JP2024018430A - Laser processing equipment, control method and program for laser processing equipment - Google Patents

Abstract

The present invention provides a technique for increasing the average laser output while maintaining the beam quality of laser light in a laser processing apparatus configured with a MOPA type fiber laser. A laser processing apparatus 100 includes a seed light source 2, excitation light sources 3, 9A, 9B, and an amplification fiber 1 configured to amplify the seed light by inputting the seed light and the excitation light. 8, a scanning mechanism 14 that scans the laser light output from the laser amplification section, and a control section 20 that controls the seed light source 2 and the excitation light sources 3, 9A, and 9B. The control unit 20 controls the seed light source 2 so that the seed light source 2 repeatedly generates a pulse train including a plurality of light pulses, and the amount of light of the plurality of light pulses increases in a curve with respect to time. The control unit 20 controls the amount of light of the first light pulse among the plurality of light pulses and the curvature of increase in the amount of light of the light pulses, according to parameters related to the pulse train. [Selection diagram] Figure 1

Description

The present disclosure relates to a laser processing device, a method of controlling the laser processing device, and a program.

A laser processing apparatus has been proposed that employs a MOPA (Master Oscillator and Power Amplifier) method using an amplifying fiber and uses light from a semiconductor laser (LD) as seed light. The above-mentioned laser processing apparatus is characterized in that the repetition frequency, peak power, pulse width, etc. of the emitted light can be changed independently of each other, so that it is easy to select the optimum parameters depending on the object to be processed.

In such laser processing apparatuses, methods for stabilizing the output power have been proposed so far. For example, Japanese Patent Application Laid-Open No. 2011-181761 (Patent Document 1) discloses that by controlling the intensity of excitation light during the non-emission period of a MOPA type fiber laser, the energy of pulsed light output from a laser processing device is reduced during the non-emission period. Discloses that it can be stabilized regardless of its length. JP2017-168549A (Patent Document 2) discloses a laser processing device having two modes for controlling the power of excitation light in a MOPA type fiber laser. In one of the two modes, the power of the pumping light is controlled so that the larger the set value of the pulse width of the amplified light is, the more the peak energy of the amplified light increases within the threshold of the minimum set value of the pulse width. Ru.

Japanese Patent Application Publication No. 2011-181761 Japanese Patent Application Publication No. 2017-168549

In recent years, there has been a need for laser printing to provide a means to achieve deeper marking in a shorter takt time. For this purpose, it is necessary to increase the pulse energy and laser average output while maintaining the beam quality of the laser light.

One way to increase the pulse energy in MOPA type fiber lasers is to decrease the repetition frequency. By lowering the repetition frequency, the pulse interval becomes longer. As a result, the amount of accumulated rare earth elements pumped by the excitation light increases in the amplification fiber, so that the energy of the optical pulse output from the amplification fiber can be increased. However, on the other hand, the increased instantaneous peak power may cause stimulated Raman scattering (SRS), which is a type of nonlinear effect. When SRS occurs, the wavelength components of the light output from the amplification fiber are broadened, resulting in a problem that the beam quality is degraded.

Generally, by lowering the amount of pumping light, the instantaneous peak power of the light output from the fiber laser is controlled to a level that does not cause SRS. However, by lowering the amount of excitation light, the average laser output also decreases.

An object of the present disclosure is to provide a technique for increasing the average laser output while maintaining the beam quality of laser light in a laser processing apparatus configured with a MOPA type fiber laser.

A laser processing device according to an example of the present disclosure includes a seed light source that generates seed light, an excitation light source that generates excitation light, and is configured to amplify the seed light by inputting the seed light and the excitation light. It includes a laser amplification section including an amplification fiber, a scanning mechanism that scans the laser light output from the laser amplification section, and a control section that controls the seed light source and the excitation light source. The control unit controls the seed light source so that the seed light source repeatedly generates a pulse train including a plurality of light pulses, and the amount of light of the plurality of light pulses increases in a curved manner with respect to time. The control unit controls the light amount of the first light pulse among the plurality of light pulses and the curvature of increase in the light amount of the light pulses according to parameters regarding the pulse train.

According to the above configuration, in a laser processing apparatus configured with a MOPA type fiber laser, it is possible to increase the average laser output while maintaining the laser beam quality. SRS can be suppressed by suppressing the instantaneous peak power of the output light when a plurality of light pulses are incident on the amplification fiber, so the beam quality of the laser light can be maintained. Therefore, the average laser output can be increased while suppressing the occurrence of nonlinear effects.

In the above disclosure, the amplification fiber includes a first optical fiber that amplifies seed light from a seed light source with first excitation light from an excitation light source, and a first optical fiber that amplifies seed light from a seed light source with first excitation light from an excitation light source; and a second optical fiber amplified by the second excitation light. The excitation light source includes a first excitation light source that emits first excitation light and a second excitation light source that emits second excitation light. The control unit controls the power of the first excitation light so that the amount of light of the plurality of light pulses emitted from the first optical fiber increases in a curved manner with respect to time.

According to the above configuration, laser light can be amplified while suppressing the occurrence of nonlinear effects in both optical amplification by the first-stage and second-stage optical fibers. Therefore, the average laser output can be increased.

In the above disclosure, the control unit controls the seed light source in accordance with a table that defines the relationship between parameters regarding the pulse train, the light amount of the first light pulse, and the curvature of increase in the light amount of the light pulse.

According to the above configuration, the pulse train can be easily controlled by determining the light amount of the first light pulse and the curvature of increase in the light amount of the pulse according to the table.

In the above disclosure, the parameters regarding the pulse train include the repetition frequency of the pulse train, the width of each of the plurality of optical pulses, the interval between the plurality of optical pulses, the number of the plurality of optical pulses, the average output of the pulse train, and , at least one of the excitation currents supplied to the excitation light source.

According to the above configuration, parameters such as repetition frequency and pulse width are independent from each other, so by controlling the MOPA fiber laser by arbitrarily combining these parameters, desired quality and quality can be obtained from the MOPA fiber laser. Laser light having a desired output can be output.

In the above disclosure, the control unit controls the intensity of the first optical pulse among the plurality of pulses in the pulse train of the laser light output from the laser amplification unit, the second optical pulse, the maximum light amount of the optical pulse, and Corrects the light intensity of multiple pulses in the pulse train generated from the seed light source from the next time onwards, or the light intensity of the excitation light generated from the excitation light source, using the ratio of the intensity of one of the light pulses with the minimum light intensity. performs feedback control.

According to the above configuration, the control unit performs feedback control to control the amount of the seed light or excitation light based on the intensity of the laser light output from the laser amplification unit, so that the laser output from the laser amplification unit The intensity of a plurality of pulses included in a light pulse train can be stabilized.

A method for controlling a laser processing apparatus according to an example of the present disclosure includes a seed light source that generates seed light, an excitation light source that generates excitation light, and amplification of the seed light by inputting the seed light and the excitation light. A method for controlling a laser processing device comprising: a laser amplification section including an amplification fiber configured as described above; a scanning mechanism for scanning laser light output from the laser amplification section; and a control section for controlling a seed light source and an excitation light source. . The control method includes the steps of repeatedly generating a pulse train including a plurality of light pulses from the seed light source and controlling the seed light source so that the amount of light of the plurality of light pulses increases in a curved manner with respect to time. The step of controlling the seed light source includes the step of controlling the light intensity of the first light pulse of the plurality of light pulses and the curvature of increase in the light intensity of the light pulses according to parameters regarding the pulse train.

According to the above configuration, in a laser processing apparatus configured with a MOPA type fiber laser, it is possible to increase the average laser output while maintaining the laser beam quality. SRS can be suppressed by suppressing the instantaneous peak power of the output light when a plurality of light pulses are incident on the amplification fiber, so the beam quality of the laser light can be maintained. Therefore, the average laser output can be increased while suppressing the occurrence of nonlinear effects.

A program according to an example of the present disclosure includes a seed light source that generates seed light, an excitation light source that generates excitation light, and an amplification fiber configured to amplify the seed light by inputting the seed light and the excitation light. A program that causes a control unit to execute a method for controlling a laser processing apparatus including a laser amplification unit including a laser amplification unit, a scanning mechanism that scans a laser beam output from the laser amplification unit, and a control unit that controls a seed light source and an excitation light source. It is. The control method includes the steps of repeatedly generating a pulse train including a plurality of light pulses from the seed light source and controlling the seed light source so that the amount of light of the plurality of light pulses increases in a curved manner with respect to time. The step of controlling the seed light source includes the step of controlling the light intensity of the first light pulse of the plurality of light pulses and the curvature of increase in the light intensity of the light pulses according to parameters regarding the pulse train.

According to the above configuration, in a laser processing apparatus configured with a MOPA type fiber laser, it is possible to increase the average laser output while maintaining the laser beam quality. SRS can be suppressed by suppressing the instantaneous peak power of the output light when a plurality of light pulses are incident on the amplification fiber, so the beam quality of the laser light can be maintained. Therefore, the average laser output can be increased while suppressing the occurrence of nonlinear effects.

According to the present disclosure, in a laser processing apparatus configured with a MOPA type fiber laser, it is possible to increase the average laser output while maintaining the laser beam quality.

1 is a diagram schematically illustrating an example of a usage scene of a laser processing apparatus according to an embodiment of the present disclosure. 2 is a diagram showing an example of the structure of the amplification fiber shown in FIG. 1. FIG. It is a figure explaining control of seed light and excitation light in an embodiment. FIG. 2 is a diagram schematically showing an energy level diagram of an amplification fiber and optical amplification by the amplification fiber. FIG. 3 is a diagram showing the relationship between residual population inversion, input optical energy, and output optical energy. 2 is a diagram showing an example of functional blocks of the control device shown in FIG. 1. FIG. It is a figure showing an example of composition of a table stored in a storage part of a control device. 8 is a diagram schematically showing an example of controlling a multi-pulse waveform for one of the patterns defined by the table shown in FIG. 7. FIG. 9 is a diagram showing an example of the waveform of an input signal (multipulse) controlled according to the tables shown in FIGS. 7 and 8. FIG. FIG. 7 is a diagram showing another example of controlling the waveform of a seed light pulse. FIG. 3 is a diagram showing a specific example of the waveform of a pulse output from an amplification fiber by controlling a seed light pulse in the present embodiment. FIG. 2 is a diagram showing an example of a waveform of a seed light pulse obtained by controlling the seed light pulse according to the present embodiment, and an example of an output waveform from a MOPA type fiber laser. 3 is a flowchart showing an example of a method of controlling the laser processing apparatus according to the present embodiment. FIG. 3 is a diagram showing an example of a configuration for feedback control of laser light output. FIG. 2 is a block diagram showing the configuration of a control device for feedback control. FIG. 3 is a diagram showing an example of feedback control according to the present embodiment. FIG. 3 is a diagram illustrating a correction amount of input light control used for feedback control. 7 is a flowchart showing a flow when a seed LD current value is corrected by feedback control according to the present embodiment. 7 is a flowchart showing a flow when the current value of the excitation LD of the first stage amplifier is corrected by feedback control according to the present embodiment.

Embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the same or corresponding parts in the figures are designated by the same reference numerals, and the description thereof will not be repeated.

As used herein, the terms "pulse train" and "multipulse" refer to a group of a plurality of optical pulses arranged on the time axis at certain time intervals. Further, in this specification, the frequency of repetition of multi-pulses is referred to as "repetition frequency". In the following description, a laser diode will be referred to as "LD".

<A. Application example>
FIG. 1 is a diagram schematically illustrating an example of a usage scene of a laser processing apparatus 100 according to an embodiment of the present disclosure. As shown in FIG. 1, the laser processing apparatus 100 is configured to amplify the laser signal light of a seed light semiconductor laser (seed LD) using multistage amplification fibers and output a laser light having high power. Ru. Specifically, the laser processing apparatus 100 includes optical fibers 1 and 8, a seed LD 2, excitation LDs 3, 9A, and 9B, isolators 4, 6, and 11, a bandpass filter (BPF) 7, a combiner 5, 10, an end cap 12, and drivers 21, 22, 23A, and 23B. The laser processing apparatus 100 further includes a laser beam scanning mechanism 14, a control device 20, and an input section 25.

In the configuration shown in FIG. 1, the laser amplification section includes an amplification section 101 and an amplification section 102. The amplifying section 101 includes an optical fiber 1, a seed LD2, and a pumping LD3, and amplifies the seed light from the seed LD2. Amplifying section 102 includes optical fiber 8 and pumping LDs 9A and 9B, and amplifies the laser light output from amplifying section 101.

The optical fibers 1 and 8 are amplification fibers and have a core doped with a rare earth element as an optical amplification component, and a cladding provided around the core. The type of rare earth element added to the core is not particularly limited, and examples include Er (erbium), Yb (ytterbium), and Nd (neodymium). As an example, the optical fibers 1 and 8 are amplification fibers in which Yb is added to the core.

Each of the optical fibers 1 and 8 may be, for example, a single-clad fiber with one layer of cladding around the core, or a double-clad fiber with two layers of cladding around the core. Note that in this embodiment, both optical fibers 1 and 8 are double clad fibers.

FIG. 2 is a diagram showing an example of the structure of the amplification fiber shown in FIG. 1. FIGS. 2(A) and 2(B) are cross-sectional views of an example of a single-clad fiber, showing cross sections in a direction perpendicular to and parallel to the extending direction of the fiber, respectively. Referring to FIGS. 2(A) and 2(B), the single clad fiber includes a core 31 doped with a rare earth element, and a cladding 32 provided around the core 31 and having a lower refractive index than the core 31. including. The outer surface of the cladding 32 is covered with an outer skin 34.

FIG. 2(C) and FIG. 2(D) are cross-sectional views of an example of a double-clad fiber, showing cross sections in a direction perpendicular and parallel to the extending direction of the fiber, respectively. Referring to FIG. 2(C) and FIG. 2(D), the double clad fiber includes a core 35 doped with a rare earth element, and a first layer provided around the core 35 and having a lower refractive index than the core 35. It includes a cladding 36 and a second cladding 37 that is provided around the first cladding 36 and has a lower refractive index than the first cladding 36. For example, the material of the first cladding 36 is glass, and the material of the second cladding 37 is a low refractive index resin. The outer surface of the second cladding 37 is covered with an outer skin 38.

Returning to FIG. 1, the seed LD2 is a laser light source that emits seed light. The wavelength of the seed light is, for example, a wavelength selected from the range of 1000 to 1100 nm. The driver 21 pulse-drives the seed LD2 by repeatedly injecting a pulsed current into the seed LD2. Therefore, a pulse of seed light is emitted from the seed LD2.

The seed light emitted from the seed LD2 passes through the isolator 4. The isolator 4 has the function of transmitting light in only one direction and blocking light incident in the opposite direction. In this embodiment, the isolator 4 transmits the seed light from the seed LD 2 and blocks the return light from the optical fiber 1. This can prevent the return light from the optical fiber 1 from entering the seed LD 2.

The excitation LD 3 is an excitation light source that emits first excitation light for exciting the rare earth element added to the core of the optical fiber 1 . When the rare earth element is Yb, the wavelength of the excitation light is, for example, 940±10 nm. The driver 22 drives the excitation LD3.

The combiner 5 combines the seed light from the seed LD2 and the excitation light from the excitation LD3, and makes the combined light enter the optical fiber 1, which is the first optical fiber.

The excitation light incident on the optical fiber 1 is absorbed by the rare earth element contained in the core, and the rare earth element is excited. When the seed light from the seed LD 2 propagates through the core of the optical fiber 1, the excited rare earth element causes stimulated emission by the seed light, so that the seed light is amplified. Note that when the optical fiber 1 is a single-clad fiber, both the seed light and the excitation light enter the core. On the other hand, when the optical fiber 1 is a double-clad fiber, the seed light enters the core and the excitation light enters the first cladding. The first cladding of the double-clad fiber functions as a waveguide for pumping light. During the process in which the excitation light incident on the first cladding propagates through the first cladding, the rare earth element in the core is excited by the mode passing through the core.

The isolator 6 allows the seed light (light pulse) that has been amplified by the optical fiber 1 and is emitted from the optical fiber 1 to pass therethrough, and blocks the light that returns to the optical fiber 1 .

The bandpass filter 7 passes light in a wavelength band including the peak wavelength of the optical pulse output from the optical fiber 1, and removes light in a wavelength band different from this wavelength band.

The excitation LDs 9A and 9B emit second excitation light for exciting the rare earth element contained in the core of the optical fiber 8, which is the second optical fiber. Drivers 23A and 23B drive excitation LDs 9A and 9B, respectively. In the example shown in FIG. 1, the number of pump LDs in the amplification section 102 is two, but the number of pump LDs is not limited to this.

The combiner 10 combines the optical pulse that has passed through the bandpass filter 7 and the excitation light from the excitation LDs 9A and 9B, and makes the combined light pulses enter the optical fiber 8. The optical pulse incident on the optical fiber 8 is amplified by the excitation light by the same optical amplification effect as in the optical fiber 1.

Isolator 11 blocks light returning to optical fiber 8 . The end cap 12 is provided to prevent damage occurring at the interface between the end face of the optical fiber and the atmosphere when a light pulse with a high peak power is emitted from the optical fiber into the atmosphere.

The laser beam scanning mechanism 14 is a scanning mechanism for scanning the laser beam output from the laser amplification section. Although not shown, the laser beam scanning mechanism 14 includes a collimator lens for adjusting the diameter of the laser beam that is emitted from the end cap 12 to a predetermined size, and processes the laser beam after passing through the collimator lens. It may also include a galvano scanner for scanning the surface of the object 50 in two-dimensional directions, an fθ lens for focusing the laser beam, and the like. The surface of the workpiece 50 made of metal or the like is processed by scanning the laser beam L, that is, the output light from the laser amplification section, in two-dimensional directions on the surface of the workpiece 50 . For example, information consisting of characters, figures, etc. is printed (marked) on the surface of the workpiece 50.

The control device 20 comprehensively controls the operation of the laser processing apparatus 100 by controlling the drivers 21, 22, 23A, 23B and the laser beam scanning mechanism 14. Therefore, the control device 20 controls the seed LD2 and the excitation LD3, 9A, and 9B.

The input unit 25 receives, for example, information from a user (for example, information on characters, symbols, etc. printed on the surface of the workpiece 50), and transmits the received information to the control device 20. The control device 20 controls the start and end of the operations of the drivers 21, 22, 23A, and 23B based on information from the input unit 25, for example, and while operating the drivers 21, 22, 23A, and 23B, Controls the operation of the laser beam scanning mechanism 14.

The control device 20 changes the power of the excitation light emitted by the excitation LDs 3, 9A, and 9B by controlling the drivers 22, 23A, and 23B. The excitation LDs 3, 9A, and 9B output excitation light having powers corresponding to drive currents supplied from the drivers 22, 23A, and 23B, respectively. The magnitude of the drive current output from each driver 22, 23A, 23B is controlled by the control device 20.

The control device 20 is realized, for example, by a personal computer that executes a predetermined program. The input unit 25 is not particularly limited as long as it is a device that allows the user to input information, and for example, a mouse, keyboard, touch panel, etc. can be used.

FIG. 3 is a diagram illustrating control of seed light and excitation light in the embodiment. As shown in FIG. 3, in the embodiment, the seed LD repeatedly outputs a pulse train of seed light, that is, a multipulse at a predetermined frequency. The repetition frequency is variable within a range of, for example, 10 kHz to 1000 kHz. The number of pulses included in a multi-pulse can be set arbitrarily.

In FIG. 3, a portion of a plurality of pulses included in a multi-pulse is temporally expanded and shown. The pulse width within a multipulse and the interval between pulses are, for example, on the nanosecond level (for example, on the order of 10 nanoseconds). Note that the pulse width can be defined by the FWHM (full width at half maximum) of each pulse.

The "peak power" of a pulse is defined as the maximum optical intensity of that pulse. "Pulse energy" is the energy of one pulse, and is determined by integrating the energy and pulse width. "Laser average output" is the average value of laser output over a certain period of time, and in the case of a pulsed laser, it is defined by the integration of pulse energy and repetition frequency.

As shown in FIG. 3, before inputting the seed light into the amplification fiber, excitation light is input into the amplification fiber in order to excite the rare earth element, which is an optical amplification substance, in advance. The amount of excitation light at this time is smaller than the amount of excitation light during amplification of the seed light. The amount of pumping light input into the amplification fiber is increased in synchronization with the input of seed light.

In this embodiment, by making the seed light pulse into a multi-pulse, the energy of the amount of excitation light accumulated in the amplification fiber is consumed by each pulse in the multi-pulse. This reduces the peak power per pulse output from the laser processing device. As a result, the instantaneous peak power of the output light (particularly the peak power of the first pulse) can be suppressed, so the occurrence of nonlinear effects such as SRS can be suppressed.

In this embodiment, the amount of light of each pulse within the multi-pulse is further increased in a curved manner. "Increasing in a curved manner" means that the change in the light amount of a pulse within a multipulse becomes larger as the pulse becomes later in time. In addition, in FIG. 3, in order to explain various parameters related to the multi-pulse, for convenience, the peak power of each pulse included in the multi-pulse is shown to be approximately equal. An example of increasing the light amount of each pulse in a multi-pulse in a curved manner will be described in detail later.

Let the peak power of the k-th pulse in the multipulse be p _k (k is an integer greater than or equal to 1). For example, one example included in "increasing curvilinearly" is the relationship (p _k+1 - p _k )<(p _k+2 - _{p k+1} ). Note that "increasing in a curved manner" is not limited to being determined by the magnitude relationship of peak powers between three temporally adjacent pulses. In this embodiment, it is sufficient that the slope of the change in the light amount of the pulse becomes larger as the pulse becomes temporally later. For example, the light intensity of one pulse among multiple pulses is the same as (or may decrease) the light intensity of the previous pulse, and the light intensity of the next pulse is greater than the light intensity of that pulse. You can say that. In this embodiment, it is sufficient that the light amount of the plurality of pulses increases in a curved manner as a whole.

The first pulse has the smallest amount of light among the plurality of pulses. In this embodiment, the light amount of the first pulse and the curvature of increase in the light amount of the light pulse are determined according to parameters related to multipulses. For example, the light intensity of the first pulse and the curvature of increase in the light intensity of the light pulse are determined according to the repetition frequency of the multi-pulse. Thereby, the average laser output can be increased while keeping the peak power of each pulse of the multi-pulse below the threshold for generating stimulated Raman scattering.

<B. Optical amplification in amplification fiber>
FIG. 4 is a diagram schematically showing an energy level diagram of an amplifying fiber and optical amplification by the amplifying fiber. In FIG. 4, open circles represent Yb ions transitioning to the ground state. The hatched circles in FIG. 4 represent stimulated released Yb ions.

Yb is an element with an atomic number of 70, and the electronic configuration of the Yb ³⁺ ion has a [Xe]4f ¹³ structure, so that only the ground state ² F _7/2 and the excited state ² F _5/2 exist. The ground state ² F _7/2 is formed by four Stark levels, and the excited state ² F _5/2 is formed by three Stark levels. Therefore, the wavelength of the excitation light and the wavelength of the stimulated emission light (signal light) are different. However, in FIG. 4, the four Stark levels in the ground state and the three Stark levels in the excited state are simplified and shown simply as the ground state and the excited state.

FIG. 4A shows a state in which Yb ions are excited by excitation light. In the case of the Yb-doped fiber, for example, Yb ions at the ground level E1 are pumped up to the excitation level E2 by absorbing excitation light with a wavelength of 940 nm. In this state, when a signal light of, for example, 1062 nm is incident, stimulated emission occurs as shown in FIGS. 4(B) and 4(C). As a result, the signal light is amplified, and the Yb ions at the excited level E2 are relaxed to the ground level E1. Note that while the pumping by the excitation light is continued, stimulated emission occurs and the signal light pulse is amplified every time the signal light pulse enters the amplification fiber.

FIG. 4(B) schematically shows stimulated emission due to the incidence of the first pulse of the multipulses. FIG. 4(C) schematically shows stimulated emission due to the incidence of the second pulse of the multipulses. The pumping of Yb ions by the excitation light reaches its maximum just before the first pulse is incident. Therefore, the first pulse is greatly amplified. On the other hand, if the interval between pulses is sufficiently small (for example, about 10 nanoseconds), fewer Yb ions will be excited by the second and subsequent pulses compared to the Yb ions consumed in the first pulse, so The amplification factor of the amplifying fiber decreases for pulses of

In this embodiment, the light intensity of the first pulse of the multipulses is reduced. This reduces the number of Yb ions relaxing from the excited level to the ground level. The atomic density distribution of Yb ions at the excited level is maintained to some extent even for the second and subsequent pulses. Therefore, by gradually increasing the light intensity of the second and subsequent pulses, the peak power of the laser light pulse output from the amplification fiber by stimulated emission can be increased. Thereby, the average laser output can be increased while keeping the peak power of each pulse after amplification below the SRS generation threshold.

The energy of the pulse output from the amplification fiber can be controlled mainly by the amount of excitation light and the amount of signal light. However, if each pulse in the multipulse is a nanosecond level pulse, it is not easy to control the amount of excitation light for each pulse. Therefore, in this embodiment, the laser average output is controlled by controlling the light amount of each pulse in the multi-pulse without changing the excitation light amount.

<C. Multipulse waveform>
The power P of the laser beam output from the amplification fiber can be expressed using the atomic distribution density N2 of the excited level, the signal light amount I, and the characteristic parameters of the amplification fiber (emission cross section, coupling efficiency, etc.).

A plurality of pulses within a multi-pulse are labeled n1, n2, . . . , n* in order from the earliest in time. The amplification fiber output optical energy for the input optical energy I1, I2, . . . , I* due to the pulse of each pulse number is expressed as P1, P2, . P1, P2, . . . , P* can be expressed as follows.

P1=I1+A×σ21×I1
P2=I2+(C1+B(t))×σ21×I2
P3=I3+(C2+B(t))×σ21×I3
...
Here, A is the population inversion density immediately before the n1 pulse enters, and B(t) is the population inversion density that increases due to the excitation light from the n1 pulse until the n2 pulse enters. where C1 is the population inversion density remaining immediately after the incidence of the n1 pulse, and σ21 is the emission cross section of the amplification fiber. Note that B(t) depends on time and the amount of excitation light.

The first term in each equation of P1, P2, P3, . . . is ignored as it is sufficiently smaller than the second term. Further, assuming that the pulse interval is constant, B(t) is regarded as a constant B. Furthermore, if Pn, In (n=1, 2, 3, . . . ) are expressed as a function of time, the output optical energy P can be expressed as in the following equation (1).

P(t)=(C(t)+B))×σ21×I(t)...(1)
On the other hand, the following equation (2) holds according to energy conservation measurement. In Equation (2), a represents the ratio of the inverted density distribution used for stimulated emission by the incidence of the n1 pulse and the above A.

Cn=Cn-1+B(t)-a×Pn-1...(2)
When formula (2) is modified, it is expressed as Cn-Cn-1=B(t)-a×Pn-1. When B(t) is replaced with a constant B and the above equation is expressed as a function of time, it can be expressed as dC(t)/dt=B-a×P(t).

Here, assuming that P(t) is constant regardless of time, P(t) can be set as a constant P. Therefore, dC(t)/dt=B-a×P. By integrating both sides of this equation over time t, the following equation (3) is obtained. Note that D is a constant.

C(t)=(B-a×P)×t+D...(3)
The residual population inversion C(t) is a linear expression with respect to time t. Furthermore, if the rate at which atoms relax from the excited level to the ground level is faster than the rate at which atoms are excited from the ground level to the excited level, then B<a×P, so the proportionality constant ( B-a×P) is negative. Therefore, the residual population inversion C(t) is a function that monotonically decreases with time.

Next, by substituting equation (2) into equation (1), output optical energy (power) P is expressed by equation (4) below.

P=((B-a×P)×t+D+B))×σ21×I(t)...(4)
By transforming equation (4), input optical energy I(t) can be expressed as equation (5).

I(t)=P/{((B-a×P)×t+D+B)}/σ21...(5)
If we set B-a×P=α, P/σ21=β, D+B=γ (α, β, γ are constants, α<0, β>0, γ>0), the input optical energy I(t) is , can be expressed as in equation (6).

I(t)=β/(α×t+γ)...(6)
FIG. 5 is a diagram showing the relationship between residual population inversion C(t), input optical energy I(t), and output optical energy P(t). As shown in FIG. 5, the residual inverted population C(t) expressed by equation (3) is a linear monotonically decreasing function with respect to time. In contrast, the input optical energy I(t) according to equation (5) is a function that increases in a curved manner with respect to time. The output optical energy extracted from the amplifying fiber for each pulse in the multi-pulse is determined by the combination of the residual population inversion C(t) expressed by equation (3) and the input optical energy I(t) according to equation (5). P(t) becomes constant.

Looking at equation (6) in detail here, the input optical energy I(t) is a function based on time t to the -1 power. Specifically, α/β, which is the coefficient of t, is negative, and the denominator becomes 0 when t = -γ/α, so the function expressed by equation (6) is t = -γ/α. It can be seen that it is an inversely proportional function with the origin as the origin and the sign reversed. Therefore, when increasing the input optical energy, it is more desirable to increase the input optical energy so as to follow a function based on the -1 power of time t.

<D. Configuration for pulse control>
FIG. 6 is a diagram showing an example of functional blocks of the control device shown in FIG. 1. As shown in FIG. 6, the control device 20 includes a storage section 201, a condition setting section 202, a seed LD control section 203, and an excitation LD control section 206. The configuration shown in FIG. 6 may be realized by hardware (electronic circuit) or software.

The storage unit 201 stores conditions regarding seed light and excitation light in association with conditions for output light from a laser processing device (hereinafter also simply referred to as "output light"). The stored contents include, for example, conditions for seed light (multipulse) and excitation light power with respect to output light power. Such conditional relationships are stored in the storage unit 201 in a format such as a table, function, or map.

The condition setting unit 202 sets driving conditions for the seed LD and the excitation LD based on the information input to the input unit 25 and the conditions stored in the storage unit 201. For example, conditions such as the output (average output) of the laser processing device and the repetition frequency of multi-pulses are input to the input section 25. The condition setting unit 202 sets conditions for controlling the seed light and the excitation light according to the conditions input to the input unit 25 and the conditions of the seed light (multipulse) and excitation light stored in the storage unit 201. .

The seed LD control section 203 controls the driver 21 for driving the seed LD 2 according to the conditions set by the condition setting section 202. The driver 21 supplies a drive current to the seed LD 2 under the control of the seed LD control section 203 .

The excitation LD control unit 206 controls the driver 22 for driving the excitation LD 3, the driver 23A for driving the excitation LD 9A, and the driver 23B for driving the excitation LD 9B according to the conditions set by the condition setting unit 202. do. Each of the drivers 22, 23A, and 23B supplies a drive current to the corresponding excitation LD under the control of the excitation LD control section 206.

In one embodiment, the seed light (multipulse) conditions are stored in the storage unit 201 in the form of a table, for example. FIG. 7 is a diagram showing an example of the configuration of a table stored in the storage unit 201 of the control device 20. FIG. 8 is a diagram schematically showing an example of controlling the multi-pulse waveform for one of the patterns defined by the table shown in FIG. 7.

As shown in Figure 7, the table includes the average output, the repetition frequency of the multipulse, the number of pulses included in the multipulse, the interval between pulses in the multipulse, the width of each pulse in the multipulse, and the seed LD. The pattern of the current injected into the current is set. As an example, the seed LD current pattern is pattern 1 when the average output is A (mJ), the repetition frequency f (kHz), the number of pulses is 10, the pulse interval is t1 (nsec), and the pulse width is t2 (nsec). defined. The pulse interval t1 and the pulse width t2 may be fixed values for the device regardless of the pattern. Alternatively, the pulse interval t1 and pulse width t2 may be values that are controlled according to the pattern.

FIG. 8 shows an example in which the seed LD current pattern is pattern 1. In the table, seed LD current values (i1, i2, . . . , i10) are defined for each pulse number (n1, n2, . . . , n10). Basically, the seed LD emits light from the point in time when the seed LD current exceeds the threshold current, and after that, the output of the seed LD increases in proportion to the amount of increase in the seed LD current. As can be understood from FIGS. 7 and 8, the pattern of the seed LD current includes the period of change of the seed current (pulse interval t1 and pulse width t2 as shown in FIG. 7), and the pattern of the seed LD current (pulse interval t1 and pulse width t2 as shown in FIG. By setting the value of the seed current for each pulse, the interval and output of the pulses emitted from the seed LD can be arbitrarily set.

In this embodiment, since parameters such as average output, repetition frequency, number of pulses, pulse interval, and pulse width are mutually independent, the MOPA type fiber laser can be controlled by arbitrarily combining these parameters. A type fiber laser can output laser light having a desired quality and a desired output. According to an example of this embodiment, seed light pulses are controlled according to FIGS. 7 and 8. Therefore, the light intensity of the first pulse in the multipulse and the curvature of the increase in the light intensity of the pulses are determined according to at least one of the repetition frequency, the width of each pulse in the multipulse, and the spacing between the pulses. can do.

FIG. 9 is a diagram showing an example of the waveform of an input signal (multipulse) controlled according to the tables shown in FIGS. 7 and 8. FIG. 9 shows changes in the amount of light of the input signal over time for examples in which the number of pulses is 10, 20, and 30. It can be seen that by controlling the seed LD current, the amount of light of the pulse can be controlled so as to increase in a curve with respect to time.

FIG. 10 is a diagram showing another example of controlling the waveform of the seed light pulse. In the example shown in FIG. 10, after the light amount of the seed light pulse (input signal) reaches a certain value, the light amount is maintained at that value.

As described above, the output of the seed LD increases in proportion to the amount of increase in the seed LD current relative to the threshold current. However, it is fully assumed that there is an upper limit to the output of the seed LD. If a current exceeding the upper limit of the output of the seed LD is supplied to the seed LD, the seed LD may fail. When the number of pulses is large, or when the curvature of increase in the intensity of the seed light pulse is increased, the intensity of the seed light pulse increases before the number of pulses emitted from the seed LD reaches the preset number. The upper limit may be reached.

Therefore, as shown in FIG. 10, a limit value may be set for the output of the seed LD so that the output of the seed LD does not reach the upper limit. The limit value may be set, for example, to a value obtained by multiplying the upper limit value of the output of the seed LD by a predetermined percentage (for example, 90%). By setting the current pattern as shown in FIG. 10, it is possible to obtain the effect of increasing the average output of the laser processing apparatus while preventing failure of the seed LD.

Note that the contents of the tables shown in FIGS. 7 and 8 show an example of seed light pulse control according to this embodiment. Therefore, the seed light pulse can be controlled more flexibly according to the table settings. Other examples of seed light pulse control will be shown below. However, the control of the seed light pulse is not limited to what is described below.

For example, the curvature of the change in the amount of light of a pulse within a multi-pulse may be set depending on the number of pulses. Therefore, the curvature of the change in the amount of light of the pulses may differ depending on the number of pulses. However, as the number of pulses in a multipulse increases, more pumping electrons are used for stimulated emission within the amplification fiber, which reduces the peak power. Therefore, the light amount of the first pulse of the multi-pulse and the curvature of the change in the light amount of the pulse may be made the same as the conditions when the number of pulses is smaller (for example, the number of pulses is 10). Thereby, beam quality can be maintained even when the number of pulses increases (for example, when the number of pulses is 20 or 30).

Furthermore, when the repetition frequency is decreased, the pumping time increases, and the amount of pumping electrons increases immediately before the first pulse in the multi-pulse is incident. Therefore, the peak power of the pulse emitted from the amplification fiber tends to increase due to the first pulse in the multi-pulse. Furthermore, the peak power of the second and subsequent pulses emitted from the amplification fiber may be significantly attenuated. Therefore, the light amount of the first pulse of the multi-pulse and the curvature of the change in the light amount of the pulse may be made equal to the conditions when the repetition frequency is low. Alternatively, the light intensity of the first pulse may be set such that the lower the repetition frequency, the smaller the light intensity of the first pulse of the multipulses. Thereby, when the repetition frequency is changed, the peak power of the pulse output from the MOPA type fiber laser can be stabilized.

Also, the larger the width of each pulse within the multipulse, the more pumping electrons are used for stimulated emission. Taking this into consideration, the greater the width of each pulse, the greater the light intensity of the first pulse within the multi-pulse.

Also, the shorter the interval between pulses within a multipulse, the more pumping electrons are used for stimulated emission. Therefore, the shorter the interval between pulses, the smaller the curvature of the change in the amount of light of the pulses may initially be. For example, the shorter the interval between pulses, the larger the light intensity of the first pulse in a multipulse, the smaller the curvature of the change in light intensity of the pulse with respect to the first pulse, and the smaller the curvature of the change in light intensity of the pulse with respect to the first pulse. It may be possible to make it larger.

<E. Example of pulse control and output>
FIG. 11 is a diagram showing a specific example of the waveform of the pulse output from the amplification fiber by controlling the seed light pulse in this embodiment.

FIG. 11 shows, as waveform patterns of seed light pulses, a pattern in which the amount of pulse light changes linearly with respect to time, and a pattern in which the amount of light in the pulse changes curvedly with respect to time. Furthermore, regarding the patterns in which the light intensity of the pulse changes in a curved manner with respect to time, there are patterns in which the first pulse light intensity is larger and patterns in which the first pulse light intensity is smaller (denoted as "input decrease" in Fig. 11). is shown. Note that the pattern in which the seed light pulse waveform changes linearly over time is a pattern for comparison with this embodiment.

FIG. 11 shows the waveforms of pulses input to the amplification stage and the waveforms of pulses output from the amplification stage as pulses output from the amplification fiber. The "amplification stage" corresponds to the amplification section 102 shown in FIG. Therefore, the input waveform of the amplification stage corresponds to the waveform of the pulse output from the amplification section 101 in FIG. The output waveform of the amplification stage is the waveform of the pulse output from the amplification section 102 when the pulse output from the amplification section 101 is input to the amplification section 102.

First, the seed light pulse waveform pattern and the input waveform of the amplification stage are compared. In both patterns, in which the light intensity of the pulse changes linearly with respect to time, and in patterns in which it changes curvedly with respect to time, the change in the light intensity of the pulse in the input waveform of the amplification stage is the same as that in the original seed light pulse waveform pattern. It reflects the change in the amount of light of the pulse. That is, in the case of a pattern in which the amount of light of the pulse changes linearly with respect to time, the amount of light of the pulse in the input waveform of the amplification stage also changes linearly with respect to time. In the case of a pattern in which the amount of light of the pulse changes in a curved manner with respect to time, the amount of light of the pulse in the input waveform of the amplification stage also changes in a curved manner with respect to time. In this specification, such a relationship is referred to as "proportional." That is, the intensity of the pulse output from the amplifying section 101 is proportional to the intensity of the seed light pulse.

The optical fiber 1 of the amplifying section 101 amplifies the input seed light pulse. In the optical fiber 1, although some of the atoms at the excited level are consumed by the input multi-pulse, a sufficient number of atoms at the excited level remain. This is because in optical fiber 1, the fiber eigenvalues such as the emission cross section are smaller than in optical fiber 8, so while the output of optical fiber 1 is small, the pumping light power is sufficiently supplied to optical fiber 1. be. That is, in the optical fiber 1 which is the first stage amplification fiber, the pumping light energy supplied to the optical fiber 1 is sufficiently larger than the pumping light energy used for multi-pulse amplification. As a result, the intensity of the pulsed light output from the optical fiber 1 is proportional to the intensity of the input pulsed light. In order to increase the pumping light energy supplied to the optical fiber 1, the power of the pumping light may be appropriately controlled. The control device 20 controls the excitation current supplied from the driver 22 to the excitation LD 3 by controlling the driver 22 . Therefore, the control device 20 controls the power of the pumping light that enters the optical fiber 1 from the pumping LD 3. Thereby, the excitation light energy supplied to the optical fiber 1 can be increased.

On the other hand, the input waveform of the amplification stage and the output waveform of the amplification stage are compared. In the case of a pattern in which the intensity of the pulses input to the amplification stage changes linearly with respect to time, the peak power of the first pulse is large. As a result, the peak power of the second pulse is significantly attenuated relative to the peak power of the first pulse. The output waveform of the amplification stage is, so to speak, "inverted" with respect to the input waveform of the amplification stage.

In the case of a pattern in which the intensity of the pulse input to the amplification stage changes in a curved manner with respect to time, in the case of a pattern in which the intensity of the pulse input to the amplification stage changes in a curved manner, in the output waveform of the amplification stage, the intensity of the pulse decreases with respect to time. However, the degree of attenuation is gentler than the output waveform of the amplification stage for a linearly varying input waveform pattern. Furthermore, by reducing the initial pulse intensity of the multi-pulse, the degree of attenuation in the output waveform of the amplification stage can be suppressed.

FIG. 12 is a diagram showing an example of a waveform of a seed light pulse obtained by controlling the seed light pulse according to this embodiment, and an example of an output waveform from a MOPA type fiber laser. From FIG. 12, it can be seen that by increasing the intensity of the multiple pulses in the multipulse curvedly with respect to time and decreasing the intensity of the first pulse in the multipulse, the first output from the amplification stage It can be seen that the peak power of the pulses can be suppressed and the fluctuations in the peak power of each pulse can be reduced. By increasing the power of the pumping light input to the amplification fiber of the amplification stage in this state, it is possible to increase the average output while preventing the occurrence of SRS.

FIG. 13 is a flowchart showing an example of a method for controlling the laser processing apparatus according to the present embodiment. The processing shown in this flowchart may be executed, for example, by the control device 20 reading a program from the storage unit 201. In other words, the program is configured to cause the control device 20, which is a computer, to execute the control method shown in FIG.

Referring to FIG. 13, when the process is started, in step S1, control device 20 (condition setting section 202) stores data in storage section 201 based on the conditions input to input section 25 (see FIG. 1). A seed light pulse pattern is selected with reference to the stored table (see FIGS. 7 and 8) (S1). The condition setting unit 202 refers to the table stored in the storage unit 201 and selects a multi-pulse that corresponds to the conditions (for example, average output, repetition frequency, etc.) input to the input unit 25 (see FIG. 1). The conditions (multi-pulse repetition frequency, number of pulses, pulse interval, pulse width, and seed LD current pattern) are determined. This determines the intensity of the first optical pulse of the plurality of optical pulses and the curvature of the change in intensity of the plurality of pulses within the multipulse.

The control device 20 controls the seed LD2 by controlling the driver 21 according to the determined seed light pulse pattern (step S2). The seed LD 2 emits multi-pulses under the control of the control device 20 such that the intensity of the plurality of optical pulses increases in a curved manner with respect to time. Similarly, in step S2, the control device 20 controls the excitation LDs 3, 9A, and 9B by controlling the drivers 22, 23A, and 23B, respectively (step S2). As a result, excitation light for amplifying the seed light pulse is input from the excitation LD 3 into the optical fiber 1. Furthermore, excitation light for amplifying the pulse output from the optical fiber 1 is input into the optical fiber 8 from the excitation LDs 9A and 9B. As a result, the optical fiber 8 outputs laser light for processing the workpiece 50.

<F. Other embodiments>
In the examples described with reference to FIGS. 7 to 10, it is assumed that the power of the pump light incident on the optical fiber 1 from the pump LDs 9A and 9B is constant. However, as the number of pulses in a multi-pulse increases, the power of the pumping light incident on the optical fiber 1 from the pumping LDs 9A and 9B may be increased. This allows the average laser output to be increased. Therefore, in this embodiment, the parameters regarding the pulse train include the repetition frequency of the pulse train, the width of each of the plurality of optical pulses, the interval between the plurality of optical pulses, the number of the plurality of optical pulses, the average output of the pulse train, The amount of light of the first light pulse of the plurality of light pulses and the curvature of increase in the amount of light of the light pulses may be controlled according to at least one of the excitation currents supplied to the excitation light source.

Further, according to this embodiment, the laser processing apparatus can perform feedback control to control the power of the seed light or the excitation light based on the laser light output power. The configuration for feedback control will be explained below.

FIG. 14 is a diagram showing an example of a configuration for feedback control of laser light output. As shown in FIG. 14, the laser processing apparatus 100A includes an optical splitter 13 and a light receiving element 15 in addition to the components of the laser processing apparatus 100 (see FIG. 1). The optical splitter 13 branches the pulsed light emitted from the optical fiber 8. The optical splitter 13 is, for example, a fiber tap, but is not limited thereto. The light receiving element 15 receives the pulsed light branched by the optical splitter 13 and outputs a light reception signal indicating the intensity of the received pulsed light to the control device 20. Therefore, the pulse pattern after amplification by the second-stage optical fiber 8 (pattern of light pulses with pulse numbers n1 to n* acquired by the light receiving element 15) is input to the control device 20.

The position at which the pulse pattern after amplification by the second-stage optical fiber 8 is detected is not limited to the above. For example, the pulsed light may be branched in the laser beam scanning mechanism 14, and the light receiving element 15 may receive the branched pulsed light. The intensity of the light input to the light receiving element 15 may be initialized on the spot, or the upper limit may be determined by adjusting it in advance with an optical element (such as an attenuation layer). By initializing it to the set value, it is possible to check how much margin there is for the predetermined destruction threshold of the light receiving element 15.

The control device 20 corrects the seed light pattern or adjusts the excitation light power of the first stage amplification section 101 based on the light reception signal from the light receiving element 15. Note that feedback control of the pump LD 3 of the first stage amplifier 101 is easier than control of the pump LDs 9A and 9B of the second stage amplifier 102. However, in the feedback control according to the present embodiment, the excitation LDs 9A and 9B of the amplification section 102 may be controlled based on the light reception signal from the light reception element 15.

FIG. 15 is a block diagram showing the configuration of a control device for feedback control. In addition to the configuration shown in FIG. 6, the control device 20 includes a correction section 205. The correction unit 205 corrects the drive conditions for the seed LD 2 or the drive conditions for the excitation LD 3 set by the condition setting unit 202 based on the amplified pulse pattern that is the input signal from the light receiving element 15 .

In one example, the correction unit 205 calculates a control correction value from the pulse pattern input from the light receiving element 15. The correction unit 205 uses the correction value to correct the pattern of the current injected into the seed LD2. Alternatively, the correction unit 205 corrects the magnitude of the current injected into the excitation LD 3 using the calculated correction value. By correcting the magnitude of the current injected into the pump LD 3, the power of the pump light output from the pump LD 3 is corrected. As a result, the amount of amplification of the pulse by the first-stage optical fiber 1 is adjusted, so that the intensity and pattern of the pulsed light input to the second-stage optical fiber 8 can be corrected.

FIG. 16 is a diagram showing an example of feedback control according to this embodiment. Note that the numerical values shown in FIG. 16 are just an example, and are not intended to limit this embodiment. As shown in FIG. 16, the items "Max/n1", "Min/n1", and "n2/n1" related to output light are associated with the items "correction" and "correction amount" related to input light. The "output light" is the multi-pulse after being amplified by the second-stage optical fiber 8. "Input light" means seed light or excitation light input into the first-stage optical fiber 1.

The item "Max/n1" is the intensity ratio of the pulse having the maximum intensity to the intensity of the pulse n1 in the multipulse after amplification. "Min/n1" is the intensity ratio of the pulse with the minimum peak power to the intensity of the pulse n1 in the multipulse after amplification. "n2/n1" is the intensity ratio of the n2 pulse to the intensity of the n1 pulse in the multipulse after amplification. The item "correction" regarding input light means whether or not the value of the current supplied to the seed LD2 is corrected or the value of the current supplied to the excitation LD3 is corrected. “Correction amount” indicates the amount of correction in the correction.

The closer all of "Max/n1", "Min/n1", and "n2/n1" are to 1, the more consistent the intensities of the pulses included in the multipulse of output light are. In the example shown in FIG. 16, it is assumed that the correction amount value of the input light is specified as Max/n1=1.03, for example. That is, when Max/n1=1.03, the correction of the input light is "none" and the correction amount is "0".

In the multi-pulse of output light, if the intensity of the n1 pulse is the maximum and the intensity attenuates in the pulses after n2, the value of Max/n1 is 1.00, and the values of Min/n1 and n2/n1 are 1. smaller than In particular, the greater the intensity attenuation between multiple pulses within a multipulse, the smaller the values of Min/n1 and n2/n1 become. Therefore, in such a case, for example, the current supplied to the seed LD2 is reduced by the correction amount. The smaller the values of Min/n1 and n2/n1, the larger the correction amount.

On the other hand, when the value of Max/n1 is larger than 1.03, the intensity of the pulses after n2 is greater than the peak power of the n1 pulse among a plurality of pulses in the multi-pulse. In such a case, the correction amount is determined according to the values of "Max/n1", "Min/n1", and "n2/n1", and the current value supplied to the seed LD2 is adjusted according to the correction amount. Corrected. In this case, for example, the current supplied to the seed LD2 is increased by the correction amount. Note that, compared to the case where the correction amount is decreased, the correction amount is smaller when the correction amount is increased.

FIG. 17 is a diagram illustrating the amount of correction for input light control used in feedback control. The two graphs shown in FIG. 17 are examples of the amount of correction for the output light Min/n1 (indicated as "n_min/n1" in FIG. 17) and the correction amount for the output light Max/n1 (indicated as "n_max/n1" in FIG. 17). An example of the correction amount for (notation) is shown below. In the graph of FIG. 17, the value of the correction amount is specified by the output light Max/n1=1.3. Further, for comparison, the two graphs have the same scale on the vertical axis and the same scale on the horizontal axis.

As shown in FIG. 17, it is better to determine the correction amount according to the output light item Min/n1 (n_min/n1) than to determine the correction amount according to the output light item Max/n1 (n_max/n1). The amount of correction for controlling becomes larger. This is because the smaller Min/n1 of the output light, the greater the intensity of the n1 pulse in the multi-pulse waveform of the output light, and the greater the attenuation of the intensity of the pulses after n2.

Regarding the determination of the correction amount, the control device 20 may store, for example, the relationship shown in FIG. 16 in the form of a table. The correction unit 205 can determine the amount of correction according to the table. Furthermore, as shown in FIG. 17, the relationship between the correction amount and n_min/n1 and the relationship between the correction amount and n_max/n1 can be approximated by appropriate functional expressions. Therefore, the control device 20 may store in advance an approximate expression representing the tendency of the correction amount with respect to n_min/n1 and an approximate expression representing the tendency of the correction amount with respect to n_max/n1. The correction unit 205 can determine the correction amount from the value of n_min/n1 and the value of n_max/n1 based on these approximate expressions.

When applying the determined correction amount to the control of the current of the seed LD2, the correction amount may be uniformly applied to the seed LD current values corresponding to the pulses n1 to n*. That is, the seed LD current value may be increased or decreased overall by an amount corresponding to the correction amount. However, the application of the correction amount is not limited to this. The correction amount may be applied only to the seed current value of a pulse with a specific number. For example, in order to correct the light intensity of the n1 pulse in the multi-pulse of seed light, only the seed LD current value corresponding to the n1 pulse may be corrected. Alternatively, the seed LD current value corresponding to one or more specific pulses may be corrected in order to adjust the curvature of increase in light intensity of multiple pulses within a multi-pulse of seed light.

FIG. 18 is a flowchart showing a flow when the seed LD current value is corrected by feedback control according to the present embodiment. As shown in FIG. 18, when the process is started, the light receiving element 15 receives a laser light pulse in step S11. As a result, a pulse pattern of laser light pulses is input from the light receiving element 15 to the control device 20.

In step S12, the control device 20 determines whether each of the items n_min/n1, n_max/n1, and n2/n1 regarding the intensity of the laser light pulse is within a set threshold based on the pulse pattern of the laser light pulse. Note that a set threshold value is input into the control device 20 in advance for this determination. Although the setting of the threshold values serving as the criteria for determination is not limited to the following example, for example, n_min/n1 is set to 0.5 or more, n_max/n1 is set to 1.3 or less, and n2/n1 is set to 0.5 or more. Note that in step S12, n2/n1 may be used as a criterion for determination. Further, the determination in step S12 is executed by, for example, the correction unit 205 within the control device 20.

If it is determined that each of the items n_min/n1, n_max/n1, and n2/n1 is within the set threshold (YES in step S12), the correction is completed. On the other hand, if a certain item is not within the set threshold (NO in step S12), the process proceeds to step S13. In step S13, the control device 20 determines the current injected into the seed LD2 based on the relationship between multiple pulses (pulses with pulse numbers n1, n2, ..., n*) in the pulse pattern (multipulse) of the laser light pulse. A correction value is calculated. As described above, the correction unit 205 can determine the correction amount according to a table or a function (see FIGS. 16 and 17). Regarding the correction, the correction unit 205 may rewrite the values registered in the table (see FIGS. 7 and 8) stored in advance in the storage unit 201 according to the correction amount determined in step S13. Alternatively, the correction unit 205 may read values registered in a table stored in advance in the storage unit 201 and correct the read values. In this case, the values registered in the table are maintained as they are.

Following step S13, in step S14, the corrected current pattern is injected from the control device 20 into the driver 21 (see FIG. 1) that drives the seed LD2. After the process in step S14, the entire process returns to step S11.

FIG. 19 is a flowchart showing a flow when the current value of the excitation LD 3 of the first stage amplification section 101 is corrected by the feedback control according to the present embodiment. The flow shown in FIG. 19 is basically the same as the flow shown in FIG. 18. Therefore, processing similar to the processing in the flow shown in FIG. 18 will be briefly described.

When the process is started, the light receiving element 15 receives a laser light pulse in step S21. In step S22, the control device 20 determines whether each of the items n_min/n1, n_max/n1, and n2/n1 regarding the intensity of the laser light pulse is within a set threshold based on the pulse pattern of the laser light pulse. If it is determined that each of the items n_min/n1, n_max/n1, and n2/n1 is within the set threshold (YES in step S22), the correction is completed. On the other hand, if a certain item is not within the set threshold (NO in step S22), the process proceeds to step S23.

In step S23, in the control device 20, the first stage amplifier 101 A correction value for the current injected into the excitation LD3 is calculated. The correction unit 205 can determine the correction amount according to a table or a function (see FIGS. 16 and 17). The correction unit 205 may rewrite the values registered in the table (see FIGS. 7 and 8) stored in advance in the storage unit 201 according to the correction amount determined in step 23, or The value registered in the table may be read out and the read value may be corrected.

Following step S23, in step S24, the corrected current pattern is injected from the control device 20 into the driver 22 (see FIG. 1) that drives the excitation LD 3. After the process in step S24, the entire process returns to step S21.

The timing for executing the feedback control shown in FIG. 18 or 19 is not particularly limited. For example, the feedback control may be performed with the shutter of the laser beam scanning mechanism 14 closed prior to actual processing, or may be performed during processing.

<G. Additional notes>
As described above, this embodiment includes the following disclosures.

(Configuration 1)
a seed light source (2) that generates seed light;
an excitation light source (3, 9A, 9B) that generates excitation light;
a laser amplification unit including an amplification fiber (1, 8) configured to amplify the seed light by inputting the seed light and the excitation light;
a scanning mechanism (14) that scans the laser light output from the laser amplification section;
A control unit (20) that controls the seed light source (2) and the excitation light source (3, 9A, 9B),
The control unit (20) repeatedly generates a pulse train including a plurality of optical pulses from the seed light source (2), and controls the control unit (20) so that the amount of light of the plurality of optical pulses increases in a curved manner with respect to time. controlling the seed light source (2);
A laser processing device (100), wherein the control unit (20) controls the light intensity of the first light pulse among the plurality of light pulses and the curvature of increase in the light intensity of the light pulse, according to parameters related to the pulse train. .

(Configuration 2)
The amplification fiber (1, 8) is
a first optical fiber (1) that amplifies the seed light from the seed light source (2) with first excitation light from the excitation light source (3, 9A, 9B);
a second optical fiber (8) that amplifies the light output from the first optical fiber with a second excitation light from the excitation light source (3, 9A, 9B),
The excitation light source (3, 9A, 9B) is
a first excitation light source (3) that emits the first excitation light;
a second excitation light source (9A, 9B) that emits the second excitation light,
The control unit (20) is configured to control the power of the first excitation light so that the amount of light of the plurality of light pulses emitted from the first optical fiber increases in a curved manner with respect to time. 1. The laser processing apparatus (100) according to 1.

(Configuration 3)
The control unit (20) controls the seed light source (2) in accordance with a table that defines the relationship between the parameters regarding the pulse train, the light intensity of the first light pulse, and the curvature of increase in the light intensity of the light pulse. The laser processing apparatus (100) according to Configuration 1 or Configuration 2.

(Configuration 4)
The parameters regarding the pulse train are:
the repetition frequency of the pulse train;
a pulse width of each of the plurality of light pulses;
an interval between the plurality of light pulses;
the number of the plurality of optical pulses,
the average output of the pulse train;
The laser processing apparatus (100) according to any one of configurations 1 to 3, including at least one of excitation currents supplied to the excitation light source (3, 9A, 9B).

(Configuration 5)
The control unit (20) is configured to control the intensity of the first optical pulse of a plurality of pulses in the pulse train of the laser beam output from the laser amplification unit, the intensity of at least the second optical pulse, and the optical pulse with the maximum amount of light. The light intensity of the plurality of pulses in the pulse train to be generated from the seed light source (2) from the next time onwards, or the light intensity of the excitation light source ( 3, 9A, 9B), the laser processing device (100) according to any one of configurations 1 to 4, which performs feedback control to correct the amount of the excitation light generated from the laser processing device (100).

(Configuration 6)
A seed light source (2) that generates seed light, an excitation light source (3, 9A, 9B) that generates excitation light, and the seed light and the excitation light are input to amplify the seed light. a laser amplification unit including the configured amplification fibers (1, 8), a scanning mechanism (14) that scans the laser light output from the laser amplification unit, the seed light source (2) and the excitation light source (3, 9A, 9B) A control method for a laser processing apparatus (100) comprising:
The seed light source (2) is controlled so that the seed light source (2) repeatedly generates a pulse train including a plurality of light pulses, and the amount of light of the plurality of light pulses increases in a curve with respect to time. comprising steps (S1, S2),
The step of controlling the seed light source (2) comprises:
Control of the laser processing apparatus (100), including a step (S2) of controlling the light intensity of the first optical pulse of the plurality of optical pulses and the curvature of increase in the light intensity of the optical pulses according to parameters related to the pulse train. Method.

(Configuration 7)
A seed light source (2) that generates seed light, an excitation light source (3, 9A, 9B) that generates excitation light, and the seed light and the excitation light are input to amplify the seed light. a laser amplification unit including the configured amplification fibers (1, 8), a scanning mechanism (14) that scans the laser light output from the laser amplification unit, the seed light source (2) and the excitation light source (3, 9A, 9B), the program causes the control unit (20) to execute a method for controlling a laser processing apparatus (100), the program comprising:
The control method includes:
The seed light source (2) is controlled so that the seed light source (2) repeatedly generates a pulse train including a plurality of light pulses, and the amount of light of the plurality of light pulses increases in a curve with respect to time. comprising steps (S1, S2),
The step of controlling the seed light source (2) comprises:
A program comprising a step (S2) of controlling a light amount of a first light pulse among the plurality of light pulses and a curvature of increase in the light amount of the light pulses according to a parameter regarding the pulse train.

Although the embodiments of the present invention have been described, the embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, and it is intended that all changes within the meaning and range equivalent to the claims are included.

1, 8 optical fiber, 2 seed LD, 3, 9A, 9B excitation LD, 4, 6, 11 isolator, 5, 10 combiner, 7 band pass filter, 12 end cap, 13 optical splitter, 14 laser beam scanning mechanism, 15 light receiving element, 20 control device, 21, 22, 23A, 23B driver, 25 input section, 31, 35 core, 32 cladding, 34, 38 outer skin, 36 first cladding, 37 second cladding, 50 workpiece, 100 Laser processing device, 101 amplification section, 102 amplification section, 201 storage section, 202 condition setting section, 203 seed LD control section, 205 correction section, 206 excitation LD control section, E1 base level, E2 excitation level, N1, N2 Atomic distribution density, S1, S2, S11-S14, S21-S24 steps.

Claims (7)

a seed light source that generates seed light;
an excitation light source that generates excitation light;
a laser amplification section including an amplification fiber configured to amplify the seed light by receiving the seed light and the excitation light;
a scanning mechanism that scans the laser light output from the laser amplification section;
comprising a control unit that controls the seed light source and the excitation light source,
The control unit controls the seed light source so that the seed light source repeatedly generates a pulse train including a plurality of light pulses, and the amount of light of the plurality of light pulses increases in a curved manner with respect to time,
A laser processing apparatus, wherein the control unit controls a light amount of a first light pulse among the plurality of light pulses and a curvature of increase in the light amount of the light pulse according to a parameter regarding the pulse train. The amplification fiber is
a first optical fiber that amplifies the seed light from the seed light source with first excitation light from the excitation light source;
a second optical fiber that amplifies the light output from the first optical fiber with a second excitation light from the excitation light source,
The excitation light source is
a first excitation light source that emits the first excitation light;
a second excitation light source that emits the second excitation light,
2. The control unit according to claim 1, wherein the control unit controls the power of the first excitation light so that the amount of light of the plurality of light pulses emitted from the first optical fiber increases in a curved manner with respect to time. The laser processing device described. 2. The control unit controls the seed light source according to a table that defines a relationship between the parameter regarding the pulse train, the light amount of the first light pulse, and the curvature of increase in the light amount of the light pulse. The laser processing device described. The parameters regarding the pulse train are:
the repetition frequency of the pulse train;
a pulse width of each of the plurality of light pulses;
an interval between the plurality of light pulses;
the number of the plurality of optical pulses,
The laser processing apparatus according to any one of claims 1 to 3, comprising at least one of an average output of the pulse train and an excitation current supplied to the excitation light source. The control unit is configured to control the intensity of a first optical pulse among a plurality of pulses in the pulse train of the laser beam output from the laser amplification unit, at least a second optical pulse, a maximum light amount optical pulse, and a minimum light amount. The light intensity of the plurality of pulses in the pulse train to be generated from the seed light source from the next time onwards, or the amount of the excitation light to be generated from the excitation light source, using the ratio with the intensity of any one of the optical pulses of The laser processing apparatus according to any one of claims 1 to 3, which performs feedback control to correct the amount of light. A laser amplification unit including a seed light source that generates seed light, a pump light source that generates pump light, and an amplification fiber configured to amplify the seed light by receiving the seed light and the pump light. A method for controlling a laser processing apparatus, comprising: a scanning mechanism that scans laser light output from the laser amplification section; and a control section that controls the seed light source and the excitation light source.
comprising the step of repeatedly generating a pulse train including a plurality of light pulses from the seed light source, and controlling the seed light source so that the amount of light of the plurality of light pulses increases in a curved manner with respect to time;
The step of controlling the seed light source includes:
A method for controlling a laser processing apparatus, comprising the step of controlling the amount of light of a first light pulse of the plurality of light pulses and the curvature of increase in the amount of light of the light pulses according to a parameter regarding the pulse train. A laser amplification unit including a seed light source that generates seed light, a pump light source that generates pump light, and an amplification fiber configured to amplify the seed light by receiving the seed light and the pump light. and a scanning mechanism that scans a laser beam output from the laser amplification unit, and a control unit that controls the seed light source and the excitation light source. There it is,
The control method includes:
comprising the step of repeatedly generating a pulse train including a plurality of light pulses from the seed light source, and controlling the seed light source so that the amount of light of the plurality of light pulses increases in a curved manner with respect to time;
The step of controlling the seed light source includes:
A program comprising: controlling a light amount of a first light pulse among the plurality of light pulses and a curvature of increase in the light amount of the light pulse according to a parameter regarding the pulse train.

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