JP7462220B2 - Laser Oscillator - Google Patents

Description

This disclosure relates to a laser oscillator.

One example of a laser oscillator is a direct diode laser (DDL) oscillator that uses external resonance (see, for example, Patent Document 1).

Figure 6 shows a conventional DDL oscillator described in Patent Document 1.

In FIG. 6, the cavity 200a is a wavelength beam combining type direct diode laser oscillator in which multiple laser beams emitted from laser input modules 252 with different wavelengths are arranged coaxially through a diffraction grating 214. The laser input module 252 has a laser element 250, an FAC optical system 206, and a conversion optical system 208. The output coupler 216 returns a portion of the laser beam incident through the diffraction grating 214 to each laser input module 252 as reflected light, and this light is put into a state called wave locking in which only a predetermined wavelength is oscillated by the emitter of the laser element 250, thereby oscillating the laser beam.

Patent document 2 also discloses a conventional laser oscillator that controls the current value of the LD. Figure 7 shows the conventional laser oscillator described in Patent document 2.

In FIG. 7, the laser oscillator has a Nd:YAG rod 312, a total reflection mirror 315, an internal AOQ-SW element 314, an excitation LD 313, and an output mirror 316, and has a laser oscillator head 311 that outputs an oscillator output 357, a Q switch pulse width setting circuit 317 that receives an emission pulse signal 351 and outputs a Q switch pulse width setting signal 352, an LD current control circuit 318 that outputs an LD current control signal 353, an LD driver 319 that controls an LD drive current 356, an RF amplitude control circuit 320 that outputs an RF power modulation control signal 354, and an RF driver 321 that controls an RF power 355. The LD current control circuit 318 and the LD driver 319 control the current applied to the excitation LD 313 to be equal to or lower than the threshold of laser oscillation in synchronization with the timing of one or more Q switch pulse oscillations of the optical resonator in the laser oscillator head 311.

Patent No. 5981855 Patent No. 5082798

By the way, the gain curve of a laser diode with respect to wavelength has the characteristic that it changes depending on the temperature of the laser diode.

In this regard, in the DDL oscillator shown in Patent Document 1, when attempting to perform pulse oscillation, it is necessary to change the current value of the laser diode, so the amount of heat generated by the laser diode differs from that in the case of CW oscillation, and the gain curve with respect to wavelength changes.

In the DDL oscillator shown in Patent Document 1, the laser diode performs external resonance using diffraction, and the oscillating wavelength is fixed due to wavelocking. Therefore, if the gain curve changes, the laser light output also fluctuates. Therefore, typically, in an oscillator that has been aligned for CW oscillation, the oscillation efficiency deteriorates during pulse oscillation. Furthermore, even if the alignment adjustment is performed for pulse oscillation with a standard pulse width and oscillation frequency, if parameters such as the pulse width and oscillation frequency change, the amount of heat generated by the laser diode changes and the gain curve shifts, which similarly deteriorates the oscillation efficiency and makes the oscillation state unstable.

In addition, in the laser oscillator shown in Patent Document 2, the timing of the internal AOQ-SW element and the LD current control circuit are synchronized, but no consideration is given to temperature control of the pumping LD. If the configuration shown in Patent Document 2 is applied to an external resonance type DDL oscillator, when parameters such as the oscillation frequency are changed, the temperature of the LD fluctuates, causing a shift in the gain curve, which reduces the oscillation efficiency and makes the oscillation of the DDL oscillator unstable.

This disclosure has been made in consideration of the above problems, and aims to provide a laser oscillator that can achieve good oscillation characteristics even when the oscillation conditions of the laser light are changed.

The present disclosure mainly solves the above-mentioned problems.
A laser diode that emits laser light;
an external cavity mirror disposed in an optical path of the laser light emitted from the laser diode;
an optical shutter disposed between the laser diode and the external cavity mirror in an optical path of the laser light emitted from the laser diode;
an LD power supply for driving the laser diode;
an optical shutter driver that drives the optical shutter;
a control device for controlling the LD power supply and the optical shutter driver;
the control device controls a current level of the drive current output from the LD power supply in accordance with an opening and closing timing of the optical shutter so that the drive current supplied from the LD power supply to the laser diode when the optical shutter is in a closed state is reduced.
It is a laser oscillator.

In other respects,
A plurality of laser diodes for emitting laser light;
an external cavity mirror disposed in an optical path of the laser light emitted from each of the plurality of laser diodes;
a diffraction grating that is disposed between the plurality of laser diodes and the external cavity mirror in optical paths of the laser beams emitted from the plurality of laser diodes, respectively, and that coaxially superimposes the laser beams emitted from the plurality of laser diodes;
an optical shutter disposed between the diffraction grating and the external cavity mirror;
an LD power supply for driving the plurality of laser diodes;
an optical shutter driver that drives the optical shutter;
a control device for controlling the LD power supply and the optical shutter driver;
the control device controls a current level of the drive current output from the LD power supply in accordance with an opening and closing timing of the optical shutter so that the drive current supplied from the LD power supply to each of the plurality of laser diodes is reduced when the optical shutter is in a closed state.
It is a laser oscillator.

The laser oscillator disclosed herein can achieve good oscillation characteristics even when the oscillation conditions of the laser light are changed.

Schematic diagram of a laser oscillator according to an embodiment of the present disclosure. FIG. 2(a) is a conceptual diagram showing a gain curve in one embodiment of the present disclosure; FIG. 2(b) is a conceptual diagram showing a shift in the gain curve due to temperature in one embodiment of the present disclosure; A diagram showing the parameters during conventional pulse oscillation. FIG. 13 is a diagram showing each parameter during current value control in one embodiment of the present disclosure. Schematic diagram of a laser oscillator according to an embodiment of the present disclosure. Schematic diagram showing a conventional laser oscillator Schematic diagram showing a conventional laser oscillator

Embodiments of the present disclosure will be described below with reference to the drawings.

<Embodiment 1>
FIG. 1 is a schematic diagram of a laser oscillator according to a first embodiment of the present disclosure.

The laser oscillator has a laser diode 2 that emits laser light 5. The laser diode (hereinafter also referred to as LD) 2 generates and emits laser light 5. The laser diode 2 is, for example, a chip-shaped LD chip. As the LD chip, an edge-emitting type (EEL: Edge Emitting Laser) LD chip is preferably used. In the edge-emitting LD chip, for example, a long bar-shaped resonator is formed in the chip parallel to the substrate surface. One end face in the longitudinal direction of the resonator is covered with a film with high reflectivity so that the light is almost totally reflected. On the other hand, the other end face in the longitudinal direction of the resonator is covered with an anti-reflection film so that the light can easily pass through, and the light is partially reflected and returned from the external resonator mirror 1, which is a partial reflector provided outside the laser diode 2, and an amplified and phase-aligned laser beam is emitted from the external resonator mirror 1.

The oscillation wavelength of the laser diode 2 is preferably in the range of 300 nm or more and 2000 nm or less. In other words, the wavelength of the laser light 5 is preferably in the range of 300 nm or more and 2000 nm or less. By using the laser light 5 in this range, a high-output laser processing device can be obtained using a laser oscillator.

The laser diode 2 is preferably at least one of a single emitter and a multi-emitter. A single emitter may be an LD chip having one emitter, and a multi-emitter may be an LD bar having multiple emitters.

It is preferable that the laser diode 2 is equipped with a temperature measuring element 3 for measuring the temperature of the laser diode 2. The temperature measuring element 3 is in contact with the laser diode 2, measures the temperature of the laser diode 2, and transmits the temperature measurement data 31 to the control device 7.

The laser oscillator has an LD power supply 22 that drives the laser diode 2. The LD power supply 22 supplies a drive current 21 to the laser diode 2 according to a current command signal 23 transmitted from the control device 7.

The laser oscillator has an external resonator mirror 1 arranged in the optical path of the laser light emitted from the laser diode 2. The external resonator mirror 1 reflects a portion of the laser light 5 emitted from the laser diode 2 back to the laser diode 2, causing external resonance. The external resonator mirror 1 and the laser diode 2 form an external resonator cavity.

The laser oscillator has an optical shutter 4 arranged between an external resonator mirror 1 and a laser diode 2. By opening and closing the optical shutter 4 to transmit or block the laser light 5, a pulsed laser light 5 or a CW laser light 5 can be obtained.

The optical shutter 4 is preferably an acousto-optical element (hereinafter also referred to as AOM). The acousto-optical element acts as a diffraction grating and diffracts a portion of the laser light 5 emitted from the laser diode 2.

It is also preferable that the optical shutter 4 is a Pockels cell. In this case, it is preferable that the laser oscillator has a polarizer. The Pockels cell is capable of changing the polarization direction of the laser light 5. The polarizer separates the polarization of the laser light 5.

The laser oscillator has an optical shutter driver 42. The optical shutter driver 42 transmits an optical shutter drive signal 41 to the optical shutter 4 in accordance with an opening/closing command signal 43 transmitted from the control device 7, thereby opening and closing the optical shutter 4.

The laser oscillator preferably has an output monitor unit 8. The output monitor unit 8 can measure fluctuations in the laser light 5 by sampling a portion of the laser light 5 emitted from the external resonator mirror 1 and measuring the output, and can transmit output measurement data 81 to the control device 7.

The laser oscillator has a control device 7 that controls the LD power supply 22 and the optical shutter driver 42. The control device 7 controls the opening and closing of the optical shutter 4 by sending an opening/closing command signal 43 to the optical shutter driver 42, and also controls the output drive current 21 supplied to the laser diode 2 by sending a current command signal 23 to the LD power supply 22 in accordance with the opening and closing of the optical shutter 4.

When the laser oscillator has a temperature measuring element 3, it is preferable that the control device 7 receives temperature measurement data 31 of the laser diode 2 from the temperature measuring element 3 and controls the LD power supply 22 and the optical shutter driver 42 based on this. Also, when the laser oscillator has an output monitor unit 8, it is preferable that the control device 7 receives output measurement data 81 from the output monitor unit 8 and controls the LD power supply 22 and the optical shutter driver 42 based on this. It is more preferable that the control device 7 receives both the temperature measurement data 31 and the output measurement data 81. In this case, laser oscillation can be performed particularly efficiently.

Referring to Figure 2, the shift in the gain curve due to temperature in this embodiment will be described. Figure 2(a) is a graph conceptually showing the relationship between the gain curve 25 and the optical output 51 when the laser diode 2 is in CW oscillation. Figure 2(b) is a graph showing the change in the gain curve when the laser diode 2 is switched from the CW oscillation mode to the pulse oscillation mode.

The laser diode 2 has a gain curve 25 with a certain wavelength width, and when CW oscillation is performed in the system with external resonance shown in this embodiment, the wavelocking wavelength 24 of the external resonance is adjusted to a position where the maximum efficiency of the gain curve 25 is obtained, and an optical output 51 can be obtained.

However, when pulse oscillation is performed by opening and closing the optical shutter 4, the amount of heat generated by the laser diode 2 increases, and the temperature of the laser diode 2 increases. As a result, the gain curve of the laser diode 2 becomes a gain curve 26 at high temperatures, which is shifted toward longer wavelengths than the gain curve 25 during CW oscillation, as shown in FIG. 2(b). At this time, the wave-locking wavelength 24 is typically in a fixed state due to external resonance, so the laser diode 2 is forced to oscillate at a wavelength corresponding to the wave-locking wavelength 24. Therefore, the optical output 52 during the gain curve shift is lower than the optical output 51 during CW oscillation.

Figure 3 shows the parameters during conventional optical shutter operation. In Figure 3, the same components as in Figure 1 are designated by the same reference numerals, and their explanations are omitted.

In FIG. 3, the opening/closing command signal 43 for opening and closing the optical shutter 4 and the drive current 21 supplied to the laser diode 2 are parameters that can be controlled by the control device 7, and the LD heat generation amount 32, the LD temperature 33, and the optical output 51 are parameters that are ultimately affected by the drive current 21 and the opening/closing command signal 43.

When attempting to emit pulsed light using the optical shutter 4 installed in the cavity of a laser oscillator performing CW oscillation, when the opening/closing command signal 43 is in the "open" state, the optical shutter 4 is in the open state, the laser diode 2 is in the light-emitting state, and the optical output 51 is emitted from the laser oscillator to the outside.

When the opening/closing command signal 43 is in the "closed" state, the optical shutter 4 is closed, so the laser diode 2 in the external resonance state does not emit light, and the optical output 51 is not emitted from the laser oscillator. At this time, the current level of the drive current 21 supplied to the laser diode 2 remains constant, and the energy that would be dissipated as the optical output 51 when the opening/closing command signal 43 is in the "open" state remains in the laser diode 2 when the opening/closing command signal 43 is in the "closed" state, so the LD heat generation amount 32 increases. When the LD heat generation amount 32 increases, the LD temperature 33 rises, and a shift in the gain curve 25 occurs in the external resonance type laser oscillator, so the optical output 51 gradually decreases over time.

Figure 4 shows the parameters during current value control in this embodiment. In Figure 4, the same components as those in Figures 1 to 3 are designated by the same reference numerals, and their explanations are omitted.

As shown in FIG. 4, the control device 7 in this embodiment controls the LD power supply 22 so that the current level of the drive current 21 when the optical shutter 4 is in the "closed" state (i.e., when the LD is not emitting light) is smaller than the current level of the drive current 21 when the optical shutter 4 is in the "open" state (i.e., when the LD is not emitting light). At this time, by appropriately adjusting the current level of the drive current 21, the LD heat generation amount 32 when the optical shutter 4 is in the "open" state can be made equal to the LD heat generation amount 32 when the optical shutter 4 is in the "closed" state.

Note that the LD heat generation amounts 32 being equal does not only mean that they are completely equal, but also includes cases where the LD heat generation amounts 32 are nearly equal, so long as they do not significantly reduce the optical output 51. In this way, by synchronously controlling the opening and closing operation of the optical shutter 4 and the change in the current level of the drive current 21 with the control device 7, it is possible to keep the LD temperature 33 nearly constant regardless of the opening and closing state of the optical shutter 4. This allows the pulsed optical output 51 to operate stably without fluctuating. In other words, this allows efficient laser oscillation.

In addition, when the desired pulse parameters (pulse width, frequency, peak output, etc.) are input, the control device 7 of this embodiment acquires the temperature measurement data 31 and output measurement data 81 of the laser diode 2, generates an appropriate current command signal 23, and issues a command to the LD power supply 22. This makes it possible to appropriately control the ratio between the current level of the drive current 21 when the optical shutter 4 is in the "closed" state and the current level of the drive current 21 when the optical shutter 4 is in the "open" state, and to quickly and appropriately stabilize the output 51 of the laser oscillator.

The calculation model for calculating the output parameters (current command signal 23 indicating the current level of drive current 21) from the input parameters (pulse parameters, temperature measurement data 31, output measurement data 81) to the control device 7 is, for example, a data table determined by prior verification. However, more preferably, the calculation model is configured to be updated autonomously by feedback using machine learning. This makes it possible to more appropriately determine the current level of drive current 21 so that the pulsed light output 51 operates stably without fluctuating.

As described above, the laser oscillator according to this embodiment can operate stably without fluctuations in the pulsed light output 51 even when the oscillation conditions of the laser light are changed. This enables stable and precise laser processing, for example.

<Embodiment 2>
5 is a schematic diagram of a laser oscillator according to the second embodiment of the present disclosure. In FIG. 5, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the laser oscillator is a wavelength beam-coupled external resonance DDL laser oscillator, and has multiple laser diodes 2 that each emit laser light. It is preferable that each of the multiple laser diodes 2 oscillates by external resonance at a different wavelength. Each of the multiple laser diodes 2 may be the same as the laser diode 2 described in embodiment 1.

In this embodiment, the laser oscillator has a diffraction grating 6 disposed between the multiple laser diodes 2 and the optical shutter 4. The laser light emitted from each of the multiple laser diodes 2 is superimposed on the same axis by the diffraction grating 6 and is emitted as a single laser light 5 from the external resonator mirror 1. By using multiple laser diodes in this manner, it is possible to obtain a laser oscillator with a higher output than that of embodiment 1.

The control device 7 according to this embodiment controls the drive current 21 supplied to each of the multiple laser diodes 2, as in the first embodiment. That is, the control device 7 according to this embodiment controls the LD power supply 22 in accordance with the opening and closing of the optical shutter 4 so that the drive current 21 supplied from the LD power supply 22 to each of the multiple laser diodes 2 is reduced when the optical shutter 4 is closed.

In addition, when multiple laser diodes 2 are connected in series, for example, and the drive current 21 is common, the control device 7 may be configured to input the respective temperature measurement data 31 from the respective temperature measurement elements 3 attached to each laser diode 2 into the control device 7, perform calculations, and output as a single current value. In this case, the control device 7 may, for example, monitor the output measurement data 81 transmitted from the output monitor unit 8, and calculate the current command signal 23 so that the fluctuation of the LD temperature 33 of each laser diode 2 during pulse emission operation is minimized.

<Other embodiments>
In the above, the control device 7 has been shown to control the LD power supply 22 and the optical shutter 4 so that the opening and closing timing of the optical shutter 4 coincides with the timing at which the current level of the drive current 21 is changed (i.e., the rising and falling timings). However, the opening and closing timing of the optical shutter 4 does not necessarily have to coincide completely with the timing at which the current level of the drive current 21 is changed, and the control device 7 may change the current level of the drive current 21 with a certain delay time after the opening and closing timing of the optical shutter 4, or may change the current level of the drive current 21 in stages.

The laser oscillator disclosed herein has good oscillation characteristics and can be used for stable and precise laser processing.

REFERENCE SIGNS LIST 1 External cavity mirror 2 Laser diode 21 Current 22 LD power supply 23 Current command signal 24 Wavelocking wavelength 25 Gain curve 26 Gain curve at high temperature 3 Temperature measurement element 31 Temperature measurement data 32 LD heat generation amount 33 LD temperature 4 Optical shutter 41 Optical shutter drive signal 42 Optical shutter driver 43 Opening/closing command signal 5 Laser light 51 Optical output 52 Optical output at the time of gain curve shift 6 Diffraction grating 7 Control device 8 Output monitor unit 81 Output measurement data 200a Cavity 206 FAC optical system 208 Conversion optical system 214 Diffraction grating 216 Output coupler 250 Laser element 252 Laser input module 311 Laser oscillator head 312 Nd:YAG rod 313 Pumping LD
314 Internal AO Q-SW element 315 Total reflection mirror 316 Output mirror 317 Q switch pulse width setting circuit 318 LD current control circuit 319 LD driver 320 RF amplitude control circuit 321 RF driver 351 Extraction pulse signal 352 Q switch pulse width setting signal 353 LD current control signal 354 RF power modulation control signal 355 RF power 356 LD drive current 357 Oscillator output

Claims (12)

A laser oscillator configured to be switchable between CW oscillation and pulse oscillation,
A laser diode that emits laser light;
an external cavity mirror disposed in an optical path of the laser light emitted from the laser diode;
an optical shutter disposed between the laser diode and the external cavity mirror in an optical path of the laser light emitted from the laser diode;
an LD power supply for driving the laser diode;
an optical shutter driver that drives the optical shutter;
a control device for controlling the LD power supply and the optical shutter driver;
the control device controls a current level of the drive current output from the LD power supply in accordance with an opening and closing timing of the optical shutter so that the drive current supplied from the LD power supply to the laser diode is reduced when the optical shutter is closed in the pulse oscillation mode to cause laser oscillation from the laser oscillator to be non-output.
Laser oscillator. A plurality of laser diodes for emitting laser light;
an external cavity mirror disposed in an optical path of the laser light emitted from each of the plurality of laser diodes;
a diffraction grating that is disposed between the plurality of laser diodes and the external cavity mirror in optical paths of the laser beams emitted from the plurality of laser diodes, respectively, and that coaxially superimposes the laser beams emitted from the plurality of laser diodes;
an optical shutter disposed between the diffraction grating and the external cavity mirror;
an LD power supply for driving the plurality of laser diodes;
an optical shutter driver that drives the optical shutter;
a control device for controlling the LD power supply and the optical shutter driver;
the control device controls a current level of the drive current output from the LD power supply in accordance with an opening and closing timing of the optical shutter so that the drive current supplied from the LD power supply to each of the plurality of laser diodes is reduced when the optical shutter is in a closed state.
Laser oscillator. The optical shutter is an acousto-optical element.
3. The laser oscillator according to claim 1 or 2. the optical shutter is a Pockels cell;
3. The laser oscillator according to claim 1 or 2. controlling the drive current so that the amount of heat generated by the laser diode when the optical shutter is open is equal to the amount of heat generated by the laser diode when the optical shutter is closed;
5. The laser oscillator according to claim 1. Further comprising a temperature measuring element attached to the laser diode for measuring a temperature of the laser diode.
6. The laser oscillator according to claim 1 . Further comprising an output monitor unit for measuring the output of the laser light.
7. The laser oscillator according to claim 6. the control device issues a current command related to the drive current to the LD power supply and issues an open/close command to the optical shutter based on the temperature measurement data of the laser diode and the output measurement data of the laser light.
8. The laser oscillator according to claim 7. The computational model for the control device to determine the current level of the drive current is updated autonomously by feedback through machine learning.
9. The laser oscillator according to claim 8. The laser diode is at least one of a single emitter and a multi-emitter.
10. The laser oscillator according to claim 1 . The oscillation wavelength of the laser diode is in the range of 300 nm or more and 2000 nm or less.
11. The laser oscillator according to claim 1. the laser oscillator is a wavelength beam combined laser oscillator,
The wavelengths of the laser beams emitted by the plurality of laser diodes are different from each other.
3. The laser oscillator according to claim 2.