JP2013222897A - Pulse fiber laser device and pulse light output control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse fiber laser device of an MOPA system for preventing spontaneous emission light generated at power amplification parts (PA parts) from being made incident on a seed pulse generation part (MO part) and a front stage PA part without using an expensive isolator with high power resistance, and whose device size does not become large even when the PA parts are provided at multistage, and a pulse light output control method.SOLUTION: The pulse fiber laser device is constituted so as to emit a laser beam as pulse light, to prevent spontaneous emission light generated at a resonance path, a sub-amplification path, an emission path or an amplification emission path from being made incident on other path, and to take isolation among the respective paths by providing the resonance path of the pulse fiber laser device with optical path branching means, connecting the sub-amplification path, the emission path or the amplification emission path to the optical path branching means, and switching propagation paths of the laser beam which resonates in the resonance path by the optical path branching means.

Description

  The present invention relates to a fiber laser device that outputs pulsed light and a pulsed light output control method.

  A pulse fiber laser device having an excitation light source and an amplification optical fiber is widely used for laser processing, measurement using a laser device, and the like. In many cases, a semiconductor laser is used as the excitation light source. The amplification optical fiber is an optical fiber in which a rare earth element such as yttrium (Yb) or erbium (Er) is added as an excitation element capable of generating a desired laser beam oscillation wavelength in the core portion.

  In the pulse fiber laser apparatus, the spontaneous emission (ASE) noise from the amplification optical fiber increases as the repetition frequency of the outgoing pulse light is lower or the output energy is higher. This causes a decrease in light efficiency and an increase in noise.

  In particular, in a MOPA (Master Oscillator and Power Amplifier) type pulse fiber laser device capable of obtaining high-power pulsed light, the ASE light generated in the power amplification unit (PA unit) returns to the seed pulse generation unit (MO unit). Therefore, there is a problem that the return light becomes disturbance light and the output of the seed signal light becomes unstable in time. In general, by inserting an isolator or a filter between the MO unit and the PA unit, ASE light generated in the PA unit is prevented from entering the MO unit, and the above problem is solved.

  However, depending on the application of the MOPA type pulse fiber laser device, a power as high as several hundred W may be required. In such a case, a plurality of PA units are provided in the MOPA type pulse fiber laser device. Yes. In the MOPA type pulse fiber laser device that performs such multi-stage amplification, ASE light is generated in each PA unit, and the ASE light propagates in both the incident direction and the outgoing direction of each PA unit. It is necessary to install an isolator and a filter for preventing optical loss in the MO unit and the PA unit due to ASE return light between the PA unit immediately after and between each PA unit. As a result, there is a problem that the number of parts of the MOPA type pulse fiber laser device is increased and the entire device is enlarged. In addition, since optical elements such as isolators and filters inserted between the MO unit and each PA unit are expensive, the cost of the MOPA pulse fiber laser is also increased.

  In Patent Document 1, the optical nonlinearity of an acousto-optic tunable filter (AOTF) is used to extend the tuning wavelength range of the emitted laser light, thereby maintaining the broadband property of the laser device. A fiber laser device and a laser control method that can reduce ASE noise generated in the resonator of the laser device are disclosed.

When an RF (Radio Frequency) signal is supplied from a high frequency power source, the AOTF forms a refractive index distribution having a period determined by the frequency of the RF signal inside the AOTF crystal, and has a wavelength corresponding to the frequency of the RF signal. It has a function to diffract light.
According to the oscillation method of the fiber laser resonator described in Patent Document 1, using the AOTF,
1. Switching the wavelength of the emitted laser light by changing the frequency of the RF signal to be supplied;
2. By giving a high loss to the ASE noise, a low noise laser beam is emitted.
It has been shown that it is possible.

  Patent Document 2 discloses a MOPA optical fiber laser that prevents generation of ASE return light and improves safety and lifetime. This MOPA optical fiber laser is a rare earth-doped optical fiber that is a laser medium, a plurality of pumping light sources for pumping the rare-earth-doped optical fiber, and pumping light from the pumping light source to the rare-earth-doped optical fiber. And an optical coupler for making the light incident. A monitor unit that receives a part of the return light from the rare earth-doped optical fiber toward the pumping light source is connected to the rare earth-doped optical fiber via the optical coupler. In this fiber laser, when the intensity of the return light is measured by the monitor unit, if the value exceeds a predetermined value, control is performed to reduce the output of the excitation light source, thereby preventing amplification of the return light. This prevents the ASE return light from the PA section from entering the MO section.

  However, even in the fiber lasers of Patent Document 1 and Patent Document 2, when providing a plurality of PA units, it is necessary to provide an isolator at the laser beam emission portion of each PA unit. As a result, not only the number of parts of the MOPA-type pulse fiber laser device is increased, but there is a problem that the device is increased in size by connecting a plurality of PA units in series, and the cost is increased by using a plurality of expensive isolators.

  As described above, also in the prior art shown in the prior art document, in order to prevent the ASE light generated in the PA unit from returning to the MO unit and the operation of the MO unit becoming unstable, the MO unit and the PA unit are prevented. The isolator had to be inserted between. The higher the power tolerance, the higher the cost of the isolator, and in the case where the PA section is multistaged, the number of the isolators required is the same as the number of MO sections and PA sections installed. There is also a problem that the MOPA pulse fiber laser device itself becomes large.

JP 2010-67698 A JP 2007-42981 A

The present invention has been made against the background described above, and the return light of the ASE generated in the PA section (hereinafter referred to as ASE light) is multi-stage amplified without using an expensive and high power-resistant isolator. It is an object of the present invention to provide a pulsed fiber laser device that prevents incidence on a plurality of PA sections when performing the above-described process and that does not increase the size of the apparatus even if the PA sections are multistaged.
The present invention also provides a method for controlling the pulsed light output using such a pulse fiber laser device.

The present inventors have provided an optical path branching means in the resonance path of the MOPA-type pulse fiber laser device, and connected one output path having an emission part or an amplified output path to the optical path branching means, and resonated in the resonance path. The laser beam to be reciprocated in the resonance path by the optical path branching means, and the state in which the laser beam is guided to the emission path or the amplification emission path and emitted to the outside from the emission path or the amplification emission path. By switching, the above-mentioned problem was solved. Here, the optical path branching means is a device having a function capable of selecting diffraction and transmission according to an external signal. Light incident on the device is diffracted at different angles depending on the wavelength.
Further, when it is desired to provide PA sections in multiple stages, one or a plurality of sub-amplification paths having optical amplifiers are connected to the optical path branching means.

  Therefore, the pulse fiber laser device according to the first aspect of the present invention is a resonance path that constitutes a resonator including a first pumping light source and a first optical amplifier, and pumping light from the first pumping light source. Is connected to the resonance path via the optical path branching means, and is branched from the resonance path through the third optical amplifier, the third excitation light source, and the resonance path. A sub-amplification path comprising a wavelength conversion element for converting the wavelength of the reflected light and a reflection part for reflecting the light wavelength-converted by the wavelength conversion element, and connected to the resonance path via the optical path branching means, Each of the resonance paths divided into two by the optical path branching means is defined as a divided resonance path, and the optical path branching means is divided into two sections. A first transmitting light between the resonance paths; The optical path is selectively switched between the switching state and the second switching state in which light incident from one of the divided resonance paths is emitted to the sub-amplification path and light incident from the sub-amplification path is emitted to the emission path. The sub-amplification path amplifies the light branched from the resonance path by the optical path branching means and emits it to the emission path, and the emission path is branched from the sub-amplification path by the optical path branching means. The light is emitted.

According to the pulse fiber laser device of the first aspect, the ASE light generated in the sub-amplification path is prevented from entering the resonance path while adopting the two-stage amplification method, and the resonance path-sub-amplification path Can be isolated between. For this reason, it is possible to obtain stable output pulse light with small temporal output fluctuation.
Further, since the sub-amplification path and the emission path are connected to the optical path branching means, the pulse fiber laser is compared with the conventional MOPA type pulse fiber laser device in which all of the resonance path, the sub-amplification path and the emission path are connected in series. Space saving of the apparatus can be achieved.
In the pulse fiber laser device of the first aspect, the wavelength of light emitted to the sub-amplification path by the optical path branching means is converted in the sub-amplification path. When an active diffractive optical element having a diffraction function is used as the optical path branching means, the diffraction angle of light incident on the diffractive optical element from each amplification path is incident by wavelength conversion in the sub-amplification path. Since each path differs, even if the period of the diffraction grating formed by the diffractive optical element at the time of path switching is constant, light from all paths can be emitted simultaneously and accurately to a predetermined next path. This also applies to the second and third aspects described below.

  A pulse fiber laser device according to a second aspect of the present invention is the pulse fiber laser device according to the first aspect, wherein the emission path is provided with a second optical amplifier and a second excitation light source, so that the emission path is branched. A first switching state in which the optical path branching means is configured to be an amplification output path for amplifying and emitting light branched from the sub-amplification path by the switch, and the optical path branching means transmits light between the two sectioned resonance paths; The light path is selectively switched to the second switching state in which the light incident from any one of the divided resonance paths is emitted to the sub-amplification path and the light incident from the sub-amplification path is emitted to the amplification output path. It is comprised by these.

  According to the pulse fiber laser device of the second aspect, the ASE light generated in the amplification output path is incident on the sub-amplification path while adopting the two-stage amplification method similarly to the pulse fiber laser apparatus of the first aspect. In addition to the resonance path and the sub-amplification path, isolation between the sub-amplification path and the amplification output path can be obtained. Thereby, it is possible to obtain stable output pulse light with small temporal output fluctuation.

  A pulse fiber laser device according to a third aspect of the present invention is the pulse fiber laser device according to the first and second aspects, wherein a plurality of sub-amplification paths are connected to the optical path branching means, and each sub-amplification path is A third optical amplifier, a third excitation light source, a wavelength conversion element for converting the wavelength of the light branched from the resonance path, and a reflection part for reflecting the light wavelength-converted by the wavelength conversion element A first switching state in which the light path branching means transmits light between two section resonance paths, and light incident from one of the section resonance paths is one of the plurality of sub-amplification paths. The light is emitted to one sub-amplification path, and the light incident from each sub-amplification path is emitted to another sub-amplification path different from the sub-amplification path, and is incident from the sub-amplification path different from the one sub-amplification path. Into a second switching state to be emitted to the emission path or amplification emission path, and is characterized in that it is configured to selectively switch the optical path.

According to the pulse fiber laser device of the third aspect, the ASE light generated in each sub-amplification path and the amplification output path is incident on the resonance path and each sub-amplification path while adopting a multi-stage amplification system of two or more stages. Can be prevented.
Further, since all the sub-amplification paths and the emission paths or the amplification emission paths are connected to the same optical path branching means, the resonance path, the plurality of sub-amplification paths and the emission paths or the amplification emission paths are all connected in series. Compared with the MOPA-type pulse fiber laser apparatus, the space of the pulse fiber laser apparatus can be greatly reduced.

  A pulsed light output control method according to a fourth aspect of the present invention is a resonance path that constitutes a resonator including a first optical amplifier, and is in the middle of a resonance path through which pumping light from a first pumping light source is guided. The optical path branching means, and the optical path branching means includes a third optical amplifier, a third pumping light source, and a sub-amplifying path having a reflection part for reflecting the wavelength-converted light by the wavelength conversion element, and an emission A part of the resonance path that is divided into two by the optical path branching means is set as a divided resonance path, and pumping light is injected into the first optical amplifier in the resonance path to emit laser light. In the state where the laser beam resonates in the resonance path, the path switching by the optical path branching means is performed three times, one pulse of the pulsed light is emitted from the emission path, and the optical path branching means The first of three route switching By the path switching and the second switching, the laser light resonating in the resonance path is emitted as a pulsed light to the sub-amplification path, and the sub-amplification path is reciprocated at least once. Of the path switching, the third path switching causes the pulsed light reciprocating in the sub-amplification path to be emitted to the emission path and emitted from the emission unit.

According to the pulsed light output control method of the fourth aspect, when the pumping light is guided to the resonance path and a fixed time elapses, the pumping light is injected into the first optical amplifier, and the ASE having a wide wavelength band from the first optical amplifier. Light is generated. Thereafter, when a certain time elapses, only light having a wavelength in the reflection band at both ends of the resonance path is reflected among the light included in the ASE light. As time further elapses, the light reflected at both ends of the resonance path passes through the optical amplifier and is amplified, and the light intensity is increased each time the reflected light circulates in the resonance path. Thereafter, when the circular gain in the resonance path of the reflected light exceeds the circular loss, the light in the reflection band in the high reflection fiber Bragg grating provided at both ends of the resonance path is in resonance.
Therefore, the laser beam can be resonated in the resonator without being emitted to the outside until the laser beam is emitted to the sub-amplification route by the optical path branching unit. Moreover, since the resonance path and the sub-amplification path can be cut off except for the time when the laser beam resonating in the resonance path is emitted to the sub-amplification path by the optical path branching means, without using an expensive isolator, It is possible to prevent the ASE light generated in the sub-amplification path from entering the resonance path. That is, it is possible to prevent the ASE light generated by the optical amplifier provided in the sub-amplification path from entering the resonance path, and to isolate the resonance path and the sub-amplification path.

  A pulsed light output control method according to a fifth aspect of the present invention is the pulsed light output control method according to the fourth aspect, wherein the emission path is amplified by providing a second optical amplifier and a second excitation light source in the emission path. In the state in which excitation light is injected into the first optical amplifier in the resonance path to generate laser light and the laser light resonates in the resonance path, the path switching by the optical path branching unit is performed as 3 The laser is resonated in the resonance path by the first path switching and the second switching among the three path switching by the optical path branching means. Light is emitted as pulsed light to the sub-amplification path, the sub-amplification path is reciprocated at least once, and the path is reciprocated in the sub-amplification path by the third path switching among the three path switching by the optical path branching means. That the pulsed light is emitted to the amplifier emission path, it is characterized in that to emit from the amplified emission path.

  According to the pulse light output control method of the fifth aspect, the ASE light generated by the second optical amplifier provided in the amplification emission path is prevented from entering the sub amplification path, and is added between the resonance path and the sub amplification path. Thus, isolation between the sub-amplification path and the amplification output path can be obtained.

  A pulsed light output control method according to a sixth aspect of the present invention is the pulsed light output control method according to the fourth or fifth aspect, wherein either one of an emission path or an amplified emission path (hereinafter, referred to as an optical path branching means) In this mode, in addition to (amplification) emission path), a third optical amplifier and a third excitation light source are respectively used as sub-amplification paths for amplifying light branched from the resonance path by the optical path branching means. And a plurality of sub-amplification paths having a reflection part that reflects light converted by the wavelength conversion element, the number of sub-amplification paths being m (m is a natural number of 2 or more), In the state where the pump light is injected into the first optical amplifier to generate laser light and the laser light resonates in the resonance path, the path switching by the optical path branching means is performed (2m + 1) times, and (amplification) 1 pulse light from the emission path The laser beam that resonates in the resonance path by the first path switching and the second path switching out of (2m + 1) times of path switching by the optical path branching means is used as the pulsed light. Of the sub-amplification paths, and at least one reciprocation of the sub-amplification path, and by switching from the third to (2m) times of the (2m + 1) times of path switching, Pulse light incident from any one of the section resonance paths and the plurality of sub-amplification paths is emitted to a different sub-amplification path, and the sub-amplification path is reciprocated at least once, (2m + 1) In addition to the operation up to the (2m) -th time, the sub-amplification path is different from the one sub-amplification path by the (2m + 1) -th switching among the path switching times The pulse light incident from the wide path (amplification) by emission to the emission path, is characterized in that to emit as output pulse light from the (amplified) emission path.

  According to the pulse light output control method of the sixth aspect, when performing multi-stage amplification of two or more stages, the ASE light generated in each optical amplifier provided in the sub-amplification path and the amplification output path is the resonance path and sub-amplification path. Can be prevented.

  A pulsed light output control method according to a seventh aspect of the present invention is the pulsed light output control method according to any one of the fourth to sixth aspects, wherein one pulse of pulsed light is emitted from the emission path or the amplified emission path. , The third and subsequent odd-numbered path switching holding times in the optical path branching means are equal to or longer than the first-time path switching holding time, and the third and subsequent odd-numbered path switching holding times. It is characterized by controlling.

  According to the pulsed light output control method of the seventh aspect, the pulsed light having the pulse width of the first path switching holding time is generated, the pulse width and the energy are held, and branched to the outgoing path or the amplified outgoing path Therefore, it is possible to emit pulsed light with very little ASE noise and high power from the emission path or the amplification emission path.

  A pulsed light output control method according to an eighth aspect of the present invention is the pulsed light output control method according to any one of the fourth to seventh aspects, wherein one pulse of pulsed light is emitted from the emission path or the amplified emission path. The time interval for switching the path is the time from when the laser light is incident on the sub-amplification path during the path switching holding time until it is reflected by the reflector in the sub-amplification path and returns to the optical path branching means. The path switching holding time and the path switching time interval are controlled so as to be equal to.

  According to the pulsed light output control method of the eighth aspect, the path switching time interval is set so that the laser light incident on one sub-amplification path is guided to the exit path, the amplification exit path, or another sub-amplification path without loss. It is possible to set the shortest time, minimizing the possibility that the ASE light generated by the respective optical amplifiers provided in the sub-amplification path and the amplification output path is incident on the resonance path and the sub-amplification path. Pulse light with very little ASE noise can be emitted from the amplification emission path.

  According to the pulse fiber laser device of the present invention, by switching the light propagation path by the optical path branching means, the light can be emitted from the emission path or the amplification emission path after at least one reciprocation of the sub-amplification path. Therefore, it is possible to generate pulsed light with high output power, and to effectively prevent the ASE light generated in the sub-amplification path and the output path or the amplified output path from entering the resonance path and the sub-amplification path.

In addition, since the MOPA pulse fiber laser device of the present invention is configured without using an isolator between the resonance path and the sub-amplification path, an expensive isolator inserted between the MO section and the PA section is not used. It becomes unnecessary.
In particular, even when optical amplifiers are installed in multiple stages, the cost of the pulse fiber laser device can be reduced by performing multi-stage amplification by switching control using one optical path branching means regardless of the number of optical amplifiers installed. Can do.
Furthermore, in the pulse fiber laser device of the present invention, all the sub-amplification paths and the emission paths or the amplification emission paths are connected with the optical path branching means provided in the middle of the resonance path as the base point. It is possible to save the space of the apparatus regardless of the number of installed.

1 is a schematic diagram illustrating an overall configuration of a pulse fiber laser device according to a first embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows a part of structure of the pulse fiber laser apparatus by the 1st Embodiment of this invention, (a) is the structure of the reflection part of the subamplification path | route which used the mirror, (b) used the loop. It is a figure which shows the structure of the reflection part of a subamplification path | route. It is a figure for demonstrating the pulse light output control method in the pulse fiber laser apparatus by the 1st Embodiment of this invention. In order to explain the relationship between the switching between the first switching state and the second switching state of the shutter in the pulse fiber laser device according to the first embodiment of the present invention and the pulsed light incident on the optical path branching means from the sub-amplification path. FIG. It is a schematic diagram which shows the whole structure of the pulse fiber laser apparatus by the 2nd Embodiment of this invention. It is a figure for demonstrating the pulse light output control method in the pulse fiber laser apparatus by the 2nd Embodiment of this invention. It is a figure for demonstrating the pulse light output control method in the pulse fiber laser apparatus by the 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to FIGS.

  FIG. 1 shows a pulse fiber laser device according to a first embodiment of the present invention. This pulse fiber laser device is configured by a MOPA system that performs multistage amplification having a plurality of PA units, and includes a resonance path 1 having two divided resonance paths 1a and 1b divided by a shutter 50, a sub-amplification path 3, and the like. The resonance path 1 functions as an MO unit, and the sub-amplification path 3 functions as a PA unit.

The resonance path 1 constitutes a resonator in the fiber laser. The resonance path 1 functions as a high reflection fiber Bragg grating (FBG) 11 and a high reflection FBG 12 as a reflection portion, an amplification optical fiber 13 as a first optical amplifier, and the optical path branching means. The excitation light source 10 is connected to the resonance path 1 by a fiber coupler 15. Further, the resonance path 1 is divided into a divided resonance path 1 a and a divided resonance path 1 b by the shutter 50. Note that FBGs having a reflectance of 80% or more are used for the high reflection FBGs 11 and 12.
Connected to the shutter 50 is a driver 51 for controlling a first / second switching state (details will be described later) in the shutter 50 and supplying an RF signal to the shutter 50 in the second switching state.

It is desirable to use a device having a diffractive function (diffractive optical element) for the shutter 50, and here, an acousto-optic element (hereinafter referred to as AOM) is applied as a representative diffractive optical element. Assume and explain. The AOM has a function of inputting a high-frequency RF signal to form a refractive index distribution having a period determined by the frequency of the RF signal inside the AOM and diffracting incident light at an angle based on diffraction theory. In this embodiment, the light incident portion of the sub-amplification path 3 is connected to the shutter 50 at an angle θ1 formed with the resonance path 1, and the light incident portion of the emission path 2 ′ is connected to the shutter 50 with the sub-amplification path 3. Are connected at an angle θ3 formed by an extension line.
The AOM functioning as the shutter 50 diffracts the light of wavelength λ1 of the resonance path 1 into the sub-amplification path 3 at an angle θ1, and simultaneously diffracts the light of wavelength λ3 of the sub-amplification path 3 into the emission path 2 ′ at an angle θ3. The frequency of the RF signal for this purpose is checked in advance, and the RF signal of the frequency can be output from the driver 51 to the AOM at an arbitrary timing. Therefore, when the shutter 50 is in the first switching state, light is transmitted between the section resonance path 1a and the section resonance path 1b. When the shutter 50 is in the second switching state, the light incident from the sectioned resonance path 1a is emitted to the sub-amplification path 3 and the light incident from the sub-amplification path 3 is emitted to the emission path 2 ′.

The sub-amplification path 3 includes an excitation light source 30, an amplification optical fiber 33, a wavelength conversion element 34, and a high reflection FBG 36, and the excitation light source 30 is connected to the amplification optical fiber 33 by a fiber coupler 35. .
Note that the arrangement of the amplification fiber 33 and the wavelength conversion element 34 in the sub-amplification path 3 of FIG. 1 may be interchanged. In this case, the wavelength conversion element 34 passes both the signal light having the wavelength λ1 and the signal having the wavelength λ2 (the fundamental wave remains), but the grating 36 is designed to selectively reflect only the wavelength λ2. The signal light of λ1 is not reflected by the totally reflecting grating 36 disposed in the subsequent stage. Therefore, the light that reflects from the grating 36 and returns is only λ2.

In addition, instead of the highly reflective FBG 36, as shown in FIGS. 2A and 2B, the wavelength λ2 of the outgoing pulse light of the wavelength conversion element 34 is transmitted, but the light propagating in the resonance path 1 is transmitted. A band-pass filter 37 and a mirror 38, or a band-pass filter 37 and a loop 39 having a characteristic that does not transmit the wavelength λ1 may be disposed.
Further, the wavelength conversion element 34 may be configured to generate Raman scattering using a fiber and selectively reflect the wavelength of the Raman scattered light by the high reflection FBG 36 provided in the subsequent stage. As another wavelength conversion method, a nonlinear optical crystal may be used as the wavelength conversion element.

  Further, it is possible to adopt a configuration in which the pulsed light having the wavelength λ1 is incident on the sub-amplification path 3 and the emission path 2 ′ without providing the wavelength conversion element 34. In this case, when the wavelength of the light traveling back and forth in the sub-amplification path 3 is the same at λ1, and the frequency of the RF signal of the AOM is the same, the light incident on the shutter 50 from the sub-amplification path 3 Therefore, the RF signal frequency of the AOM is changed to the second switching state for causing the pulse light to be incident from the resonance path 1 to the sub-amplification path 3, and for the pulse light to be incident from the sub-amplification path 3 to the emission path 2 '. It is necessary to change according to the second path switching state.

  In the emission path 2 ′, the light incident portion is connected to the shutter 50 at an angle θ 3 formed with the resonance path 1. The isolator 26 provided in the emission path 2 ′ prevents reflected light from an irradiated object such as a laser processing object from entering and returning in the emission path 2 ′ in the direction opposite to that when emitting pulsed light. belongs to.

  Next, the operation of the pulse fiber laser device shown in FIG. 1 will be described with reference to FIGS.

First, the operation of the pulse fiber laser device when the shutter 50 is in the first switching state will be described with reference to FIG.
When pumping light is emitted from the pumping light source 10, the pumping light passes through the fiber coupler 15, passes through the highly reflective FBG 11, and propagates through the resonance path 1. The excitation light passes through the shutter 50, enters the amplification optical fiber 13, and excites the excitation element added to the amplification optical fiber 13. ASE occurs in the amplification optical fiber 13, and light in a wavelength band including the signal wavelength λ 1 is selectively reflected by the high reflection FBG 12 among the emitted light, and is incident on the amplification optical fiber 13 again. The light amplified by stimulated emission in the amplification optical fiber 13 propagates in the resonance path 1, is reflected by the high reflection FBG 11, and resonates and is amplified until the shutter 50 is switched to the second switching state.

Next, the operation of the pulse fiber laser device when the shutter 50 is in the second switching state will be described.
3 shows a laser output signal (S0), a driving current (S1) of the excitation light source 10, a switching signal (S2) of the shutter 50, a driving current (S5) of the excitation light source 30, and pulsed light incident on the sub-amplification path 3 ( S6), the operations of the pulsed light (S4) incident on the emission path 2 ′ and the pulsed light (S10) emitted from the emission path 2 ′ and the mutual relationship are shown.
FIG. 4 shows the temporal relationship between (S2) and (S4).

In this pulse fiber laser device, switching from the resonance path 1 to the sub-amplification path 3 is performed until one pulse of laser light is emitted, then switching from the resonance path 1 to the sub-amplification path 3 is performed, and the sub-amplification path Since switching from 3 to the emission path 2 ′ is necessary, the path switching at the shutter 50 is performed three times before one pulse of laser light is emitted.
here,
t0: P1-i shutter 50 path switching holding time, which is the time from when the first switching state is switched to the second switching state until the first switching state is restored again, that is, P3-i, P2-i , P2-i ′ pulse width (where i is 0 or a positive even number),
t1: Time interval between P1- (j-1) and P1-j when (S0) is in the OFF state (where j is a positive odd number),
t2: P1-j shutter 50 holding time in the second switching state, that is, pulse widths of P3-j, P2-j, P2-j ′,
t3: time interval between P1- (j-1) and P1-j when (S0) is in the ON state,
t4: Time interval between P1- (k-1) and P1-k after (S0) first turned ON (k is a positive even number, and (S0) with respect to P1- (k-1)) Only when ON is ON)
t5: time interval between P2- (k-2) ′ and P2-k ′ when (S0) is in the ON state,
And

  Next, the operation of the pulse fiber laser device when the ON / OFF states of (S0), (S1), and (S5) and the first / second switching states of (S2) are switched will be specifically described. explain.

When (S0) is OFF, (S1) is ON, and (S5) is OFF ((E) in FIG. 3):
When the shutter 50 is changed from the first switching state to the second switching state in the state where the laser light is resonating in the resonance path 1 (first path switching by the shutter 50), the section resonance path 1a changes to the shutter 50. The incident laser light is diffracted at an angle θ 1 and emitted toward the sub-amplification path 3. If the shutter 50 is switched to the first switching state after the time t0 has elapsed (second path switching by the shutter 50), the light from the segmented resonance path 1a incident on the sub-amplification path 3 is light having the pulse width t0. It becomes a pulse P3-0.
The optical pulse P3-0 is incident on the amplification optical fiber 33 in the sub-amplification path 3, but P3-0 is absorbed because the excitation light source 30 is in the OFF state.
Subsequently, the time interval t1 with P1-0 by the switching operation of the shutter 50, P1-1 at the second switching state holding time t2 (path switching from the first switching state to the second switching state at P1-1: shutter 50 3), the laser light enters the amplification optical fiber 33 of the sub-amplification path 3 as the pulsed light P3-1. However, since the excitation light source 30 is in the OFF state, P3- 1 is absorbed. That is, in the case of FIG. 3E, since (S5) is in the OFF state, no signal light is emitted. As described above, the path switching at the shutter 50 is performed three times until one pulse of the laser beam is emitted. However, when continuously outputting the pulsed beam, the laser beam is output as shown in FIG. When emitting one pulse of light, the path switching from the second switching state to the first switching state may be added to the three path switching, and the path switching at the shutter 50 may be performed a total of four times. The number of path switching is not limited to four, but can be changed according to the function of the shutter 50 and the control method.

Here, if the propagation distance of light from the shutter 50 to the highly reflective FBG 36, that is, the one-way distance through which light propagates in the sub-amplification path 2, is L, the optical pulse is diffracted from the sectioned resonance path 1a, and the sub-amplification path 3 The time T required for the light pulse to reach the position of the shutter 50 after reciprocating is as follows: n is the refractive index of the core of the amplification optical fiber 33 and c is the speed of light in vacuum.
T = 2L (n / c)
It becomes.
In the above case, t1 and t2 are set to t1 + t2 <T
If it is set so as to satisfy, the light from the sub-amplification path 3 to the output path 2 'is not diffracted, and a weak light pulse does not leak from the pulse fiber laser device during the OFF state of (S0). .
Further, the third path switching hold time t2 at the shutter 50 needs to be set to a time longer than the time width t0 of the first ON state, but in order to increase the isolation as much as possible, it is about the same as t0. It is desirable to do.

When (S0) is in the ON state, (S1) is in the ON state, and (S5) is in the ON state (FIGS. 3 (F) and (H)):
When (S5) is turned on, the rare earth element added to the amplification optical fiber 33 is excited. When P3-2 that has entered the sub-amplification path 3 enters the amplification optical fiber 33, high-power pulsed light is generated. The pulsed light of wavelength λ1 enters the wavelength conversion element 34, is converted to pulsed light of wavelength λ2, is reflected by the highly reflective FBG 36, is incident on the wavelength conversion element 34 again, and is converted to pulsed light of wavelength λ3. The pulsed light of wavelength λ3 propagates through the amplification optical fiber 33 to the shutter 50.

  When the time t3 elapses from when the light pulse P3-2 is incident on the sub-amplification path 3, when the shutter 50 is switched to the second switching state for the time interval t2, the laser light from the sectioned resonance path 1a has the wavelength λ1, At the same time as an optical pulse P3-3 having a pulse width t2 is diffracted toward the sub-amplification path 3, an optical pulse P3-2 having a wavelength λ3 and a pulse width t0 that has propagated through the sub-amplification path 3 is P2-2. It is diffracted toward the exit path 2 '.

  However, in order for the light pulse P3-2 having the wavelength λ3 and the pulse width t0 propagated through the sub-amplification path 3 as described above to be diffracted to the emission path 2 ′ as P2-2 by the operation of P1-3, Certain conditions must be met. Therefore, the fixed condition will be described in detail with reference to FIG.

t3 is a time interval between the first switching of the first / second switching state and the third switching in the shutter 50, which is performed when one pulse of the pulsed light is emitted from the emission path 2 ′. The timing for performing the third path switching by the shutter 50 is preferably the same as or before the pulsed light incident on the sub-amplifying path 3 from the resonance path 1 returns to the shutter 50 again. That is, t3 ≦ T. Further, it is necessary to maintain the second switching state until the pulsed light has passed through the shutter. That is, t2 + t3 ≧ t0 + T. In particular, when t3 = T and t2 = t0, the possibility that the ASE light generated in the amplification fiber 33 provided in the sub-amplification path 3 is incident on the resonance path 1 is minimized, and the ASE light from the output path 2 'is extremely reduced. Pulse light with less noise can be emitted.
t4 is a time interval for determining the timing of emitting the next optical pulse. At least the optical pulse is diffracted from the sectioned resonance path 1a, and the pulsed light reaches the position of the shutter 50 by reciprocating along the sub-amplification path 3. It is necessary to set it longer than the time T until. By setting so as to satisfy the conditions described in the next paragraph together with t5 which is the repetition period of the optical pulse output from the emission path 2 ', pulse light with a high power with little ASE noise and a small temporal output fluctuation can be obtained. Generated.

More specifically, when the shutter 50 is switched from the first switching state to the second switching state by the operation of P1-3, the optical pulse P3-2 having the wavelength λ3 and the pulse width t0 propagating through the sub-amplification path 3 is obtained. If the time difference from the point of time when the light is diffracted as the light pulse P2-2 by the shutter 50 to the emission path 2 ′ is Δt
Δt = T−t3 = 2L (n / c) −t3
It becomes. In order for the light pulse P3-2 to be diffracted to the emission path 2 ′ as the light pulse P2-2 during the holding time t2 of the second switching state P1-3 of the shutter 50, as shown in FIG.
Δt + t0 ≦ t2,
t2 + t3 ≧ t0 + T,
(Hereinafter, this condition is referred to as an optimum condition).
Therefore, it is desirable to set t0, t1, t2, t3, n, and L in advance so as to satisfy the optimum condition before the operation of the pulse fiber laser device is started.

  When the above-mentioned optimum conditions are satisfied and the light pulse P3-2 is diffracted as the light pulse P2-2 on the emission path 2 ′ during the holding time t2 of the second switching state P1-3 of the shutter 50, the light pulse P3 -2 passes through the isolator 26 and is emitted as an optical pulse P2-2 '.

Further, when the shutter 50 is in the second switching state at P1-3, P3-2 that has propagated through the sub-amplification path 3 as described above enters the shutter 50, diffracts at an angle θ3, and exit path 2 At the same time, the laser beam resonating in the resonance path 1 is diffracted to the sub-amplification path 3 in the same manner as in the case of the section resonance path 1a to P1-2, and an optical pulse having a wavelength λ1 and a pulse width t0 It becomes P3-3.
P3-3 passes through the amplification optical fiber 33 and the wavelength conversion element 34, is reflected by the high reflection FBG 36, passes through the wavelength conversion element 34 and the amplification optical fiber 33 again, and (S5) is in the ON state. The light pulse is incident on the shutter 50 as a light pulse having a wavelength of λ3 and a pulse width t0. Since the shutter 50 is in the first switching state at this time, the light pulse is emitted in the direction out of the path by the shutter 50 or is applied to the shutter 50. It is absorbed and is not emitted to the emission path 2 ′.

  When n is an even number of 4 or more and P1-n is as shown in FIGS. 3F and 3H, the operations of P1-n and P1- (n + 1) are the same as the operations of P1-2 and P1-3 described above. Since it can be made to correspond, description is abbreviate | omitted.

The time interval between P2-2 ′ and P2-4 ′, that is, the pulse interval t5 of the high-power output pulsed light of the pulse fiber laser device, enters the output path 2 ′ after P3-2 enters the sub-amplification path 3. By setting the time sufficiently longer than the shortest time T until diffraction, P2-2 ′ and P2-4 ′ can be completely separated on the time axis.
T2 + t3 + t4 >> T = 2L (n / c) that satisfies the optimal condition and is desirable
Only when is satisfied
t5 = t2 + t3 + t4,
t4 = t5-t3-t2
It becomes. Since t4 is a time interval for determining the timing of emitting the next optical pulse, it must be set longer than the time T for which the optical pulse reciprocates in the sub-amplification path 3 as indicated by the above conditions. It is desirable to set t4 in advance so as to satisfy the above-described conditions along with the optimum condition in accordance with the desired t5.

When (S0) is in an OFF state, (S1) is in an ON state, and (S5) is in an ON state ((G) in FIG. 3):
In order to simplify the control as much as possible, (S1) basically holds the second switching state before starting the switching operation of the shutter 50. Further, for the same reason as (S1), the excitation light source 30 of the sub-amplification path 3 is also kept in the second switching state after switching to the second switching state once. In that case, (S2) is ( Regardless of the first / second switching state of S0), as shown in P1-6, P1-7, P1-8, P1-9 in FIG. Switch from 1) to the second switching state (2).
This operation is performed even if (S0) switches to the OFF state in the middle of the ON state, and the laser light amplified in the resonance path 1 due to the (S1) being in the ON state and the switching of (S2). Is incident on the sub-amplification path 3 at regular time intervals, and the power of the light in the resonance path 1 is amplified with a substantially constant increase / decrease pattern, so that the first time immediately after (S0) is switched from the OFF state to the ON state. This is because the peak power of one light pulse P2-10 ′ can be aligned with the output peak power of P2-2 ′ and P2-4 ′.

  With the above-described operation, when the shutter 50 is in the first switching state, the resonance path 1 and the sub-amplification path 2 are not connected, so that the ASE light generated in the amplification optical fiber 33 during this time does not return to the resonance path. In addition, the isolation between the MO unit and the PA unit can be obtained.

FIG. 5 shows a pulse fiber laser apparatus according to the second embodiment of the present invention. This pulse fiber laser device is configured by a MOPA system that performs multistage amplification having a plurality of PA units, and includes a resonance path 1 having two divided resonance paths 1a and 1b divided by a shutter 50, a sub-amplification path 3, and the like. The resonance path 1 functions as an MO unit, the sub-amplification path 3 functions as a PrePA unit, and the amplification output path 2 functions as a PA unit.
In FIG. 5, the same components as those of the pulse fiber laser device shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The amplification output path 2 is a path provided with a second excitation light source 20 and an amplification optical fiber 23 as a second optical amplifier in the output path 2 ′ of the pulse fiber laser apparatus of the first embodiment. The incident portion is connected to the shutter 50 at an angle θ3 formed with the resonance path. The excitation light source 20 is connected to the amplification optical fiber 23 via the fiber coupler 25.

Next, the operation of the pulse fiber laser device shown in FIG. 5 will be described with reference to FIG.
In the following description, the description of the same operation as that of the pulse fiber laser device of the first embodiment is omitted.

  6 shows a laser output signal (S0), a driving current (S1) of the excitation light source 10, a switching signal (S2) of the shutter 50, a driving current (S5) of the excitation light source 30, and a pulsed light incident on the sub-amplification path 3 ( S6), the drive current (S3) of the excitation light source 20, the operation of the pulsed light (S4) incident on the amplified output path 2, and the operation of the pulsed light (S10) output from the amplified output path 2 are shown in a mutual relationship. .

  Next, the operation of the pulse fiber laser device when the ON / OFF states of (S0), (S1), (S5), and (S3) and the first / second switching state of (S2) are switched. This will be described in detail.

When (S0) is OFF, (S1) is ON, (S5) is OFF, and (S3) is OFF (FIG. 5 (E)):
When the optical pulse P3-0 is incident on the amplification optical fiber 33 in the sub-amplification path 3, the pumping light source 30 is in the OFF state, so that the process until P3-0 is absorbed is the same as in FIG. .
Subsequently, the laser beam is emitted from the resonance path 1 to the amplification emission path 3 as the pulsed light P3-1 at the time interval t1 with P1-0 by the switching operation of the shutter 50 and P1-1 at the second switching state holding time t2. Then, P3-1 is incident on the amplification optical fiber 33. Since S3 and S5 are OFF, a part of the power of the signal light is absorbed by the excitation element in the same manner as P3-0.
Similarly to the pulse fiber laser device of the first embodiment, the third path switching holding time t2 at the shutter 50 needs to be set to a time longer than the time width t0 of the first ON state. In order to increase the isolation as much as possible, it is desirable to set it to the same level as t0.

When (S0) is on, (S1) is on, (S5) is on, and (S3) is on (FIGS. 5F and 5H):
The incident light pulse P3-2 diffracted into the sub-amplification path 3 is converted into pulsed light having the wavelength λ3, and is the same as in FIGS. 3F and 3H until it propagates to the shutter 50.
When the time t3 elapses from when the light pulse P3-2 is incident on the sub-amplification path 3, when the shutter 50 is switched to the second switching state for the time interval t2, the laser light from the sectioned resonance path 1a has the wavelength λ1, At the same time as an optical pulse P3-3 having a pulse width t2 is diffracted toward the sub-amplification path 3, an optical pulse P3-2 having a wavelength λ3 and a pulse width t0 that has propagated through the sub-amplification path 3 is P2-2. The light is diffracted toward the amplified output path 2.

However, similarly to the pulse fiber laser apparatus of the first embodiment, the optical pulse P3-2 having the wavelength λ3 and the pulse width t0 that has propagated through the sub-amplification path 3 as described above is generated by the operation of P1-3 as described above. In order to be diffracted as 2 into the amplification output path 2, the above-mentioned certain condition must be satisfied.
When the predetermined condition is satisfied and the light pulse P3-2 is diffracted as the light pulse P2-2 in the amplification emission path 2 during the holding time t2 of the second switching state P1-3 of the shutter 50, P2-2 is The light enters the amplification optical fiber 23. P2-2 increases the inversion distribution ratio of the amplification optical fiber 23, and as a result, high-power pulsed light is generated by stimulated emission of the excitation element.
The light pulse is emitted as P2-2 'through the isolator 26.

When the shutter 50 is in the second switching state at P1-3, P3-2 that has propagated through the sub-amplification path 3 as described above enters the shutter 50 and is diffracted at an angle θ3 to be amplified and output path. At the same time, the laser beam resonating in the resonance path 1 is diffracted to the sub-amplification path 3 in the same manner as in the case of the section resonance path 1a to P1-2, and an optical pulse having the wavelength λ1 and the pulse width t0. It becomes P3-3.
P3-3 passes through the amplification optical fiber 33 and the wavelength conversion element 34, is reflected by the high reflection FBG 36, passes through the wavelength conversion element 34 and the amplification optical fiber 33 again, and (S5) is in the ON state. The light pulse is incident on the shutter 50 as a light pulse having a wavelength of λ3 and a pulse width t0. Since the shutter 50 is in the first switching state at this time, the light pulse is emitted in the direction out of the path by the shutter 50 or is applied to the shutter 50. It is absorbed and is not emitted to the amplified emission path 2.
Further, similarly to the pulse fiber laser device of the first embodiment, it is desirable to set t0, t1, t2, t3, n, L, and t4 in advance so as to satisfy the optimum condition and the above-described certain condition. .

  The operation of the pulse fiber laser device of this embodiment when (S0) is in the OFF state, (S1) is in the ON state, (S5) is in the ON state, and (S3) is in the OFF state (FIG. 5G) This is the same as the pulse fiber laser device of the first embodiment.

  By the above-described operation, when the shutter 50 is in the first switching state, the resonance path 1 and the sub amplification path 2 are not connected. Further, by holding the second switching state of the shutter 50 so as to satisfy the predetermined condition, the ASE light generated in the amplification optical fibers 23 and 33 does not return to the sub-amplification path and the resonance path, respectively. Thereby, isolation between the MO unit and the PrePA unit and between the PrePA unit and the PA unit can be obtained.

FIG. 7 shows a pulse fiber laser device according to a third embodiment of the present invention. This pulse fiber laser device is configured by a MOPA system that performs multi-stage amplification having a plurality of PA units, and includes a resonance path 1 having sectioned resonance paths 1a and 1b, two sub-amplification paths 3 and 4, and an amplification emission path. 2, the resonance path 1 functions as an MO section, the sub-amplification paths 3 and 4 function as a PrePA section, and the amplification output path 2 functions as a PA section.
In FIG. 7, the same components as those of the pulse fiber laser device shown in FIG. 5 are denoted by the same reference numerals, and the description thereof is omitted.

  In the pulse fiber laser device of FIG. 7, when the shutter 50 is in the first switching state, light is transmitted between the sectioned resonance path 1a and the sectioned resonance path 1b, and the sub-amplification paths 3 and 4 and the amplified emission are transmitted. The light propagating in the path 2 is not emitted to any path. When the shutter 50 is in the second switching state, the light incident from the sectioned resonance path 1a is emitted to the sub-amplification path 3 having an angle θ1 with the resonance path 1 and the light incident from the sub-amplification path 3 is the shutter 50. The light that has been emitted to the sub-amplification path 4 that forms an angle θ4 with the extension line of the sub-amplification path 3 across the line, and the light incident from the sub-amplification path 4 has an angle θ5 with the extension line of the sub-amplification path 4 across the shutter 50 The light is emitted to the amplification outgoing path 2 formed. Even when the number of installed sub-amplification paths is increased, all the sub-amplification paths are connected to the shutter 50. Therefore, the operation of the shutter 50 in the second switching state may be considered in the same manner as described above.

In addition, since the MOPA type pulse fiber laser device is provided with two sub-amplification paths 3 and 4, in order to emit one pulse of the pulsed light from the amplification emission path 2, it is necessary to switch the shutter 50 five times. The operation in the five times of switching may be considered in the same manner as the operation in the MOPA pulse fiber laser apparatus of FIG. When the pulsed light is continuously output by this MOPA type pulse fiber laser device, the second switching state after the fifth path switching is performed instead of the five path switching when emitting one pulse of laser light. The route switching from the first to the first switching state is added and the route switching by the shutter 50 may be performed a total of six times, but is not necessarily limited to six times.
The MOPA-type pulse fiber laser apparatus that performs multistage amplification shown in FIGS. 1, 5, and 7 can avoid an increase in the size of the apparatus compared to a conventional multistage amplification MOPA-type pulse fiber laser apparatus in which PrePA units are connected in series. it can.

  According to the method for controlling the shutter 50 as described above, the paths are not connected while the first switching state of the shutter 50 is maintained. Therefore, the ASE light generated in the amplification optical fibers 13, 23, 33, and 43 while the shutter 50 is in the first switching state is not emitted to other paths, and the resonance path 1 and the sub-amplification path 3 and 4 and the amplification output path 2 can be isolated.

  Although preferred embodiments of the present invention have been described above, the present invention is of course not limited to these embodiments. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention.

  The pulse fiber laser device of the present invention is optimal as a light source for laser processing, but is not limited thereto, and can be applied to all applications where high-power pulsed light is required.

DESCRIPTION OF SYMBOLS 1 ... Resonance path, 1a, 1b ... Sectional resonance path, 2 '... Output path, 2 ... Amplification output path, 3, 4 ... Sub-amplification path, 10, 20, 30, 40 ... Excitation light source, 11, 12, 36, 46... Highly reflective FBG as a reflection part, 13, 23, 33, 43... Amplifying optical fiber as an optical amplifier, 34 and 44... Wavelength conversion element, 26. …driver

Claims (8)

A first excitation light source;
A resonance path constituting a resonator including a first optical amplifier, and a resonance path through which pumping light from the first pumping light source is guided;
An optical path branching means disposed in the middle of the resonance path;
A wavelength conversion element connected to the resonance path via the optical path branching means, for converting a wavelength of light branched from the resonance path, a third optical amplifier, a third excitation light source, and a wavelength by the wavelength conversion element A sub-amplification path comprising a reflection part for reflecting the converted light;
An emission path connected to the resonance path via the optical path branching means and provided with an emission section;
Having
Furthermore, each section of the resonance path divided into two by the optical path branching means is a section resonance path,
The optical path branching unit emits light incident from one of the sectioned resonance paths to the sub-amplification path and transmits the light between the two sectioned resonance paths. The light path can be selectively switched to a second switching state in which incident light is emitted to the emission path.
The sub-amplification path amplifies the light branched from the resonance path by the optical path branching means and emits the light to the emission path,
The pulse fiber laser device, wherein the emission path emits light branched from the sub-amplification path by the optical path branching means. In the pulse fiber laser device according to claim 1,
Since the second optical amplifier and the second excitation light source are provided in the output path, the output path becomes an amplified output path that amplifies and outputs the light branched from the sub-amplification path by the optical path branch switch. Is composed of
The optical path branching unit emits light incident from one of the two divided resonance paths to the subamplification path and transmits the light between the two divided resonance paths. A pulse fiber laser device configured to selectively switch an optical path to a second switching state in which incident light is output to the amplification output path. In the pulse fiber laser device according to claim 1 or 2,
A plurality of the sub-amplification paths are connected to the optical path branching means,
Each of the sub-amplification paths is wavelength-converted by a third optical amplifier, a third excitation light source, a wavelength conversion element for converting the wavelength of light branched from the resonance path, and the wavelength conversion element. It is configured to include a reflection part that reflects light,
A first switching state in which the light path branching means transmits light between the two sectioned resonance paths; and light that has entered from one of the sectioned resonance paths is sub-amplified in one of the plurality of sub-amplification paths. And the light incident from each sub-amplification path is emitted to another sub-amplification path different from the sub-amplification path, and the light incident from the sub-amplification path different from the one sub-amplification path is A pulse fiber laser device configured to selectively switch an optical path between an emission path or a second switching state in which the light is emitted to the amplification emission path. An optical path branching means is provided in the resonance path that constitutes the resonator including the first optical amplifier and is in the middle of the resonance path to which the pumping light from the first pumping light source is guided. A sub-amplification path having a third optical amplifier, a third pumping light source, and a reflection part that reflects light converted in wavelength by the wavelength conversion element, and an emission path having an emission part,
Each part of the resonance path divided into two by the optical path branching means is a section resonance path,
In the state in which excitation light is injected into the first optical amplifier in the resonance path to generate laser light and the laser light resonates in the resonance path, path switching by the optical path branching means is performed 3 And one pulse of pulsed light is emitted from the emission path,
Laser light resonating in the resonance path is emitted to the sub-amplification path as pulse light by the first path switching and the second path switching among the three path switching in the optical path branching means. Then, the sub-amplification path is reciprocated at least once, and the pulse light that reciprocates in the sub-amplification path is emitted to the emission path by the third path switching among the three path switching in the optical path branching means. And emitting light from the emitting part. In the pulse light output control method according to claim 4,
By providing a second optical amplifier and a second excitation light source in the emission path, the emission path is used as an amplification emission path,
In the state in which excitation light is injected into the first optical amplifier in the resonance path to generate laser light and the laser light resonates in the resonance path, path switching by the optical path branching means is performed 3 And one pulse of pulsed light is emitted from the amplification emission path,
Laser light resonating in the resonance path is emitted to the sub-amplification path as pulse light by the first path switching and the second path switching among the three path switching in the optical path branching means. Then, the sub-amplification path is reciprocated at least once, and the pulse light reciprocating in the sub-amplification path is transferred to the amplification output path by the third path switching among the three path switching in the optical path branching means. A pulsed light output control method, characterized in that the light is emitted and emitted from the amplified emission path. In the pulse light output control method according to claim 4 or 5,
In addition to any one of the exit path and the amplified exit path (hereinafter referred to as (amplified) exit path) in the optical path branching means, the optical path branching means removes the resonance path from the resonance path. As sub-amplification paths for amplifying the branched light, a plurality of sub-amplification paths each including a third optical amplifier, a third pumping light source, and a reflection unit that reflects light wavelength-converted by the wavelength conversion element are provided. connection,
The number of sub-amplification paths is m (m is a natural number of 2 or more),
In the state in which excitation light is injected into the first optical amplifier in the resonance path to generate laser light and the laser light resonates in the resonance path, the path switching by the optical path branching means ( 2m + 1) times, one pulse of the pulsed light is emitted from the (amplification) emission path,
Of the (2m + 1) times of path switching by the optical path branching means, the laser light resonating in the resonance path by the first path switching and the second path switching is used as pulse light, and the plurality of sub-paths are switched. One of the amplification paths is emitted to the sub-amplification path, the sub-amplification path is reciprocated at least once, and the second to second switching is performed by switching from the third to the (2m) times of the (2m + 1) times of path switching. The pulse light incident from any one of the section resonance paths and the plurality of sub-amplification paths is emitted to a different sub-amplification path, and the sub-amplification path is reciprocated at least once, Of the 2m + 1) path switching operations, the (2m + 1) th switching operation causes the one sub-amplification path of the sub-amplifying path in addition to the operation up to the (2m) th operation. The pulse light incident from different sub amplifier path and (amplification) by emission to the emission path, the (amplified) pulsed light output control method for causing emitted from the emission path as the output pulsed light. In the pulse light output control method according to any one of claims 4 to 6,
When one pulse of pulsed light is emitted from the emission path or the amplified emission path,
The odd-numbered path switching holding time after the third time in the optical path branching means is controlled so that the odd-numbered path switching holding time after the third time is equal to or longer than the first path switching holding time. A pulse light output control method characterized by the above. In the pulse light output control method according to any one of claims 4 to 7,
When one pulse of pulsed light is emitted from the emission path or the amplified emission path,
The time interval for performing the path switching is the time from when the laser light is incident on the sub-amplification path during the path switching holding time until it is reflected by the reflector in the sub-amplification path and returns to the optical path branching means. A pulse light output control method characterized by controlling a path switching holding time and a path switching time interval so as to be equal.

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