【Engineering Popular Science】Mysterious Light — Laser

The colorful lights on the stage can always drive our enthusiasm, attract our attention, and let us quickly integrate into this cheerful atmosphere. But do you know how these laser lights are produced?

In an atomic system, electrons basically move in layers. When atoms are affected by the external environment, when high-energy electrons transition to low-energy levels, there will be two manifestations of "spontaneous emission" and "stimulated emission". Lasers are produced by stimulated radiation.

Laser is the "light radiation" that the atoms of the object are "excited" under the action of a specific "pump source", which is laser.

In 1960, American scientist Theodore Harold Maiman used a high-intensity flash tube to illuminate ruby, so that the chromium atoms in the ruby were excited to emit a red light.

A hole is drilled in the surface of a mirror-coated ruby through which the red light can escape, thus producing a thin column of red light that is fairly concentrated, and when it hits a certain point, it can reach a height higher than the surface of the sun. high temperature. So the world's first laser, the ruby laser, came out.

In China, the first ruby laser was born in 1961 at the Changchun Institute of Optics, Fine Instruments and Mechanics, Chinese Academy of Sciences . my country's first laser is only one year away from the world's first laser, which is of great significance to the history of China's optical development and the history of China's science and technology development.

So, what is it about lasers that makes them so popular?

Ordinary light sources emit light in all directions. To allow ordinary light to spread in one direction, it is necessary to install a certain light-gathering device on the light source. For example, the headlights and searchlights of cars are all equipped with light-gathering reflectors.

The laser emitted by the laser is naturally emitted in one direction, and the divergence of the beam is extremely small and close to parallel.

Laser is the brightest light source in contemporary times, only comparable to the intense flash at the moment of hydrogen bomb explosion. The output brightness of a high-power laser can be 7 to 14 orders of magnitude higher than that of sunlight.

The light emitted by ordinary light sources usually contains various wavelengths and is a mixture of various colors of light. Sunlight includes visible light in seven colors of red, green, yellow, green, blue, blue, and purple, as well as invisible light such as infrared light and ultraviolet light.

The wavelength of a certain laser is only concentrated in a very narrow spectral band or frequency range. For example, the wavelength of the helium-neon laser is 632.8 nanometers, and its wavelength variation range is less than one ten-thousandth of a nanometer. The good monochromaticity of the laser provides an extremely favorable means for scientific experiments such as precision instrument measurement and stimulation of certain chemical reactions.

Based on the characteristics of high directivity and high monochromaticity of laser light, it must be light with excellent coherence. This property of laser light makes holography a reality.

Laser communication is a communication method that uses laser to transmit information, including atmospheric laser communication and optical fiber communication. With the rapid development of China's information technology, people's requirements for the network are getting higher and higher, which promotes the development of optical fiber technology to a certain extent, and it is necessary to improve the level of optical fiber communication technology.

There are also many applications of laser in science and technology and military affairs. Such as lidar, laser weapons [3] , etc., due to the characteristics of high detection accuracy, low power consumption, small size, and easy equipment, lidar has been widely used in early warning detection, guidance, fuze and other technologies in recent years. Laser weapons will become an important means of strategic checks and balances for major powers and changes in the style of warfare. At present, they have shown a trend of rapid development, gradually moving towards actual combat, and providing new combat capabilities for future combatants.

Laser cosmetology is to penetrate the epidermis and dermis with laser beams of specific wavelengths to destroy pigment cells and pigment granules. The fragments are processed and absorbed by macrophages in the body, leaving no scars safely and effectively achieving the purpose of whitening. Use appropriate amount of laser irradiation to make the skin tender and smooth, such as treating acne, black moles, age spots, etc.

Femtosecond laser is a laser emitted in the form of pulses with a duration of only a few femtoseconds (1 femtosecond = one quadrillionth of a second), which is the shortest pulse that humans can obtain under experimental conditions. Femtosecond laser is used in ophthalmic surgery and is known as "another revolution in refractive surgery" after wavefront aberration technology.

Because the laser itself has a lot of energy, it will cause harm to the human body and the environment when it is not operated properly. Among the laser damage, the damage to the eyes in the body is the most serious. High-intensity visible or near-infrared light will cause the temperature of the photoreceptor cell layer of the retina to rise rapidly, degeneration and necrosis will occur, and the light-sensing effect will be lost. Once damaged, it will cause permanent blindness of the eyes.