Why is ceramic used as a laser material?
Laser is a kind of light emitted by excitation that does not exist in nature. It has four major characteristics that ordinary light does not possess: good directionality, high brightness, good monochromaticity, and good coherence, making it widely used in various technical fields.
An important development direction of laser technology is solid-state lasers with high average power and high peak power, and the core of solid-state lasers is the solid-state laser working material. At present, there are three main solid-state laser matrix materials commonly used: glass, single crystal and ceramics, among which "ceramics" are more favored by high-power lasers. This is because high power will produce a thermal gradient, which in turn will cause beam distortion or thermal birefringence, thereby affecting the quality of the laser beam. Therefore, ceramic materials with a low thermal expansion coefficient and low refractive index are ideal laser working materials.
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In fact, in the past, some high-performance, more complex ceramics could not be used in laser technology, and due to the different composition of rare earth metals in ceramics (especially doped ceramics), the interaction and phase with the crucible Problems such as change and poor solubility will affect other applications. However, these are all in the past. The advancement of processing technology now provides a variety of feasible transparent ceramic synthesis methods. The surface of the prepared ceramic material is single crystal, polycrystalline at the atomic level, and the grain boundaries are clean and thin, without pores and no Impurities, ceramics are highly transparent, very suitable for generating laser beams. It can also be doped with different rare earth elements to make various complicated shapes, which greatly increases its practicability.
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In general, the current laser ceramics have the following advantages:
①The preparation time is short, the sintering device does not require precious metal materials, and the sintering does not need to be carried out in a high-purity protective atmosphere, and the preparation cost is low;
②Materials with large size and complex shapes can be prepared;
③The concentration of doped particles in ceramics is high, and the distribution of doped particles is uniform on the whole;
④ The sintering temperature of ceramics is much lower than the melting point of crystals, and the composition of the prepared ceramics has little deviation;
⑤ Ceramics can be made into multilayer materials for sintering, and it is possible to develop multifunctional ceramics.
In contrast, although the glass matrix can obtain large-scale samples, its thermal conductivity is too low to realize high-power lasers; the thermal conductivity of single crystals is higher than that of glass, but single crystals have a long growth cycle and are expensive. It is difficult to obtain high-quality, large-sized crystals.