Method and system for internal processing of materials based on bessel beam deflection

Abstract

The application belongs to the technical field of femtosecond laser application technology, and particularly relates to a material internal processing method and system based on Bessel beam deflection. The method comprises the following steps: two laser beams with short pulse width and long pulse width are incident into a conical lens to generate a Bessel beam; the shaped light beam is introduced into a galvanometer light path, two pairs of parallel galvanometer wafers are arranged, and the two pairs of wafers are deflected around the x-axis and the y-axis respectively; the light beam is horizontally translated after passing through the galvanometer, and is incident into a glass to realize modification after passing through a 4f system. The method can realize rapid processing of high-depth-diameter-ratio modification structures in transparent materials by using the method of double-pulse-width laser Bessel beam multi-axis galvanometer rapid deflection, and can greatly improve the processing efficiency compared with traditional large-inertia processing devices.

Description

Technical Field

[0001] This invention belongs to the technical field of femtosecond laser application technology, specifically relating to a method and system for internal material processing based on Bessel beam deflection. Background Technology

[0002] Currently, Bessel beams are widely used in laser processing, such as cutting hard and brittle materials, microfluidic processing, and glass through-hole processing. Using optical elements such as conical lenses and spatial light modulators, a Gaussian laser beam can be shaped into a Bessel beam with a long depth of focus. Introducing the beam into a beam-contraction system increases the beam energy density. Increasing the beam energy above the material modification or ablation threshold enables internal material processing. Currently, a beam-contraction factor of around 16 is commonly used; if the beam-contraction factor is too low, internal processing of specific materials cannot be achieved. Femtosecond and picosecond lasers are currently widely used in Bessel beam processing. However, when the pulse width is too short, such as below 1.7 ps, the Bessel beam experiences strong nonlinear effects during focusing within the material, leading to axial intensity discontinuities. Conversely, longer pulse widths, due to their low peak energy, cannot achieve internal material processing. Therefore, the Bessel beam processing process involves an energy-pulse width-beam-contraction factor window, resulting in low efficiency and poor processing quality for processing large-format, multi-structure applications.

[0003] Bessel beam processing is also widely used in the fabrication of through-glass vias (TGVs) in IC substrates. Currently, there are similar patents (such as the invention patent "A Multi-Point Bessel Beam Glass Drilling Device and Method") and related papers (such as the journal article "Investigation of Low-Cost Through Glass Vias Formation on Borosilicate Glass by Picosecond Laser-Induced Selective Etching"). By incident a compressed femtosecond / picosecond laser Bessel beam into the glass to achieve modification, followed by etching with hydrofluoric acid or potassium hydroxide solution, glass vias can be obtained. Current patents and papers mainly use a translation stage to achieve relative movement between the glass substrate and the Bessel beam for processing group holes on the substrate; however, the processing efficiency is limited by the movement speed of the translation stage, and further breakthroughs in efficiency are not possible. While common galvanometers or acousto-optic deflectors can achieve rapid deflection of the Bessel beam, the deflected beam will form an angle with the normal of the processed substrate, making it impossible to achieve rapid deflection where the beam is completely perpendicular to the sample surface. Summary of the Invention

[0004] In view of this, the present invention provides a material internal processing method and system based on Bessel beam deflection, which can realize rapid translation of a large field area of ​​Bessel beam without producing large beam tilt and can realize material internal processing.

[0005] To achieve the objectives of this invention, the following technical solutions are provided.

[0006] A method for internal material processing based on Bessel beam deflection includes:

[0007] A short-pulse laser beam and a long-pulse laser beam are combined. The pulse width of the short-pulse laser is on the order of femtoseconds to picoseconds, and the pulse width of the long-pulse laser is on the order of picoseconds to microseconds. There is a preset time delay between the two laser pulses. The combined beam is then introduced into a Bessel beam shaping device to generate a Bessel beam. The Bessel beam is introduced into a multi-axis galvanometer system, which includes a pair of parallel mirrors rotating about the x-axis and a pair of parallel mirrors rotating about the y-axis, each mirror being at a 45° angle to the laser propagation direction. The four reflectors are deflected synchronously, so that the two reflectors around the x-axis rotate synchronously by the same angle to achieve translation of the beam in the y-direction, and the two reflectors around the y-axis rotate synchronously by the same angle to achieve translation of the beam in the x-direction, thereby achieving arbitrary translation of the beam in the plane. The translated beam is introduced into a beam-concentrating system for energy focusing, and then incident into the interior of a transparent material. Short-pulse lasers are used to excite electrons and plasma in the material, and after the time delay, long-pulse lasers continue to inject energy to achieve internal modification or ablation of the material.

[0008] The Bessel beam shaping device is a conical lens or a spatial light modulator.

[0009] The beam-shrinking system is a 4f beam-shrinking system, consisting of two achromatic lenses, with the center distance between the two lenses equal to the sum of their focal lengths.

[0010] In this process, the Bessel beam is moved along a closed curve by controlling the deflection of the galvanometer, forming a closed modified surface or ablation surface inside the material, and after etching, forming irregular micropores perpendicular to the material surface.

[0011] The present invention also provides a material internal processing system based on Bessel beam deflection for implementing the method described in the present invention, comprising: A dual laser source module is used to provide a short-pulse laser and a long-pulse laser; The beam combining and detection module, including a dichroic mirror, a folding mirror, and a photodetector, is used to combine two laser beams and adjust the time delay between them. The Bessel beam shaping module is used to shape the combined Gaussian beam into a Bessel beam. The multi-axis galvanometer deflection module includes two pairs of parallel mirrors, one pair rotating around the x-axis and the other pair rotating around the y-axis. Each mirror is at a 45° angle to the laser propagation direction. By synchronously controlling the four mirrors, the beam can be translated arbitrarily in the plane. The beam-contraction and focusing module is used to focus the energy of the translated beam and incident the focused Bessel beam into the interior of the transparent material to achieve modification or ablation.

[0012] The dichroic mirror is used to reflect one laser beam and transmit the other laser beam, so as to combine the two laser beams.

[0013] In the multi-axis galvanometer deflection module, two pairs of mirrors are arranged sequentially along the optical path, and the rotation axes of each mirror are perpendicular to each other.

[0014] The beam-contraction focusing module is a 4f beam-contraction system, consisting of two confocal lenses.

[0015] Beneficial effects 1. Existing Bessel beam processing techniques suffer from low processing efficiency, small processing windows, and inability to achieve rapid translation of Bessel beams over a large area. The present invention addresses these issues by introducing a novel method for rapidly deflecting Bessel beams to modify the interior of transparent materials. This method is based on laser temporal shaping and multi-axis galvanometer deflection technology. Specifically, the multi-axis galvanometer enables rapid parallel movement of the beam, improving laser processing efficiency (existing technologies do not allow the laser to move), enabling rapid translation of a large field area of ​​the Bessel beam without significant beam tilting, and facilitating internal material processing.

[0016] 2. This invention achieves the translation of the Bessel beam by setting up a beam-shrinking system after deflection. No beam tilt is generated during the rapid beam deflection process, which enables rapid laser processing of mutually parallel structures inside transparent materials. It is a method for rapidly translating Bessel beams to modify the interior of transparent materials.

[0017] 3. This invention enables internal material processing by combining short-pulse laser-excited electrons with long-pulse laser processing under the focusing of a beam-contraction system with a small beam ratio and a large field area, thereby improving the processing range of a single galvanometer deflection.

[0018] 4. This invention reduces the material processing threshold, reduces laser energy in the optical path, and extends the service life of the processing device by combining short-pulse laser-excited electrons with long-pulse laser processing. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system of the present invention.

[0020] Figure 2This is a schematic diagram of the multi-axis galvanometer setup and deflection in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of Bessel beam deflection simulation in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of drilling holes at different locations inside the substrate achieved by mirror deflection in an embodiment of the present invention.

[0023] Figure 5 This is a schematic diagram of irregular hole processing in a Bessel beam deflection drilling experiment using the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides a method for internal material processing based on Bessel beam deflection. Utilizing laser temporal shaping and multi-axis galvanometer deflection technology, it enables rapid translation of a large field region of the Bessel beam without significant beam tilt, while still allowing for internal material processing. The specific steps are as follows: Step 1: Combine a short-pulse laser beam with a long-pulse laser beam to obtain a laser beam. Adjacent short-pulse and long-pulse pulses have a certain time delay. The pulse width of the short-pulse laser is controlled in the femtosecond to picosecond range, while the pulse width of the long-pulse laser is controlled in the picosecond to microsecond range. After the short-pulse laser is incident, electrons in the material are excited. With the subsequent incident of the long-pulse laser, the excited electrons continue to grow, reaching the material modification threshold to achieve material modification or processing. Using a dual-beam configuration enables laser processing at low focusing magnification, and a larger aperture focusing lens can be selected in the system, thereby increasing the processing range of the equipment. Step 2: Introduce the laser beam into the Bessel beam shaping device to perform laser spatial shaping on the original Gaussian pulse beam to generate a Bessel beam; Step 3: Construct a multi-axis galvanometer system. The shaped laser beam is introduced into the multi-axis galvanometer system, which includes a pair of parallel mirrors rotating around the x-axis and a pair of parallel mirrors rotating around the y-axis. The mirrors are placed at a 45° angle to the laser propagation direction. After passing through a pair of mirrors, the laser propagation direction remains unchanged, but the optical axis center shifts. Step 4: Simultaneously control the four mirrors. Rotate the two mirrors rotating around the x-axis by the same angle to achieve translation of the beam in the y-direction; similarly, rotate the two mirrors rotating around the y-axis by the same angle to achieve translation of the beam in the x-direction. Step 5: Focus the energy of the beam using a beam-concentrating system (a 4f beam-concentrating system can be used). Inject the Bessel beam into the transparent material, and control the short pulse excitation to first excite electrons and plasma within the material. After a certain delay, a long pulse laser is then injected to further modify or ablate the material.

[0026] For different materials being processed, different laser light source wavelengths must be selected and the time delay between the two laser pulses adjusted. Simultaneously, the beam-shrinking system must be replaced to ensure that the focused laser beam can achieve internal processing of the material.

[0027] The Bessel beam shaping device in step two includes beam shaping modules such as a conical lens and a spatial light modulator.

[0028] In step three, the galvanometer lens needs to be selected according to the degree of beam divergence to ensure that the beam is confined within the reflected light path.

[0029] The beam deflection path in step four needs to be optimized according to the processing requirements.

[0030] This invention also provides a material internal processing system based on Bessel beam deflection for implementing the method of this invention. The system of this invention is as follows: Figure 1As shown, the system includes: a dual laser source module, a beam combining and detection module, a Bessel beam shaping module, a multi-axis galvanometer deflection module, and a beam shrinking and focusing module. The dual laser source module provides one short-pulse laser beam (in the femtosecond to picosecond range) and one long-pulse laser beam (in the picosecond to microsecond range). The two laser beams are combined using a dichroic mirror (such as a high-pass filter dichroic mirror) and then enter a photodetector via a folding mirror. The time delay between the two laser pulses is precisely adjusted by a signal generator (e.g., a delay of 10 ns). The combined laser beam is first introduced into a Bessel beam shaping device (which can be a conical lens, such as a 2° cone lens, or a spatial light modulator), shaping the original Gaussian pulse beam into a Bessel beam with a longer depth of focus. Subsequently, the shaped beam enters a multi-axis galvanometer system, which includes two pairs of parallel mirrors: one pair rotating around the x-axis and one pair rotating around the y-axis. Each pair of mirrors is placed at a 45° angle to the laser propagation direction, ensuring that the beam's propagation direction remains unchanged after passing through each pair of mirrors, while the optical axis center is translated. By simultaneously controlling the four mirrors, rotating the two mirrors around the x-axis by the same angle achieves beam translation in the y-direction, and rotating the two mirrors around the y-axis by the same angle achieves beam translation in the x-direction, thus enabling arbitrary translation of the beam within the plane. Afterward, the beam exits the galvanometer module and enters a beam-sinking system (a 4f beam-sinking system can be used), for example, a beam-sinking system composed of two achromatic lenses with focal lengths of 400 mm and 50 mm and a center distance of 450 mm, to focus the beam's energy. Finally, the Bessel beam, after being narrowed, is incident on the interior of a transparent material (such as a 500 μm thick glass sample). Short-pulse lasers excite electrons and plasma in the material, and after a certain time delay, long-pulse lasers continue to inject energy, achieving internal modification or ablation of the material. This allows for the rapid processing of high aspect ratio modified structures or irregularly shaped micropores. By using a deflection-and-narrowing beam system, this system prevents beam tilting during rapid beam deflection, enabling rapid laser processing of parallel structures within transparent materials. Furthermore, the use of dual-pulse lasers lowers the processing threshold, allowing for the use of larger aperture focusing lenses to increase the processing range and extend the device's lifespan.

[0031] Processing Example 1: Taking glass as an example, the working steps of the processing method based on the system of the present invention are explained. Specifically, it is a method for rapid processing of the internal modified structure of glass by high-speed deflection of a Bessel beam, including the following steps: Processing systems such as Figure 1As shown, a laser with a repetition frequency of 1 kHz, a center wavelength of 1030 nm, and a pulse width of 270 fs, and a laser with a repetition frequency of 1 kHz, a center wavelength of 1550 nm, and a pulse width of 2 ns are simultaneously incident on a high-pass filtered dichroic mirror. The 1550 nm nanosecond laser passes through the dichroic mirror, while the 1030 nm femtosecond laser is reflected. After the two laser beams are combined, they pass through a folding mirror and enter a photodetector. The peak time delay between the femtosecond laser pulse and the nanosecond laser pulse is adjusted to 10 ns using a signal generator. The laser beam is incident on a conical lens with a 2° cone angle. Two pairs of parallel galvanometers are placed 180 mm away from the conical lens. A schematic diagram of the galvanometer setup is shown below. Figure 2 As shown. The first pair of reflectors, 6 and 7, are slightly deflected around the x-axis, with a distance of 30 mm between them; in the second pair of reflectors, 8 is 50 mm away from reflector 7. Reflectors 8 and 9 are 30 mm apart, and the two reflectors are slightly deflected around the y-axis, achieving lateral translation of the light beam in the horizontal plane.

[0032] Zemax simulation of beam translation distance, i.e., Bessel beam deflection simulation, is as follows: Figure 3 As shown, when reflectors 6 and 7 are simultaneously deflected by 1° while reflectors 8 and 9 remain stationary, the beam center translates 135μm along the y-axis; when simultaneously deflected by 3°, the beam center translates 500μm along the y-axis. Similarly, when reflectors 8 and 9 are simultaneously deflected by 1° while reflectors 6 and 7 remain stationary, the beam center translates a corresponding distance along the x-axis. Simultaneously deflecting all four mirrors allows for arbitrary translation of the beam within a plane.

[0033] After the laser beam exits the galvanometer module, it enters the beam-constricting system. The first achromatic lens has a focal length of 400mm, and the second achromatic lens has a focal length of 50mm. The center distance between the two lenses is set to 450mm, so that the two lenses form a beam-constricting system. After being focused by a beam-constricting system, the laser beam is incident on a glass sample with a thickness of 500 μm. The femtosecond laser, once inside the glass, achieves free electron and plasma excitation in the material. Due to the long axial depth of field of the Bessel beam, the electron excitation region can extend from the upper surface to the lower surface.

[0034] After 1 ns, the plasma inside the material has not yet decayed significantly. The second nanosecond laser beam is incident on the previously generated plasma region, further exciting the material. This causes the ring structure composed of silicon and oxygen atoms in the glass material to recombine, generating a ring structure with a lower number of atoms. The material is then modified or forms micropores.

[0035] By modifying different locations on the same glass substrate, multiple high aspect ratio modified structures can be rapidly processed, improving processing efficiency and quality. Figure 4This involves drilling holes at different locations inside the substrate by deflecting a galvanometer. Each hole is spaced 30 μm apart, and by controlling the galvanometer to deflect in the same direction, multiple parallel micropores can be obtained.

[0036] Processing Example 2: Taking the processing of irregularly shaped micropores inside a material as an example, this paper explains the processing principle. Specifically, it describes a method for rapidly processing irregularly shaped micropores inside transparent materials using high-speed deflection of a Bessel beam. The processing system is as follows: Figure 1 As shown, in this machining example, a Bezier beam capable of rapid translation is used for machining irregularly shaped holes, such as... Figure 5 As shown, the Bessel beam, after passing through the beam-contraction system, is moved along a specific closed curve by controlling the deflection of the galvanometer. During the beam movement, material modification or ablation is achieved along the entire path, forming closed modified or ablated surfaces within the processed material. After solution etching, the central region surrounded by the modified or ablated surfaces detaches, thereby forming irregularly shaped micropores perpendicular to the material surface.

[0037] This invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the scope of protection of this invention.

Claims

1. A method for internal material processing based on Bessel beam deflection, characterized in that, include: A short-pulse laser beam and a long-pulse laser beam are combined. The pulse width of the short-pulse laser is on the order of femtoseconds to picoseconds, and the pulse width of the long-pulse laser is on the order of picoseconds to microseconds. There is a preset time delay between the two laser pulses. The combined beam is then introduced into a Bessel beam shaping device to generate a Bessel beam. The Bessel beam is introduced into a multi-axis galvanometer system, which includes a pair of parallel mirrors rotating about the x-axis and a pair of parallel mirrors rotating about the y-axis, each mirror being at a 45° angle to the laser propagation direction. The four reflectors are deflected synchronously, so that the two reflectors around the x-axis rotate synchronously by the same angle to achieve translation of the beam in the y-direction, and the two reflectors around the y-axis rotate synchronously by the same angle to achieve translation of the beam in the x-direction, thereby achieving arbitrary translation of the beam in the plane. The translated beam is introduced into a beam-concentrating system for energy focusing, and then incident into the interior of a transparent material. Short-pulse lasers are used to excite electrons and plasma in the material, and after the time delay, long-pulse lasers continue to inject energy to achieve internal modification or ablation of the material.

2. The method according to claim 1, characterized in that, The Bessel beam shaping device is a conical lens or a spatial light modulator.

3. The method according to claim 1, characterized in that, The beam-shrinking system is a 4f beam-shrinking system, consisting of two achromatic lenses, with the center distance between the two lenses equal to the sum of their focal lengths.

4. The method according to claim 1, characterized in that, By controlling the deflection of the galvanometer, the Bessel beam is moved along a closed curve to form a closed modified surface or ablation surface inside the material, which, after etching, forms irregular micropores perpendicular to the material surface.

5. A material internal processing system based on Bessel beam deflection, used to implement the method according to any one of claims 1 to 4, characterized in that, include: A dual laser source module is used to provide a short-pulse laser and a long-pulse laser; The beam combining and detection module, including a dichroic mirror, a folding mirror, and a photodetector, is used to combine two laser beams and adjust the time delay between them. The Bessel beam shaping module is used to shape the combined Gaussian beam into a Bessel beam. The multi-axis galvanometer deflection module includes two pairs of parallel mirrors, one pair rotating around the x-axis and the other pair rotating around the y-axis. Each mirror is at a 45° angle to the laser propagation direction. By synchronously controlling the four mirrors, the beam can be translated arbitrarily in the plane. The beam-contraction and focusing module is used to focus the energy of the translated beam and incident the focused Bessel beam into the interior of the transparent material to achieve modification or ablation.

6. The system according to claim 5, characterized in that, The dichroic mirror is used to reflect one laser beam and transmit the other laser beam, so as to combine the two laser beams.

7. The system according to claim 5, characterized in that, In the multi-axis galvanometer deflection module, two pairs of mirrors are arranged sequentially along the optical path, and the rotation axes of each mirror are perpendicular to each other.

8. The system according to claim 5, characterized in that, The beam-contraction focusing module is a 4f beam-contraction system, consisting of two confocal lenses.

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