Method of modifying axial intensity profile of bessel beam with the same bessel beam spot size

Abstract

A method for deforming the machining axis intensity of a Bessel beam while maintaining the Bessel beam size according to the machining axis is disclosed. The method for deforming the intensity of the processing axis of a Bessel beam according to the present invention comprises: a step of deforming the incident beam by a first phase in a first phase-deforming optical system; and a step of deforming the beam by a second phase in a second phase-deforming optical system, wherein the first phase-deforming step results in an intensity distribution of a desired shape, particularly a flat-top shape, in the direction of travel (z-direction), and the second phase-deforming step results in the Bessel beam having a constant size in the direction of travel (z-direction) by refracting the angle of contact with the z-axis equally.

Description

Technology Field

[0001] The present invention relates to a method for deforming the machining axis intensity of a Bessel beam.

[0002] More specifically, the present invention relates to a method for deforming the machining axis intensity while maintaining the size of the Bessel beam according to the position of the machining axis. Background Technology

[0004] Figure 1 schematically shows the processing axis intensity distribution by a laser with a Gaussian distribution and an axicon lens.

[0005] To cut or drill tens to hundreds of micrometers into transparent or brittle materials, a Bessel beam using an ultrashort infrared laser is typically irradiated onto the target material.

[0006] A Bessel beam made of an axicon lens optical system can process transparent / brittle materials with a size of several micrometers to tens of micrometers and a long depth.

[0007] However, generally, a Bessel beam produced through an axicon lens with a laser having a Gaussian beam profile as in (a) of Fig. 1 has an intensity distribution similar to a Gaussian as in Equation 1 below in the direction of the processing axis, which becomes the form shown in (b) of Fig. 1.

[0008] [Equation 1]

[0009]

[0010] Since the intensity distribution of the deep machining axis is in the form of a Gaussian as shown in (b) of Fig. 1, machining is performed only at an intensity above a certain threshold, and the machining energy varies depending on the position of the machining axis.

[0011] To address these issues, conventional techniques have primarily utilized methods such as forming a laser beam with a long depth of focus (DOF) along the processing axis or employing lenses of specific curvature to modify the intensity of the processing axis. However, in these methods, the realization of processing axis intensity is significantly influenced by the degree of lens processing and the shape and quality of the incident laser beam. Furthermore, limitations on lens curvature processing (such as curvature magnitude and aspherical lens coefficients) make it difficult to achieve the desired processing axis intensity. Additionally, while Bessel beams are commonly used for laser beams with long processing lengths along the processing axis, the typical processing axis intensity distribution of a Bessel beam takes on a Gaussian shape, resulting in varying machinability depending on the processing axis.

[0012] Figure 2 schematically shows an example of converting a Gaussian distribution of the processing axis into a flat-top shape.

[0013] To solve this problem, a method was proposed to convert the Gaussian distribution of the processing axis into a flat-top shape, as shown in the example in Fig. 2.

[0014] In this method, the Gaussian intensity distribution (GB) in the direction of the processing axis was transformed into a flat-top intensity distribution (MGB) by modifying the axicon phase in Fig. 2.

[0015] However, if the phase of a Bessel beam with a standard Gaussian distribution is modified, the angle of the beam refracted at the axicon changes, resulting in the disadvantage that the size of the Bessel beam at the machining axis changes.

[0016] Figure 3 shows the simulation results of the phase deformation of a Bessel beam having an intensity distribution in the form of a flat-top shape of the machining axis. Figure 4 shows (a) the intensity deformation of the machining axis according to the position of the Bessel beam and (b) the change in the size of the Bessel beam according to the position of the machining axis accordingly.

[0017] Referring to Figures 3 and 4, as shown in the simulation above, a Bessel beam with a flat-top processing axis intensity can be realized by modifying the phase to make the processing axis intensity of the Bessel beam into a flat-top shape. However, it can be observed that the size of the Bessel beam (the size between zero and lob) varies depending on the position of the processing axis due to the phase modification. Generally, the size (D0) of the Bessel beam is determined by the angle (α0) at which the refracted light ray from the optical system (DOE (Diffractive Optical Element), SLM (Spatial Light Modulator), axicon lens, etc.) that generates the Bessel beam meets the processing axis, and the laser wave number (k o It is calculated as shown in the equation below using ).

[0018]

[0019] In a standard Bessel beam, the angle of refraction in the optical system is constant due to the linear phase, so the size of the Bessel beam remains the same regardless of the position of the machining axis. However, if the phase is modified to create a machining axis with a flat-top intensity distribution as described above, the angle of refraction in the optical system becomes non-constant, causing the size of the Bessel beam to vary depending on the position of the machining axis. Consequently, even if the intensity distribution of the machining axis is made identical to the flat-top shape, the size of the Bessel beam changes; thus, the energy processed (the product of intensity and Bessel beam size (intensity × Bessel spot size)) varies depending on the position of the machining axis, preventing the effect of the flat-top intensity distribution from being achieved during machining. Prior art literature

[0021] Published Patent Application No. 10-2017-0019855 (Feb. 22, 2017) US Patent Application US 11,548,093 B2 (Issued Jan. 10, 2023) The problem to be solved

[0022] As previously mentioned, currently proposed intensity profiles with long machining lengths along the machining axis primarily utilize Bessel beams; however, since Gaussian profiles appear along the machining axis, machinability varies depending on the axis. Accordingly, methods have been proposed to implement flat-top or desired shape machining axis intensity using SLMs, DOEs, and aspherical lenses; however, in such cases, a phenomenon occurs where the size of the Bessel beam varies depending on the position of the machining axis.

[0023] The problem that the present invention aims to solve is, therefore, to provide a method for deforming the machining axis intensity while maintaining the size of the Bessel beam according to the position of the machining axis.

[0024] In particular, the present invention proposes a method for implementing an intensity distribution of a desired shape, specifically a flat-top shape, in the direction of the processing axis by applying a Gaussian phase to a conventional Bessel beam. means of solving the problem

[0026] To solve the above problem, a method for deforming the processing axis intensity of a Bessel beam according to an embodiment of the present invention comprises: a step of first phase-deforming an incident beam in a first phase-deforming optical system; and a step of second phase-deforming the first phase-deformed beam in a second phase-deforming optical system.

[0027] In the above first-order phase-shifting optical system, an intensity apodization algorithm defined by the following equations (1) to (3) is applied to change the processing axis intensity of the Bessel beam, and

[0028] Equation (1)

[0029] Equation (2)

[0030] Equation (3)

[0031] In Equations 1 to 3,

[0032] ρ: Position of the vertical axis of the Bessel beam's direction of travel

[0033] z: Position of the Bessel beam's direction of travel

[0034] I(ρ): Intensity distribution of the incident beam

[0035] I0: Incident beam intensity reference

[0036] w0: Size of the incident laser beam

[0037] P(z): Intensity distribution in the direction of the machining axis to be determined

[0038] P0: Reference to intensity strength in the direction of the machining axis to be calculated

[0039] z C : Super Gaussian center when the intensity of the desired machining axis direction is set to a Super Gaussian form

[0040] z0: Super Gaussian magnitude when the intensity in the desired machining axis direction is set to a Super Gaussian form

[0041] In the above second-order phase-shifting optical system, the angle of the beam incident on the above second-order phase-shifting optical system is refracted at a constant angle in the z-axis direction by the phase shifted by the above first-order phase-shifting optical system, thereby making the size of the Bessel beam equal in the beam's direction of propagation (z-axis).

[0042] The first phase-shifting optical system may include an axicon lens or an axicon phase lens. The second phase-shifting optical system may refract the angle of refraction of the beam modified by the first phase-shifting optical system by the same angle in the z-axis direction.

[0043] By the first phase-shifting optical system and the second phase-shifting optical system, the intensity of the processing axis of the Bessel beam can be transformed into a flat-top shape or a super-Gaussian shape while maintaining the Bessel beam size according to the processing axis position.

[0044] Both the first phase-shifting optical system and the second phase-shifting optical system may be composed solely of DOE or SLM. Alternatively, either of the first phase-shifting optical system and the second phase-shifting optical system may be composed solely of DOE or SLM, and the other optical system may have an axicon lens coupled to the DOE or SLM. Alternatively, both the first phase-shifting optical system and the second phase-shifting optical system may have an axicon lens coupled to the DOE or SLM.

[0046] The laser processing method according to the present invention performs laser processing on a workpiece using a Bessel beam having a processing axis intensity modified by the method described above. Effects of the invention

[0048] According to the present invention, an intensity distribution of a desired shape, particularly a flat-top shape, can be formed in the direction of the machining axis. Accordingly, an intensity distribution of the machining axis can be formed while maintaining the size of the Bessel beam along the machining axis.

[0049] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the detailed description below. Brief explanation of the drawing

[0051] Figure 1 schematically shows the processing axis intensity distribution by a laser with a Gaussian distribution and an axicon lens. Figure 2 schematically shows an example of converting a Gaussian distribution of the processing axis into a flat-top shape. Figure 3 shows the simulation results of the phase deformation of a Bessel beam having an intensity distribution in the form of a flat-top shape of the processing axis. Figure 4 shows (a) deformation of the machining axis intensity according to the position of the Bessel beam and (b) change in the size of the Bessel beam according to the position of the machining axis. Figure 5 schematically illustrates a method for deforming the machining axis intensity profile by two phase deformations. Figure 6 shows the equation of a laser beam passing through an axicon lens. Figure 7 shows the phase (curvature) of the first phase deformation stage and the phase (curvature) of the second phase deformation stage obtained by simulation. Figure 8 is a 3D profile of a beam propagation simulation using two phase-shifted optical systems. FIG. 9 schematically illustrates examples in which the processing axis intensity of a Bessel beam according to the present invention is deformed. Specific details for implementing the invention

[0052] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity of description.

[0053] When an element or layer is referred to as another element or "above" or "on top," it includes not only cases where it is directly above another element or layer, but also cases where another layer or element is interposed in between. On the other hand, when an element is referred to as "directly above" or "immediately above," it indicates that no other element or layer is interposed in between. Furthermore, where it is stated that a component is "connected," "combined," or "connected" to another component, it should be understood that said components may be directly connected or connected to each other, but that another component may be "interposed" between each component, or that each component may be "connected," "combined," or "connected" through another component.

[0054] Spatially relative terms such as "below," "lower," "above," and "upper" may be used to facilitate the description of the relationship between one element or component and another, as illustrated in the drawings. Spatially relative terms should be understood as encompassing different orientations of the element during use or operation, in addition to the orientations illustrated in the drawings. For example, if an element illustrated in the drawings is flipped, an element described as being "below" another element may be placed "above" that other element. Therefore, the exemplary term "below" may encompass both the lower and upper directions.

[0055] The terms used herein are for describing the embodiments and are therefore not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used in this specification, "comprising" and / or "comprising" does not exclude the presence or addition of one or more other components, steps, actions, and / or elements to the mentioned components, steps, actions, and / or elements. Throughout the specification, the same reference numerals refer to the same components.

[0056] A method for deforming the machining axis intensity while maintaining the Bessel beam size according to a preferred embodiment of the present invention will be described in detail below with reference to the attached drawings.

[0058] In conventional technology, the primary method used involves employing lenses of a specific curvature to form a laser beam with a depth of focus (DOF) along the processing axis or to modify the intensity of the processing axis. In this case, the realization of the processing axis intensity is significantly influenced by the degree of lens processing and the shape and quality of the incident laser beam. Furthermore, due to limitations regarding the curvature of the lenses—such as the magnitude of the curvature and aspherical lens coefficients—it is difficult to achieve the desired processing axis intensity.

[0059] In addition, laser beams with long processing lengths along the processing axis, as previously proposed, primarily use Bessel beams; however, the intensity distribution along the processing axis of a typical Bessel beam is Gaussian, resulting in varying machinability depending on the processing axis.

[0060] The present invention provides a method for modifying the machining axis intensity while maintaining the size of the Bessel beam according to the position of the machining axis by applying a Gaussian phase to a conventional Bessel beam to realize an intensity distribution of a desired shape, particularly a flat-top shape, in the direction of the machining axis.

[0062] In order to maintain the same size of the Bessel beam according to the machining axis position even with phase changes of the Bessel beam, two phase changes are used as follows.

[0063] Figure 5 schematically illustrates a method for deforming the machining axis intensity profile by two phase deformations.

[0064] FIG. 5 illustrates an example in which the processing axis intensity profile is deformed by two phase-shifting optical systems, namely the first phase-shifting optical system (510) and the second phase-shifting optical system (520).

[0065] Referring to FIG. 5, the incident beam generally has a Gaussian intensity distribution (501) in the direction perpendicular to the propagation (z-axis) (ρ-axis, origin symmetry). To obtain a Bessel beam (503) of the desired processing axis intensity profile in the processing axis direction (z-axis) through an intensity profile change (502) caused by phase deformation of this Gaussian distribution, a first phase deformation optical system (510) that deforms the phase and a second phase deformation optical system (520) that meets the processing axis at a constant angle to make the size of the Bessel beam equal along the processing axis are used.

[0066] In the first phase deformation optical system (510), an intensity apodization algorithm defined by the following equations (1) to (3) is applied to deform the processing axis intensity of the Bessel beam.

[0067] Equation (1)

[0068] Equation (2)

[0069] Equation (3)

[0070] In Equations 1 to 3,

[0071] ρ: Position of the vertical axis of the Bessel beam's direction of travel

[0072] z: Position of the Bessel beam's direction of travel

[0073] I(ρ): Intensity distribution of the incident beam

[0074] I0: Incident beam intensity reference

[0075] w0: Size of the incident laser beam

[0076] P(z): Intensity distribution in the direction of the machining axis to be determined

[0077] P0: Reference to intensity strength in the direction of the machining axis to be calculated

[0078] z C : Super Gaussian center when the intensity of the desired machining axis direction is set to a Super Gaussian form

[0079] z0: Super Gaussian magnitude when the intensity in the direction of the machining axis to be calculated is set to a Super Gaussian form.

[0080] In the second phase-shifting optical system (520), the angle of the beam incident on the second phase-shifting optical system (520) is refracted at a constant angle in the z-axis direction by the phase shifted by the first phase-shifting optical system (510), thereby making the size of the Bessel beam equal in the beam's direction of travel (z-axis).

[0082] The first phase deformation optical system (520) may include, for example, an axicon lens or an axicon phase lens.

[0083] Figure 6 shows an equation for a laser beam passing through an axicon lens.

[0084] According to the first phase-shifting optical system, as shown in Fig. 6, when the direction of beam propagation is the z-axis, the intensity profile of the ρ-axis perpendicular to it exhibits a Gaussian distribution in a general laser.

[0085] Due to this Gaussian distribution, the z-axis (processing axis) intensity profile of the Bessel beam in optical systems using axicon lenses or axicon phases becomes similar to the Gaussian shape described above.

[0086] In order to transform this z-axis Gaussian distribution into a flat-top or super-gaussian distribution, the axicon phase can be obtained by utilizing an intensity apodization algorithm such as the aforementioned equations (1) to (3).

[0087] Intensity apodization algorithms are generally used as a technique to modify the beam intensity profile along the same axis (vertical to the direction of beam propagation) after the beam has traveled a certain section, but the present invention proposes a technique to modify the intensity profile along the direction of beam propagation.

[0088] Equation (3) represents the intensity distribution of the incident beam and the processing axis to be obtained, and each intensity is normalized by Equation (2). The intensity distribution of the processing axis to be obtained at position ρ of the incident beam can be obtained by Equation (1).

[0090] Figure 7 shows (a) the phase (curvature) of the first phase deformation stage obtained by simulation and (b) the phase (curvature) of the second phase deformation stage.

[0091] To implement a super-Gaussian profile in the z-axis direction, equations (1) to (3) can be used to obtain z(ρ), which is refracted by the Bessel beam optical system at the position ρ of the incident beam and meets the z-axis. If the angle of contact with the z-axis is maintained the same by the second phase optical system, ρ1 can be obtained at the second phase deformation position for the incident beam position ρ. Therefore, since ρ1 has been obtained at the second phase deformation position for the incident beam position ρ, the angle of refraction from the first phase deformation optical system to the second phase deformation optical system can be determined by the distance D between the first phase deformation optical system and the second phase deformation optical system, and the phase or curvature due to the phase difference of the first phase deformation optical system can be obtained to keep the angle of contact with the z-axis constant regardless of the position of the angle of refraction obtained by the first phase deformation optical system.

[0092] That is, the second phase-shifting optical system refracts the angle of refraction of the beam modified by the first phase-shifting optical system, which includes an axicon lens or an axicon phase lens, by the same angle in the z-axis direction.

[0094] Figure 8 is a 3D profile of a beam propagation simulation using two phase-shifted optical systems.

[0095] The intensity distribution in the z-axis direction of the deformed axicon phase can be confirmed as shown in Fig. 8 through the first phase-deformed optical system and the electromagnetic beam propagation simulation using the first phase-deformed optical system. As can be seen in Fig. 8, the intensity distribution in the z-axis direction takes the form of a flat-top, and the size of the Bessel beam is constant regardless of the position of the processing axis (z-axis).

[0096] In this way, according to the present invention, the intensity of the processing axis of the Bessel beam can be deformed into a flat-top shape or a super-Gaussian shape while maintaining the Bessel beam size according to the processing axis position by means of the first phase-shifting optical system (510) and the second phase-shifting optical system (520).

[0098] FIG. 9 schematically illustrates examples in which the processing axis intensity of a Bessel beam according to the present invention is deformed.

[0099] The Bessel beam may be derived from an axicon lens, an axicon phase lens, or a DOE lens. In the present invention, a DOE (Diffractive Optical Element) or SLM (Spatial Light Modulator) to which the intensity apodization algorithm according to the present invention described above is applied, and a DOE or SLM that makes the Bessel beam size equal through equal angle refraction may be additionally arranged.

[0100] In FIG. 9 (a) to (d), the square is an exemplary DOE or SLM, and the triangle is an exemplary axicon lens.

[0101] Each of (a) to (d) in FIG. 9 contains two DOEs or SLMs. The first DOE or SLM can be a DOE to which an intensity apodization algorithm is applied, i.e., a first phase-shifting optical system. The second DOE or SLM can be a DOE or SLM to which the Bessel beam spot size is made equal by refracting at the same angle, i.e., a second phase-shifting optical system.

[0102] As shown in FIG. 9(a), the processing axis intensity deformation device according to the present invention may be composed of both the first phase deformation optical system and the second phase deformation optical system using only DOE or SLM. Additionally, as shown in FIG. 9(b), the processing axis intensity deformation device according to the present invention may be composed of the first phase deformation optical system using only DOE or SLM, and the second phase deformation optical system may be composed of an axicon lens coupled to the DOE or SLM. Furthermore, as shown in FIG. 9(c), the processing axis intensity deformation device according to the present invention may be composed of the first phase deformation optical system using an axicon lens coupled to the DOE or SLM, and the second phase deformation optical system using only DOE or SLM. Additionally, as shown in FIG. 9(d), the processing axis intensity deformation device according to the present invention may be composed of both the first phase deformation optical system and the second phase deformation optical system using an axicon lens coupled to the DOE or SLM.

[0103] The machining axis intensity can be modified while maintaining the size of the Bessel beam along the machining axis through a first phase-shifting optical system and a second phase-shifting optical system, such as the examples shown in FIG. 9 (a) to (d).

[0105] Although embodiments of the present invention have been described above with reference to the attached drawings, the present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical concept or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 The method comprises the steps of: first phase-shifting an incident beam in a first phase-shifting optical system; and second phase-shifting the first phase-shifted beam in a second phase-shifting optical system, wherein an intensity apodization algorithm defined by the following equations (1) to (3) is applied in the first phase-shifting optical system to deform the processing axis intensity of the Bessel beam, and Equation (1) Equation (2) Equation (3) In Equations 1 to 3, ρ: position in the direction of the vertical axis of the Bessel beam's propagation direction z: position in the direction of the Bessel beam's propagation I(ρ): intensity distribution of the incident beam I0: reference to the intensity of the incident beam w0: magnitude of the incident laser beam P(z): intensity distribution in the direction of the processing axis to be determined P0: reference to the intensity in the direction of the processing axis to be determined z C : Super Gaussian center z0 when the intensity in the direction of the processing axis to be obtained is set in a super Gaussian form; Super Gaussian magnitude when the intensity in the direction of the processing axis to be obtained is set in a super Gaussian form. A method for deforming the processing axis intensity of a Bessel beam, wherein the angle of the beam incident on the second phase-shifting optical system is refracted at a constant angle in the z-axis direction by the phase deformed by the first phase-shifting optical system, thereby making the Bessel beam magnitude equal in the direction of beam propagation (z-axis). Claim 2 A method for deforming the processing axis intensity of a Bessel beam, wherein, in claim 1, the first phase deformation optical system comprises an axicon lens or an axicon phase lens. Claim 3 A method for deforming the processing axis intensity of a Bessel beam, wherein, in paragraph 2, the second phase deformation optical system refracts the angle of refraction of the beam deformed by the first phase deformation optical system by the same angle in the z-axis direction. Claim 4 A method for deforming the processing axis intensity of a Bessel beam, wherein, in claim 1, the Bessel beam size is maintained according to the processing axis position by the first phase-shifting optical system and the second phase-shifting optical system, and the intensity of the processing axis of the Bessel beam is deformed into a flat-top shape or a super-Gaussian shape. Claim 5 A method for deforming the processing axis intensity of a Bessel beam, wherein, in any one of claims 1 to 4, both the first phase deformation optical system and the second phase deformation optical system are composed solely of DOE or SLM. Claim 6 A method for deforming the processing axis intensity of a Bessel beam, wherein, in any one of claims 1 to 4, either the first phase deformation optical system and the second phase deformation optical system is composed only of a DOE or SLM, and the other optical system is an axicon lens coupled to the DOE or SLM. Claim 7 A method for deforming the processing axis intensity of a Bessel beam, wherein, in any one of claims 1 to 4, both the first phase-shifting optical system and the second phase-shifting optical system are coupled to an axicon lens in a DOE or SLM. Claim 8 A laser processing method in which laser processing is performed on a workpiece using a Bessel beam having a processing axis intensity modified by any one of claims 1 to 4.

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