Short for light amplification by stimulated emission of radiation. A device that creates and amplifies electromagnetic radiation of a specific frequency through the process of stimulated emission. The radiation emitted by a laser consists of a coherent beam of photons, all in phase and having the same polarization. Lasers have many uses, such as cutting hard or delicate substances, reading data from compact disks and other storage devices, and establishing straight lines in geographical surveying.
Before the invention of the laser, the artificial light source in high voltage pulse xenon lamp has the highest brightness, like as the brightness of the sun. Ruby laser brightness high than xenon lamp more than tens of billions of times. Because of the high brightness of the laser, it can illuminate the distance of the object. Ruby laser beam on the moon of illumination is about 0.02 lux (light illumination units), the color red, laser spot is visible to the naked eye. If the most powerful searchlight on the moon, illuminance of only about one / 10000 billion of lux, the human eye cannot detect. The main reason for the high brightness of laser is directional luminescence. A large number of photons are emitted in a very small space, and the energy density is very high.
The ratio between the brightness of the laser and the sunlight is a million, and it is created by human beings.
The color of the laser depends on the wavelength of the laser, and the wavelength of the laser is determined by the activity material. A laser beam come from ruby which color like deep rose, is used in the medical field, for the treatment of skin diseases and surgery. Argon, one of the most valuable gases, can produce a blue-green laser beam, which has many uses, such as laser printing, and is also essential in the microsurgery of eye surgery. A semiconductor laser can emit infrared light, so our eyes can not see, but its energy just can “read” the laser disc, and can be used for optical fiber communication. But some laser device can adjust the wavelength of the output laser.
Laser device output of the light, the wavelength range is very narrow, so the color is very pure. For example, the red helium neon laser, the wavelength of the light distribution range can be narrowed down to micrometer level, one of ten thousand of krypton lamp emits red light wavelength. This shows that the laser’s monochromatic far more than any one of the monochromatic light source.
How laser come ?
A laser emits a thin, intense beam of nearly monochromatic visible or infrared light that can travel long distances without diffusing. Most light beams consist of many waves traveling in roughly the same direction, but the phases and polarizations of each individual wave (or photon) are randomly distributed. In laser light, the waves are all precisely in step, or in phase, with each other, and have the same polarization. Such light is called coherent. All of the photons that make up a laser beam are in the same quantum state. Lasers produce coherent light through a process called stimulated emission. The laser contains a chamber in which atoms of a medium such as a synthetic ruby rod or a gas are excited, bringing their electrons into higher orbits with higher energy states. When one of these electrons jumps down to a lower energy state (which can happen spontaneously), it gives off its extra energy as a photon with a specific frequency. But this photon, upon encountering another atom with an excited electron, will stimulate that electron to jump down as well, emitting another photon with the same frequency as the first and in phase with it. This effect cascades through the chamber, constantly stimulating other atoms to emit yet more coherent photons. Mirrors at both ends of the chamber cause the light to bounce back and forth in the chamber, sweeping across the entire medium. If a sufficient number of atoms in the medium are maintained by some external energy source in the higher energy state—a condition called population inversion—then emission is continuously stimulated, and a stream of coherent photons develops. One of the mirrors is partially transparent, allowing the laser beam to exit from that end of the chamber. Lasers have many industrial, military, and scientific uses, including welding, target detection, microscopic photography, fiber optics, surgery, and optical instrumentation for surveying.
The theoretical basis of laser originated from the great physicist Einstein. In 1917, Einstein put forward a new set of technical theory, the interaction between light and matter. The theory is that in material is composed of atoms, different number of particles (electrons) distribution in different level, the particles in high energy level by a photon excitation, will be from high level to jump (transition) to a low level, then will radiate and its optical properties are the same light excitation, and in a certain state, can appear a weak light excited by a bright light. This is called “light amplification by stimulated emission of radiation“, referred to as the laser.
Summary: first, the laser is monochrome, or the single frequency. Some laser device can produce different frequency of laser at the same time , but the laser is isolated from each other, the use of separate. Secondly, the laser is a coherent light. The characteristics of coherent light is all its waves are synchronized, the beam of light is just like a “wave”. Again, the laser is highly concentrated, that is to say it will take a long distance before the phenomenon of dispersion or convergence.
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