RU2797961C1 - Laser beam expander with continuously variable magnification - Google Patents

Abstract

FIELD: laser technology.

SUBSTANCE: invention can be used as a beam diameter expander used in laser process equipment. A laser beam expander with continuously variable magnification includes three optically coupled components separated by air gaps. The first component contains a biconvex lens, which has the ability to move along the optical axis relative to the stationary second component, which consists of one biconcave lens with the same radii. The third component also has the ability to move along the optical axis relative to the second component and consists of two lenses - plano-concave, facing the flat surface towards the second component, and biconvex.

EFFECT: increasing the manufacturability of the optical elements of the expander by reducing the number of different lens radii, as well as increasing the maximum beam diameter at the expander output, reducing the maximum length of the optical diagram and increasing the degree of aberration correction.

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Description

The invention relates to the field of laser technology and can be used as a laser beam diameter expander used in laser process equipment.

Laser radiation, due to its features such as monochromaticity, coherence, low divergence and high brightness, is widely used for laser welding, cutting, engraving and other technological processes of material processing.

Most types of lasers used in installations are characterized by small beam diameters - about 0.5÷2 mm. At the same time, in the material processing zone, when solving a number of problems, it is necessary to focus the radiation into a spot with the smallest diameter, either in order to create a higher power density, for example, when cutting or welding a material, or to increase the accuracy of processing, for example, when engraving material. The minimum spot diameter δ into which laser radiation can be focused is theoretically given by the well-known Rayleigh formula: δ=2.44λƒ/D, where λ is the laser wavelength, ƒ is the focal length of the objective, and D is the diameter of the entrance pupil of the objective. Obviously, in order to focus the radiation into a small spot, it is necessary to increase the diameter of the entrance pupil of the lens D, which must be completely filled with laser radiation, that is, it is necessary to expand the laser beam. For this purpose, beam expanders or zooms with constant or variable magnification are used.

Known laser beam expanders U S5305150 A, 04/19/1994, "Laser beam expander: 10x"; US 5329404 A, 07/12/1994, "Laser beam expander: 5x"; CN 101738730 A, 06/16/2010, "Laser beam expander featuring adjustable lens spacing".

A common disadvantage of these expanders is the inability to change the beam diameter at the exit, which significantly limits the range of their application.

Known laser beam expander for a high-power UV laser [CN 113376844 A, 09/10/2021, "Continuous zoom beam expander suitable for high-power-density ultraviolet laser"], consisting of three optically coupled lenses located on the same axis along the incident laser beam radiation. The first and second (along the beam) lenses are plano-concave, located with a concave surface in the direction of the laser, the third lens is plano-convex, located with a plane in the direction of the laser. The first and third lenses can move along the optical axis relative to the fixed second lens to change the magnification. The expander is designed for an input beam diameter of 0.5÷1 mm and a magnification range of 6÷12 times.

The disadvantages of the known expander are:

- limited diameter of the input beam of laser radiation and a limited range of magnifications. So, for beams with a maximum declared diameter of 1 mm, it does not exceed 9 times, and the maximum declared increase of 12 times is realized only for an input beam diameter of up to 0.7 mm. Thus, the maximum diameter of the output beam is only 9 mm. This circumstance limits the functionality of laser equipment equipped with a known expander;

- the possibility of a focused glare as a result of reflection from the concave surface of the first lens facing the laser, which can lead to undesirable consequences;

- large maximum length of the expander optical circuit - 212.6 mm.

The closest in technical essence to the proposed invention is a laser beam expander [CN 111283320 A, 06/16/2020, "Laser beam expander and laser processing equipment"]. The expander consists of four optically coupled lenses located on the same axis along the incident laser beam. The second lens can move along the optical axis relative to the first lens, and the third and fourth lenses can move together relative to the second lens to change the diameter of the laser beam at the expander output. The first lens is a meniscus with its convex side facing the laser, the second and third lenses are biconcave, the fourth lens is biconvex. All optical surfaces of lenses have different radii of curvature, with the exception of the second, which has the same radii of curvature.

The disadvantages of this expander are:

- low manufacturability of its optical elements due to the large range of radii, for each of which it is necessary to produce test glasses and tools;

- small diameter of the output beam at maximum magnification - 9 mm;

- low degree of aberration correction at high magnifications and large beam diameters at the expander input.

The technical objective of the invention is to reduce the number of lenses of different radii.

The technical result of the invention is the creation of a laser beam expander with increased manufacturability of its optical elements, lower cost, large output beam diameter, reduced maximum length of the optical scheme and increased degree of aberration correction.

The technical result is achieved by the fact that the laser beam expander with a smoothly variable magnification includes three optically coupled components separated by air gaps, while the first component contains a lens with radii R ₁ and R ₂ , the second component is made in the form of a biconcave lens with the same radii R ₃ , R ₄ , the third component contains two lenses - the third negative plano-concave with radii R ₅ =∞ and R ₆ and the fourth biconvex positive with radii R ₇ , R ₈ , according to the invention, the first and third components are made to move along the optical axis relative to the fixed second component, the lens of the first component is made positive biconvex, with the following ratios for the radii of the lenses: R ₁ =R ₈ , R ₂ =R ₆ .

The expander can operate with input beam diameters of 1÷2 mm at magnifications of 6÷12 times, and the maximum output beam diameter at which the diffraction image quality is maintained reaches 20 mm (2 mm × 10 ^x ), while the wave aberration is less than λ/ 20, where λ is the operating wavelength of the laser. Wave aberration at input beam diameter 1 mm and magnification 12 times less than λ/200.

The essence of the invention is illustrated by drawings, where in Fig. 1 shows the optical scheme of a laser beam expander with a continuously variable magnification and the following designations are adopted:

1 - biconvex positive first lens of the first component,

2 - biconcave negative second lens of the second component,

3 - plano-concave negative third lens of the third component,

4 - biconvex positive fourth lens of the third component,

d ₁ - thickness of the first lens,

d ₂ - variable distance between the first and second components,

d ₃ - thickness of the second lens,

d ₄ - variable distance between the second and third components,

d ₅ - thickness of the third lens,

d ₆ - the size of the air gap between the third and fourth lenses,

d ₇ - the thickness of the fourth lens.

In FIG. Figure 2 shows a plot of the energy concentration in the spot as a function of the radius.

In FIG. 3 shows a graph of the change in the transfer function modulus from the spatial frequency.

In FIG. Figure 4 shows a graph of the wave aberrations of the expander for an input beam diameter of 1 mm and an expander magnification of 12 ^x .

In FIG. Figure 5 shows a graph of the wave aberrations of the expander for an input beam diameter of 2 mm and an expander magnification of 6 ^x .

In FIG. Figure 6 shows a graph of the wave aberrations of the expander for an input beam diameter of 2 mm and an expander magnification of 10 ^x .

The laser beam expander with continuously variable magnification includes three optically coupled components separated by air gaps, the first component contains a positive biconvex lens with radii R ₁ and R ₂ , the second component is made in the form of a biconcave lens with the same radii R ₃ , R ₄ , the third component contains two lenses - the third negative plano-concave with radii R ₅ =∞ and R ₆ and the fourth biconvex positive with radii R ₇ , R ₈ , while the first and third components are configured to move along the optical axis relative to the stationary second component, while for the radii of the lenses are the following relationships: R ₁ =R ₈ , R ₂ =R ₆ .

The continuously variable magnification laser beam expander shown in FIG. 1 operates as follows: a pseudo-parallel laser beam emanating from a laser emitter hits the first lens 1 of the first component, which has a positive optical power, after which it becomes converging, and on the first surface of the second lens 2 of the second component, the beam cross-sectional diameter decreases. After passing through the second lens, which has a negative optical power, the beam begins to diverge and hits first the third 3 and then the fourth 4 lenses of the third component, after which it becomes parallel and enlarged in diameter. The distance d ₂ changes to change the diameter of the beam section, and the distance d ₄ changes in accordance with the change in d ₂ to compensate for the changed beam convergence and radiation collimation. Thus, a variation of the beam diameter at the expander output is carried out and, accordingly, its increase, the divergence of laser radiation decreases.

It should be emphasized that the expander according to the proposed scheme can be designed for any lasers with an operating wavelength in the range from UV to near-IR radiation. In accordance with the proposed solution, as a specific example, an expander for a Nd:YAG laser with a wavelength of 1.064 μm is calculated, which has the following technical characteristics:

working wavelength 1.064 µm;

input beam diameter: 1÷2 mm;

magnification range:

- 6÷12 times for inlet diameter 1 mm (wave aberration is less than λ/200),

- 6÷10 times for an inlet diameter of 2 mm (wave aberration is less than λ/100÷λ/20);

мм).maximum optical circuit length: 150.8 mm (6 ^x ,

mm).

The design parameters of the calculated laser beam expander with a continuously variable magnification are given in Table 1, where the radii of the lens surfaces, their thicknesses and material are indicated.

All optical surfaces of the expander lenses are spherical. Fused quartz is used as a material for the expander lenses, which has good transmission in a wide range from UV to near-IR and a low thermal expansion coefficient, which makes this material universal for solving a wide range of problems.

Table 2 shows the values of the variable distances d ₂ and d ₄ at magnifications of the expander 6, 8 and 12 times.

The high quality of the calculated expander is confirmed by the attached graphic materials (Fig. 2 - Fig. 6)

The analysis of the aberrations of the optical scheme of the laser beam expander was carried out using the model of a paraxial (aberration-free) lens with a focal length of 50 mm, which makes it possible to focus the collimated beam.

In FIG. 2 shows that the graph practically coincides with the theoretical limit.

In FIG. 3 shows that the graph practically coincides with the diffraction limit.

In FIG. 4 with an input beam diameter of 1 mm and an expander magnification of 12 ^x -wave aberration is less than λ/200.

In FIG. 5 with an input beam diameter of 2 mm and an increase in the expander 6 ^x -wave aberration is less than λ/100.

In FIG. 6 with an input beam diameter of 2 mm and an expander magnification of ^10x , the wave aberration is less than λ/20.

The use of the invention makes it possible to improve the manufacturability of the optical elements of the expander by reducing the number of different lens radii, which leads to a decrease in the number of test glasses required for lens control and a reduction in the range of tools for lens manufacture. Thus, the cost of manufacturing expander lenses is reduced. The use of the invention also makes it possible to increase the maximum beam diameter at the expander output, to reduce the maximum length of the optical scheme, and to increase the degree of aberration correction.

Claims (1)

Laser beam expander with continuously variable magnification, comprising three optically coupled components separated by air gaps, wherein the first component contains a lens with radii R ₁ and R ₂ , the second component is made in the form of a biconcave lens with the same radii R ₃ , R ₄ , the third component contains two lenses - the third negative plano-concave with radii R ₅ =∞ and R ₆ and the fourth biconvex positive with radii R ₇ , R ₈ , characterized in that the first and third components are made to move along the optical axis relative to the fixed second component, the lens of the first the component is made positive biconvex, with the following ratios for the radii of the lenses: R ₁ =R ₈ , R ₂ =R ₆ .

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