As is well known, the emission of any light source is related to the motion of particles inside the material. Ordinary light sources emit light in all directions. Laser, on the other hand, is a type of light that is not naturally occurring but is emitted due to stimulation. It has characteristics such as good directionality, high brightness, good monochromaticity, and good coherence. Now that laser technology is applied in every aspect of our life, do you really know about laser technology?
The United States successfully developed the world’s first ruby laser in 1960, and China followed suit in 1961 with its first domestically produced ruby laser. Following quantum physics, radio technology, atomic energy technology, semiconductor technology, and electronic computer technology, laser technology is regarded as another major scientific and technological achievement of the twentieth century.
Four characteristics of lasers
- Good directionality: Ordinary light sources, such as the sun, incandescent lamps, or fluorescent lamps, emit light in all directions, whereas laser light can be confined to a solid angle of a few milliradians or less. This provides for a substantially higher illuminance in the direction of irradiation. Every 200 kilometers, the laser beam diameter diffuses by less than one meter. If it is projected onto the moon, which is about 380,000 kilometers away from the Earth, the beam would spread less than 2 kilometers, while an ordinary searchlight would spread to tens of meters at a distance of several kilometers. Laser collimation, guidance, and ranging make use of this good directionality.
- High brightness: Laser is the brightest light source available today, comparable only to the intense flash of a hydrogen bomb explosion. The brightness of sunlight is approximately 1.865×10^9 cd/m², while the output brightness of a high-power laser can exceed that of sunlight. Although a laser’s total energy may not be very large, its highly concentrated energy can easily generate high pressures and temperatures ranging from tens of thousands to millions of degrees Celsius at a tiny point. Practical applications such as laser drilling, cutting, welding, and laser surgery make use of this characteristic.
- Good monochromaticity: Light is an electromagnetic wave, and its color depends on its wavelength. Ordinary light sources typically emit a mixture of wavelengths that represent a variety of colors. Sunlight contains seven visible light colors (red, orange, yellow, green, cyan, blue, and purple), as well as infrared and ultraviolet light. A laser’s wavelength, on the other hand, is concentrated within a very narrow spectral or frequency range. A helium-neon laser, for example, has a wavelength of 632.8 nanometers and a wavelength variation range of less than one tenth of a nanometer. Lasers’ high monochromaticity makes them an excellent tool for precise instrument measurements and the excitation of specific chemical reactions in scientific experiments.
- Good correlation: Interference is a property of wave phenomena. Based on the high directionality and good monochromaticity of lasers, they naturally exhibit excellent coherence. This characteristic of lasers makes holography a reality.
Classification of Lasers
The most common classification of lasers includes solid-state, gas, liquid dye, semiconductor, and fiber lasers.
- Solid-state lasers use a solid crystalline material such as ruby rod or other solid-state materials, with a flashlamp wrapped around it to pump its energized atoms. To operate effectively, the solid-state material must be doped, which is a process of replacing some atoms with impurity ions to create desirable energy levels for generating laser light at a specific frequency. Solid-state lasers produce high-power beams, often in very short pulses. In contrast, gas lasers use inert gases or compounds such as carbon dioxide (CO2) as the medium to generate continuous bright light.
- CO2 lasers are powerful and efficient, commonly used in industrial cutting and welding processes.
- Liquid dye lasers use a solution of organic dye molecules as the medium. Their main advantage is the ability to generate a wider range of light frequencies compared to solid-state and gas lasers, and even produce different frequencies.
- In terms of wavelength, lasers cover a range from far infrared, infrared, visible light, ultraviolet, all the way to deep ultraviolet. Recently, X-ray lasers have been developed, and there are ongoing developments in Y-ray lasers.
- In terms of output modes, lasers can be continuous, single-pulsed, continuous-pulsed, or ultrashort-pulsed.
Different types of lasers meet different application requirements. Laser processing, for example, and certain military applications necessitate high-power or high-energy lasers. Some applications, such as studying ultrafast processes, necessitate decreasing pulse duration. Improved monochromaticity, output mode, spatial intensity distribution, and wavelength tunability are also in high demand. These needs encourage laser researchers to constantly investigate and push the boundaries, resulting in unparalleled advances in the depth and breadth of laser study and applications.
Laser application
1. Application of laser in information field
Semiconductor lasers and fiber amplifiers are two critical fiber optic communications technologies. The semiconductor laser’s laser not only has good monochromaticity and coherence, but it also has a light wave frequency ten thousand times greater than the microwave frequency. It has a high level of interference and confidentiality, and its communication capacity is tens of thousands of times greater than microwave communication. The use of laser technology for optical storage has revolutionized data storage.
2. Application of laser in the field of holography
People can only record the wavelength and amplitude by using light-sensitive photography method, so no matter how realistic the photo is, the picture and the scene are always different. The laser has high coherence, and can obtain all the information including the phase of the interference wave space. Therefore, when laser is used for holography, all the information of the object to be photographed is recorded on the film, and through the diffraction of light, the lifelike three-dimensional image of the object to be captured can be reproduced.
Holography has the characteristics of three-dimensional imaging, can be recorded repeatedly, and each small piece of holographic film can reproduce the complete three-dimensional image of the object, and can be widely used in precision interferometric measurement, non-destructive flaw detection, holographic photoelasticity, micro-strain analysis and vibration analysis, etc. scientific research. The use of holograms as anti-counterfeiting marks for commodities and credit cards has formed an industry. Using holograms to shoot precious artworks not only makes people appreciate it, but also provides a reliable and realistic basis for the restoration of artworks.People’s lives will be enhanced by the development of holographic television.
3. Application of laser in medical field
The application of laser in medicine is divided into two categories: laser diagnosis and laser therapy. The former uses laser as an information carrier, while the latter uses laser as an energy carrier.
In terms of laser diagnosis, the laser can penetrate deep into the tissue for diagnosis, directly reflect the condition of the tissue, and provide a sufficient basis for the doctor’s diagnosis.
In terms of laser therapy, laser technology has become an effective means of clinical treatment and a key technology for the development of medical diagnosis. It solves many difficult problems in medicine, such as laser surgery with small incisions, little or no damage to tissues, and few toxic and side effects.
4. Laser processing
Using the high intensity (brightness) of the laser to focus the laser beam can emit 100J of light energy within 1ms, which is enough to melt or vaporize the material in a short time, so as to process materials with different characteristics that are difficult to process, such as: welding, Drilling, cutting, heat treatment, photolithography, etc.
Laser processing has the advantages of high precision, small distortion, no contact, energy saving, etc. Its application fields can cover almost the entire machinery manufacturing industry, including mining machinery, petrochemical, electric power, railways, automobiles, ships, metallurgy, medical equipment, aviation, Machine tool, power generation, printing, packaging, mold, pharmaceutical and other industries. Among them, the wear and corrosion of key components and precision equipment can be well repaired and optimized by laser cladding technology, and it has become a powerful tool to turn decay into magic.
5. Precision measurement
Precise measurement is based on the advantages of laser monochromaticity, strong coherence and good directionality. Compared with other rangefinders, laser ranging has the advantages of long detection distance, high precision, anti-interference, good confidentiality, small size and light weight. The range finder sends out light pulses, and after being reflected by the target to be measured, the light pulses return to the receiving system to measure the time interval between emission and reception.
Laser light has high brightness and high coherence at the same time, which enables the Doppler effect of light to be applied in speed measurement. Lidar is a radar system that emits laser beams to detect characteristic quantities such as the position and speed of targets.
Laser is one of the most important inventions of mankind in the 20th century. Laser technology is widely employed in industry, agriculture, military, health, and even all parts of life. It is becoming increasingly important in the advancement of human society. It is a miracle that is drastically altering our world.
