JP6420726B2 - Laser amplification system - Google Patents

Description

  The present invention relates to a laser amplification system.

  There are various amplification methods in the laser amplification system. As one of the amplification methods, an optical excitation method in which laser light is amplified using excitation light is known. In the optical excitation method, for example, the laser gain medium is irradiated with excitation light and laser light.

  The excitation light is used as an energy source for amplifying the laser light. When a part of the excitation light enters the laser gain medium, it is absorbed by the laser gain medium. When a part of the pumping light is absorbed by the laser gain medium, the laser gain medium is in an excited state. The excited laser gain medium gives energy to the laser light by interacting with the laser light.

  However, not all of the excitation light incident on the laser gain medium is absorbed by the laser gain medium. The excitation light that is not absorbed by the laser gain medium passes through the laser gain medium without contributing to the amplification of the laser light.

  Patent Document 1 discloses the following laser system as one method for effectively utilizing the excitation light transmitted through the laser gain medium. The laser system disclosed in Patent Document 1 includes an excitation source laser, a main laser, and a feedback path. The excitation light output from the excitation source laser is incident on the main laser. The transmitted light that has passed through the main laser returns to the excitation source laser via the feedback path.

JP-A-1-95580

  An object of the present invention is to provide a laser amplification system capable of effectively utilizing excitation light transmitted through a laser gain medium.

  Hereinafter, means for solving the problem will be described using the reference numerals used in the “DETAILED DESCRIPTION OF THE INVENTION”. These symbols are added in order to clarify the correspondence between the description of “Claims” and “Mode for Carrying Out the Invention”. These symbols are not used for interpreting the technical scope of the invention described in “Claims”.

The laser amplification system in the embodiment is:
An excitation light source (1);
A laser gain medium (2) to which excitation light (EL) output from the excitation light source is supplied;
An excitation light supply path (OP _EL ) disposed between the excitation light source and the laser gain medium;
A feedback path (OP _RE ) through which the excitation light transmitted through the laser gain medium returns to the laser gain medium as feedback light (EL _RE );
An optical property converter (3) disposed in the return path and changing an optical property of the feedback light;
An excitation light combiner (4) arranged in the excitation light supply path, for combining the excitation light output from the excitation light source and the feedback light whose optical characteristics have been changed by the optical characteristic converter; Have.

The optical property converter may include a light polarization element (30) for converting the polarization state of the feedback light from the first polarization state to the second polarization state.
The excitation light combiner may include a first optical element (40).
The first optical element (40)
Transmitting one of the excitation light in the first polarization state output from the excitation light source and the feedback light in the second polarization state converted by the light polarization element;
One of the excitation light in the first polarization state output from the excitation light source and the feedback light in the second polarization state converted by the light polarization element may be reflected.

The optical property converter may include a wavelength conversion element (31) that converts the wavelength of the feedback light from a first wavelength to a second wavelength.
The excitation light combiner may include a second optical element (41).
The second optical element is
Transmitting one of the excitation light of the first wavelength output from the excitation light source and the feedback light of the second wavelength converted by the wavelength conversion element;
One of the excitation light having the first wavelength output from the excitation light source and the feedback light having the second wavelength converted by the wavelength conversion element may be reflected.

The laser amplification system includes:
A first polarization maintaining fiber (5 ₁ ) disposed in the excitation light supply path;
A first optical lens (6 ₁ ) disposed between the excitation light source and the optical property converter, for introducing the excitation light output from the excitation light source into the first polarization maintaining fiber; May further be included.

The laser amplification system includes:
The second polarization maintaining fiber which is arranged in the feedback path (5 _2),
And a second optical lens (6 ₂ ) for introducing the feedback light as excitation light transmitted through the laser gain medium into the second polarization maintaining fiber.

The optical property converter may be a half-wave plate.
The excitation light combiner may be a polarizer.

  Provided is a laser amplification system capable of effectively utilizing excitation light transmitted through a laser gain medium.

FIG. 1 is a schematic diagram for explaining excitation light transmitted through a laser gain medium in the optical excitation method. FIG. 2 is a block diagram showing an example of a laser amplification system to which the laser gain medium shown in FIG. 1 is applied. FIG. 3 is a block diagram illustrating a configuration example of the laser amplification system SYS1. FIG. 4 is a block diagram of the laser amplification system SYS1 focusing on the propagation path of the excitation light. FIG. 5A is a block diagram showing the laser amplification system SYS1 when the feedback light EL _RE passes through the feedback path OP _RE for the first time. FIG. 5B is a block diagram showing the laser amplification system SYS1 when the feedback light EL _RE passes through the feedback path OP _RE a second time. FIG. 6 is a schematic diagram illustrating a specific configuration example of the laser amplification system SYS1. FIG. 7 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1a. FIG. 8 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1b. FIG. 9 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1c. FIG. 10 is a block diagram of the laser amplification system SYS1d focusing on the propagation path of the excitation light. FIG. 11 is a block diagram of the laser amplification system SYS1e focusing on the propagation path of the excitation light. FIG. 12 is a block diagram illustrating a configuration example of a laser system SYS2 to which the laser amplification system SYS1 is applied. FIG. 13 is a block diagram illustrating a configuration example of a laser amplification system SYS1f used as an optical resonator.

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

1. Matters Recognized by the Inventor First, the excitation light transmitted through the laser gain medium will be described. FIG. 1 is a schematic diagram for explaining excitation light transmitted through a laser gain medium in the optical excitation method. FIG. 1A is a top view of the laser gain medium a1 arranged in the XY plane. FIG. 1B is a cross-sectional view of the laser gain medium a1 along X1-X1 in FIG. In the description of FIGS. 1A and 1B, an end surface excitation type (End Pump) is taken as an example of the excitation light irradiation method. Note that the following description also applies to the side pump type.

  As shown in FIGS. 1A and 1B, in the end face excitation type, for example, the excitation light EL and the laser light L are coaxially irradiated to the incident surface a11 of the laser gain medium a1. When the laser light L enters the laser gain medium a1, the laser light L travels straight through the laser gain medium a1 and is emitted from the emission surface a12. The laser light L receives energy from the excitation light EL in the laser gain medium a1. As a result, the laser light L is amplified. In other words, it can be said that the laser light is amplified in a region in the laser gain medium that overlaps with the excitation light. Similarly to the laser light L, when the excitation light EL is incident on the laser gain medium a1, it proceeds through the laser gain medium a1 and is emitted from the emission surface a12.

  Compared with the laser light L, the excitation light EL intended for excitation does not require high beam quality. Further, not all of the excitation light EL incident on the laser gain medium a1 is absorbed by the laser gain medium a1. The excitation light EL that has not been absorbed by the laser gain medium a1 is emitted from the emission surface a12 of the laser gain medium a1 while having relatively high energy.

FIG. 2 is a block diagram showing an example of a laser amplification system to which the laser gain medium shown in FIG. 1 is applied. The laser amplification system shown in FIG. 2 is configured so that the excitation light (EL _RE ) transmitted through the laser gain medium a1 can be reused. Specifically, the laser amplification system includes, for example, a laser gain medium a1 and an excitation light source a2.

An excitation light supply path OPa is disposed between the excitation light source a2 and the incident surface a11 of the laser gain medium a1. Between the exit surface a12 of the laser gain medium a1 an excitation light source a2 is feedback path OP _b is provided. The laser light L is supplied from the outside of the laser amplification system to the laser gain medium a1.

  The laser amplification system shown in FIG. 2 operates as follows. First, the excitation light source a2 generates excitation light EL. Then, the generated excitation light EL is supplied to the laser gain medium a1 together with the laser light L. The laser light L amplified in the laser gain medium a1 is output from the laser gain medium a1.

On the other hand, excitation light transmitted through the laser gain medium a1 as returned light EL _RE, is introduced to the excitation light source a2 via the feedback path OP _b. That is, the feedback light EL _RE returns to the excitation light source a2. Then, the excitation light source a2 outputs the feedback light EL _RE together with the newly generated excitation light.

  However, in the case of the laser amplification system shown in FIG. 2, there is a limit to the configuration of the applicable excitation light source a2. In order to reuse the excitation light transmitted through the laser gain medium a1, the excitation light source a2 is configured so that the excitation light can be introduced.

  For example, consider a case where a solid laser gain medium is applied as the excitation light source a2. In the case of a solid-state laser gain medium, it is technically possible to introduce excitation light into the solid-state laser gain medium from the outside. However, for example, when a semiconductor laser device is applied as the excitation light source a2, it is technically difficult to introduce excitation light from the outside into the semiconductor laser device. This is because it is difficult to introduce excitation light into the active region due to the structure of the semiconductor laser device.

  In the case of the laser amplification system shown in FIG. 2, even if the excitation light source a2 is configured so that the excitation light itself can be introduced, the irradiation accuracy of the excitation light source a2 may decrease. The reason why the irradiation accuracy is lowered is that it is difficult to output the excitation light EL returned to the excitation light source a2 from the excitation light source a2 with the same diameter and the same diameter as the excitation light newly generated by the excitation light source a2.

2. First Embodiment 2.1. Outline An outline of the first embodiment will be described. FIG. 3 is a block diagram illustrating a configuration example of the laser amplification system SYS1. The laser amplification system SYS1 is a laser amplification system that can collect and reuse the pumping light (EL _RE ) transmitted through the laser gain medium 2 without depending on the configuration of the pumping light source 1. As shown in FIG. 3, the laser amplification system SYS1 is configured such that the pumping light (EL _RE ) transmitted through the laser gain medium 2 is fed back to the laser gain medium 2 instead of the pumping light source 1.

For excitation light transmitted through the laser gain medium 2 is fed back to the laser gain medium 2 as a feedback light EL _RE is between the excitation light source 1 and the laser gain medium 2, the backward light EL _RE is output from the pumping light source 1 What is necessary is just to merge with the excitation light EL. Therefore, the optical property converter 3 and the excitation light combiner 4 are provided.

(Constitution)
The laser amplification system SYS1 is configured as follows. The laser amplification system SYS1 includes an excitation light source 1, a laser gain medium 2, an optical property converter 3, an excitation light combiner 4, an excitation light supply path OP _EL, and a feedback path OP _RE .

  The laser amplification system SYS1 is an optical excitation type laser amplification system that amplifies laser light using excitation light. An example of the excitation light irradiation method is an end face excitation type. Note that a side excitation type may be used instead of the end face excitation type. The laser amplification system SYS1 is, for example, a continuous oscillation method.

The laser gain medium 2 includes an entrance surface 21 and an exit surface 22. The incident surface 21 is a surface on which laser light L and excitation light EL (including return light EL _RE described later) are incident. The emission surface 22 is a surface from which the laser light L and the excitation light transmitted through the laser gain medium 2 are emitted. The laser gain medium 2 is supplied with the laser light L output from the seed light source and the excitation light EL output from the excitation light source 1.

The excitation light supply path OP _EL is disposed between the excitation light source 1 and the laser gain medium 2. In other words, the pumping light supply path OP _EL is an optical path from the pumping light source 1 to the incident surface 21 of the laser gain medium 2.

The feedback path OP _RE is a part of a path through which the excitation light transmitted through the laser gain medium 2 returns to the laser gain medium 2 as feedback light EL _RE . Specifically, the feedback path OP _RE is an optical path from the emission surface 22 of the laser gain medium 2 to the pumping light combiner 4 via the optical characteristic converter 3.

The optical property converter 3 is disposed in the feedback path OP _RE and changes the optical property of the feedback light EL _RE .

The excitation light combiner 4 is arranged in the excitation light supply path OP _EL, and combines the excitation light EL output from the excitation light source 1 and the feedback light EL _RE whose optical characteristics have been changed by the optical characteristic converter 3. .

(Operation)
The laser amplification system SYS1 operates as follows. As shown in FIG. 3, the excitation light source 1 supplies the excitation light EL to the excitation light supply path OP _EL . The laser gain medium 2 is supplied with the laser light L output from the seed light source and the excitation light EL output from the excitation light source 1 through the excitation light supply path OP _EL . The laser light L is amplified by the laser gain medium 2 and output from the laser gain medium 2.

On the other hand, a part of the excitation light EL excites the laser gain medium 2. A part of the pumping light passes through the laser gain medium 2. The excitation light that has passed through the laser gain medium 2 is supplied as feedback light EL _RE to the feedback path OP _RE . Optical property converter 3 receives the returned light _{EL RE,} changing the optical characteristics of the feedback light _{EL RE} was received. Then, the excitation light combiner 4 combines the excitation light EL output from the excitation light source 1 and the feedback light EL _RE whose optical characteristics have been changed by the optical characteristic converter 3. Then, the feedback light EL _RE is supplied to the laser gain medium 2 together with the excitation light EL merged by the excitation light combiner 4. That is, feedback to the laser gain medium 2 excitation light transmitted through the laser gain medium 2 through the return path OP _RE.

(effect)
As described above, the laser amplification system SYS1 is configured such that the pump light transmitted through the laser gain medium 2 is fed back to the laser gain medium 2 instead of the pump light source 1. Therefore, the excitation light transmitted through the laser gain medium 2 can be recovered without depending on the configuration of the excitation light source 1. Furthermore, since the excitation light transmitted through the laser gain medium 2 does not return to the excitation light source 1, it is possible to suppress the irradiation accuracy of the excitation light source 1 from being lowered.

2.2. Optical property converter / excitation light combiner The excitation light is light. Therefore, the excitation light has optical characteristics. The optical characteristic includes, for example, a polarization state or a wavelength. An optical property converter and an excitation light combiner are arranged between the excitation light source and the laser gain medium so that the feedback light merges with the excitation light output from the excitation light source.

  Below, the structure of an optical characteristic converter and an excitation light confluencer is demonstrated. FIG. 4 is a block diagram of the laser amplification system SYS1 focusing on the propagation path of the excitation light. In the description of FIG. 4, the description regarding the laser beam is omitted.

(Constitution)
First, the configuration of the optical property converter 3 and the excitation light combiner 4 will be described. As shown in FIG. 4, the optical property converter (3) is, for example, a light polarizing element 30. The light polarizing element 30 is an element that changes the optical characteristics of light. In the first embodiment, the light polarizing element 30 changes the polarization state of the feedback light EL _RE . Specifically, the light polarization element 30 changes the polarization state of the feedback light EL _RE from the first polarization state (for example, longitudinal polarization) to the second polarization state (for example, lateral polarization). The light polarizing element 30 is, for example, a half-wave plate (λ / 2 plate).

The excitation light combiner (4) is, for example, the first optical element 40. The first optical element 40 is an element that transmits light having specific optical characteristics and reflects light having other optical characteristics. Simply put, the first optical element 40 has both the role of a filter that transmits light having specific optical characteristics and the role of a mirror that reflects light having other optical characteristics. In the first embodiment, the first optical element 40 transmits the excitation light EL in the first polarization state (for example, longitudinal polarization) output from the excitation light source 1 and is converted by the light polarization element 30. The return light EL _RE in the polarization state (for example, laterally polarized light) is reflected. That is, the first optical element 40 transmits only the excitation light having the same polarization state as the excitation light EL output from the excitation light source 1 and reflects the excitation light in other polarization states. Specifically, the light polarizing element 30 is composed of, for example, a polarizer. The first optical element 40 is arranged so that the reflected feedback light EL _RE is supplied to the laser gain medium 2 at the intersection of the excitation light supply path OP _EL and the feedback path OP _RE .

(Function of the first optical element 40)
The function of the first optical element 40 will be described. The first optical element 40 is disposed at the intersection of the excitation light supply path OP _EL and the return path OP _RE . Therefore, the excitation light combiner 4 is preferably an element having the following characteristics. The first is to transmit the excitation light EL output from the excitation light source 1. The second is to reflect the feedback light EL _RE and supply it to the excitation light supply path OP _EL . As an element having two characteristics, the first optical element 40 (for example, a polarizer) is suitable.

(Function of the light polarizing element 30)
The function of the light polarizing element 30 will be described. As described above, the first optical element 40 transmits only the excitation light having the same polarization state as the polarization state of the excitation light EL output from the excitation light source 1 and reflects the excitation light in other polarization states. If the light polarizing element 30 is not provided, the feedback light EL _RE is not reflected by the first optical element 40. Why the feedback light EL _RE is not reflected, the polarization state of the returned light EL _RE is because the same as the polarization state of the excitation light EL. Therefore, returned light EL _RE is to be reflected by the first optical element 40, it is necessary to change the polarization state of the returned light EL _RE.

  Below, a specific example is given and the function of the light polarizing element 30 is demonstrated. However, in the following description, the laser amplification system SYS1 is simplified as follows. First, the case where the excitation light source 1 is constituted by a laser diode (semiconductor laser) will be exemplified. In this case, the excitation light EL is generally linearly polarized light. Secondly, the case where the polarization state of the excitation light EL is linearly polarized is taken as an example. Thirdly, a case where the first optical element 40 transmits longitudinally polarized excitation light and reflects excitation light in another polarization state will be described as an example. Here, the longitudinally polarized light is, for example, polarized light in a direction along the Y axis. The symbols “↑” and “↓” shown in FIG. 4 represent longitudinally polarized light. The other polarization state is polarization other than longitudinal polarization, for example, lateral polarization. The laterally polarized light is, for example, polarized light in a direction along the X axis. The symbols “→” and “←” shown in FIG. 4 represent laterally polarized light.

First, attention is paid to the process until the excitation light EL output from the excitation light source 1 is supplied to the laser gain medium 2. When the polarization state of the excitation light EL is longitudinal polarization, the first optical element 40 transmits the longitudinal polarization excitation light EL. Therefore, the excitation light EL is supplied to the laser gain medium 2 through the pumping light supply path OP _EL.

Next, attention is paid to the process until the excitation light (feedback light EL _RE ) transmitted through the laser gain medium 2 merges with the excitation light EL output from the excitation light source 1. The polarization state of the excitation light transmitted through the laser gain medium 2 remains longitudinally polarized. That is, the polarization state of the return light EL _RE is longitudinal polarization. If the light polarizing element 30 is not provided, the first optical element 40 receives the vertically polarized feedback light EL _RE . The first optical element 40 has a role of a filter that transmits longitudinally polarized excitation light. Accordingly, the feedback light EL _RE is transmitted through the first optical element 40. Therefore, the feedback light EL _RE cannot merge with the excitation light EL. That is, the feedback light EL _RE does not return to the laser gain medium 2.

From the above, in order for the feedback light EL _RE to merge with the excitation light EL, the light polarizing element 30 has a function of changing the polarization state of the feedback light EL _RE . For example, the optical polarization element 30 converts longitudinally polarized feedback light EL _RE into laterally polarized feedback light EL _RE . Therefore, the first optical element 40 can reflect the feedback light EL _RE converted by the light polarizing element 30. As a result, the feedback light EL _RE returns to the laser gain medium 2.

2.3. Recovery of Excitation Light In the case of the laser amplification system SYS1 shown in FIG. 4, the excitation light transmitted through the laser gain medium is recovered only once in the laser gain medium. That is, the feedback light returns only once to the laser gain medium 2. The recovery of the excitation light will be described with reference to FIGS. 5A and 5B.

FIG. 5A is a block diagram showing the laser amplification system SYS1 when the feedback light EL _RE passes through the feedback path OP _RE for the first time. FIG. 5B is a block diagram showing the laser amplification system SYS1 when the feedback light EL _RE passes through the feedback path OP _RE a second time. The symbols “↑” and “↓” shown in FIGS. 5A and 5B represent longitudinally polarized light. The symbols “→” and “←” represent transversely polarized light. In the description of FIGS. 5A and 5B, the description regarding the laser light is omitted.

(First time)
First, with reference to FIG. 5A, the case where the feedback light EL _RE passes through the feedback path OP _RE for the first time will be described. Consider a case where the polarization state of the excitation light EL output from the excitation light source 1 is longitudinal polarization. In this case, the excitation light EL passes through the first optical element 40 and is supplied to the laser gain medium 2. The polarization state of the excitation light transmitted through the laser gain medium 2 remains longitudinally polarized. That is, the feedback light EL _RE is longitudinally polarized light. The vertically polarized feedback light EL _RE is supplied to the light polarization element 30 through the feedback path OP _RE . The optical polarization element 30 converts the polarization state of the feedback light EL _RE from vertical polarization to horizontal polarization. Then, the first optical element 40 reflects the laterally polarized feedback light EL _RE converted by the light polarizing element 30 and introduces it into the excitation light supply path OP _EL . The horizontally polarized feedback light EL _RE returns to the laser gain medium 2 through the excitation light supply path OP _EL .

(Second time)
Next, with reference to FIG. 5B, the case where the feedback light EL _RE passes through the feedback path OP _RE for the second time will be described. There are two types of pumping light transmitted through the laser gain medium 2 after the feedback light EL _RE has returned to the laser gain medium 2. One is laterally polarized excitation light. The horizontally polarized excitation light is the return light EL _RE reflected by the first optical element 40. The other is longitudinally polarized excitation light. The vertically polarized excitation light is excitation light EL output from the excitation light source 1. Here, for simplicity of explanation, feedback light EL RE reflected by the first optical element _40, i.e., focusing on the feedback light EL _RE of horizontally polarized light.

The laterally polarized feedback light EL _RE is introduced into the optical polarization element 30 through the feedback path OP _RE . The optical polarization element 30 converts the polarization state of the feedback light EL _RE from horizontal polarization to vertical polarization. Since the polarization state of the feedback light EL _RE has been converted from lateral polarization to longitudinal polarization, the first optical element 40 transmits the longitudinal polarization feedback light EL _RE converted by the light polarization element 30. In other words, when changing the polarization state of the same feedback light EL _RE for the second time, the optical polarization element 30 returns the polarization state of the feedback light EL _RE to the original state. Then, the first optical element 40 transmits the return light EL _RE whose polarization state has been returned to the original polarization state by the light polarization element 30. Therefore, the vertically polarized feedback light EL _RE does not return to the laser gain medium 2.

  From the above, it can be seen that in the case of the laser amplification system SYS1 shown in FIG. 4 (FIGS. 5A and 5B), the excitation light transmitted through the laser gain medium is collected only once by the laser gain medium. The role of the pumping light is to pump (pump) the atoms of the laser gain medium. Therefore, from the viewpoint of effectively using the pumping light, it is beneficial if the pumping light can be collected even once in the laser gain medium. Further, even if transversely polarized light and longitudinally polarized excitation light are supplied to the laser gain medium, the laser amplification system is not adversely affected from the viewpoint of the role of the excitation light.

2.4. Specific Configuration FIG. 6 is a schematic diagram illustrating a specific configuration example of the laser amplification system SYS1. As shown in FIG. 6, the laser amplification system SYS1 includes an excitation light source 1, a laser gain medium 2, an optical polarization element 30, a first optical element 40, an excitation light supply path OP _EL, and a feedback path OP _RE . in addition to having a first polarization maintaining fiber 5 _1.

Laser amplification system SYS1 includes ₁ a first optical lens _6, and the second optical lens _{6 2,} a third optical lens _{6 3,} and a fourth optical lens _{6 4,} the first dichroic mirror _{7 1,} second dichroic mirror 7 _{2, 1} and the first mirror 8, it may include at least one of the _two second mirror 8. The laser gain medium 2 is included in a laser amplifier (AMP) 20. The description of the configuration of the light polarizing element 30 and the first optical element 40 is omitted.

The excitation light source 1 is, for example, a laser diode. The excitation light source 1 generates excitation light EL and supplies it to the excitation light supply path OP _EL . The wavelength of the excitation light EL is different from the wavelength of the laser light L. The configuration of the excitation light source 1 is arbitrary. For example, the excitation light source 1 may be composed of a solid laser gain medium.

A material suitable for the wavelength of the laser beam L is used for the laser gain medium 2. When a solid laser gain medium is applied to the laser gain medium 2, examples of the solid include yttrium aluminum garnet (YAG) containing ytterbium trivalent ions (Yb ³⁺ ). When a liquid laser gain medium is applied to the laser gain medium 2, examples of the liquid include a liquid in which a fluorescent organic dye (for example, an oxazine dye) is dissolved in a solvent (for example, alcohol). Note that a gas laser gain medium may be applied to the laser gain medium 2 or a fiber type laser gain medium may be applied.

The laser amplifier 20 is configured to amplify laser light L as seed light. The laser amplifier 20 may include various optical components in addition to the laser gain medium 2. The various optical components include, for example, a mirror for coaxially guiding laser light and excitation light supplied to the laser amplifier 20 to the laser gain medium 2. The laser amplifier 20 outputs the laser light L amplified by the laser gain medium 2 and the excitation light (feedback light EL _RE ) transmitted through the laser gain medium 2. Note that the intensity of the laser light L is arbitrary.

The first polarization maintaining fiber _{5 1} includes an input terminal 51 _1, and an output terminal 51 _2. The first polarization maintaining fiber _{5 1} is disposed in the excitation light supply path _{OP EL.} The first polarization maintaining fiber 5 _1, the polarization state of the introduced light (state of polarization) is configured to be outputted while being held. In other words, the polarization state of the first light output from the polarization maintaining fiber 5 ₁ is the same as the polarization state of the light introduced into the first polarization-maintaining fiber 5 _1. In the example of FIG. 6, the excitation light EL is introduced to an input terminal 51 _1. Introduced excitation light EL to the first polarization-maintaining fiber 5 ₁ is outputted to the output terminal 51 ₂ while maintaining the polarization state.

As shown in FIG. 6, if the first polarization-maintaining fiber 5 ₁ is provided, it is easy to feedback light EL _RE to the excitation light EL coaxially. In addition, it is easy to make the diameter of the feedback light EL _RE the same as the diameter of the excitation light EL.

Furthermore, since the first polarization-maintaining fiber 5 ₁ is used, the following effect can be obtained. The optical path (for example, the excitation light supply path OP _EL ) should be as simple as possible. However, the optical path is likely to be restricted by the configuration of the laser amplification system SYS1. Therefore, for example, it may be difficult to arrange both the excitation light source 1 and the laser amplifier 20 in a linear optical path. Therefore, the first polarization-maintaining fiber 5 ₁ is provided. The first polarization maintaining fiber 5 ₁ has a flexibility such as an optical fiber. Moreover, in the first polarization-maintaining fiber 5 _1, be applied external vibration (impacts) is, there is a feature that the polarization state is maintained. Therefore, for example, both the excitation light source 1 and the laser amplifier 20 can be arranged in a non-linear optical path. That is, the degree of freedom in designing the laser amplification system SYS1 is increased.

The first optical lens _61, in the pumping light supply path OP _EL, is disposed between the excitation light source 1 and the first optical element 40. The first optical lens ₆₁ is introduced into the input end 51 ₁ of the first polarization-maintaining fiber 5 ₁ condenses the excitation light EL that has been output from the pumping light source 1. The first optical lens _61, as the excitation light EL is introduced into the input end 51 ₁ of the first polarization-maintaining fiber 5 _1, the first optical element 40 first polarization-maintaining fiber 5 _first input it may be disposed between the end 51 _1.

₂ the second optical lens _6, in the feedback path _{OP RE,} is disposed between the second dichroic mirror _{7 2} and the first mirror _{8 1.} In the example of FIG. 6, the second optical lens _{6 2,} for example, in the feedback path _{OP RE,} may be disposed between the first mirror _{8 1} and ₂ the second mirror _8. In the example of FIG. 6, the second optical lens 6 ₂ may not be provided.

Third optical lens 6 _3, in the excitation light supplying path OP _EL, is disposed between the first polarization maintaining fiber 5 ₁ and the first dichroic mirror 7 _1. Third optical lens 6 _3, the excitation light EL that has been output from the first polarization maintaining fiber 5 _first output terminal 51 ₂ is received, to introduce the excitation light EL to the first dichroic mirror 7 _1. Briefly, the third optical lens 6 ₃ introduces the excitation light EL that has been output from the first polarization maintaining fiber 5 ₁ to the laser gain medium 2.

The fourth optical lens _{6 4,} in the feedback path _{OP RE,} is arranged between the light polarizing element 30 and the first optical element 40. The fourth optical lens _{6 4} receives the backward light _{EL RE} output from the light polarizing element 30 is introduced by condensing the returned light _{EL RE} to the first optical element 40. The fourth optical lens 6 ₄ may not be provided.

The first dichroic described dichroic mirror _71. Basically, the wavelength of the excitation light EL is different from the wavelength of the laser light L. In the example of FIG. 6, the laser beam L is incident in the positive direction from the negative direction orientation of the Y axis perpendicular to the excitation light supply path OP _EL. In order to supply the laser light L output from the seed light source and the excitation light EL output from the excitation light source 1 to the laser amplifier 20 (laser gain medium 2), a dichroic mirror is suitable as an optical element. The dichroic mirror transmits light of a specific wavelength and reflects light of other wavelengths.

The first dichroic mirror 7 ₁ supplies the laser beam L to the laser amplifier 20 has a role of transmitting the excitation light EL. More specifically, the first dichroic mirror 7 _1, is transmitted through the excitation light EL that has been output from the first polarization maintaining fiber 5 ₁ reflects the laser beam L emitted from the seed light source. The first dichroic mirror 7 _1, as the laser beam L is reflected in the positive direction of the X axis, are arranged in the excitation light supply path OP _EL.

The second dichroic mirror 7 _2, like the first dichroic mirror 7 ₁ transmits light of a specific wavelength and reflects light of other wavelengths. However, the second dichroic mirror 7 ₂ differs from the first dichroic mirror ₇₁ in the following ways. The second dichroic mirror _{7 2} is responsible for feeding back the feedback light _{EL RE} to the laser amplifier 20. Therefore, the second dichroic mirror 7 _2, feedback light EL _RE is to reflect the negative direction of the Y axis, it is arranged in the feedback path OP _RE. The second dichroic mirror 7 _2, and transmits the laser beam L emitted from the laser amplifier 20. Further, the second dichroic mirror _{7 2} reflects toward the backward light _{EL RE} as an excitation light to the first mirror _{8 1.}

The first mirror _{8 1} is, for example, a total reflection mirror. The first mirror 8 _1, in the feedback path OP _RE, is disposed at a position at a predetermined distance in the negative direction of the Y-axis from the second dichroic mirror 7 _2. The first mirror _{8 1,} the returned light _{EL RE} reflected by the second dichroic mirror _{7 2} receives, reflects toward the backward light _{EL RE} to the second mirror _82.

The second mirror ₈₂ is, for example, a total reflection mirror. ₂ second mirror 8, in the feedback path OP _RE, is disposed at a position at a predetermined distance in the negative direction of the X axis from the first mirror 8 _{1. 2} second mirror _8, the feedback light _{EL RE} reflected by the first mirror _{8 1} receives, is reflected toward the backward light _{EL RE} to the optical polarizing element 30.

2.5. Operation Focusing on the excitation light, the operation of the laser amplification system SYS1 will be described. Excitation light EL that has been output from the pumping light source 1 is introduced into the first optical element 40 passes through the first optical lens _61. Then, the excitation light EL is transmitted through the first optical element 40, it is introduced into the first polarization-maintaining fiber 5 _1. Introduced excitation light EL to the first polarization-maintaining fiber 5 _1, the polarization state is output while being held. Excitation light EL that has been output from the first polarization maintaining fiber 5 ₁ is introduced through the third optical lens 6 ₃ to the first dichroic mirror 7 _1. Then, the excitation light EL is transmitted through the first dichroic mirror 7 _1, is supplied to the laser amplifier 20 (the laser gain medium 2).

The excitation light transmitted through the laser gain medium 2 is output from the laser amplifier 20 as feedback light EL _RE . Feedback light _{EL RE} is reflected by the second dichroic mirror _{7 2,} it is introduced into the feedback path _{OP RE.} The returned light _{EL RE} is reflected by the first mirror _{8 1} and the second mirror _82, it is introduced into the light polarizing element 30. For example, when the polarization state of the feedback light EL _RE is longitudinal polarization, the optical polarization element 30 converts the polarization state of the feedback light EL _RE from longitudinal polarization to lateral polarization. Then, the first optical element 40 reflects the laterally polarized feedback light EL _RE converted by the light polarizing element 30 and introduces it into the excitation light supply path OP _EL . Thereafter, the feedback light EL _RE follows a path similar to the path followed by the excitation light EL and returns to the laser gain medium 2.

According to the first embodiment, the excitation light (EL _RE ) transmitted through the laser gain medium 2 can be collected and reused without depending on the configuration of the excitation light source 1.

3. Second Embodiment A second embodiment will be described. In 1st Embodiment, the example which collect | recovers excitation light was given by utilizing the polarization state of excitation light. In collecting the excitation light, the wavelength of the excitation light can be used instead of the polarization state of the excitation light.

  FIG. 7 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1a. As shown in FIG. 7, in the laser amplification system SYS1a, a wavelength conversion element 31 is provided as an alternative to the optical polarization element 30 shown in FIG. Furthermore, a second optical element 41 is provided as an alternative to the first optical element 40 shown in FIG. In other words, the optical property converter (3) shown in FIG. 3 includes the wavelength conversion element 31. The excitation light combiner (4) shown in FIG. 3 includes a second optical element 41.

  The wavelength of the excitation light EL generated by the excitation light source 1 is determined by the specification of the excitation light source 1. In the following description, it is assumed that the excitation light EL has the first wavelength.

The wavelength conversion element 31 converts the wavelength of the feedback light EL _RE from the first wavelength to the second wavelength. The second wavelength may be longer than the first wavelength or shorter than the first wavelength. The second wavelength may be a wavelength different from the first wavelength.

The second optical element 41 transmits the excitation light having the first wavelength output from the excitation light source 1 and reflects the feedback light EL _RE having the second wavelength converted by the wavelength conversion element 31.

Similar to the first embodiment, the feedback light EL _RE merges with the excitation light EL output from the excitation light source 1 by changing the optical characteristics of the feedback light EL _RE . As a result, two types of excitation light are supplied to the laser gain medium 2. One is excitation light of the first wavelength. The other is the second wavelength feedback light EL _RE . The laser gain medium 2 is excited by interacting with each of the two types of excitation light.

  Also in the second embodiment, similarly to the first embodiment, the excitation light transmitted through the laser gain medium 2 can be collected and reused without depending on the configuration of the excitation light source 1.

4). Third Embodiment A third embodiment will be described. As described in the first embodiment, the polarization maintaining fiber contributes to increasing the degree of freedom in designing the laser amplification system. In the third embodiment, a laser amplification system that further increases the degree of freedom in designing the laser amplification system will be described.

FIG. 8 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1b. As shown in FIG. 8, the laser amplification system SYS1b further comprises a second polarization-maintaining fiber _{5 2.} Since the second polarization-maintaining fiber _{5 2} is provided feedback path _{OP RE,} the first mirror _{8 1} and the second mirror ₈₂ is unnecessary.

The second polarization-maintaining fiber _{5 2} includes an input end 52 _1, and an output terminal 52 _2. The second structure itself of the polarization-maintaining fiber 5 ₂ is the same as the first polarization-maintaining fiber 5 ₁ structure. However, the second polarization-maintaining fiber _{5 2} is placed in the feedback path _{OP RE.}

The second optical lens _{6 2,} the excitation light transmitted through the laser gain medium 2 as a feedback light _{EL RE,} is introduced into the input end 52 ₁ of the second polarization-maintaining fiber _{5 2.}

The fourth optical lens _{6 4} feedback light _{EL RE} output from the output terminal 52 of the _second polarization-maintaining fiber _{5 2} received, to introduce a feedback light _{EL RE} to the first optical element 40. Briefly, the fourth optical lens 6 ₄ introduces the backward light EL _RE output from the second polarization-maintaining fiber 5 ₂ to the first optical element 40.

According to the third embodiment, a portion of the feedback path OP _RE is constituted by a second polarization maintaining fiber 5 _2. Accordingly, it becomes easier to make the return light EL _RE coaxial with the excitation light EL in the excitation light supply path OP _EL . In addition, in the excitation light supply path OP _EL , it is easy to make the diameter of the feedback light EL _RE the same as the diameter of the excitation light EL. In addition, the degree of freedom in designing the laser amplification system can be further increased. Needless to say, the same effects as those of the first embodiment can be obtained.

5. Fourth Embodiment A fourth embodiment will be described. The polarization maintaining fiber can be arranged in the return path instead of the pumping light supply path.

FIG. 9 is a schematic diagram illustrating a configuration example of the laser amplification system SYS1c. As shown in FIG. 9, the laser amplification system SYS1c further comprises a second polarization-maintaining fiber _{5 2.} The second polarization-maintaining fiber _{5 2} are provided in the feedback path _{OP RE.} In the example of FIG. 9, the first optical lens 6 _first and third optical lens 6 _{3 (see} FIG. 6) is not provided. Of course, the first optical lens _{6 first} and third optical lens _{6 3} may be provided to the excitation light supply path _{OP EL.}

The second polarization-maintaining fiber _{5 2} is placed in the feedback path _{OP RE.} The second optical lens 6 ₂ introduces the excitation light transmitted through the laser gain medium 2 as a feedback light EL _RE to the second polarization-maintaining fiber 5 _2. The fourth optical lens _{6 4} introduces the backward light _{EL RE} output from the second polarization-maintaining fiber _{5 2} to the first optical element 40.

According to the fourth embodiment, a portion of the feedback path OP _RE is constituted by a second polarization maintaining fiber 5 _2. Therefore, the degree of freedom in designing the laser amplification system can be increased. Needless to say, the same effects as those of the first embodiment can be obtained.

6). Fifth Embodiment A fifth embodiment will be described. In the first embodiment, the pump light output from the pump light source is transmitted and the feedback light output from the laser gain medium 2 is reflected when collecting the pump light. In the fifth embodiment, a case will be described in which excitation light output from an excitation light source is reflected and feedback light output from a laser gain medium is transmitted.

  FIG. 10 is a block diagram of the laser amplification system SYS1d focusing on the propagation path of the excitation light. Symbols “↑” and “↓” shown in FIG. 10 represent longitudinally polarized light. The symbols “→” and “←” represent transversely polarized light.

  The configuration of the laser amplification system SYS1d shown in FIG. 10 is different from the configuration of the laser amplification system SYS1 shown in FIG. 4 in the following points. In the following description, it is assumed that the polarization state of the excitation light EL output from the excitation light source 1 is longitudinal polarization, as in the description of FIG.

The first is the function of the light polarizing element 30a. For example, the optical polarization element 30a converts the polarization state of the feedback light EL _RE from vertical polarization to horizontal polarization. The second is the function of the first optical element 40a. The first optical element 40 a transmits the horizontally polarized feedback light EL _RE converted by the light polarizing element 30 a and reflects the vertically polarized excitation light output from the excitation light source 1. The third is the arrangement of the excitation light source 1. Excitation light EL that has been output from the pumping light source 1 is reflected by the first optical element 40a, the excitation light source 1 to the position reflected excitation light EL is supplied to the pumping light supply path OP _EL are arranged.

The operation of the laser amplification system SYS1d is as follows. Excitation light EL of vertically polarized light output from the pumping light source 1 is supplied to reflected by pumping light supply path OP _EL by the first optical element 40a. The longitudinally polarized excitation light EL is supplied to the laser gain medium 2. The feedback light EL _RE transmitted through the laser gain medium 2 remains longitudinally polarized. The vertically polarized return light EL _RE is introduced into the light polarization element 30a through the return path OP _RE . The optical polarization element 30a converts the polarization state of the feedback light EL _RE from vertical polarization to horizontal polarization. The laterally polarized feedback light EL _RE converted by the light polarizing element 30a is introduced into the first optical element 40a. The first optical element 40a transmits laterally polarized feedback light EL _RE . The laterally polarized feedback light EL _RE transmitted through the first optical element 40a returns to the laser gain medium 2.

  In the fifth embodiment, similarly to the first embodiment, the excitation light transmitted through the laser gain medium 2 can be collected and reused without depending on the configuration of the excitation light source 1.

7). Sixth Embodiment A sixth embodiment will be described. In the sixth embodiment, a case will be described in which the pumping light output from the pumping light source is reflected and the feedback light output from the laser gain medium is transmitted by using the wavelength of the pumping light.

  FIG. 11 is a block diagram of the laser amplification system SYS1e focusing on the propagation path of the excitation light. As shown in FIG. 11, in the laser amplification system SYS1e, a wavelength conversion element 31a is provided as an alternative to the optical polarization element 30a shown in FIG. Furthermore, a second optical element 41a is provided as an alternative to the first optical element 40a shown in FIG. In the following description, it is assumed that the excitation light EL generated by the excitation light source 1 has the first wavelength.

The wavelength conversion element 31a converts the wavelength of the feedback light EL _RE from the first wavelength to the second wavelength. The second optical element 41a reflects the first wavelength excitation light output from the excitation light source 1 and transmits the second wavelength feedback light EL _RE converted by the wavelength conversion element 31a.

  Also in the sixth embodiment, similarly to the first embodiment, the excitation light transmitted through the laser gain medium 2 can be collected and reused without depending on the configuration of the excitation light source 1.

8). Seventh Embodiment The seventh embodiment relates to a laser system to which a laser amplification system is applied. FIG. 12 is a block diagram illustrating a configuration example of a laser system SYS2 to which the laser amplification system SYS1 is applied.

  As shown in FIG. 12, the laser system SYS2 includes a laser amplification system SYS1 and a seed light source 9. The seed light source 9 is a generation source of the laser light L. The seed light source 9 supplies the generated laser light L to the laser gain medium 2. Optionally, any one of the laser amplification systems SYS1a to SYS1e in the second to sixth embodiments may be applied to the laser system SYS2.

  According to the seventh embodiment, it is possible to provide a laser system that collects and reuses the excitation light transmitted through the laser gain medium without depending on the configuration of the excitation light source.

9. Eighth Embodiment A laser amplification system can be used as an optical resonator (laser oscillator). FIG. 13 is a block diagram illustrating a configuration example of the laser amplification system SYS1f when used as an optical resonator. As illustrated in FIG. 13, the laser amplification system SYS1f may further include a mirror 23 and a half mirror 24. For example, the mirror 23 is disposed at the end of the laser gain medium 2. The half mirror 24 is disposed at the other end of the laser gain medium 2 so as to face the mirror 23. In FIG. 13, the arrangement of the mirror 23 and the half mirror 24 is shown in a simplified manner for convenience of explanation.

  As shown in FIG. 13, when the laser amplification system is used as an optical resonator, it is not necessary to introduce laser light into the laser gain medium 2. When the excitation light EL is introduced into the laser gain medium 2, a part of the excitation light EL is absorbed by the laser gain medium 2. As a result, light is generated from the laser gain medium 2 by natural radiation. The generated light is reflected many times between the mirror 23 and the half mirror 24. The generated light reciprocates between the mirror 23 and the half mirror 24 many times, thereby generating coherent light, that is, laser light. As described above, the laser amplification system SYS1f can be used as an optical resonator.

  As described above, all the embodiments have been described. Various modifications can be made to the present invention without departing from the spirit of the present invention. For example, by devising the feedback path, it is possible to collect the excitation light transmitted through the laser gain medium twice or more.

  All the embodiments can be suitably combined within a range in which no technical contradiction occurs. For example, the second embodiment may be combined with the third embodiment.

DESCRIPTION OF SYMBOLS 1 ... Excitation light source, 2 ... Laser gain medium, 3 ... Optical characteristic converter, 4 ... Excitation light combiner, 5 ₁ ... 1st polarization maintaining fiber, 5 ₂ ... 2nd polarization maintaining fiber, 6 ₁ ... 1st Optical lens, 6 ₂ ... 2nd optical lens, 6 ₃ ... 3rd optical lens, 6 ₄ ... 4th optical lens, 7 ₁ ... 1st dichroic mirror, 7 ₂ ... 2nd dichroic mirror, 8 ₁ ... 1st mirror, 8 ₂ ... 2nd mirror, 9 ... Seed light source, 20 ... Laser amplifier, 30 ... Light polarizing element, 31 ... Wavelength converting element, 40 ... First optical element, 41 ... Second optical element, EL ... Excitation light, EL _RE ... feedback light, L ... laser light, OP _EL ... excitation light supply path, OP _RE ... feedback path, SYS1, SYS1a, SYS1b, SYS1c ... laser amplification system, SYS2 ... laser system

Claims (4)

An excitation light source that outputs excitation light;
An excitation light synthesizer that combines the excitation light from the excitation light source and the excitation light from the excitation light source to generate synthetic excitation light;
A laser gain medium for amplifying a laser beam by excitation using the combined excitation light, and outputting the amplified laser beam and the combined excitation light after excitation ;
Wherein disposed between the pump light combiner and the laser gain medium, and the combined excitation light from the excitation light combiner, the laser beam and receiving the said synthetic excitation light the laser beam wider than And an excitation light supply path for supplying the synthetic excitation light and the laser beam to the laser gain medium so as to include the laser beam within the width of the synthetic excitation light ,
Taking out the synthesized excitation light from the output from the laser gain medium, and the excitation light combining device in supplying feedback excitation light path as the feedback excitation light
Have
The excitation light supply path is
A first polarization maintaining fiber;
A first dichroic mirror that reflects the laser beam and transmits the combined excitation light from the first polarization maintaining fiber to supply the laser beam and the combined excitation light to the laser gain medium;
The synthetic pumping light provided between the first polarization maintaining fiber and the first dichroic mirror and output from the first polarization maintaining fiber has a width wider than the laser beam and the laser. A third lens for focusing on the laser gain medium via the first dichroic mirror so as to include a beam;
Including
The excitation light synthesizer
A first optical element that transmits the excitation light from the excitation light source to the excitation light supply path and generates the synthesized excitation light by reflecting the feedback excitation light to the excitation light supply path;
A first lens for condensing the excitation light at an entrance of the first polarization maintaining fiber via the first optical element;
A second lens for reflecting the feedback pump light from the feedback pump light path by the first optical element having the same diameter as the pump light and condensing it at the entrance of the first polarization maintaining fiber;
Including
The feedback pumping light path is
A laser amplification system having a second dichroic mirror that extracts the synthesized pumping light after pumping from the output light of the laser gain medium as the feedback pumping light . The excitation light synthesizer
Further comprising a light polarizing element for converting the polarization state of the feedback excitation light from the return excitation light path from the first polarization state to a second polarization state,
Before Symbol first optical element,
The rewritable transmitting the excitation light of the first polarization state which is output from the pumping light source to said excitation light supply path from the excitation light source,
Laser amplification system as defined in claim 1 you reflecting the feedback excitation light of the second polarization state from the previous SL light polarizing element to the excitation light supply path. The excitation light synthesizer
Further comprising a wavelength conversion element for converting the second wavelength the wavelength of the feedback excitation light from the return excitation light path from the first wavelength,
Before Symbol first optical element,
The rewritable transmitting the excitation light of the first wavelength outputted from the pumping light source to said excitation light supply path from the excitation light source,
Laser amplification system as defined in claim 1 you reflecting the feedback excitation light of the second wavelength from the previous SL wavelength converting element to the excitation light supply path. The feedback pumping light path is
A second polarization maintaining fiber;
The laser amplification system according to any one of claims 1 to 3 , further comprising: a second optical lens that introduces the feedback pumping light output from the second dichroic mirror into the second polarization maintaining fiber.

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