JP2022002257A - Pulse laser light source device and rare-earth-doped fiber manufacturing method - Google Patents

Abstract

To provide a pulse laser light source device of which the entire energy efficiency is improved even while increasing output by an amplifier.SOLUTION: A seed laser element 11 provided in a seeder 1 is excited by light of a wavelength of 804 nm from a seeder excitation laser source 3, resonated by a resonator 10 consisting of an output mirror 12 and a SESAM 13, and oscillated with a wavelength of 1064 nm. The oscillated seed laser light is incident on an amplification element 21 which is excited by light of a wavelength of 975 nm from an amplification excitation laser source 22, and amplified by inductive emission. The seed laser element 11 is a neodymium-doped silica glass fiver, and the amplification element 21 is an ytterbium-doped silica glass fiber.SELECTED DRAWING: Figure 1

Description

The invention of this application relates to a pulsed laser light source device that emits pulsed laser light.

Pulsed laser light source devices that emit pulsed laser light are used in various applications. For example, a pulse laser light source device is used for various processing such as laser cutting and laser drilling. This is because in the case of a pulse laser, appropriate energy can be applied by adjusting the repetition frequency of the pulse, and it is easy to perform desired processing while avoiding damage to the object.

A typical example of such a pulse laser is a solid-state laser to which a rare earth material or a transition metal is added as a laser medium. The laser medium is added to a translucent material (hereinafter referred to as a host material). The host material to which the laser medium is added is formed into a fiber shape or a rod shape to form a laser element, and a resonator is provided to form a laser oscillator. Normally, the laser element is excited by a laser beam from an excitation laser source to oscillate a laser.

In such a solid-state light emitting pulse laser, a laser amplification configuration is often adopted in order to increase the output energy. When performing laser amplification, an amplification element made of the same material as the laser medium in laser oscillation is used. A laser beam from another excitation laser source is introduced into the amplification element to be excited, and the laser beam output from the laser resonator is incident on the amplification element and amplified by stimulated emission.

Japanese Patent No. 4919463 Japanese Patent No. 4979960

"Ablation-cooled material removal with ultrafast bursts of pulses", Can Kerse et al, Nature, Vol. 537, p84-89 "3.5-GHz intra-burst repetition rate ultrafast Yb-doped fiber laser", Can Kerse et al, Optics Communications 366 (2016), p404-409

In the above-mentioned solid-state laser, neodymium (Nd) and ytterbium (Yb) are often used as the laser medium. Of these, Nd has a larger stimulated emission cross section than Yb, but has some drawbacks. One is the problem when the concentration is increased. In order to increase the energy efficiency and increase the output, the amount of Nd and Yb added is increased, but in the case of Nd, a phenomenon called concentration quenching becomes remarkable. When the amount of Nd added is large, it is difficult to disperse the Nd atoms uniformly, so that the Nd atoms come close to each other and concentration quenching tends to occur.

The other is the problem of quantum deficiency. The quantum efficiency at the time of excitation of the stimulated emission level is 90% or more in the case of Yb, but it is about 76.1% in Nd because the quantum defect is large. Therefore, Nd is less energy efficient than Yb. Under these circumstances, Yb is often selected as the laser medium, and a configuration is often adopted in which the laser beam output from the Yb-added seeder is excited and amplified by the Yb-added amplification medium.

However, on the other hand, in the case of Yb, absorption is large at the amplifier and a large loss occurs. For this reason, it is devised to shift the oscillation wavelength to a wavelength with less absorption, but as a result, the cedar oscillates at a wavelength with a relatively small stimulated emission cross section, and the functionality as a light source cannot be enhanced. ..
The present invention has been made in consideration of such a technical problem of a pulsed laser light source device equipped with an amplifier, and is a pulse in which the overall energy efficiency is sufficiently ensured while enhancing the functionality as a light source. It is intended to provide a laser light source device.

In order to solve the above problems, the pulsed laser light source device of the present invention includes a seeder that outputs seed laser light and an amplifier that amplifies the seed laser light output from the seeder.
In this pulsed laser light source device, the seeder includes a seed laser element made of a host material to which a first rare earth material is added, and the amplifier is an amplification element made of a host material to which a second rare earth material is added. Includes.
Further, in the oscillation wavelength of the seed laser light output from the seeder, the first rare earth material is a material having a larger stimulated emission cross section than the second rare earth material.
In order to solve the above problems, the pulsed laser light source device of the present invention includes a seeder that outputs seed laser light and an amplifier that amplifies the seed laser light output from the seeder.
In this pulsed laser light source device, the seeder excites the seed laser element made of the host material to which the first rare earth material is added and the seed laser element to the level that induces and emits light of the oscillation wavelength. The amplifier includes an amplification element made of a host material to which a second rare earth material is added, and an amplification excitation laser source that excites the amplification element to a level that induces and emits light of the oscillation wavelength. The wavelength of the amplification excitation laser source is longer than the wavelength of the seeder excitation laser source.
In order to solve the above problems, the pulsed laser light source device of the present invention may have a configuration in which the quantum efficiency of the second rare earth material when inducing and emitting light having an oscillation wavelength is higher than that of the first rare earth material. ..
In order to solve the above problems, in the pulse laser light source device of the present invention, the first rare earth material is neodymium and the second rare earth material is ytterbium, or the first rare earth material is turium and the second. The rare earth material may be holmium, or the first rare earth material may be erbium and the second rare earth material may be holmium.
In order to solve the above problems, in the pulse laser light source device of the present invention, the seed laser element is a fiber having a host material to which the first rare earth material is added as a core, and the amplification element is a second rare earth material. It may have a configuration in which the fiber has a host material to which the laser is added as a core.
In order to solve the above problems, in the pulse laser light source device of the present invention, the seeder includes a resonator having a built-in laser element for seeding, and one of the mirrors constituting the resonator is a saturable mirror, which causes resonance. The instrument may have a configuration that achieves a Q-switched mode lock at the oscillation wavelength.
In order to solve the above problems, the pulsed laser light source device of the present invention may have a configuration in which the repetition frequency of the pulse output from the seeder is 1 GHz or more.
In order to solve the above problems, the pulsed laser light source device of the present invention may have a configuration in which a thinning unit for thinning out pulses from a pulse train is provided on an optical path between a seeder and an amplifier.
In order to solve the above problems, the pulsed laser light source device of the present invention may be for ablation.
In order to solve the above problems, in the pulsed laser light source device of the present invention, the host material may be silica glass.
In order to solve the above problems, the method for producing a rare earth-added fiber of the present invention is a method for producing a rare earth-added fiber as a stimulated emission element of light.
A step of obtaining a rare earth-added molded product by mixing and firing a zeolite powder to which a rare earth material is fixed and a host material powder, and
A step to obtain a columnar core base material by cutting out from a rare earth-added molded body and polishing it.
The step of inserting the core base material into the circular tubular clad base material to obtain the fiber base material,
It has a step of drawing a line while heating the fiber base material to obtain a rare earth-added fiber.
In order to solve the above problems, the host material may be silica glass in the method for producing a rare earth-added fiber of the present invention.

As described below, according to the pulsed laser light source device of the present invention, different rare earth materials are selected for the seed laser element and the amplification element, and the seed laser element has a larger stimulated emission cross section than the amplification element. Since it has, the function of the light source is enhanced. Further, since a rare earth material having little absorption at the oscillation wavelength can be selected for the amplification element, it is possible to suppress a decrease in efficiency of the light source as a whole.
Further, according to the pulsed laser light source device of the present invention, since the wavelength of the excitation laser source for amplification is longer than the wavelength of the excitation laser source for cedar, stable performance can be achieved at low cost.
Further, if a rare earth material having a higher quantum efficiency than the rare earth material in the laser element for seeds is adopted for the amplification element, the efficiency at the time of amplification becomes high, so that the above effect becomes higher.
Further, the laser element for seed is a fiber having a host material to which the first rare earth material is added as a core, and the amplification element is a fiber having a host material to which a second rare earth material is added as a core. Then, it is possible to stably irradiate a high-quality pulsed laser beam regardless of the environment, and it becomes easy to irradiate the object in a condensed state of minute spots.
In addition, the seeder includes a resonator with a built-in laser element for seeding, one of the mirrors that make up the resonator is a saturable mirror, and the resonator achieves Q-switch mode lock at the oscillation wavelength. In a certain configuration, it is possible to output a pulse train having a high repetition frequency without any loss as in the case of repeating demultiplexing and merging, and without problems such as deterioration of processing accuracy due to intensity fluctuation between pulses.
Further, in the configuration provided with the thinning unit for thinning out the pulse from the pulse train, it is easy to irradiate the pulse train with the optimum energy for the object, which is particularly suitable for ablation.
Further, according to a manufacturing method for obtaining a rare earth-added fiber from a core base material obtained by mixing and firing a zeolite powder to which a rare earth material is fixed and a host material powder, a rare earth-added fiber having good optical characteristics can be easily obtained. Obtainable.
Further, in the configuration in which the host material is silica glass, the performance is stable at low cost, and high quality pulsed laser light can be stably obtained regardless of the environment such as temperature and humidity.

It is a schematic diagram of the pulse laser light source apparatus which concerns on embodiment. It is the schematic which showed the stimulated emission cross section and absorption cross section of the silica glass fiber which added Yb. It is the schematic which showed the stimulated emission cross section and absorption cross section of Nd added silica glass fiber. It is a figure which showed typically the laser excitation in the configuration of an embodiment. It is the schematic which showed the manufacturing method of the laser element for a seed provided in the pulse laser light source apparatus of embodiment.

Hereinafter, embodiments (embodiments) for carrying out the invention of this application will be described.
FIG. 1 is a schematic view of a pulsed laser light source device according to an embodiment. The pulsed laser light source device of the embodiment includes a seeder 1 that outputs seed laser light and an amplifier 2 that amplifies the seed laser light output from the seeder 1. The seeder 1 includes a seed laser device 11 that is excited to a level (laser level) during stimulated emission.

In this embodiment, the seed laser element 11 is configured to be excited by laser light, and a seeder excitation laser source 3 is provided. As the excitation laser source 3 for the seeder, a continuously oscillating semiconductor laser is used.
As shown in FIG. 1, the seeder coupling fiber 42 is provided for the seeder 1 via the lens group 41. The coupling fiber 42 for a seeder is provided with a coupling element 4 for a seeder such as a WDM (Wavelength Division Multiplexing) coupler, and the laser light from the excitation laser source 3 for the seeder passes through the coupling element 4 for the seeder and the output mirror 12. It is configured to be incident on the seed laser element 11 in the seeder 1 to excite the seed laser element 11.

As shown in an enlarged manner in FIG. 1, the seed laser element 11 is in the form of a fiber composed of a core 111 and a clad 112, and has a structure covered with a ferrule 113 for protection and reinforcement. Since the length is about 10 to 100 mm, it can be said to be a short fibrous member. The core 111 of the seed laser element 11 contains a rare earth material as a laser medium and is a substantially laser element. In this embodiment, the rare earth material in the seed laser device 11 is neodymium (Nd), and silica glass is selected as the host material. That is, the core 111 is made of Nd-added silica glass. Further, the clad 112 is silica glass without addition of Nd. The diameter of the core 111 in the seed laser element 11 is about 1 to 20 μm, and the total diameter including the clad 112 is about 80 to 1000 μm. The propagation mode of the seed laser element 11 which is a fiber is a single mode (single mode fiber).

The seeder 1 incorporating such a seed laser element 11 includes a resonator 10. The resonator 10 achieves both resonance and pulse oscillation, and in this embodiment, the Q-switch mode lock is performed. More specifically, in the resonator 10 of the seeder 1, a saturable mirror (SAM) is used. In this embodiment, among the SAMs, the semiconductor saturable mirror (SESAM) 13 is particularly used.
The SESAM 13 is one of the mirrors constituting the resonator 10. The other mirror constituting the resonator 10 is an output mirror 12. The output mirror 12 is, for example, a mirror that reflects 30 to 99%, and is a mirror that transmits the rest and outputs the mirror.

As shown enlarged in FIG. 1, SESAM 13 is a mirror having a structure in which a saturable absorber 132 is laminated on the incident side of a DBR (Distributed Bragg Reflector) 131, and SESAM 13 is a saturable absorption mirror. The body 132 is made of a semiconductor such as InGaAs. In the SESAM 13, the saturable absorber 132 has a quantum well structure, and when the light reaches a certain intensity, the absorption is saturated, and more light is transmitted to reach the DBR 131. The DBR131 has a structure (for example, GaAs / AlAs) in which layers having a thickness of 1/4 wavelength and different refractive indexes are laminated, and particularly only light of a specific wavelength by utilizing Bragg reflection and light interference. It reflects strongly.

When the laser beam (CW) from the seeder excitation laser source 3 is introduced into the seed laser element 11, the rare earth material (laser medium) in the seed laser element 11 is excited, and a population inversion occurs to induce light. It is released. At this time, as is well known, a plurality of vertical mode standing waves may be generated in the resonator 10, but when SESAM 13 is reached in a state where the phases are not aligned, the light is weak due to interference, so that the saturable absorber 132 Is absorbed by. In the state where the phases are aligned, it becomes stronger due to interference, so that it passes through the saturable absorber 132 due to the saturation of absorption, reaches the DBR 131, and is reflected. That is, a particularly strong resonance occurs when the phases are aligned, stimulated emission occurs at once, and laser oscillation in the Q-switch mode lock is achieved. The DBR131 is designed and manufactured so as to selectively reflect light having a set oscillation wavelength.

On the other hand, as shown in FIG. 1, the amplifier 2 includes an amplification element 21, an amplification excitation laser source 22, an amplification coupling fiber 23, and the like. The amplification coupling fiber 23 is provided with an amplification coupling element 24 such as a WDM coupler. Laser light from the amplification excitation laser source 22 is introduced into the amplification element 21 via the amplification coupling element 24. It is configured to excite the amplification element 21.

The amplification element 21 is an element that amplifies the seed laser light output from the seeder 1 by being stimulated by the amplification excitation laser light from the amplification excitation laser source 22 and performing stimulated emission. In this embodiment, the amplification element 21 is formed of a translucent material to which a rare earth material is added, similarly to the laser element 11 for seeding.
More specifically, the amplification element 21 is made of silica glass to which ytterbium (Yb) is added. The shape is fibrous. That is, the Yb-added silica glass fiber is used as the amplification element 21.

When an amplifier is provided in the subsequent stage of the seeder as in the embodiment, since the same stimulated emission process is usually used, an element made of the same material as the laser element in the cedar is used as the amplification element. However, in this embodiment, contrary to the conventional wisdom, an element made of a different material is intentionally used as the amplification element 21, and the Yb-added silica glass fiber is used as described above.

The use of an element to which a rare earth material different from the rare earth material in the seed laser element 11 is added as the amplification element 21 is the result of diligent research by the inventor who intends to improve the functionality as a light source. This point will be described below.
As described above, Nd and Yb are used in the laser device to which the rare earth material is added, but Yb is often adopted due to the problems of concentration quenching and quantum deficiency. FIG. 2 is a schematic view showing a stimulated emission cross section and an absorption cross section of Yb-added silica glass fiber. FIG. 2 (1) shows a stimulated emission cross section, and FIG. 2 (2) shows an absorption cross section.

As shown in FIG. 2 (1), in the case of Yb, since the stimulated emission cross section has a peak near 1030 nm, 1030 nm is often used as the oscillation wavelength. In this case, in the configuration in which the same rare earth material is used for the seed laser element 11 and the amplification element 21, Yb-added silica glass is also used for the amplification element 21, but as shown in FIG. 2 (2), Yb addition is used. Silica glass causes some absorption even at 1030 nm. This absorption causes a loss, which reduces energy efficiency. In addition, cooling means is required to suppress heat generation due to absorption, and further energy is required, which reduces efficiency.

In order to avoid these problems, it is conceivable to shift the oscillation wavelength to 1080 nm where the absorption becomes almost zero, and design and manufacture the seeder so as to oscillate at 1080 nm. However, in this configuration, since the laser oscillation is attempted at a place where the stimulated emission cross section is small, the laser oscillation threshold becomes high and the original function as a seeder deteriorates.
Therefore, contrary to common sense, the inventors have come up with the idea that the material of the seed laser element 11 and the material of the amplification element 21 are intentionally different materials. In this embodiment, Nd is used for the seed laser element 11 with priority given to the stimulated emission cross section, and Yb, which is excellent in terms of quantum efficiency, is used for the amplification element 21.

FIG. 3 is a schematic view showing a stimulated emission cross section and an absorption cross section of Nd-added silica glass fiber. Similarly, FIG. 3 (1) shows a stimulated emission cross section, and FIG. 3 (2) shows an absorption cross section.
In this embodiment, 1064 nm is selected as the oscillation wavelength. That is, the seeder 1 including SESAM 13 is configured to oscillate at 1064 nm. As shown in FIG. 2 (2), the absorption of the Yb-added silica glass fiber is small at 1064 nm and is almost zero. As shown in FIG. 3 (1), the stimulated emission cross section of the Nd-added silica glass at 1064 nm greatly exceeds ^{1.0 × 10 -20} cm ^2. On the other hand, as shown in FIG. 2 (1), the stimulated emission cross-sectional area of the Yb-added silica glass at 1064 nm is ^{about 0.2 × 10 -20} cm ² , and the Nd-added silica glass fiber is compared with the Yb-added silica glass fiber. It has a very large stimulated emission cross section at 1064 nm. That is, in the seed laser element 11, Nd is adopted with priority given to a large stimulated emission cross section.

In a configuration where an excitation laser is used for both laser oscillation and amplification, it is also important to reduce the amount of pumping (energy amount). The configuration of the embodiment also has an advantage in this respect. This point will be described with reference to FIG. FIG. 4 is a diagram schematically showing laser excitation in the configuration of the embodiment.

In the embodiment, in the seed laser element 11 which is an Nd-added silica glass fiber, _{pumping is performed from the ground level E 0} by the seeder excitation laser light, and Nd is excited to the excitation level E ₁ . Nd, there is a level of _{E 2} lower than _{E 1} level, the Nd excited to _{E 1,} fell in _{E 2} by a non-radiative transition, and further incident light 1064nm from the level _{E 2} fall in _{E 3} close to the ground level _{E 0.} At this time, light of 1064 nm is stimulated and emitted. Then, Nd drops from E _{3 to E 0} due to the non-radiative transition. The excitation light that excites the ground level E ₀ to E ₁ has a wavelength of 804 nm.
On the other hand, the Yb-doped silica glass fiber a is amplifying element 21, there is an energy level _{E 2} 'for emitting light of 1064nm wavelength. Similarly, Yb fell _{'E 2} by non-radiative transitions after being _excited' E _1, to stimulated emission light of 1064nm when falling to the ground level E _{0 'therefrom.} The _{'E 1 from'} ground level E _0, is excited by the excitation laser light.

What is important here is the difference Delta] E of the energy level from _{E 0} to _{E 1,} 'Comparing the, case of a combination of Nd and Yb, ΔE>ΔE' difference Delta] E of the _{'E 1} from' _{E 0} and It is a point that has become. That is, the pumping amount in the case of laser amplification can be made smaller than the pumping amount in the case of laser oscillation. In fact, in this embodiment, a semiconductor laser having a wavelength of 975 nm is used as the amplification excitation laser source 22, and a laser diode having a wavelength longer than that of the seeder excitation laser source 3 is used.

Generally, the longer the wavelength of the laser source, the easier it is to oscillate, the more stable it is, and the cheaper it is. Therefore, it is significant that the configuration of the embodiment using the excitation laser having a long wavelength due to the small pumping amount can achieve stable performance at low cost. Further, in the amplifier 2, it is necessary to lengthen the optical path length of the amplification element 21 in order to increase the amplification factor, and therefore, the amplification excitation laser source 22 also has a high output. In this sense as well, the one with a long wavelength is preferable.

On the other hand, in the seeder 1, it is prioritized to oscillate the laser, and as long as the oscillation threshold is exceeded, the output of the pumped laser source 3 for the seeder does not need to be so large. Therefore, there is no problem even if a laser source having a large pumping amount and a short wavelength is used. The configuration of the above embodiment is an optimized configuration in consideration of these circumstances.
As can be seen from FIG. 4, the above point can be regarded as a difference with respect to the oscillation wavelength, and the wavelength of the amplification excitation laser source 22 is expressed as having a smaller difference with respect to the oscillation wavelength than the seeder excitation laser source 3. You can also.

The pulsed laser light source device of the embodiment also has a great feature in the method of manufacturing the laser element 11 for seeds, which is an Nd-added silica glass fiber. This point will be described below.
FIG. 5 is a schematic view showing a method of manufacturing the seed laser element 11 included in the pulsed laser light source device of the embodiment.

In this embodiment, the seed laser element 11 is a fiber composed of a core 111 and a clad 112, and the seeder 1 is a kind of fiber laser oscillator. The seed laser element 11 is suitably manufactured by drawing using a base material obtained by the zeolite method.
Specifically, as shown in FIG. 5, the Nd ion-exchanged zeolite powder 61 and the silica glass powder 62 are uniformly mixed, placed in a container, heated, pressurized and fired to obtain a fired body. The fired body is further heated in vacuum to obtain a glass molded body, and an Nd-added glass molded body 63 is obtained.

Then, the Nd-added glass molded body 63 is cut out and ground to obtain a cylindrical (or linear cross-section) core base material 64 having a diameter of about 1 to 10 mm. The core base material 64 is inserted into a silica tube (clad base material) 65 having a circular cross section to form a fiber base material, which is heated and drawn into a fiber shape. By cutting the obtained fiber 66 to a predetermined length, the seed laser element 11 according to the embodiment can be obtained. The cross-sectional shape of the core base material 64 does not have to be circular, and the clad base material 65 may be an annular shape other than a circular tube.

In the above manufacturing method, the Nd-added glass molded body 63 obtained by the zeolite method is used as the core base material 64, but the manufacturing of the Nd-added glass molded body by the zeolite method is described in Patent Document 1 and Patent Document 2. Since it is disclosed in, it can be referred to.
Conventionally, in the case of producing silica glass fiber to which a rare earth material such as Nd is added, a method of heating a silica glass wire and immersing it in a solution containing Nd to infiltrate Nd from the outer surface into the inside is adopted. However, with such a method, it is difficult to uniformly disperse Nd, and a product having good optical characteristics cannot be obtained. According to the method of the embodiment, Nd-added silica glass fiber having good optical properties can be easily obtained.

Next, the feature points of other parts of the pulsed laser light source device of the embodiment will be described.
As shown in FIG. 1, in this embodiment, a thinning unit 5 is provided between the seeder 1 and the amplifier 2. The thinning unit 5 is a mechanism for adjusting the irradiation energy by periodically thinning the pulse from the pulse train of the short pulse and high-repetition laser light oscillated from the seeder 1.

Specifically, the thinning unit 5 has a mechanism using an AO modulator (acousto-optic modulator) 51. The AO modulator 51 is provided with an RF driver 52. Like the acousto-optics Q-switch, the RF driver 52 is a driver that intermittently inputs an RF signal to the AO modulator 51 to operate it. When the RF signal is on, the pulsed light is diffracted and the primary diffracted light travels in the optical path. When the RF signal is off, only the 0th order light is emitted, and the pulsed light is out of the optical path. Therefore, the pulse train is thinned out by turning the RF signal on and off.

Since the light propagates in space on the incident side and the emitted side of the AO modulator 51, the incident side lens 53 and the exit side lens 54 are arranged. The light from the seeder coupling fiber 42 becomes a parallel beam (or is focused) by the incident side lens 53, passes through the AO modulator 51, and then is focused by the exit side lens 54 to the amplification element 21. It is configured to be incident.

The operation of the pulsed laser light source device of the embodiment according to the above configuration will be described below.
First, the seeder excitation laser source 3 operates, and the seeder excitation laser light is introduced into the seed laser element 11 via the seeder coupler 4. As a result, Nd in the seed laser element 11 is excited, a population inversion occurs, and light in the 1064 nm band is induced and emitted. Light having a slightly different wavelength in the longitudinal mode has a particularly high intensity due to interference at a portion where the positions of the peaks are aligned, resonates between the SESAM 13 and the output mirror 12, and laser oscillates by the Q-switch mode lock. Laser oscillation is pulse oscillation with a repeating period according to the resonator length. The pulse train oscillated from the seeder 1 is shown as P1 in FIG.

The pulse train P1 of the oscillated laser light is thinned out by the thinning unit 5 to become P2 as shown in the lower side of FIG. The output waveform (ultrasonic output control waveform) of the RF driver 52 that performs digital modulation at this time is shown as D. After that, the pulse train P2 reaches the amplifier 2 and is amplified to become the pulse train P3, which is emitted from the amplification coupling fiber 23.

According to the pulsed laser light source device of the embodiment related to such an operation, Nd is used as the laser medium in the seed laser element 11, and Yb is used as the amplification medium in the amplification element 21, so that the function as a light source is used. It is a light source device that is comparable in terms of overall efficiency while improving its performance. That is, the seed laser element 11 emits sufficient seed laser light even with a short length due to the large stimulated emission cross section, and the amplification element 22 amplifies the seed laser light with high quantum efficiency and a small absorption cross section. There is. Therefore, it is possible to emit pulsed laser light having a high repetition frequency, and the efficiency at that time can be sufficiently sufficient.

The fact that the seed laser element 11 and the amplification element 21 are fibers means that in addition to being able to efficiently obtain high-quality pulsed laser light, it is easy to irradiate an object in a state of being focused on a minute spot. There is an advantage. That is, since the seed laser light and each excitation laser light are introduced into a narrow space called the core and stimulated and stimulated emission are performed in a confined state, high-quality pulsed laser light is efficiently output.
In addition, since the host material is silica glass in this embodiment, it is inexpensive and has stable performance, and high-quality pulsed laser light can be stably obtained regardless of the environment such as temperature and humidity.
However, in carrying out the present invention, the host material does not have to be silica glass, and other host materials such as YAG and fluoride glass can be appropriately selected and used.
The fact that the seed laser element 11 is a single mode fiber has an advantage that spatial mode control such as mode lock becomes easy.

Further, in the pulse laser light source device of the embodiment, since the pulse oscillation is performed by using the Q-switch mode lock in the resonator 10 including the SESAM 13, energy efficiency can be increased even when outputting a pulse train having a high repetition frequency. ing. This point will be described below.

One of the important applications of the pulsed laser light source device as in the embodiment is ablation. The term "ablation" is widely used in the medical field such as treatment of affected areas, but generally the surface of the material is decomposed by laser irradiation, resulting in cutting, evaporation, peeling or foreign body removal, etc. Means the process that takes place. Therefore, the pulse laser light source device is used for ablation not only in the medical field but also in the industrial field such as laser processing.

It is known that such a pulsed laser light source device for ablation may be able to be processed without damaging the object by increasing the pulse repetition frequency. For example, in Non-Patent Document 1, in the case of laser irradiation for dental treatment, a pulse of 4 μJ per pulse is 1.7 GHz as compared with a case of irradiating a pulse of 100 μJ per pulse at a repetition frequency of 1 kHz. It has been reported that irradiation without a set repetition frequency of 1 kHz can be performed without carbonization or cracks by irradiating an irradiation set with a repetition frequency at a set repetition frequency of 1 kHz.

As a method for realizing such a high repetition frequency (1 GHz or more), Non-Patent Document 2 discloses a technique for increasing the repetition frequency using division and delay. Here, the 108 MHz laser light is divided into two (demultiplexed), one laser light is delayed with respect to the other laser light by a pulse period of 1/2 minute, and then the two are combined, and this is 5 By repeating this time, the frequency is increased to 3.46 GHz.

However, in the method of Non-Patent Document 2, since the peak intensity of the pulse is halved each time the demultiplexing is performed, the peak of each pulse having a high repetition frequency is reduced to 1/32 of the original. Further, since a loss occurs each time the demultiplexing and the combined wave occur, the peak intensity is further lowered, and a large loss that cannot be ignored as a whole occurs. For example, if there is a loss of 3 dB for each demultiplexing wave, and if there is originally 100 μJ of energy per pulse, the total loss is 18 dB, which is reduced to 0.25 μJ.

As a method of realizing a high repetition frequency exceeding 1 GHz, it is conceivable to divert a semiconductor laser for communication in the 10 GHz band. However, since the wavelength of a semiconductor laser for communication is as long as 1.55 μm, the efficiency at the time of amplification is poor, and since the output is weak, noise is also amplified, and there is a problem that the intensity fluctuation between pulses becomes large. Intensity fluctuations between pulses bring about problems such as a decrease in machining accuracy and damage to an object.

On the other hand, in the pulsed laser light source device of the embodiment, since the Q-switch mode lock in the seeder 1 including SESAM 13 is used, there is no loss as in the case of repeating demultiplexing and merging, and processing due to intensity fluctuation between pulses is not performed. There is no problem such as deterioration of accuracy. In the state where the absorption by the saturable absorber 132 in SESAM 13 is not saturated, the stimulated emission has not started, but during this period, the laser medium (rare earth material) is excited to the laser level one after another to generate energy. There is no loss because it is accumulated and stimulated emission occurs at once when the absorption reaches saturation (the stage where the overlapping part of the mountain in the vertical mode passes) and the energy is discharged.

In the embodiment, the resonator length in the seeder 1 may be made variable so that the repetition frequency can be adjusted. As described above, one pulse of laser oscillation occurs when the peak and the overlapping portion of the vertical mode pass through the seed laser element 11 once. Therefore, if the resonator length is changed, the interval in one passage is changed. The length of is changed. That is, the repetition frequency of the pulse is changed. Specifically, for example, a precision position adjustment such as a mechanism using a piezo element is provided on either the SESAM 13 or the output mirror 12 so that the position can be changed. The SESAM 13 and / or the output mirror 12 may be in contact with the seed laser element 11, but are usually arranged in a separated state.

In the above embodiment, Nd is used as the laser medium in the seed laser element 11, and Yb is used as the amplification medium in the amplification element 21, but these are examples of rare earth materials. In addition to this, there are combinations of rare earth materials that can be adopted in the present invention. For example, thulium (Tm) and erbium (Er) can have a larger stimulated emission cross section than holmium (Ho). Therefore, a combination in which Tm-added silica glass is used for the seed laser element 11 and Ho-added silica glass is used for the amplification element 21, and Er-added silica glass is used for the seed laser element 11, and the amplification element 21 is used. There may be a combination that employs Ho-added silica glass.

Further, in the configuration in which the excitation laser source is used in both the seeder 1 and the amplifier 2, the energy (level difference) when the seeder excitation laser source 3 excites the seed laser element 11 to the laser level is amplified. There may be a combination other than the above combination of Nd and Yb in which the energy required by the excitation laser source 22 for exciting the amplification element 21 to the laser level is smaller. By adopting such a combination, a pulsed laser light source device having a large amplification factor (and therefore high output) can be easily configured.

In the above description, an example of the use of ablation in the medical field has been taken up, but ablation is performed not only in the medical field but also in various processing (laser processing). Therefore, the pulsed laser light source device of the embodiment can be used for various processing involving ablation.
Further, in the above embodiment, the thinning unit 5 using the AO modulator 51 is adopted, but it can be appropriately changed to another configuration such as one adopting a mechanical mechanism such as a shutter.

It should be noted that thinning out the pulse train is not essential in the present invention, and the object may be irradiated without thinning out.
Further, as the coupling element, in addition to WDM, various couplers such as a planar waveguide can be used, and a spatial coupling element such as a half mirror may be used.
Further, it is not essential to use a fiber for the optical path from the seeder 1 to the amplifier 2, and if necessary, a lens or a mirror may be arranged to guide the light in space.

Further, although SESAM 13 is used in the seeder 1, it is not essential to use the SESAM 13, and it is possible that the seeder 1 is configured by using an optical element of another reflection system. That is, another SAM using a saturable absorber other than the semiconductor may be used, or another reflecting element such as an FBG (Fiber Bragg Grating) may be used to configure the seeder 1.

As a configuration for realizing the Q-switch mode lock, in addition to the case of using the SAM, a configuration of performing the active mode lock using an electro-optical modulator such as a Pockels cell, an AO modulator, or the like may be adopted. .. However, in the case of the configuration in which the passive mode lock is performed using the SAM as described above, it is easy to manufacture and adjust, which is suitable in this respect.
Further, in the configuration of the embodiment, the seed laser element 11 and the seeder coupling fiber 42 may be fused via the output mirror 12 without using the lens group 41. The same applies to the thinning unit 5, and when a fiber coupling type AO modulator is used, the lenses 53 and 54 may not be used because the fibers are fused to each other.

Hereinafter, examples belonging to the above embodiment will be described.
First, a silica glass molded body in which 1.2% by weight of Nd was added was produced by a zeolite method, and a columnar shape having a diameter of 3 mm was formed by cutting and grinding. This was inserted into a silica glass circular tube and used as a base material, and was drawn with a drawing device so as to have an outer diameter (diameter) of 125 μm to obtain Nd-added silica glass fiber.

This fiber was cut to a length of 60 mm, both ends were polished, and then coated with an antireflection film or the like to obtain a seed laser element 11. The seed laser element 11 was placed in a resonator 10 using SESAM 13 manufactured so as to resonate at 1064 nm.
As the amplifier 2, a Yb-added silica glass fiber manufactured by Nufern of the United States (East Granby, Connecticut, 7 Airport Park Road East Granby, CT) is used with a length of 3 m, and the excitation laser source 22 for amplification is used. A semiconductor laser having a wavelength of 975 nm was used.

When the pulsed laser light source device configured in this way was operated and its output was measured with an optical spectrum analyzer, it was confirmed that the pulse laser light source device oscillated at a wavelength of 1064 nm. Moreover, when the frequency was repeatedly confirmed with an RF spectrum analyzer, it was 2.7 GHz.
When the output was measured with a laser power meter, it was 0.15 mW at the time of the output of the seeder 1, and 22.3 mW as the output of the amplifier 2. Therefore, it was confirmed that the amplification factor by the amplifier 2 was 150.

1 Cedar 10 Resonator 11 Laser element 12 Output mirror 13 SESAM
131 DBR
132 Saturable absorber 2 Amplifier 21 Amplifier 21 Amplification element 22 Excitation laser source for amplification 3 Excitation laser source for seeder 4 Coupling element for seeder 5 Thinning unit 51 AO modulator

Claims (12)

A pulsed laser light source device including a seeder that outputs seed laser light and an amplifier that amplifies the seed laser light output from the seeder.
The seeder contains a laser element for seeding, which consists of a host material to which the first rare earth material has been added.
The amplifier contains an amplification element consisting of a host material to which a second rare earth material has been added.
A pulsed laser light source device characterized in that the first rare earth material has a larger stimulated emission cross-sectional area than the second rare earth material at the oscillation wavelength of the seed laser light output from the seeder. A pulsed laser light source device including a seeder that outputs seed laser light and an amplifier that amplifies the seed laser light output from the seeder.
The seeder includes a seed laser element made of a host material to which a first rare earth material is added, and a seeder excitation laser source that excites the seed laser element to a level that induces and emits light of oscillation wavelength. ,
The amplifier includes an amplification element made of a host material to which a second rare earth material is added, and an amplification excitation laser source that excites the amplification element to a level that induces and emits light of an oscillation wavelength.
A pulsed laser light source device characterized in that the wavelength of the excitation laser source for amplification is longer than the wavelength of the excitation laser source for cedar. The pulsed laser light source device according to claim 1 or 2, wherein the quantum efficiency of the second rare earth material when stimulated emission of light having an oscillation wavelength is higher than that of the first rare earth material. The first rare earth material is neodymium and the second rare earth material is ytterbium, the first rare earth material is turium and the second rare earth material is holmium, or the first. The pulse laser light source device according to any one of claims 1 to 3, wherein the rare earth material is erbium and the second rare earth material is holmium. The seed laser element is a fiber having a host material to which the first rare earth material is added as a core.
The pulse laser light source device according to any one of claims 1 to 4, wherein the amplification element is a fiber having a host material to which a second rare earth material is added as a core. The seeder includes a resonator having a built-in laser element for seeding.
The pulse laser according to any one of claims 1 to 5, wherein one mirror constituting the resonator is a saturable mirror, and the resonator achieves Q-switch mode lock at the oscillation wavelength. Light source device. The pulse laser light source device according to claim 6, wherein the repetition frequency of the pulse output from the seeder is 1 GHz or more. The pulse laser light source device according to any one of claims 1 to 7, wherein a thinning unit for thinning a pulse from a pulse train is provided on an optical path between the seeder and the amplifier. The pulsed laser light source device according to claim 7 or 8, characterized in that it is for ablation. The pulsed laser light source device according to any one of claims 1 to 9, wherein the host material is silica glass. It is a rare earth-added fiber manufacturing method for manufacturing a rare earth-added fiber as a stimulated emission element of light.
A step of obtaining a rare earth-added molded product by mixing and firing a zeolite powder to which a rare earth material is fixed and a host material powder, and
A step to obtain a columnar core base material by cutting out from a rare earth-added molded body and polishing it.
The step of inserting the core base material into the tubular clad base material to obtain the fiber base material,
A method for producing a rare earth-added fiber, which comprises a step of drawing a line while heating a fiber base material to obtain a rare earth-added fiber. The method for producing a rare earth-added fiber according to claim 11, wherein the host material powder is a silica powder, which is a method for producing a rare earth-added silica glass fiber.

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