The laser light, to do everything

Initially considered as a mere object of curiosity, the laser is now ubiquitous and indispensable. This year is the 50th anniversary of its invention

How common is there between a tiny pen-pointer at the red light and the huge and heavy machine installed in CEA Landes called Laser Megajoule? The answer is suggested in the question is the existence of a very special light called "laser".
Famous acronym whose meaning, "light amplification by stimulated emission of radiation" is somewhat obscure - the height for a light! (1) - This term refers to a variety of concepts or objects more or less accurate.
Today, in fact, the laser is everywhere and affects areas of research, medicine, industry and defense. Plumb, printer, cutter metals or textiles, welder, barcode reader, CD and DVD, carrier information via optical fibers, optical lightning rod, guide the work of construction (Montparnasse Tower, Tunnel Channel, Millau viaduct) and missiles (guided bombs during the first Iraq war), surgical scalpel ultrafine (ophthalmology, dermatology), special effects from 3D images (holograms) in the air and no screen or epee and saber intergalactic knights in works of science fiction??, the laser is now ubiquitous in our daily lives.


Not to mention the "natural lasers" are only some interstellar clouds and the atmospheres of Venus and Mars recently discovered by astrophysicists.
Invented in the 1960s, the laser is a very special type of light, which differs from the visible light seen by our eyes. The "white" light from the sun, which is none other than the superposition of all the colors of the rainbow sky, is emitted in all directions and is "incoherent".
This is why the power loss of the "white" light projectors within a few hundred meters. In contrast, the laser is a beam of light of a single color, very energy emitted in one direction, it is a light "coherent".


In principle, things are a bit more complex. Light corresponds to a flux of photons emitted by the excited atoms and thus have a high energy. In nature, these billions of atoms do not emit their photons at the same time, giving this white light, inconsistent.
The trick is to select the laser atoms by high energy "optical pumping", then their trap photons between two mirrors, in a kind of box until they are in phase. When the beam is powerful enough, it will form a laser beam.
"The laser light is more disciplined than the sun, a light beam is domesticated, tamed, the dispersion is minimal," says Evelyn Gil, teacher-researcher at the University of Clermont-Ferrand (2). However, the laser has a low yield (between 0.01 and 30%) and requires a large input of energy to excite the atoms.
Historically, the design and the development of the first laser experiments lasted more than thirty years, thanks to the contributions of many physicists. In 1917, Albert Einstein had the intuition to stimulate the emission of photons.
In France, it is Alfred Kastler (1902-1984) and his student Jean Brossel (1918-2003) who, in the laboratories of the Ecole Normale Supérieure in Paris, discovered the properties of resonance atoms where was born technique of "optical pumping".


However, the first laser was made in May 1960 by Theodore Maiman American (1927-2007) who received a red beam using a ruby ​​crystal.Engineer at Hughes Aircraft Company in Malibu (California), he applied for a patent and is regarded as "the father of industrial electro-optics."
Soon known, his work will be imitated by the major manufacturers such as Bell Labs, RCA Labs, IBM, and Siemens Westinghouse. He created his company, was twice nominated for the Nobel Prize, and received the prestigious Japan.
The industrial world takes hold of this precious object. We developed the laser gas. Today it is no bigger than a loaf of bread: a cylinder 20 cm long and 4 cm in diameter, containing a mixture of helium and neon.
The first applications appear. As the laser tracking, real "plumb the twentieth century," says Evelyne Gil. The tower has been erected Montparnasse through the alignment of four laser beams of helium-neon red.
The property of high directivity of laser is used for operations telemetry to measure very, very far even. Thus, the astronomers of the Observatory of Nice-Côte d'Azur have they measured with an infrared laser - laser solid garnet and yttrium aluminum atom of neodymium (Nd: YAG) - whose diameter is as wide an oak tercentenary (1.50 m), the Earth-Moon distance with small mirrors placed on the lunar surface by the American missions Apollo.


Result: an average distance of 384,000 km, with an accuracy of 3 mm. The round trip lasts 2.6 seconds, and the researchers found that the Moon away from 3 to 5 centimeters per year!
Another telemetry program owes much to the laser, it is the mapping of the surface of Mars, made in 2000 by Mola altimeter onboard the Mars Global Surveyor. With 2.6 million firing an infrared laser, planetary scientists at NASA could draw a card with a vertical accuracy ranging from 30 cm to 2 m and a horizontal accuracy of 160 m.
Finally, closer to home, the famous 'radar' of the police, which is a laser speedometer in fact, a simple diode laser infrared (invisible) which, in theory, evaluates the speed with an accuracy of 0.1 km / h.
Powerful industrial lasers are used in metallurgy. Using Nd: YAG or CO2, one obtains the powers of a few hundred watts continuous 000 watts or 10 during ultrashort pulses, which can vary from milliseconds to a billionth of a second (nanoseconds).
How, with the same instruments, technicians can they both cut, puncture or weld? In fact, they play on the power, it can go up to 1 million watts per cm2. What two plates welded steel 8 mm in less time than it takes to say.


Application a bit special is to use the laser to etch the facades of historic monuments or objects of art it is more accurate and less destructive than the high-pressure jets.
As for the power used in surgery, they are, of course, much lower and vary between 5 and 50 watts. This is the case for example a scalpel CO2 gas laser that can operate on 1 mm2. In ophthalmology, laser gases argon and fluorine, a thousand times thinner than a scalpel blade can remove 1 micron square cornea to correct myopia.
In addition, the heat ray cauterize blood vessels, reducing bleeding. Finally, it is thanks to infrared lasers, red and blue, you can play music burned onto a CD or DVD.
In view of kaleidoscope applications, the laser is now a technology that men could not possibly happen. Moreover, "it is a scientific adventure copy which shows that the search is always a matter of time and men," says Evelyne Gil.
"The twentieth century has been the electronics and microelectronics. The XXI century will be that of photonics and laser, "says Costel Subran, CEO of Opton Laser International, also president of the National Organizing Committee of the fiftieth anniversary of the laser.

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