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Laser Systems. Fredrick Brown ELEC 6750 Spring 2004. Questions. What is a laser? What are the primary parts of a gas laser system?. Overview. Primary Parts of a laser Population Inversion Gases Used in lasers Summary Answers to questions. Primary Parts.

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laser systems

Laser Systems

Fredrick Brown

ELEC 6750

Spring 2004

  • What is a laser?
  • What are the primary parts of a gas laser system?
  • Primary Parts of a laser
  • Population Inversion
  • Gases Used in lasers
  • Summary
  • Answers to questions
primary parts
Primary Parts
  • A laser consists of two primary parts: a cavity consisting of at least two mirrors and a gas discharge tube with a means of establishing a population inversion.
  • The mirrors in a gas laser are highly specialized and will be used to form the ends of the laser cavity. They are coated with thin films that make them highly reflective for the exact wavelength. One of the mirrors is 100% reflective while the other is about 99%. This will allow a thin beam to be reflected from the difference in the 1%.

Figure 1. Diagram of a laser beam reflecting between mirrors in tube.

population inversion
Population Inversion
  • A population inversion is when molecules or gas particles are excited to a higher energy state larger than that of a lower energy state.
  • The gas inside of the cavity will amplify the number of photons that are put in, for example, for every photon which passes through the substance, two others leave it creating an extremely coherent beam of light all in phase.
  • The process of exciting molecules to create the population inversion is call “pumping”. Electrons in a gas discharge do the job of exciting molecules from low energy states to high energy states.

Figure 2. Example of population inversion of gas particles.

  • Helium-Neon
  • Argon-Ion
  • Carbon Dioxide
helium neon
  • The most common and inexpensive gas laser is the HeNe. It is usually constructed to operate in the red wavelength at 632.8nm. It can also produce laser action in the green at 543.5nm and in the infrared at 1523nm. Also, it contains about 85% helium and 15% neon gas and about 1/300 of atmospheric pressure.

hene cont
HeNe (Cont.)
  • The lighter Helium atoms are excited by collisions with electrons in the discharge. Next, the Helium atoms collide with the heavier Neon atoms which excites them to their metastable state where population inversion builds up.

Bridges, W.B. and Chester, A.N. "Ionized Gas Lasers," in handbook of lasers. Presley, R.J. editor. Chemical Rubber Co., 1971

argon ion
  • The Argon-Ion laser is capable of producing approximately 10 wavelengths in the ultraviolet and up to 25 in the visible region, ranging from 275-363.8nm and 408.9-686.1nm.
  • The typical Argon laser has a high melting point and allows the laser to operate at a higher power level with longer tube life than the HeNe.

argon ion cont
Argon-Ion (Cont.)
  • An unfortunate side effect of the high discharge current and the low gas pressure employed by the Argon-Ion laser is an extremely high plasma electron temperature, which generates a significant amount of heat. Therefore, this lasers system are water cooled through an external chiller or an efficient fan.
carbon dioxide
Carbon Dioxide
  • CO2 laser emits an invisible infrared beam of a single wavelength in the form of a small, intense beam. Specifically, CO2 emits photons at 10.6 and 9.6um.
  • The beam produces a very high temperature that may be used for engraving, cutting, drilling, marking, welding and in various medical applications such as dermatology and as a medical tool for producing clean cuts with little bleeding.

co2 cont
CO2 (Cont.)

  • In conclusion, energy in the form of heat, light, and chemical reaction can be used to excite electrons within atoms and push them to higher energy states within a laser system to create a population inversion. The relaxation of electrons to lower energy states, ultimately, to their ground state using the correct primary parts can produce ultraviolet light, visible light, and infrared radiation in a laser system.
  • What is a laser?Light Amplification by Stimulated Emission of Radiation.
  • What are the primary parts of a gas laser system?A cavity consisting of at least 2 mirrors and a gas discharge tube.