3 main Components of Laser

The term Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. There are main 3 components of Laser device:

  1. The active Medium or laser gain medium.
  2. A pumping device.
  3. A resonant cavity.


The basic laser components are active or gain medium, pumping device or source and resonant cavity is shown in figure below.

  • The active Medium or laser gain medium.
  • A pumping device.
  • A resonant cavity.

The active Medium (or laser gain medium)

The main component of a laser is a certain medium in the form of a solid, liquid or gas called active medium. The main characteristics of the active medium are as follows:

  • It must have a pair of energy levels separated by a certain amount of energy. The energy level having high energy is known as upper energy level or higher excited energy level and the energy level having low energy is known as lower energy level or ground state.
  • It must allow a population inversion between two energy levels.

Examples of Active Media

  1. Ruby which is Al₂O3 with some of the aluminium (Al) atoms replaced by the chromium (Cr) ions. In this case, chromium (Cr) ions are the active centre or active media.
  2. Atoms such as helium-neon (He-Ne) in the Helium-Neon laser emitting red light.
  3. Molecules such as carbon-dioxide (CO₂) in infrared laser.
  4. Liquids (organic dye molecules dissolved in solvent solutions).
  5. Dielectric solids like neodymium atoms doped in YAG to make Nd: YAG crystal.
  6. Semiconductor material such as gaflium arsenide or indium phosphide crystals.

A pumping device

It is an external source of energy which provides the necessary energy to the active medium to produce a state of population inversion, essential for lasing action.

The most commonly used methods of pumping are:

  • Optical pumping,
  • Electric discharge
  • Inelastic atomic collisions,
  • Chemical reaction energy called chemical pumping.

A resonant cavity

Population inversion is achieved to amplify the signal via (or photon) stimulated emission. However, in practice, most of atoms in the excited state emit spontaneously and do not contribute to the overall output.

Only few atoms in the excited state emit via stimulated emission and hence overall gain of the output is small. Therefore, we require a positive feedback mechanism to make most of the atoms in the excited state to emit via stimulated emission for contributing to the coherent output.

A device used to have positive feedback mechanism for maximum coherent output is known as resonator or resonant cavity. Thus, resonant cavity or resonator is a feed back device that makes the photons to move back and forth through the active medium.

In this process, the number of photons emitted due to stimulated emission are multiplied. A resonant cavity consists of a pair of plane or spherical mirrors placed parallel to each other at the ends of the active medium.

One of the mirror is fully reflecting mirror and the other is partially transmitting mirror. The laser output is taken out through the partially transmitting mirror which is also called output coupler mirror.