is calculated.   The fiber laser processing apparatus according to claim 3 or 4, wherein the first laser diode is optically coupled to the amplification optical fiber via a first transmission optical fiber.   The active medium excitation unit oscillates and outputs a second excitation laser beam for exciting the active medium, and a second LD driving current is supplied to the second laser diode. The fiber laser processing apparatus according to claim 1, comprising two LD power supplies.   The fiber laser processing apparatus according to claim 6, wherein the second laser diode is optically coupled to the active medium via a second transmission optical fiber. A seed laser oscillation unit having a Q-switch type optical resonator oscillates and outputs a seed laser beam having a Q-switch pulse at a predetermined repetition frequency, and the core of the optical fiber for amplification is driven by the first pumping laser light that is continuously oscillated The seed laser beam is propagated from one end of the core to the other end while being excited, and a processing laser beam extracted as a seed laser beam amplified from the other end of the amplification optical fiber is irradiated toward the workpiece. A fiber laser processing method for performing desired laser processing on the workpiece,
When starting or restarting the repetitive oscillation of the Q switch pulse, the Q laser in the optical resonator has a constant gradient with respect to the first to several seed laser beams of the Q switch pulse. At the same time, the output of the first excitation laser beam is raised with a second upslope waveform having a certain gradient, and the first rise of the second upslope waveform is started. A fiber laser processing method comprising: completing a seed laser beam of the Q switch pulse up to several times after being oscillated and output.   When the Q switch pulse is repeatedly oscillated, the output of the first excitation laser beam is controlled to an amplification laser output value suitable for a desired laser processing, and the Q switch pulse is repeatedly oscillated. 9. The output of the first excitation laser beam is controlled to a standby laser output value that is lower than the amplification laser output value and suitable for a desired rise characteristic when the operation is stopped or interrupted. The fiber laser processing method as described in 2.   The fiber laser processing method according to claim 9, wherein the standby laser output value is selected in accordance with the processing laser output value.

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