Rare earth Laser Materials

Rare earth Laser Materials

一、Rare earth Laser Materials
Laser is a new type of light source, it has good monochrome, directional and coherent, and can achieve high brightness. Various crystals, such as nonlinear crystals, which are corresponding to the laser technology, can adjust the laser beam for frequency modulation, amplitude modulation, deflection and phase modulation, and can correct the distortion of the laser image during transmission, and the pyroelectric detection crystal can detect the infrared light sensitively. These features enable lasers to be applied quickly to the industrial, agricultural, medical and defense sectors.

Lasers and rare earth laser materials were born at the same time. So far, about 90% of all laser materials involve rare earths. Since the advent of the laser in Ruby in the 1960, the same year has seen the use of samarium-doped calcium fluoride (caf2:sm2+) to output pulsed lasers. In the 1961, the use of neodymium-doped silicate glass to obtain pulsed lasers has opened up a wide range of uses of rare earth glass lasers. 1962 first using cawo4:nd3+ Crystal output CW Laser, 1963 first developed rare earth chelate liquid laser materials, the use of europium-doped benzene acetone alcohol solution to obtain pulsed laser, 1964 found in the room temperature can be output continuous laser neodymium doped yttrium aluminum garnet crystals (y3al5o12: nd3+).

It has become a widely used solid-state laser material, for the first time in 1973 to achieve europium-helium laser oscillation of rare earth metal vapor. Thus, in a short span of more than 10 years, the solid, liquid and gaseous state of rare earths have been stimulated. In laser working materials, rare earths have become a very important element of the family. This is related to its special electronic configuration, many available energy levels and spectral properties.

Rare earth laser materials can be divided into: solid, liquid and gas three major categories. But the latter two categories are far inferior to solid materials due to their properties, types and applications. So it is generally said that rare earth laser materials usually refer to solid-state lasers. Solid materials are divided into crystal, glass and fiber laser materials, while laser crystals dominate.

二、Rare earth Solid-State laser material

1. Rare earth Crystal laser materials
About 320 kinds of laser crystals are known, mainly oxygen-containing compounds or fluorine-containing compounds, about 290 species are doped with rare earth as activated ions, that is, rare earth laser crystals accounted for 90.6% of the rare earth has been achieved in the laser output CE, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, YB, and so on, although there are many laser crystals, but only dozens of of important, but less practical.

Typical, excellent laser crystals are as follows: (1) Rare earth Garnet System (YAG)
YAG is the most active system in research, development and application at home and abroad, in which the neodymium-doped yttrium aluminum garnet crystal (yag:nd) has the best performance, the most widely used and the largest production. It is used as a pulsed laser with high repetition frequency. In recent years, more efficient neodymium and chromium-doped gadolinium-scandium gallium garnet have been developed.

(2) ND-doped yttrium aluminate system yalo3:nd (YAP:ND)
Yap is an orthogonal crystal system with anisotropy, so different laser properties can be obtained by using different o rientations of crystals. In addition, the Yap crystal is faster than YAG. The output power is not easy to saturate.

Its disadvantage is that there is phase instability at high temperature and the coefficient of thermal expansion is anisotropic, which leads to the defects of cracking, color heart and scattering particles in the growth process of crystals. (3) Lithium fluoride yttrium (YLF) laser material

YLF is a kind of excellent laser matrix, many of which are laser output. It is the advantage of light irradiation, does not produce color heart and discoloration, matrix absorption of the cut-off wavelength to the short wave. The Ylf:nd Crystal has a long fluorescent life and a large emitter area, which is suitable for diode-pumped laser crystals.

2. Rare earth Glass Laser material
In the glass can produce laser rare earth activation ion than in the crystal, there are known ND, Er, Ho, TM and other trivalent ions. The advantages of rare earth glass laser materials are: Easy preparation, the use of hot forming and cold processing technology can be produced in different sizes and shapes of glass, flexibility than crystal, can be pulled into a small diameter to micron fiber, and can be made into a few centimeters diameter and a few meters long rods or discs. Rare Earth glass is a solid-state laser material with maximum output pulse energy and highest output power, which is used in the study of thermonuclear fusion by a large laser made of this laser material. 3. Chemical Metrology Laser Material

In this type of laser material, the Rare-earth activated ions are not added in the form of doping, but as a component of the crystals. Its potential applications are for integrated optics, optical communication, ranging, and future ternary and semiconductor lasers will compete.

4. Rare earth Conversion Laser material
At present, the laser wavelength is mainly red and infrared, which is very short of blue and green laser band, so the development and application of laser is affected. In recent years, the anti-Stokes effect in the hair optics has been used to develop the conversion of laser materials, and to achieve practicality and commercialization, in addition to the frequency doubling technique which transforms the long wavelength laser into short wavelength laser.

5. Rare earth Fiber laser material
With the development of integrated optics and optical fiber communication, miniature lasers and amplifiers are needed. Since 90 's, the information superhighway has put forward the higher request to the information transmission, the multimedia technology request can simultaneously transmit the graph, the text, the sound, the image, moreover is the highly clear sound, the image.

Information superhighway to achieve a high speed, the general optical fiber communication technology transmission of information is far from the speed, hope to be ultra-high speed, ultra long distance transmission of information need to cross many technical obstacles, one of them is how to supplement the long-distance transmission in the process of light attenuation of energy. So the direct amplification of light signal becomes a subject to be solved. Erbium-doped fiber amplifier can enlarge the optical information directly, carry on the large capacity, long-distance communication, make the optical fiber communication made great progress.

In recent years, a great progress has been made in the development of erbium-doped fiber amplifiers. Erbium doped with ordinary quartz fiber, coupled with 980 nm, 1480 nm wavelength of two semiconductor lasers, the basic form of a direct expansion of the 1550 nano-optical signal amplifier. The light emitted from the high energy transition to the ground state is supplemented by the attenuation signal light, which acts as a light amplification. In order to avoid unwanted absorption, erbium doping in fiber is dozens of to hundreds of PPM, and high gain can be obtained by doping in the center of the core with high density of light.

三、Application devices of rare earth laser materials

1. Yag:nd Laser
This is the most dosage, the most mature laser crystals, the demand for the laser crystal 90% or so, in the next 5 years will remain the main body. Material processing is one of the great market of lasers. The sales ratio of CO2 laser and yag:nd laser in material processing is 2:1.

2. Optical storage Lasers
As an important part of the information superhighway, the market potential is very large, some of which belong to optical storage. The way to increase storage density is to use a shorter wavelength of laser, the best choice is 808 micron led pump yvo4:nd crystals.

3. 2 Micron Lasers
Ho and TM Lasers have great market potential. Because Ho and TM laser output wavelength of 2 microns or so, and water absorption peaks close to, there is excellent tissue cutting and coagulation effect, can be transmitted by ordinary optical fiber, is an ideal surgical laser light source. The United States has approved more than 20 kinds of 2 micron lasers in medical clinical use. Can treat a variety of diseases. The 2 micron laser can be used as laser radar light source for the safety of human eyes and the atmosphere penetrating well, and its comprehensive performance is superior to yag:nd and CO2 lasers.

4. LED pumped solid-state lasers
The LED pumped solid-state laser is 10 times times more efficient than the lamp pump, and the whole solid reliability is increased 100 times times, which has a huge market in the fields of optical storage, microfabrication, cable TV, remote sensing and radar. LED pump laser materials are mainly yag:nd, Yag:tm, Yvo4:nd, y2sio5:nd and so on.

四、Development direction of rare earth laser materials
Rare earth materials are the heart of the laser system and are the basis of laser technology, the Photoelectron technology developed by laser is not only widely used in military, but also has been widely applied in many fields of national economy, such as optical communication, medical treatment, material processing (cutting, welding, punching, heat treatment, etc.), information storage, scientific research, testing and anti-counterfeiting etc. form a new industry. In military, rare earth laser materials are widely used in laser ranging, guidance, tracking, radar, laser weapons and optical confrontation, telemetry, precision positioning and optical communication.

To improve and change the operational capabilities and methods of the various services and classes, play an important role in tactical attack and defense. High-power laser materials can be equipped with laser blinding weapons, as well as photoelectric countermeasures and other weapons. Light Emitting diode (LED) pumped laser crystal laser output beam quality, high nonlinear frequency shift efficiency, can be a nano-watt-grade laser frequency to blue, green and red areas for optical storage, display, remote sensing, radar and scientific research. Sales of lasers worldwide increased from 460 million to $1.5 billion in 1996.1985-1986.

The average annual growth rate is 11%. Laser Product Sales Distribution: The United States accounted for 45%, Europe accounted for 30%, the Pacific region accounted for 25%. Sales accounted for the top six applications in materials processing, medical, optical communications, scientific research, optical storage and measurement equipment. By the beginning of the next century, optoelectronic technologies such as optical communication, optical storage and information superhighway will be developed rapidly. The sales of China's laser industry rose from 60 million in 1985 to 582 million yuan in 1994. The average annual rate is 32%.