An adjustable axial bifocal laser focusing module

Abstract

The application discloses a kind of adjustable axial bifocal laser focusing module, belong to laser precision machining technical field.The adjustable axial bifocal laser focusing module includes incident laser module, defocus control module, and focusing module.The adjustable axial bifocal laser focusing module presented by the application can realize the focusing laser bifocal of axial scanning, can realize the multi-focus array of axial in combination with Daman wave band piece, greatly improve the axial action range of laser processing including laser cutting, laser welding etc.The application provides a kind of bifocal laser focusing module solution scheme with focal spot energy, interval adjustable simultaneously, and with higher optical path stability compact.The adjustable axial bifocal laser focusing module has important application value in the field such as glass or semiconductor material invisible cutting, thick steel plate laser cutting, new energy battery electrode and alloy laser welding, laser fluorescence imaging etc.

Description

Technical Field

[0001] This invention relates to a novel common-path laser focusing module, particularly an adjustable common-path axial dual-focus laser focusing module, belonging to the field of laser precision machining technology. Background Technology

[0002] With the continuous development and advancement of laser technology, laser processing has become an important component of modern advanced intelligent manufacturing. The basic principle of laser processing is to utilize highly focused laser light to achieve extremely high local energy density, thereby enabling thermal and thermochemical ablation of the processed material to achieve cutting, welding, and fusion. Traditional laser focusing fields often only produce a single axial focused spot, thus achieving high energy density only within a very small axial region, while defocusing rapidly occurs far from the focal point. For many laser processing applications, a smaller lateral size of the focused spot and a larger axial effective range are often desirable. For laser cutting or scribing, this means greater cutting or scribing thickness or depth; for laser welding, for thick metal plates exceeding 20mm in thickness, traditional bevel cutting pre-operations can be avoided to directly achieve thick plate welding, thus greatly improving efficiency and saving costs.

[0003] In recent years, with the continuous expansion of laser technology applications, axial multifocal, especially axial bifocal, technologies have received increasing attention. Currently, the main technologies for generating axial multifocal / bifocal points include: 1) diffractive optical elements, such as Damien zone plates [Previous Technology 201010585480.4; 201610024854.2]; 2) pre-wavelength splitting double-lens systems, such as [Previous Technology 202110316515.2; 201711315448.2; 202011368293.0]; 3) multifocal points generated using dual optical paths [Previous Technology 201720868946.9]. Diffractive optical elements can easily realize multiple axial focal points, with the advantage of compact structure and no need for complex optical paths. However, once these elements are fabricated, they often lack the ability to adjust the focal spacing and focal energy. Pre-wavelength splitting dual-lens systems often employ two sub-apertures, each focusing a portion of the laser to achieve axial dual-foci. However, this method also lacks adjustability. While separate dual-beam paths offer greater adjustability, such systems are complex, and the stability of the two laser beams is susceptible to interference from air disturbances and mechanical vibrations due to their separate configuration. Dual-foci focused lasers, on the other hand, offer greater flexibility and compatibility due to their adjustable focus capabilities, including the axial spacing and energy distribution ratio between the two focal points. In laser cutting and welding, the focal point spacing and energy ratio can be adjusted in real-time, allowing for better optimization of laser processing techniques. The stability of the optical path determines the relative stability of the energy distribution and spacing between the two focal points, ultimately determining the consistency and yield of laser processing.

[0004] Therefore, for applications such as laser processing, there is currently a lack of a compact dual-focus laser focusing module that simultaneously possesses focal spot energy, adjustable spacing, and high optical path stability. Summary of the Invention

[0005] To address the current technical challenge of lacking a compact dual-focus laser module that simultaneously possesses focal spot energy, adjustable spacing, and high optical path stability, this invention proposes an adjustable axial dual-focus laser focusing module. This dual-focus laser module primarily utilizes a polarization-splitting / combining Saniac interferometer optical path to introduce different sphericities into orthogonal polarized dual optical paths, achieving a common-path axial dual-focus system through conventional focusing lenses. The relative energy distribution ratio of the dual focuses can be adjusted by regulating the orientation of the polarized light incident on the orthogonal polarized optical paths; the axial distance between the dual focuses can be adjusted by regulating the axial position of the sphericity-introducing element. Furthermore, by incorporating Damienz zone plate technology, this system can achieve axial dual-path multi-focus, thereby significantly improving the axial operating range of the focusing module.

[0006] The technical solution of the present invention is as follows:

[0007] An adjustable axial dual-focus laser focusing module, characterized in that it comprises:

[0008] The incident laser module is used to collimate and expand the incident laser beam, and to adjust the polarization orientation and sphericity of the output linearly polarized light.

[0009] The defocus control module is used to receive the linearly polarized light and output two linearly polarized lights with different sphericities and orthogonal polarization directions, and to realize the dynamic adjustment of the sphericity carried by the two orthogonally polarized light paths.

[0010] The focusing module is used to receive the two orthogonally linearly polarized beams with different sphericity and form dual-focus laser spots with adjustable axial position and spacing.

[0011] The incident laser module performs transmission, collimation, beam expansion, and output sphericity adjustment of the incident laser. The incident laser module outputs linearly polarized light with a high polarization selectivity, and the polarization orientation of this linearly polarized light can be adjusted angularly. The sphericity of the laser beam emitted by the incident laser module can be dynamically adjusted.

[0012] The defocus control module can be a transmission defocus control module or a reflection defocus control module.

[0013] The transmission defocus control module includes a first polarization beam splitter, a first mirror group, a second mirror group, and a pair of confocal lens groups. The first lens in the confocal lens group is located between the first mirror group and the second mirror group in the optical path, and the axial position of the lens along the optical path direction is adjustable. The second lens is located in front of or after the first polarization beam splitter.

[0014] When the second lens is positioned before the first polarization beam splitter, the optical path in the transmission defocus control module is as follows: the linearly polarized light emitted from the incident laser module first passes through the second lens, and then is split into two beams with perpendicular polarization states by the first polarization beam splitter. The horizontally polarized beam passes through the polarization beam splitter, enters the first reflecting mirror group, is reflected and exited, enters the first lens, is transmitted, enters the second reflecting mirror group, is reflected and exited, and enters the first polarization beam splitter for transmission and exit. The other vertically polarized beam is reflected by the first polarization beam splitter and deflected by 90 degrees, enters the second reflecting mirror group, is reflected and exited, enters the first lens, is transmitted, enters the first reflecting mirror group, is reflected and exited, enters the first polarization beam splitter, is reflected and deflected by 90 degrees, and then exits. At this time, the two beams propagating in opposite directions overlap again.

[0015] When the second lens is positioned after the first polarization beam splitter, the optical path in the transmission defocus control module is as follows: the linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization states after passing through the first polarization beam splitter. The horizontally polarized beam passes through the first polarization beam splitter, enters the first reflecting mirror group, is reflected and exits, enters the first lens, is transmitted, enters the second reflecting mirror group, is reflected and exits, enters the first polarization beam splitter, is transmitted, and exits through the second lens. The other vertically polarized beam is reflected by the first polarization beam splitter and deflected by 90 degrees, enters the second reflecting mirror group, is reflected and exits, enters the first lens, is transmitted, enters the first reflecting mirror group, is reflected and exits, enters the first polarization beam splitter, is reflected and deflected by 90 degrees, and exits through the second lens. At this time, the two beams propagating in opposite directions overlap again.

[0016] The second lens in the transmission defocus control module can be axially translated along the optical axis, ultimately realizing the adjustment of the axial distance df between the two focal points formed by the laser focusing module.

[0017] The reflection defocus control module includes a first polarizing beam splitter, a first mirror group, a first quarter-wave plate, a first objective lens, a double-sided mirror, a second objective lens, a second quarter-wave plate, and a second mirror group; and the axial position of the double-sided mirror is adjustable along the optical path direction.

[0018] The optical path in the reflection defocusing control module is as follows: The linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization after passing through the first polarization beam splitter. The horizontally polarized beam passes through the polarization beam splitter, enters the first reflecting mirror group, is reflected and exits, passes through the first quarter-wave plate to become circularly polarized light, enters the first objective lens for focusing, is reflected back through the double-sided reflecting mirror, passes through the first objective lens again and through the first quarter-wave plate to become vertically polarized light, then enters the first reflecting mirror group again for reflection, enters the first polarization beam split again for reflection and is deflected by 90 degrees before exiting; The other vertically polarized beam is reflected and deflected by 90 degrees after passing through the first polarization beam splitter, enters the second reflecting mirror group for reflection and exits, passes through the second quarter-wave plate to become circularly polarized light, enters the second objective lens for focusing, is reflected back through the double-sided reflecting mirror, passes through the second objective lens again and through the second quarter-wave plate to become horizontally polarized light, then enters the first reflecting mirror group again for reflection, enters the first polarization beam split again for transmission and exiting.

[0019] The focusing module completes the polarization and multi-focus control of the beam emitted from the transmission defocus control module, and finally realizes two sets of axially separated laser focusing multi-focus spots; the polarization and multi-focus control elements can also be removed; after removal, the focusing module realizes two axially separated laser focusing spots.

[0020] The double-sided mirror is characterized by having a high-reflectivity reflective film coated on both its front and rear surfaces, and is mounted on a linear scanning actuator along the optical path. The double-sided mirror can be axially translated along the optical axis to ultimately adjust the axial distance df between the two focal points formed by the laser focusing module.

[0021] Preferably, the optical path elements of the incident laser module are incident in sequence as follows: laser coupling fiber, Glan prism, collimating lens, second polarizing beam splitter prism, third quarter-wave plate, third objective lens, third reflecting mirror, and half-wave plate;

[0022] Preferably, the third reflecting mirror of the incident laser module is provided with an actuator;

[0023] Preferably, the half-wave plate of the incident laser module can be angularly rotated and adjusted;

[0024] Preferably, the optical path elements of the focusing module are provided in sequence as a polarizer, a Damien zone plate, and a focusing lens;

[0025] Preferably, the polarizer is mounted on an angularly adjustable adjustment frame, which enables angular adjustment of the polarization direction;

[0026] Preferably, in the transmission defocus control module or the reflection defocus control module, the reflectors in the first and second reflector groups are pentagonal cylindrical reflective prisms made of fused silica; the cross-section of the pentagonal cylindrical reflective prism is a pentagon symmetrical about the normal to the incident / outgoing rays, with its five interior angles being 135 degrees, 90 degrees, 112.5 degrees, 112.5 degrees, and 90 degrees respectively; the reflecting slope of the pentagonal cylindrical reflective prism is coated with a high-reflectivity film for the working wavelength, with a reflectivity greater than 99%; both incident / outgoing surfaces are coated with an anti-reflection film for the working wavelength, with a transmittance greater than 98%;

[0027] Preferably, the two sets of multifocal points of the focused laser formed by the laser focusing module can be moved axially as a whole. This is achieved by scanning (translating) along the optical axis direction by the third reflecting mirror of the incident laser module under the drive of the actuator. The axial working distance of the laser focusing module can be adjusted within a certain range.

[0028] Preferably, the incident laser coupling fiber emitting end, collimating lens, and third objective lens of the laser working module are kept centered; and the incident laser coupling fiber emitting end, collimating lens, and third objective lens in the laser working module are kept centered with the first lens, second lens or first objective lens and second objective lens in the defocus control module, as well as the Damien zone plate and focusing lens in the focusing module.

[0029] Preferably, the incident laser coupling fiber of the incident laser module is a single-mode polarization-maintaining fiber; the Glan prism is a Brost Glan prism with a transmittance better than 96% and a polarization extinction ratio better than 10000:1; the half-wave plate mounting rotating frame is an electrically adjustable angle frame, and further, its angular rotation repeatability is better than 0.001 degrees.

[0030] The mirrors in the first and second mirror groups can be dielectric mirrors coated with a high-reflection film, or they can be metal mirrors coated with a high-reflection film. The metal mirrors can be metal film mirrors coated with gold, silver, or aluminum.

[0031] Preferably, the Damman zone plate can be a two-step phase element or a multi-step phase element, and its substrate material is fused silica.

[0032] Preferably, the Damman zone plate is a 1×5 Damman zone plate.

[0033] Preferably, under the conditions of a working wavelength of 1064 nm, a numerical aperture of 0.1 for the focusing objective, and an apodization factor G = 1, the axial spot spacing of the Damman zone plate is 400 micrometers, and the corresponding normalized radii of each ring are 0.1612, 0.1685, 0.1919, 0.2007, 0.2460, 0.2636, 0.3022, 0.4442, 0.4504, 0.4609, 0.6150, 0.6261, 0.7159, 0.7175, 0.7234, 0.7257, 0.7395, 0.7455, 0.7600, 0.8266, 0.8300, 0.8357, 0.9294, 0.9368, and 0.9988.

[0034] Preferably, the Damman zone plate is a 1×7 Damman zone plate.

[0035] Preferably, under the conditions of a working wavelength of 1064 nm, a numerical aperture of the focusing objective of 0.1, and an apodization factor G = 1, the axial spot spacing of the Damman zone plate is 500 μm, and the corresponding normalized radii of each ring are 0.2929, 0.2955, 0.3656, 0.4395, 0.4479, 0.4517, 0.4724, 0.4731, 0.5092, 0.5119, 0.5176, 0.5723, 0.5727, and 0.57 μm. 89, 0.6183, 0.6233, 0.6892, 0.6902, 0.7230, 0.7629, 0.7678, 0.7700, 0.7823, 0.7827, 0.8050, 0.8067, 0.8103, 0.8463, 0.8465, 0.8507, 0.8780, 0.8815, 0.9291, 0.9299, 0.9544, 0.9850, 0.9887, 0.9904.

[0036] Preferably, the Damman zone plate is mounted on a mechanically adjustable frame that can be pushed forward / retracted, which allows for easy replacement of Damman zone plates with different beam splitting ratios, and also allows for easy removal of Damman zone plates according to actual needs.

[0037] The beneficial effects of this invention are:

[0038] (1) Axial focusing laser dual focal points with adjustable spacing and energy distribution ratio can achieve high stability in common / quasi-common optical paths.

[0039] (2) It can realize high-speed axial spacing adjustment, that is, axial dual-focus scanning within a certain range.

[0040] (3) Combining with Damman zone plates can achieve axial dual-group focusing multi-focus, which will greatly expand the axial range of laser action.

[0041] (4) The technical effect of the present invention can greatly improve the cutting thickness of laser cutting or improve the depth ratio of laser welding. Attached image description:

[0042] Figure 1 This is a schematic diagram of a transmissive adjustable axial dual-focus focusing module system. The left image shows the defocus module with the first lens in front; the right image shows the defocus module with the first lens in the rear.

[0043] In the diagram: 100—Incident laser module; 200—Defocus control module; 201—First polarizing beam splitter; 202—First reflecting mirror group; 203—Second reflecting mirror group; 204—First lens; 204—Second lens; 300—Focusing module.

[0044] Figure 2This is a schematic diagram of a reflective adjustable axial dual-focus focusing module system.

[0045] In the diagram: 100—Incident laser module; 200—Defocus control module; 201—First polarizing beam splitter; 202—First reflecting mirror group; 203—Second reflecting mirror group; 206—First quarter-wave plate; 207—First objective lens; 208—Second objective lens; 209—Second quarter-wave plate; 210—Double-sided reflecting mirror; 300—Focusing module.

[0046] Figure 3 This is a schematic diagram of an embodiment of a transmissive adjustable axial dual-focus focusing module. The left diagram shows the case where the dual-focus interval is zero; the right diagram shows the case where the dual-focus interval is not zero.

[0047] In the diagram: 101—Incident laser coupling fiber; 102—Glan prism; 103—Collimating lens; 104—Second polarizing beam splitter prism; 105—Third quarter-wave plate; 106—Third objective lens; 107—Third reflecting mirror; 108—Half-wave plate; 205—Second lens; 201—First polarizing beam splitter prism; 202—First reflecting mirror; 204—First lens; 203—Second reflecting mirror; 301—Polarizer; 302—Damman zone plate; 303—Focusing lens.

[0048] Figure 4 This is a schematic diagram of Embodiment 2 of a reflective adjustable axial dual-focus focusing module. The left diagram shows the case where the dual-focus interval is zero; the right diagram shows the case where the dual-focus interval is not zero.

[0049] In the diagram: 101—Incident laser coupling fiber; 102—Glan prism; 103—Collimating lens; 104—Second polarizing beam splitter prism; 105—Third quarter-wave plate; 106—Third objective lens; 107—Third reflecting mirror; 108—Half-wave plate; 201—First polarizing beam splitter prism; 202—First reflecting mirror; 206—First quarter-wave plate; 207—First objective lens; 210—Double-sided reflecting mirror; 208—Second objective lens; 209—Second quarter-wave plate; 203—Second reflecting mirror; 301—Polarizer; 302—Damman zone plate; 303—Focusing lens.

[0050] Figure 5 This is a schematic diagram of the geometric relationship of the bifocal focusing model.

[0051] In the diagram: dz is the focal deviation distance, f1 is the focal length of the first lens, f2 is the focal length of the second lens or the second objective lens and the third objective lens; d is the distance between the second lens or the second objective lens and the focusing lens; f is the focal length of the focusing lens; df is the distance between the two focal points of the focusing lens.

[0052] Figure 6The diagram shows the geometric relationship of the reflecting prism: the left diagram corresponds to the center of the incident beam being offset from the center of the incident surface (β<1 / 2); the right diagram corresponds to the center of the incident beam being directly opposite the center of the incident surface (β=1 / 2).

[0053] In the diagram, the upper left corner is a 3D schematic; the upper right, lower left, and lower right corners correspond to the left view, top view, and front view of the 3D diagram, respectively. Surfaces A and B are the incident / exit surfaces of two orthogonally polarized light beams, and surface C is the reflecting surface.

[0054] Figure 7 A schematic diagram of embodiment three of the adjustable axial dual-focus focusing module: a coated polarizing beam splitter is used instead of a polarizing beam splitter prism, and a regular mirror is used instead of a reflecting prism. The left image shows the transmission mode; the right image shows the reflection mode.

[0055] Figure 8 A schematic diagram of the principle of the fourth embodiment of the adjustable axial dual-focus focusing module: A coated polarizing beam splitter is used instead of a polarizing beam splitter prism, and each set of reflectors adopts an asymmetric optical path structure with two ordinary reflectors. The left image shows the transmission mode; the right image shows the reflection mode.

[0056] Figure 9 The curves showing the relationship between the axial displacement of the double-sided mirror and the distance between the two focal points of the focusing lens are: (a) corresponding to the initial position dz=0; (b) corresponding to the initial position dz=1mm.

[0057] Figure 10 The simulation results of the light intensity distribution of two sets of multifocal arrays after the addition of the Damman zone plate are as follows: (a) corresponding to the 1×5 Damman zone plate; (b) corresponding to the 1×7 Damman zone plate. Detailed Implementation

[0058] Please see Figure 1 , Figure 2 The adjustable axial dual-focus laser focusing module proposed in this invention includes an incident laser module (100), a defocus control module (200), and a focusing module (300).

[0059] The main function of the incident laser module (100) is to complete the transmission, collimation and beam expansion of the incident laser and the adjustment of the outgoing sphericity. The incident laser module outputs linearly polarized light with a high polarization selectivity, and the polarization orientation of the linearly polarized light can be adjusted angularly. The sphericity of the laser beam emitted by the incident laser module can be dynamically adjusted.

[0060] The defocus control module (200) can be a transmissive type. Figure 1 ) or reflective ( Figure 2 ).

[0061] The transmission defocus control module includes a first polarization beam splitter (210), a first reflector group (202), a second reflector group (203), and a pair of confocal lens groups (204) and (205). The first lens (204) in the confocal lens group is located between the first reflector group and the second reflector group in the optical path, and the axial position of the lens along the optical path direction is adjustable. The second lens (205) is positioned before or after the first polarization beam splitter (201). When the second lens (205) is positioned before the first polarization beam splitter (201), the optical path in the transmission defocus control module is as follows: the linearly polarized light emitted from the incident laser module first passes through the second lens (205), and then is split into two beams with perpendicular polarization states by the first polarization beam splitter (201). The horizontally polarized beam passes through the first polarization beam splitter (201), enters the first reflector group (202), is reflected and emitted, enters the first lens (204), is transmitted, and then enters the second reflector group (202). The two reflecting mirrors (203) are reflected out and enter the first polarization beam splitter (201) for transmission and exit; the other vertically polarized beam is reflected by the first polarization beam splitter (201) and deflected by 90 degrees, then enters the second reflecting mirror group (203), is reflected out, enters the first lens (204) for transmission, enters the first reflecting mirror group (202), is reflected out, enters the first polarization beam splitter (201) for reflection and deflected by 90 degrees for exit. At this time, the two beams propagating in opposite directions overlap again. When the second lens (205) is positioned after the first polarization beam splitter (201), the optical path in the transmission defocus control module is as follows: the linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization states after passing through the first polarization beam splitter (201). The horizontally polarized beam passes through the first polarization beam splitter (201), enters the first reflecting mirror group (202), is reflected out, enters the first lens (204), is transmitted, enters the second reflecting mirror group (203), is reflected out, and enters... The first polarization beam splitter (201) passes through and exits through the second lens (205); another vertically polarized beam is reflected by the first polarization beam splitter (201) and deflected by 90 degrees, then enters the second mirror group (203) and exits after reflection, enters the first lens (204) and is transmitted, enters the first mirror group (202) and exits after reflection, enters the first polarization beam splitter (201) and is reflected by 90 degrees, then exits through the second lens (205). At this time, the two beams propagating in opposite directions overlap again.

[0062] The second lens (205) in the transmission defocus control module can be axially translated along the optical axis, ultimately realizing the adjustment of the axial distance df between the axial dual focal points formed by the laser focusing module;

[0063] The reflection defocus control module includes a first polarizing beam splitter (201), a first mirror group (202), a first quarter-wave plate (206), a first objective lens (207), a double-sided mirror (210), a second objective lens (208), a second quarter-wave plate (209), and a second mirror group (203); and the axial position of the double-sided mirror along the optical path direction is adjustable;

[0064] The optical path in the reflection defocusing control module is as follows: the linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization after passing through the first polarization beam splitter (201). The horizontally polarized beam passes through the first polarization beam splitter (201), enters the first mirror group (202), is reflected, and then passes through the first quarter-wave plate (206) to become circularly polarized light. It enters the first objective lens (207) and is focused. After being reflected by the double-sided mirror (210), it returns along the same path, passes through the first objective lens (207) again, and then passes through the first quarter-wave plate (206) to become vertically polarized light. It then enters the first mirror group (202) again and is reflected. The first beam enters the first polarization beam splitter (201), is reflected, and deflected by 90 degrees before exiting; the other vertically polarized beam enters the second mirror group (203), is reflected, and deflected by 90 degrees before exiting. It passes through the second quarter-wave plate (209) and becomes circularly polarized light. It enters the second objective lens (208) and is focused. It is reflected by the double-sided mirror (210) and returns along the same path. It passes through the second objective lens (208) again and the second quarter-wave plate (209) and becomes horizontally polarized light. It then enters the first mirror group (202) again, is reflected, and enters the first polarization beam splitter (201) again before being transmitted and exiting.

[0065] The focusing module completes the polarization and multi-focus control of the beam emitted from the transmission defocus control module, and finally realizes two sets of axially separated laser focusing multi-focus spots; the polarization and multi-focus control elements can also be removed; after removal, the focusing module realizes two axially separated laser focusing spots.

[0066] Figure 3A schematic diagram of a preferred embodiment of a transmissive adjustable axial dual-focus laser focusing module is provided. The incident laser module (100) primarily performs functions such as polarization control, collimation and beam expansion, and divergence angle adjustment of the emitted laser. The optical path components of the incident laser module are sequentially arranged as follows: incident laser coupling fiber (101), Glan prism (102), collimating lens (103), second polarization beam splitter prism (104), third quarter-wave plate (105), third objective lens (106), third reflecting mirror (107), and half-wave plate (108). The third reflecting mirror (107) is mounted on a piezoelectric ceramic-driven one-dimensional scanning stage for axial scanning. The half-wave plate (108) is mounted on a mechanically adjustable frame that can rotate angularly, enabling fast-axis angular adjustment of the half-wave plate and ultimately adjusting the polarization orientation of the linearly polarized incident laser light. The output end of the incident laser coupling fiber maintains a coaxial alignment with the collimating lens (103) and the third objective lens (106).

[0067] The incident laser beam exits through the port of the incident laser coupling fiber (101), and after passing through a Glan prism (102) to achieve high extinction ratio polarization selection, the exited laser beam is approximately ideal linearly polarized light. The linearly polarized light becomes a collimated and expanded parallel laser beam after passing through a collimating lens (103). This collimated laser beam passes through a second polarizing beam splitter (104) and a third quarter-wave plate (105) in sequence and becomes circularly polarized light. This circularly polarized light is focused by a third objective lens (106) onto the reflecting surface of a third reflecting mirror (107). After reflection, it passes through the third objective lens (106) and the third quarter-wave plate (105) again and becomes vertically polarized linearly polarized light. After being reflected by the second polarizing beam splitter (104) and deflected by 90 degrees, it passes through a half-wave plate (108) to change its polarization orientation before exiting.

[0068] By adjusting the position of the third reflecting mirror (107) along the optical axis, the sphericity (spherical divergence angle) of the beam reflected from the second polarizing beam splitter (104) can be adjusted, thereby ultimately achieving axial translation of the focused spot. The axial position of the third reflecting mirror (107) can be changed by rapidly scanning with a piezoelectric ceramic translation stage, thus achieving rapid axial scanning of the focused spot. The divergence angle θ0 and the axial displacement dz0 of the third reflecting mirror (107) satisfy the following relationship:

[0069]

[0070] In the formula, R is the radius of the light spot incident on the third objective lens (106), and f0 is the focal length of the third objective lens (106).

[0071] Preferably, the incident laser coupling fiber (101) is a polarization-maintaining fiber; further, the fiber is a single-mode fiber for the operating wavelength band.

[0072] Preferably, the Glan prism is a Brost Glan prism; further, its polarization extinction ratio is better than 1×10 for the working wavelength band. -4 .

[0073] Preferably, the half-wave plate is mounted on an electric angular rotation table, and further, the repeatability of its angular rotation is better than 0.001 degrees.

[0074] The defocus control module (200) can be divided into two types: transmissive and reflective.

[0075] The optical path components of the transmissive defocus control module are sequentially configured as follows: a second lens (205), a first polarizing beam splitter prism (201), a first reflector (202), a first lens (204), and a second reflector (203). The first reflector (202) and the second reflector (203) are pentagonal cylindrical reflecting prisms (as shown in the attached diagram). Figure 6 (As shown).

[0076] The linearly polarized collimated laser beam modulated by the incident laser module (100) passes through the second lens (205) and then enters the first polarization beam splitter (201). After passing through the first polarization beam splitter (201), one of its vertically polarized components (polarization direction perpendicular to the plane of the paper) is deflected and reflected by 90 degrees. It then enters the second reflecting mirror (203) composed of a pentagonal cylindrical reflecting prism through surface A, and after being reflected by surface C, it exits through surface B. After passing through the first lens (204), it enters the first reflecting mirror (202) composed of a pentagonal cylindrical reflecting prism through surface B, and after being reflected by surface C, it exits through surface A. The exiting laser beam is then again incident on the first polarization beam splitter. The beam splitter prism (201) is deflected by 90 degrees and exits from the first polarization beam splitter prism (201); another horizontal polarization component (polarization direction parallel to the plane of the paper) passes directly through the first polarization beam splitter prism (202), then enters the first reflecting mirror (202) composed of a pentagonal cylindrical reflecting prism through surface A, and exits through surface B after being reflected through surface C. After passing through the first lens (204), it enters the second reflecting mirror (203) composed of a pentagonal cylindrical reflecting prism through surface B, and exits through surface A after being reflected through surface C. The exited laser beam is again incident on the first polarization beam splitter prism (201) and directly transmitted, and is combined with the vertical polarization component again.

[0077] The first lens (204) is mounted on a linear translation stage that can move axially along the optical path. Adjusting the axial position of the first lens adjusts the spacing between the two focal points. When the axial spacing between the two focal points is zero, the second lens (205) and the first lens (204) are confocal lens groups in both optical paths. At this time, the axial position of the first lens (204) (the position of the extended diagonal of the polarizing beam splitter in the figure) ensures symmetry between the two optical paths. When the first lens (205) is moved a distance dz along the optical axis, an axial spacing df will be formed between the two orthogonally polarized focused laser spots (see Appendix). Figure 5 a) For the transmission-type operating mode, the deviation displacement dz and the dual-focus interval df satisfy the following conditions:

[0078]

[0079] Where f is the focal length of the focusing lens, f2 is the focal length of the second lens, and d is the distance between the second lens and the focusing lens.

[0080] The optical path components of the reflective defocus control module are arranged sequentially as follows: a first polarizing beam splitter prism (201), a first reflector (202), a first quarter-wave plate (206), a first objective lens (207), a double-sided reflector (210), a second objective lens (208), a second quarter-wave plate (209), and a second reflector (203). Among these, the first reflector (202) and the second reflector (203) are pentagonal cylindrical reflecting prisms (as shown in the attached diagram). Figure 6 (As shown).

[0081] The linearly polarized collimated laser beam modulated by the incident laser module (100) is incident on the first polarization beam splitter prism (201). After passing through the first polarization beam splitter prism (201), one of its vertically polarized components (polarization direction perpendicular to the plane of the paper) is deflected and reflected by 90 degrees. It then enters the second reflecting mirror (203) composed of a pentagonal cylindrical reflecting prism through surface A, and after being reflected by surface C, it exits through surface B. After passing through the second quarter-wave plate (209), it becomes circularly polarized light. After being focused by the second objective lens (208), it is reflected by the double-sided reflecting mirror (210), and after passing through the second objective lens (208) and the second quarter-wave plate (209), it becomes horizontally polarized light. It then enters the second reflecting mirror (203) composed of a pentagonal cylindrical reflecting prism through surface B, and after being reflected by surface C, it exits through surface A and re-enters the second polarization beam splitter prism (201), directly passing through... The light exits through the second polarizing beam splitter (201); the other horizontally polarized component (polarization direction parallel to the plane of the paper) passes through the first polarizing beam splitter (201), enters the first reflecting mirror (202) composed of a pentagonal cylindrical reflecting prism through surface A, is reflected through surface C, exits through surface B, becomes circularly polarized light after passing through the first quarter-wave plate (206), is focused by the first objective lens (207), is reflected by the double-sided reflecting mirror (210), passes through the first objective lens (207) again, and becomes vertically polarized light after passing through the first quarter-wave plate (206), enters the first reflecting mirror (203) composed of a pentagonal cylindrical reflecting prism through surface B, is reflected through surface C, exits through surface A, and is incident again on the first polarizing beam splitter (201), is deflected and reflected by 90 degrees, and exits from the first polarizing beam splitter (201) to achieve common path transmission with the other beam.

[0082] The double-sided mirror (210) is mounted on a one-dimensional piezoelectric ceramic actuator, with the movement direction along the optical axis of the optical path. The first objective lens (207) and the second objective lens (208) have equal focal lengths and are a pair of objective lenses with identical parameters, and their centers must be aligned coaxially. When the axial distance between the two focal points is zero, the two reflecting surfaces of the double-sided mirror (210) are located on the focal planes of the first objective lens (207) and the second objective lens (208), respectively. The axial position of the double-sided mirror (210) is adjusted by the piezoelectric ceramic actuator, thereby adjusting the distance between the two focal points. When the double-sided mirror (210) deviates from the symmetrical position of the optical path (the position of the extended diagonal line of the polarizing beam splitter in the figure), an axial distance df will be generated between the two orthogonally polarized focused laser spots (see Appendix). Figure 5 b). For the reflective operating mode, the offset displacement dz and the dual-focus interval df satisfy...

[0083]

[0084] Where f is the focal length of the focusing lens, f2 is the focal length of the second lens, and d is the distance between the second lens and the focusing lens.

[0085] Note that when f2 2 +2(f²-df)dz=0, that is, dz th =f2 2 When the value is 2(f²-df), the interval df is infinite. Therefore, the range of axial displacement dz is 0 ≤ dz. <dz th .

[0086] Comparing the transmission and reflection modes, it can be seen that the reflection dual-focus axial spacing df is more sensitive to relative axial displacement.

[0087] Please refer to Figure 6 The pentagonal cylindrical reflecting prism has a regular pentagonal cross-section, with its five interior angles being 135 degrees, 90 degrees, 112.5 degrees, 112.5 degrees, and 90 degrees, respectively. The incident / exit surfaces of the pentagonal cylindrical reflecting prism are surfaces A and B in the diagram, and the reflecting surface is surface C. The reflecting surface is coated with a high-reflectivity film; preferably, the high-reflectivity film is a dielectric film for the laser working wavelength band, and further, the reflectivity of the high-reflectivity film is greater than 99%. Preferably, both the incident and exit surfaces are coated with an anti-reflection film for the working wavelength, and further, the transmittance of the anti-reflection film is greater than 98%. The incident / exit surfaces are square faces with a side length of a. The distance from the center of the incident / exit beam to the 135-degree vertex is βa, where 0 < β ≤ 1 / 2. The side length b and the hypotenuse c in the diagram satisfy the relationship with side length a.

[0088]

[0089] c=2a cos(22.5°)-2bsin(22.5°)

[0090] When β = 1 / 2, b = a, and c = 1.0824a, in this case, the center of the incident / outgoing beam is aligned with the center of the incident / outgoing surface of the reflecting prism.

[0091] Furthermore, for ultrashort pulse broadband lasers, a coated polarizing beam splitter can replace the polarizing beam splitter prism, and a broadband dielectric mirror can replace the reflecting prism (as shown in the attached image). Figure 7 (As shown).

[0092] The focusing module's optical path components are sequentially arranged with a polarizer (301), a Damman zone plate (302), and a focusing lens (303), wherein the Damman zone plate (302) and the focusing lens (303) are coaxially aligned. Two co-path vertically polarized laser beams emitted from the defocus control module pass sequentially through the polarizer (301), the Damman zone plate (302), and the focusing lens (303), forming two axially spaced multifocal arrays with an axial spacing of df before and after the geometric focal plane of the focusing lens. Depending on the actual application requirements, the polarizer (301) can be removed. After removal, the two co-path propagating laser beams do not interfere with each other. Furthermore, the Damman zone plate can also be removed, after which the optical path becomes a conventional axial dual-focal laser focusing module.

[0093] Preferably, the polarizer (301) and the Damman zone plate (302) can be mounted on a mechanical adjustment frame that can be pushed in / retracted, which can facilitate the replacement of Damman gratings with different beam splitting ratios, and can also facilitate the removal of the polarizer and Damman grating according to actual needs.

[0094] The Damman zone plate can be a two-step phase element or a multi-step phase element. Preferably, the substrate material of the Damman zone plate can be fused silica.

[0095] Appendix Figure 8 An implementation of an asymmetric optical path based on mirrors is presented. Each mirror group consists of two separate mirrors, ultimately achieving an asymmetric optical path structure. The first lens (204) or double-sided mirror (210) is located near the midpoint of the optical path of the two opposing optical paths, with the first polarizing beam splitter as the node, thereby enabling adjustment of the axial spacing between the two focal points of the adjustable axial dual-focal laser focusing module.

[0096] In this embodiment, the optical path components of this transmissive focusing module asymmetric structure are sequentially provided as a second lens (205), a first polarization beam splitter (201), a first reflector group including two reflectors (2021) and (2022), a first lens (204), and a second reflector group including two separate reflectors (2031) and (2032). The optical path is as follows: the linearly polarized laser beam modulated by the incident laser module (100) passes through the second lens (205) and is incident on the first polarization beam splitter (201). After passing through the first polarization beam splitter (201), one of its vertically polarized components (polarization direction perpendicular to the paper plane) is deflected by 90 degrees and reflected by reflectors (2031) and (2032). It then passes through the first lens (204), and after passing through reflectors (2022) and (2021), the emitted laser beam is again incident on the first reflector. The polarization beam splitter (201) is deflected by 90 degrees and emitted from the first polarization beam splitter (201); the other horizontal polarization component (polarization direction parallel to the paper plane) passes directly through the first polarization beam splitter (202), then passes through the mirrors (2021) and (2022) in sequence, and then passes through the first lens (204), and then passes through the mirrors (2032) and (2031) in sequence before emitting. The emitted laser beam is then incident on the first polarization beam splitter (201) again and transmitted directly, and then combined with the vertical polarization component again.

[0097] The asymmetric optical path components of the reflective defocus control module are arranged in sequence as follows: a first polarizing beam splitter prism (201), mirrors (2021) and (2022) in the first mirror group, a first quarter-wave plate (206), a first objective lens (207), a double-sided mirror (210), a second objective lens (208), a second quarter-wave plate (209), and mirrors (2032) and (2031) in the second mirror group. The optical path is as follows: the linearly polarized collimated laser beam modulated by the incident laser module (100) is incident on the first polarization beam splitter prism (201). After passing through the first polarization beam splitter prism (201), one of the vertically polarized components (polarization direction perpendicular to the paper plane) is deflected and reflected by 90 degrees. It then exits through mirrors (2031) and (2032), passes through the second quarter-wave plate (209) and becomes circularly polarized light. After being focused by the second objective lens (208), it is reflected by the double-sided mirror (210), passes through the second objective lens (208) and the second quarter-wave plate (209) and becomes horizontally polarized light. It then exits through mirrors (2032) and (2031) and is incident on the second polarization beam splitter prism (201) again. One beam passes directly through the second polarizing beam splitter (201) and exits; the other horizontally polarized component (polarization direction parallel to the plane of the paper) passes through the first polarizing beam splitter (201), then passes through the mirrors (2021) and (2022) and exits. After passing through the first quarter-wave plate (206), it becomes circularly polarized light. After being focused by the first objective lens (207), it is reflected by the double-sided mirror (210), and then passes through the first objective lens (207) and the first quarter-wave plate (206) again and becomes vertically polarized light. It then passes through the mirrors (2022) and (2021) and exits. After being incident on the first polarizing beam splitter (201) again, it is deflected by 90 degrees and exits from the first polarizing beam splitter (201) to achieve co-path transmission with the other beam.

[0098] Specific Implementation Example: YAG Infrared Laser Welding Head

[0099] The principle of laser welding substrates is to use a focused laser beam as the welding heat source. The focused laser beam irradiates the area to be welded, causing the material to absorb heat and rise in temperature. When the temperature reaches the melting point of the welding material, it melts to form a molten pool. As the laser beam moves, the previously formed molten pool gradually cools down until it solidifies, ultimately forming a weld, thus achieving the welding purpose. Compared to traditional welding processes, laser welding has advantages such as a smaller heat-affected zone, resulting in less deformation; higher power density, allowing for welding of alloys with high melting points; and high welding precision due to its non-contact nature, without the need for special shielding gases. Currently, laser welding has been applied in various alloys, gold, silver, copper, aluminum, and precision welding of new energy battery tabs and mobile phone connectors.

[0100] The following is a specific implementation plan for a dual-focus laser module for laser welding applications, taking a 1064nm Nd:YAG laser as an example.

[0101] The incident laser is a passively Q-switched nanosecond laser with a wavelength of 1064 nm, a pulse bandwidth of 10 ns, a power of 50 W, and a repetition rate adjustable from 1 to 50 kHz. The laser outputs with a fundamental mode horizontal polarization. The numerical aperture of the coupling fiber is NA0.1, and the focal length of the collimating lens is 100 mm. Therefore, the collimated and expanded beam size after exiting the incident laser through the coupling fiber and passing through the collimating lens is approximately 20.9 mm.

[0102] The optical path employs a reflective defocus control module. The polarizing beam splitter is a 1-inch laser polarizing beam splitter with a wavelength of 1064 nm and an extinction ratio better than 2000:1. The first, second, and third objectives are all high numerical aperture (NA) lenses with an effective focal length of 9 mm. The first reflecting mirror is a 1 / 2-inch dielectric high-reflectivity mirror designed for 1064 nm wavelength; the double-sided reflecting mirror is a 1 / 2-inch dielectric laser reflecting mirror with high-reflectivity dielectric films on both sides. The piezoelectric ceramic actuator uses a one-dimensional scanning stage with a through-hole, a scanning range of 600 micrometers, and a repeatability of 400 nanometers. The focusing lens has a focal length of f = 100 mm, corresponding to a focused spot size of approximately 10–40 micrometers. (See attached image.) Figure 9 The curves showing the variation of the interval between the axial dual focal points with scanning distance under this condition are presented. It can be seen that an axial dual focal point array with an interval of 0–2.6 mm can be achieved through one-dimensional scanning using this piezoelectric ceramic. Furthermore, by selecting different initial positions, the interval range between the two sets of axial multifocal points can be further adjusted, such as… Figure 9 As shown in b, when the initial position of the double-sided high-reflectivity mirror is placed at dz = 1 mm, an axial dual-focal array with an interval of 4.5–7.8 mm can be achieved. For laser welding, coherence of the two laser beams is not required, and the polarizer (301) can be removed.

[0103] Furthermore, two sets of axial multifocal arrays can be achieved by adding Damman zone plates. Here, a 1×5 Damman zone plate is required, with an axial spacing of 400 micrometers, corresponding to an incident laser Gaussian apodization factor G = 1. The corresponding Gaussian light field intensity can be expressed as U. in =exp(iG(x) 2 +y 2At this point, the normalized radius of the 1×5 Damman grating is 0.1612, 0.1685, 0.1919, 0.2007, 0.2460, 0.2636, 0.3022, 0.4442, 0.4504, 0.4609, 0.6150, 0.6261, 0.7159, 0.7175, 0.7234, 0.7257, 0.7395, 0.7455, 0.7600, 0.8266, 0.8300, 0.8357, 0.9294, 0.9368, 0.9988. (Appendix) Figure 10 a presents numerical simulation results of the intensity distribution of two 1×5 multifocal arrays when dz = 15 micrometers.

[0104] Furthermore, the Damman zone plate can be replaced with Damman zone plates of other beam splitting ratios. Here, based on the above conditions, we designed a 1×7 Damman zone plate, whose corresponding normalized radii are 0.2929, 0.2955, 0.3656, 0.4395, 0.4479, 0.4517, 0.4724, 0.4731, 0.5092, 0.5119, 0.5176, 0.5723, 0.5727, 0.5789, 0.6183, 0.6233, and 0.68. 92, 0.6902, 0.7230, 0.7629, 0.7678, 0.7700, 0.7823, 0.7827, 0.8050, 0.8067, 0.8103, 0.8463, 0.8465, 0.8507, 0.8780, 0.8815, 0.9291, 0.9299, 0.9544, 0.9850, 0.9887, 0.9904. (Attachment) Figure 10 b presents the numerical simulation results of the intensity distribution of two sets of 1×7 multifocal arrays when dz = 30 micrometers.

[0105] It should be noted that the preferred embodiments and specific examples of the present invention described in detail above with reference to the accompanying drawings are merely preferred implementations of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various non-inventive modifications and improvements can be made to the specific implementation details and representative devices proposed in this patent without departing from the basic idea of ​​the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0106] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without departing from the basic idea of ​​the present invention. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, the various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the basic idea of ​​the present invention.

[0107] In summary, this invention proposes an adjustable common-path axial dual-focus laser focusing module, which can be widely used in laser cutting, laser welding, and other fields. Furthermore, this axially adjustable dual-focus laser module also holds promise for applications in laser optical tweezers, laser fluorescence imaging, and other fields.

Claims

1. An adjustable axial bifocal laser focusing module, characterized in that, include: The incident laser module (100) is used to collimate and expand the incident laser beam, and to adjust the polarization orientation and sphericity of the output linearly polarized light. The defocus control module (200) is used to receive the linearly polarized light and output two linearly polarized lights with different sphericities and orthogonal polarization directions, and realize the dynamic adjustment of the sphericity carried by the two orthogonally polarized light paths. The focusing module (300) is used to receive the two orthogonally linearly polarized beams with different sphericity and form a dual-focus laser spot with adjustable axial position and spacing; The incident laser module includes, in sequence, an incident laser coupling fiber (101), a Glan prism (102), a collimating lens (103), a second polarizing beam splitter (104), a third quarter-wave plate (105), a third objective lens (106), a third reflecting mirror (107), and a half-wave plate (108). The third reflecting mirror (107) is mounted on a piezoelectric ceramic-driven one-dimensional scanning stage for axial scanning. The half-wave plate (108) is mounted on a mechanically adjustable frame that can rotate angularly to achieve fast-axis angular adjustment of the half-wave plate, thereby adjusting the polarization orientation of the linearly polarized light of the incident laser. The output end of the incident laser coupling fiber is aligned coaxially with the collimating lens (103) and the third objective lens (106). The incident laser is emitted through the port of the incident laser coupling fiber (101), and the polarization selection with a high extinction ratio is achieved by the Glan prism (102). The emitted laser is approximately ideal linearly polarized light. The linearly polarized light becomes a collimated and expanded parallel laser beam after passing through the collimating lens (103). The collimated laser beam passes through the second polarizing beam splitter (104) and the third quarter-wave plate (105) in sequence and becomes circularly polarized light. The circularly polarized light is focused on the reflecting surface of the third mirror (107) by the third objective lens (106). After reflection, it passes through the third objective lens (106) and the third quarter-wave plate (105) again and becomes vertically polarized linearly polarized light. After being reflected by the second polarizing beam splitter (104) and deflected by 90 degrees, it passes through the half-wave plate (108) to change the polarization orientation before being emitted. The focusing module includes a coaxial Damman zone plate (302) and a focusing lens (303) arranged in sequence. Two co-path vertically polarized laser beams emitted from the defocus control module pass through the Damman zone plate (302) and the focusing lens (303) in sequence, forming two sets of axial double-focal arrays with an axial spacing of df in front and behind the geometric focal plane of the focusing lens. The defocus control module is a transmission-type defocus control module, including a first polarizing beam splitter, a first mirror group, a second mirror group, and a pair of confocal lens groups. The first lens in the confocal lens group is located between the first mirror group and the second mirror group in the optical path, and the axial position of the first lens along the optical path direction is adjustable. The second lens is located in front of the first polarizing beam splitter. The second lens in the transmissive defocus control module can be axially translated along the optical axis, ultimately achieving adjustment of the axial spacing between the two focal points formed by the laser focusing module.

2. The tunable axial bifocal laser focusing module of claim 1, wherein, The Damman zone plate is a 1×5 Damman zone plate. With a working wavelength of 1064 nm, a numerical aperture of the focusing objective of 0.1, and an apodization factor G=1, the axial spot spacing is 400 μm. The corresponding normalized radii of each ring are 0.1612, 0.1685, 0.1919, 0.2007, 0.2460, 0.2636, 0.3022, 0.4442, 0.4504, 0.4609, 0.6150, 0.6261, 0.7159, 0.7175, 0.7234, 0.7257, 0.7395, 0.7455, 0.7600, 0.8266, 0.8300, 0.8357, and 0.9294. 0.9368, 0.9988.

3. The adjustable axial dual-focus laser focusing module according to claim 1, characterized in that: The Damman zone plate is a 1×7 Damman zone plate. With a working wavelength of 1064 nm, a numerical aperture of the focusing objective of 0.1, and an apodization factor G=1, the axial spot spacing is 500 μm. The corresponding normalized radii of each ring are 0.2929, 0.2955, 0.3656, 0.4395, 0.4479, 0.4517, 0.4724, 0.4731, 0.5092, 0.5119, 0.5176, 0.5723, 0.5727, 0.5789, 0.6183, 0.6233, 0.6892, 0.6902, 0.7230, 0.7629, 0.7678, 0.7700, and 0.7823. 0.7827, 0.8050, 0.8067, 0.8103, 0.8463, 0.8465, 0.8507, 0.8780, 0.8815, 0.9291, 0.9299, 0.9544, 0.9850, 0.9887, 0.9904.

4. The adjustable axial dual-focus laser focusing module according to any one of claims 1-3, characterized in that, A polarizer (301) is also provided in the incident light path of the Damman zone plate (302).

5. The adjustable axial dual-focus laser focusing module according to claim 1, characterized in that, The linearly polarized light emitted from the incident laser module passes through the second lens, and then is split into two beams with perpendicular polarization states by the first polarization beam splitter. The horizontally polarized beam passes through the first polarization beam splitter, enters the first reflector group, is reflected and emitted, enters the first lens and is transmitted, enters the second reflector group, is reflected and emitted, enters the first polarization beam splitter and is transmitted and emitted. Another vertically polarized beam is deflected by 90 degrees after being reflected by the first polarization beam splitter. It then enters the second mirror group, is reflected out, enters the first lens, is transmitted, enters the first mirror group, is reflected out, enters the first polarization beam splitter, is reflected out, is deflected by 90 degrees, and then exits. At this time, the two beams propagating in opposite directions overlap again.

6. The adjustable axial dual-focus laser focusing module according to claim 1, characterized in that, The defocus control module is a transmission-type defocus control module, including a first polarizing beam splitter, a first mirror group, a second mirror group, and a pair of confocal lens groups. The first lens in the confocal lens group is located between the first mirror group and the second mirror group in the optical path, and the axial position of the first lens along the optical path direction is adjustable. The second lens is located after the first polarizing beam splitter. The linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization states after passing through the first polarization beam splitter. The horizontally polarized beam passes through the first polarization beam splitter, enters the first reflecting mirror group, is reflected and exits, enters the first lens, is transmitted, enters the second reflecting mirror group, is reflected and exits, enters the first polarization beam splitter, is transmitted, and exits through the second lens. The other vertically polarized beam is reflected by the first polarization beam splitter and deflected by 90 degrees, enters the second reflecting mirror group, is reflected and exits, enters the first lens, is transmitted, enters the first reflecting mirror group, is reflected and exits, enters the first polarization beam splitter, is reflected and deflected by 90 degrees, and exits through the second lens. At this time, the two beams propagating in opposite directions overlap again.

7. The adjustable axial dual-focus laser focusing module according to claim 1, characterized in that, The defocus control module is a reflective defocus control module, including a first polarizing beam splitter, a first mirror group, a first quarter-wave plate, a first objective lens, a double-sided mirror, a second objective lens, a second quarter-wave plate, and a second mirror group; and the axial position of the double-sided mirror is adjustable along the optical path direction. The linearly polarized light emitted from the incident laser module is split into two beams with perpendicular polarization states after passing through the first polarization beam splitter. The horizontally polarized beam passes through the first polarization beam splitter, enters the first reflecting mirror group, is reflected and exits, becomes circularly polarized light after passing through the first quarter-wave plate, enters the first objective lens, is focused, is reflected back through the double-sided reflecting mirror, passes through the first objective lens again and the first quarter-wave plate, becomes vertically polarized light, then enters the first reflecting mirror group again, is reflected, enters the first polarization beam splitter again, is reflected and deflected by 90 degrees before exiting. The other vertically polarized beam is reflected and deflected by 90 degrees after passing through the first polarization beam splitter, enters the second reflecting mirror group, is reflected and exits, becomes circularly polarized light after passing through the second quarter-wave plate, enters the second objective lens, is focused, is reflected back through the double-sided reflecting mirror, passes through the second objective lens again and the second quarter-wave plate, becomes horizontally polarized light, enters the first reflecting mirror group again, is reflected, enters the first polarization beam splitter again, and is transmitted and exiting.

8. The adjustable axial dual-focus laser focusing module according to claim 7, characterized in that, The double-sided reflector is characterized by having a high-reflectivity reflective film coated on both its front and rear surfaces, and is mounted on a linear scanning actuator along the optical path. The double-sided reflector can be axially translated along the optical axis to ultimately adjust the axial distance df between the two focal points formed by the laser focusing module.

9. The adjustable axial dual-focus laser focusing module according to any one of claims 6-8, characterized in that, The mirrors in the first and second mirror groups are pentagonal cylindrical prisms made of fused silica. The cross-section of the pentagonal cylindrical prism is a pentagon symmetrical about the normal to the incident / outgoing rays, with its five interior angles being 135 degrees, 90 degrees, 112.5 degrees, 112.5 degrees, and 90 degrees, respectively. The reflecting slope of the pentagonal cylindrical prism is coated with a high-reflectivity film for the working wavelength, with a reflectivity greater than 99%. Both incident / outgoing surfaces are coated with an anti-reflection film for the working wavelength, with a transmittance greater than 98%.

Images