Laser is a kind of light that does not exist in nature and is emitted due to excitation. It has the characteristics of good directivity, high brightness, good monochromaticity and good coherence. It has four characteristics that ordinary light does not have: good directivity, high brightness, good monochromaticity and good coherence, which makes it have a large number of applications in various technical fields.
An important development direction of laser technology is solid-state laser with high average power and high peak power, and the core of solid-state laser is solid-state laser working material. At present, there are mainly three kinds of solid-state laser matrix materials: glass, single crystal and ceramic, among which “ceramic” is more favored by high-power lasers. This is because high power will produce thermal gradient, which will lead to beam distortion or thermal birefringence, thus affecting the quality of laser beam. Therefore, ceramic materials with low thermal expansion coefficient and low refractive index are very ideal laser working materials.
In fact, in the past, some ceramics with high performance and complex components could not be applied in laser technology, and other applications would be affected because of the different composition of rare earth metals in ceramics (especially doped ceramics), the interaction with crucible, phase transformation and poor solubility. However, these are the past. Today, the progress of processing technology provides a variety of feasible synthesis methods of transparent ceramics. The surface of the prepared ceramic materials is single crystal, polycrystalline at the atomic level, the grain boundary is clean and thin, there are no pores and impurities, and the ceramics are highly transparent, which is very suitable for generating laser beams. Moreover, it can also be doped with different rare earth elements to make various complex shapes, which greatly increases its practicability.
In general, laser ceramics have the following advantages:
① The preparation time is short, the sintering device does not need precious metal materials, the sintering does not need to be carried out in high-purity protective atmosphere, and the preparation cost is low;
② Large size and complex shape materials can be prepared;
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 component deviation of ceramics is small;
⑤ Ceramics can be made into multilayer materials for sintering, and it is possible to develop multifunctional ceramics.
In contrast, although glass matrix can obtain large-scale samples, its thermal conductivity is too low to realize high-power laser; The thermal conductivity of single crystal is higher than that of glass, but the growth cycle of single crystal is long and the cost is expensive, so it is difficult to obtain high-quality and large-size crystals.
What are the types of laser ceramics?
The preparation of laser ceramics is to sinter nano-sized powder at a certain temperature and ambient atmosphere, so that the powder particles condense into grain combination, and the porous body becomes dense body. In ceramics, the activated ions are randomly distributed in the interior and surface of the grain, and there is no obvious segregation phenomenon. The action of the crystal field, the energy level structure of the activated ions and the electronic energy level jump of the activated ions are similar to those in the crystal. In view of this, corresponding to the crystal classification, the classification of laser ceramics can be roughly divided into three categories: oxide ceramics, fluoride ceramics (including ⅱ – ⅵ compound ceramics) and metal acidifier ceramics.
Oxide ceramics are similar to crystals. They have good mechanical properties such as hardness and brittleness, high thermal conductivity and stable chemical properties. They are suitable for doping rare earth ions (Ln3 +) and transition metal ions (Tm3 +, TM4 +). They are very important matrix materials. Among oxide ceramics with cubic grain structure, the typical representatives are artificial garnet and some Sesquioxides. Artificial garnets include yttrium aluminum garnet (Y3Al5O12 → YAG), yttrium scandium aluminum garnet (y3scal4o12 → YSAG) and gadolinium gallium garnet (Gd3Ga5O12 → GGG). Nd3 +, Er3 +, Yb3 +, Tm3 +, Cr4 + plasma have been doped in the first two substrates and laser oscillation has been realized. YAG Ceramics Doped with these ions have also been commercially applied. Cubic sesquioxide ceramics include Y2O3, Lu2O3, Sc2O3, ygdo3, etc. they are some high melting point laser ceramics that are difficult to grow single crystals. Nd3 + or Yb3 + ions have been doped in these substrates and laser oscillation has been realized. These laser ceramics are superior to YAG ceramics in physical and chemical properties and laser properties, and have great potential in high-power laser and ultrashort pulse applications.
So far, only dysprosium doped calcium fluoride (dy2 +: CaF2) has been reported, and the laser wavelength is 2.36 μ m. It is also the earliest research on laser ceramics. At present, only chromium doped zinc selenide (CR2 +: ZnSe) has been reported. It has a wide tunable band (2000 ~ 3100nm range) in the mid infrared. It will have important applications in high-resolution spectroscopy, medical treatment, lidar and optical parametric oscillator OPO in the future. The research on metal acidification laser ceramics has not been reported.
报错 笔记
However, in any case, science and technology have been making progress. I believe that with the expansion and deepening of the research scope of laser ceramics, better laser ceramic materials will be produced than their predecessors, and finally solid-state lasers will be more widely used.
Source:
Laser ceramics — a new hot spot in the exploration of solid laser working materials, Liu Songhao.
Research status of transparent laser ceramics at home and abroad, Li Xianxue, Qiu Guobiao, Luo Xiaoming, Su Shijie, Chen Yixiang.
Analysis on the development status and future trend of transparent laser ceramics, Chen Jing, Yang Fu, Gao xiane, Zhou Zhipeng.
Whatare Ceramic Laser Materials and How Have they Developed，LiamCritchley.