Laser pumping

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Laser pumping is the act of energy transfer from an external source into the laser gain medium. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in ground state or a less-excited state, population inversion is achieved. In this condition, the mechanism of stimulated emission can take place and the medium can act as a laser or an optical amplifier. The pump power must be higher than the lasing threshold of the laser.

The lasers can be pumped by multiple ways.

Optical pumping
* Flash lamps are the oldest energy source for lasers. They are used for lower energies in both solid state and dye lasers. They produce a broad spectrum, causing most of the energy to be wasted as heat in the gain medium. Flash lamps also tend to have short lifetime.
* Lasers of a suitable type can be used to pump another laser. Their narrow spectrum makes them more efficient way of energy transfer than flash lamps. Diode lasers are used to pump DPSS lasers.
* Microwaves are used to excite gas lasers.
Electrical pumping
* Electric glow discharge is common in gas lasers. Eg. in the helium-neon laser the electrons from the discharge collide with the helium atoms, the helium atoms get excited, they transfer their energy by collision with neon atoms, and inverse population of neon atoms builds up.
* Electric current is typically used to pump semiconductor lasers.
Electron beams are used in special applications, eg. the free electron lasers or excimer lasers.
Chemical reaction is used as a power source in chemical lasers. This allows for very high output powers difficult to reach by other means.
Nuclear fission is used in exotic nuclear pumped lasers (NPL), directly employing the energy of the fast neutrons released in a nuclear reactor. [link] [link]

Laser pumping

See also