Classification of common light sources for laser engraving machines
Common light sources for laser engraving machines mainly include CO2 light source, fiber light source, and diode light source. Since different materials absorb different wavelengths of laser light, it is necessary to choose according to the characteristics, thickness, processing quality of the processing material, and the requirements for the quality of the laser beam and thermal influence.
Working principle: When direct current is input into the discharge tube, the nitrogen molecules in the gas mixture in the discharge tube are excited by the impact of electrons. The excited nitrogen molecules collide with CO2 molecules. The N2 molecules transfer their own energy to the CO2 molecules. The CO2 molecules change from a low energy level to a high energy level, forming a population reversal to generate laser light.
Features: In the working process, the increase in gas temperature will lead to de-excitation of laser energy level and thermal excitation of lower laser energy level, which will reduce the number of inversion of particles. In addition, the increase in gas temperature will broaden the spectral lines, resulting in a decrease in the gain factor. The increase in gas temperature also causes the decomposition of CO2 molecules and reduces the concentration of CO2 molecules in the discharge tube. These factors will reduce the output power of the laser.
Main fields of application: CO2 laser cutting enables the cutting of highly complex components at a very high speed without stressing and deforming the workpiece. Especially for thermoplastic materials, the cutting section is smooth, but it is also very good at cutting polyester and polycarbonate materials. It is also very effective for cutting clear acrylic sheets.
Working principle: Fiber laser refers to a laser that uses rare earth element-doped glass fiber as the gain media. Under the action of pump light, it is easy to form high power density in the fiber, resulting in the laser energy level “particle population inversion” of the laser working material. Appropriately adding a positive feedback loop (to form a resonant cavity) can form a laser oscillation output.
Features: Due to the small diameter of the fiber core, it is easy to form a high power density in the fiber core, and it has a high conversion rate and a high gain. Fiber lasers use optical fibers as gain media with a large surface area, which enables them to dissipate heat better and have higher energy conversion efficiency than solid-state lasers and gas lasers. Compared with semiconductor lasers, the optical path of fiber lasers is entirely composed of optical fibers and optical fiber components. The optical fiber and optical fiber components are connected by fiber fusion technology. The entire optical path is completely enclosed in the fiber waveguide, which greatly enhances reliability and realizes isolation from the outside world.
Main fields of application: laser marking, black marking on anodized aluminum, laser ink removal, deep hole drilling in ceramics such as zirconia material drilling, glass material drilling, and metal cutting;
Working principle: The P-N junction in a laser diode is formed by two layers of doped gallium arsenide. It has two flat end structures, parallel to one end mirrored (highly reflective surface) and one partially reflective. The wavelength of the light to be emitted is related to the length of the junction. When the P-N junction is forward biased by an external voltage source, electrons move through the junction; when electrons recombine with holes, photons are released. These photons hit the atoms, causing more photons to be released. As the forward bias current increases, more electrons enter the depletion region and cause more photons to be emitted. Eventually, some photons drifting randomly in the depletion region hit the reflective surface vertically, thus reflecting back along their original path, and the reflected photons are reflected back from the other end of the P-N junction again, which repeat many times in succession. As the photons move, more atoms release more photons, creating a very intense laser beam. In order to generate a laser beam, the laser diode current must exceed a certain threshold level.
Features: The intensity of its output light can be directly modulated from the current. In practical applications, the APC circuit is usually used to drive the laser diode, which is built into the same package, and the PD is used for feedback and monitoring the output of LD, so that the output of LD can reach the required constant optical power.
Main fields of application: personalized gift customization, personal home DIY, small and medium-sized business small batch production, etc.