LASERS

Mariana Bell and Haakon Weyel


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Overview


Lasers have a direct relationship with light, made up of photons. This light, or energy, is a common technology created, though not so simply, with a few mirrors, a photon, and an excited atom. They are a controlled light source , which means they are focused in a specific direction (unlike a light bulb, which projects light in all directions). The beams formed from these light sources usually are channeled by a cylindrical piece of active material that can be solid, liquid, or gas.


The Practical Reality


Lasers have been used recently for multiple purposes today. One full purpose commonly known of today is the use on eye surgery, to correct for impurities in the retina or the cornea. If the retina has a bad spot on it that could impair seeing, lasers can be focused on it and slowly burn it off. With the same logic, if the cornea is bent incorrectly due to the person’s eye use, lasers can be used to remove parts of the cornea and restore the proper shape to the eye and better vision .

Dentists use this process as well, though in a different way. Using the process of laser subgingival curettage, dentists are able to aim at the base of a cancerous section or disease-causing bacteria and destroy it. Following what they are trying to vaporize, the dentists can simply “zap” what they see.

Doctors, surgeons, and other medical personnel use lasers to quite effective use. Surgeons can destroy chronic infectious diseases including in the bronchial tubes and lungs, as well as lesions of the body. In fact, cancer has been targeted as a possible candidate for use. Neurosurgeons have the option to use the PDT (photodynamic derivative) approach to kill cancers in the brain safely, and other surgeons can do just the same for other regions. The patient must first absorb or intake the HpD (hematoporphyrin derivative) dye two or three days before the surgery. The HpD will target the cancer cells, clustering around them. As the main portion of the dye comes from hemoglobin (that colors blood red), it will absorb red color. So, when the day of surgery arrives, the doctors must simply point the dye laser at the cancerous region and shoot the laser to get absorbed by the cancer cells. The heat will kill them outright.

“With the laser we can clean out diseased pockets of gum tissue to the point where the body can heal itself. We can also make the teeth more resistant to future decay by sterilizing the deep crevices toothbrushes can’t reach.”
-Dr. Delwin McCarthy (
Billings, Lasers the New Technology of Light)

Chemically Speaking


Light Amplification by the Stimulated Emission of Radiation, commonly known as its acronym laser, has been an idea shared by many since the first build by Theodore Maiman in 1960. Stimulated is representing the process of photons being input into excited atoms, which will then result in another photon. Emission adds to this, reaching to the term Stimulated Emission, devised by Albert Einstein . This is the description as to how photons bounce between two mirrors (within the laser device) as they pass through the excited atoms. This continues until there are enough photons to produce a focused, controlled and coherent, phase wavelength.

Photons and electrons are a central piece of how lasers work, and are actually one of the main concepts to this technology. The Quantum Theory (Burking, Photonics...) in essence says that all electrons in atoms can only have specific, predetermined energy levels. These levels are mainly the ground state (bottom level) and excited state (higher level). To raise the electrons, processes like photoelectric affect and electrical, chemical nuclear occurrences, and energetic photons or the ionizing of the atoms must take place.
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So How Does the Laser Work?


Each laser device has an energy source to function. Its active medium, or material, within the system must also be able to absorb and release energy. The last and most important piece of the laser is what is called the feedback mechanism. This consists of two mirrors, one at each end. One is fully reflective, while the other known as the output coupler is only partially reflective.

The laser beam is created first when the energy source, be it electrical or a chemical reaction, releases a flash of light that is absorbed by the medium. This energy inside the active medium excites the atoms to reach a higher energy level. More flashes of light continue to pump, or excite, these atoms. Once more excited atoms exist within the medium than not, a population inversion occurs. This is the last step before a laser reaction happens.

At this point, the high-energy atoms lose their energy to become low-energy atoms. This excess energy is sent out as very small units of light, called photons. These photons excite more atoms to release light as well. This creates what one may call a chain-reaction. Such a massive release of energy has come to be known as stimulated emission, the last step for the light amplification.

As more light is being released by the protons, the mirrors on either end of the laser reflect the light into the active medium. This strengthens the light further in the process of amplification. Once the light gets strong enough, it passes through the output coupler as the laser we see.
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SOURCES




http://www.laserfocusworld.com/display_article/317042/12/none/none/News/QUANTUM-MECHANICS:-Double-slit-experiment-succeeds-in-a-single-hydrogen-molecul

http://education.jlab.org/qa/laser_01.html

http://www.colorado.edu/physics/2000/lasers/index.html

http://www.thetech.org/exhibits/online/lasers/overview.html

http://laserstars.org/history/einstein.html

http://www.epanorama.net/links/laser.html

http://www.asds.net/LaserResurfacingInformation.aspx\


Burking, Valerie. "Photonics: The New Science of Light". Enslow Publishers, inc. 1986.

Billings, Charlene W. Lasers the New Technology of Light//. New York: Facts on File, 1992.