Laser Systems

1
Laser Systems

• Fredrick Brown
• ELEC 6750
• Spring 2004

2
Questions

• What is a laser?
• What are the primary parts of a gas laser system?

3
Overview

• Primary Parts of a laser
• Population Inversion
• Gases Used in lasers
• Summary
• Answers to questions

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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.
http//vcs.abdn.ac.uk/ENGINEERING/lasers/gas.html
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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.
http//hyperphysics.phy-astr.gsu.edu/hbase/optmod/
lasgas.html
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Gases

• Helium-Neon
• Argon-Ion
• Carbon Dioxide

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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.

http//hyperphysics.phy-astr.gsu.edu/hbase/optmod/
lasgas.html
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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
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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.

http//vcs.abdn.ac.uk/ENGINEERING/lasers/gas.html
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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.

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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.

http//www.repairfaq.org/sam/lasercc2.htm
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CO2 (Cont.)
http//www.repairfaq.org/sam/lasercc2.htm
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Summary

• 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.

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Answers

• 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.