Reflective bessel beam cutting head and method of designing the same

Abstract

The application relates to a reflective Bessel light cutting head and a design method thereof. The reflective Bessel light cutting head comprises a light source, a conical reflecting surface mirror, a first aspheric concave off-axis mirror and a second aspheric concave off-axis mirror arranged in sequence along the direction of the light path. The conical reflecting surface mirror shapes the collimated light beam into an initial Bessel light beam. The first aspheric concave off-axis mirror receives the initial Bessel light beam and converges it to the optical axis direction to form an annular focal point. The second aspheric concave off-axis mirror receives the light beam shaped by the first aspheric concave off-axis mirror to form a long focal depth and a spherical aberration-free action area for laser cutting. The application shapes the light path through the conical reflecting surface mirror and the aspheric concave off-axis mirror, eliminates the spherical aberration influence, makes the incident light beam realize ideal Bessel light beam transmission, and ensures that the Bessel light beam obtains a small main lobe close to the diffraction limit and a super-long focal depth.

Description

Technical Field

[0001] This invention relates to a reflective Bezier cutting head and its design method, belonging to the technical field of laser applications. Background Technology

[0002] Laser precision cutting technology utilizes a high-energy-density laser beam to irradiate the workpiece, rapidly bringing the material to its vaporization temperature or melting state, thus achieving material separation. Compared to traditional cutting methods, which suffer from tool wear, material deformation due to cutting forces, large kerf, and limited processing efficiency, laser cutting offers significant advantages such as high precision, high speed, non-contact operation, and high flexibility. It is particularly suitable for applications requiring extremely high processing accuracy and edge integrity. Currently, laser precision cutting is widely used in the consumer electronics industry for sapphire glass and ultra-thin glass covers, and in the semiconductor industry for dicing and cutting silicon wafers, demonstrating immense technological value and a broad market prospect.

[0003] In laser precision cutting, the shape and quality of the laser beam are the core factors determining the cutting effect. Laser cutting based on a spherical lens focusing system focuses a Gaussian beam into a highly concentrated focal point. However, because the depth of focus of a Gaussian beam is limited after focusing, it results in a large taper of the kerf or even failure to cut through when cutting thicker materials, which severely restricts its application in thick plates and brittle and hard materials.

[0004] The light field distribution of a Bessel beam is described by a Bessel function. Unlike a Gaussian beam, the size and intensity distribution of the central spot of a Bessel beam remain essentially constant within a certain propagation distance, exhibiting an extremely long focal length. This characteristic allows the Bessel beam to maintain a dimensionally stable and energy-sufficient effective action area across the entire thickness of thick materials, achieving a cut surface with almost no taper and extremely high perpendicularity.

[0005] The most common methods for generating Bessel beams are using axial conical mirrors, spatial light modulators, diffractive optical elements, or annular slits. When a collimated Gaussian beam passes through, its wavefront undergoes a conical phase delay, causing interference as the outgoing light propagates in free space, thus forming a near-ideal zero-order Bessel beam region near the optical axis. However, Bessel beams based on refractive optical elements are significantly affected by spherical aberration. Furthermore, in traditional refractive Bessel cutting head optical path systems composed of multiple lenses, spherical lenses are inevitably used to scale, focus, or image the Bessel beam generated by the axial conical mirror. The spherical aberration introduced by the lenses severely distorts the ideal wavefront of the Bessel beam, destroying its diffraction-free characteristics, directly leading to a decrease in energy density during cutting, a reduction in effective processing depth, and a decrease in cutting quality and accuracy. In addition, for high-power laser processing applications, lenses in refractive systems also face problems such as thermal lensing effects, further exacerbating beam quality degradation.

[0006] Chinese patent CN116160140A discloses a laser cutting head and a laser processing device having the same. This laser cutting head reduces the laser beam transmission distance and beam loss after emission by using a cemented lens. The output depth of focus is increased by adjusting the magnification of the combination of a first biconvex lens and the cemented lens, as well as the incident beam radius. However, this invention does not fundamentally solve the spherical aberration problem introduced by the lens and also faces the problem of thermal lensing in refractive systems.

[0007] Therefore, developing a novel optical path system that can effectively eliminate spherical aberration and maintain the excellent characteristics of Bessel beams has become the key to promoting the wider application of this technology in demanding industrial scenarios. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a reflective Bezier cutting head.

[0009] The present invention also provides a design method for the above-mentioned Bessel cutting head. Invention Overview: Based on the technical problems existing in the background technology, this invention proposes a reflective Bezier beam cutting head and its design method, which solves the problem that the processing accuracy is reduced due to the influence of spherical aberration on the shaping quality of the Bezier beam used for laser cutting.

[0011] The technical solution of this invention is as follows: A reflective Bezier optical cutting head includes a light source, a conical reflector, a first aspherical concave off-axis reflector, and a second aspherical concave off-axis reflector arranged sequentially along the optical path. The light source is a collimated Gaussian beam; used to generate a laser beam that interacts with the material being processed. The working surface of the conical reflector is a concave cone, with the apex of the cone coinciding with the optical axis of the collimated beam. The principal axis of the conical reflector is at 45° to the optical axis of the collimated beam. The conical reflector shapes the collimated beam into an initial hollow cone, i.e., an initial Bessel beam, and folds the optical axis by 90° to form a second optical axis. The principal axis refers to the axis connecting the apex of the mirror surface to the center of the sphere and is perpendicular to the tangent plane at the center of the lens. The optical axis refers to the axis parallel to the direction of beam propagation and located at the center of the beam. The working surface of the first aspherical concave off-axis mirror is a concave aspherical surface, and the vertex of the aspherical surface coincides with the second optical axis. The angle between the principal axis of the first aspherical concave off-axis mirror and the second optical axis is 35° to 55°. The first aspherical concave off-axis mirror receives the initial Bessel beam and converges it in the direction of the optical axis. The initial hollow light cone forms an annular focal point behind the first aspherical concave off-axis mirror. At this time, the second optical axis is deflected by 90° to form the third optical axis. The working surface of the second aspherical concave off-axis mirror is a concave aspherical surface, with the vertex of the aspherical surface coinciding with the third optical axis. The angle between the principal axis of the second aspherical concave off-axis mirror and the third optical axis is 35° to 55°. The second aspherical concave off-axis mirror receives the light shaped by the first aspherical concave off-axis mirror, forming a second hollow light cone that is proportionally reduced to the initial hollow light cone. The terminal Bessel beam region corresponding to the second hollow light cone is proportionally reduced by the corresponding factor, ultimately forming a long focal depth, aberration-free working region for laser cutting.

[0012] Preferably, the optical axes of the conical reflector, the first aspherical concave off-axis reflector, and the second aspherical concave off-axis reflector are located in the same plane, forming a coplanar off-axis reflective optical path.

[0013] Preferably, all optical surfaces used for beam shaping and transmission in the optical path system are reflective surfaces and do not contain any transmissive optical elements.

[0014] Preferably, the light source is a pulsed laser with a pulse width of femtosecond to nanosecond.

[0015] Preferably, the optical surfaces of the first aspherical concave off-axis reflector and the second aspherical concave off-axis reflector are coated with a high damage threshold reflective film corresponding to the wavelength of the light source, and the reflectivity is greater than 99.5% in the incident angle range of 20° to 70°.

[0016] Preferably, the base angle α of the conical reflecting mirror ranges from 10° to 30°, the light source diameter D ranges from 5 mm to 10 mm, and the diffraction-free length L of the initial Bessel beam region is: The initial hollow light cone has a cone angle of β along the optical axis, and the initial Bessel beam's central main lobe radius is r0, satisfying: The second aspherical concave off-axis mirror receives the light shaped by the first aspherical concave off-axis mirror, forming a second hollow light cone that is proportionally reduced by a factor of m compared to the initial hollow light cone; the first and second aspherical concave off-axis mirrors constitute a reflective 4f imaging system; wherein, the Bessel beam region emitted from the conical mirror is located at the input surface of the 4f imaging system, and the long depth-of-focus region emitted from the second aspherical concave off-axis mirror is located at the output surface of the 4f imaging system; the radii of curvature R1 and R2 of the first and second aspherical concave off-axis mirrors range from 20mm to 200mm, and R1 > R2, and the beam reduction ratio m of the 4f imaging system satisfies: The hollow cone of the terminal Bessel beam has a cone angle of θ along the optical axis, and the diffraction-free working distance of the Bessel cutter head is L2, satisfying the following: The center spot size r of the terminal Bessel beam satisfies: .

[0017] Preferably, the conical reflector, the first aspherical concave off-axis reflector, and the second aspherical concave off-axis reflector are each provided with a metal substrate.

[0018] The above-mentioned design method for Bessel cutting heads: Step 1: Determine the aperture of the conical reflector, the first aspherical concave off-axis reflector, and the second aspherical concave off-axis reflector based on the maximum diameter of the incident light source; the aperture is the minimum diameter of the light spot that the lens can receive. Step 2: Determine the non-diffraction working distance L2 and the center beam size r of the terminal Bessel beam based on the design goals of processing resolution, kerf width, and cutting thickness. Specifically, L2 = cutting thickness, and center beam size r = processing resolution = kerf width. The base angle α of the conical reflector, the radius of curvature R1 of the first aspherical concave off-axis reflector, and the radius of curvature R2 of the second aspherical concave off-axis reflector are calculated based on the non-diffraction working distance L2 and the center beam size r. Step 3: Simulate the designed Bezier cutting head using simulation software or programs; Step 4: Optimize system parameters, including the conic coefficient of the conic reflector, the aspheric coefficients of the first and second aspheric concave off-axis reflectors, the center distance between the conic reflector and the first aspheric concave off-axis reflector, the deflection angles of the first and second aspheric concave off-axis reflectors, and the center distance between the first and second aspheric concave off-axis reflectors. Step 5: Analyze the cross-sectional intensity distribution of the Bessel beam and feed it back to Step 4 for repeated optimization, ultimately achieving a Bessel beam that meets the design objectives.

[0019] Furthermore, by replacing the first aspherical concave off-axis mirror and the second aspherical concave off-axis mirror, the diffraction-free working distance L2 of the Bessel cutting head and the size r of the center spot of the terminal Bessel beam can be changed.

[0020] The beneficial effects of this invention are as follows: (1) The present invention uses a conical reflecting mirror and an aspherical concave off-axis reflecting mirror to shape the optical path, eliminate the influence of spherical aberration, enable the incident light to achieve ideal Bessel beam transmission, and ensure that the Bessel beam obtains a small main lobe close to the diffraction limit and an ultra-long focal depth. (2) The present invention uses a reflective optical lens, which is less sensitive to temperature than a transmissive optical lens, and the heat generated is efficiently dissipated through the metal substrate, effectively reducing the thermal lensing effect, making it suitable for high-power, long-term, and high-intensity continuous industrial processing. (3) The present invention uses a reflective optical lens, and the beam only acts on the surface of the reflector and does not penetrate the medium, thus fundamentally avoiding nonlinear effects in the material; ensuring the temporal and spatial integrity of the ultrashort pulse is a key guarantee for realizing cold processing and suppressing the heat-affected zone; (4) The optical path of the present invention is simple and stable, and it is suitable for integrated production and industrial applications. Attached Figure Description

[0021] Figure 1 This is an overall schematic diagram of the reflective Bezier light cutting head of the present invention; In the figure: 1-conical reflector, 2-first aspherical concave off-axis reflector, 3-second aspherical concave off-axis reflector.

[0022] Figure 2 This is a schematic diagram of the optical system parameters of the reflective Bezier optical cutting head of the present invention; In the diagram: 1-conical reflector, 2-first aspherical concave off-axis reflector, 3-second aspherical concave off-axis reflector, α-base angle of the conical reflector, D-diameter of the light source, f1-focal length of the first aspherical concave off-axis reflector, R1-radius of curvature of the first aspherical concave off-axis reflector, f2-focal length of the second aspherical concave off-axis reflector, R2-radius of curvature of the second aspherical concave off-axis reflector.

[0023] Figure 3 This is a dimensional diagram of the reflective Bezier light cutting head of the present invention; In the figure: 1-conical reflector, 2-first aspherical concave off-axis reflector, 3-second aspherical concave off-axis reflector, D-source diameter, β-cone angle of the initial hollow light cone along the optical axis, r0-radius of the central main lobe of the initial Bessel beam, L-diffraction-free length of the initial Bessel beam region, L2-diffraction-free working distance of the Bessel cutter, θ-cone angle of the hollow light cone of the terminal Bessel beam along the optical axis, r-size of the central spot of the terminal Bessel beam.

[0024] Figure 4 This is a cross-sectional light intensity distribution diagram of the reflective Bezier light cutting head of the present invention. Detailed Implementation

[0025] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings.

[0026] Example 1 like Figure 1 As shown.

[0027] A reflective Bezier optical cutting head includes a light source, a conical reflector mirror 1, a first aspherical concave off-axis reflector 2, and a second aspherical concave off-axis reflector 3 arranged sequentially along the optical path. The light source is a collimated Gaussian beam; the working surface of the conical reflector 1 is a concave cone, with the apex of the cone coinciding with the optical axis of the collimated beam, and the principal axis of the conical reflector 1 is at 45° to the optical axis of the collimated beam; the conical reflector 1 shapes the collimated beam into an initial hollow light cone, i.e., an initial Bessel beam, and folds the optical axis by 90° to form a second optical axis; the principal axis refers to the axis connecting the apex of the mirror surface and the center of the sphere, and is perpendicular to the tangent plane at the center of the lens; the optical axis refers to the axis parallel to the direction of beam propagation and located at the center of the beam. The working surface of the first aspherical concave off-axis mirror 2 is a concave aspherical surface, and the vertex of the aspherical surface coincides with the second optical axis. The angle between the principal axis of the first aspherical concave off-axis mirror 2 and the second optical axis is 35° to 55°. The first aspherical concave off-axis mirror receives the initial Bessel beam and converges it in the direction of the optical axis. The initial hollow light cone forms an annular focal point behind the first aspherical concave off-axis mirror 2. At this time, the second optical axis is deflected by 90° to form the third optical axis. The working surface of the second aspherical concave off-axis mirror 3 is a concave aspherical surface, with the vertex of the aspherical surface coinciding with the third optical axis. The angle between the principal axis of the second aspherical concave off-axis mirror 3 and the third optical axis is 35° to 55°. The second aspherical concave off-axis mirror 3 receives the light shaped by the first aspherical concave off-axis mirror 2, forming a second hollow optical cone that is proportionally reduced to the initial hollow optical cone. The terminal Bessel beam region corresponding to the second hollow optical cone is proportionally reduced by a corresponding factor, ultimately forming a long focal depth, aberration-free working region for laser cutting. Figure 4 The image shown is a cross-sectional light intensity distribution diagram of the reflective Bezier light cutting head of the present invention. (Observation) Figure 4 It is known that the reflective Bessel cutter head enables the incident light to achieve ideal Bessel beam transmission, ensuring that the Bessel beam obtains a small main lobe close to the diffraction limit and an ultra-long focal depth.

[0028] Example 2 As described in Example 1, the optical axes of the conical reflective mirror 1, the first aspherical concave off-axis reflector 2, and the second aspherical concave off-axis reflector 3 are located in the same plane, forming a coplanar off-axis reflective optical path.

[0029] Example 3 As described in Example 1, the reflective Bezier optical cutting head further includes all optical surfaces in the optical path system used for beam shaping and transmission that are reflective and do not contain any transmissive optical elements.

[0030] Example 4 As described in Example 1, the reflective Bezier laser cutting head further includes a pulsed laser as the light source, with a pulse width ranging from femtoseconds to nanoseconds. The wavelength λ of the light source is a commonly used laser processing wavelength, including 1064nm, 1030nm, 532nm, and 266nm. In this embodiment, the wavelength λ of the light source is 1030nm.

[0031] Example 5 As described in Example 1, the reflective Bezier optical cutting head further includes an optical surface coated with a high damage threshold reflective film corresponding to the wavelength of the light source on the optical surfaces of the first aspherical concave off-axis mirror 2 and the second aspherical concave off-axis mirror 3, with a reflectivity greater than 99.5% in the incident angle range of 20° to 70°.

[0032] Example 6 like Figure 2 , Figure 3 As shown.

[0033] As described in Example 1, the reflective Bessel light cutting head further includes a base angle α of the conical reflecting mirror 1 ranging from 10° to 30°, a light source diameter D ranging from 5 mm to 10 mm, and a diffraction-free length L of the initial Bessel beam region: The initial hollow light cone has a cone angle of β along the optical axis, and the initial Bessel beam's central main lobe radius is r0, satisfying: .

[0034] The second aspherical concave off-axis mirror 3 receives the light shaped by the first aspherical concave off-axis mirror 2, forming a second hollow light cone that is proportionally reduced by a factor of m compared to the initial hollow light cone; the first aspherical concave off-axis mirror 2 and the second aspherical concave off-axis mirror 3 constitute a reflective 4f imaging system; wherein, the Bessel beam region emitted from the conical mirror 1 is located on the input surface of the 4f imaging system, and the long depth-of-focus region emitted from the second aspherical concave off-axis mirror 3 is located on the output surface of the 4f imaging system; the radii of curvature R1 and R2 of the first aspherical concave off-axis mirror 2 and the second aspherical concave off-axis mirror 3 range from 20mm to 200mm, and R1 > R2, and the beam reduction ratio m of the 4f imaging system satisfies: .

[0035] The hollow cone of the terminal Bessel beam has a cone angle of θ along the optical axis, and the diffraction-free working distance of the Bessel cutter head is L2, satisfying the following: The center spot size r of the terminal Bessel beam satisfies: .

[0036] Example 7 As described in Example 1, the reflective Bezier optical cutting head has a conical reflective mirror 1, a first aspherical concave off-axis reflector 2, and a second aspherical concave off-axis reflector 3, each with a metal substrate.

[0037] Example 8 The design method of the Bessel cutting head as described in Example 6: Step 1: Determine the aperture of the conical reflector 1, the first aspherical concave off-axis reflector 2, and the second aspherical concave off-axis reflector 3 based on the maximum diameter of the incident light source. Step 2: Determine the non-diffraction working distance L2 and the center beam size r of the terminal Bessel beam based on the design goals of processing resolution, kerf width, and cutting thickness. Specifically, L2 = cutting thickness, and center beam size r = processing resolution = kerf width. The base angle α of the conical reflector 1, the radius of curvature R1 of the first aspherical concave off-axis reflector 2, and the radius of curvature R2 of the second aspherical concave off-axis reflector 3 are calculated based on the non-diffraction working distance L2 and the center beam size r. Step 3: Simulate the designed Bezier cutting head using simulation software or programs; Step 4: Optimize system parameters, including the conic coefficient of the conic reflector, the aspheric coefficients of the first aspheric concave off-axis mirror 2 and the second aspheric concave off-axis mirror 3, the center distance between the conic reflector 1 and the first aspheric concave off-axis mirror 2, the deflection angles of the first aspheric concave off-axis mirror 2 and the second aspheric concave off-axis mirror 3, and the center distance between the first aspheric concave off-axis mirror 2 and the second aspheric concave off-axis mirror 3. Step 5: Analyze the cross-sectional intensity distribution of the Bessel beam and feed it back to Step 4 for repeated optimization, ultimately achieving a Bessel beam that meets the design objectives.

[0038] Example 9 As described in Example 8, the design method of the Bessel cutter head further improves by replacing the first aspherical concave off-axis mirror 2 and the second aspherical concave off-axis mirror 3 to change the diffraction-free working distance L2 of the Bessel cutter head and the size r of the center spot of the terminal Bessel beam.

Claims

1. A reflective Bezier cutting head, characterized in that, The system includes a light source, a conical reflector, a first aspherical concave off-axis reflector, and a second aspherical concave off-axis reflector, arranged sequentially along the optical path. The light source is a collimated Gaussian beam. The working surface of the conical reflector is a concave cone, with the apex of the cone coinciding with the optical axis of the collimated beam. The principal axis of the conical reflector is at a 45° angle to the optical axis of the collimated beam. The conical reflector shapes the collimated beam into an initial hollow light cone, i.e., an initial Bessel beam, and folds the optical axis by 90° to form a second optical axis. The working surface of the first aspherical concave off-axis mirror is a concave aspherical surface, and the vertex of the aspherical surface coincides with the second optical axis. The angle between the principal axis of the first aspherical concave off-axis mirror and the second optical axis is 35° to 55°. The first aspherical concave off-axis mirror receives the initial Bessel beam and converges it in the direction of the optical axis. The initial hollow light cone forms an annular focal point behind the first aspherical concave off-axis mirror. At this time, the second optical axis is deflected by 90° to form the third optical axis. The working surface of the second aspherical concave off-axis mirror is a concave aspherical surface, with the vertex of the aspherical surface coinciding with the third optical axis. The angle between the principal axis of the second aspherical concave off-axis mirror and the third optical axis is 35° to 55°. The second aspherical concave off-axis mirror receives the light shaped by the first aspherical concave off-axis mirror, forming a second hollow light cone that is proportionally reduced to the initial hollow light cone. The terminal Bessel beam region corresponding to the second hollow light cone is proportionally reduced by the corresponding factor, ultimately forming a long focal depth, aberration-free working region for laser cutting.

2. The reflective Bezier cutting head according to claim 1, characterized in that, The optical axes of the conical reflector, the first aspherical concave off-axis reflector, and the second aspherical concave off-axis reflector are located in the same plane, forming a coplanar off-axis reflective optical path.

3. The reflective Bezier cutting head according to claim 1, characterized in that, All optical surfaces used for beam shaping and transmission in the optical path system are reflective surfaces and do not contain any transmissive optical elements.

4. The reflective Bezier optical cutting head according to claim 1, characterized in that, The light source is a pulsed laser with a pulse width ranging from femtoseconds to nanoseconds.

5. The reflective Bezier cutting head according to claim 1, characterized in that, The optical surfaces of the first aspherical concave off-axis mirror and the second aspherical concave off-axis mirror are coated with a high damage threshold reflective film corresponding to the wavelength of the light source, and the reflectivity is greater than 99.5% in the incident angle range of 20° to 70°.

6. The reflective Bezier cutting head according to claim 1, characterized in that, The conical reflector, the first aspherical concave off-axis reflector, and the second aspherical concave off-axis reflector are each provided with a metal substrate.

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