What is Laser and it’s major types?


LASERS



A laser is a device that creates an intense beam of light called a laser beam. A laser beam is monochromatic: it is made up of light of just one colour of the spectrum. This means that all the light waves in it have the same wavelength. Just as importantly, all the waves are “in phase”, which means that as they leave the laser, their crests and troughs all line up with each other.



The lasing material is contained in a tube with a mirror at one end and half-silvered mirror at the other. Light bounces up and down, gaining strength until it is powerful enough to break out.



The word “laser” is short for Light Amplification by Stimulated Emission of Radiation. Inside the laser is lasing material, which can be a solid, a liquid or a gas. The atoms of the material are excited or “stimulated” by giving them energy, either in the form of light or electricity. This makes them emit light (a type of radiation), which in turn makes other atoms emit light of the same wavelength. This process creates an intense laser beam. The wavelength and so the colour, of a laser beam depends on the lasing material. Some lasers produce ultraviolet or infrared radiation rather than visible light. The first working laser was built by American physicist Theodore Maiman in 1960.



A high-power laser is being used to perform eye surgery. If the retina, the part of the eye that contains light-sensitive cells, becomes detached, a laser beam can stick it back in place.



USES FOR LASERS



The most common uses of lasers are playing compact discs and reading bar codes. These lasers are normally red lasers that use semiconductor lasing materials. They are low-power lasers, but they are still dangerous to look at directly. Low-power lasers are also used in communications, where they send signals along optical-fibre cables, in laser printers, in surveying, and for light shows. High-power lasers can be focused to create intense heat in materials. They are used in manufacturing for accurate cutting and in medicine for delicate surgery.



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Define Light and explain its main features?



LIGHT



Light is a kind of energy. It is the form of energy that our eyes can detect, enabling us to see. It is produced by very hot things - the Sun, fire and the tiny wire inside electric light-bulbs. Certain animals also have light-producing organs.



Light from the Sun is essential to life on Earth. Some creatures live off minerals in the ocean depths but these are exceptions. Most plants use sunlight to make their food. All plant-eating animals, together with other animals that eat plant-eaters, also therefore depend on sunlight.



Light rays can only travel in straight lines. If they strike an object which does not allow light to pass through it (an opaque object), a shadow is cast on the unlit side. Light can be reflected, however. Light reflected from objects allows us to see them. Light rays strike and bounce off a flat, shiny surface like a mirror at the same angle. This enables us to see our reflection.



THE SPEED OF LIGHT



When we switch on an electric light, it seems that the room is filled with light instantaneously. But light rays do take time to travel from their source. They travel extremely quickly: about 300,000 kilometres (or seven-and-a-half times around the world) per second in outer space. The speed of light is, in fact, the speed limit for the Universe: nothing can travel faster. Light waves are able to travel through empty space - a vacuum - whereas sound waves cannot. Light actually moves less quickly through air, water or glass than through empty space.



Because stars are very far from Earth - at least thousands of billions of kilometres - astronomers measure their distances in light years, the amount of time it takes for light to travel to us from them.



REFRACTION OF LIGHT



Light rays bend, or refract, when they pass through different transparent materials. This is because light travels at different speeds through different materials. At the boundary between two materials, for example, air and water, the light changes speed slightly and is refracted from its straight path. You can see this effect when looking at the bottom of swimming pool. It looks much shallower than it really is.



FOCUSING LIGHT



A lens, a shaped piece of glass or plastic, can bend light, either spreading it out or bringing it closer together. A convex lens, one that is thicker in the middle than at the edge, brings light rays together at a single point called a focus. The eye contains a natural convex lens which focuses an image on to the retina at the back of the eye. If you hold a convex lens so that the object you are looking at lies between the lens and the focus, the object will appear larger and further from the lens than it really is. A simple magnifying glass is a convex lens, and is useful for studying minute detail as, for example, on a postage stamp or a tiny insect or flower.



A concave lens is the opposite of a convex lens: it is thicker around the edge than in the middle. This kind of lens diverges (spreads out) light rays. It is used in glasses to correct short-sightedness.



Picture Credit : Google