Combined conical reflector and diffraction-free Bessel beam generation method thereof

Abstract

The invention discloses a combined conical reflector and a diffraction-free Bessel beam generation method thereof. Comprising a negative cone angle annular conical surface reflector, a positive cone angle conical surface reflector and a plane diaphragm which are coaxially arranged along a main optical axis; the negative cone angle annular conical surface reflector is provided with a central through hole, one side of the negative cone angle annular conical surface reflector facing the positive cone angle conical surface reflector is provided with a first conical surface reflecting surface, and the included angle between the generatrix of the first conical surface reflecting surface and the axis vertical line is alpha; a second conical surface reflecting surface is arranged on the side, facing the negative cone angle annular conical surface reflecting mirror, of the positive cone angle conical surface reflecting mirror, the included angle between the generatrix of the second conical surface reflecting surface and the axis vertical line is beta, and alpha is larger than beta; the path of the light beam is regulated and controlled through two times of reflection, and the diffraction-free Bessel light beam is generated. The method solves the processing problem and wavelength limitation of the traditional refraction axicon, has the advantages of low cost, high stability, wide adaptability and the like, and is suitable for high-precision beam application scenes in the laser field.

Description

Technical Field

[0001] The present invention relates to the field of laser optics, in particular to a combined conical reflector and a method for generating a non-diffraction Bessel beam thereof. Background Art

[0002] Due to its unique optical properties, diffraction-free Bessel beams have a lateral intensity distribution perpendicular to the propagation direction consisting of a central bright spot (main lobe) and concentric rings (side lobes). This intensity distribution remains constant over the diffraction-free transmission distance, making them valuable applications in laser processing, optical inspection, biomedicine, and other fields. Since J. Durnin first proposed this concept in 1987, the industry has conducted extensive research on their generation methods. Key technologies include lenses, mirrors, and diffraction elements. The refractive axis (Axicon) has become the most commonly used element due to its simple structure, high optical damage threshold, and high conversion efficiency.

[0003] A refractive axicon is a rotationally symmetrical structure and is divided into positive and negative axicons. A positive axicon focuses parallel light through refraction, forming a diffraction-free zone. The maximum length of this zone is given by the formula: Zmax≈(n-1)γR, where R is the radius of the incident parallel light, n is the material's refractive index, and γ is the axicon's base angle. A negative axicon diverges the light beam and is often used in conjunction with a positive axicon to extend the optical path.

[0004] However, in applications where a refractive axis pyramid is used to generate a non-diffracting beam, the tip of the refractive axis pyramid is easily worn down into a dome structure due to physical grinding during processing. The larger the dome radius r, the more significant the distortion of the central light intensity distribution, which affects the central light intensity. In addition, the non-diffracting length Zmax of the refractive axis pyramid directly depends on the material refractive index n, and the refractive index of light of different wavelengths in the same material varies. The Zmax of a traditional refractive axis pyramid is uniquely determined by the material parameters (n) and the geometric parameters (γ) and cannot be dynamically adjusted. If the non-diffracting length needs to be changed, the entire axicon element must be replaced, which makes it difficult to adapt to diverse application scenarios.

[0005] Therefore, there is an urgent need to invent a combined conical reflector and a method for generating a non-diffraction Bessel beam thereof. Summary of the Invention

[0006] Based on this, it is necessary to provide a combined conical reflector and a method for generating a non-diffraction Bessel beam thereof to address the above problems.

[0007] A combined conical reflector comprises a negative cone angle annular conical reflector, a positive cone angle conical reflector and a plane window arranged coaxially along a main optical axis;

[0008] The negative cone angle annular conical reflector has a central through hole, and a first conical reflective surface is provided on a side thereof facing the positive cone angle conical reflector, wherein the angle between the generatrix of the first conical reflective surface and the axis perpendicular is α;

[0009] A second conical reflective surface is provided on the side of the positive cone angle conical reflector facing the negative cone angle annular conical reflector, and the included angle between the generatrix of the second conical reflective surface and the axis perpendicular is β, and α>β;

[0010] The side of the positive cone angle conical reflector away from the negative cone angle annular conical reflector is fixedly connected to the plane window piece, and the plane window piece is used for light beam transmission;

[0011] The collimated parallel light is incident on the second conical reflective surface through the central through hole, and diverges into a ring-shaped light beam after the first reflection. The ring-shaped light beam is incident on the first conical reflective surface and reflects for the second time. The reflected light beam passes through the planar window and converges behind it to form a non-diffraction Bessel beam.

[0012] In one embodiment, the diameter of the central through hole of the negative cone angle annular conical reflector is D2, the diameter of the positive cone angle conical reflector is D3, and the diameter of the incident parallel light is D1, satisfying: D2>D3>D1.

[0013] In one embodiment, the bonding surface between the planar window and the positive cone-angle conical reflector is a first plane, the light-emitting surface of the planar window is a second plane, and the first plane and the second plane are parallel and perpendicular to the principal optical axis.

[0014] In one embodiment, the maximum non-diffraction transmission distance Zmax of the non-diffraction Bessel light beam satisfies the formula: Zmax≈1 / 2×D1×cot[2(α-β)].

[0015] In one embodiment, the first conical reflective surface and the second conical reflective surface are processed by a one-time forming process using a single-point metal turning machine tool, and the cone tip of the second conical reflective surface is a sharp tip without arc transition, and the tip apex is located on the main optical axis.

[0016] In one embodiment, the negative cone angle annular conical reflector and the positive cone angle conical reflector are made of metal or ceramic with a high reflective film on the surface, and the reflectivity of the material to incident light is ≥95% and the absorptivity is ≤3%.

[0017] In one embodiment, the positive cone-angle conical reflector and the flat window are bonded and fixed by an optical-grade epoxy resin adhesive layer, the adhesive layer thickness is ≤0.05 mm, and the coaxiality deviation between M2 and P1 is ≤5 μm.

[0018] In one embodiment, a ring-shaped window area with a width of H is opened on the plane window piece, and the inner diameter of the ring-shaped window area is larger than the outer diameter of the positive cone angle conical reflector, and its outer diameter is equal to the outer diameter of the negative cone angle annular conical reflector.

[0019] A method for generating a non-diffracting Bessel beam based on a combined conical reflector, wherein the collimated parallel light passes through the central through hole along the main optical axis and undergoes a first reflection on the second conical reflective surface. The reflected light diverges in a direction forming an angle of 2β with the main optical axis to form a ring-shaped beam;

[0020] The annular light beam is incident on the first conical reflective surface and undergoes a second reflection in a direction forming an angle of 2(α-β) with the main optical axis. After the reflected light is transmitted through the planar window, it converges at a distance Wd behind the planar window to form a non-diffraction Bessel beam with stable central light intensity.

[0021] The above-mentioned combined conical reflector and method for generating non-diffraction Bessel beams replace traditional refraction with two reflections, eliminating the influence of the material refractive index on the beam performance and achieving wide wavelength compatibility; the positive cone angle conical reflector can avoid cone tip wear by lathe processing and form a sharp cone tip; the negative cone angle annular reflector can be processed by lathe processing with a center hole, and there is no problem that the negative angle cone tip cannot be processed.

[0022] Innovation in parametric control: Establishing the mathematical relationship between α, β, D1, and Zmax, the optical structure is precisely designed through formulas, avoiding the blindness of traditional trial-and-error methods. Dynamic adjustment of the α-β difference is supported, achieving real-time adjustment of the diffraction-free length to meet the needs of different application scenarios.

[0023] Expanded material adaptability: Non-optical crystal materials such as metals and ceramics can be used to break through the physical limitations of traditional optical crystals; high-temperature and corrosion-resistant materials make the system suitable for extreme environments and expand the application range of non-diffraction beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 It is a side sectional view of the present invention;

[0026] Figure 3 Schematic diagram of the non-diffraction Bessel beam generated by the present invention.

[0027] 1. Negative cone angle annular conical reflector; 11. Central through hole; 12. First cone base angle; 13. Central through hole diameter; 14. First cone reflective surface; 2. Positive cone angle conical reflector; 21. Second cone base angle; 22. Diameter of positive cone angle conical reflector; 23. Second cone reflective surface; 3. Plane window; 31. First plane; 32. Second plane; 4. Incident parallel light diameter; 5. Tip; 6. Angle window area. DETAILED DESCRIPTION

[0028] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0029] As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0030] When amount, concentration or other value or parameter is represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, no matter whether this range is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0031] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e., the number of times the elements or components appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the number is obviously intended to be singular.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] See Figure 1-Figure 3 A combined conical reflector comprises a negative cone angle annular conical reflector 1, a positive cone angle conical reflector 2 and a plane window 3 coaxially arranged along a principal optical axis;

[0034] The negative cone angle annular conical reflector 1 has a central through hole 11, and a first conical reflective surface 14 is provided on the side thereof facing the positive cone angle conical reflector 2. The included angle between the generatrix of the first conical reflective surface 14 and the axis perpendicular is α, i.e., the first conical base angle 12;

[0035] A second conical reflective surface 23 is provided on the side of the positive cone angle conical reflector 2 facing the negative cone angle annular conical reflector 1. The included angle between the generatrix of the second conical reflective surface 23 and the axis perpendicular is β, i.e., the second cone base angle 21, and α>β;

[0036] The side of the positive cone angle conical reflector 2 away from the negative cone angle annular conical reflector 1 is fixedly connected to the plane window 3, and the plane window 3 is used for light beam transmission;

[0037] Collimated parallel light passes through the central through-hole 11 and is incident on the second conical reflective surface 23. After the first reflection, it diverges into a ring-shaped beam. The ring-shaped beam then enters the first conical reflective surface 14 for a second reflection. The reflected beam passes through the flat window 3 and converges behind it to form a non-diffracting Bessel beam. The combined structure of the negative-angle annular conical reflector 1 and the positive-angle conical reflector 2 achieves a high-quality non-diffracting Bessel beam. The use of a reflective structure instead of the traditional refractive axicon eliminates the influence of the material's refractive index (n) on the non-diffracting length, allowing light of different wavelengths to share the same structure.

[0038] Furthermore, the central through-hole diameter 13 of the negative-angle annular conical reflector 1 is D2, the diameter 22 of the positive-angle annular conical reflector is D3, and the incident parallel light diameter 4 is D1, satisfying the following: D2>D3>D1; the central through-hole 11 allows the light beam to directly enter M2, preventing M1 from blocking the central light; D3>D1 ensures that M2 completely covers the incident light spot, achieving full-aperture reflection and improving energy utilization. Furthermore, D2>D3 prevents the annular light beam from interfering with the inner wall of M1, reducing edge stray light and increasing the central light intensity concentration to over 90%.

[0039] Furthermore, the mating surface between the planar window 3 and the positive-angle conical reflector 2 is a first plane 31, and the light-emitting surface of the planar window 3 is a second plane 32. The first plane 31 and the second plane 32 are parallel and perpendicular to the principal optical axis. By designing the parallelism of the first plane 31 and the second plane 32, the beam is ensured to have no angular deviation during emission, thus achieving a suspended and fixed position of the positive-angle conical reflector 2 in the optical path. This avoids the increased beam divergence angle caused by machining errors in traditional axicons.

[0040] In addition, the corresponding plane window 3 can be replaced under different working wavelengths without changing the non-diffracting Bessel beam.

[0041] Furthermore, the maximum non-diffraction transmission distance Zmax of the non-diffraction Bessel beam satisfies the formula: Zmax≈1 / 2×D1×cot[2(α-β)]. The non-diffraction length can be linearly adjusted by the difference between the two cone base angles (α-β) (or expressed as Zmax≈D1 / 2tan[2(α-β)]), without the need for component replacement, to accommodate diverse needs from the micron to meter scale.

[0042] In addition, when α>β, different non-diffracting Bessel beams can be combined by using different α and β.

[0043] Furthermore, the first conical reflective surface 14 and the second conical reflective surface 23 are machined in a single-step process using a single-point metal turning machine. The tip of the second conical reflective surface 23 is a sharp tip 5 without a circular transition, with the apex of the tip 5 located on the principal optical axis. The reflector's tip is formed through turning, maintaining a sharp tip 5 (radius ≤ 1μm), avoiding dome wear caused by traditional grinding processes and improving beam stability. Furthermore, turning replaces multiple grinding and polishing steps, significantly reducing single-piece processing time and costs. Furthermore, the sharp tip can withstand long-term high-power laser irradiation.

[0044] Furthermore, the negative-angle annular conical reflector 1 and the positive-angle conical reflector 2 are made of metal or ceramic with a highly reflective coating on the surface. The material has a reflectivity of ≥95% and an absorptivity of ≤3% for incident light. By providing a full-band highly reflective coating, the reflectivity is maintained at ≥95% within the range of 400-10600nm, while the absorptivity of traditional refractive axis pyramids in the infrared band is ≥8% (such as the absorption of 10.6μm light by K9 glass), improving energy efficiency by approximately 20%. Furthermore, the metal and ceramic materials are resistant to high temperatures (above 300°C) and corrosion, making them suitable for use in industrial furnaces and highly corrosive liquids, whereas traditional optical crystals are prone to cracking at high temperatures.

[0045] Furthermore, the positive cone angle conical reflector 2 and the flat window piece 3 are bonded and fixed by an optical grade epoxy resin adhesive layer, the adhesive layer thickness is ≤0.05mm, and the coaxiality deviation of M2 and P1 is ≤5μm. The ultra-thin adhesive layer is provided to avoid the gap error of the traditional mechanical connection, ensure the optical contact accuracy of M2 and P1, and reduce the refraction deviation when the light beam passes through; and after the adhesive layer is cured, a rigid connection is formed, and the coaxiality deviation is maintained at ≤5μm in a vibration environment. The positive cone angle conical reflector 2 and the flat window piece 3 can also be fixed by inlaying and threading.

[0046] Furthermore, the planar window 3 defines an annular window region 6 having a width H. The inner diameter of the annular window region 6 is larger than the outer diameter of the positive cone-angle conical reflector 2, and its outer diameter is equal to the outer diameter of the negative cone-angle annular conical reflector 1. The annular window precisely matches the diameter of the annular beam, blocking non-reflected light at the edges of M1 and M2, reducing the sidelobe energy share and significantly improving the central light intensity concentration.

[0047] A method for generating a non-diffracting Bessel beam based on a combined conical reflector, wherein the collimated parallel light passes through the central through hole 11 along the main optical axis and undergoes a first reflection at the second conical reflective surface 23, and the reflected light diverges in a direction forming an angle of 2β with the main optical axis to form a ring-shaped beam;

[0048] The annular beam is incident on the first conical reflective surface 14, undergoing a second reflection at an angle of 2(α-β) with the principal optical axis. After passing through the planar window 3, the reflected light converges at a distance Wd behind the planar window 3, forming a non-diffracting Bessel beam with a stable central intensity. The independently adjustable reflection angles allow for rapid switching of beam modes (e.g., from focusing mode to non-diffracting mode) based on demand. While traditional refractive axicons require component replacement, switching time is reduced from hours to seconds. Furthermore, the same structure can generate either a Gaussian beam or a Bessel beam by adjusting the values ​​of α and β, expanding the system's versatility.

[0049] Core parameter adjustment logic

[0050]

[0051] Key parameter design rules

[0052]

[0053] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A combined conical reflector, characterized in that: The invention comprises a negative cone angle annular conical reflector, a positive cone angle conical reflector and a plane window piece coaxially arranged along the main optical axis; The negative cone angle annular conical reflector has a central through hole, and a first conical reflective surface is provided on a side thereof facing the positive cone angle conical reflector, wherein the angle between the generatrix of the first conical reflective surface and the axis perpendicular is α; A second conical reflective surface is provided on the side of the positive cone angle conical reflector facing the negative cone angle annular conical reflector, and the included angle between the generatrix of the second conical reflective surface and the axis perpendicular is β, and α>β; The side of the positive cone angle conical reflector away from the negative cone angle annular conical reflector is fixedly connected to the plane window piece, and the plane window piece is used for light beam transmission; The collimated parallel light is incident on the second conical reflective surface through the central through hole, and diverges into a ring-shaped light beam after the first reflection. The ring-shaped light beam is incident on the first conical reflective surface and reflects for the second time. The reflected light beam passes through the planar window and converges behind it to form a non-diffraction Bessel beam.

2. A combined conical reflector according to claim 1, characterized in that: The diameter of the central through hole of the negative cone angle annular conical reflector is D2, the diameter of the positive cone angle conical reflector is D3, and the diameter of the incident parallel light is D1, satisfying: D2>D3>D1.

3. The combined conical reflector according to claim 1, wherein: The bonding surface between the planar window and the positive cone angle conical reflector is a first plane, the light emitting surface of the planar window is a second plane, and the first plane is parallel to the second plane and perpendicular to the main optical axis.

4. A combined conical reflector according to claim 1, characterized in that , the maximum non-diffraction transmission distance Zmax of the non-diffraction Bessel beam satisfies the formula: Zmax≈1 / 2×D1×cot[2(α-β)].

5. A combined conical reflector according to claim 1, characterized in that The first conical reflective surface and the second conical reflective surface are processed by a single-point metal turning machine tool in a one-time forming process. The tip of the second conical reflective surface is a sharp tip without arc transition, and the tip vertex is located on the main optical axis.

6. A combined conical reflector according to claim 1, characterized in that The negative cone angle annular conical reflector and the positive cone angle conical reflector are made of metal or ceramic with a high reflective film on the surface. The reflectivity of the material to the incident light is ≥95% and the absorptivity is ≤3%.

7. The combined conical reflector according to claim 1, characterized in that The positive cone angle conical reflector and the flat window piece are bonded and fixed by an optical grade epoxy resin layer, the thickness of the layer is ≤0.05mm, and the coaxiality deviation between M2 and P1 is ≤5μm.

8. The combined conical reflector according to claim 1, characterized in that The plane window piece is provided with an annular window area with a width of H, the inner diameter of the annular window area is larger than the outer diameter of the positive cone angle conical reflector, and its outer diameter is equal to the outer diameter of the negative cone angle annular conical reflector.

9. A method for generating a non-diffracting Bessel beam based on the combined conical reflector according to any one of claims 1 to 8, characterized in that The collimated parallel light passes through the central through hole along the main optical axis and undergoes a first reflection on the second conical reflective surface, and the reflected light diverges in a direction forming an angle of 2β with the main optical axis to form a ring-shaped beam; The annular light beam is incident on the first conical reflective surface and undergoes a second reflection in a direction forming an angle of 2(α-β) with the main optical axis. After the reflected light is transmitted through the planar window, it converges at a distance Wd behind the planar window to form a non-diffraction Bessel beam with stable central light intensity.

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