What is Laser and how do it work ?

In practice, there are only a handful of common kinds, of which the five best known are solid-state, gas, liquid dye, semiconductor, and fiber.

Solids, liquids, and gases are the three main states of matter—and give us three different kinds of lasers

Solid-state lasers are like the ones I illustrated up above. The medium is something like a ruby rod or other solid crystalline material, and a flashtube wrapped around it pumps its atoms full of energy.

To work effectively, the solid has to be doped, a process that replaces some of the solid's atoms with ions of impurities, giving it just the right energy levels to produce laser light of a certain, precise frequency. Solid-state lasers produce high-powered beams, typically in very brief pulses. Gas lasers, by contrast, produce continuous bright beams using compounds of noble gases (in what are called excimer lasers) or carbon dioxide (CO2) as their medium, pumped by electricity.

CO2 lasers are powerful, efficient, and typically used in industrial cutting and welding. Liquid dye lasers use a solution of organic dye molecules as the medium, pumped by something like an arc lamp, a flash lamp, or another laser.

Their big advantage is that they can be used to produce a broader band of light frequencies than solid-state and gas lasers, and they can even be "tuned" to produce different frequencies.

While solid, liquid, and gas lasers tend to be large, powerful, and expensive, semiconductor lasers are cheap, tiny, chip-like devices used in things like CD players, laser printers, and barcode scanners.

They work like a cross between a conventional Light-emitting diode (LED) and a traditional laser.

Like an LED, they make light when electrons and "holes" (effectively, "missing electrons") hop about and join together; like a laser, they generate coherent, monochromatic light.

That's why they're sometimes referred to as laser diodes (or diode lasers). You can read more about them in our separate article about semiconductor laser diodes.

Finally, fiber lasers work their magic inside optical fibers; in effect, a doped fiber-optic cable becomes the amplifying medium. They're powerful, efficient, reliable, and make it easy to pipe laser light to wherever it's needed.

When Theodore Maiman developed the first practical laser, few people realized how important these machines would eventually become. Goldfinger

the 1964 James Bond movie, offered a tantalizing glimpse of a future where industrial lasers could slice like magic through anything in their path—even secret agents! Later the same year, reporting on the award of the Nobel Prize in Physics to the laser pioneer Charles Townes, The New York Times suggested that "a laser beam could, for example, carry all the radio and television programs in the world plus several hundred thousand telephone calls simultaneously.

It is used extensively for range-finding and missile-tracking." Over half a century later, applications like this—precision tools, digital communication, and defense—remain among the most important uses of lasers.

Cutting tools based on CO2 lasers are widely used in industry: they're precise, easy-to-automate, and, unlike knives, never need sharpening. Where pieces of cloth were once cut by hand to make things like denim jeans, now fabrics are chopped by robot-guided lasers.

They're faster and more accurate than humans and can cut multiple thicknesses of fabric at once, which improves efficiency and productivity.

The same precision is equally important in medicine: doctors routinely use lasers on their patients' bodies. for everything from blasting cancer tumors and cauterizing blood vessels to correcting problems with people's vision (laser-eye surgery, fixing detached retinas, and cataract treatments all involve lasers).

Lasers form the bedrock of all kinds of 21st-century digital technology.

Every time you swipe your shopping through a grocery store barcode scanner, you're using a laser to convert a printed barcode into a number that the checkout computer can understand.

When you watch a DVD or listen to a CD, a semiconductor laser beam bounces off the spinning disc to convert its printed pattern of data into numbers; a computer chip converts these numbers into movies, music, and sound. Along with fiber-optic cables, lasers are widely used in a technology called photonics—using photons of light to communicate, for example, to send vast streams of data back and forth over the Internet.

The military has long been one of the biggest users of this technology, mainly in laser-guided weapons and missiles.

Despite its popularization in movies and on TV, the sci-fi idea of laser weapons that can cut, kill, or blind an enemy remained fanciful until the mid-1980s. In 1981, The New York Times went so far as to quote one "military laser expert" saying: "It's just silly.

It takes more energy to kill a single man with a laser than to destroy a missile." Two years later, long-range laser weapons officially became the bedrock of US President Ronald Reagan's controversial Strategic Defense Initiative (SDI), better known as the "Star Wars program".

In NIF, as in most large lasers, intense flashes of white light from giant flashlamps “pump” electrons in large slabs of laser glass to a higher-energy state that lasts only about one-millionth of a second.

The original idea was to use space-based, X ray lasers (among other technologies) to destroy incoming enemy missiles before they had time to do damage, though the plan gradually fizzled out following the collapse of the Soviet Union and the end of the Cold War.