JP2017022351A - Position detection system for reflection spot of laser light, laser optical axis alignment system and laser optical axis alignment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust a laser optical axis without newly providing a light source for adjusting a laser optical axis.SOLUTION: A position detection system (SYS1) for a reflection spot of a laser light comprises: a laser gain medium (1) to which an excitation light (EL) and a laser light (L) are incident and which emits a fluorescent light (FL) by absorbing a part of the excitation light; and a detector (2) for detecting a position of a reflection spot (RS) of the laser light in the laser gain medium. The detector detects a position of a region where an intensity of the fluorescent light is lower than that in a peripheral region, as the reflection spot.SELECTED DRAWING: Figure 3C

Description

  The present invention relates to a position detection system for a reflected spot of laser light, a laser optical axis alignment system, and a laser optical axis alignment method.

  There is a demand for laser systems with high irradiation accuracy. In order to obtain high irradiation accuracy, it is desirable that the laser optical axis is optimally adjusted.

  However, even if the laser optical axis is optimally initialized in advance, the laser optical axis may deviate from the desired laser optical axis depending on the environment in which the laser system is placed. One reason is that the components (for example, optical components) of the laser system are easily affected by vibration and heat. From this point of view, it is essential to adjust the laser optical axis (laser optical axis alignment).

  As a related technique, Patent Document 1 discloses a laser optical axis adjusting device applied to a copper vapor laser amplifying device. According to Patent Document 1, a copper vapor laser amplifying apparatus includes a laser oscillator, a laser amplifier, and a total reflection mirror. A total reflection mirror is used to adjust the laser optical axis from the laser oscillator to the laser amplifier. A dichroic mirror is used as the total reflection mirror. The dichroic mirror totally reflects the copper vapor laser. A reference laser is incident in parallel to the laser optical axis. The reference laser has a wavelength different from that of the copper vapor laser. The laser optical axis adjusting device detects the position of the reference laser that has passed through the dichroic mirror with a position detector. The laser optical axis adjusting device adjusts the angle of the total reflection mirror when the beam position of the reference laser is shifted.

Japanese Examined Patent Publication No. 7-97672

  In the method of Patent Document 1, a reference laser is used to adjust the laser optical axis. For this purpose, it is necessary to newly provide a light source for the reference laser. An object of the present invention is to provide a laser beam reflection spot position detection system, a laser beam axis alignment system, and a laser beam that can adjust the laser beam axis without newly providing a light source for adjusting the laser beam axis. An axial alignment method is provided.

  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 position detection system (SYS1) of the reflected spot of the laser beam according to the first aspect of the embodiment is
A laser gain medium (1) that receives excitation light (EL) and laser light (L) and emits fluorescence by absorbing a part of the excitation light;
A detector (2) for detecting a position of a reflection spot (RS) of the laser beam in the laser gain medium.
The detector detects a position of a region (RS) where the intensity of the fluorescence is lower than a surrounding region as the reflection spot.

The laser optical axis alignment system (SYS2) according to the second aspect of the embodiment is
A position detection system (SYS1) of a reflected spot of the laser beam according to the first aspect;
A plurality of optical elements ( ₁ , 30 ₁ , 30 ₂ ) comprising the laser gain medium;
And a control device (4) for controlling the angle or position of at least one of the plurality of optical elements.
The control device controls the angle or position of the at least one optical element based on a distance (D) between the position of the reflection spot and a reference position (C _FR ).

The reference position may be a position where the center (C _RS ) of the reflection spot should exist.
The control device calculates a distance (D) between the center of the reflection spot and the reference position (C _FR ) as a shift amount, and the at least one of the at least one so that the calculated shift amount becomes zero. The angle or position of the optical element may be controlled.

The at least one optical element to be controlled by the control device may be a mirror (30 ₁ , 30 ₂ ) disposed in the optical path (OP) of the laser light.

The laser gain medium is
You may have the surface (11) in which the said laser beam injects, and the back surface (12) opposite to the said surface.
The detector may be disposed on the front side, and may detect the position of the reflection spot generated on the back side from the front side.

The plurality of optical elements are:
A first laser gain medium (1A) as the laser gain medium;
And a second laser gain medium (1B) that emits fluorescence by receiving the excitation light and the laser light and absorbing a part of the excitation light.
The detector detects a position of a first reflection spot (RS ₁ ) that is the reflection spot of the laser light in the first laser gain medium, and further, a second reflection of the laser light in the second laser gain medium. The position of the spot (RS ₂ ) may be detected.
The control device includes a first distance between a position of the first reflection spot and a first reference position (C _FR1 ) that is the reference position in the first laser gain medium, and a position of the second reflection spot. The angle or position of the at least one optical element may be controlled based on a second distance from a second reference position (C _FR2 ) in the second laser gain medium.

The detector detects a position of a first reflection spot (RS ₁ ) that is the reflection spot of the laser light in the laser gain medium, and further detects a position of the second reflection spot (RS ₂ ) of the laser light. It may be detected.
The control device includes a first distance between the position of the first reflection spot and the first reference position (C _FR1 ), which is the reference position, and the position of the second reflection spot and the second reference position (C _FR2). ) To control the angle or position of the at least one optical element.

  The phase state of the laser gain medium may be solid or liquid.

The control device, the addition to the distance (D) between the position and the reference position of the reflection spot (C _FR), on the basis of the said reference position of the reflection spot (C _FR) around the angle (alpha), the The angle or position of the at least one optical element may be controlled.

The control device includes the first distance between the position of the first reflection spot and the first reference position (C _FR1 ), and the position of the second reflection spot and the second reference position (C _FR2 ). In addition to the second distance between the first reflection spot, a first angle around the first reference position (C _FR1 ) of the first reflection spot and a second angle around the second reference position (C _FR2 ) of the second reflection spot. The angle or position of the at least one optical element may be controlled based on two angles.

The laser optical axis alignment system according to the second aspect of the embodiment is
A cooling unit (100) for cooling the laser gain medium;
And a cooling unit control device (6) for controlling the cooling unit.
The detector may further detect a fluorescence spectrum emitted from the laser gain medium.
The cooling unit control device may control the cooling intensity of the cooling unit based on the fluorescence spectrum detected by the detector.

The at least one optical element to be controlled by the control device may include a lens (9) disposed in the optical path of the laser light.
The detector may detect a fluorescence intensity distribution of the reflected spot.
The control device may control the angle or position of the lens based on the intensity distribution of the fluorescence of the reflected spot detected by the detector.

The method for detecting the position of the reflected spot of the laser beam according to the third aspect of the embodiment is as follows:
An incident step (ST1) in which excitation light and laser light are incident on the laser gain medium;
A detecting step (ST2) for detecting a position of a reflected spot of the laser beam in the laser gain medium.
The laser gain medium emits fluorescence by absorbing a part of the excitation light.
In the detection step, the position of the region where the intensity of the fluorescence is lower than the surrounding region is detected as the reflection spot.

  A laser beam reflection spot position detection system, a laser beam axis alignment system, and a laser beam axis alignment method capable of optimally adjusting the laser beam axis without newly providing a light source for adjusting the laser beam axis Can be provided.

FIG. 1 is a schematic diagram for explaining an example of laser optical axis alignment applied to a laser system. FIG. 2 is a schematic diagram for explaining another example of the laser optical axis alignment applied to a certain laser system. FIG. 3A is a schematic diagram illustrating a configuration example of a reflection spot position detection system SYS1. FIG. 3B is a schematic diagram for explaining a phenomenon that occurs when only the excitation light is irradiated onto the laser gain medium 1. FIG. 3C is a schematic diagram for explaining a phenomenon that occurs when excitation light is irradiated on a laser gain medium coaxially with laser light. FIG. 3D is a schematic diagram for explaining a reflection spot generated when there is a deviation in the laser optical axis. FIG. 3E is a schematic diagram for explaining a modification of the reflection spot position detection system SYS1. FIG. 4 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2. FIG. 5A is a diagram illustrating a display screen 51 when there is no deviation in the laser optical axis. FIG. 5B is a diagram illustrating a display screen 51 when the laser optical axis is displaced. FIG. 6 is a conceptual diagram for explaining the control mechanism of the optical system 3. FIG. 7 is a flowchart illustrating a laser optical axis alignment method. FIG. 8 is a block diagram illustrating a configuration example of a laser system SYS3 to which the laser optical axis alignment system SYS2 is applied. FIG. 9 is a block diagram showing the laser optical axis alignment system SYS2 when the control target by the control device 4 is the laser gain medium 1. As shown in FIG. FIG. 10 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2a. FIG. 11 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2b. FIG. 12 is a block diagram showing the laser optical axis alignment system SYS2c when the number of detectors 2 is one. FIG. 13 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2d. FIG. 14 is a diagram showing an example of the distribution of the fluorescence spectrum detected by the detector 2a. 15, although the center C _RS reflective spot RS is coincident with the center C _FR fluorescent region FR, is a schematic diagram showing a case where the deviation angle of the reference position direction in the X-Y plane is generated . FIG. 16 is a partially enlarged view of the reflection spot and the periphery of the reflection spot. FIG. 17 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2e.

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

1. Matters recognized by the inventor Matters recognized by the inventor will be described using two examples.

1.1. Example 1 of laser optical axis alignment
FIG. 1 is a schematic diagram for explaining an example of laser optical axis alignment applied to a laser system. The laser system shown in FIG. 1 includes, for example, a seed light source a ₁ , a total reflection mirror a ₂ , a partial transmission mirror a ₃ , a detector a ₄ , a control device a _5, and a laser amplifier a ₆ . As shown in FIG. 1, a total reflection mirror a ₂ and a partial transmission mirror a ₃ are arranged in a laser light path OP (see the broken line) from the seed light source a ₁ to the laser amplifier a ₆ . Focusing on the laser light path OP, the laser light L _a output from the seed light source a ₁ is reflected by the total reflection mirror a ₂ and the partial transmission mirror a ₃ and supplied to the laser amplifier a ₆ along the laser light path OP. . Laser amplifier a ₆ amplifies and outputs the supplied laser beam La.

For example, consider the case where the angle of the total reflection mirror a ₂ is deviated from a desired angle (initial set angle). In this case, it means that the current laser optical axis AX (see the one-dot chain line) is deviated from the initially set laser optical axis. In this case, the following disadvantages occur.

The first is a decrease in the output of the laser system. That is, the amplification factor of the laser beam L _a which is amplified by a laser amplifier a ₆ falls below a desired amplification factor. As reason for this one, the laser beam L _a which is output from the seed light source a ₁ is, it is considered not to be incident on a predetermined position of the laser gain medium in the interior of the laser amplifier a ₆ (irradiation). In this case, the laser amplifier a ₆ can not amplify the supplied laser beam L _a at a desired amplification factor. The second is a decrease in irradiation accuracy. If there is a deviation of the laser optical axis AX, it remains displaced also the optical axis of the laser beam L _a which is output from the laser amplifier a _6.

Therefore, in the laser system shown in FIG. 1, a detector a ₄ and a control device a ₅ are used to perform laser optical axis alignment. Partially transmissive mirror a ₃ has a property of transmitting a part of the laser beam L _a which is received. Detector a ₄ receives the laser beam L _a that has passed through the partial transmission mirror a _3, to detect the deviation between the laser beam axis AX and the desired laser optical axis. If the deviation is detected, the control unit a _5, in accordance with the detected deviation amount, to adjust the angle or position of the total reflection mirror a ₂ to a desired angle or position.

However, in the example of FIG. 1, it is used partially transmissive mirror a _3. Partially transmissive mirror a ₃ has a property of transmitting a part of the laser beam L _a which is received. Therefore, the energy loss of the laser beam L _a is generated by the partial transmission mirror a _3. In other words, by a portion of the laser beam L _a is transmitted through the partial transmission mirror a _3, the energy of the laser beam L _a to be supplied to the laser amplifier a ₆ decreases. As a result, the output of the laser system is also reduced.

1.2. Example 2 of laser optical axis alignment
Therefore, the following method can be considered. FIG. 2 is a schematic diagram for explaining another example of the laser optical axis alignment applied to a certain laser system. The laser system shown in FIG. 2 further includes, for example, a dichroic mirror a ₇ and an alignment light source a ₈ . In the example of FIG. 2, a dichroic mirror a ₃ is used instead of the partial transmission mirror a ₃ shown in FIG. The dichroic mirror a ₇ is disposed in the laser light path OP between the seed light source a ₁ and the total reflection mirror a ₂ . Alignment light source a ₈ generates a is a type of laser beam alignment light L _b. The alignment light _Lb has _a wavelength different from the wavelength of the laser light La.

The laser optical axis alignment performed in the laser system shown in FIG. 2 differs from the laser optical axis alignment described in the example of FIG. 1 in the following points. One is no such a laser beam L _a, is to implement a laser optical axis alignment using the alignment light L _b. For this purpose, the alignment light L _b (see the hatched portion) output from the alignment light source a ₈ is supplied to the laser optical path OP so that the alignment optical axis coincides with the laser optical axis. The second relates to the characteristic of the dichroic mirror a _3. The dichroic mirror a _3, as can be supplied a part of the alignment light L _b to the detector a _4, having the property of transmitting portion of the alignment light L _b.

Specifically, the alignment light L _b output from the alignment light source a ₈ is reflected by the dichroic mirror a ₇ and supplied to the laser light path OP. The alignment light L _b is reflected by the total reflection mirror a ₂ and enters the dichroic mirror a ₃ . Detector a ₄ is receiving the alignment light L _b transmitted through the dichroic mirror a _3. Then, the detector a _4, instead of the laser optical axis, using the alignment optical axis (the optical axis of the alignment light L _b), detecting a shift between the alignment optical axis and the desired laser optical axis. Operation of the control device a ₅ is as described in the example of FIG.

Compared to the example of FIG. 1, in the example of FIG. 2, the laser beam L _a no, the alignment light L _b is supplied to the detector a4 through the dichroic mirror a _3. Therefore, the energy loss of the laser beam L _a per se by the dichroic mirror a ₃ may not occur.

However, in the example of FIG. 2 must be prepared separately alignment light source a _8. Since the number of light sources increases, the configuration of the laser system becomes complicated. In the example of FIG. 2 must be supplied to the laser optical path OP alignment light L _b to the laser beam L _a coaxially. If the alignment optical axis does not coincide with the laser optical axis, it is difficult to accurately detect the deviation between the laser optical axis and the desired laser optical axis by detecting the alignment optical axis. Moreover, it takes time to adjust for supplying alignment light L _b to the laser beam L _a coaxially. Furthermore, in order to supply the alignment light L _b to the laser beam L _a coaxial shall use the hard optic wavelength dependent.

2. First Embodiment A first embodiment relates to a position detection system for a reflected spot, an optical axis alignment system, and an optical axis alignment method.

2.1. Reflection spot position detection system (Overview)
FIG. 3A is a schematic diagram illustrating a configuration example of a reflection spot position detection system SYS1. The outline is as follows. When the laser beam L is irradiated with the excitation light EL and the laser beam L, a reflection spot RS of the laser beam L is generated in the laser gain medium 1. The reflection spot position detection system SYS1 is configured to detect the position of the reflection spot RS. If there is deviation in the laser optical axis AX _L, the position of the reflected spot RS deviates from a desired position. In the reflection spot position detection system SYS1, the laser gain medium 1 emits fluorescence by the excitation light EL. Furthermore, in the reflection spot position detection system SYS1, the position of the reflection spot RS is detected by utilizing the fact that the fluorescence intensity decreases in the reflection spot RS.

(Constitution)
As shown in FIG. 3A, the reflected spot position detection system SYS 1 includes a laser gain medium 1 and a detector 2. The laser gain medium 1 includes a front surface (front surface) 11 and a back surface 12 parallel to the front surface 11. The laser gain medium 1 is arranged on the XY plane so that the surface 11 is parallel to the XY plane. The coordinate system is, for example, orthogonal coordinates having an X axis, a Y axis, and a Z axis.

  The detector 2 is disposed, for example, above the laser gain medium 1. Alternatively, the detector 2 may be disposed below the laser gain medium 1. When the excitation light EL and the laser light L are incident on the laser gain medium 1, the detector 2 detects the position of the reflection spot RS of the laser light in the laser gain medium 1. At that time, the detector 2 detects the position of the region where the fluorescence intensity is lower than the surrounding region as the position of the reflection spot RS.

  The excitation light EL is, for example, excitation laser light. The excitation light EL may be laser light generated by a laser diode (semiconductor laser), for example. Note that the excitation light irradiation method is, for example, an end pump method. Instead of the end face excitation method, for example, a side pump method may be used.

The magnitude of the output of the laser light L is arbitrary. The laser beam L may be a high-power laser beam, for example. In the following description, a case where the spot diameter φ _L of the laser light L is smaller than the spot diameter φ _EL of the excitation light EL is taken as an example (φ _L <φ _EL ).

2.2. Method for Detecting Reflection Spot Position As shown in FIG. 3A, in the end face excitation method, for example, the excitation light EL is coaxial with the laser light L and obliquely from above the laser gain medium 1 toward the surface 11 of the laser gain medium 1 Is irradiated. The present inventor paid attention to the fact that the excitation light EL is used in the end face excitation method (or the side surface excitation method), and considered detecting the position of the reflection spot RS using the excitation light EL.

Below, the detection method of the position of a reflective spot is demonstrated in the following order. First, (A) what phenomenon occurs when only the excitation light EL is irradiated onto the laser gain medium 1 will be described. Next, (B) how the reflection spot RS is generated when the laser light medium 1 is irradiated with the excitation light EL coaxially with the laser light L will be described. Here, the case there is no deviation in the laser beam axis AX _L as an example. Finally, we describe the reflected spot RS occurs when there is a shift in (C) the laser optical axis AX _L.

(A) When Excitation Light Only is Irradiated to the Laser Gain Medium FIG. 3B is a schematic diagram for explaining a phenomenon that occurs when only the excitation light is irradiated to the laser gain medium 1. FIG. 3B is a cross-sectional view of the laser gain medium 1 at X ₁ -X ₁ shown in FIG. 3B (b). FIG. 3B is a plan view showing the surface 11 of the laser gain medium 1.

  As shown in (a) of FIG. 3B, when the excitation light EL is incident on the laser gain medium 1, it is reflected by the laser gain medium 1 and emitted from the laser gain medium 1.

The incident angle θ _IN of the excitation light EL is determined in advance. Furthermore, the position where the excitation light EL is incident on the laser gain medium 1 is also determined in advance. The reflection angle θ _OUT of the excitation light EL is equal to the incident angle θ _IN . Here, the incident angle θ _IN is an angle formed by the excitation optical axis AX _EL at the time of incidence and the normal line H perpendicular to the laser gain medium 1. Similarly, the reflection angle θ _OUT is an angle formed by the excitation optical axis AX _EL at the time of emission and the normal line H.

  For example, the excitation light EL may be reflected by the back surface 12. Hereinafter, in order to simplify the description, a case where the excitation light EL is reflected by the back surface 12 will be described as an example. In practice, the excitation light EL is refracted inside the laser gain medium 1. However, in order to simplify the explanation, the refraction of the excitation light EL is ignored. Similarly, refraction of laser light is also ignored.

  When the excitation light EL is incident, the laser gain medium 1 emits fluorescence by absorbing a part of the excitation light EL. In other words, when the laser gain medium 1 receives the excitation light EL, the laser gain medium 1 emits light from the region where the excitation light EL is absorbed by the interaction between the laser gain medium 1 and the excitation light EL. A region where the laser gain medium 1 absorbs the excitation light EL and emits fluorescence is referred to as a “fluorescence region”. Note that the phenomenon that the laser gain medium 1 fluoresces by the excitation light EL is caused by spontaneous emission that occurs when electrons in the excited state return to the ground state, as already known. The laser light L is amplified in the fluorescent region.

As shown in FIG. 3B (b), when the laser gain medium 1 is viewed from the front surface 11 to the back surface 12, the fluorescent region FR can be seen. The fluorescent region FR is generated in a region where the excitation light EL is transmitted in the laser gain medium 1. In practice, the fluorescent region FR has a spatial extent. In addition, the intensity of the fluorescence in the fluorescent region FR gradually decreases as the _distance from the center C _FR of the fluorescent region FR increases. However, in the description of (a) and (b) in FIG. 3B, it is simplified that the intensity of the fluorescence in the fluorescence region FR is constant.

(B) When excitation light is irradiated on laser gain medium coaxially with laser light FIG. 3C is a schematic diagram for explaining a phenomenon that occurs when excitation light is irradiated on laser gain medium coaxially with laser light. It is. FIG. 3C is a cross-sectional view of the laser gain medium 1 at X ₁ -X ₁ shown in FIG. 3C (b). FIG. 3C is a plan view showing the surface 11 of the laser gain medium 1. FIG. 3C is a partially enlarged view of the fluorescent region FR and the reflection spot RS in A shown in FIG. 3C (b).

  As shown to (a) of FIG. 3C, the laser beam L is irradiated to the surface 11 of the laser gain medium 1 coaxially with the excitation light EL. At this time, in the end face excitation method, the laser light L basically follows the same locus as the excitation light EL. That is, when the laser beam L enters the laser gain medium 1, it is reflected by the laser gain medium 1 and emitted from the laser gain medium 1. A region where the laser light L is reflected in the laser gain medium 1 is referred to as a “reflection spot”.

The laser beam L is reflected by the back surface 12, for example. In addition, the back surface 12 points out the surface where the laser beam L is reflected (total reflection). A reflective coating may be provided in the negative direction of the Z-axis of the back surface 12. Further, there is no problem even if the excitation optical axis AX _EL does not exactly coincide with the laser optical axis AX _L.

If there is no shift in the laser optical axis AX _L, when viewed in the direction of the back surface 12 of the laser gain medium 1 from the surface 11, visible reflection spot RS shown in (b) of FIG. 3C. The reflection spot RS is generated at the center of the fluorescent region FR. In other words, the center _{C RS} reflective spot RS coincides with the center _{C FR} fluorescent region FR. In addition, the size (area) of the reflection spot RS is smaller than the size (area) of the fluorescent region FR. This is because the laser optical axis AX _L is coaxial with the excitation optical axis AX _EL, and the spot diameter φ _L of the laser light L is smaller than the spot diameter φ _EL of the excitation light EL. Note that the center _CRS of the reflection spot RS may be, for example, the center of gravity of the reflection spot RS. Similarly, the center C _FR of the fluorescent region FR may be the center of gravity of the fluorescent region FR, for example.

  As shown in FIG. 3C (c), the intensity (level) of fluorescence differs between the area of the reflection spot RS and the area around the reflection spot RS. Specifically, the intensity of the fluorescence in the area of the reflection spot RS is lower than the intensity in the area around the reflection spot RS. This can be said that the intensity of the fluorescence is relatively lowered in the region where the reflection spot RS overlaps the fluorescent region FR. In the following description, it is simplified that the intensity of fluorescence in the region of the reflection spot RS is constant.

  The intensity of fluorescence is represented by a relative numerical value, for example. As shown in the legend of FIG. 3C (c), the intensity of the fluorescence is expressed in three stages from level 1 to level 3, for example. In this case, level 1 represents the highest intensity. Level 2 represents a lower intensity than level 1. Level 3 represents a lower intensity than level 2. As shown in FIG. 3C (c), the intensity of the fluorescence in the fluorescent region FR (excluding the region of the reflection spot RS) is represented by, for example, level 1 or 2. The intensity of the fluorescence in the area of the reflection spot RS is represented by level 3, for example.

(C) When the laser optical axis is displaced FIG. 3D is a schematic diagram for explaining a reflection spot generated when the laser optical axis is displaced. FIG. 3D is a cross-sectional view of the laser gain medium 1 at X ₁ -X ₁ shown in FIG. 3D (b). FIG. 3D is a plan view showing the surface 11 of the laser gain medium 1. FIG. 3D is a partially enlarged view of the fluorescent region FR and the reflection spot RS in A shown in FIG. 3D (b).

If there is deviation in the laser optical axis AX _L, see a laser gain medium 1 from the surface 11 in the direction of the back surface 12, visible reflection spot RS shown in (b) of FIG. 3D. In this case, the center _{C RS} reflective spot RS is not coincident with the center _{C FR} fluorescent region FR. That is, a deviation occurs between the reflection spot RS and the fluorescent region FR.

Basically, this deviation is caused by at least one of the irradiation angle (incident angle) of the laser light L and the irradiation position (incident position) of the laser light L. FIGS. 3A and 3B illustrate a case where the irradiation angle of the laser light L is smaller than the desired irradiation angle, and the irradiation position of the laser light L is shifted from the desired position in the negative direction of the X axis. doing. Compared to the example shown in FIGS. 3C and 3B, the size of the fluorescent spot FR is not changed, but the size of the reflection spot RS is smaller. Here, the irradiation angle of the laser light L is, for example, refers to the angle and the laser optical axis AX _L and the normal H is. The irradiation position of the laser light L indicates, for example, a position on the surface 11 of the laser gain medium 1.

As described above, it can be said that the fluorescent region FR generated by the excitation light EL has a role as a reference for knowing the positional deviation of the reflection spot. By obtaining the position of the reflection spot RS, it is possible to know the laser optical axis AX _L to be adjusted is deviated from a desired laser optical axis. Therefore, the detector 2 that detects the position of the region where the intensity of fluorescence is lower than the surrounding region as the reflection spot RS is provided.

2.3. Effects Compared with the example shown in FIG. 2, the reflected spot position detection system SYS1 has the following effects. First, since excitation light is used, it is not necessary to prepare an alignment light source separately. This can prevent the configuration of the laser system from becoming complicated. Secondly, compared with the alignment light source, the excitation light does not require high irradiation accuracy to the laser gain medium 1. Therefore, it is not always necessary to supply the excitation light to the laser light path coaxially with the laser light. Thirdly, restrictions on optical components (for example, mirrors) to be used are relaxed. For example, in the example shown in FIG. 2, since alignment light having a wavelength different from the wavelength of the laser light is used, it is necessary to use an optical component that is less dependent on the wavelength.

2.4. Modified Example As described above, the excitation light serves as a reference for knowing the shift of the position of the reflected spot. From this viewpoint, for example, a side surface excitation method can be applied instead of the end surface excitation method.

FIG. 3E is a schematic diagram for explaining a modification of the reflection spot position detection system SYS1. In the side surface excitation method, as shown in FIG. 3E, for example, the excitation light EL is irradiated from the back surface 12 to the front surface 11 of the laser gain medium 1. The entire laser gain medium 1 can be irradiated with the excitation light EL. From this point of view, the spot diameter phi _EL of the excitation light EL may be the same as the spot diameter phi _L of the laser beam L, it may be larger than the spot diameter phi _L of the laser beam L.

2.5. Laser optical axis alignment system (Overview)
The reflected spot position detection system is applied to a laser optical axis alignment system. FIG. 4 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2. The outline is as follows. The laser optical axis alignment system SYS2 is configured to adjust the optical system 3 based on the position of the reflected spot detected by the position detection system SYS1 of the reflected spot. If there is deviation in the laser optical axis AX _L, as described above, the position of the reflected spot deviates from a desired position. In that case, the control device 4 adjusts the optical system 3 so that the position of the reflection spot becomes a desired position. This allows the laser beam axis AX _L which deviates matches the desired laser optical axis. For example, when a lens for narrowing the laser light L emitted from the laser gain medium 1 is provided, the optical axis of the lens coincides with the optical axis of the laser light L emitted from the laser gain medium 1.

(Constitution)
As shown in FIG. 4, the laser optical axis alignment system SYS <b> 2 includes an optical system 3, a control device 4, and a display 5 in addition to the laser gain medium 1 and the detector 2. As described above, the reflection spot position detection system SYS 1 includes the laser gain medium 1 and the detector 2. For convenience of explanation, a cooling unit 100 described later is virtually illustrated.

The laser gain medium 1 is formed of a solid crystal (including glass) or a liquid. A material suitable for the wavelength of the laser beam L is used for the laser gain medium 1. Examples of the solid crystal include yttrium aluminum garnet (YAG) containing ytterbium trivalent ions (Yb ³⁺ ). Examples of the liquid include a liquid in which a fluorescent organic dye (for example, oxazine-based dye) is dissolved in a solvent (for example, alcohol). Note that it is technically difficult to use a gaseous laser gain medium from the viewpoint of clearly detecting the position of the reflection spot RS. Therefore, the phase state of the laser gain medium 1 is solid or liquid. The laser gain medium 1 is used as an oscillator or an amplifier, for example.

  The detector 2 is composed of a solid-state image sensor, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor. A CMOS image sensor has a characteristic that its sensitivity is very high compared to other solid-state imaging devices. The detector 2 images the surface 11 of the laser gain medium 1 in order to detect the position of the reflection spot RS. Therefore, the detector 2 is arranged above the surface 11 of the laser gain medium 1 (in the positive direction of the Z axis). In other words, the detector 2 is arranged not on the back surface 12 side of the laser gain medium 1 but on the front surface 11 side of the laser gain medium 1. This is due to the following reason.

  The temperature rise that occurs on the back surface 12 of the laser gain medium 1 tends to be greater than the temperature rise that occurs on the front surface 11. Therefore, by disposing the detector 2 on the front surface 11 side of the laser gain medium 1, the cooling unit 100 can be disposed on the rear surface 12 side of the laser gain medium 1. As a result, the back surface 12 of the laser gain medium 1 can be effectively cooled.

  The detector 2 is electrically connected to the control device 4 and the display 5 respectively. The detector 2 images the reflection spot RS and its surroundings in real time, and generates imaging data DA. The detector 2 outputs the generated imaging data DA to the control device 4 and the display 5 respectively. The imaging data DA is, for example, image data (including moving image data) subjected to RGB (Red Green Blue) processing. The imaging data DA may be luminance data, for example. The detector 2 may image the entire surface 11 of the laser gain medium 1 including the reflection spot RS.

Optical system 3, for example, has a first total reflection mirror 30 _1, and a second total reflection mirror 30 _2. The first total reflection mirror 30 ₁ and the second total reflection mirror 30 _2, so that the laser beam L is incident on the incident point _{P IN} of the laser gain medium 1, on the side of the incident point _{P IN} than emission point _{P OUT,} Arranged above the laser gain medium 1.

The laser optical path OP is designed in advance. As shown in FIG. 4, the laser optical path OP passes, for example, a point P ₁ , a point P ₂ , a point P ₃ , an incident point P _IN , a reflection spot RS, and an emission point P _OUT . Here, the point P ₁ is above the laser gain medium 1 on the incident point _PIN side with respect to the emission point P _OUT . Point P ₂ is from the point P ₁ to the position spaced a predetermined distance in the positive direction of the X axis. Point P ₃ is from point P ₂ to the position spaced a predetermined distance downward (negative direction of Z-axis). The incident point _PIN is a point where the laser light L is incident on the laser gain medium 1. The emission point P _OUT is a point where the laser light L is emitted from the laser gain medium 1 and is symmetric with respect to the incident point _PIN and the normal line H.

The first total reflection mirror 30 _1, so that the laser beam L is totally reflected toward the point P ₂ to the point P _3, it is arranged in the laser light path OP. The second total reflection mirror 30 _2, as the laser light L totally reflected by the first total reflection mirror 30 ₁ is reflected toward the point P ₃ to the incident point P _IN, it is arranged in the laser light path OP. The two total reflection mirrors 30 ₁ and 30 ₂ allow the laser gain medium 1 to be irradiated with the laser light L at a predetermined angle at a predetermined angle.

The configuration of the optical system 3 is arbitrary. The optical system 3 may be suitably configured according to a desired laser optical path OP. For example, the optical system 3, a second total reflection mirror 30 ₂ may be omitted. Other types of optical components (for example, lenses) may be provided in the laser optical path OP.

  The control device 4 receives the imaging data DA from the detector 2. The control device 4 controls the angle or position of at least one optical component among a plurality of optical components (optical elements) based on the imaging data DA. For example, since the control device 4 is provided, the optical system 3 can be automatically adjusted.

The plurality of optical components, the first total reflection mirror 30 ₁ and the second addition to the total reflection mirror 30 _2, includes a laser gain medium 1. The laser gain medium 1 has a property of reflecting the excitation light EL and the laser light L. Therefore, the laser gain medium 1 can be handled as one of the optical components. In the example of FIG. 4, the control unit 4, the optical system 3, for example, it controls the first total reflection mirror 30 ₁ and the second total reflection mirror 30 _2. Control In the control device 4, the first total reflection mirror 30 ₁ and the second may be controlled in conjunction with the total reflection mirror 30 _2, it may be individually controlled both. Incidentally, the control target of the control device 4, may be either one of the first total reflection mirror 30 ₁ and the second total reflection mirror 30 _2.

  The display 5 includes a display screen 51. By providing the display 5, the operator can easily confirm the deviation of the reflection spot RS visually. The display 5 receives the imaging data DA from the detector 2. The display 5 displays the reflection spot RS and its surroundings on the display screen 51 based on the received imaging data DA. If the detector 2 is imaging the entire surface 11 of the laser gain medium 1 including the reflection spot RS, the display 5 displays the entire surface 11 of the laser gain medium 1 on the display screen 51.

2.6. Display screen The reflected spot is displayed on the display screen as follows. First, a case where there is no deviation in the laser optical axis will be described. Next, a case where there is a deviation in the laser optical axis will be described.

(When there is no deviation of the laser optical axis)
FIG. 5A is a diagram illustrating a display screen 51 when there is no deviation in the laser optical axis. In this case, the display screen 51 displays an image in which the center C _RS of the reflection spot RS matches the center C _FR of the fluorescent region FR. Therefore, laser optical axis alignment is unnecessary. FIG. 5A shows the periphery of the reflection spot RS and the fluorescent region FR.

(When there is a deviation in the laser beam axis)
FIG. 5B is a diagram illustrating a display screen 51 when the laser optical axis is displaced. In this case, the display screen 51 displays an image in which the center C _RS of the reflection spot RS is shifted from the center C _FR of the fluorescent region FR. Therefore, laser optical axis alignment is necessary. To offset the laser beam axis to coincide with the desired laser beam axis, so that the center C _RS reflective spots RS coincides with the center C _FR fluorescent region FR, it can be seen that it is sufficient to adjust the optical system 3 . FIG. 5B shows the periphery of the reflection spot RS and the fluorescent region FR. As described later, reference symbol "D" indicates the center C _RS reflective spot RS, the distance between the center C _FR fluorescent region FR.

2.7. Control System of Optical System A control mechanism of the optical system will be described with reference to FIG. FIG. 6 is a conceptual diagram for explaining the control mechanism of the optical system 3. See also FIGS. 5A and 5B as appropriate. Hereinafter, as the control target of the control device 4, it includes a first total reflection mirror 30 ₁ Example. The following description, when the second control target total reflection mirror 30 ₂ are also applied to the second with the total reflection mirror 30 _2. First, the optical system will be described.

(First total reflection mirror)
As shown in FIG. 6, the first total reflection mirror 30 ₁ is provided with a mirror 301. The first total reflection mirror 30 ₁ is rotated about the two axes. One of the two axes is the φ axis. The φ axis is a rotation axis that passes through the center of the mirror surface 301 and is parallel to the Z axis. Therefore, the angle around the φ axis can be adjusted. The other is the θ axis. The θ axis is a rotation axis at the center of the mirror surface 301 and is parallel to the X axis (or Y axis). Therefore, the angle around the θ axis can be adjusted. Furthermore, the first total reflection mirror 30 ₁ is freely movable over a predetermined axis in the X-Y plane. In the example of FIG. 6, the first total reflection mirror 30 ₁ is free to move along the X axis. The first movement direction of the total reflection mirror 30 _is an optionally in the X-Y plane. The first total reflection mirror 30 ₁ may freely movable in the Z-axis direction.

(Mirror unit)
As shown in FIG. 6, the optical system 3 includes a mirror unit 31. The first total reflection mirror 30 _1, for example, is attached to the mirror unit 31. Mirror unit 31 is a device for fixing the first total reflection mirror 30 ₁ to a desired angle and position. The mirror unit 31 is arranged so that the laser optical axis is incident on the center O of the mirror surface 301. Mirror unit 31 is configured to be able to first totally reflecting mirror 30 ₁ rotates freely about the φ axis and θ-axis. Moreover, the mirror unit 31 is, for example, the first total reflection mirror 30 ₁ is also configured to move predetermined axis (e.g., X-axis) over freely. Further, as the first total reflection mirror 30 ₁ is movable freely along the Z-axis, the mirror unit 31 may be configured.

  Specifically, the mirror unit 31 includes, for example, a base 311, a rail 312, a block 313, a support base 314, a mirror fixing portion 315, a first adjustment fitting 316, and a second adjustment fitting 317. . The mirror fixing portion 315 has a first shaft portion 3151 and a second shaft portion 3152.

The base 311 is disposed on the XY plane. The rail 312 is disposed on the base 311. In the example of FIG. 6, the rail 312 extends in the X-axis direction. The block 313 moves freely on the rail 312. The support base 314 is a base for supporting the mirror fixing portion 315 and is fixed on the block 313. The inside of the support base 314 has, for example, a cylindrical cavity. Mirror fixing section 315, desired φ axis angle, or θ by an angle around the axis, a first part for fixing the total reflection mirror 30 _1. Therefore, the first shaft portion 3151, as the first total reflection mirror 30 ₁ is rotated about the φ axis, it is inserted into the support base 314. Furthermore, as the first total reflection mirror 30 ₁ is movable along the Z-axis, the first shaft portion 3151 inside the supporting table 314 may be movable in the positive or negative direction of the Z-axis. Second shaft portion 3152, as the first total reflection mirror 30 ₁ is rotated about the θ axis, it is attached to the first total reflection mirror 30 _1. First adjusting metal fitting 316 is a fitting for fixing an angle of φ axis to desired first total reflection mirror 30 _1. Second adjustment bracket 317 is a metal fitting for fixing an angle of θ axis to desired first total reflection mirror 30 _1.

(Outline of control device)
The control device 4 will be described. The outline is as follows. The controller 4, based on the distance between the position and the reference position of the reflection spot, controls the first angle or the position of the total reflection mirror 30 _1. As shown in FIGS. 5A and 5B, the reference position is, for example, the center C _FR of the fluorescent region FR. That is, the center _{C FR} fluorescent region FR of a reference position is a position to be present center _{C RS} reflective spot RS. More specifically, the control device 4, the center _{C RS} reflective spot RS, calculated as the distance D shift amount (see FIG. 5B) between the center _{C FR} fluorescent region FR. Center _{C FR} center _{C RS} and fluorescence region FR of the reflection spot RS, for example, represented by relative coordinates. The distance D can, for example, can be calculated using the coordinates of the center C _RS reflective spot RS, the coordinates of the center C _FR fluorescent region FR.

In the above description, the center C _FR fluorescent region FR is employed in the reference position. However, the reference position may be an arbitrary position as long as the position shift of the reflection spot RS can be detected. The reference position may be the center of the surface 11 of the laser gain medium 1, for example. For example, when the shape of the surface 11 of the laser gain medium 1 is a quadrangle, the center of the surface 11 is determined from the positions of the four corners of the laser gain medium 1. Therefore, the center of the surface 11 determined from the positions of the four corners can be used as the reference position. Alternatively, an alignment mark can be applied to the laser gain medium 1 and the position of the applied alignment mark can be used as a reference position.

As shown in FIG. 5A, when the center C _RS of the reflection spot RS is coincident with the center C _FR of the fluorescent region FR, the distance D is zero. In this case, since the laser optical axis alignment is unnecessary, the control device 4 does nothing. On the other hand, as shown in FIG 5B, when the center _{C RS} reflective spot RS is displaced from the center _{C FR} fluorescent region FR, the distance D has a value greater than 0. In this case, laser optical axis alignment is necessary. Therefore, the control unit 4, the calculated shift amount (i.e., distance D) is such that the zero, controls the first angle or the position of the total reflection mirror 30 _1.

(Configuration of control device)
The control device 4 described above is configured as follows. The control device 4 includes, for example, an arithmetic unit 41, a motor 412 and a drive mechanism 413.

The arithmetic unit 41 includes, for example, a microcomputer, a storage device (for example, a memory), and various control circuits. The arithmetic unit 41 performs control processing based on the imaging data received from the detector. Control process is one of a process for controlling the first angle or the position of the total reflection mirror 30 _1. For example, when the motor 412 receives the control signal CNRL from the arithmetic unit 41, the motor 412 rotates the rotating shaft based on the control signal CNRL. The drive mechanism 413 includes, for example, various gears and a plurality of shafts. The drive mechanism 413 is configured to individually drive the block 313, the first adjustment fitting 316, and the second adjustment fitting 317, for example, using the rotational power transmitted from the rotation shaft of the motor 412.

(Operation of control device)
The control processing executed by the arithmetic unit 41 is roughly divided into the following three types. The first is A) calculation of the distance D. The second is B) Judgment of laser optical axis alignment. The third is C) control of the drive mechanism 413.

A) Calculation of Distance D The arithmetic unit 41 receives the imaging data from the detector, and calculates the distance D (for example, see FIG. 5B) based on the imaging data. At that time, the arithmetic unit 41 performs image analysis on the imaging data, and coordinates C _RS (x ₁ , y ₁ ) of the center C _RS of the reflection spot RS and coordinates C _FR (x of the center C _FR of the fluorescent region FR) ₂ , y ₂ ). The image analysis method may be a known method. For example, two coordinates can be acquired by using a fluorescence intensity distribution represented by a relative numerical value. Then, the calculation unit 41 calculates the distance D by executing the calculation: √ [(x ₁ −x ₂ ) ² + (y ₁ −y ₂ ) ² ]. The calculation method of the distance D may be another method.

B) Judgment on Implementation of Laser Optical Axis Alignment As a result of the calculation, when the distance D = 0, the arithmetic unit 41 determines (determines) that there is no deviation in the laser optical axis and does nothing. On the other hand, when the distance D> 0, the arithmetic unit 41 determines that there is a deviation in the laser optical axis.

C) Control of Drive Mechanism 413 When the distance D> 0, the arithmetic unit 41 controls the drive mechanism 413 so that the distance D becomes zero. For this purpose, the arithmetic unit 41 uses the two coordinates {C _RS (x ₁ , y ₁ ), C _FR (x ₂ , y ₂ )} to set the first total reflection mirror 30 ₁ having a distance D of zero. Get the angle or position. That is, the arithmetic unit 41, the distance D to obtain a first amount of adjustment of the total reflection mirror 30 ₁ becomes zero. The method for obtaining the adjustment amount may be a known method. The arithmetic unit 41 outputs a control signal CNRL to the motor 412 so that the distance D becomes zero. The control signal itself is, for example, a high level or low level voltage signal.

  When the distance D> 0, upon receiving the control signal CNRL from the arithmetic unit 41, the motor 412 rotates the shaft of the motor 412 based on the control signal CNRL. The drive mechanism 413 individually drives the block 313, the first adjustment fitting 316, and the second adjustment fitting 317 using the rotational power transmitted from the shaft of the motor 412.

For example, when only the angle of the first θ axis total reflection mirror 30 ₁ is offset from a desired angle. In this case, the drive mechanism 413, as a 1 theta axis angle of the total reflection mirror 30 ₁ is consistent with the desired angle, drives the second adjustment bracket 317. For example, consider the case where only the position of the first total reflection mirror 30 ₁ in the X-axis direction is deviated from a desired position. In this case, the drive mechanism 413, as a 1 X axis direction position of the total reflection mirror 30 ₁ coincides with the desired position, is moved along the blocks 313 to the rail 312.

2.8. Laser Optical Axis Alignment Method A laser optical axis alignment method will be described. FIG. 7 is a flowchart illustrating a laser optical axis alignment method. As shown in FIG. 8, the laser optical axis alignment method includes four steps ST1 to ST4. In the following description, given a first adjustment of the total reflection mirror 30 ₁ Example. Please refer to FIG. 4 as appropriate.

  First, the excitation light EL and the laser light L are incident on the laser gain medium 1 (ST1). Then, a reflection spot RS of the laser light L is generated in the laser gain medium 1. Next, the detector 2 detects the position of the reflection spot RS of the laser light L in the laser gain medium 1 (ST2).

If there is a deviation of the reflection spot RS, that is, if the center of the reflection spot RS is deviated from the center of the fluorescent region FR (ST3: YES), laser optical axis alignment is necessary. Therefore, the control device 4, the center of the reflected spot RS is to coincide with the center of the fluorescent region FR, controls the first angle or the position of the total reflection mirror 30 ₁ (ST4). By executing the step ST4, the first adjustment of the total reflection mirror 30 ₁ it is completed. By step ST4, the laser optical axis coincides with the desired laser optical axis. For example, when a lens for narrowing the laser light L emitted from the laser gain medium 1 is provided, the optical axis of the lens coincides with the optical axis of the laser light L emitted from the laser gain medium 1.

  If there is no deviation of the reflection spot RS (ST3: NO), laser optical axis alignment is unnecessary. Therefore, the control device 4 does nothing.

(Supplement)
The adjustment of the optical system 3 may be performed manually. In this case, in step ST3, the operator may determine whether the center of the reflection spot RS coincides with the center of the fluorescent region FR while viewing the display screen 51 of the display 5. In step ST4, the operator may adjust the angle or position of the optical component to be adjusted so that the distance D becomes zero. For example, consider the case where there is a shift to the first total reflection mirror 30 ₁ of φ axis angle. In this case, the operator, by moving the first adjustment bracket 316, the first may be adjusted angle φ about the axis of the total reflection mirror 30 _1.

2.9. Effect With the laser optical axis alignment system SYS2 to which the reflection spot position detection system SYS1 is applied, the laser optical axis can be adjusted without newly providing a light source for adjusting the laser optical axis. Furthermore, the same effect as described in the reflection spot position detection system SYS1 can be obtained.

2.10. Laser System The laser optical axis alignment system SYS2 is suitable for a laser system. FIG. 8 is a block diagram illustrating a configuration example of a laser system SYS3 to which the laser optical axis alignment system SYS2 is applied. The laser system SYS3 may be a system (optical excitation system) that amplifies or generates seed light (for example, laser light) using excitation light. The laser system SYS3 may continuously oscillate the laser beam L or may oscillate it.

  As shown in FIG. 8, the laser system SYS3 includes a laser gain medium 1, a detector 2, an optical system 3, a control device 4, a display 5, a computer device (PC) 6, an excitation light source 7, A seed light source 8 and a laser amplifier 10 are included. The laser optical axis alignment system SYS2 further includes a computer device 6 in addition to the laser gain medium 1 (laser amplifier 10), the detector 2, the optical system 3, the control device 4, and the display 5. The laser optical axis alignment system SYS2 includes a reflection spot position detection system SYS1. Here, the computer apparatus 6, the excitation light source 7, the seed light source 8, and the laser amplifier 10 will be described.

  The computer device 6 is, for example, a personal computer (physical machine). The computer device 6 includes, for example, a CPU (Central Processing Unit), a volatile memory, a nonvolatile storage device (for example, a hard disk), and an input device (for example, a keyboard). For example, the computer device 6 may be used to execute control processing executed by the arithmetic unit of the control device 4. In this case, the computer device 6 executes the control process described above in cooperation with the detector 2, the control device 4, and the display 5.

  The excitation light source 7 is a generation source of the excitation light EL, and is, for example, a laser diode (semiconductor diode). Excitation light EL output from the excitation light source 7 enters the laser amplifier 10 via the optical system 3.

  The seed light source 8 is a generation source of the laser light L. The laser light L output from the seed light source 8 enters the laser amplifier 10 via the optical system 3.

  The laser amplifier 10 includes a laser gain medium 1 and a cooling unit 100. The laser amplifier 10 amplifies and outputs the laser light L supplied from the seed light source 8. The type of laser amplifier is, for example, an active mirror type. For example, a rod type may be used instead of the active mirror type. The cooling unit 100 is composed of, for example, a heat sink. When the cooling unit 100 is configured by a heat sink, the heat sink is attached to the back surface of the laser gain medium 1, for example.

  Since the laser optical system alignment system SYS2 is applied to the laser system SYS3, there is an advantage that the irradiation accuracy is high.

2.11. Modified Example As described above, the laser gain medium 1 can be handled as a kind of optical component. FIG. 9 is a block diagram showing the laser optical axis alignment system SYS2 when the control target by the control device 4 is the laser gain medium 1. As shown in FIG. When the position of the reflection spot RS is deviated from a desired position, the control device 4 may control the angle or position of the laser gain medium 1 as shown in FIG.

3. Second Embodiment 3.1. Outline The second embodiment relates to a laser optical axis alignment system. As a method for obtaining high-power laser light, for example, a system in which a plurality of laser gain media are optically connected in multiple stages (cascade) is known. In order to support this method, one detector is provided for each of the plurality of laser gain media.

3.2. Details Differences from the first embodiment will be described below. FIG. 10 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2a. As shown in FIG. 10, the laser optical axis alignment system SYS2a has a plurality of optical components (optical elements), _{2 1} and the first detector, and a second detector _{2 2.} A plurality of optical components includes a first laser gain medium 1A, and the second laser gain medium 1B, the first total reflection mirror 30 _1, and a second total reflection mirror 30 _2.

The first laser gain medium 1A is as described in the first embodiment. When the excitation light EL and the laser beam L is incident on the first laser gain medium 1A, first reflection spot RS ₁ is generated in the first laser gain medium 1A. First reference position corresponding to the first reflection spot RS ₁ is a first center _{C FR1} of the fluorescent regions FR ₁ generated in the first laser gain medium 1A.

The configuration of the second laser gain medium 1B itself is the same as the configuration of the first laser gain medium 1A. However, since the second laser gain medium 1B is connected to the first laser gain medium 1A in multiple stages, the arrangement of the two is different. Specifically, the second laser gain medium 1B is arranged so that the excitation light EL and the laser light L emitted from the first laser gain medium 1A are incident thereon. Thus, in the example of FIG. 10, the second laser gain medium 1B is a side of the exit point P _OUT than the incident point P _IN of the first laser gain medium 1A, it is disposed higher than the first laser gain medium 1A Yes. Further, the direction of the surface 11 of the second laser gain medium 1B is opposite to the direction of the surface 11 of the first laser gain medium 1A. When the excitation light EL and the laser beam L is incident on the second laser gain medium 1B, the second reflection spot RS ₂ is generated in the second laser gain medium 1B. Second reference position corresponding to a second reflection spot RS ₂ is the second center _{C FR2} fluorescent region FR ₂ generated in the second laser gain medium 1B.

First detector 2 ₁ detects the first position of the reflection spot RS ₁ generated in the first laser gain medium 1A.

The second detector 2 ₂ itself of the configuration is the same as the first detector 2 ₁ configuration. However, both arrangements are different from each other. In the example of FIG. 10, the second detector 2 ₂ is disposed below (negative direction of Z-axis) than the surface 11 of the second laser gain medium 1B. By those arrangement, it is possible to arrange the cooling unit 100 ₂ on the side of the back surface 12 of the second laser gain medium 1B. The second detector 2 ₂ detects the second position of the reflected spot RS ₂ generated in the second laser gain medium 1B.

The control device 4, the imaging data DA ₁ received from the first detector 2 _1, based on the imaging data DA ₂ received from the second detector 2 _2, at least one optical component of the plurality of optical components The angle or position of (for example, the first total reflection mirror 30 ₁ ) is controlled.

  The second embodiment has been described above. The laser optical axis alignment system SYS2a is effective not only for the above-described effect but also for a system in which a plurality of laser gain media are connected in multiple stages. Note that the second embodiment can also be applied when three or more laser gain media are connected in multiple stages. This will be readily understood by those skilled in the art.

4). Third Embodiment 4.1. Outline The third embodiment relates to a laser optical axis alignment system. As a method for obtaining a high-power laser beam, for example, a method of reflecting a laser beam a plurality of times in a single laser gain medium is known. In the case of this method, two or more reflection spots are generated in the laser gain medium. In order to adjust the laser optical axis, it is only necessary to know the position of at least one reflection spot.

  However, it may take time and effort to grasp the direction in which the laser optical axis is deviated from the position of only one reflection spot. Also, adjustment of the optical component itself may take time. From this point of view, it is desirable that the number of reflection spot positions to be detected is plural (for example, two). In that case, it is possible to easily grasp in which direction the laser optical axis is displaced.

4.2. Details Differences from the first and second embodiments will be described below. FIG. 11 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2b. As shown in FIG. 11, the laser optical axis alignment system SYS2b includes a laser gain medium 1C, _{2 1} a first detector, a second detector _{2 2.}

  The laser gain medium 1C is formed longer in the X-axis direction than the laser gain medium 1 described in the first embodiment. This is because the laser beam L is reflected a plurality of times. Of course, in order to reflect the laser beam L a plurality of times, the irradiation angle of the laser beam L may be adjusted.

When the excitation light EL and the laser light L are incident on the laser gain medium 1C, the laser light L is reflected a plurality of times in the laser gain medium. Therefore, a number of reflection spots equal to the number of reflections are generated in the laser gain medium 1C. In the example of FIG. 11, the first reflection spot RS ₁ , the second reflection spot RS ₂ , and the third reflection spot RS ₃ are generated.

The first reflection spot RS ₁ occurs, for example, the back surface 12 of the laser gain medium 1C. Reference position corresponding to the first reflection spot RS ₁ is a first center _{C FR1} of the fluorescent regions FR _1. The second reflection spot RS ₂ occurs, for example, the surface 11 of the laser gain medium 1C. The second reflection spot RS ₂ is spaced apart from the first reflection spot RS ₁ in the positive direction of the X axis. Reference position corresponding to a second reflection spot RS ₂ is the center _{C FR2} of the second fluorescent region FR _2. Third reflecting spot RS ₃ occurs, for example, the back surface 12 of the laser gain medium 1C. Third reflecting spot RS ₃ is spaced from the second reflection spot RS ₂ in the positive direction of the X axis. Reference position corresponding to the third reflecting spot RS ₃ is the center _{C FR3} of the third fluorescent region FR _3.

In the following description, the first reflection spot RS ₁ and the third reflection spot RS ₃ are given as examples as the reflection spot RS to be used. Of course, for example, the first reflection spot RS ₁ and the second reflection spot RS ₂ may be used as the reflection spots to be used. In principle, the positions of all the reflection spots RS generated in the laser gain medium 1C can be used. However, in order to uniquely determine the position and direction of the laser optical axis, two reflection spots RS should be used.

First detector _{2 1} detects the first position of the reflection spot RS _1.

The second detector 2 ₂ itself of the configuration is the same as the first detector 2 ₁ configuration. However, both arrangements and detection targets are different from each other. In the example of FIG. 11, the second detector _{2 2} detects the position of the third reflection spot RS _3. The second detector 2 ₂ so as to be able to image the third reflecting spot RS _3, at a position spaced apart from the first detector 2 ₁ in the positive direction of the X axis, are arranged above the laser gain medium 1C ing.

The control device 4, the imaging data DA ₁ received from the first detector 2 _1, based on the imaging data DA ₂ received from the second detector 2 _2, at least one optical component of the plurality of optical components The angle or position of (for example, the first total reflection mirror 30 ₁ ) is controlled.

  The third embodiment has been described above. The laser optical axis alignment system SYS2b not only has the above-described effects, but is also effective for a system that reflects laser light multiple times in a single laser gain medium. Furthermore, since the positions of the two reflection spots RS are used, laser optical axis alignment can be more easily performed.

4.3. Modification The number of detectors 2 may be one. FIG. 12 is a block diagram showing the laser optical axis alignment system SYS2c when the number of detectors 2 is one. In the laser optical axis alignment system SYS2c, one detector 2 detects the position of each of the plurality of reflection spots RS. In the example of FIG. 12, the detector 2 detects the position of the first reflection spot RS _{1 and} the position of the third reflection spot RS ₃ . The detector 2 is disposed above the laser gain medium 1 so that both positions can be imaged simultaneously.

5. Fourth embodiment 5.1. Outline The fourth embodiment relates to cooling of a laser gain medium. As described above, the laser gain medium emits fluorescence when receiving laser light or excitation light. Therefore, the distribution of the fluorescence spectrum emitted from the laser gain medium is known. If the distribution of the fluorescence spectrum is known, the temperature of the laser gain medium can be known. By using the obtained temperature, the laser gain medium can be cooled to an optimum temperature.

  FIG. 13 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2d. In the example of FIG. 13, the detector 2 a is configured to detect the spectrum of the fluorescence emitted from the laser gain medium 1 in addition to the position of the reflection spot RS. When detecting the fluorescence spectrum, the detector 2 a outputs the detected fluorescence spectrum to the computer device 6. The computer device 6 is used as a cooling unit control device that controls the cooling unit 100. The cooling unit 100 includes a cooling mechanism (for example, a fan) that can control the strength of cooling. The cooling unit 100 cools the laser gain medium 1 under the control of the computer device 6.

  FIG. 14 is a diagram showing an example of the distribution of the fluorescence spectrum detected by the detector 2a. In FIG. 14, the horizontal axis represents the frequency f of the detected fluorescence spectrum. The vertical axis represents the relative intensity I of the fluorescence spectrum. The latest (current) temperature of the laser gain medium 1 is known from the distribution of the fluorescence spectrum.

  The computer device 6 controls the cooling intensity of the cooling unit 100 based on the fluorescence spectrum detected by the detector 2a. Specifically, the computer device 6 analyzes the detected fluorescence spectrum and acquires the distribution of the fluorescence spectrum. The method for obtaining the distribution of the fluorescence spectrum may be a known method. The computer device 6 calculates (estimates) the latest temperature of the laser gain medium 1 using the distribution of the fluorescence spectrum. Calculation of the temperature of the laser gain medium 1 may be performed based on the correspondence between the temperature of the laser gain medium 1 and the distribution of the fluorescence spectrum and the acquired distribution of the fluorescence spectrum. The correspondence relationship between the temperature of the laser gain medium 1 and the distribution of the fluorescence spectrum can be obtained in advance by experiments or the like. Then, the computer device 6 controls the cooling unit 100 so that the calculated temperature becomes a target value (desired temperature of the laser gain medium 1). The control method of the cooling unit 100 may be negative feedback control, for example.

  Alternatively, the control device 4 may execute acquisition of the fluorescence spectrum distribution and calculation of the temperature of the laser gain medium 1. The laser optical axis alignment system SYS2d may be configured so that the display 5 can display the distribution of the fluorescence spectrum.

  According to the fourth embodiment, not only the effects described in the first embodiment can be achieved, but also the laser gain medium can be cooled to an optimum temperature.

6). Fifth embodiment 6.1. Outline The fifth embodiment relates to laser optical axis alignment. For example, in the first embodiment, as shown in FIGS. 3D (a), (b), and (c), the irradiation position of the laser light L is shifted from the desired position in the negative direction of the X axis. The laser optical axis alignment in FIG. In the first embodiment, the laser optical axis is adjusted so that the distance (shift amount) between the center of the reflection spot and the reference position (for example, the center of the fluorescent region) becomes zero. However, even if the center of the reflection spot coincides with the reference position, the laser optical axis may be shifted. In this case, in addition to the above-described distance, the angle around the reference position in the plan view (XY plane) is adjusted. By using two parameters (distance and angle described above), the accuracy of laser optical axis alignment is further improved.

6.2. Details First, a description will be given of a case where the laser optical axis is shifted even though the center of the reflection spot coincides with the reference position. FIG. 15 shows the case where the center C _RS of the reflection spot RS coincides with the reference position (for example, the center C _{FR of the} fluorescent region), but there is a deviation in the angle α around the reference position in the XY plane. It is a schematic diagram which shows. In FIG. 15, the fluorescent region and the excitation light are not shown.

As shown in FIG. 15, the laser light L is incident on the laser gain medium 1 obliquely with respect to the first reference axis 13. Here, the first reference axis 13, for example, through the center _{C RS} reflective spot RS, is an axis parallel to the X axis. Note that the second reference axis 14, for example, through the center _{C RS} reflective spot RS, an axis perpendicular to the first reference axis 13.

In the example illustrated in FIG. 15, the reflection spot RS (for example, the major axis of the reflection spot) is shifted around the reference position (that is, the center C _FR of the fluorescent region _FR ). Therefore, the control device (for example, see FIG. 4) controls the angle or position of the optical system (for example, see FIG. 4) based on the angle α (alpha) around the reference position in the XY plane. That is, the control device controls the angle or position of the optical system so that the angle α becomes a desired angle. Here, the angle alpha, for example, an angle between the first reference axis 13 and the laser optical axis AX _L. In the example of FIG. 15, the angle or position of the optical system is controlled so that the angle α is zero. The angle α may be, for example, it addressed at an angle between the second reference axis 14 and the laser optical axis AX _L. Alternatively, the control device may control the angle or position of the laser gain medium 1 that is one of the optical systems based on the angle α.

  Next, a case where there is a deviation between the position of the reflection spot RS and the reference position (that is, the distance D> 0) will be described. In this case, the control device may control the angle or position of the optical system based on the angle α in addition to the distance between the position of the reflection spot RS and the reference position. This will be readily understood by those skilled in the art. Also, it will be easily understood by those skilled in the art that the method of the fifth embodiment can be applied when there are a plurality of reflection spots (for example, the examples shown in FIGS. 11 and 12). .

  According to the fifth embodiment, the laser optical axis is adjusted based on the angle around the reference position in addition to the distance between the position of the reflection spot and the reference position. Therefore, the accuracy of the laser optical axis alignment is further improved as compared with the case where the laser optical axis alignment is performed using only the distance. In addition, laser optical axis alignment can be more easily performed. Of course, the effects described in the first embodiment can also be obtained.

  7). Sixth embodiment

  In order to introduce laser light into the laser gain medium, for example, a lens is used. In order to appropriately introduce the laser light into the laser gain medium, the lens is required to be disposed at a desired angle and position. Comparing the case where the lens is arranged at a desired angle and position and the case where the lens is not arranged at the desired angle and position, the fluorescence intensity distribution is different inside the reflection spot. An example will be given below in which the fluorescence intensity distribution is different inside the reflection spot in both cases.

FIG. 16 is a partially enlarged view of the reflection spot and the periphery of the reflection spot. When the lens is arranged at a desired angle and position, it is assumed that the intensity of fluorescence is constant (for example, level 3) inside the reflection spot RS, as shown in FIG. If the lens is not disposed at a desired angle and position, for example, as shown in FIG. 16B, a region where the intensity of fluorescence is lower than level 3 (eg, level) within the reflection spot RS. 4) may occur. That is, the fluorescence intensity distribution shown in FIG. 16B is different from the fluorescence intensity distribution shown in FIG. The center _{C RS} reference position of the reflected spot RS (e.g., the center _{C FR} fluorescent region) in some cases deviates from.

In the example of FIG. 16, when the fluorescence intensity changes inside the reflection spot RS, the angle or position of the lens may be adjusted so that the fluorescence intensity is constant inside the reflection spot RS. I understand. Moreover, as the center C _RS reflective spot RS becomes the reference position may be also adjusted angle or position of the optical system.

  FIG. 17 is a block diagram illustrating a configuration example of the laser optical axis alignment system SYS2e. As shown in FIG. 17, the laser optical axis alignment system SYS2e further includes a lens 9. The lens 9 is one of optical elements. The lens 9 is disposed in the optical path OP of the laser light L and introduces the laser light L into the laser gain medium 1. A plurality of lenses 9 may be provided. For example, in the example of FIG. 17, the lens 9 is disposed in front of the optical system 3 (in the negative direction of the X axis). The detector 2b is configured to detect the intensity distribution of the fluorescence of the reflected spot emitted from the laser gain medium 1. The control device 4a controls the angle or position of the lens 9 based on the fluorescence intensity distribution of the reflected spot RS detected by the detector 2b. For example, it is assumed that the fluorescence intensity distribution of the reflected spot RS detected by the detector 2b is the intensity distribution shown in FIG. In this case, it is only necessary that the fluorescence intensity distribution of the detected reflection spot RS is the intensity distribution shown in FIG. The control device 4a compares the fluorescence intensity distribution of the detected reflection spot RS with a desired intensity distribution, and controls the angle or position of the lens 9 so that they match. In the example of FIG. 16, the control device 4a includes a storage device that stores the intensity distribution shown in FIG. 16A as a desired intensity distribution. The desired intensity distribution can be obtained by experiments or the like.

  As described above, it is possible to grasp whether or not the lens needs to be adjusted by acquiring the fluorescence intensity distribution of the reflection spot. Therefore, not only laser optical axis alignment but also lens adjustment can be performed.

  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.

  All the embodiments and all the modified examples can be suitably combined within a range where no technical contradiction occurs. For example, the second embodiment may be combined with the third embodiment. For example, the modification described in the third embodiment may be combined with the second embodiment.

DESCRIPTION OF SYMBOLS 1 ... Laser gain medium, 2 ... Detector, 3 ... Optical system, 4 ... Control apparatus, 5 ... Display, 6 ... Computer apparatus, 7 ... Excitation light source, 8 ... Seed light source, 10 ... Laser amplifier, 11 ... Surface, 12 ... back surface, 30 ₁ ... first total reflection mirror, 30 ₂ ... second total reflection mirror, 100 ... cooling unit, AX _EL ... excitation optical axis, AX _L ... laser optical axis, EL ... excitation light, FR ... fluorescent region, L ... Laser beam, OP ... Laser beam path, RS ... Reflection spot

Claims (13)

A laser gain medium that receives the excitation light and the laser light and emits fluorescence by absorbing a part of the excitation light;
A detector for detecting a position of a reflected spot of the laser light in the laser gain medium,
The detector detects a position of a region where the intensity of the fluorescence is lower than a surrounding region as the reflection spot. A position detection system according to claim 1;
A plurality of optical elements comprising the laser gain medium;
A controller for controlling the angle or position of at least one of the plurality of optical elements, and
The control device controls an angle or a position of the at least one optical element based on a distance between a position of the reflection spot and a reference position. Laser optical axis alignment system. The reference position is a position where the center of the reflection spot should exist,
The control device calculates a distance between the center of the reflection spot and the reference position as a deviation amount, and sets the angle or position of the at least one optical element so that the calculated deviation amount becomes zero. The laser optical axis alignment system according to claim 2 to be controlled. The laser optical axis alignment system according to claim 2, wherein the at least one optical element that is a control target of the control device is a mirror disposed in an optical path of the laser light. The laser gain medium is
A front surface on which the laser light is incident and a back surface opposite to the front surface,
5. The laser optical axis alignment according to claim 2, wherein the detector is disposed on the front surface side and detects the position of the reflection spot generated on the back surface from the front surface side. 6. system. The plurality of optical elements are:
A first laser gain medium as the laser gain medium;
A second laser gain medium that receives the excitation light and the laser light and emits fluorescence by absorbing a part of the excitation light;
The detector detects a position of a first reflection spot that is the reflection spot of the laser light in the first laser gain medium, and further detects a position of the second reflection spot of the laser light in the second laser gain medium. Detect
The control device includes a first distance between a position of the first reflection spot and a first reference position that is the reference position in the first laser gain medium, a position of the second reflection spot, and the second laser. The laser optical axis alignment system according to any one of claims 2 to 5, wherein an angle or a position of the at least one optical element is controlled based on a second distance between the second reference position and the gain medium. . The detector detects a position of a first reflection spot that is the reflection spot of the laser light in the laser gain medium, and further detects a position of a second reflection spot of the laser light;
The control device includes a first distance between the position of the first reflection spot and the first reference position which is the reference position, and a second distance between the position of the second reflection spot and the second reference position. The laser optical axis alignment system according to any one of claims 2 to 5, wherein an angle or a position of the at least one optical element is controlled based on: The position detection system of a reflected spot of laser light according to claim 1, wherein the phase state of the laser gain medium is solid or liquid. The control device controls an angle or a position of the at least one optical element based on an angle around the reference position of the reflection spot in addition to a distance between the position of the reflection spot and a reference position. 3. The laser optical axis alignment system according to 2. The control device sets the first distance between the position of the first reflection spot and the first reference position, and the second distance between the position of the second reflection spot and the second reference position. In addition, an angle of the at least one optical element based on a first angle around the first reference position of the first reflection spot and a second angle around the second reference position of the second reflection spot, The laser optical axis alignment system according to claim 6 or 7, wherein the position is controlled. A cooling unit for cooling the laser gain medium;
A cooling unit control device for controlling the cooling unit;
The detector further detects a fluorescence spectrum emitted from the laser gain medium;
The laser optical axis alignment system according to any one of claims 2 to 10, wherein the cooling unit control device controls the cooling intensity of the cooling unit based on the fluorescence spectrum detected by the detector. . The at least one optical element to be controlled by the control device includes a lens disposed in an optical path of the laser light,
The detector detects the intensity distribution of the fluorescence of the reflected spot;
The laser optical axis according to any one of claims 2 to 11, wherein the control device controls an angle or a position of the lens based on an intensity distribution of the fluorescence of the reflected spot detected by the detector. Alignment system. An incident step in which excitation light and laser light are incident on the laser gain medium;
Detecting a position of a reflected spot of the laser beam in the laser gain medium, and
The laser gain medium emits fluorescence by absorbing a part of the excitation light,
In the detecting step, the position of a region where the intensity of the fluorescence is lower than the surrounding region is detected as the reflected spot.

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