Spectral beam combining device for reducing distance between adjacent laser sub-beams

Abstract

The invention belongs to the technical field of laser, and discloses a spectrum beam combining device capable of reducing the distance between adjacent laser sub-beams, which comprises a laser sub-beam dense array, a plate prism group, a convergence system and a diffraction grating, and is characterized in that laser emitted by the laser sub-beam dense array is incident on the plate prism group in parallel; after refraction deflection at different angles occurs, the laser beams are emitted in parallel after spacing reduction from the plate prism group, the laser beams enter the convergence system, and different laser beams are converged on the diffraction grating and finally are diffracted by the diffraction grating to be combined into one beam to be emitted. According to the invention, the prism group configuration with different refractive indexes is utilized, the distance between adjacent sub-beams is reduced, and the miniaturization of the spectrum beam combining device is realized; the device is simple in configuration principle, convenient to operate, high in expansibility and suitable for reducing the space between dozens of or even hundreds of paths of laser sub-beams.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser, and relates to a spectral beam combination device for reducing the interval of adjacent laser sub-beams. BACKGROUND

[0002] In recent years, the output power of fiber lasers is increasing, and fiber lasers are widely used in the fields of laser processing, laser weapons, and photoelectric countermeasures. In view of the current situation that the output power of a single fiber laser is limited, spectral synthesis is an effective way to achieve higher power while maintaining good beam quality.

[0003] Spectral synthesis is to arrange different wavelength laser sub-beams in one dimension in the near field, and to make them incident on a diffraction grating at a specific angle. After diffraction by the grating, a high-power laser output with a common aperture is formed. The beam quality of the output laser can be represented as follows by using the method of double-grating spectral synthesis:

[0004]

[0005] Wherein, M0 is the beam quality of the sub-beam, D is the interval of adjacent laser sub-beams, d is the diameter of the sub-beam, Δλ is the linewidth of the sub-beam, and δλ is the wavelength interval of adjacent sub-beams.

[0006] In the spectral beam combination system, the interval D of adjacent laser sub-beams is an important parameter affecting the beam quality of the combined laser and the optical path of the spectral beam combination system. If the laser sub-beams are directly spliced and arranged, the interval of adjacent fiber laser sub-beams cannot be further reduced due to the size of the fiber laser sub-beam output head and the size of the mechanical structure for fixing the fiber laser sub-beam output head, which is not conducive to achieving high beam quality spectral synthesis, and also requires a larger grating interval and grating size, greatly increasing the volume and cost of the spectral synthesis system. SUMMARY

[0007] (I) Invention purpose

[0008] The purpose of the present application is to provide a spectral beam combination device for reducing the interval of adjacent laser sub-beams, which solves the problem that a large interval of adjacent laser sub-beams leads to a large volume of the spectral synthesis system and deteriorates the beam quality of spectral synthesis.

[0009] (II) Technical solution

[0010] In order to solve the above technical problems, the present application provides a spectral beam combination device for reducing the distance between adjacent laser sub-beams, which comprises: a laser sub-beam dense array 1, a flat prism group 2, a converging system 3, and a diffraction grating 4; the laser emitted by the laser sub-beam dense array 1 is incident on the flat prism group 2 in parallel, is deflected by refraction at different angles, and is then emitted in parallel after being reduced in distance from the flat prism group 2; the laser sub-beams enter the converging system 3, are converged to the diffraction grating 4, and are finally diffracted by the diffraction grating 4 to be emitted as one beam.

[0011] Further, the laser sub-beam dense array 1 is composed of a plurality of optical fiber laser sub-beams with different wavelengths and is arranged in parallel in one dimension.

[0012] Further, the flat prism group 2 is composed of a plurality of prisms with different refractive indexes, the thicknesses of the prisms are the same, and the number of the prisms is equal to the number of the laser sub-beams, which is used to reduce the distance between adjacent laser sub-beams.

[0013] Further, each prism of the flat prism group 2 is rectangular, the laser sub-beams are incident on the upper edge of the prism and are emitted from the lower edge, and the upper and lower edges are coated with an anti-reflection film.

[0014] Further, the flat prism group 2 is composed of a plurality of plane mirrors, and the number of the plane mirrors is equal to the number of the laser sub-beams.

[0015] Further, the flat prism group 2 is composed of a single concave mirror.

[0016] Further, the flat prism group 2 is composed of a lens group.

[0017] Further, the flat prism group 2 is composed of a single diffraction grating.

[0018] Further, the length of each prism of the flat prism group 2 is a, and the thickness of each prism is h; before being incident on the flat prism group 2, the distance between adjacent laser sub-beams is D1=a*cosα, where α is the incident angle of the laser sub-beams relative to the flat prism group 2; each laser sub-beam is incident on the flat prism group 2 and is refracted in each prism, respectively, according to the refraction law: sinα=n i *sinβ i =n i+1 *sinβ i+1 , where n i , n i+1 , β i , and β i+1 are the refractive indexes and the refraction angles of the i-th prism and the i+1-th prism, respectively, where n i+1 >n i >···>n1, β1>···>β i >β i+1 .

[0019] Further, after the laser sub-beams exit from the flat prism group 2, the interval between adjacent laser sub-beams is reduced to:

[0020] D2=D1-h*cosα*(tanβ i -tanβ i+1 )

[0021] Compared with the initial incident interval D1 between adjacent sub-beams, the reduction is:

[0022] ΔD=D2-D1=h*cosα*(tanβ i -tanβ i+1 )>0.

[0023] (III) Beneficial effects

[0024] The spectral beam combining device for reducing the interval between adjacent laser sub-beams provided by the above technical solution reduces the interval between adjacent sub-beams by using a prism group configuration with different refractive indexes, thereby realizing the miniaturization of the spectral beam combining device; the configuration principle is simple, the operation is convenient, and the expansibility is strong, and the spectral beam combining device can be applied to the reduction of the interval between tens or even hundreds of laser sub-beams; the beam combining device is suitable for single-grating spectral beam combining, double-grating spectral beam combining, and other beam combining fields of narrow linewidth fiber lasers. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a spectral beam combining optical path schematic diagram of an embodiment of the present application;

[0026] Figure 2 is a schematic diagram of the refractive optical path of adjacent laser sub-beams before and after passing through the flat prism group in the embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, content and advantages of the present application clearer, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0028] As shown in Figure 1 and Figure 2 , the spectral beam combining device for reducing the interval between adjacent laser sub-beams includes a laser sub-beam dense array 1, a flat prism group 2, a converging system 3, and a diffraction grating 4; the laser emitted by the laser sub-beam dense array 1 is incident on the flat prism group 2 in parallel, and is refracted; due to the inconsistency of the refractive indexes of the adjacent two prisms in the flat prism group 2, the laser is refracted and deflected at different angles, and then the laser sub-beams exit from the flat prism group 2 in parallel, but the interval between adjacent laser sub-beams is reduced; the laser sub-beams after the interval is reduced enter the converging system 3, and different laser sub-beams are converged on the diffraction grating 4, and finally are diffracted by the diffraction grating 4 to be combined into one beam.

[0029] The laser beam dense array 1 is a fiber laser array composed of multiple beams of different wavelengths and arranged in parallel one-dimensionally, which can have 2, 3, …, n beams.

[0030] The flat prism group 2 is composed of a series of prisms with different refractive indexes, which is used to reduce the spacing between adjacent laser beams. Each prism has the same thickness and high transmittance to laser. The number of prisms is equal to the number of laser beams, which is used to reduce the spacing between adjacent laser beams.

[0031] Each prism of the flat prism group 2 is rectangular, and the laser beam enters from the upper edge and exits from the lower edge of the prism. The upper and lower edges are coated with an anti-reflection film.

[0032] The length of each prism of the flat prism group 2 is a, and the thickness is h.

[0033] The spacing between adjacent laser beams before the laser beam enters the flat prism group 2 is D1=a*cosα, where α is the incident angle of the laser beam relative to the flat prism group 2.

[0034] Each laser beam enters the flat prism group 2 and refracts in each prism. According to the law of refraction, we have sinα=n i *sinβ i =n i+1 *sinβ i+1 , where n i , n i+1 and β i , β i+1 are the refractive index and the refraction angle of the i-th and i+1-th prisms, respectively, where n i+1 >n i >…>n1, β1>…>β i >β i+1 .

[0035] Since the refractive index of the i+1-th prism is greater than that of the i-th prism, the laser beam has stronger refractive ability, and the refraction angle β i+1 is smaller than the previous one β i . After the laser beam exits from the flat prism group 2, it still maintains parallel to each other, and the spacing between adjacent laser beams is reduced to:

[0036] D2=D1-h*cosα*(tanβ i -tanβ i+1 )

[0037] Compared with the initial incident spacing D1 between adjacent beams, the reduction is:

[0038] △D=D2-D1=h*cosα*(tanβ i -tanβ i+1 )>0

[0039] It can be seen that by designing the thickness h of the flat prism group 2, the laser beam incidence angle a, and the refractive index n of each prism i The reduction of the adjacent laser beam spacing can be achieved.

[0040] There are various designs for the converging system 3, for example, it can be composed of multiple plane mirrors, the number of plane mirrors being the same as the number of laser beams; it can be composed of a single concave mirror; it can be composed of a lens group; or it can be composed of a single diffraction grating.

[0041] The parallel laser beams exiting from the flat prism group 2 pass through the converging system 3, converging each beam onto the diffraction grating 4, and after diffraction by the grating, a common-aperture laser output is formed.

[0042] The following is an example with specific parameters. The laser beam dense array 1 is composed of 12 laser beams with different wavelengths, the central wavelengths being 1060.000 nm, 1060.401 nm, 1060.794 nm, 1061.179 nm, 1061.556 nm, 1061.926 nm, 1062.289 nm, 1062.644 nm, 1062.993 nm, 1063.335 nm, 1063.671 nm, 1064.000 nm, each laser beam being collimated at an incidence angle of 57° and incident onto the flat prism group 2, the spacing D1 between adjacent beams being 3 mm, the thickness h of the flat prism group being 90 mm, the width a being 1.634 mm, the spacing D2 between adjacent beams after exiting being 2 mm, the refractive index n of each flat prism and the corresponding beam refraction angle being shown in Table 1.

[0043] Table 1 Refractive index n of each flat prism and corresponding beam refraction angle

[0044]

[0045] Each laser beam passes through the prism with a different refractive index in Table 2, and the spacing between adjacent beams is reduced from 3 mm to 2 mm. Subsequently, the beams enter the converging system 3 and the diffraction grating 4 for spectral beam combining. Assuming that the converging system 3 and the diffraction grating 4 are both reflective multilayer dielectric film gratings with a ruling density of 1740 lines / mm, each beam enters the double-grating spectral beam combining system at an incidence angle of 64°.

[0046] Without the flat prism group 2 to reduce the beam spacing, the center spacing of the double-grating spectral beam combining system is 1072.01 mm; with the flat prism group 2 to reduce the beam spacing, the center spacing of the double-grating spectral beam combining system is 714.71 mm. The center spacing of the double-grating spectral beam combining system is shortened to 2 / 3 of the original, and the spectral beam combining device is miniaturized.

[0047] Assuming that the beam quality of each sub-beam is 1.3, the line width is 0.2 nm, the spot diameter is 2 mm, and the minimum wavelength interval between adjacent sub-beams is 0.329 nm, according to the double-grating spectral beam combining quality formula, the final output beam quality is respectively:

[0048] When the adjacent sub-beam spacing D is 3 mm:

[0049] When the adjacent sub-beam spacing D is 2 mm:

[0050] The beam quality of the double-grating spectral beam combining is improved.

[0051] As can be seen from the above technical solution, the prism group configuration with different refractive indexes is used to reduce the adjacent sub-beam spacing, realize the miniaturization of the spectral beam combining device, and improve the beam quality of the spectral beam combining.

[0052] The above description is only the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should be considered as the protection scope of the present application.

Claims

1. A spectral beam combining device for reducing the distance between adjacent laser beamlets, characterized in that: include: The laser sub-beam condensed array (1), the flat prism group (2), the converging system (3), and the diffraction grating (4) are provided. The laser light emitted by the laser sub-beam condensed array (1) is incident on the flat prism group (2) in parallel, undergoes refraction and deflection at different angles, and then is emitted in parallel from the flat prism group (2) after the spacing is reduced. The laser sub-beams enter the converging system (3), and the different laser sub-beams are converged on the diffraction grating (4). Finally, the laser light is diffracted by the diffraction grating (4) and combined into one beam for emission.

2. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 1, characterized in that: The laser sub-beam dense array (1) is a fiber laser array composed of multiple fiber laser sub-beams with different wavelengths and arranged in parallel in one dimension.

3. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 2, characterized in that: The flat prism group (2) is composed of a plurality of prisms with different refractive indices, each prism has the same thickness, and the number of prisms is equal to the number of laser sub-beams, and is used to reduce the distance between adjacent laser sub-beams.

4. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 3, characterized in that: Each prism of the flat prism group (2) is rectangular, the laser beam is incident from the upper side of the prism and emitted from the lower side, and both the upper and lower sides are coated with anti-reflection films.

5. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 4, characterized in that: The flat prism group (2) is composed of a plurality of plane reflecting mirrors, and the number of the plane reflecting mirrors is the same as the number of the laser sub-beams.

6. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 5, characterized in that: The flat prism group (2) consists of a single concave reflecting mirror.

7. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 6, characterized in that: The flat prism group (2) is composed of a lens group.

8. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 7, characterized in that: The flat prism group (2) consists of a single diffraction grating.

9. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 8, characterized in that: The length of each prism of the flat prism group (2) is a, and the thickness is h; before the laser sub-beams are incident on the flat prism group (2), the spacing between adjacent laser sub-beams is D1=a*cosα, wherein α is the incident angle of the laser sub-beam relative to the flat prism group (2); each laser sub-beam is incident on the flat prism group (2) and refracted in each prism respectively, according to the refraction law: sinα=n i *sinβ i =n i+1 *sinβ i+1 , where n i 、n i+1 and β i , β i+1 are the refractive index and refractive angle of the ith and i+1th prisms respectively, where n i+1 >n i >···>n1,β1>···>β i >β i+1 .

10. The spectral beam combining device for reducing the distance between adjacent laser beamlets according to claim 9, characterized in that: After the laser beams are emitted from the flat prism group (2), the distance between adjacent laser beams is reduced to: D2=D1-h*cosα*(tanβ i -tanβ i+1 ) Compared with the initial incident adjacent beamlet spacing D1, the reduction is: △D=D2-D1=h*cosα*(tanβ i -tanβ i+1 )>0。

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