Television:
Television (TV) is the most widely used telecommunication medium for transmitting and receiving moving images that are either monochromatic ("black and white") or color, usually accompanied by sound. The word is derived from mixed Latin and Greek roots, meaning "far sight": Greek tele , far, and Latin visio, sight. The television set has become ubiquitous in homes, businesses and institutions, particularly as a source of entertainment and news.
Working
A television system consists primarily of two parts: picture transmission and picture reception. A television camera used to photograph a television program is similar in some ways to a still camera. Light bounces off the subject being photographed and enters the lens at the front of the television camera. The lens forms a clear image of the subject being photographed on a screen, which is located behind the lens.
The surface of the screen contains millions of tiny particles of selenium or some other photosensitive (sensitive to light) material. These particles act like tiny photocells. That is, when struck by light, they emit a small electrical pulse. An electron gun at the back of the television camera scans back and forth, up and down across the screen at the front of the camera. As it scans, it detects electrical pulses being given off by various parts of the screen. A bright region in the scene being photographed will give off a lot of light. That light will be converted by the selenium into a relatively large electrical pulse. The electron gun will detect that electrical pulse as being greater than other pulses around it.
Laser
A laser (standing for Light Amplification by Stimulated Emission of Radiation) is a device which produces electromagnetic radiation, often visible light, using the process ofoptical amplification based on the stimulated emission of photons within a so-called gain medium. The emitted laser light is notable for its high degree of spatial and temporalcoherence, unattainable using other technologies. Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam."
Working
A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.
Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.
The process of supplying the energy required for the amplification is called pumping. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.
For diagram see attachment*
1 gain medium
2 Laser pumping energy
3 High reflector
4 output coupler
5 Laser beam
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