What is Singlemode and Multimode

The mode of a laser usually refers to the state of energy distribution in the plane of the laser perpendicular to the direction of propagation and is divided into single mode and multi-mode. Single mode refers to the laser in the work, only one mode of laser output. Single mode energy intensity from the center to the outer edge of the gradual weakening of the energy distribution in the form of a Gaussian curve, the beam is called the base mode Gaussian beam. Single mode output laser beam has high beam quality, small beam diameter, small divergence angle, energy distribution close to the ideal Gaussian curve, and other characteristics. In addition, the single mode has better-focusing characteristics, small focused spots, and strong mode stability, which is suitable for cleaning scenes that require strong removal, such as rust.

Multi-mode laser output spot is often combined by a variety of modes, the spot energy distribution is more uniform, and the more modes, the more uniform the energy distribution, the beam is also known as the flat-top beam. Compared with single mode, multi-mode laser beam quality is poorer, the divergence angle is larger, requiring a larger aperture optical system transmission and the focusing spot is larger than single mode. However, multimode makes it easier to achieve large single-pulse energy, high peak power, and high average power output with uniform energy distribution, which is advantageous for cleaning scenarios that require low damage and high efficiency, such as molds and dies.

What are the advantages and disadvantages of single-mode vs. multi-mode laser cleaning?

Single-mode lasers are suitable for removing strongly adherent contaminants such as green rust due to their good beam quality, small focused spot,s and high energy density, as well as for cleaning thin materials and precision parts that are sensitive to heat input. However, due to the single-mode energy being too concentrated, in the cleaning may cause some damage to the substrate material.

For the mold and other requirements of the cleaning of the substrate material after the scene without damage, it is necessary to choose a multi-mode laser. The multi-mode beam energy distribution is uniform, high peak power, and the peak power density is higher than the damage threshold of the pollutants and lower than the substrate, so the cleaning can effectively remove the pollutants without destroying the structure of the material surface. In addition, the focused spot of the multimode is larger, and for scenarios in which single-mode and multimode can achieve the same cleaning effect, the cleaning efficiency of the multimode is usually higher. However, for strongly adhering contaminants, multimode laser cleaning may not be sufficient.

Application scenarios of single-mode and multi-mode lasers

Single mode main application scenarios:

Metal Descaling: The high energy density of single-mode lasers makes them ideal for metal descaling, which can efficiently remove the rust layer on metal surfaces, the higher the laser power, the stronger and more efficient the rust spot removal ability. 1000W high power single mode pulsed laser, QBH output for easy integration, with strong cleaning ability, high efficiency, and other advantages.

Weld Oxide Cleaning: In the welding process, due to the high temperature of the process, the weld seam and around the formation of oxides and material precipitation debris is easy to affect the quality and appearance of the weld, 200 ~ 500W single-mode laser, can accurately remove oxides, to ensure that the appearance of the weld and the quality of the weld.

Precision parts cleaning: 100~200W single-mode laser, QCS output, strong cleaning ability, small heat output, small deformation of the material after cleaning, small thermal impact.

Multi-mold main application scenarios:

Mold Cleaning: Molds may accumulate residues during use, such as plastic, metal fragments, dust, etc. These residues will affect the surface quality of the product and cause product defects. Regular cleaning of molds can prevent corrosion and wear, thus extending the service life of the molds. Due to the large difference in the characteristics of the mold substrate and the contaminants, the use of tophat beam can effectively remove the contaminants and do not hurt the mold. 500~1000W square spot multimode laser, high efficiency in cleaning the mold, no damage to the substrate.

Calcium Titanium Ore Cell Edge Cleaning: refers to cleaning the film layer at the edge of the thin film solar cell, creating an insulated area for subsequent encapsulation.1000W pulsed laser, square spot output, uniform energy distribution, high peak power, able to clean the film layer in one go, no damage to the glass, high efficiency.

Laser texturing: Using the laser to burr the material surface can significantly improve the adhesion of the material surface. According to the different requirements of the roughness of the burring, can use 5mJ, 15mJ, and 50mJ different single pulse energy of the multi-mode laser, to ensure the efficiency of the burring at the same time to achieve the different requirements of the roughness?

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1. The energy source (often called the pump or pump source)

2. The gain medium or laser medium

3. Two or more mirrors to form an optical resonant cavity

Pump Sources

The pump source is the part of the laser system that provides the energy for the laser. Examples of pump sources include electrical discharges, flash lamps, arc lamps, light from other lasers, chemical reactions, and even explosive devices. The type of pump source used depends largely on the gain medium, which also determines how the energy is transferred to the medium.

HeNe lasers use a discharge from a helium-neon gas mixture, Nd: YAG lasers use light focused from a xenon flashlamp or diode laser, and excimer lasers use a chemical reaction.

Gain Medium/Laser Medium

The gain medium is the main determinant of the operating wavelength and other characteristics of the laser. Gain media in different materials have a linear spectrum or a broad spectrum. Gain media with a broad spectrum allow the laser frequency to be adjusted. There are hundreds of different gain media that enable laser operation (see the list of laser types for the most important list). Gain media are excited by a pump source to produce a particle number inversion, where spontaneous and excited emission of photons occurs in the gain media, leading to the phenomenon of optical gain or amplification.

Examples of different gain media include:

Liquids, such as dye lasers. These are typically organic chemical solvents, such as methanol, ethanol, or ethylene glycol, to which chemical dyes, such as coumarin, rhodamine, and fluorescein, are added. The exact chemical structure of the dye molecule determines the operating wavelength of the dye laser.

Gases, such as mixtures of carbon dioxide, argon, krypton, and helium-neon. These lasers are usually pumped by a discharge.

Solids, such as crystals and glass. Solid-body materials are usually doped with impurities such as chromium, neodymium, erbium, or titanium ions. Typical hosts include YAG (Yttrium Aluminum Garnet), YLF (Yttrium Lithium Fluoride), Sapphire (Aluminum Oxide), and various types of glass. Examples of solid-state laser media include Nd: YAG, Ti: sapphire, Cr: sapphire (often referred to as ruby), Cr: LiSAF (chromium-doped lithium strontium aluminum fluoride), Er: YLF, Nd: glass, and Er: glass. Solid-state lasers are usually pumped by flash lamps or light from other lasers.

A semiconductor is a solid with a uniform dopant distribution, a crystal, or a material with varying dopant levels in which the movement of electrons can cause lasing. Semiconductor lasers are usually very small and can be pumped with a simple current, allowing them to be used in consumer devices such as compact disk players. See laser diode.

Optical resonator

Optical resonators or optical cavities in their simplest form are two parallel mirrors placed around a gain medium that provide feedback of light. The mirrors are given an optical coating which determines their reflective properties. Typically, one is a high reflector, and the other a partial reflector. The latter is called an output coupler because it allows a portion of the light to leave the cavity to produce the output beam of the laser.

Light from the medium produced by spontaneous radiation is reflected back to the medium by mirrors where it can be amplified by stimulated emission. The light may be reflected from the mirrors and therefore pass through the gain medium hundreds of times before leaving the cavity. In more complex lasers, configurations with four or more mirrors forming the cavity are used. The design and alignment of the mirrors relative to the medium is critical in determining the exact operating wavelength and other properties of the laser system.

Other optical devices, such as rotating mirrors, modulators, filters, and absorbers, can be placed within the optical resonant cavity to have various effects on the laser output, such as changing the operating wavelength or generating laser pulses.

Instead of using an optical cavity, some lasers rely on very high optical gain to produce significantly amplified spontaneous emission (ASE) without the need to feed light back into the gain medium. Such lasers are said to be superluminous and emit low-coherence but high-bandwidth light. Since they do not use optical feedback, these devices are usually not lasers.

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Difference in principle

Pulsed laser cleaning machine: Pulsed laser cleaning machine utilizes high-energy, high-frequency pulsed laser beams to instantly heat and cool the surface of objects, forming instantaneous temperature gradients and thermal stresses, so that pollutants and thin layers of coverings are dislodged from the surface. The principle is to produce high temperature and high pressure instantly through the brief, high-energy irradiation of laser pulses, which rapidly vaporizes or smashes the pollutants and achieves the cleaning effect.

Continuous laser cleaning: Continuous laser cleaning is the continuous emission of laser beams to heat the surface of the object to realize the cleaning effect. Continuous laser is characterized by a continuous and stable output of energy and tends to clean the object’s surface more gently.

Differences in the range of applications

Pulsed Laser Cleaners: Pulsed laser cleaners are widely used in various industries such as automotive manufacturing, electronic equipment, aerospace, semiconductor processing etc. It can be used to remove a variety of contaminants such as paint, oxides, welding slag, and so on. Since pulsed laser cleaning is characterized by high energy and short action time, it is suitable for cleaning objects with high surface requirements.

Continuous laser cleaning: Continuous laser cleaning has some applications in the fields of medical equipment sterilization and paper cleaning. Compared with the pulsed laser, the continuous laser has lower energy and is more suitable for objects that need a continuous heating effect.

Difference three: comparison of cleaning effect

Pulsed laser cleaning machine: A pulsed laser cleaning machine can produce instantaneous high temperature and high pressure, effectively remove the pollutants on the surface of the object, and have a better cleaning effect. Since the pulse laser cleaning machine has less impact on the substrate, it can clean all kinds of surfaces more safely.

Continuous laser cleaning: Due to the lower temperature of continuous laser, the cleaning effect is relatively weak and cannot deal with fragile or easily melted materials. However, continuous laser cleaning is usually effective in cleaning some rougher surfaces.

Separation of equipment cost and operation

Pulsed laser cleaner: Pulsed laser cleaner usually requires higher equipment cost, because it can do zero damage to the collection, suitable for cleaning products with high requirements on the surface of the substrate. At the same time, the operator needs to have certain professional knowledge and skills to ensure safe operation.

Continuous laser cleaners: Compared to pulsed laser cleaners, continuous laser cleaners have lower equipment costs and are suitable for large-scale industrial cleaning needs.

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