Definition of the gain medium

In laser physics, the laser gain medium is the medium (usually in the form of a beam of light) that intensifies the power of light. In a laser, the medium is required to make up for the resonator’s loss and is often referred to as the energetic laser medium. The gain medium can additionally apply it to optical fiber amplifiers. Gain refers to the level of amplification.

Given that the gain medium increases the energy of the intensified light beam, the medium itself needs to obtain the power, that is, via a pumping process, generally made to either present (electrical pumping) or input light wave (optical pumping). The pump wavelength is smaller sized than that of the signal light.

Kinds of laser gain media

There are numerous kinds of gain media. The typical ones are the following:

Some straight bandgap semiconductors.

GaAs, AlGaAs, and InGaAs are typically pumped by an electric existing in the form of quantum Wells (see semiconductor lasers).

Laser crystals or glasses

Such as Nd: YAG( neodymium-doped yttrium aluminum garnet, see yttrium aluminum garnet laser), Yb: YAG( Ytterbium aluminum garnet laser), Yb: glass, Er: YAG (Erbium doped YAG), or titanium sapphire, in solid sheet kind (see volume laser) or optical glass fiber (fiber laser, fiber amplifier). These crystals or glasses are doped with laser-active ions (mostly trivalent rare-earth ions, sometimes change metal ions) and pumped with light waves. Lasers using these media are often referred to as drugged insulator lasers.

Ceramic gain media are normally additionally doped with rare earth component ions. A laser dye, normally a liquid service, is used in color lasers. Gas lasers use several gases or a blend of gases, generally pumped by a discharge tool.

Such as CO2 and excimer lasers. Special gain arbitrators include chemical gain conciliators (which convert chemical power right into light). Nuclear pumping arbitrators and oscillators in free electron lasers (which transfer power from a fast electron light beam right into a beam).

Important physical results

In many cases, the physical basis of the boosting process is boosted radiation, in which the event photon creates even more photon radiation, and the fired-up laser-active ion initially transitions to a slightly lower energy thrilling state. There is a difference between the four-level gain medium and the three-level gain medium.

A boosting procedure that occurs much less often is boosted Raman spreading, which involves changing several of the greater power-pumped photons into reduced power photons and phonons (about latticework vibrations). If the event light power is very high, the gain will certainly lower after the gain medium reaches gain saturation. The amplifier can not include an arbitrarily large power to the case beam at a limited pump power. In laser amplifiers, the variety of ions in the top degree reduces at saturation because of promoted radiation.

The gain medium has a thermal impact because part of the pump light power is converted into heat. The resulting temperature level gradient, mechanical stress, and anxiety will cause the prism result and distort the intensified light beam. These results can damage the beam of light high quality of the laser, decrease its efficiency, and destroy the gain medium (thermal breaking).

Associated physical buildings of laser gain medium

In laser applications, numerous gain media’s physical residential or commercial properties are important.

It mostly consists of the following:

• In the laser change process requiring wavelength region, the most effective height gain happens in this region.
• The substrate has a high degree of openness in the functional wavelength area.
• Excellent pump light and efficient pump absorption.
• Suitable high-ranking lifetime: long enough for Q-switched applications and short enough for rapidly modulated power.
• High quantum performance is obtained from typical quenching impacts, fired-up state absorption, and comparable procedures or useful results such as multiphoton transitions or power transfers.
• Ideal four-level actions because quasi-three-level habits presents a few other extra restraints.
• High toughness and long life, chemical security.

For solid-state gain media:

Base media need to be of excellent optical quality, can be reduced or polished of extremely premium quality (appropriate solidity), enable high concentration of laser-active ions to be doped without forming clusters, have good chemical stability, have a great thermal conductivity as well as a reduced thermo-optical coefficient (weak thermal prism impact at high power operation), resistance to mechanical stress and anxiety, optical isotropy is generally required, however in some cases birefringence (reducing the effect of thermal depolarization) and gains connected with polarization is needed (see the polarization of laser radiation).

• Reduced pump power threshold at a high gain: The radiation cross-section and high-ranking lifetime are bigger.

• The high beam quality of the pump light source is low: High pump absorption is called for.

• Wavelength tuning: Requires large gain transmission capacity

• Ultrashort pulse generation: gain spectrum is vast and level; Ideal diffusion and nonlinearity.

• Passive mode-locked lasers without Q-switching security: sufficiently large laser cross-sections.

• High power pulse boosting (good feedback amplifier): Result of high optical damage limit and not expensive saturation on gain.

Note that there are situations where contradictory needs are called for. For example, reduced quantum defects are incompatible with a four-level system. A huge gain transmission capacity represents a smaller laser cross-section than the perfect case, and the quantum issue is not so tiny. The disorder in the solid-state gain medium increases the gain transmission capacity and lowers thermal conductivity.

A brief pump absorption length is advantageous yet aggravates the thermal effect. The requirements for the gain medium differ from instance to case. Therefore, many gain media are crucial for applications, and it is necessary to choose the ideal gain media when optimizing the layout of the laser.