How does a Laser Work?
The LASER (Light Amplification by Stimulated Emission of Radiation) is a triumph of modern optics. By exploiting a quantum mechanical effect called stimulated emission, lasers generate a coherent, nearly monochromatic beam of photons. Non-laser light sources typically generate incoherent, unfocused beams of light at a variety of wavelengths, prohibiting certain applications. To create a laser, two components are necessary – a gain medium and a resonant optical cavity. For a gain medium, certain crystals, glasses, gasses, semiconductors and even dyed liquids may be used. The gain medium is stimulated by an energy pump source such as an electrical current or another laser. The medium absorbs the energy, exciting the states of the particles in the medium. After a certain threshold, called population inversion, is achieved, shining light through the medium causes more stimulated emission, or release of energy, than absorption. A resonant optical cavity is a specially sized chamber with a m
Invented less than 50 years ago, lasers have become ubiquitous. They are used in store checkout scanners; in CD players; as surgical instruments; for industrial welding and cutting; to transport data through optical fibers; in precision measuring devices; and in presentation pointers, to name just a few common applications. There is a laser in the computer mouse used to write this column. The military uses laser-guided bombs and is developing laser weapons. There are many different kinds of lasers, but they all operate on the same general principles. Laser is an acronym: Light Amplification by the Stimulated Emission of Radiation. This is a very descriptive name; a laser works by stimulating a material to emit a very specific type of light. For a more in-depth answer, we will need a very basic foundation in atomic physics. The following is an extremely simplified discussion, but is adequate to our needs. All things-air, water, steel, wood, plastic, and your Uncle Jerry-are made of tiny
Einstein was awarded the Nobel Prize for his discovery and interpretation of the formula – E=mc2 – right? Wrong. He won the Nobel Prize for his explanation of the phenomena referred to as the photoelectric effect. When light (electomagnetic energy) is shined on a metal surface in a vacuum, it may free electrons from that surface. These electrons can be detected as a current flowing in the vacuum to an electrode. The light was not always strong enough to cause this effect, however. When the scientists made the light brighter, no increase in electrons was seen. Only when they changed the color of the light (the wavelength) did they see a change in photoemission of electrons. This was explained by Einstein using a theory that light consists of photons, each with discrete quantum of energy proportional to their wavelength. For an electron to be freed from the metal surface it would need a photon with enough energy to overcome the energy that bound it to the atom. So, making the light brigh
