Lasers And Their Applications Essay Research Paper

Lasers And Their Applications Essay, Research Paper

Laser is an acronym for light amplification by stimulated emission of radiation. In the last century many types of lasers have been used for many different applications from welding to surgery to military and even many uses in every day life by harnessing the principles of light and stimulated emission.

To understand how lasers work we must first understand the physics behind light waves. Light is emitted from a source and travels in straight lines and when it strikes an object is either absorbed, reflected, or refracted. Light behaves primarily like a wave and its this wave nature of light that allows lasers to work. Constructive interference is what amplifies light. Since light is a wave it has a frequency calculated by the equation:

f = c/

and

= c/f

where f is the frequency c is the speed of light which is equal to 3.00 x 108 m/s and is the wave length of light. Also waves have crests, the high points of waves, and troughs, the low points. Constructive interference occurs when two waves of the same frequency meet at a crest or trough therefore combining to form a wave that has an amplitude equal to the sum of the individual amplitudes of the original waves. Stimulated emission is the process that the laser works on, which was first proposed by Albert Einstein in 1917. When a sufficient number of atoms, either gas solid or liquid, absorb energy so that they are in an excited state of higher energy stimulated emission can occur. Light of a specific wavelength can produce more light with the same phase and direction these light waves will be coherent. Stimulated emission amplifies the coherency of this radiation and gives the radiation a very narrow beam spread.

The combination of light amplification and stimulated emission creates a laser. Laser light is coherent because the atoms are stimulated to emit waves of light that are in phase creating constructive interference producing a powerful and intense laser light. The emitted light is monochromatic, meaning only one wavelength, and one directional. For a laser to work three components are needed. First a gain medium that can amplify light through it. Second an energy pump source to create a population inversion, (this is a condition when electrons in high energy levels are more numerous than electrons in lower energy levels), in the gain medium. Finally two mirrors that form a resonator cavity where small units of energy released from the atoms called photons move back and forth between the mirrors triggering more stimulated emissions. The energy of a photon is calculated using the equation:

E =hv

where E is the energy of a photon, h is Planck’s constant (equal to 6.63 x 10-34) and v is the frequency. As the photons are moving back and forth between the mirrors an intense, directional, and monochromatic laser light seeps through one of the mirrors which is only partially silvered.

Lasers are generally based on the medium used, and are classified as solid state, gas, semiconductor, or liquid. Solid state lasers have a solid gain medium in which atoms are excited. The first ever laser was a solid state laser with a ruby core and pumped buy a xenon flash tube. This laser was made by Theodore Maiman in 1960. The most common solid state lasers are constructed out of ruby crystal, neodymium-doped or yttrium-aluminum and coated with a highly reflecting nonmetallic film. These lasers have the highest power output and are usually operated in a pulsed manner to generate bursts of light over a short period of time. These short bursts are useful for studying physical phenomena over a extremely short time interval. The frequency of these lasers fall in the infrared spectrum, but can be multiplied to ultraviolet by multiplying the laser with potassium dihydrogen phosphate and X-ray wavelengths by aiming the beams at yttrium.

Gas lasers have a medium of pure gas, a mixture of gases or metal vapor enclosed in a glass or quartz tube with one fully reflective mirror and one partially reflective mirror (see illustration above). Gas lasers are pumped by ultraviolet light, electric current, chemical reactions, or electron beams. Some gas lasers have wavelength with in the visible spectrum. A helium-neon laser has a wavelength of 632.8 nm, an Argon ion laser is measured at about 488.0 nm. These lasers have high frequency stability, color purity and a very low beam spread.

The most compact laser is the semiconductor laser. It consists of a junction between layers of material that have electrical conductivity between metals and insulators called semiconductors, usually constructed of gallium arsenide, the laser cavity is confined to this junction by two reflective plates. Semiconductor lasers are pumped by a direct electric current across the junction. These lasers can operate in a continuous wave mode with over fifty percent efficiency.

A liquid or dye laser has an inorganic dye as its medium contained in glass prisms. These lasers are pumped by intense flash lamps in a pulse mode or by a gas laser in a continuous wave mode. A dye laser is tunable,

that is that the frequency can be adjusted by rotating the dye prism inside the laser cavity.

The free electron laser is one using electrons unattached to the atoms and pumped to their lasing capacity by an array of magnet