There are only about 100 different kinds of atoms in the entire universe. Everything we see is made up of these 100 atoms in an unlimited number of combinations. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around in class. Atoms can be in ?different states of excitation? (Bertolotti 48) or they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and go to an excited level. The level of excitation depends on the amount of energy that is applied to the atom by heat, light, or electricity.
An atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. The electrons in this cloud ?circle the nucleus in many different orbits? (Bertolotti 51). In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower energy orbital would shift to higher energy orbitals further away from the nucleus. Once an electron moves to a higher-energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon, a particle of light. You see atoms releasing energy as photons all the time. For example, when the wires in a toaster turns bright red, the red color is caused by atoms, excited by heat, releasing red photons. When you see a picture on a TV, what you are seeing is atoms, excited by high-speed electrons, emitting different colors of light. Anything that produces light, such as fluorescent lights and bulbs, does it through the ?action of electrons changing orbits and releasing photons? (Bertolotti 51).
A laser is a device that controls the way energized atoms release photons that had ever been seen before 1960. Theodore H. Maiman of United States mounted a ?specially prepared a rod of ruby inside a powerful flash lamp? (Hecht) similar to the type used for high-speed photography. The laser age was born. Within a very short time, in addition to many more solid state materials, laser action was demonstrated in liquids, semiconductor crystals, and other forms. Although there are many types of lasers, all have certain essential features. In a laser, the ?lasing medium is pumped to get the atoms into an excited state? (Bertolotti 65). Usually, very intense flashes of light or ?electrical discharges pump the lasing medium and create a large collection of excited-state atoms? (Bertolotti 71). It is necessary to have a large collection of atoms in the excited state for the laser to work efficiently. In general, the atoms are excited to a level that is two or three levels above the ground state. This increases the degree of population inversion. The population inversion is the number of atoms in the excited state versus the ground state. Once the lasing medium is pumped, it contains a collection of atoms with some electrons sitting in excited levels. The excited electrons have energies greater than the more relaxed electrons. Just as the electron absorbed some amount of energy to reach this excited level, it can also? release this energy, as the electron can simply relax and in turn rid itself of some energy? (Bertolotti 73). This emitted energy comes in the form of photons. The photon emitted has a very specific wavelength (color) that depends on the state the electron?s energy when the photon is released. Two identical atoms with electrons in identical states will release photons with identical wavelengths.
Laser light is very different from normal light. Laser light has three main properties. First of all, the light released is monochromatic. It contains one specific wavelength of light (one specific color). The wavelength of light is ?determined by the amount of energy released when the electron drops to a lower orbit? (Hecht 15). Secondly, the light ?released is coherent? (Hecht 16). The light is organized and each photon moves in step with the others. This means that all of the photons have wave fronts that launch randomly. Lastly, the light is very directional. A laser light has a very tight beam and is very strong and concentrated. A flashlight, on the other hand, releases light in many directions and the light is very weak and diffuse. To make these three properties occur takes something called stimulated emission. This does not occur in your ordinary flashlight; in a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized. The photon that any atom releases ?has a certain wavelength that is dependent on the energy difference between the excited state and the ground state? (Hecht 23). If this photon should encounter another atom that has an electron in the same excited state, a case called stimulated emission can occur. The other key to a laser is a pair of mirrors, one at each end of the lasing medium. Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium. In the process, they stimulate other electrons to ?make the downward energy jump and can cause the emission of more photons of the same wavelength and phase?. An effect occurs, and soon we may have multiply many, many photons of the same wavelength and phase. The mirror at one end of the laser is “half-silvered? (Bertolotti 48); meaning it reflects some light and lets some light through. The light that makes it through is the laser light.
There are many different types of lasers. The laser medium can be a solid, gas, liquid, or semiconductor. Lasers are commonly designated by the type of lasing material employed. The first type of laser was called a ruby laser. A ruby laser is a type of solid-state laser that has lasing material given out in a solid matrix. Gas lasers are the most common lasers that have a primary output of visible red light. Some lasers, such as the CO2 laser, are very powerful and can cut through steel (a personal favorite). The reason that the CO2 laser is so dangerous is because it emits laser light in the infrared and microwave region of the spectrum. Semiconductor lasers, sometimes called diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. These are the types that may be built into in some laser printers or compact disk players in our everyday life. Lasers are used in industry and research to do many things, including using the intense laser light to excite other molecules to observe what happens to them.