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Cristal titanium sapphire laser pumped by a green. These lasers use solid media such as crystals or glass as a medium emission of photons. The crystal or glass is that the matrix and must be doped with an ion which is the laser medium. The oldest is the ruby laser whose emission comes from the ion Cr 3 + . Other ions are used (most of the rare earth  : Nd , Yb , Pr , Er , Tm … the titanium and chromium , among others). The wavelength of the laser emission depends essentially on the dopant ion, but also affects the matrix. Thus, the Neodymium glass does not transmit at the same wavelength (1053 nm) that the YAG doped with neodymium (1064 nm). They operate continuously or pulsed (pulse a few microseconds to a few femtoseconds – a millionth of a billionth of a second). They are able to issue both in the visible, near infrared than the ultraviolet . The amplifying medium can be a bar in the case of a Nd-YAG laser (Nd-doped and therefore the matrix of YAG: an aluminum garnet to yttrium ), but it can also be in the form of a fiber in the case of fiber lasers (Yb-doped and therefore the matrix is silica). Today, as the amplifying medium used to generate femtosecond titanium-doped sapphire is. It has two absorption bands centered at 488 and 560 nm. It has a broad emission spectrum centered at 800 nm. Beyond one-dimensional crystal of optical quality acceptable, these lasers allow to obtain powers of the order of kilowatts of continuous and pulsed GW. They are used for both scientific and industrial applications, especially for welding, marking and cutting of materials. Dye (molecular)  In liquid lasers, the emission is surrounded by an organic dye ( rhodamine 6G , for example) in liquid solution enclosed in a glass vial. The radiation may also be continuous and intermittent depending on the pumping mode. The transmitted frequencies can be set using a lens controller, which makes such devices very accurate. The choice of dye essentially determines the color range of the radius that issue. The color (wavelength) can be accurately adjusted by optical filters. At gas (atomic or molecular)  The environment is a photon generator gases contained in a tube of glass or quartz . The emitted beam is particularly narrow and the emission frequency is very extensive. The best known examples are the helium-neon lasers ( red at 632.8 nm) used in the alignment systems (public works, laboratories), and lasers shows. Lasers carbon dioxide can produce very high power (pulse operation) of the order of 10 6 W. Laser marking is the most widely used worldwide. The laser CO 2 (infrared to 10.6 microns) can be, for example, used for engraving or cutting material. There is also a sub-family of gas lasers: lasers, excimer emitting in the ultraviolet. In most cases they are composed of at least one noble gas and usually a halogen gas. The term “excimer” comes from the English excited dimer which means an excited molecule composed of two identical atoms (eg Xe 2 ). But some so-called excimer lasers using exciplex which are molecules composed of two different atoms (for example, noble gas and halogen : ArF , XeCl ). So we should call them lasers exciplex lasers instead of excimer . . The electrical excitation of the mixture produced these molecules exciplex which exist only in excited state. After issuance of the photon , the exciplex disappears because its atoms are separated, so the photon can be reabsorbed by the non-excited excimer, which allows an efficient laser. Ex: Lasik Laser diode  Main article: Diode laser . In a laser diode (laser or semiconductor), the pumping is done using an electric current that enhances the environment generator holes (a hole is an area of ​​the crystal with a positive charge as an electron is missing) on one side and extra electrons on the other. Light is produced at the junction by the recombination of holes and electrons. Often, this type of laser does not mirror cavity: the simple act of cleaving the semiconductor of high refractive index, gives a reflection coefficient sufficient to trigger the laser effect. This type of laser that represents the vast majority (in number and sales ) lasers used in industry. Indeed, the benefits are many: first, it allows a direct coupling between electric power and light, where applications Telecommunications (entrance networks fiber ). In addition, this energy conversion is done with a good yield (about 30 to 40%). These lasers are inexpensive, very compact (the active zone is micrometer or less, and the whole device has a size of one millimeter). It is now known manufacture such lasers for light on almost all the visible range, but the laser delivering red or near infrared are the most used and least expensive. Their fields of application are numerous: optical drives (CD), telecommunications, printers, devices “pumping” for larger lasers (such as solid state lasers), pointers, etc.. Note that the regulations in force in France forbidden to manufacture illuminating beyond 1000 meters. A few flats anyway, the emitted light is generally less directional and less “pure” spectrally than other types of lasers (gas in particular). This is not a problem in most applications. A device very similar in its operation, but that is not a laser, is the LED  : the pumping device is the same, but the production of light is not stimulated , it is produced by spontaneous de-excitation, so that the light produced does not have the coherence properties characteristic of the laser. Free electron (LEL)  This type of laser is very special, because its principle is quite different from that described above. The light is not produced by atoms previously excited, but by a synchrotron radiation produced by accelerated electrons. An electron beam from an accelerator electron, is sent to an inverter creating a periodic magnetic field (due to an assembly of permanent magnets). This inverter is placed between two mirrors, as in the diagram of a conventional laser: synchrotron radiation is amplified and becomes consistent , that is to say, it acquires the characteristics of the light produced in lasers. Just set the speed of electrons to provide a light frequency finely adjusted over a very wide range, from the far infrared (terahertz) X-ray and laser power can also be adjusted by the flow of electrons to higher levels. It can also have laser pulses of short interval and accurate. This makes this type of laser versatile and useful in research applications. However, it is more expensive to produce because it is necessary to build a particle accelerator . Fiber  This type of laser is similar to the solid state laser. By amplifying medium is an optical fiber doped with ions of rare earths . The wavelength obtained depends on the ion selected (Samarium 0.6 microns, 1.05 microns Ytterbium, Erbium 1.55 microns; Thulium 2.1 mm). This technology is relatively new (the first date of 1964), but today there are single-mode laser whose power is in the order of tens of kilowatts. These lasers have the advantage of less expensive and have a small footprint. Moreover it is not necessary to cool below 10 kilowatts 4 , 5 . Teramobile  The laser Teramobile a mobile that delivers ultra-powerful and ultrashort laser pulses. Teramobile laser can be used to detect and measure pollutants or spawn lightning a straight path 6 . Security