A dual-wavelength, high-magnification, continuously variable laser beam expander

Abstract

The present invention discloses a dual-wavelength, large-rate, continuously variable-magnification laser beam expander, comprising a first lens, a second lens, a third lens and a fourth lens coaxially arranged in sequence on an optical axis along the laser incident direction; the first lens and the second lens are plano-concave negative lenses, and the concave surface faces the laser incident direction; the third lens is a meniscus positive lens, and the fourth lens is a biconvex positive lens. The beam expansion ratio of the present application can be adjusted in the range of 20 to 40 times, which is significantly higher than the beam expansion capability of the variable-magnification beam expander in the prior art. According to the Rayleigh spot formula, this is conducive to further reducing the spot size after laser focusing, thereby improving the laser processing efficiency and accuracy.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to a dual-wavelength, high-magnification, continuously variable-magnification laser beam expander. Background Art

[0002] Lasers have been widely used in cutting, drilling, welding and other material processing fields due to their excellent monochromaticity, coherence, directionality and high brightness. In the laser processing process, in order to improve the power / energy density of the laser beam and achieve efficient material removal, it is generally necessary to focus the laser beam and place the focus near the area to be processed. According to the laser Rayleigh spot formula: δ = 2.44λf / D, when the laser wavelength λ and the focal length f of the focusing lens are constant, the spot diameter at the focus is inversely proportional to the incident spot diameter of the focusing lens object. However, the spot diameter directly output by most lasers is small. If it is focused directly, the spot size at the focus is large, and the power density is not high enough, which is not conducive to material processing. Therefore, in order to obtain a smaller focal spot size after focusing, the laser beam needs to be expanded by a beam expander before focusing, and the larger the beam expansion ratio, the easier it is to obtain a focal spot size close to the diffraction limit.

[0003] On the other hand, ultraviolet lasers have developed rapidly in the field of fine material processing in recent years with the advantages of high single photon energy, strong material absorption, small thermal effect, and small focusable spot size. However, the spot size directly output by ultraviolet lasers is smaller, because most industrial ultraviolet lasers are currently produced by infrared fundamental frequency lasers through nonlinear effects such as frequency doubling and sum frequency. In this process, only when the power density of the fundamental frequency laser beam is high enough can ultraviolet light be efficiently excited, and the power density of the generated ultraviolet laser beam is also high; so at the same output power level, the spot size of the beam directly generated by the ultraviolet laser is smaller than that of the beam directly generated by the laser with a longer wavelength. Therefore, ultraviolet laser processing systems require a beam expander with a large beam expansion ratio. In addition, green lasers are also frequently used laser light sources in the field of material processing. Industrial green lasers generally require infrared fundamental frequency light to be generated through the frequency doubling effect, and the spot size of the directly output light is also relatively small, so a beam expander with a large beam expansion ratio is also required in the material processing process.

[0004] During the laser processing, the optimal laser wavelength or beam expansion ratio for different application scenarios is likely to be different. If the same laser beam expander can be used in different usage environments, such as different laser wavelengths and different beam expansion ratios, it will undoubtedly greatly increase the applicability and flexibility of the laser processing equipment. The beam expansion of existing ultraviolet / green laser variable-power beam expanders is relatively small, generally not exceeding 10 times, see patents CN 101887173 B, CN 102004319 B, CN 105527716 B, CN106199983B, etc. If a larger beam expansion ratio is required, only a fixed-power laser beam expander can be used, which brings inconvenience to laser processing and affects the efficiency of laser processing. Therefore, further improving the maximum beam expansion ratio of ultraviolet / green light variable-power beam expanders is a task that urgently needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a dual-wavelength, high-magnification, continuously variable-magnification laser beam expander to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A dual-wavelength, high-magnification, continuously variable laser beam expander, comprising a first lens L1, a second lens L2, a third lens L3 and a fourth lens L4 coaxially arranged in sequence on an optical axis along a laser incident direction;

[0008] The first lens L1 and the second lens L2 are plano-concave negative lenses, and the concave surface of the first lens L1 faces the incident direction of the laser;

[0009] The third lens L3 is a meniscus positive lens, and the fourth lens L4 is a biconvex positive lens;

[0010] The first lens L1 includes two surfaces, S1 and S2, wherein the S1 surface is a concave surface with a curvature radius R1=-7.7 mm; the S2 surface is a plane with a curvature radius R2=∞; the center thickness d1 between the two surfaces on the optical axis is 2 mm;

[0011] The second lens L2 includes two surfaces, S3 and S4, wherein the S3 surface is a plane with a curvature radius R3=∞; the S4 surface is a concave surface with a curvature radius R4=-7.7mm; and the center thickness d3 between the two surfaces on the optical axis is 2mm;

[0012] The third lens L3 is a meniscus positive lens, including two surfaces S5 and S6, wherein the curvature radius of the S5 surface R5=-261.5mm; the curvature radius of the S6 surface R6=-87mm; the center thickness d5 between the two surfaces on the optical axis=5mm;

[0013] The fourth lens L4 is a biconvex positive lens, including two surfaces S7 and S8, wherein the curvature radius of the S7 surface R7=690mm; the curvature radius of the S8 surface R8=-168.6mm; the center thickness d7 between the two surfaces on the optical axis=5mm

[0014] As a further solution of the present invention: the material used for the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 is fused quartz, whose refractive index Nd2=1.46 and Abbe number Vd2=68.

[0015] As a further solution of the present invention: the refractive index Nd2 of the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 is 1.46, and the Abbe number Vd2 is 68.

[0016] As a further solution of the present invention: the S3 surface and the S4 surface of the second lens L2 are coated with anti-reflection films of 355nm and 532nm wavelengths;

[0017] The S1 surface and the S2 surface of the first lens L1 are coated with anti-reflection films of 355nm and 532nm wavelengths;

[0018] The S5 surface and the S6 surface of the third lens L3 are coated with anti-reflection films of 355nm and 532nm wavelengths;

[0019] The S7 surface and the S8 surface of the fourth lens L4 are coated with anti-reflection films with wavelengths of 355nm and 532nm.

[0020] As a further solution of the present invention: the distance between the first lens and the second lens on the optical axis is d2; the distance between the second lens L2 and the third lens L3 on the optical axis is d4; the distance between the third lens L3 and the fourth lens L4 on the optical axis is d6;

[0021] Under two incident laser wavelengths, the beam expansion ratio can be continuously adjusted by adjusting the values ​​of d2 and d4 respectively; different from the general four-lens beam expander, d6 is always kept at a fixed value, that is, the third lens L3 and the fourth lens L4 can be assembled into a fixed lens group, and the distance between the two does not need to be adjusted when changing the magnification, but only d2 and d4 need to be adjusted.

[0022] As a further solution of the present invention: the wavelength of the incident light passing through the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 is 355 nm or 532 nm, and the beam expansion ratio is continuously adjustable between 20 and 40 times.

[0023] As a further solution of the present invention: the diameter of the incident light spot passing through the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 is 0.5-1 mm, and can withstand a nanosecond ultraviolet laser with a maximum average power exceeding 20W or a nanosecond green laser exceeding 50W.

[0024] As a further solution of the present invention: for an incident ultraviolet laser with a wavelength of 355 nm, a distance d2 between the first lens L1 and the second lens L2 on the optical axis is 2.0 to 38.1 mm; a distance d4 between the second lens L2 and the third lens L3 on the optical axis is 124.9 to 127.7 mm. By adjusting the values ​​of d2 and d4, the beam expansion ratio can be continuously adjusted, and the adjustment range of the beam expansion ratio is 20 to 40 times.

[0025] As a further solution of the present invention: for a green laser with an incident wavelength of 532 nm, a distance d2 between the first lens L1 and the second lens L2 on the optical axis is 2.1 to 39.5 mm; a distance d4 between the second lens L2 and the third lens L3 on the optical axis is 129 to 132.1 mm. By adjusting the values ​​of d2 and d4, the beam expansion ratio can be continuously adjusted, and the adjustment range of the beam expansion ratio is 20 to 40 times.

[0026] Compared with the prior art, the beneficial effects of the present invention are: 1. The adjustable range of the beam expansion ratio is 20 to 40 times, which is significantly higher than the beam expansion capability of the variable-magnification beam expander in the prior art. According to the Rayleigh spot formula, this is conducive to further reducing the spot size after laser focusing, thereby improving the laser processing efficiency and accuracy.

[0027] 2. It can be used for both ultraviolet laser and green laser variable magnification beam expansion, which enhances the application range of the beam expander and improves the flexibility and applicability of the laser processing system.

[0028] 3. The overall structure is compact and easy to adjust. Even at the highest beam expansion ratio of 40 times, the total optical length is only 180mm. Although the beam expander involves four lenses, only the distances between the two lenses, d2 and d4, need to be adjusted when changing the magnification.

[0029] 4. The two lenses at the front end of the beam expander use two concave lenses with exactly the same specifications and a large surface curvature, which can make the incident laser beam diverge quickly without any focusing effect on the entire optical path, thereby effectively protecting the lens from being damaged by an overly strong laser. Moreover, the first optical surface is a concave surface, which can avoid the return light interference caused by the vertical reflection effect of the lens surface on the laser. This design makes the beam expander particularly suitable for high-power ultraviolet laser and green laser beam expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the optical structure of the dual-wavelength, high-magnification, continuously variable-magnification laser beam expander of the present invention.

[0031] Figure 2(a) is the dispersion pattern when the ultraviolet laser beam is expanded 20 times.

[0032] FIG2( b ) is a wavefront optical path difference distribution diagram when the ultraviolet laser beam is expanded 20 times.

[0033] Figure 3(a) is the dispersion pattern when the ultraviolet laser beam is expanded 40 times.

[0034] FIG3( b ) is a wavefront optical path difference distribution diagram when the ultraviolet laser beam is expanded 40 times.

[0035] FIG4( a ) is a dispersion pattern of a green laser beam expanded 20 times.

[0036] FIG4( b ) is a wavefront optical path difference distribution diagram when the green laser beam is expanded 20 times.

[0037] FIG5( a ) is a dispersion pattern of a green laser beam expanded 40 times.

[0038] FIG5( b ) is a wavefront optical path difference distribution diagram when the green laser beam is expanded 40 times.

[0039] Among them: a first lens L1, a second lens L2, a third lens L3 and a fourth lens L4. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] See also Figure 1 -5, in an embodiment of the present invention, a dual-wavelength, high-magnification, continuously variable laser beam expander includes a first lens L1, a second lens L2, a third lens L3 and a fourth lens L4 coaxially arranged in sequence on the optical axis along the incident direction of the laser. Among them, the first lens L1 and the second lens L2 are plano-concave negative lenses, and the concave surface of the first lens L1 faces the incident direction of the laser. This design ensures that when a high-power laser is incident, it will not interfere with the normal operation of the laser due to vertical reflection from the front surface mirror, and the power density can be reduced by rapid divergence of the laser beam after passing through L1, thereby effectively protecting the second lens L2 from laser damage. The third lens L3 is a meniscus positive lens, and the fourth lens L4 is a biconvex positive lens.

[0042] The first lens L1 includes two surfaces, S1 and S2, wherein the S1 surface is a concave surface with a curvature radius of R1 = -7.7 mm; the S2 surface is a plane with a curvature radius of R2 = ∞; the center thickness d1 on the optical axis between the two surfaces is 2 mm; the lens material is fused quartz with a refractive index of Nd1 = 1.46 and an Abbe number of Vd1 = 68. The S1 surface and the S2 surface are both coated with anti-reflection films of 355 nm and 532 nm wavelengths.

[0043] The second lens L2 includes two surfaces, S3 and S4, wherein the S3 surface is a plane with a curvature radius R3=∞; the S4 surface is a concave surface with a curvature radius R4=-7.7mm; the center thickness d3 between the two surfaces on the optical axis is 2mm; the lens material is fused quartz with a refractive index Nd2=1.46 and an Abbe number Vd2=68. The S3 and S4 surfaces are both coated with anti-reflection films of 355nm and 532nm wavelengths.

[0044] The third lens L3 is a meniscus positive lens, including two surfaces S5 and S6, wherein the curvature radius of the S5 surface R5 = -261.5mm; the curvature radius of the S6 surface R6 = -87mm; the center thickness d5 between the two surfaces on the optical axis = 5mm; the lens material is fused quartz, with a refractive index Nd3 = 1.46 and an Abbe number Vd3 = 68. The S5 surface and the S6 surface are both coated with anti-reflection films of 355nm and 532nm wavelengths.

[0045] The fourth lens L4 is a biconvex positive lens, including two surfaces S7 and S8, wherein the curvature radius of the S7 surface R7 = 690mm; the curvature radius of the S8 surface R8 = -168.6mm; the center thickness d7 between the two surfaces on the optical axis = 5mm; the lens material is fused quartz, with a refractive index Nd4 = 1.46 and an Abbe number Vd4 = 68. The S7 and S8 surfaces are both coated with anti-reflection films of 355nm and 532nm wavelengths.

[0046] The distance between the first lens L1 and the second lens L2 on the optical axis is d2; the distance between the second lens L2 and the third lens L3 on the optical axis is d4; the distance between the third lens L3 and the fourth lens L4 on the optical axis is d6. Under the two incident laser wavelengths, the beam expansion ratio can be continuously adjusted by adjusting the values ​​of d2 and d4 respectively. Unlike the general four-lens beam expander, d6 always remains at a fixed value, that is, the third lens L3 and the fourth lens L4 can be assembled into a fixed lens group. When changing the magnification, the distance between the two does not need to be adjusted, but only d2 and d4 need to be adjusted. This undoubtedly simplifies the overall structure, helps to reduce the difficulty of assembly and use of the beam expander, and improves the accuracy of the zoom operation.

[0047] The specific data parameters of the continuously variable laser beam expander of this embodiment are summarized in Table 1.

[0048] Table 1 Specific parameters of UV laser zoom beam expander

[0049]

[0050] In Table 1, the curvature radius of ∞ represents that the surface is a plane; the sign of the curvature radius is positive when the center of the surface curvature is on the right side of the vertex between the surface and the optical axis, and negative otherwise. As can be seen from Table 1, the specifications of the first lens L1 and the second lens L2 are the same, and although the curvature radius is small enough to allow the incident laser to diverge quickly, it also meets the normal processing level of existing spherical lenses. There are no aspherical surfaces on the front and back surfaces of all four lenses, and the processing and manufacturing difficulty is relatively low.

[0051] By respectively changing the d2 and d4 values ​​of the beam expander of the present invention, the beam expansion ratio can be continuously adjusted.

[0052] When the incident laser is an ultraviolet laser with a wavelength of 355 nm, the relationship between the beam expansion factors corresponding to the combination of d2 and d4 in this embodiment is shown in Table 2.

[0053] Table 2 Ultraviolet laser beam expansion, beam expansion multiples corresponding to the combination of d2 and d4:

[0054] d2(mm) d4(mm) Beam expansion ratio 2.0 127.7 20 11.2 126.2 25 20.3 125.3 30 29.3 124.8 35 38.1 124.9 40

[0055] When the incident laser is a green laser with a wavelength of 532 nm, the relationship between the beam expansion factors corresponding to the combination of d2 and d4 in this embodiment is shown in Table 2.

[0056] Table 3 Green laser beam expansion, beam expansion multiples corresponding to the combination of d2 and d4:

[0057] d2(mm) d4(mm) Beam expansion ratio 2.1 132.1 20 11.6 130.7 25 21 129.7 30 30.4 129.2 35 39.5 129 40

[0058] From the data in Table 2 and Table 3, it can be seen that the greater the beam expansion factor, the longer the overall optical length. However, even when the beam expansion is 40 times the maximum, the overall optical length does not exceed 180 mm.

[0059] The beam expander of the present invention can achieve high-quality beam expansion between 20 and 40 times for both ultraviolet wavelengths and green light wavelengths. The standard for defining "high-quality" beam expansion here is that at an incident field angle of 0 to 0.06°, the radius of the diffuse spot of the expanded laser beam after being focused by the ideal lens does not exceed the radius of the diffraction-limited spot (Airy disk), and the peak-to-valley (PV) value of the wavefront optical path difference is less than 0.1 times the laser wavelength. Figures 2 (a) and (b) are the diffuse spot diagrams and wavefront optical path difference distribution diagrams when the ultraviolet laser is expanded 20 times. Figures 3 (a) and (b) are the diffuse spot diagrams and wavefront optical path difference distribution diagrams when the ultraviolet laser is expanded 40 times. Figures 4 (a) and (b) are the diffuse spot diagrams and wavefront optical path difference distribution diagrams when the green laser is expanded 20 times. Figures 5 (a) and (b) are the diffuse spot diagrams and wavefront optical path difference distribution diagrams when the green laser is expanded 40 times. It can be seen that at both wavelengths, the lower limit of 20 times beam expansion and the upper limit of 40 times beam expansion meet the high-quality beam expansion standard. The beam expansion ratio between 20 and 40 times also meets the high-quality beam expansion standard, which does not need to be given in detail here.

[0060] The working principle of the present invention is: to adapt to different laser processing application scenarios, a dual-wavelength, high-magnification, continuously variable laser beam expander can expand the ultraviolet and green high-power lasers with a wavelength of 355nm or 532nm, and the beam expansion ratio is continuously adjustable between 20 and 40 times. The incident spot diameter is designed to be 0.5 to 1mm, and can withstand nanosecond ultraviolet lasers with a maximum average power of more than 20W or nanosecond green lasers with a maximum average power of more than 50W.

[0061] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

Claims

1. A dual-wavelength, high-magnification, continuously variable laser beam expander, characterized in that: The dual-wavelength large-magnification continuously variable laser beam expander comprises: a first lens (L1), a second lens (L2), a third lens (L3) and a fourth lens (L4) which are coaxially arranged in sequence on the optical axis along the incident direction of the laser; The first lens (L1) and the second lens (L2) are plano-concave negative lenses, and the concave surface of the first lens (L1) faces the incident direction of the laser; The third lens (L3) is a meniscus positive lens, and the fourth lens (L4) is a biconvex positive lens; The first lens (L1) includes two surfaces, S1 and S2, wherein the S1 surface is a concave surface with a curvature radius of R1 = -7.7 mm; the S2 surface is a plane surface with a curvature radius of R2 = ∞; the center thickness d1 between the two surfaces on the optical axis is 2 mm; The second lens (L2) includes two surfaces, S3 and S4, wherein the S3 surface is a plane surface with a curvature radius R3 = ∞; the S4 surface is a concave surface with a curvature radius R4 = -7.7 mm; and the center thickness d3 between the two surfaces on the optical axis is 2 mm; The third lens (L3) is a meniscus positive lens, including two surfaces S5 and S6, wherein the curvature radius of the S5 surface is R5 = -261.5 mm; the curvature radius of the S6 surface is R6 = -87 mm; the center thickness d5 between the two surfaces on the optical axis is 5 mm; The fourth lens (L4) is a biconvex positive lens, including two surfaces S7 and S8, wherein the curvature radius of the S7 surface R7 = 690 mm; the curvature radius of the S8 surface R8 = -168.6 mm; the center thickness d7 between the two surfaces on the optical axis = 5 mm; The material used for the first lens (L1), the second lens (L2), the third lens (L3) and the fourth lens (L4) is fused quartz; The distance between the first lens (L1) and the second lens (L2) on the optical axis is d2; the distance between the second lens (L2) and the third lens (L3) on the optical axis is d4; and the distance between the third lens (L3) and the fourth lens (L4) on the optical axis is d6; Under two incident laser wavelengths, the beam expansion ratio can be continuously adjusted by adjusting the values ​​of d2 and d4 respectively; d6 is always kept at a constant value, that is, the third lens (L3) and the fourth lens (L4) can be assembled into a fixed lens group, and the distance between the two does not need to be adjusted when changing the magnification, but only d2 and d4 need to be adjusted.

2. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: The refractive index Nd of the first lens (L1), the second lens (L2), the third lens (L3) and the fourth lens (L4) is 1.46, and the Abbe number Vd is 68.

3. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: The S3 surface and the S4 surface of the second lens (L2) are coated with anti-reflection films of 355 nm and 532 nm wavelengths; The S1 surface and the S2 surface of the first lens (L1) are coated with anti-reflection films of 355 nm and 532 nm wavelengths; The S5 surface and the S6 surface of the third lens (L3) are coated with anti-reflection films of 355 nm and 532 nm wavelengths; The S7 surface and the S8 surface of the fourth lens (L4) are coated with anti-reflection films of 355 nm and 532 nm wavelengths.

4. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: The wavelength of the incident light passing through the first lens (L1), the second lens (L2), the third lens (L3) and the fourth lens (L4) is 355 nm or 532 nm, and the beam expansion ratio is continuously adjustable between 20 and 40 times.

5. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: The incident spot diameter through the first lens (L1), the second lens (L2), the third lens (L3) and the fourth lens (L4) is 0.5 ~ 1 mm, and can withstand nanosecond ultraviolet lasers with a maximum average power of more than 20W or nanosecond green lasers with a maximum average power of more than 50W.

6. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: For an ultraviolet laser with an incident wavelength of 355 nm, the distance d2 between the first lens (L1) and the second lens (L2) on the optical axis is 2.0 to 38.1 mm; the distance d4 between the second lens (L2) and the third lens (L3) on the optical axis is 124.9 to 127.7 mm. By adjusting the values ​​of d2 and d4, the beam expansion ratio can be continuously adjusted, and the adjustment range of the beam expansion ratio is 20 to 40 times.

7. The dual-wavelength, high-magnification, continuously variable laser beam expander according to claim 1, characterized in that: For a green laser with an incident wavelength of 532 nm, the distance d2 between the first lens (L1) and the second lens (L2) on the optical axis is 2.1 to 39.5 mm; the distance d4 between the second lens (L2) and the third lens (L3) on the optical axis is 129 to 132.1 mm. By adjusting the values ​​of d2 and d4, the beam expansion ratio can be continuously adjusted, and the adjustment range of the beam expansion ratio is 20 to 40 times.

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