Ultrahigh repetition frequency ultrafast laser welding method for transparent material

Abstract

The invention provides an ultrahigh repetition frequency ultrafast laser welding method for a transparent material, which comprises the following steps of: stacking the transparent material to be welded above a welding material, and forming optical contact between the transparent material and the welding material; transient electrons are excited in the transparent material by using an ultrahigh repetition frequency ultrafast laser sequence, and pulse sequence parameters of the ultrahigh repetition frequency ultrafast laser sequence are regulated and controlled, so that laser energy required for reaching a melting threshold value of the transparent material and a welding material is minimum, and the welding of the transparent material is realized. According to the method, the interaction process of ultrafast laser and substances is regulated and controlled from the femtosecond-nanosecond time scale through multi-mode ultrahigh repetition frequency ultrafast laser, laser energy deposition is optimized through the transient electron effect excited by the ultrafast laser in a transparent material, and therefore laser energy needed for achieving the material melting threshold value is reduced, and the melting speed of the material is increased. And generation of self-limiting electrons can be inhibited, so that welding stress, local welding defects and the like are optimized, and high-strength and high-stability welding is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of laser processing, and in particular relates to a method for ultra-high repetition rate ultra-fast laser welding of transparent materials. Background Art

[0002] Ultrafast laser welding technology is widely used in high-strength welding of transparent materials because of its selective energy injection characteristics, which can achieve high-precision local material melting and welding. However, laser welding of transparent materials often has local defects, which will limit the achievable welding strength.

[0003] Generally, it is believed that the total energy of the injected ultrafast laser and the surface quality of the sample are the main factors that determine the welding strength. Therefore, when the surface quality of the sample is the same, the smaller the laser energy required to achieve welding, the higher the welding strength that can be obtained. For example, when the samples are in optical contact, compared with a telecentric lens with a large focal length or a general single lens, the spot that can be achieved by focusing with a high-power objective lens is much smaller, the smaller the pulse energy required to melt the material, the smaller the thermal stress generated by welding, and the higher the strength that can be achieved. Therefore, how to further improve the welding strength under the premise of the same sample surface quality and the same focusing state has become a new problem. Summary of the invention

[0004] The purpose of the present invention is to provide a method for ultra-high repetition rate ultra-fast laser welding of transparent materials, which can at least solve some of the defects existing in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for ultra-high repetition rate ultra-fast laser welding of transparent materials, comprising the following process:

[0007] stacking the transparent material to be welded on top of the weld material and forming an optical contact between the two;

[0008] An ultra-high repetition rate ultrafast laser sequence is used to excite transient electrons inside the transparent material, and the pulse sequence parameters of the ultra-high repetition rate ultrafast laser sequence are adjusted to minimize the laser energy required to reach the melting threshold of the transparent material and the welding material, thereby achieving welding of the transparent material.

[0009] Furthermore, the ultra-high repetition rate ultrafast laser sequence adopts MHz-GHz or MHz-THz Bi-Burst mode output.

[0010] Furthermore, in the Bi-Burst mode, the number of sub-pulses within a single pulse sequence is 1-128, the time interval between sub-pulses within a single pulse sequence is 1 fs-100 ps, ​​and the pulse energy is 10 nJ-100 μJ.

[0011] Furthermore, the Bi-Burst mode achieves MHz Bi-Burst output by directly modulating the seed laser pulse of a THz or GHz laser.

[0012] Furthermore, the Bi-Burst mode uses multiple acousto-optic crystals to form P light and S light in space each time the MHz pulse laser passes through an acousto-optic crystal, and utilizes the time delay between the P light and the S light to achieve Bi-Burst output.

[0013] Furthermore, the Bi-Burst mode uses a multi-layer dielectric film to make the MHz pulse laser incident on the multi-layer dielectric film and form multiple reflections, control the thickness of the dielectric film, and shape the single pulse into a THz or GHz pulse output.

[0014] Furthermore, the focusing condition of the ultra-high repetition rate ultrafast laser sequence on the transparent material is that the NA of the objective lens is controlled in the range of 0.1-0.8.

[0015] Furthermore, the ultra-high repetition rate ultrafast laser sequence can melt the transparent material to a diameter no greater than 1 μm and a focal depth greater than 5 μm.

[0016] Furthermore, the welding defect ratio of the transparent material is no more than 1%.

[0017] Furthermore, the transparent material is transparent glass, and the welding material is ceramic material or metal material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method for ultrahigh repetition rate ultrafast laser welding of transparent materials provided by the present invention uses a multi-mode ultrahigh repetition rate ultrafast laser to regulate the interaction process between ultrafast laser and matter from a femtosecond to nanosecond time scale, and utilizes the transient electron action excited by the ultrafast laser inside the transparent material to optimize laser energy deposition, thereby greatly reducing the laser energy required to reach the material melting threshold, achieving micron to hundred nanosecond selected area (micro-area) welding, and can suppress the generation of self-limiting electrons, thereby greatly optimizing welding stress, local welding defects, etc., and achieving high-strength and high-stability welding.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the Bi-Burst output mode of the ultrahigh repetition rate ultrafast laser in the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The prior art CN117773323A discloses a method for high repetition rate ultrafast laser welding of ceramics and transparent materials, which utilizes the action of a high repetition rate ultrafast laser to form a continuous high-temperature plasma to achieve heating and melting of the material. The working principle is to regulate the thermal accumulation effect formed by the ultrafast laser action within a microsecond-nanosecond time scale through a high repetition rate ultrafast laser, thereby increasing the laser energy absorbed by the material and reducing the laser energy required for welding. However, the laser energy that can be injected through the thermal accumulation effect is limited.

[0024] Since the energy absorption process between ultrafast laser and matter is an ultrafast action process, in addition to the heat accumulation and heat diffusion behavior on the microsecond-nanosecond time scale, more importantly, the transient electron activation and the accompanying transient electron density on the femtosecond-picosecond time scale determine the laser energy deposition process and efficiency at the initial stage of ultrafast laser action, fundamentally affecting the welding area, welding strength, defect formation process, etc.; Based on this, this embodiment provides a method for ultrahigh repetition rate ultrafast laser welding of transparent materials, which specifically includes the following processes by regulating the action process between ultrafast laser and matter on the femtosecond-picosecond time scale:

[0025] S1. Overlay the transparent material to be welded on the welding material and form an optical contact between the two. The transparent material may be transparent glass, including but not limited to sapphire glass, quartz glass, soda-lime glass, borosilicate glass, etc.; the welding material may be but not limited to ceramic material, metal material, etc., and the ceramic material may be alumina ceramic, zirconia ceramic, silicon carbide ceramic, etc.

[0026] S2. Use ultra-high repetition rate ultrafast laser to excite transient electrons inside the transparent material, and control the laser energy to reach a preset value so that the transparent material and the welding material reach their melting thresholds to achieve welding of the transparent materials.

[0027] Specifically, the ultra-high repetition rate ultrafast laser is output in a MHz-GHz or MHz-THz Bi-Burst mode (i.e., a pulse sequence fusion mode), such as Figure 1As shown; wherein, the MHz-GHz Bi-Burst mode is that the repetition frequency between pulse sequences is in the MHz order, and the repetition frequency of sub-pulses within the pulse sequence is in the GHz order; the MHz-THz Bi-Burst mode is that the repetition frequency between pulse sequences is in the MHz order, and the repetition frequency of sub-pulses within the pulse sequence is in the THz order. In this embodiment, the ultrafast laser with a MHz repetition frequency between pulse sequences acts on the welding material to generate high-temperature plasma, forming a heat accumulation effect. On this basis, the GHz or THz sub-pulses within a single pulse sequence excite transient electrons with higher density and higher temperature inside the transparent material, thereby improving the laser energy deposition, and then can greatly reduce the laser energy required for the material to achieve the same melting effect, and can achieve high-strength connection of selected transparent materials in a smaller scale (several microns to hundreds of nanometers); and because the overall injected laser energy is smaller, the thermal stress generated by welding is very small, and the heat-affected zone is almost negligible, which has more significant advantages in the field of microelectronic packaging.

[0028] The above-mentioned MHz-GHz or MHz-THz Bi-Burst mode can be realized by shaping the ultrafast laser output by the laser generator in time. Specifically, in some embodiments, the MHz Bi-Burst output can be realized by directly modulating the seed laser pulse of the THz or GHz laser, which is equivalent to the THz or GHz pulse that has been outputting all the time, and adjusting the time to output (on) for a period of time and not output (off) for a period of time to form MHz on / off light. In other embodiments, multiple pieces of acousto-optic crystals can be used. When each MHz pulse laser passes through an acousto-optic crystal with a specific angle, the laser forms P light and S light in space. The two light beams can form a time delay (i.e., the combination of P light and S light forms a THz or GHz pulse) according to the thickness of the crystal due to the difference in transmission speed. According to the thickness and quantity of the acousto-optic crystals, different Bi-Burst outputs can be formed. Special multilayer dielectric films can also be used. Each layer of the dielectric film has a specific reflectivity, transmittance and thickness. When a MHz pulse laser is incident on the crystal, multiple reflections will be formed on the multilayer dielectric film. By controlling the thickness of the dielectric film, a single pulse can be shaped into a specific THz or GHz pulse output.

[0029] Specifically, in the Bi-Burst mode, the number of sub-pulses within a single pulse sequence is designed to be 1-128, the time interval between sub-pulses within a single pulse sequence is 1fs-100ps, and the pulse energy is 10nJ-100μJ; by designing the parameters of this ultrahigh repetition rate ultrafast laser output mode, on the one hand, the plasma shielding of laser excitation can be reduced, and on the other hand, the density of activated transient electrons can be increased, and high-density transient electrons can be used to enhance the laser energy deposition in the initial stage of ultrafast laser action, thereby making the laser injection energy that reaches the material melting threshold smaller.

[0030] In addition, the above-mentioned Bi-Burst mode can also optimize the distribution of transient electrons, form material melting in a deeper focal range, and suppress the generation of self-limiting electrons, thereby greatly optimizing welding stress, local welding defects, etc., and greatly improving welding strength and stability. Specifically, the ultra-high repetition rate ultrafast laser sequence can make the diameter of transparent material melting no greater than 1μm, and the focal depth can reach greater than 5μm; the welding defect ratio of the transparent material is no more than 1%, while the conventional Burst mode, the welding defect ratio will be greater than 5%.

[0031] Optionally, the focusing condition of the ultra-high repetition rate ultrafast laser sequence on the transparent material is that the NA of the objective lens is controlled in the range of 0.1-0.8. By adjusting the NA value of the objective lens and cooperating with the above-mentioned Bi-Burst mode, the melting diameter of the transparent material can be adjusted so that its melting diameter can reach no more than 1μm, and high-strength connection of selected areas of transparent materials can be achieved in a smaller scale (several microns to hundreds of nanometers).

[0032] Through experimental comparison, under the same focusing conditions, the Bi-Burst mode can reduce the laser energy required for the material to reach the melting threshold by about 20%, the welding size by 25%, and the welding depth (i.e., focal depth) by 50%, compared with the existing single-pulse mode. The welding stability is improved to more than 95%.

[0033] The process and effect of ultra-high repetition rate ultrafast laser welding of transparent materials according to the present invention are described below through specific embodiments.

[0034] Embodiment 1:

[0035] This embodiment provides a method for ultra-high repetition rate ultrafast laser welding of transparent materials, including the following process: first, the transparent material to be welded is stacked on top of the welding material, and optical contact is formed between the two; then, the laser outputs ultrafast laser, and the ultrafast laser is output into a MHz-THz Bi-Burst mode through time shaping, and then it is focused on the transparent material after passing through a light speed scanning device and a focusing mirror. Specifically, the laser output ultrafast laser parameters are set as follows: wavelength 1030nm, pulse width 180fs; in the MHz-THz Bi-Burst mode after time shaping, the number of sub-pulses in a single pulse sequence is 5, the sub-pulse time interval is 100fs, the pulse energy is 0.5μJ, and the pulse sequence repetition rate is 10MHz; the focusing NA value is 0.8.

[0036] According to the welding method of this embodiment, it was tested that the melting diameter of the transparent material was 0.8 μm, the welding strength was 70 MPa, and the welding defect ratio was 0.5%.

[0037] Comparative Example 1:

[0038] This comparative example provides a transparent material laser welding method, and its process is roughly the same as that of the above-mentioned embodiment 1, except that the ultrafast laser output by the laser in this comparative example does not undergo time shaping, but is directly focused on the transparent material after passing through a light speed scanning device and a focusing mirror. The ultrafast laser output parameters and the focusing NA value of the laser are consistent with those of the above-mentioned embodiment 1.

[0039] After testing, the melting diameter of the transparent material in this comparative example was 5 μm, the welding strength was 30 MPa, and the welding defect ratio was 8%.

[0040] Comparative Example 2:

[0041] This comparative example provides a transparent material laser welding method, and its process is roughly the same as that of the above-mentioned embodiment 1, except that the laser of this comparative example outputs ultrafast laser and is time-shaped into MHz Burst mode output, and its laser parameters are set as follows: wavelength 1030nm, pulse width 180fs; the number of sub-pulses in a single pulse sequence is 16, the sub-pulse time interval is 10ns, the pulse energy is 2μJ, and the pulse sequence repetition rate is 0.5MHz; the focusing NA value is 0.8.

[0042] After testing, the melting diameter of the transparent material in this comparative example was 10 μm, the welding strength was 35 MPa, and the welding defect ratio was 5%.

[0043] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A method for ultra-high repetition rate ultra-fast laser welding of transparent materials, characterized in that: The process includes the following: stacking the transparent material to be welded on top of the weld material and forming an optical contact between the two; An ultra-high repetition rate ultrafast laser sequence is used to excite transient electrons inside the transparent material, and the pulse sequence parameters of the ultra-high repetition rate ultrafast laser sequence are adjusted to minimize the laser energy required to reach the melting threshold of the transparent material and the welding material, thereby achieving welding of the transparent material.

2. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials according to claim 1, characterized in that: The ultra-high repetition rate ultrafast laser sequence adopts MHz-GHz or MHz-THz Bi-Burst mode output.

3. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: In the Bi-Burst mode, the number of sub-pulses within a single pulse sequence is 1-128, the time interval of sub-pulses within a single pulse sequence is 1 fs-100 ps, ​​and the pulse energy is 10 nJ-100 μJ.

4. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The Bi-Burst mode achieves MHz Bi-Burst output by directly modulating the seed laser pulse of a THz or GHz laser.

5. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The Bi-Burst mode uses multiple acousto-optic crystals to form P light and S light in space each time a MHz pulse laser passes through an acousto-optic crystal. The Bi-Burst output is achieved by utilizing the time delay between the P light and the S light.

6. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The Bi-Burst mode uses a multi-layer dielectric film to make MHz pulse laser incident on the multi-layer dielectric film and form multiple reflections, control the thickness of the dielectric film, and shape the single pulse into THz or GHz pulse output.

7. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The focusing condition of the ultra-high repetition rate ultrafast laser sequence on the transparent material is that the NA of the objective lens is controlled in the range of 0.1-0.

8.

8. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The ultra-high repetition rate ultrafast laser sequence melts the transparent material with a diameter no greater than 1 μm and a focal depth greater than 5 μm.

9. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials as claimed in claim 2, characterized in that: The welding defect ratio of the transparent material is no more than 1%.

10. The method for ultra-high repetition rate ultra-fast laser welding of transparent materials according to claim 1, characterized in that: The transparent material is transparent glass, and the welding material is ceramic material or metal material.

Images