How Lasers Work


Laser Classifications

Laser warning sign

Lasers are classified into four broad areas depending on the potential for causing biological damage. When you see a laser, it should be labeled with one of these four class designations:

  • Class I - These lasers cannot emit laser radiation at known hazard levels.
  • Class I.A. - This is a special designation that applies only to lasers that are "not intended for viewing," such as a supermarket laser scanner. The upper power limit of Class I.A. is 4.0 mW.
  • Class II - These are low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
  • Class IIIA - These are intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.
  • Class IIIB - These are moderate-power lasers.
  • Class IV - These are high-power lasers (cw: 500 mW, pulsed: 10 J/cm2 or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potential fire hazard and a skin hazard. Significant controls are required of Class IV laser facilities.

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About the Author
Matthew Weschler holds an MS degree in Physical Organic Chemistry from Florida State University. His thesis topic was picosecond laser spectroscopy, and he studied how molecules react picoseconds after being bombarded by laser light.

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