Transparent laser ceramics is a new type of laser material that has developed vigorously in recent years. The current laser materials on the market are mainly Nd:YAG (neodymium yttrium aluminum garnet) single crystal and neodymium glass. Nd:YAG single crystal has the characteristics of high thermal conductivity, chemical stability and good workability. It is currently widely used as a solid laser medium. Due to its impurity segregation coefficient and size limitation, it has low output power and luminous efficiency. Low and other shortcomings, thus hindering the application of single crystals, and transparent YAG polycrystalline ceramics have easy manufacturing, low cost, large size, high doping concentration, high thermal conductivity, good thermal shock resistance, and can be mass-produced and easily Realizing the advantages of multilayer and multi-functional ceramic structure, it can be used as a laser medium with excellent performance, so as to make up for the lack of single crystal as a laser working material. It is a new type of solid laser material with great potential.
Laser ceramics is one of the research hotspots of laser materials in the 21st century. It was not until 1995 that Japan produced highly transparent Nd:YAG ceramics for the first time. This material has a single crystal, glass laser material incomparable in terms of preparation technology and material properties. The advantages of lasers have received great attention, and the laser output power and laser efficiency have been rapidly improved. The laser output of 1.0at%Nd:YAG transparent ceramics was realized for the first time in China by researchers from Shanghai Institute of Ceramics, Chinese Academy of Sciences in May 2006.
"King of Transparent Ceramics"-Laser Ceramics
Figure. Application of solid-state lasers in laser weapons, laser fusion ignition, laser cutting, laser cladding and other fields via the official website of the Chinese Academy of Sciences Shanghai Institute of Silicon
Laser transparent ceramics are expected to replace the position of crystals and become one of the most widely used laser materials. This is mainly due to the use of mature ceramic production methods in the preparation of laser ceramics, which have very obvious cost advantages. In addition, there are some advantages that single crystals cannot have. In general, laser ceramics have the following advantages over crystals:
① The ceramic 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;
② Ceramics can be prepared into a variety of shapes, and the preparation of large-sized ceramics is an inherent advantage of the preparation method;
③ The 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 different shapes or multilayer materials for sintering, and it is possible to develop multifunctional ceramics.
Compared with glass, laser ceramics have more obvious advantages. This is because the thermal conductivity, hardness, mechanical strength and other properties of laser ceramics are equal to or better than crystals. The main disadvantages of glass laser working materials are in these aspects.
1. Technical difficulties of laser ceramics
As a polycrystalline material, ceramics have internal grain boundaries, pores, and lattice imperfections that will cause opacity of the material and increase light scattering loss, thereby affecting the generation of laser light. On the whole, the difficulties in the preparation of transparent laser ceramics lie in two aspects:
①Transmittance. This is mainly affected by the porosity, grain boundary structure, grain size, raw material purity, etc. inside the material.
② Uniformity. This is affected by the particle size distribution of the raw material powder, the uniformity of the formed body, and the sintering process.
Among them, the optical loss of laser ceramics in light transmittance is mainly caused by optical scattering and optical absorption. Optical absorption involves the conversion of light energy to energy of other properties, while optical scattering does not involve energy conversion, only changing the direction of light propagation. Therefore, the control of the optical loss center is the key to the preparation of high-quality laser ceramics. In-depth research on the formation mechanism of optical scattering and absorption centers is needed, and effective methods to suppress optical loss are proposed.
To solve the above problems, and then to use high-purity raw materials to externally adjust the particle size distribution of the raw material powder, optimize the molding process and sintering process, it is much easier to prepare large-size and excellent performance transparent laser ceramic materials.
2. The strategic significance of transparent laser ceramics
Laser technology has extremely important strategic significance for economic and social development and national security, and laser materials are the core and foundation of laser technology development. As a new generation of solid laser materials-transparent laser ceramics, it is of great significance to national security and the sustainable development of the national economy. It is a model of the integration of structure and function in the field of ceramic materials research. The research of large-size, low-optical scattering loss laser ceramics is very forward-looking, critical and basic, which is of great significance not only to the development of materials science, but also to the development of high-tech industries.