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