READING QUIZ

       Laser is an acronym for light amplification by stimulated emission of radiation. Stimulated emission is a variation of spontaneous emission, a process that occurs in atoms when an electron in a ground, or unexcited state, is knocked into a higher state, a photon, or particle of light, is released. As de-excitation occurs in millions of atoms, photons are released in a random fashion and light is emitted in every direction. Stimulated emission, however, causes an increase in the number of photons travelling in a particular direction. An optical cavity, the space formed by two reflective surfaces facing each other, is used to control the direction of the beam. There are solid-state, gas, and liquid lasers, and by subjecting lasing materials to various types of energy – electrical, magnetic, or sonic – scientists have been able to control the laser output to suit various functions and applications.

     In industry, the laser has proven to be a very versatile tool, particularly for cutting and welding. Lasers are now also used in high-speed printing and in the creation of three-dimensional images, called holograms. Laser tracking and ranging systems have been developed, using light signals to measure distance rather than the radio signals of radar. The use of the laser in biological and medical applications is also rapidly expanding, and the laser is already being used with great success in certain surgical procedures. In the field of communications the laser, used in conjunction with fiber optic networks, is capable of carrying much more information than conventional wires and is setting the stage for the "electronic superhighway" of the near future.

1) The main topic of the second paragraph is fiber optic networks. measuring distances with lasers the uses of lasers in medicine the applications of the laser.