Science | laser and laser crystal

1. Introduction

Laser (light amplification by stimulated emission of radiation) is a major invention in the 20th century. It is called "the fastest knife", "the most accurate ruler" and "the brightest light". It has been widely used in manufacturing and processing, information communication, medical treatment, laser weapons and other military and civilian fields. With the continuous emergence of new lasers and new applications of lasers, laser technology will play an important role in the construction of innovative countries and the promotion of international industrial competitiveness. The development of laser technology in China is very rapid, which can be comparable to the international level in quantity and quality. In view of the importance of the development of laser technology and application, in 2018, the Chinese Academy of Engineering organized the key consulting and research project of "Research on the development strategy of China's laser technology and application in 2035", which is conducive to accelerating the development of China's laser technology and application, and promoting and leading the transformation and upgrading of economic industry.

2. Development history of laser

Laser is a special electromagnetic wave, which is the interaction between light and matter. The basic physical basis of its generation is the theory of stimulated radiation proposed by Einstein in his paper on quantum theory of radiation in 1916. That is, the electrons in the atom will transition from the low energy level to the high energy level after absorbing energy. The atoms at the high energy level can transition to the low energy level under the stimulation or induction of external photons and emit a photon exactly the same as it. In 1953, according to Einstein's principle of stimulated radiation, American physicist Thomas Townes successfully developed a microwave amplifier and won the Nobel Prize in physics in 1964. In 1960, American scientist Meiman developed the world's first ruby laser, marking the beginning of laser research. In the following months, China's first ruby laser was born in the Institute of precision machinery of the Chinese Academy of Sciences. Since then, China's laser technology has developed rapidly.

3. Application of laser

Laser is widely used in industrial manufacturing, information communication, medical beauty, military equipment and other fields because of its high brightness, high directivity, monochromatic and good coherence. The development and integration of laser and related technologies have formed cross technology disciplines such as laser manufacturing, laser detection, laser medical treatment, laser communication and laser weapons, and bred and developed various types of laser industries and series of equipment. Laser technology is an important tool technology. Its application can accelerate the change and reconstruction of the processing and manufacturing industry, medical industry, information communication and other fields. Laser technology is also a basic technology with strong permeability. The economic value of its derived laser products far exceeds its own economic value. In addition, laser technology has a strong ability to incubate new applications, and can continuously integrate with other technologies to create new applications and new industries, with outstanding industry leading characteristics.

In the field of intelligent manufacturing industry, the use of laser technology is the future development trend, which can reflect a country's production and processing level and market competitiveness in manufacturing equipment. It mainly includes laser welding, laser drilling, laser cutting, surface treatment and micro machining, laser ranging, etc. In the process of processing and manufacturing, laser technology has the advantages of high brightness, high efficiency, small focus spot, small heat affected zone, and large deformation of workpiece due to processing. In addition, the processing of laser technology is non-contact, with long service life and high stability. Therefore, laser technology is known as "universal processing tool" and "common processing means of future manufacturing system", which promotes the development of advanced manufacturing industry and has a profound impact on the process of industrial intelligence.

In the field of information communication, laser communication has the advantages of good confidentiality, high communication rate, wide band, anti electromagnetic interference, simple construction and small volume, which is very suitable for large data transmission. It mainly includes atmospheric laser communication, cosmic laser communication, optical fiber laser communication and underwater laser communication. Laser communication is the main way of high-speed Internet and 5g data transmission, and also an important basis for high-precision measurement and sensing, unmanned driving and quantum communication. It is conducive to promoting the implementation of China's development plan for the integration of space, space and sea and the strategy of "maritime power".

In the medical field, laser technology has become an irreplaceable technical means, which is widely used in the treatment of more than 300 diseases such as internal medicine, surgery, dentistry, gynecology, otolaryngology, cardiovascular department, dermatology, and also in the examination and diagnosis of malignant diseases such as tumors. Compared with the effect of traditional surgery, laser surgery has shorter action time, can reduce bleeding and reduce the risk of postoperative bacterial infection. Laser technology leads the transformation of medical treatment mode with its accuracy, minimally invasive or non-invasive.

In the field of national defense, laser has been applied to radar, ranging, imaging, pointing, guidance, communication and countermeasure, which not only improves the performance of weapons and equipment, but also changes the appearance of modern war in a certain sense. The first laser gun was born in the United States. It can blind and detonate at close range. It is called the most powerful individual equipment. In recent years, affected by the rapid development of small UAV applications, the low altitude defense laser system has been rapidly developed as an indispensable means of security for important places and major activities in peacetime.

4. Structure of laser

According to the different working materials, lasers can be divided into solid-state lasers, gas lasers, liquid lasers, semiconductor lasers and free electron lasers. Solid state lasers play an important role in all kinds of lasers due to their high conversion efficiency, good beam quality, high stability, small size and long service life.

The solid-state laser is composed of a laser gain medium, an excitation source and a resonator. The gain medium is the core and consists of a matrix material and an active ion. The matrix materials mainly include glass, ceramic, optical fiber and crystal, and the activated ions mainly include transition group ions and rare earth ions. Crystals have attracted much attention due to their periodicity and anisotropy. Common matrix crystal materials include oxides, fluorides, bromides, etc. After years of development, three kinds of mature laser crystals are: Nd: YAG Crystal suitable for high-power lasers; Nd: YVO4 crystal suitable for low and medium power lasers; Ti: Al2O3 crystal suitable for wavelength tunable and ultrafast lasers. Combined with nonlinear optical effect, ultraviolet, visible, near-infrared and mid far infrared laser output has been realized in various crystal materials, which basically meets the needs of production and life.

5. Future development trend

In the future, China's laser industry will continue to develop rapidly. With the improvement of energy conservation and environmental protection requirements, traditional manufacturing technology upgrading and structural adjustment requirements, mass data high-speed transmission and storage requirements, and long-distance communication requirements, there is a huge development space for laser processing, laser display, laser storage, laser radar, laser radio communication and other technologies, which will require the laser to move towards high power (beat Watt) New wave band (deep ultraviolet, far infrared), miniaturization and integration.