What is Laser light?


It punches through steel. It pierces diamonds. It performs tiny, delicate operations. Is it a superhero? No, it is a special kind of light. The light that can do these things is called a laser beam. A laser beam is made up of bundles of energy called photons, just like ordinary light. But the photons in a laser beam act in an unusual way.



The photons in ordinary light have different amounts of energy. They go in all directions, and they start and stop at different times. They are like people in a crowd, walking in all different directions. But in laser light, all the photons work in the same way. They are exactly the same colour, so they all have the same amount of energy. They are also given off at regular times, and they travel in only one direction. They are like marchers in a parade.



With all the photons moving together, laser light is very powerful. But don’t worry! You aren’t going to run into any laser beams out on the street. Laser beams have to be made in special machines. Then they can burn through metal or even drill a tiny hole in a diamond.






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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.



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How can I make my own periscope?


This periscope is made from a box containing two mirrors held at 45°. It can reflect light so that you can see over walls and around corners!



What you need



Two small mirrors (both the same size), some card; a protractor for measuring the angles of the mirrors; a ruler; a pencil; scissors; sticky tape; and a box of paints.



Measure the distances shown as ‘a’ and ‘b’ in the diagram. Make sure that the mirror is held at an angle of 45° while you do this (a protractor will help).



The casing



Now you can draw the pattern for your periscope onto the card. Make sure you use the measurements you have just taken. You can make the periscope as tall as you like. Cut around the outline of the pattern. Now draw two rectangles onto your box — like the ones in the diagram. Cut these out to make two openings. Fold the box into shape and hold the edges together with sticky tape.



Fixing the mirrors



Your two mirrors should fit into opposite corners of the box with their shiny sides facing the openings. Use strips of card to keep the mirrors in place, whichever way up you hold the periscope. Decorate the box as you choose. Your periscope is now ready to use. Just look into the bottom opening and see what you can see!





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What are various uses of Lasers?


Lasers are one of the most important developments in recent years. There are many ways in which lasers can be used. As well as making good cutting tools in industry, lasers make excellent ‘knives’ for surgeons. The laser ‘knife’ is completely sterile and seals small blood vessels as it cuts, so that less blood is lost. Laser light is often used to ‘weld’ a retina, which has become detached, to the back of the eye.



Holograms are three-dimensional pictures made by illuminating objects with laser light. They look solid and real. They are used on credit cards as they are very difficult to forge.



Lasers are used in the aviation industry.



Lasers are often used in medicine, particularly in delicate surgery.




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