I believe everyone is familiar with the following terms: fiber laser, continuous laser, YAG laser, nanosecond laser, etc. There are so many types and names of lasers that it is hard to remember them all. Today, we will systematically classify the lasers:
01 What is a laser?
Laser is the abbreviation of “Light Amplification by Stimulated Emission of Radiation”, which refers to the enhanced photon beam generated by stimulating atoms to release radiation energy through electron transitions. Compared with other types of light, laser has a series of characteristics such as small divergence, high brightness, good monochromaticity, and good coherence. Therefore, it is widely used in many fields such as industrial manufacturing, information communication, biomedicine, scientific research and military, and has played an extremely important role in social production activities. Therefore, laser is also called the new four great inventions of the 20th century together with computers, atomic energy and semiconductors.
Laser is a device that emits lasers based on the principle of stimulated radiation.
The pump source is the energy supply source of the laser; the gain medium is the core of the laser, which absorbs the energy provided by the pump source and amplifies the laser; the resonant cavity is two parallel mirrors, which reflect the light back and forth between the reflectors and pass through the gain medium many times, so as to shorten the length of the working material and amplify the laser power.
The material is excited by light, electricity or other methods, so that some of the particles are excited to a state with higher energy. When the number of particles in this state is greater than the number of particles in the state with lower energy, due to stimulated radiation, the material can amplify the light radiation of a certain wavelength, that is, when the light radiation of this wavelength passes through the material, the emission intensity will be amplified, and the light radiation consistent with the incident light wave position, frequency and direction is called a laser amplifier.
If the excited material is placed in the resonant cavity, the light radiation will be reflected and propagated back and forth in the resonant cavity along the axis direction, passing through the material many times, and the light radiation will be amplified many times, forming a beam of laser with high intensity and concentrated direction, which is a laser oscillator.
02 Laser Classification
Lasers can be classified according to different dimensions such as pumping mode, gain medium, working mode, output power, and output wavelength. The specific classification methods are as follows:
(1) According to the different pumping modes, lasers can be mainly divided into optically pumped lasers, electrically pumped lasers, chemically pumped lasers, thermally pumped lasers, and nuclear pumped lasers. Generally speaking, different types of pump sources are adapted to different absorption wavelengths of laser crystals.
(2) According to different gain media, they can be divided into liquid lasers, gas lasers, and solid lasers (fiber, semiconductor, all-solid-state, hybrid). Among them, fiber lasers are generally distinguished from other solid lasers in academic and production practice because of their special gain media and their high market share. At present, there are nearly a thousand substances that can be used as gain media, the most common of which are rare earth-doped optical fibers, dyes, inert gases, carbon dioxide, neodymium-doped yttrium aluminum garnet (YAG), and titanium sapphire. Each type of gain medium laser has different characteristics, and different gain media determine parameters such as laser wavelength.
Solid-state lasers and fiber lasers are the two most widely used mainstream lasers in the market. However, their processing characteristics and application scenarios are quite different. They are two different technical routes that are developed in parallel and are difficult to replace each other. In general, fiber lasers are widely used in metal material cutting, welding, drilling, sintering, etc. in the field of macro processing due to their high average power and strong thermal effect. Solid-state lasers have the characteristics of high peak power, small thermal effect and high processing accuracy. They are generally used in the field of fine micro processing of thin, brittle materials and non-metallic materials.
(3) According to different working modes, lasers can be divided into continuous lasers and pulsed lasers. Continuous lasers can output continuously for a long period of time and have high thermal effect. Pulsed lasers output in the form of pulses. Their main characteristics are high peak power and small thermal effect. According to the length of the pulse time, pulsed lasers can be further divided into long pulse (milliseconds, microseconds), short pulse (nanoseconds), and ultrashort pulse (picoseconds, femtoseconds) lasers. Generally speaking, the narrower the pulse width and the shorter the wavelength, the higher the processing accuracy that can be achieved.
(4) According to the output power, fiber lasers can be divided into low power (0-1kW), medium power (1kW-3kW), and high power (3kW-6kW or more). For solid lasers mainly used in fine micro-machining, in practice, those below 10W are generally classified as low power, and those above 10W are classified as medium and high power. Lasers of different powers are suitable for different application scenarios.
(5) According to the output wavelength, lasers can be divided into infrared lasers, visible light lasers, ultraviolet lasers, etc. Different structures of materials can absorb different wavelengths of light, so lasers of different wavelengths are needed for fine processing of different materials.
