In industrial production, cleaning is a vital link. Although traditional cleaning methods, such as mechanical cleaning and chemical cleaning, can meet production needs to a certain extent, they often have problems such as low flexibility and environmental pollution. With the advancement of science and technology, laser cleaning technology has gradually become a new favorite in the cleaning field with its high efficiency, environmental protection, and non-contact characteristics. Among them, single-mode and multi-mode in fiber pulse lasers are the two most commonly used laser types. So, what are the differences between them? What are their respective advantages and disadvantages? What application scenarios are they suitable for? This article will reveal them to you one by one.
What are multi-mode and single mode laser?
The mode of a laser usually refers to the energy distribution state in a plane perpendicular to the propagation direction of the laser, which can be divided into single-mode and multi-mode. Single mode laser refers to the single distribution mode of laser energy in a two-dimensional plane when the laser is working. The energy intensity of a single mode gradually decreases from the center to the outer edge, and the energy distribution is in the form of a Gaussian curve. Its beam is called a fundamental mode Gaussian beam. The laser beam output by a single mode has the characteristics of high beam quality, small beam diameter, small divergence angle, and energy distribution close to the ideal Gaussian curve. In addition, the single mode has better focusing characteristics, a small focused spot and strong mode stability, which is suitable for cleaning scenarios that require strong removal, such as rust.
Figure 1：Schematic diagram of single-mode energy distribution
Multimode lasers are spatial energy distribution modes formed by the superposition of multiple distribution modes. The energy distribution in the spot is relatively uniform, and the more modes there are, the more uniform the energy distribution is. Its beam is also called a flat-top beam. Compared with single-mode, multimode lasers have poorer beam quality and a larger divergence angle. They require an optical system with a larger aperture for transmission, and the focused spot is larger than that of single-mode. However, multimode is easier to achieve large single pulse energy, high peak power, and high average power output, and the energy distribution is uniform, which is more advantageous for cleaning scenarios that require less damage and high efficiency, such as molds.
Figure 2：Schematic diagram of multi-mode energy distribution
What are the advantages and disadvantages of multi mode and single mode laser cleaning?
Single mode lasers are suitable for removing strongly adherent contaminants such as rust, and for cleaning thin materials and precision parts that are sensitive to heat input, due to their good beam quality, small focused spot, and high energy density. However, since the single-mode energy is too concentrated, it may cause some damage to the base material during cleaning.
For scenes such as molds that require no damage to the substrate after cleaning, multi-mode lasers must be used. Multi-mode beams have uniform energy distribution and high peak power, and can control the peak power density to be higher than the damage threshold of the contaminants but lower than the substrate. Therefore, during cleaning, contaminants can be effectively removed without damaging the surface structure of the material. In addition, the multi-mode focused spot is larger. For scenes where single-mode and multi-mode can achieve the same cleaning effect, the multi-mode cleaning efficiency is usually higher. However, for strongly attached contaminants, multi-mode laser cleaning may not be able to do it.
Figure 3：Comparison of single-mode and multi-mode cleaning capabilities
Application scenarios of multi-mode and single mode lasers
Based on the respective advantages and disadvantages of single-mode and multi-mode cleaning lasers, the application scenarios in which they are applicable are also different.
Single mode laser main application
- Metal rust removal: The high energy density of single-mode lasers makes them an ideal choice for metal rust removal. They can efficiently remove the rust layer on the metal surface. The higher the laser power, the stronger the rust removal ability and the higher the efficiency. Choose a 1000W high-power single-mode pulsed laser. The QBH output is easy to integrate and has the advantages of strong cleaning ability and high efficiency.
Figure 4：Metal rust removal
- Weld oxide cleaning: During the welding process, due to the high processing temperature, oxides and material precipitation debris are easily formed in the weld and its surroundings, affecting the welding quality and appearance. Selecting a 200~500W single-mode laser can accurately remove oxides to ensure the appearance and quality after welding.
Figure 5：Weld oxide cleaning
- Precision parts cleaning: 100~200W single-mode laser, QCS output, strong cleaning ability, low heat output, small deformation of materials after cleaning, and small thermal impact.
Figure 6：Precision parts cleaning
Main application of multi-mode laser
- Mold cleaning: During the use of the mold, residues such as plastic, metal fragments, dust, etc. may accumulate. These residues will affect the surface quality of the product and cause product defects. Regular mold cleaning can prevent corrosion and wear, thereby extending the service life of the mold. Due to the large difference in the characteristics of the mold substrate and the contaminants, the use of a flat-top beam can effectively remove the contaminants without damaging the mold. Choose a 500~1000W square spot multimode laser to clean the mold efficiently without damaging the substrate.
Figure 7：Mode cleaning
- Perovskite cell edge cleaning: refers to cleaning the film layer at the edge of the thin-film solar cell to create an insulating area, which is conducive to the subsequent packaging work. Using multi-mode lasers, square spot output, uniform energy distribution, high peak power, it can clean the film layer at one time without damaging the glass and high efficiency.
Figure 8：Perovskite cell edge cleaning
- Laser texturing: Using laser to texturize the material surface can significantly improve the adhesion of the material surface. According to different texturing roughness requirements, you can choose multi-mode lasers with different single pulse energies of 5mJ, 15mJ, and 50mJ to ensure texturing efficiency while achieving different roughness requirements.
Figure 9：Laser texturing
Summarize
The single mode laser has the characteristics of high beam quality and strong cleaning ability, while the multi-mode series has the characteristics of flat-top beam, high energy, long focal depth, and little or no damage to the substrate.
When choosing a single-mode or multi-mode cleaning laser, customers can make comprehensive considerations based on their actual needs and application scenarios. For the cleaning of delicate parts or strongly attached contaminants, such as metal oxide layers and coatings, the high beam quality and small spot of the single-mode series laser will provide a more precise and powerful cleaning effect. For occasions with large cleaning areas or strict requirements on substrate damage, such as molds, rust spots, oil stains, and thin coatings, the high energy and flat top light of the multi-mode series laser will ensure higher cleaning efficiency and non-destructive cleaning.