Basics of Laser Technology
LASER is an acronym that stands for Light Amplification by Stimulated Emission of Radiation (Hecht, Guidebook 144-145). In practice, Lasers are devices that produce light in a special way so that the light has many useful properties. Usually these lights are very directional and propagate in one very narrow direction. Also, lasers produce lights of very specific frequency, or a set number of different frequencies.
Light is its traditional sense means any radiation that a normal healthy human eye can detect. Thus, other invisible types of radiation, such of ultraviolet rays A and B, radio waves, infrared beams are not considered light. The difference among these types of radiation is in their frequencies. The nerves in human eye can only react to a radiation that has a limited range of frequencies (Hecht, Guidebook 80-82). If frequency is higher or lower than threshold levels, human will report no information to the brain. However, for the puposes of Laser's difinition and properties, any radiation is considered light (Bertolotti 131). Therefore, Lasers produce all frequencies including but not limited to visible light.
Lasers is that in order to produce light, a piece of matter must release energy in the form of small particles called quantums, and each quantum propagates in one direction until another object absorbs or reflects it. One of the most amusing parts about this energy is that it does not need another medium to propagate (Csele 38-39). Unlike sound waves that need gas, liquid or solid matter, light can move in ultimate emptiness--space vacuum. A ready example of this propagation is solar power that reaches from the sun toward earth across millions of miles. Before this notion was established, many scientists believed that light too moved in an invisible medium called ether. Only after existence of ether was contradicted by experiments, it was established that light travels in forms of quantums that did not depend on existence of other matter.
One also needs to keep in mind that usually light spreads directly once it is released. The release of light particles happens on the outer surface of atoms--building blocks of gasses, liquids and solids. The direction of light released, however, depends on so many factors that is more often than not totally unpredictable (Milonni 54). The reason for that is that release of energy occurs from atoms at random times and from random angles. Indeed, sun's solar energy is thought to be uniformly released in all directions from each point on sun's surface. Similarly, a tungsten wire in an incandescent light bulb also emits light in all directions. Apart from light being dispersed in all directions, another consequence is that light's intensity diminishes with distance. For an illustration, compare between brightness of two spots : one next to a light bulb turned on, and one across the room. Thus, such light is essentially useless where one needs a narrow beam that maintains its intensity all the way until receiver.
Next, as shown above, light comes in different frequencies, and frequency of each particular quantum depends on the amount of energy that it takes away from its source. Lights gets emitted when a particular atom absorbs more energy than it can normally hold, and this atoms releases such an amount of energy that it returns to its normal level (Hecht, Lasers 230). Since light emitting surfaces, such as that of the sun, contain many different atoms, amounts of energy that each quantum possesses at exit is of very broad range of frequencies. An illustration of that mix is a rainbow, which appears when water droplets redirects each quantum of light depending on teir . Again, in case of visible light, frequency corresponds to lights color. That, too, creates problem when a light of only one frequency is desired. For instance, light of different frequencies carry different amount of energies, so if a user has a device that can withstand energy level up to a given level frequency, inability to control frequency of each quantum can damage this device (Hitz et al. 21). Just one such a device is human skin which can receive severe damage from harmful ultraviolet rays, yet can perfectly bear to visible and other softer types of light.
Lasers allow to overcome both the problem of omnidirectional propagation and the problem of broad range frequencies. Lasers produce directed light of desired frequency or set number of frequencies by controlling direction and amount of energy released on the surface of light emitters. One techinque that allows to do that involves directing electrical charge through a very clean crystal (Meyers 29). Smooth surface of crystal and regular internal structure makes most of light beam in one direction only, and homogenous chemical composition means that all atoms have same levels of threshold light emission.
Many other techniques exist, yet they all involve in one way or another an exploitation of chemical and physical properties of matter so to produce one-directional and limited frequency lights (Davis 213).
Laser beams used to be difficult to produce (Meyers 21). Eventually, because their benefits far outweighed costs in many applications, and due to economies of scale in mass production, lasers have become ubiquitous instruments in modern human life.
Works Cited
Bertolotti, M. Masers and Lasers: An Historical Approach. Bristol: Hilger, 1983.
Csele, Mark. Fundamentals of Light Sources and Lasers. Hoboken, NJ: John Wiley & Sons, Inc., 2004
Davis, C. C. Lasers and Electro-Optics: Fundamentals and Engineering. New York: Cambridge UP, 1996.
Hecht, J. The Laser Guidebook (second edition). New York: McGraw-Hill, 1992.
Hecht, J. Understanding Lasers (second edition). New York: IEEE Press, 1994.
Hitz, C. B., Ewing, J. J. and Hecht, J. Understanding Laser Technology. Piscataway, NJ: IEEE Press, 2000.
Meyers, R. A., Ed., Encyclopedia of Lasers and Optical Technology. San Diego: Academic Press, 1991.
Milonni, P. W. and Eberly, J. H., Lasers. New York: Wiley, 1988.
Davis, C. C. Lasers and Electro-Optics: Fundamentals and Engineering. New York: Cambridge UP, 1996.
Hecht, J. The Laser Guidebook (second edition). New York: McGraw-Hill, 1992.
Hecht, J. Understanding Lasers (second edition). New York: IEEE Press, 1994.
Hitz, C. B., Ewing, J. J. and Hecht, J. Understanding Laser Technology. Piscataway, NJ: IEEE Press, 2000.
Meyers, R. A., Ed., Encyclopedia of Lasers and Optical Technology. San Diego: Academic Press, 1991.
Milonni, P. W. and Eberly, J. H., Lasers. New York: Wiley, 1988.
