A laser welding method based on variable pulse width double pulse and a multi-scale observation system

Abstract

This invention relates to a laser welding method based on variable pulse width dual pulses and a multi-scale observation system, belonging to the field of femtosecond laser welding application technology. The invention splits a femtosecond laser pulse into two femtosecond laser pulses. One of these pulses is spread into a picosecond-nanosecond pulse with adjustable pulse width using a pulse stretcher. The delay between the two pulses can be controlled using a delay translation stage. This allows the interface to be welded to first be irradiated by the picosecond-nanosecond laser pulse to generate a suitable thermal effect, followed by irradiation by the femtosecond laser pulse to form a "cold weld." By controlling the thermal phase transition process, welding efficiency and performance are improved. Combined with a multi-scale observation system, the welding process can be observed in real time from the femtosecond to the second scale. This invention has the advantages of high efficiency and simplicity, enabling high-quality, high-strength, and high-efficiency welding of difficult-to-machine dissimilar materials.

Description

Technical Field

[0001] This invention relates to a laser welding method based on variable pulse width dual pulses and a multi-scale observation system, belonging to the field of femtosecond laser welding application technology. Background Technology

[0002] Laser welding is a highly efficient and precise welding method that uses a high-energy-density laser beam as a heat source. It is one of the important applications of laser material processing technology. Compared with other joining methods, such as adhesive bonding, solid-state bonding, and anodic bonding, laser welding has advantages such as high precision, small range of metallographic changes in the heat-affected zone, wide range of weldable materials, and no need for a vacuum environment. Femtosecond lasers are pulsed lasers with pulse widths on the order of femtoseconds. Due to their ultrafast and ultra-intense characteristics, femtosecond lasers have irreplaceable advantages in processing transparent sample materials. Therefore, they can join heterogeneous hard and brittle materials under instantaneous high temperature and high pressure, with high welding quality and a small heat-affected zone at the weld interface.

[0003] However, in practical femtosecond laser welding applications, the femtosecond laser is focused onto the interface between two sample layers through the upper transparent sample. Due to the competition between the optical Kerr effect and multiphoton ionization, the laser tends to propagate in a filamentary pattern within the material, causing the laser energy irradiated at the interface between the two sample layers to attenuate. This is detrimental to weld formation and causes filamentary damage to the upper material. In addition, a fixture is required during the welding process to hold the two sample layers together to ensure that the gap between the two sample layers is smaller than the size of the molten pool formed by the melting of the sample, ultimately forming a weld that connects the two sample layers. This poses a severe challenge to achieving welding between difficult-to-machine heterogeneous materials and to observing the interaction process between the laser and the material at the interface between the two sample layers.

[0004] Therefore, this invention provides a multi-scale observation system for a stretchable femtosecond laser dual-pulse laser welding method and welding process, thereby providing a deeper understanding of the mechanistic changes at the interface during laser welding of difficult-to-machine heterogeneous materials, and laying the groundwork for the expansion and practical development of laser welding technology. Summary of the Invention

[0005] The purpose of this invention is to provide a laser welding method and multi-scale observation system based on variable pulse width dual pulses. This method involves splitting a femtosecond laser pulse into two femtosecond laser pulses. One of these pulses is then spread into a picosecond-nanosecond pulse with adjustable pulse width using a pulse stretcher. The delay between the two pulses can be controlled using a delay translation stage. This allows the interface to be welded to first be irradiated by the picosecond-nanosecond laser pulse to generate a suitable thermal effect, followed by irradiation by the femtosecond laser pulse to form a "cold weld." By controlling the thermal phase transition process, welding efficiency and performance are improved. The multi-scale observation system allows for real-time observation of the welding process from the femtosecond to the second scale, enabling an understanding of the laser's interaction mechanism with the two sample interfaces and materials. This avoids the competition between the optical Kerr effect and multiphoton ionization affecting the weld strength and damaging the interior of transparent, hard, and brittle materials. This invention has the advantages of high efficiency and simplicity, enabling high-quality, high-strength, and high-efficiency welding between difficult-to-machine heterogeneous materials. Furthermore, the observation system provides monitoring of the entire welding process across multiple time scales, providing evidence to reveal the transformation process of "thermal processing" between materials and picosecond-nanosecond pulsed lasers and "cold processing" between materials and femtosecond pulsed lasers. This lays the foundation for the application of femtosecond laser welding technology to other heterogeneous materials and has significant application value in fields such as micro-nano processing and aerospace.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] The laser welding method based on variable pulse width dual pulses disclosed in this invention involves a femtosecond laser being split into two femtosecond pulse lasers via a constructed laser processing optical path and a Michelson interferometer. One of the pulses is generated by a pulse stretcher to produce a picosecond-nanosecond pulse laser with an adjustable pulse width, while the other femtosecond pulse laser passes through a mirror on a delay translation stage. The two pulse lasers are then combined by the Michelson interferometer and finally focused by an objective lens to irradiate the sample interface. By adjusting the time interval between the two lasers, the thermal effect is combined with "cold welding" to achieve welding between difficult-to-process heterogeneous materials.

[0008] This invention discloses a variable pulse width dual-pulse laser welding system and a multi-scale observation system for the welding process, used to realize the variable pulse width dual-pulse laser welding method and its multi-scale observation method. The system includes three observation subsystems: a variable pulse width dual-pulse laser welding system, a pump-probe delay generation system, a plasma plume ICCD collection system, and a top-mounted imaging CCD collection system. Through pump-probe technology, side plasma signal observation technology, and real-time monitoring by a computer-controlled camera, the welding process is observed at multiple scales. This avoids the self-focusing effect caused by competition between optical Kerr effect and multiphoton ionization, which splits the focal point and reduces weld strength. Simultaneously, it observes in real-time the splashing of nano-fine particles around the weld caused by sample gaps, preventing welding failure. The combination of femtosecond laser welding and multi-scale observation results in reliable welding results with high repeatability and a small heat-affected zone, meeting the packaging requirements of micro-nano precision electronic devices.

[0009] The variable pulse width dual-pulse laser welding system mainly consists of a laser (and a magnification stage), a mirror, a Michelson interferometer, a pulse stretcher, a delay translation stage, a dichroic mirror, an objective lens, and a three-dimensional translation stage for placing the sample. Through the Michelson interferometer and the pulse stretcher, two laser beams, a picosecond-nanosecond pulse with adjustable pulse width and a femtosecond pulse, are generated and focused by the objective lens at the interface between the two sample layers to achieve dual-pulse laser welding.

[0010] The pump-probe delay generation subsystem mainly consists of a laser (and a magnification stage), a mirror, a BBO crystal, a delay translation stage, a color filter, a CCD camera, a 20X objective lens, and a three-dimensional translation stage for placing the sample. These components enable a femtosecond laser beam to be split into two beams by a beam splitter. The delay between these two pulsed lasers is designed so that the first laser beam serves as the pump light for exciting / ablating the material, while the second laser beam, after a certain delay via the delay translation stage, reaches the irradiation area of ​​the first laser beam for observation. Probe light signals are collected at different delays after femtosecond laser irradiation to study the complete dynamic transient evolution throughout the welding process.

[0011] The plasma plume ICCD collection subsystem mainly consists of a high-speed camera, a microscope tube, and a computer control unit. Before signal collection, the position of the high-speed camera and the magnification of the microscope tube need to be adjusted so that the focus is slightly below the center of the imaging plane. Then, the plasma signal at the weld seam is collected in real time during the welding process, which facilitates timely adjustment of the relative position of the focus and the sample contact interface.

[0012] The top imaging CCD collection subsystem mainly consists of a CCD camera, color filters, a dichroic mirror, and a computer control unit. By connecting the computer to the CCD camera, the imaging signals acquired by the CCD can be output in real time during the welding process.

[0013] This invention discloses a laser welding method based on variable pulse width dual pulses, which achieves direct welding between difficult-to-machine dissimilar materials by combining different pulsed lasers. Furthermore, a multi-scale observation system is used to monitor the welding process and collect real-time signals at multiple scales at the weld seam. The method for welding difficult-to-machine dissimilar materials using variable pulse width dual pulse lasers and the multi-scale observation method include the following steps:

[0014] Step 1: Perform mirror polishing on the materials to be welded. The upper hard and brittle transparent sample (glass, sapphire, ceramic, etc.) needs to be polished on three sides: the upper surface, the lower surface, and the side. The lower sample (metal, ceramic, semiconductor, etc.) needs to be polished on only one side of the welding surface. Place the lower sample material in the groove of the welding fixture and fix it in place. Place the hard and brittle transparent sample on top and tighten the fixture to make the two samples reach optical contact.

[0015] Step 2: Collimate the laser processing optical path. Add a pulse stretcher to one of the laser beam paths, adjust the time interval between the two laser pulses, and adjust the absolute position of the combined laser focus so that the laser passes through the upper sample and focuses on the interface between the two sample layers.

[0016] Step 3: Adjust the top CCD camera so that it can clearly image the space between the two sample layers.

[0017] Step 4: Adjust the delay platform in the pump-probe light delay generation subsystem so that the probe light pulse, after being delayed by the delay platform, illuminates the sample and is reflected into the CCD camera by the beam splitter.

[0018] Step 5: Adjust the relative position of the high-speed camera and the sample so that the side surface of the sample is aligned with the lens barrel of the high-speed camera, and the high-speed camera images the image on the vertical plane where the focal point is located.

[0019] Step 6: Determine the machining path and speed in the welding process;

[0020] Step seven involves laser welding of heterogeneous materials, monitored by a multi-scale observation system. First, pump-probe technology is used to observe the evolution of transient optical properties on the material surface during femtosecond-picosecond-nanosecond timescales, including photon-electron interactions, electron-phonon coupling, and phase transitions. Then, an electronically controlled shutter is opened to perform path laser welding on the sample. Information collected by a high-speed side camera is used to adjust the focus and the relative position of the two sample interfaces in real time. Real-time multi-angle monitoring of the welding process across nanosecond-microsecond-millisecond timescales avoids focus shift caused by self-focusing, which reduces the irradiation energy at the welding interface and results in low weld strength. Finally, top-mounted CCD imaging is used to observe the welding process on the millisecond-second timescale, checking for the ejection of fine particles from the weld seam at different sample gaps to prevent welding failure due to excessively large sample gaps. This combination of multi-scale observation and femtosecond laser welding ensures reliable welding results, a clear welding process, and a well-defined welding mechanism, meeting the packaging requirements of precision microelectronic devices.

[0021] Beneficial effects:

[0022] 1. The laser welding method based on variable pulse width dual pulse disclosed in this invention makes full use of the thermal effect of picosecond-nanosecond pulse laser processing and combines the "non-thermal" effect of femtosecond pulse laser. While ensuring welding efficiency, it can also improve the performance of laser processing. By controlling the cold and hot phase transition process, it can improve welding quality and welding strength.

[0023] 2. The multi-scale observation system for variable pulse width dual-pulse laser welding disclosed in this invention observes the welding process across 13 time scales from femtosecond to second through three subsystems. A top-mounted CCD camera observes transient reflectivity evolution images, a side high-speed camera observes the plasma morphology at the weld seam, and a top-mounted CCD camera observes weld seam formation and surrounding material particle sputtering in real time. This provides a clear view of the entire laser-material interaction process during welding, revealing the formation mechanism of weld seams at the interface of heterogeneous material samples in femtosecond laser welding. By observing the welding process through the three subsystems, nonlinear absorption and self-focusing of the laser in hard and brittle materials can be effectively avoided. This allows for timely adjustment of the relative positional relationship between the laser focus and the sample interface, reducing laser energy loss and damage to the upper hard and brittle material caused by focus splitting. In other words, the combination of multi-scale, multi-angle observation and femtosecond laser welding improves the controllability of femtosecond laser welding. This invention is applicable to welding between almost all hard and brittle materials and non-hard / brittle / hard materials (ceramics and alloys, ceramics and sapphire, etc.), producing stable, reliable, and repeatable welding results with high experimental efficiency. Attached Figure Description

[0024] Figure 1 This is a flowchart of a laser welding method based on variable pulse width dual pulses and a multi-scale observation method for the welding process.

[0025] Figure 2 This is a structural diagram of the optical path and multi-scale observation system for variable pulse width dual-pulse laser welding.

[0026] Figure 3 To capture transient reflectivity images of the alloy surface using pump-probe technology, revealing the interaction process between laser and alloy within the femtosecond-nanosecond timescale, the dynamics of femtosecond laser ablation were studied across timescales.

[0027] Figure 4 The figure shows the plasma luminescence morphology at the weld joint during the welding process. It illustrates the plasma at the interface under varying laser parameters. With different pulse numbers and laser energies, the laser's self-focusing effect is strong, leading to focal point splitting and low weld strength. Therefore, the laser focal point position must be adjusted to avoid focal point splitting and ensure weld strength.

[0028] Figure 5 The image shows the formation of the weld seam during the welding process as observed by the top CCD camera, with sample sputtering nanoparticles present around the weld seam.

[0029] Among them, 1—beam splitter, 2—first reflecting mirror, 3—Michelson interferometer, 4—pulse stretcher, 5—second reflecting mirror, 6—third reflecting mirror, 7—first delay translation stage, 8—fourth reflecting mirror, 9—fifth reflecting mirror, 10—first dichroic mirror, 11—color filter, 12—CCD camera, 13—BBO crystal, 14—sixth reflecting mirror, 15—seventh reflecting mirror, 16—second delay translation stage, 17—eighth reflecting mirror, 18—second dichroic mirror, 19—focusing objective lens, 20—processed sample, 21—three-dimensional precision translation stage, 22—lens tube, 23—high-speed camera ICCD, 24—computer control unit, 25—femtosecond laser. Detailed Implementation

[0030] To better understand the method of the present invention, the technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0031] like Figure 1As shown in this embodiment, a laser welding method based on variable pulse width dual pulses and a multi-scale observation system for the welding process are disclosed. This method combines the advantages of picosecond-nanosecond pulsed laser processing with those of femtosecond laser processing. The two laser pulses are reflected by several mirrors and focused onto the sample interface through an objective lens. This ensures both the processing efficiency and performance of laser welding. By controlling the thermal phase transition process, the welding quality and strength are improved. It also reduces the filamentary damage caused by the femtosecond laser passing through the transparent sample, reduces the focal length at the weld, and increases the light intensity, thus ensuring better welding results. Combined with the multi-scale observation system, the observation results guide the realization of high-quality welding of difficult-to-machine heterogeneous materials.

[0032] like Figure 2 As shown, the variable pulse width dual-pulse laser welding system and multi-scale observation system include three observation subsystems: a pump-probe delay generation system, a plasma plume ICCD collection system, and a top imaging CCD collection system.

[0033] The variable pulse width dual-pulse laser welding system mainly consists of a femtosecond laser 25 (and its amplification stage) emitting laser light, which is reflected by the first reflector 2 and split into two pulsed laser beams by the Michelson interferometer 3. One beam is expanded into a picosecond-nanosecond pulsed laser by the pulse stretcher 4 and reflected by the second reflector 5. The other femtosecond pulsed laser beam is reflected by the third reflector 6 on the first delay translation stage 7. The two pulsed laser beams are then combined again by the Michelson interferometer 3. Adjusting the delay translation stage 7 can control the time interval between the two pulsed laser beams. The combined pulsed laser beam is reflected by the fourth reflector 8, the fifth reflector 9, and the first dichroic mirror 10. Finally, it is focused by the focusing objective 19 onto the processing sample 20 on the three-dimensional precision translation stage 21, realizing dual-pulse laser welding of picosecond-nanosecond pulsed laser and femtosecond pulsed laser.

[0034] The pump-probe delay generation subsystem mainly consists of a femtosecond laser 25 (and its amplification stage) emitting laser light, which is split into pump light and probe light by a beam splitter 1. The pump light serves as the excitation source, is reflected by the first mirror 2, passes through a Michelson interferometer 3, is reflected by the third mirror 6, is reflected by the fourth mirror 8, is reflected by the fifth mirror 9, is reflected by the first dichroic mirror 10, passes through the second dichroic mirror 18, and is irradiated onto the processed sample 20 on the three-dimensional precision translation stage 21 by a focusing objective lens 19. The probe light is frequency-doubled to other wavelengths by a BBO crystal 13, is reflected by the sixth mirror 14, is reflected by the seventh mirror 15, and so on. The seventh mirror 15 and the seventh reflector 15 are located on the second adjustable delay translation stage 16. Adjusting the delay translation stage can change the time interval between the probe light and the pump light, thereby observing the transient reflectivity image of the sample surface under different delays. The probe light continues to be reflected by the eighth reflector 17, then by the second dichroic mirror 18, and irradiates the processed sample 20 on the three-dimensional precision translation stage 21 through the focusing objective lens 19. The light reflected from the sample surface passes through the second dichroic mirror 18 and the second dichroic mirror 10, passes through the color filter 11, and carries the detection information under different delays into the CCD camera 12. The CCD camera is connected to the computer control unit 24 via a wired connection, which displays the observed information; as shown in the image. Figure 3 As shown, the sample is excited by pump light, and the probe light generates a time difference with the pump light through the second delay translation stage. The CCD camera collects the transient surface reflectivity image with a delay of 0-1000ps, thereby guiding the high-quality processing of the welding process.

[0035] The plasma plume ICCD collection subsystem mainly consists of a high-speed camera ICCD 23, a lens barrel 22, and a computer control unit 24. During processing, the computer control unit 24 transmits the plasma signals collected during the welding process via a wired connection to the high-speed camera ICCD. Before signal collection, the position of the high-speed camera and the magnification of the lens barrel need to be adjusted so that the focus is slightly below the center of the imaging plane, ensuring the integrity of the real-time acquisition of plasma information at the weld seam during the welding process; as... Figure 4 As shown, the morphology of the plasma changes under different parameters. In particular, the nonlinear focal shift phenomenon that occurs when the laser welds through a transparent sample can lead to a decrease in welding strength. Therefore, it is necessary to analyze and collect information and adjust the relative position of the focal point and the sample contact interface in a timely manner to ensure welding strength.

[0036] The top-mounted imaging CCD collection subsystem mainly consists of a CCD camera 22 that feeds back the welding image to a computer 27 for display, a laser objective lens 23 that focuses the laser light onto the welding interface, and the reflected light passing through a dichroic mirror 19, a sleeve lens 20, and a color filter 21 before finally entering the CCD camera 22 for imaging; as shown in... Figure 5As shown, the welding process under optical contact conditions allows for clear observation of the weld shape and debris around the weld.

[0037] The operation and fine-tuning methods of the laser welding method based on variable pulse width dual pulses and the multi-scale observation system for the welding process disclosed in this example are as follows:

[0038] Step 1: Polish the materials to be welded. The upper hard and brittle transparent sample is polished on three sides (upper, lower and side surfaces), while the lower sample (metal, ceramic, semiconductor, etc.) is polished on one side only. Place the lower material on a three-dimensional translation stage, place the hard and brittle transparent sample on top, and use a special fixture to clamp the double-layer sample to achieve optical contact (judgment method: the contact surface produces Newton's rings visible to the naked eye).

[0039] Step 2: Collimate the laser processing optical path. Add the pulse stretcher 4 to one of the laser beams generated by the Michelson interferometer 3. Adjust the first delay translation stage 7 to control the time interval between the two pulsed lasers. After focusing by the focusing objective 19, adjust the absolute position of the laser focus so that the laser passes through the upper sample and is focused on the interface between the two sample layers.

[0040] Step 3: Adjust the top CCD camera 12 so that it can clearly image the image between the two sample layers 20;

[0041] Step 4: Adjust the second delay translation stage 16 in the probe light delay generation subsystem. The pump light propagates through several mirrors and is focused onto the sample surface by the focusing objective 19 to excite the sample. The probe light passes through the BBO crystal 13, the sixth mirror 14 and the seventh mirror 15 on the second delay translation stage, and is finally focused onto the sample surface by the focusing objective 19 to detect the transient reflectivity image of the sample surface under different delays.

[0042] Step 5: Adjust the relative positions between the high-speed camera ICCD 23, the lens barrel 22 and the sample 20, so that the side parabolic surface of the sample is aligned with the high-speed camera lens barrel 22, and the high-speed camera ICCD 23 images the sample onto the vertical plane where the focal point is located.

[0043] Step 6: The computer control unit 24 controls the three-dimensional precision translation stage 21 to determine the processing path and processing speed in the welding process;

[0044] Step 7: Begin laser welding of heterogeneous materials. Optimize the welding result by adjusting the time interval between the two laser pulses. Monitor the process using a multi-scale observation system. First, use pump-probe technology to observe the evolution of transient optical properties on the material surface during femtosecond-picosecond-nanosecond timescales, including photon-electron interactions, electron-phonon coupling, and phase transitions. Then, open the electronically controlled shutter to perform path laser welding on the sample. Information collected by a high-speed side camera is used to adjust the focus and the relative position of the two sample interfaces in real time. Real-time multi-angle monitoring of the welding process within the nanosecond-microsecond-millisecond timescales prevents focus shift caused by self-focusing, which reduces the irradiation energy at the welding interface and results in low welding strength. Finally, observe the welding process on the millisecond-second timescale using a top-mounted CCD imager to check for the ejection of fine particles from the weld seam under different sample gaps, preventing welding failure due to excessively large sample gaps. This combination of multi-scale observation and femtosecond laser welding ensures reliable welding results, a clear welding process, and a well-defined welding mechanism, meeting the packaging requirements of precision microelectronic devices.

[0045] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser welding method based on variable pulse width dual pulses, characterized in that: By splitting a femtosecond pulsed laser beam into two femtosecond pulsed laser beams, one of which is spread into a picosecond-nanosecond pulse with adjustable pulse width using a pulse stretcher, and adjusting the delay between the two pulses using a delay translation stage, the interface to be welded is first irradiated by the picosecond-nanosecond pulsed laser to generate an appropriate thermal effect, and then irradiated by the femtosecond pulsed laser to form a "cold weld". By combining the thermal effect with "cold weld", welding between difficult-to-machine dissimilar materials can be achieved; and welding efficiency and welding performance can be improved by controlling the cold and hot phase transition process.

2. An apparatus for implementing the method of claim 1, characterized in that: The device is called a multi-scale observation system; the system includes a variable pulse width dual-pulse laser welding system, a pump-probe delay generation subsystem, a plasma plume ICCD collection subsystem, and a top imaging CCD collection system; The variable pulse width dual-pulse laser welding system generates two laser beams, a picosecond-nanosecond pulse with adjustable pulse width and a femtosecond pulse, through a Michelson interferometer and a pulse stretcher. These beams are then focused onto the interface between two sample layers by an objective lens to achieve dual-pulse laser welding. The pump-probe delay generation subsystem splits a femtosecond laser beam into two laser beams via a beam splitter. The delay between these two pulsed laser beams is adjustable. The first laser beam is used as the pump light to excite / ablate the material. The second laser beam reaches the irradiation area of ​​the first laser beam after a certain delay via a delay translation stage for observation. The probe light signals are collected at different delays after femtosecond laser irradiation to study the complete dynamic transient evolution of the entire welding process. Before signal collection, the plasma plume ICCD collection subsystem needs to adjust the position of the high-speed camera and the magnification of the lens barrel so that the focus is located slightly below the center of the imaging plane. Then, the plasma signal at the weld seam is collected in real time during the welding process, which facilitates timely adjustment of the relative position of the focus and the sample contact interface. The top-mounted imaging CCD collection subsystem connects to a CCD camera via a computer and outputs the imaging signals acquired by the CCD in real time during the welding process.

3. A method for welding dissimilar materials using the apparatus as described in claim 2, characterized in that: Includes the following steps: Step 1: Perform mirror polishing on the materials to be welded. The upper hard and brittle transparent sample needs to be polished on three sides: the upper surface, the lower surface, and the side. The lower sample needs to be polished on the welding surface only. Place the lower sample material in the groove of the welding fixture and fix it in place. Place the hard and brittle transparent sample on top and tighten the fixture to make the two samples reach optical contact. Step 2: Collimate the laser processing optical path. Add a pulse stretcher to one of the laser beam paths, adjust the time interval between the two laser pulses, and adjust the absolute position of the combined laser focus so that the laser passes through the upper sample and focuses on the interface between the two sample layers. Step 3: Adjust the top CCD camera to enable it to clearly image the space between the two sample layers; Step 4: Adjust the delay platform in the pump-probe light delay generation subsystem so that the probe light pulse, after being delayed by the delay platform, illuminates the sample and is reflected into the CCD camera by the beam splitter. Step 5: Adjust the relative position of the high-speed camera and the sample so that the side surface of the sample is aligned with the lens barrel of the high-speed camera, and the high-speed camera images the image on the vertical plane where the focal point is located. Step 6: Determine the machining path and speed in the welding process; Step 7: Begin laser welding of heterogeneous materials and monitor the process using a multi-scale observation system. First, using pump-probe technology, observe the evolution of photon-electron interactions, electron-phonon coupling, and transient optical properties during phase transitions on the femtosecond-picosecond-nanosecond timescales of the material surface irradiated by femtosecond lasers. Then, open the electronically controlled shutter to perform path laser welding on the sample. Information collected by a high-speed side camera is used to adjust the focus and the relative position of the two sample interfaces in real time. Monitor the welding process in real time from multiple angles within the nanosecond-microsecond-millisecond timescales to avoid focal shift caused by self-focusing, which reduces the irradiation energy at the welding interface and results in low welding strength. Finally, observe the welding process in the millisecond-second timescale using top CCD imaging to check for the ejection of fine particles at the weld seam under different sample gaps, preventing welding failure due to excessively large sample gaps.

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