Meaning of the gain medium
In laser physics, the laser gain medium is the medium (typically in the form of a beam) that amplifies the power of light. In a laser, the medium needs to make up for the loss of the resonator and is commonly referred to as the “energetic laser medium.” The gain medium can additionally be applied to fiber optic amplifiers. Gain refers to the degree of boosting.
Given that the gain medium increases the energy of the amplified beam, the medium must obtain the energy itself, that is, through a pumping process, which is normally designed to either pump current (electrical pumping) or input light wave (optical pumping), and the pump wavelength is smaller than the signal light’s.
Types of laser gain media
There are numerous types of gain media. The usual ones are the following:
Semiconductors
Some direct bandgap semiconductors, such as GaAs, AlGaAs, and InGaAs, are normally pumped by an electrical source existing in the form of quantum wells (see semiconductor lasers).
Laser crystals or glass
Laser crystals or glass, such as Nd:YAG crystal (neodymium-doped yttrium aluminum garnet), Yb:YAG (ytterbium aluminum garnet laser), and Er glass, Er:YAG (erbium-doped YAG) or titanium sapphire, in solid sheet type (see volume laser) or optical glass fiber (fiber laser, fiber amplifier). These crystals or glasses are pumped with light waves and doped with laser-active ions (mostly trivalent rare-earth ions; in some cases, steel ions). Lasers utilizing these media are commonly referred to as doped insulator lasers.
Ceramic gain media
Ceramic gain media are typically doped with rare-earth component ions as well.
Laser dye
Color lasers use a laser dye, which is typically a liquid service.
Gas
Gas lasers use several gases or a combination of gases, usually pumped by a discharge device (such as carbon dioxide as well as excimer lasers).
Unique gain medium
Unique gain medium include chemical gain conciliators (which transform chemical energy into light), nuclear pumping modulators, and also oscillators in complementary electron lasers (which transfer energy from a quick electron light beam into a beam of light).
Important physical results
Most of the times, the physical basis of the boosting procedure is promoted radiation, in which the case photon creates more photon radiation and the ecstatic laser-active ion initial shifts to a slightly lower energy excited state. There is a distinction in between the four-level gain medium as well as the three-level gain medium
A boosting procedure that occurs much less often is promoted Raman scattering, which entails altering several of the higher-energy pumped photons right into lower-power photons and also phonons (related to lattice vibrations). If the case light power is really high, the gain will certainly lower after the gain medium reaches gain saturation. At a limited pump power, the amplifier cannot provide an arbitrarily huge amount of power to the occurrence beam. In laser amplifiers, the number of ions in the upper level lowers at saturation because of stimulated radiation.
The gain medium has a thermal impact because part of the pump light power is exchanged heat. The resulting temperature level slope and mechanical stress and anxiety will create the prism impact and distort the magnified beam. These effects can destroy the beam of light top quality of the laser, minimize its performance, and also destroy the gain medium (thermal splitting).
Associated physical properties of laser gain medium
- In laser applications, the physical properties of several gain media are very important. It mostly includes:
- In the laser change process calling for wavelength area, the very best optimal gain takes place in this area.
- The substrate has a high degree of transparency in the working wavelength area.
- Excellent pump light, efficient pump absorption.
- Ideal high-ranking lifetime: enough time for Q-switched applications and also brief sufficient for rapidly regulated power.
- High quantum performance is gotten from usual quenching results, fired up state absorption, as well as similar processes or beneficial impacts such as multiphoton transitions or energy transfers.
- Suitable four-level behavior since quasi-three-level actions presents a few other extra constraints.
- High strength as well as lengthy life, chemical stability.
- For solid-state gain media, the base media must have high optical quality, be able to be cut or brightened of really premium quality (ideal hardness), allow high concentrations of laser-active ions to be doped without forming clusters, have high chemical security, good thermal conductivity and low thermo-optical coefficient (weak thermal prism impact at high power operation), be resistant to mechanical tension, and have optical isotropy.
- Low pump power threshold at a high gain: The item of radiation cross-section as well as high-ranking lifetime is larger.
- The beam of light top quality of the pump source of light is reduced: high pump absorption is needed.
- Wavelength tuning: Requires huge gain data transfer
- Ultrashort pulse generation: gain range is broad and also flat; Ideal diffusion and also nonlinearity.
- Passive mode-locked lasers without Q-switching security: adequately huge laser cross-sections.
- High-energy pulse boosting (favorable responses amplifier): Result of a high optical damage threshold and not too high gain saturation.
- A short pump absorption length is beneficial but aggravates the thermal result.
- The requirements for the gain medium differ from case to case. As a result, lots of gain media are extremely vital for applications, and it is also needed to choose the ideal gain media when enhancing the style of the laser.
Read more: Er,Yb:phosphate Glass
