Lasers & Coherence Grant Jonathan Taylor Holub Mrs. Grayot, Physics, 6th Period March 19,2009

Laser Laser- A device that produces coherent light of only one wave length Coherence- The correlation between the phases of two or more waves Medium- A physical environment through which a disturbance can travel Laser “ Light Amplification by stimulated emission of radiation”

Coherent Light Waves emitted from a laser produces a narrow beam (phase) of light, and do not shirt relative to each other as time progresses. Because the waves are in phase, they interfere constructively at all points The individual waves effectively behave like a single wave with a large amplitude Light produced by a laser is monochromatic All the waves have exactly the same wavelength

Active Medium A laser is a device that converts light, electrical energy, or chemical energy into coherent light. There are many different types of lasers, but they all have the same basic features. They all use something called the active medium to which energy is added to produce coherent light. The active medium can be solid, liquid, or gas. The composition of the active medium determines the wavelength of the light produced by the laser

Basic Function of a Laser When high, electrical, or chemical energy is added to the active medium, the atoms in the active medium absorb some of the energy. When energy is added to an atom that is at a lower energy state, the atom can be excited to a higher energy state. These excited atoms then release their excess energy in the form of electromagnetic radiation when they return to their original, lower energy states

Stimulated Emission When light of a certain wavelength is applied to excited atoms, the atoms can be induced to release light waves that have the same properties. After one atom spontaneously releases its energy in the form of a light wave, the initial wave can cause other energized atoms to release their excess energy as light waves with the same wavelength, phase , and direction as the initial wave. That process has been named stimulated emission

Cont. Most light produced by stimulated emission escapes out the sides of the glass tube, however some of the light moves along the length of the tube producing more stimulated emission as it goes. Mirrors on the ends of the material return these coherent light waves into the active medium, where they stimulate the emission of more coherent light waves. As the light passes back and forth through the active medium, it becomes more and more intense, one of the mirrors is slightly transparent, which allows the intense coherent light to be emitted by the laser.

Laser Spectrum

Electromagnetic Light spectrum

Measuring distances Of the properties laser lights have, the one that is most evident is that it emerges from the laser as a narrow beam. Unlike the light from a light bulb or even the light that is focused by a parabolic reflector, the light from a laser undergoes very little spreading with distance Scientists have used lasers to measure long distances, because it can be pointed at distant reflector and the reflected light can e detected

Medicine Lasers are also used for many medical procedures by making use of the fact that specific body tissues absorb different wavelengths of laser light For example lasers can be used to lighten or remove scars from tissue Another treatment lasers are used for involves the eye Can treat lesions of the retina , inside the eye. Can correct glaucoma Lasik Surgery Tonsils and eyes

CD’s/DVD’s The light from a laser is directed through a series of optics toward a compact disc on which the music or data have been digitally recorded. The player reads the data in the way the laser light is reflected from the compact disc.