Method for realizing ultra-high-speed translation of Bessel beam by using double acousto-optic modulation elements

Abstract

The invention provides a method for realizing ultra-high-speed translation of a Bessel beam by using double acousto-optic modulation elements, which is characterized in that the displacement in the x-axis direction and the displacement in the y-axis direction are changed at a high speed by quickly switching radio frequencies f1 and f2, so that ultra-high-speed punching on the surface of a workpiece is realized; meanwhile, each hole has excellent morphology consistency due to vertical incidence, so that the problem of hole shape distortion caused by inclined incidence at the scanning edge of a traditional galvanometer is avoided; that is to say, the all-solid-state diffractive optical element is adopted, no mechanical moving part exists, the limitation of mechanical inertia is completely eliminated, the response time of light beam displacement only depends on the change speed of a driving signal and the establishment time of the diffraction effect, the MHz-level control effect can be easily achieved, and the speed is several orders of magnitude faster than that of a traditional galvanometer. The method is especially suitable for application scenes such as laser processing, optical tweezers, confocal microscopic imaging and high-speed optical switches.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, and in particular relates to a method for realizing ultra-high-speed translation of Bessel beams using dual acousto-optic modulation elements. Background Technology

[0002] For micro-hole fabrication, methods such as mechanical drilling, dry etching, and injection molding can be used. However, when it is necessary to fabricate very small micro-holes (down to a few micrometers), laser drilling is an efficient and precise method. Laser drilling places certain demands on both speed and perpendicularity: the drilling speed directly affects production efficiency; to achieve rapid drilling, high-repetition-rate pulsed lasers are typically used. For mass production, high-speed drilling is key to cost reduction. The perpendicularity of the micro-hole is crucial for many applications; the tilt angle of the through-hole can limit application performance.

[0003] In modern optical applications, high-precision and ultra-high-speed control of beam direction and position is crucial for many technologies. For example, in laser micromachining, high-speed movement of the focal point is required to improve processing efficiency; in confocal microscopy, rapid beam scanning is key to real-time imaging. Currently, the most common technique for beam displacement is based on mechanical mirror devices, such as galvanometers. A galvanometer drives a mirror to oscillate at a small angle via a motor, thereby changing the direction of light reflection. However, the inherent inertia of this mechanical motion limits its response speed and acceleration capability, making it impossible to achieve ultra-high-speed parallel beam displacement while maintaining zero-angle deflection. Another approach involves using an acousto-optic modulator (AOD) to generate ultrasonic waves from an electrical signal to form a dynamic refractive index grating in an acousto-optic crystal, achieving beam angle deflection. This is combined with a field mirror to achieve rapid, inertia-free movement of the optical path, using a Bessel beam to process through-holes. While this method can achieve ultra-high-speed, inertia-free, non-mechanical processing, it also alters the beam's incident direction, causing the through-hole to be less than perfectly perpendicular to the processing plane, resulting in a large tilt angle and less than ideal processing results.

[0004] Therefore, how to utilize the ultra-high speed advantage of acousto-optic modulation elements to construct a technical solution that is simple in structure, precise in control, and capable of realizing ultra-high speed parallel displacement of beams to achieve vertical multi-hole processing is an urgent problem to be solved in the current technical field. Summary of the Invention

[0005] To address the bottleneck issue of existing galvanometers or acousto-optic modulators being unable to simultaneously achieve both high speed and zero angle, this invention provides a method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulators. By utilizing dual acousto-optic modulators to convert dual-angle deflection into parallel displacement, ultra-high-speed parallel displacement of the beam is achieved while strictly ensuring that the incident direction of the beam is always perpendicular to the processing surface, thus guaranteeing the uniformity and stability of the multi-hole processing process.

[0006] A method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements includes the following steps: Step 1: Spatial shaping of the femtosecond laser pulse using diffractive optical elements to obtain a Bessel beam; Step 2: The Bessel beam is incident perpendicularly onto the first acousto-optic modulator with an applied radio frequency f1, so that the wavefront of the Bessel beam is modulated by the first acousto-optic modulator, causing the Bessel beam exiting the first acousto-optic modulator to deflect by a preset angle θ1 relative to the incident beam. Step 3: After being deflected by θ1, the Bessel beam propagates in a straight line in free space for a set distance L1 before being incident on the second acousto-optic modulation element. The second acousto-optic modulation element applies a driving signal that is the same frequency as the first acousto-optic modulation element but opposite in direction or conjugate with the first acousto-optic modulation element. Step 4: The second acousto-optic modulator modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the second acousto-optic modulator to change at a preset angle relative to the incident beam. The deflection of θ1 restores the propagation direction of the outgoing beam from the second acousto-optic modulator to be parallel to the incident beam from the first acousto-optic modulator, but a displacement is generated in the lateral coordinate. .

[0007] Furthermore, a method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements further includes the following steps: Step 5: Generate displacement A Bessel beam is incident perpendicularly onto a third acousto-optic modulator with an applied radio frequency f2, so that the wavefront of the Bessel beam is modulated by the third acousto-optic modulator, causing the Bessel beam exiting the third acousto-optic modulator to deflect by a preset angle θ2 relative to the incident beam; wherein the third acousto-optic modulator is orthogonal to the first acousto-optic modulator. Step 6: After being deflected by θ2, the Bessel beam propagates in a straight line in free space for a set distance L2 before being incident on the fourth acousto-optic modulation element. The fourth acousto-optic modulation element is given a driving signal that is the same frequency as the third acousto-optic modulation element but opposite in direction or the same frequency as the second acousto-optic modulation element. The fourth acousto-optic modulation element is orthogonal to the second acousto-optic modulation element. Step 7: The fourth acousto-optic modulation element modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the fourth acousto-optic modulation element to change at a preset angle relative to the incident beam. The deflection of θ2 restores the propagation direction of the outgoing beam from the fourth acousto-optic modulator to be parallel to the incident beam from the third acousto-optic modulator, but a displacement is generated in the longitudinal coordinate. .

[0008] Furthermore, displacement The calculation method is as follows: .

[0009] Furthermore, the distance L2 setting satisfies: L2≠ZDOF Among them, Z DOF The depth of field for the Bessel beam.

[0010] Furthermore, when different displacement amounts are required This is achieved by switching between different radio frequency f2 and setting a distance L2.

[0011] Furthermore, displacement The calculation method is as follows: .

[0012] Furthermore, the distance L1 setting satisfies: L1≠ZDOF Among them, Z DOF The depth of field for the Bessel beam.

[0013] Furthermore, the diffractive optical element is a conical lens.

[0014] Furthermore, when different displacement amounts are required This is achieved by switching between different radio frequency f1 and setting a distance L1.

[0015] Beneficial effects: 1. This invention provides a method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements, which rapidly changes the displacement along the x-axis by quickly switching radio frequency frequencies f1 and f2. and displacement along the y-axis This enables ultra-high-speed drilling on the workpiece surface. Simultaneously, each hole exhibits excellent morphological consistency due to perpendicular incidence, avoiding the hole shape distortion problem caused by tilted incidence at the edge of traditional galvanometer scanning. In other words, this invention employs all-solid-state diffractive optical elements without any moving mechanical parts, completely eliminating the limitations of mechanical inertia. The response time of the beam displacement depends only on the speed of change of the driving signal and the establishment time of the diffraction effect, easily achieving MHz-level control effects, several orders of magnitude faster than traditional galvanometers. It is particularly suitable for applications such as laser processing, optical tweezers, confocal microscopy, and high-speed optical switches.

[0016] 2. This invention provides a method for ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements. The displacement of the beam is directly determined by the driving signal of the acousto-optic modulation elements. Modern signal sources can synthesize frequencies with extremely high precision, thus enabling very accurate and highly repeatable beam position control with extremely high resolution. Attached Figure Description

[0017] Figure 1 A schematic diagram illustrating the working principle of the dual acousto-optic modulation element for ultra-high-speed translation of Bessel beams to prepare multiple apertures, provided by the present invention. Figure 2 This is a schematic diagram illustrating the fabrication of multiple apertures using a dual acousto-optic modulation element to achieve ultra-high-speed parallel displacement processing of a Bessel beam, as provided in this invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0019] Traditional galvanometer or other existing laser processing methods typically rely on a single-angle deflection of the beam to achieve beam scanning or displacement. This deflection inevitably causes the beam to be incident on the processing surface at an angle, introducing a series of serious processing quality problems, including but not limited to focal point shape distortion, uneven processing depth and width, and significant negative impacts on structural symmetry and overall accuracy in micro-nano scale processing. In the processing of multiple holes, this results in a certain tilt angle between the micro-holes and the processing plane, leading to a decrease in processing quality. These angular deviations caused by the tilt of the incident light are key bottlenecks limiting the application of traditional methods in high-precision and complex three-dimensional processing. However, this invention utilizes a unique dual acousto-optic modulation element to achieve ultra-high-speed translation of the Bessel beam to prepare multiple holes. This method achieves ultra-high-speed parallel displacement of the beam while strictly ensuring that the incident direction of the beam is always perpendicular to the processing surface (i.e., zero-angle incident). This completely eliminates all the aforementioned processing defects caused by changes in the incident angle in traditional methods, fundamentally guaranteeing the uniformity and stability of the multiple hole processing process.

[0020] Specifically, a method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements includes the following steps: Step 1: Use a femtosecond laser to generate femtosecond laser pulses with a Gaussian intensity distribution, and then use diffractive optical elements such as conical lenses to spatially shape the femtosecond laser pulses to obtain a Bessel beam; For example, this invention uses a femtosecond laser to generate a Gaussian laser pulse with a center wavelength of 1030 nm, a repetition rate of 100 kHz, a pulse width of 290 fs, and linear polarization. This Gaussian beam is first spatially shaped by a conical lens to transform into a Bessel beam. Bessel beams have the characteristics of no diffraction, high depth of focus, and concentrated central energy, making them very suitable for high-quality deep hole machining.

[0021] Step 2: The Bessel beam is incident perpendicularly onto the first acousto-optic modulator AOD-1 with an applied radio frequency f1, so that the wavefront of the Bessel beam is modulated at a speed on the MHz level by the first acousto-optic modulator AOD-1, so that the Bessel beam exiting from the first acousto-optic modulator AOD-1 is deflected by a preset angle θ1 relative to the incident beam. It should be noted that when ultrasound at radio frequency f1 propagates in an acousto-optic crystal, it causes a periodic change in the crystal's refractive index, similar to generating a phase grating that diffracts the incident light, i.e., it generates a directional deflection of a preset angle θ1.

[0022] Step 3: After being deflected by θ1, the Bessel beam propagates in free space along a straight line for a set distance L1 (e.g., L1 = 200 mm) before being incident on the second acousto-optic modulator AOD-2. The second acousto-optic modulator AOD-2 is given a driving signal that is in the same frequency but opposite or conjugate to the first acousto-optic modulator AOD-1. Step 4: The second acousto-optic modulation element AOD-2 modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the second acousto-optic modulation element AOD-2 to change at a preset angle relative to the incident beam. The compensatory deflection of θ1 restores the propagation direction of the outgoing beam of the second acousto-optic modulator AOD-2 to be parallel to the incident beam of the first acousto-optic modulator AOD-1, but a displacement is generated in the lateral coordinate. ; Displacement The calculation method is as follows:

[0023] The distance L1 is set to satisfy: L1 ≠ ZDOF, where Z DOF The depth of field of the Bessel beam depends on the inherent characteristics of the Bessel beam itself. Therefore, it can be seen that when different displacement amounts are required... This is achieved by switching between different radio frequency f1 and setting a distance L1.

[0024] In other words, the deflection angle can be changed in real time by ultra-high-speed control of the diffraction characteristics or relative positions of the first and second acousto-optic modulation elements. Or the effective propagation distance of the beam between the two elements This will cause the emitted beam direction to remain unchanged (i.e., perpendicular to the hole machining plane), and after the second deflection, the beam's emitted direction will return to parallel to the initial incident direction. However, it will produce a beam of size [missing information] on a plane perpendicular to the propagation direction. The parallel displacement. The displacement can be controlled by rapidly changing the driving signal, i.e., the ultrasonic signal. The ultra-high-speed control enables the processing of ultra-large-scale, irregularly distributed vertical groups of holes. Among these, when... If the angle is too small, the deflection angle An angle much larger than Brewster's angle will cause a significant reduction in diffraction efficiency.

[0025] It should be noted that the Bessel beam, after parallel displacement, enters an objective focusing system. Since the beam is parallel before entering the objective after each displacement, it will always be focused at an angle perpendicular to the workpiece surface after passing through the objective, regardless of its position in the field of view.

[0026] Based on this, the present invention further employs a pair of orthogonal acousto-optic modulators (AOD-3 and AOD-4) configured similarly to AOD-1 and AOD-2, wherein the control units of AOD-1 and AOD-2 rapidly change the displacement along the x-axis by quickly switching the radio frequency f1. The AOD-3 and AOD-4 radio frequency f2 is used to rapidly change the displacement along the y-axis. This enables ultra-high-speed drilling on the workpiece surface. Each hole exhibits excellent morphological consistency due to perpendicular incidence, avoiding the hole shape distortion problem caused by tilted incidence at the edges of traditional galvanometer scanning. See steps five through seven below for details.

[0027] Step 5: Generate displacement A Bessel beam is incident perpendicularly onto a third acousto-optic modulator with an applied radio frequency f2, so that the wavefront of the Bessel beam is modulated by the third acousto-optic modulator, causing the Bessel beam exiting the third acousto-optic modulator to deflect by a preset angle θ2 relative to the incident beam; wherein the third acousto-optic modulator is orthogonal to the first acousto-optic modulator. Step 6: After being deflected by θ2, the Bessel beam propagates in a straight line in free space for a set distance L2 before being incident on the fourth acousto-optic modulation element. The fourth acousto-optic modulation element is given a driving signal that is the same frequency as the third acousto-optic modulation element but opposite in direction or the same frequency as the second acousto-optic modulation element. The fourth acousto-optic modulation element is orthogonal to the second acousto-optic modulation element. Step 7: The fourth acousto-optic modulation element modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the fourth acousto-optic modulation element to change at a preset angle relative to the incident beam. The deflection of θ2 restores the propagation direction of the outgoing beam from the fourth acousto-optic modulator to be parallel to the incident beam from the third acousto-optic modulator, but a displacement is generated in the longitudinal coordinate. .

[0028] Displacement The calculation method is as follows:

[0029] The distance L2 is set to satisfy: L2 ≠ ZDOF, where Z DOF The depth of field of the Bessel beam depends on the inherent characteristics of the Bessel beam itself. Therefore, it can be seen that when different displacement amounts are required... This is achieved by switching between different radio frequency f2 and setting a distance L2.

[0030] Through the above implementation methods, the present invention utilizes dual acousto-optic modulation elements to convert dual-angle deflection into parallel displacement, perfectly solving a series of processing quality problems caused by excessive incident angles in the edge region when using traditional single deflectors (such as galvanometers) for large-format scanning. This provides an innovative solution for achieving ultra-high-speed, high-quality fabrication of irregularly distributed group holes.

[0031] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements, characterized in that, Includes the following steps: Step 1: Spatial shaping of the femtosecond laser pulse using diffractive optical elements to obtain a Bessel beam; Step 2: The Bessel beam is incident perpendicularly onto the first acousto-optic modulator with an applied radio frequency f1, so that the wavefront of the Bessel beam is modulated by the first acousto-optic modulator, causing the Bessel beam exiting the first acousto-optic modulator to deflect by a preset angle θ1 relative to the incident beam. Step 3: After being deflected by θ1, the Bessel beam propagates in a straight line in free space for a set distance L1 before being incident on the second acousto-optic modulation element. The second acousto-optic modulation element applies a driving signal that is the same frequency as the first acousto-optic modulation element but opposite in direction or conjugate with the first acousto-optic modulation element. Step 4: The second acousto-optic modulator modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the second acousto-optic modulator to change at a preset angle relative to the incident beam. The deflection of θ1 restores the propagation direction of the outgoing beam from the second acousto-optic modulator to be parallel to the incident beam from the first acousto-optic modulator, but a displacement is generated in the lateral coordinate. .

2. The method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 1, characterized in that, It also includes the following steps: Step 5: Generate displacement A Bessel beam is incident perpendicularly onto a third acousto-optic modulator with an applied radio frequency f2, so that the wavefront of the Bessel beam is modulated by the third acousto-optic modulator, causing the Bessel beam exiting the third acousto-optic modulator to deflect by a preset angle θ2 relative to the incident beam; wherein the third acousto-optic modulator is orthogonal to the first acousto-optic modulator. Step 6: After being deflected by θ2, the Bessel beam propagates in a straight line in free space for a set distance L2 before being incident on the fourth acousto-optic modulation element. The fourth acousto-optic modulation element is given a driving signal that is the same frequency as the third acousto-optic modulation element but opposite in direction or the same frequency as the second acousto-optic modulation element. The fourth acousto-optic modulation element is orthogonal to the second acousto-optic modulation element. Step 7: The fourth acousto-optic modulation element modulates the wavefront of the incident Bessel beam, causing the Bessel beam exiting the fourth acousto-optic modulation element to change at a preset angle relative to the incident beam. The deflection of θ2 restores the propagation direction of the outgoing beam from the fourth acousto-optic modulator to be parallel to the incident beam from the third acousto-optic modulator, but a displacement is generated in the longitudinal coordinate. .

3. The method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 2, characterized in that, Displacement The calculation method is as follows: 。 4. The method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 2, characterized in that, The distance L2 setting is satisfied as follows: L2≠ZDOF Among them, Z DOF The depth of field for the Bessel beam.

5. The method for achieving ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 2, characterized in that, When different displacements are required This is achieved by switching between different radio frequency f2 and setting a distance L2.

6. The method for ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 1, characterized in that, Displacement The calculation method is as follows: 。 7. The method for ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 1, characterized in that, The distance L1 setting is satisfied as follows: L1≠ZDOF Among them, Z DOF The depth of field for the Bessel beam.

8. The method for ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 1, characterized in that, The diffractive optical element is a conical lens.

9. The method for ultra-high-speed translation of a Bessel beam using dual acousto-optic modulation elements as described in claim 1, characterized in that, When different displacements are required This is achieved by switching between different radio frequency f1 and setting a distance L1.

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