A method and device for generating a multi-type hollow structure light field with adjustable size and rotation direction

Abstract

A method and device for generating multiple types of hollow structure light fields with adjustable size and rotation direction, relating to the field of light field control, by designing phase diagrams of multiple hollow structure light fields and loading them into Gaussian beams, thereby generating multiple hollow structure light fields. The laser light beam provided in the device passes through a laser beam expander, a half-wave plate and a polarizer, enters a spatial light modulator, is modulated and reflected by the spatial light modulator, and is captured by a CCD detection camera after being focused by a convex lens. The effect of the present invention is that by regulating the number and position of multiple off-axis vortex phase singularities loaded in a Gaussian beam, a variety of new hollow structure light fields can be generated. And by using an ordinary convex lens to focus the hollow structure light field, the size and rotation direction of the hollow structure light field can be further adjusted. The present invention enriches the diversity of off-axis vortex beam shaping results and provides a new method for laser processing, optical tweezers, surface treatment, etc.

Description

Technical Field

[0001] The present invention relates to the field of light field control, and in particular to a method and device for generating light fields of multiple types of hollow structures with adjustable sizes and rotation directions. Background Art

[0002] A vortex beam is a beam with a spiral wavefront. Because the phase at the center of the spiral wavefront is uncertain, a vortex phase singularity exists. This causes the optical field intensity at the center of the beam to cancel out, resulting in a hollow structure. Such vortex beams have important applications in fields such as light field shaping, optical communications, and biomedicine.

[0003] With the development of vortex beam manipulation technology, compared to vortex beams with only a single vortex phase singularity, the coaxial superposition of multiple vortex phase singularities can produce new light fields with richer phase structures, light intensity distributions, and orbital angular momentum. However, the light field manipulation method of multiple vortex coaxial superposition is mainly achieved by controlling the topological charge of each vortex, and cannot control the vortex position. For off-axis vortex beams with an offset between the phase singularity and the center of the main beam, the number of vortex phase singularities, the off-axis distance, and the topological charge can all be used as degrees of freedom for spatial light field manipulation. Moreover, because off-axis vortex beams produce Gouy phase shifts during propagation, causing the off-axis vortex phase singularity to rotate about the optical axis, the rotation direction of the beam can also be used as a degree of freedom for light field manipulation. Based on the above characteristics, using off-axis vortex beams for light field manipulation can obtain more novel and richer light field shaping results. On the other hand, the focusing of off-axis vortex beams has important application value in many fields, such as laser processing, optical tweezers, and microscopy. However, current research on focusing and shaping off-axis vortex beams primarily focuses on achieving tight focusing using high numerical aperture (NA) objectives (>0.7). In applications such as laser cutting, laser welding, surface treatment, and drilling, the subwavelength-scale spot size achieved by tight focusing is no longer practical. Therefore, research on using conventional lenses to produce focused beams with micrometer-scale or larger sizes is of practical significance.

[0004] In the Chinese patent "Device for Producing Propeller-Like Rotating Light Beams Using a Reflective Spatial Light Modulator" (application number 201120029196.9), by coaxially superimposing two vortex beams with opposite topological charges and different frequencies, a variety of petal-shaped light spots with controllable rotation speeds are generated; in the patent "A Method for Coding Optical Communication Based on Composite Vortex Beams" (application number 202111667708.9), Laguerre-Gaussian beams with a topological charge difference of 2 are coaxially superimposed, and by regulating the phase difference between the two beams, an annular composite light field with different light intensities is generated; in the patent "Method for Optical Information Encoding of Three-Ring Composite Vortex Beams with Interval Orbital Angular Momentum" (application number 202211052258.7), three Laguerre-Gaussian beams with different modal indices are coaxially superimposed to generate 32 groups of three-ring composite vortex light fields with different spatial structures. The above patent applications have enriched the means of light field shaping and generated more new light fields. However, since the centers of multiple vortices are loaded on the optical axis center of the incident light field and the phase singularities of multiple vortices coincide with each other, the light field control method of multi-vortex coaxial superposition is mainly achieved by controlling the topological charge number of each vortex. Therefore, this method of multi-vortex coaxial superposition lacks the freedom to control the vortex position. Summary of the Invention

[0005] In response to the above problems, the present invention provides a method and apparatus for generating multiple types of hollow structure light fields with adjustable size and rotational direction. This method can generate a variety of novel hollow structure light fields by controlling the number and position of multiple off-axis vortex phase singularities loaded into a Gaussian beam. Furthermore, focusing the hollow structure light fields using a conventional convex lens allows further adjustment of the light field size and rotational direction.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for generating multiple types of hollow structure light fields with adjustable size and rotation direction is proposed. Phase diagrams of multiple hollow structure light fields are designed and loaded into Gaussian beams to generate multiple hollow structure light fields.

[0008] The phase diagrams of the various hollow structure light fields are calculated and generated by arranging and designing n off-axis vortex phase singularities in a Gaussian beam based on the characteristics of rotational symmetry.

[0009] When there are multiple off-axis vortex phase singularities in a Gaussian beam, the complex amplitude of the light field can be expressed as follows:

[0010]

[0011] Among them, r, are the radial distance and azimuth angle of the light field, w is the waist radius of the Gaussian beam, Indicates that there are n (n = 1, 2, 3, ..., N) vortex phase singularities in the beam, m n represents the topological charge of the nth vortex phase singularity, represents the position of the nth vortex phase singularity.

[0012] The off-axis vortex phase singularities are spaced at equal arc intervals around the center of the beam. And the isometric axis distance r is arranged.

[0013] The waist radius of the Gaussian beam is w.

[0014] Optionally, when two m = +1 vortex phase singularities are spaced at equal arc intervals around the beam center When the distance from the axis is r = 0.25w, the light field presents a hollow elliptical structure; when three vortex phase singularities with m = +1 are arranged at equal arc intervals around the center of the beam When the distance from the axis is r = 0.4w, the light field presents a hollow triangle structure; when the four vortex phase singularities with m = +1 are spaced at equal arcs around the center of the beam When the isotropic axis distance is r=0.55w, the light field presents a hollow quadrilateral structure.

[0015] Optionally, when two m = +1 vortex phase singularities are spaced at equal arc intervals around the beam center When the distance from the isotropic axis is r = 0.45w, the light field presents a hollow two-hole button-like structure; when three vortex phase singularities with m = +1 are arranged at equal arc intervals around the center of the beam When the distance from the isotropic axis is r = 0.75w, the light field presents a hollow three-hole button-like structure; when the four m = +1 vortex phase singularities are spaced at equal arcs around the center of the beam When the isotropic axis distance is r=0.875w, the light field presents a hollow four-hole button-like structure.

[0016] A device for generating multiple types of hollow structure light fields with adjustable size and rotational direction, as implemented by the method of the present invention, comprises a laser, a laser beam expander, a half-wave plate, a polarizer, a spatial light modulator, a convex lens, a CCD detection camera, and a phase diagram corresponding to the hollow structure light field. The laser-generated light beam passes through the laser beam expander, half-wave plate, and polarizer before entering the spatial light modulator, where it is modulated and reflected, focused by the convex lens, and captured by the CCD detection camera.

[0017] The laser generates a linearly polarized light beam with Gaussian distribution, and the beam is expanded by a laser beam expander.

[0018] The half-wave plate and polarizing plate are used to adjust the polarization direction and polarization purity of the light beam so that the light beam meets the incident requirements of the spatial light modulator.

[0019] The spatial light modulator is loaded with a phase diagram corresponding to the hollow structure light field, performs phase modulation on the incident light beam, and focuses the modulated light beam through a convex lens.

[0020] The CCD detection camera is installed on the sliding track and can detect the light field intensity distribution at different distances before and after the focal plane of the convex lens to obtain a hollow structure light field with different light field sizes and rotation directions.

[0021] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0022] By leveraging rotational symmetry, the present invention can generate a variety of novel hollow-structured light fields by regulating the number and position of multiple off-axis vortex phase singularities loaded into a Gaussian beam. Furthermore, focusing the hollow-structured light field using a conventional convex lens allows further adjustment of its size and rotational direction. This invention enriches the diversity of off-axis vortex beam shaping results and provides a new method for laser processing, optical tweezers, surface treatment, and other applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The two-dimensional intensity distribution simulation diagram and corresponding phase diagram of the hollow structure light field of the present invention on the plane perpendicular to the optical axis;

[0024] Figure 2 The two-dimensional intensity distribution simulation diagram and corresponding phase diagram of the light field of the hollow button-shaped structure of the present invention on the plane perpendicular to the optical axis;

[0025] Figure 3 A diagram of a device for generating a light field with multiple types of hollow structures with adjustable size and rotation direction according to the present invention;

[0026] Figure 4 This is a diagram showing the light intensity distribution measurement results within the range of z = ± 80 mm before and after the hollow triangular structure light field of the present invention is focused by a convex lens 6 with a focal length of f = 750 mm (z = 0 mm at the specified focus);

[0027] Figure 5 This is a diagram showing the light intensity distribution measurement results within the range of z = ±80 mm before and after the hollow three-hole button-shaped structure light field of the present invention is focused by a convex lens 6 with a focal length of f = 750 mm (z = 0 mm at the specified focus). DETAILED DESCRIPTION

[0028] The present invention aims to provide a method and apparatus for generating multiple types of hollow structured light fields with adjustable size and rotational direction. By controlling the number and position of multiple off-axis vortex phase singularities loaded into a Gaussian beam based on rotational symmetry, a variety of novel hollow structured light fields can be generated, enriching the diversity of off-axis vortex beam shaping results. Furthermore, focusing the hollow structured light field using a conventional convex lens allows further adjustment of its size and rotational direction, providing a new method for laser processing, optical tweezers, surface treatment, and other applications.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] The present invention can select Gaussian beams with different waist radii for different spot size requirements. Based on this, when a Gaussian beam with a waist radius of w = 2 mm is selected, the parameters of other parts are also determined by the waist radius w. When the number n = 2, 3, and 4 m = +1 vortex phase singularities are distributed around the center of the beam with equal arc intervals of π, 2π / 3, and π / 2 and with isoaxial distances of 0.5mm, 0.8mm, and 1.1mm, the light field intensity distribution is as follows Figure 1 As shown in (a)-(c), the light field presents a hollow structure with an elliptical, triangular, and quadrilateral hollow area in the middle. At this time, the phase diagram of the light field is as follows: Figure 1 As shown in (d)-(f).

[0031] Furthermore, the present invention is based on Figure 1 The position of the vortex phase singularity is further increased by increasing the distance from the vortex phase singularity to the axis. The design results are as follows: Figure 2 As shown. Figure 2 In (a)-(c), when the number n=2, 3, and 4 vortex phase singularities are distributed around the center of the beam with equal arc intervals of π, 2π / 3, and π / 2, and the isotropic distances are 0.9mm, 1.5mm, and 1.75mm, respectively, the light field intensity distribution presents a hollow button-like structure with two holes, three holes, and four holes, respectively. At this time, the phase diagram of the light field is as follows Figure 2 As shown in (d)-(f).

[0032] Furthermore, for other numbers of m=+1 vortex phase singularities, a variety of new hollow structure light fields can be obtained by distributing them around the center of the light beam with equal arc intervals of 2π / n and appropriate isotropic distances.

[0033] The present invention is a device for generating a multi-type hollow structure light field with adjustable size and rotation direction. Figure 3As shown, it includes a laser 1, a laser beam expander 2, a half-wave plate 3, a polarizer 4, a spatial light modulator 5, a convex lens 6, a CCD detection camera 7, and phase diagrams of various hollow structure light fields 8;

[0034] Optionally, the laser 1 is a linearly polarized He-Ne laser with a wavelength of 632.8 nm, model 25-LHP-151-230;

[0035] Optionally, the laser beam expander 2 is a 2x LBTEK Galileo type fixed magnification laser beam expander suitable for the 400-700nm band;

[0036] Optionally, the half-wave plate 3 is a rotatable GCL-060614 half-wave plate, suitable for 632.8nm beam, with a diameter of Φ=12.7mm;

[0037] Optionally, the polarizer 4 is a rotatable GCL-051012 polarizer, suitable for the 510-800nm ​​band, with an outer diameter Φ1 = 25.4mm and an inner diameter Φ2 = 10mm;

[0038] Optionally, the spatial light modulator 5 is a pure phase spatial light modulator, model HOLOEYE, HES-6010-0467, with a pixel size of 8um×8um and a resolution of 1920×1080 pixels;

[0039] Optionally, the convex lens 6 is a GCL-010151N uncoated lens with a focal length of f=750 mm and a diameter of Φ=25.4 mm;

[0040] Optionally, the CCD detection camera 7 is set on the displacement platform, the model of the CCD detection camera is DH-130UM, the pixel size is 5.2um×5.2um, and the resolution is 1024×1280pixels;

[0041] First, a laser 1 generates a linearly polarized Gaussian beam with a wavelength of 632.8 nm. This beam is expanded by a laser beam expander 2 into a linearly polarized Gaussian beam with a waist radius of w = 2 mm. The beam's polarization direction and polarization purity are then adjusted by a half-wave plate 3 and a polarizer 4 to ensure that it meets the input requirements of a phase-only spatial light modulator 5. The beam then enters a spatial light modulator 5 loaded with a phase diagram 8 of the hollow structure light field. After modulation and reflection by the spatial light modulator 5, the beam is focused by a convex lens 6 with a focal length of f = 750 mm. The focal length of the convex lens can be selected based on the desired spot size in the actual application scenario. After the convex lens 6 focuses the beam, a CCD detection camera 7 mounted on a sliding track detects the light field intensity distribution at different distances in front of and behind the focal plane of the convex lens 6. This produces hollow structure light fields with varying light field sizes and rotation directions.

[0042] Furthermore, in order to adjust the size and rotation direction of the light field, the present invention uses a convex lens 6 to focus the light field and uses a CCD camera to detect the light intensity distribution at z = ± 80 mm before and after the focus. Figure 1 (b) After the phase diagram, the hollow triangle light field is focused by the convex lens 6. At this time, the light field intensity distribution within ±80 mm before and after the focus is recorded by the CCD detection camera 7 as shown in the figure below. Figure 4 As shown (z=0mm at the specified focus). Figure 4 It can be seen that this method can realize the clockwise rotation of the light field in the range of z < 0 in front of the focus, and the counterclockwise rotation of the light field in the range of z > 0 in front of the focus.

[0043] Further, when the spatial light modulator 5 is loaded Figure 2 (b) After the phase diagram, the hollow three-hole button-shaped structure is focused by the convex lens 6. At this time, the light field intensity distribution within ±80 mm before and after the focus is recorded by the CCD detection camera 7 as shown in the figure. Figure 5 As shown (z=0mm at the specified focus). Figure 5 It can be seen that this method can realize the clockwise rotation of the light field in the range of z < 0 in front of the focus, and the counterclockwise rotation of the light field in the range of z > 0 in front of the focus.

[0044] The present invention can generate light spots of other sizes and hollow structures by adjusting the lens focal length and the off-axis distance and number of vortex phase singularities, respectively. Therefore, the use of lasers with different wavelengths, different focusing lenses, and different off-axis distances and numbers of vortex phase singularities will produce light spots of different sizes and hollow structures, all of which are within the scope of protection of this patent.

[0045] In summary, the present invention proposes a method and device for generating multiple types of hollow structure light fields with adjustable size and rotation direction. According to the characteristics of rotational symmetry, by regulating the number and position of multiple off-axis vortex phase singularities loaded in the Gaussian beam, it is possible to design and generate hollow elliptical, hollow triangle, hollow quadrilateral and various hollow button-shaped structure light fields. And by focusing the hollow structure light field with a convex lens, the light field can be further adjusted, and hollow structure light fields with different light field sizes and rotation directions can be obtained at different distances before and after the focus. Among them, the focal length of the convex lens can be selected according to the requirements of the spot size magnitude in the actual application scenario. The present invention provides a new method for off-axis vortex beams in the fields of laser etching of precision parts, laser processing of shape-controllable and shape-dependent materials, and capture and manipulation of large-sized particles.

Claims

1. A method for generating a multi-type hollow structure light field with adjustable size and rotation direction, characterized by: By designing phase patterns of various hollow structure light fields and loading them into Gaussian beams, various hollow structure light fields can be generated; The phase diagrams of the various hollow structure light fields are calculated and generated by arranging and designing n off-axis vortex phase singularities in a Gaussian beam based on the characteristics of rotational symmetry; When there are multiple off-axis vortex phase singularities in a Gaussian beam, the complex amplitude of the light field can be expressed as follows: Among them, r, are the radial distance and azimuth angle of the light field, w is the waist radius of the Gaussian beam, Indicates that there are n (n = 1, 2, 3, ..., N) vortex phase singularities in the beam, m n represents the topological charge of the nth vortex phase singularity, represents the position of the nth vortex phase singularity; The off-axis vortex phase singularities are spaced at equal arc intervals around the center of the beam. And the isometric axis distance r is arranged.

2. The method for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 1, characterized in that: When two m n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the distance between the two axes is r = 0.25w, the light field presents a hollow elliptical structure; when the three m n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the distance between the two axes is r=0.4w, the light field presents a hollow triangle structure. n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the isotropic axis distance is r=0.55w, the light field presents a hollow quadrilateral structure.

3. The method for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 1, characterized in that: When two m n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the distance between the two axes is r = 0.45w, the light field presents a hollow two-hole button-like structure; when the three m n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the distance between the two axes is r=0.75w, the light field presents a hollow three-hole button-like structure; when the four m n = +1 vortex phase singularities are spaced at equal arc intervals around the center of the beam When the isotropic axis distance is r=0.875w, the light field presents a hollow four-hole button-like structure.

4. A device for generating a multi-type hollow structure light field with adjustable size and rotation direction for implementing the method of any one of claims 1 to 3, characterized in that: It includes a laser, a laser beam expander, a half-wave plate, a polarizer, a spatial light modulator, a convex lens, a CCD detection camera, and a phase diagram corresponding to the above-mentioned hollow structure light field; the laser generates a light beam that passes through the laser beam expander, the half-wave plate, and the polarizer, enters the spatial light modulator, is modulated and reflected by the spatial light modulator, and is focused by the convex lens and captured by the CCD detection camera; when different wavelength lasers, different focusing lenses, and different off-axis distances and numbers of vortex phase singularities are selected, light spots of different sizes and hollow structure light fields are generated.

5. The device for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 4, characterized in that: The laser generates a linearly polarized light beam with Gaussian distribution, and the beam is expanded by a laser beam expander.

6. The device for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 4, characterized in that: The half-wave plate and polarizing plate are used to adjust the polarization direction and polarization purity of the light beam so that the light beam meets the incident requirements of the spatial light modulator.

7. The device for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 4, characterized in that: The spatial light modulator is loaded with a phase diagram corresponding to the hollow structure light field, performs phase modulation on the incident light beam, and focuses the modulated light beam through a convex lens.

8. The device for generating a multi-type hollow structure light field with adjustable size and rotation direction according to claim 4, characterized in that: The CCD detection camera is installed on the sliding track and can detect the light field intensity distribution at different distances before and after the focal plane of the convex lens to obtain a hollow structure light field with different light field sizes and rotation directions.

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