In laser physics, the laser gain medium is the medium (typically in the form of a beam) that intensifies the power of light. In a laser, the medium requires to compensate for the loss of the resonator and is usually described as the active laser medium. The gain medium can likewise use for optical fiber amplifiers. Gain refers to the degree of amplification.
Since the gain medium boosts the power of the intensified light beam. The medium itself requires to obtain energy. That is, through a pumping procedure, usually developed to either existing (electric pumping) or input light wave (optical pumping). The pump wavelength is smaller sized than that of the signal light.
Kinds of laser gain medium
There are numerous kinds of gain media. The common ones are the following:
– Some direct bandgap semiconductors, such as GaAs, AlGaAs, and InGaAs.They are usually pumped by an electrical existing in the form of quantum Wells (see semiconductor lasers).
– Laser crystals or glasses, such as Nd: YAG, Nd: YVO4, Yb: YAG( Ytterbium aluminum garnet laser), Yb: glass, Er: YAG (Er: YAG Laser), or titanium sapphire, in solid sheet form (see volume laser) or optical glass fiber (fiber laser, fiber amplifier). These crystals or glasses are doped with laser-active ions (primarily trivalent rare-earth ions, sometimes shift metal ions) and pumped with light waves. Lasers utilizing these media are typically described as drugged insulator lasers.
– Ceramic gain media are generally also doped with rare earth aspect ions.
– A laser dye, normally a liquid remedy, is utilized in dye lasers.
– Gas lasers make use of numerous gases or a combination of gases, generally pumped by a discharge device (such as CO2 and also excimer lasers).
– Special gain moderators consist of chemical gain arbitrators (which transform chemical power into light), nuclear pumping conciliators, and also oscillators in cost-free electron lasers (which transfer energy from a quick electron light beam into a beam).
Important physical impacts
For the most part, the physical basis of the amplification process is boosted radiation, in which the event photon causes more photon radiation as well as the exciting laser-active ion first changes to a somewhat reduced power excited state. There is a distinction between the four-level gain medium and the three-level gain medium.
An amplification process that occurs much less regularly is boosted Raman spreading. Which entails altering some of the higher energy pumped photons into lower energy photons and also phonons. If the occurrence of light power is very high, the gain will lower after the gain medium reaches gain saturation. The amplifier can not add an arbitrarily big amount of power to the incident light beam at a minimal pump power. In laser amplifiers, the variety of ions in the upper level decreases at saturation as a result of promoted radiation.
The gain medium has a thermal effect since part of the pump light power is exchanged for warmth. The resulting temperature level gradient and also mechanical anxiety will certainly cause the prism result and misshape the amplified light beam. These results can ruin the light beam’s high quality of the laser, reduce its performance, and also ruin the gain medium (thermal breaking).
The character of laser gain medium.
In laser applications, the physical properties of lots of gain media are essential. It generally consists of:
For solid-state gain media:
Base media need to be of excellent optical quality. It can be cut or polished of really high quality (ideal firmness), enable the high focus of laser-active ions to be doped without forming clusters. have excellent chemical security, has good thermal conductivity and low thermo-optical coefficient (weak thermal prism effect at high power operation), resistance to mechanical stress and anxiety, optical isotropy is typically called for. However often birefringence (decreasing the effect of thermal depolarization) and also gain related to polarization are needed (see the polarization of laser radiation).
Low pump power limit at a high gain:
The item of radiation cross-section, as well as high-ranking lifetime, is bigger.
The light beam quality of the pump source of light is reduced:
high pump absorption is required.
Wavelength adjusting:
Needs a huge gain in transmission capacity
Ultrashort pulse generation:
the gain range is vast and level; with Suitable dispersion and also nonlinearity.
Passive mode-locked lasers without Q-switching security:
sufficiently huge laser cross-sections.
High energy pulse amplification (positive feedback amplifier):
Effect of high optical damage limit and also not too expensive saturation on gain.
Note that there are situations where contradictory needs are needed. For example, very reduced quantum issues are inappropriate with a four-level system. A large gain data transfer corresponds to a smaller laser cross-section than the ideal instance, and also the quantum issue is not so tiny. The disorder in the solid-state gain medium raises the gain bandwidth and lowers thermal conductivity.
A brief pump absorption length is beneficial but worsens the thermal result.
The demands for the gain medium differ from instance to instance. For that reason, many gain media are extremely crucial for applications. It is required to choose the best gain media when optimizing the layout of the laser.
