阅读说明：本技术 一种半导体激光器光栅外腔光谱合束装置 (Semiconductor laser grating external cavity spectrum beam combining device ) 是由 俞浩 孙舒娟 王俊 廖新胜 李泉灵 潘华东 于 2019-10-31 设计创作，主要内容包括：本发明公开了一种半导体激光器光栅外腔光谱合束装置,包括：多个单管台阶排布合束模块,用于发出第一合束光束,且各单管台阶排布合束模块呈扇形排布,且旋转90°放置,使第一合束光束的快轴慢轴方向互换；各单管台阶排布合束模块包括多个台阶排布子模块,多个台阶排布子模块用于沿出射光的快轴方向进行光束合束,构成第一合束光束；衍射光栅,用于接收多个单管台阶排布合束模块发出的第一合束光束,并以相同的衍射角衍射输出；外腔镜,用于透射一部分衍射光栅输出的光束,并原路反射另一部分衍射光栅输出的光束,生成反馈光束；各台阶排布子模块接收反馈光束,根据反馈光束确定激光波长。(The invention discloses a grating external cavity spectrum beam combining device of a semiconductor laser, which comprises: the single-tube step arrangement beam combination modules are used for emitting first combined beams, are arranged in a fan shape and are rotated by 90 degrees, so that the directions of the fast axis and the slow axis of the first combined beams are interchanged; each single-tube step arrangement beam combining module comprises a plurality of step arrangement sub-modules, and the plurality of step arrangement sub-modules are used for combining light beams along the fast axis direction of emergent light to form a first combined beam; the diffraction grating is used for receiving the first combined beam emitted by the single-tube step arrangement beam combination modules and diffracting and outputting the first combined beam at the same diffraction angle; the external cavity mirror is used for transmitting a part of light beams output by the diffraction grating and reflecting the other part of light beams output by the diffraction grating in the original path to generate feedback light beams; each step arrangement submodule receives the feedback light beam and determines the laser wavelength according to the feedback light beam.)

1. A grating external cavity spectrum beam combining device of a semiconductor laser is characterized by comprising:

the single-tube step arrangement beam combination modules are sequentially arranged in a fan shape and used for emitting first combined beams interchanged in the directions of the fast axis and the slow axis; each single-tube step arrangement beam combining module comprises a plurality of step arrangement sub-modules, and the step arrangement sub-modules are used for combining light beams along the fast axis direction of emergent light to form a first combined beam;

the diffraction grating is used for receiving the first combined beam emitted by the single-tube step arrangement beam combination modules and diffracting and outputting the first combined beam at the same diffraction angle;

the external cavity mirror is used for transmitting one part of light beams output by the diffraction grating and reflecting the other part of light beams output by the diffraction grating in the original path to generate feedback light beams;

and each step arrangement submodule receives the feedback light beam and determines the laser wavelength according to the feedback light beam.

2. The semiconductor laser grating external cavity spectral beam combining device of claim 1, wherein the step arrangement submodule comprises:

the semiconductor laser single-chip is used for emitting an initial light beam;

the fast axis collimating mirror is used for adjusting the divergence angle of the initial light beam in the fast axis direction and outputting a first adjusted light beam;

the slow axis collimating mirror is used for adjusting the divergence angle of the first adjusting light beam in the slow axis direction and outputting a second adjusting light beam;

the reflector is used for adjusting the output angle of the second adjusting light beam and outputting a third adjusting light beam;

the step arrangement sub-modules are arranged at intervals in the same plane along the direction parallel to the third adjustment light beam and are arranged in a step shape along the fast axis direction of the third adjustment light beam, and the output light of each step arrangement sub-module forms the first combined light beam.

3. The semiconductor laser grating external cavity spectral beam combining device of claim 1, further comprising:

and the fast axis collimating lens is arranged between the single-tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the fast axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules.

4. The semiconductor laser grating external cavity spectral beam combining device of claim 1, further comprising:

and the slow-axis collimating lens is arranged between the single-tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the slow-axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules.

5. The semiconductor laser grating external cavity spectral beam combining device of claim 1, further comprising:

and the spherical lens is arranged between the single-tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the fast-axis divergence angle and/or the slow-axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules.

6. The semiconductor laser grating external cavity spectral beam combining device of claim 1, further comprising:

and the filtering system is arranged between the diffraction grating and the external cavity mirror and is used for filtering the light beams output by the diffraction grating.

7. The semiconductor laser grating external cavity spectral beam combining device of claim 1,

the reflectivity of the external cavity mirror is greater than or equal to 1%.

Technical Field

The invention relates to the technical field of semiconductor lasers, in particular to a grating external cavity spectrum beam combining device of a semiconductor laser.

Background

The semiconductor laser has the excellent characteristics of high efficiency, compact structure, wide wavelength range, low cost, high reliability and the like, but due to the limitation of the quantum well waveguide structure, the semiconductor laser has poor spectral characteristics, poor beam quality, low direct output power and low brightness of an output beam. In order to expand the application of semiconductor lasers in industrial processing, laser pumping and the like, a direct semiconductor laser light source with high power, high brightness and high beam quality is usually obtained by spectral beam combination.

The conventional light source for spectrum beam combination of a semiconductor laser is a stacked array composed of bars, however, due to the fact that a 'smile' effect is introduced into the bars due to factors such as packaging, the feedback light intensity received by each beam combination unit is different due to the 'smile' effect of the bars, output power of some beam combination units is reduced, and in addition, due to directivity deviation among the bars in the stacked array, the problem that laser wavelength cannot be locked simultaneously exists in each beam combination unit, so that final electro-optic efficiency is reduced, output power is reduced, light beam quality is poor, and the stacked array is difficult to be applied as a direct semiconductor laser light source in hundreds of watts, kilowatts and ten-kilowatts.

Disclosure of Invention

In view of this, an embodiment of the present invention provides a grating external cavity spectrum beam combining device for a semiconductor laser, so as to solve the technical problems of low final output power, poor beam quality, and the like caused by using a bar stacked array as a light source to perform spectrum beam combining for the semiconductor laser.

The embodiment of the invention provides a grating external cavity spectrum beam combining device of a semiconductor laser, which comprises: the single-tube step arrangement beam combination modules are sequentially arranged in a fan shape and used for emitting first combined beams interchanged in the directions of the fast axis and the slow axis; each single-tube step arrangement beam combining module comprises a plurality of step arrangement sub-modules, and the plurality of step arrangement sub-modules are used for combining light beams along the fast axis direction of emergent light to form a first combined beam; the diffraction grating is used for receiving the first combined beam emitted by the single-tube step arrangement beam combination modules and diffracting and outputting the first combined beam at the same diffraction angle; the external cavity mirror is used for transmitting a part of light beams output by the diffraction grating and reflecting the other part of light beams output by the diffraction grating in the original path to generate feedback light beams; each step arrangement submodule receives the feedback light beam and determines the laser wavelength according to the feedback light beam.

Optionally, the step arrangement submodule includes: the semiconductor laser single-chip is used for emitting an initial light beam; the fast axis collimating mirror is used for adjusting the divergence angle of the initial light beam in the fast axis direction and outputting a first adjusted light beam; the slow axis collimating mirror is used for adjusting the divergence angle of the first adjusting light beam in the slow axis direction and outputting a second adjusting light beam; the reflector is used for adjusting the output angle of the second adjusting light beam and outputting a third adjusting light beam; the step arrangement sub-modules are arranged at intervals in the same plane along the direction parallel to the third adjustment light beam and are arranged in a step shape along the fast axis direction of the third adjustment light beam, and the output light of each step arrangement sub-module forms a first combined light beam.

Optionally, the external cavity spectrum beam combining device of the semiconductor laser grating further includes: and the fast axis collimating lens is arranged between the single tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the fast axis divergence angle of the first combined beam emitted by the single tube step arrangement beam combination modules.

Optionally, the external cavity spectrum beam combining device of the semiconductor laser grating further includes: and the slow-axis collimating lens is arranged between the single-tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the slow-axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules.

Optionally, the external cavity spectrum beam combining device of the semiconductor laser grating further includes: and the spherical lens is arranged between the single-tube step arrangement beam combination modules and the diffraction grating and is used for adjusting the fast axis divergence angle and/or the slow axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules.

Optionally, the external cavity spectrum beam combining device of the semiconductor laser grating further includes: and the filtering system is arranged between the diffraction grating and the external cavity mirror and is used for filtering the light beam output by the diffraction grating.

Optionally, the reflectivity of the external cavity mirror is greater than or equal to 1%.

The embodiment of the invention has the following beneficial effects:

(1) according to the external cavity spectrum beam combining device for the grating of the semiconductor laser, provided by the embodiment of the invention, the plurality of single-tube step arrangement beam combining modules are used as light sources for spectrum beam combining of the semiconductor laser, so that feedback light beams of an external cavity mirror can be injected into the single-tube step arrangement beam combining modules, and a resonance mode in a resonant cavity of the single-tube step arrangement beam combining modules is excited, so that the spectral bandwidth of the narrow single-tube step arrangement beam combining modules is realized by the resonance mode, the operating wavelengths in the resonant cavity of the single-tube step arrangement beam combining modules are concentrated near the central wavelength of the feedback light beams, and due to the dispersion of the diffraction grating, the different single-tube step arrangement beam combining modules receive the feedback light beams with different wavelengths, so that the different single-tube step arrangement beam combining modules are locked at different central wavelengths, and the laser wavelength of each single; the single-tube step arrangement beam combination modules are arranged in a fan shape, so that Fourier lenses can be replaced, the single-tube step arrangement beam combination modules can emit first combined beams to form angles to be incident on the diffraction grating, light spots are overlapped, and cost is saved; the single-tube step arrangement beam combination modules emit first combined beams with interchangeable fast axes and slow axes, the semiconductor laser has beam quality close to the diffraction limit in the fast axis direction, the slow axis beam quality is poor, the typical beam parameter value is about 10 times of that in the fast axis direction, so that the space for quality degradation of the slow axis beam is very limited, and the single-tube step arrangement beam combination modules emit the first combined beams with interchangeable fast axes and slow axes, so that the spectrum beam combination is performed in the fast axis direction, and the final beam quality can be improved; a plurality of step arrangement sub-modules form a single-tube step arrangement beam combining module, the step arrangement sub-modules are used for combining beams along the fast axis direction of emergent light to form a first combined beam, the single-tube step arrangement beam combining module performs primary spatial beam combining, the first combined beam is emitted, and the output power of the final spectrum combined beam can be greatly improved.

(2) According to the semiconductor laser grating external cavity spectrum beam combining device provided by the embodiment of the invention, after the collimation of the conventional fast axis collimating lens is carried out in each single-tube step arrangement beam combining module, the fast axis collimating lens is arranged on the output light path of the single-tube step arrangement beam combining module, the primary fast axis re-collimation is carried out, the fast axis residual divergence angle is further compressed, and the final spectrum beam combining is greatly improved.

(3) According to the semiconductor laser grating external-cavity spectrum beam combining device provided by the embodiment of the invention, after the collimation of the conventional slow-axis collimating lens is carried out in each single-tube step arrangement beam combining module, the slow-axis collimating lens is arranged on the output light path of the single-tube step arrangement beam combining module, the primary slow-axis re-collimation is carried out, and the residual divergence angle of the slow axis is further compressed, so that the final spectrum beam combining is greatly improved, and the single-tube step arrangement beam combining module can also use the slow-axis collimating lens with a shorter focal length to reduce the volume of the single-tube step arrangement beam combining module (the longer the focal length is, the better the collimation effect is, and the smaller the residual divergence angle is).

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 shows a schematic structural diagram of an external cavity spectral beam combining device of a grating of a semiconductor laser in an embodiment of the invention;

FIG. 2 is a schematic diagram illustrating a single-pipe step arrangement beam combining module according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of an external cavity spectral beam combining device of another semiconductor laser grating according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram illustrating an external cavity spectral beam combining device of another semiconductor laser grating according to an embodiment of the present invention;

fig. 5 shows a schematic structural diagram of an external cavity spectral beam combining device of another semiconductor laser grating in the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the embodiments of the present invention, the terms "first", "second", and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the embodiments of the present invention, it should be noted that, unless explicitly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in fig. 1, an embodiment of the present invention provides an external cavity spectrum beam combining device for a grating of a semiconductor laser, including: the single-tube step arrangement beam combination modules 1 are sequentially arranged in a fan shape and used for emitting a first combined beam with interchangeable fast axis and slow axis; each single-tube step arrangement beam combination module 1 comprises a plurality of step arrangement sub-modules, and the plurality of step arrangement sub-modules are used for carrying out beam combination along the fast axis direction of emergent light to form a first combined beam; the diffraction grating 2 is used for receiving the first combined beam emitted by the plurality of single-tube step arrangement beam combining modules 1 and diffracting and outputting the first combined beam at the same diffraction angle; the external cavity mirror 3 is used for transmitting a part of light beams output by the diffraction grating 2 and reflecting the other part of light beams output by the diffraction grating 2 in the original way to generate feedback light beams; each step arrangement submodule receives the feedback light beam and determines the laser wavelength according to the feedback light beam.

Specifically, the single-tube step arrangement beam combining module 1 comprises a plurality of step arrangement sub-modules, the step arrangement sub-modules are arranged in a step shape, each step arrangement sub-module is a light emitting unit, and primary light beams emitted by the step arrangement sub-modules are combined along the fast axis direction of emergent light to form a first combined light beam. The plurality of single-tube step arrangement beam combination modules 1 are all placed by rotating 90 degrees, so that each single-tube step arrangement beam combination module sends out a first combined beam with interchangeable fast and slow axis directions, the plurality of single-tube step arrangement beam combination modules 1 are arranged in a circular arc manner, the first combined beam sent out by the single-tube step arrangement beam combination modules is in a fan shape at a certain angle and is respectively incident on the diffraction grating 2 at a certain angle, light spots are overlapped, incident beams with different wavelengths and different angles are diffracted and output at the same diffraction angle by the dispersion effect of the diffraction grating 2, the light beam diffracted and output from the diffraction grating 2 reaches the outer cavity mirror, the outer cavity mirror 3 is a partial reflection partial transmission mirror, the light beam reaching the outer cavity mirror 3 is partially reflected by the outer cavity mirror 3, the reflectivity of the outer cavity mirror 3 is more than or equal to 1 percent, the reflected light beam returns to the step arrangement sub-module along the original path to provide feedback of the specific wavelength for the, the feedback light is injected into the step arrangement submodule to excite the resonance mode in the resonant cavity, the mode corresponds to the expected wavelength output, the feedback is provided for the step arrangement submodule to enable the operating wavelength of the resonant cavity to be concentrated near the central wavelength of the feedback light, therefore, the resonance feedback can narrow the spectral bandwidth of the step arrangement submodule and enable the spectrum of the emitted light beam to surround the central wavelength of the feedback spectrum, and due to the dispersion of the diffraction grating 2, the step arrangement submodules of different single-tube step arrangement beam combination modules 1 receive the feedback light with different wavelengths, so that the feedback light is locked at different central wavelengths. The light beam reaching the external cavity mirror 3 is transmitted in another part as an output light beam.

According to the external cavity spectrum beam combining device for the grating of the semiconductor laser, provided by the embodiment of the invention, the plurality of single-tube step arrangement beam combining modules are used as light sources for spectrum beam combining of the semiconductor laser, so that feedback light beams of an external cavity mirror can be injected into the single-tube step arrangement beam combining modules, and a resonance mode in a resonant cavity of the single-tube step arrangement beam combining modules is excited, so that the spectral bandwidth of the narrow single-tube step arrangement beam combining modules is realized by the resonance mode, the operating wavelengths in the resonant cavity of the single-tube step arrangement beam combining modules are concentrated near the central wavelength of the feedback light beams, and due to the dispersion of the diffraction grating, the different single-tube step arrangement beam combining modules receive the feedback light beams with different wavelengths, so that the different single-tube step arrangement beam combining modules are locked at different central wavelengths, and the laser wavelength of each single; the single-tube step arrangement beam combination modules are arranged in a fan shape, so that Fourier lenses can be replaced, the single-tube step arrangement beam combination modules can emit first combined beams to form angles to be incident on the diffraction grating, light spots are overlapped, and cost is saved; the single-tube step arrangement beam combination modules are placed by rotating 90 degrees, so that the fast axis and slow axis directions of the first combined beam beams can be interchanged, the semiconductor laser has beam quality close to the diffraction limit in the fast axis direction, the slow axis beam quality is poor, the value of a typical beam parameter product is about 10 times of that in the fast axis direction, the space for quality degradation of the slow axis beam is very limited, and the modules are placed by rotating 90 degrees, so that the spectrum beam combination is performed in the fast axis direction, and the final beam quality can be improved; a plurality of step arrangement sub-modules form a single-tube step arrangement beam combining module, the step arrangement sub-modules are used for combining beams along the fast axis direction of emergent light to form a first combined beam, the single-tube step arrangement beam combining module performs primary spatial beam combining, the first combined beam is emitted, and the output power of the final spectrum combined beam can be greatly improved.

In an alternative embodiment, as shown in fig. 2, the step arrangement sub-module includes: a single-tube chip 111 of a semiconductor laser for emitting an initial light beam; a fast axis collimator 112, configured to adjust a divergence angle of the initial light beam in a fast axis direction, and output a first adjusted light beam; a slow axis collimator 113 for adjusting the divergence angle of the first adjusted beam in the slow axis direction and outputting a second adjusted beam; a mirror 114 for adjusting the output angle of the second adjusted beam and outputting a third adjusted beam; the step arrangement sub-modules are arranged at intervals in the same plane along the direction parallel to the third adjustment light beam and are arranged in a step shape along the fast axis direction of the third adjustment light beam, and the output light of each step arrangement sub-module forms a first combined light beam.

Specifically, the single-tube step-arrangement beam combining module 1 includes a plurality of step-arrangement sub-modules, each of which includes a semiconductor laser single-tube chip, a fast-axis collimating lens, a slow-axis collimating lens and a reflector, light emitted from the semiconductor laser single-tube chip 111 of the first step-arrangement sub-module is collimated by the fast-axis collimating lens 112 in the fast-axis direction, the collimated light reaches the slow-axis collimating lens 113 in the fast-axis direction, the collimated light is collimated by the slow-axis collimating lens 113 in the slow-axis direction to become fully collimated light, and the fully collimated light is reflected by the reflector 114; the second step arrangement submodule and the first step arrangement submodule have a certain step height difference, light emitted by a single semiconductor laser chip 115 of the second step arrangement submodule reaches a reflector 118 after passing through a fast axis collimating mirror 116 and a slow axis collimating mirror 117, and passes through the upper part of the reflector 114 after being reflected by the reflector 118, so that light emitted by the first step arrangement submodule is combined in the fast axis direction, the combined light of the plurality of step arrangement submodules is similar, and a first combined light beam is formed.

A plurality of step arrangement sub-modules are arranged in a step shape to form a single-tube step arrangement beam combining module, and the step arrangement sub-modules are used for combining beams along the fast axis direction of emergent light to form a first combined beam, so that the single-tube step arrangement beam combining module performs primary spatial beam combining.

In an alternative embodiment, as shown in fig. 3, the external cavity spectral beam combining device of a semiconductor laser grating further includes: and the fast axis collimating lens 4 is arranged between the single-tube step arrangement beam combination modules 1 and the diffraction grating 2 and is used for adjusting the fast axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules 1.

According to the semiconductor laser grating external cavity spectrum beam combining device provided by the embodiment of the invention, after the collimation of the conventional fast axis collimating lens is carried out in each single-tube step arrangement beam combining module, the fast axis collimating lens is arranged on the output light path of the single-tube step arrangement beam combining module, the primary fast axis re-collimation is carried out, the fast axis residual divergence angle is further compressed, and the final spectrum beam combining is greatly improved.

In an alternative embodiment, as shown in fig. 3, the external cavity spectral beam combining device of a semiconductor laser grating further includes: and the slow-axis collimating lens 5 is arranged between the single-tube step arrangement beam combination modules 1 and the diffraction grating 2 and is used for adjusting the slow-axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules 1.

According to the semiconductor laser grating external-cavity spectrum beam combining device provided by the embodiment of the invention, after the collimation of the conventional slow-axis collimating lens is carried out in each single-tube step arrangement beam combining module, the slow-axis collimating lens is arranged on the output light path of the single-tube step arrangement beam combining module, the primary slow-axis re-collimation is carried out, and the residual divergence angle of the slow axis is further compressed, so that the final spectrum beam combining is greatly improved, and the single-tube step arrangement beam combining module can also use the slow-axis collimating lens with a shorter focal length to reduce the volume of the single-tube step arrangement beam combining module (the longer the focal length is, the better the collimation effect is, and the smaller the residual divergence angle is).

In an optional embodiment, the external cavity spectrum beam combining device of the grating of the semiconductor laser may include both the fast axis collimating lens 4 and the slow axis collimating lens 5, the positions of the fast axis collimating lens 4 and the slow axis collimating lens 5 may be interchanged, and in the case that the fast axis collimating lens 4 and the slow axis collimating lens 5 are simultaneously disposed, a spherical lens may be used instead, as shown in fig. 4, the external cavity spectrum beam combining device of the grating of the semiconductor laser further includes: and the spherical lens 6 is arranged between the single-tube step arrangement beam combination modules 1 and the diffraction grating 2 and is used for adjusting the fast axis divergence angle and/or the slow axis divergence angle of the first combined beam emitted by the single-tube step arrangement beam combination modules 1.

According to the semiconductor laser grating external-cavity spectrum beam combining device provided by the embodiment of the invention, after the collimation of the conventional fast-axis and slow-axis collimating lens is carried out in each single-tube-step beam combining module, the spherical lens is arranged on the output light path of the single-tube-step beam combining module, the primary fast-axis re-collimation and/or the primary slow-axis re-collimation is carried out, and the residual divergence angle of the fast axis and/or the slow axis is further compressed, so that the final spectrum combined beam is greatly improved, and the single-tube-step beam combining module can also use the slow-axis collimating lens with a shorter focal length to reduce the volume of the single-tube-step beam combining module (the longer the focal length is, the better the collimation effect is, and the smaller the residual divergence angle is).

In an alternative embodiment, as shown in fig. 5, the external cavity spectral beam combining device of a semiconductor laser grating further includes: and the filtering system 7 is arranged between the diffraction grating 2 and the external cavity mirror 3 and is used for filtering the light beam output by the diffraction grating.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.