Optics 101

Gain Medium - Definition and Use in Laser Construction

A gain medium is a material with quantum properties that allow it to amplify laser beams by means of stimulated emission. It is the source of optical gain within a laser which results from the emission of molecular or electronic transitions from a higher energy state to a lower energy state. The medium is excited by a pump source.

Gain media can have wide or linear spectra. Tunable lasers have a frequency which can be altered - this is achieved using a gain medium with a wide spectrum.

Types of Gain Media

There are a number of laser gain media. Some of the most common media include:

  • Gas lasers which include certain gases or gas mixtures pumped with electrical discharges, e.g. excimer lasers and CO2 lasers.
  • Certain glasses and laser crystals such as Nd:YAG, Yb:YAG, Rr:YAG or Ti:sapphire. These crystals and glasses are optically pumped and doped with laser- active ions.
  • Laser dyes in liquid form
  • Semiconductors such as gallium nitride, indium gallium arsenide and gallium arsenide semiconductors pumped with electrical currents in the form of quantum wells
  • Ceramic gain media, nuclear pumped media and undulators in free electron lasers.

Properties of Gain Media

Given below are the key properties of gain media:

  • High transparency of the host medium
  • Chemical stability
  • High quantum efficiency
  • Passive mode locking without instabilities in Q-switching
  • High optical damage threshold
  • Laser transition takes place in the desired wavelength
  • Low beam quality requirements on the pump source
  • High energy pulse amplification
  • Ultra-short pulse generation



  1. michelle choi michelle choi Korea says:

    Such a brief and well-summarized article.Thanks for your service

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