In laser physics, the laser gain medium is the medium (normally in the form of a beam of light) that magnifies the power of light. In a laser, the medium requires to make up for the loss of the resonator and also is typically referred to as the active laser medium. The gain medium can additionally use for optical fiber amplifiers. Gain refers to the degree of boosting.
Because the gain medium boosts the energy of the enhanced beam, the medium itself needs to get the power, that is, through a pumping procedure, typically developed to either existing (electrical pumping) or input light wave (optical pumping), as well as the pump wavelength is smaller sized than that of the signal light.
Types of laser gain media
There are numerous kinds of gain media. The common ones are the following:
Some straight bandgap semiconductors, such as GaAs, AlGaAs, as well as InGaAs, are usually pumped by an electrical current 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),Er: glass, or titanium sapphire, in strong sheet type (see quantity laser) or optical glass fiber (fiber laser, fiber amplifier). These crystals or glasses are doped with laser-active ions (mainly trivalent rare-earth ions, occasionally transition steel ions) and also pumped with light waves. Lasers using these media are often referred to as doped insulator lasers.
Ceramic gain media are normally additionally doped with rare earth component ions.
A laser dye, generally a liquid service, is utilized in dye lasers.
Gas lasers utilize several gases or a combination of gases, normally pumped by a discharge gadget (such as CO2 and also excimer lasers).
Special gain conciliators consist of chemical gain arbitrators (which transform chemical power into light), nuclear pumping conciliators, and also oscillators in complimentary electron lasers (which transfer energy from a fast electron beam of light right into a beam of light).
Crucial physical results
For the most part, the physical basis of the boosting process is stimulated radiation, in which the event photon triggers more photon radiation as well as the fired-up laser-active ion very first changes to a slightly lower power excited state. There is a distinction between the four-level gain medium as well as the three-level gain medium
A boosting process that takes place much less frequently is boosted Raman spreading, which entails transforming some of the higher energy pumped photons into lower energy photons and also phonons (related to lattice vibrations). If the incident light power is really high, the gain will lower after the gain medium gets to gain saturation. The amplifier can not add a randomly big amount of power to the occurrence beam at a restricted pump power. In laser amplifiers, the variety of ions in the top level reduces at saturation because of stimulated radiation.
The gain medium has a thermal result because part of the pump light power is exchanged for warmth. The resulting temperature level slope as well as mechanical stress will trigger the prism effect as well as misshape the enhanced light beam. These effects can destroy the light beam top quality of the laser, lower its performance, and also ruin the gain medium (thermal fracturing).
Associated physical residential properties of laser gain medium.
In laser applications, the physical residential or commercial properties of numerous gain media are important. It mainly includes:
In the laser shift process needing wavelength area, the very best height gain happens in this region.
The substrate has a high degree of transparency in the functioning wavelength region.
Excellent pump light source, reliable pump absorption.
Ideal upper-level lifetime: enough time for Q-switched applications and also brief sufficient for promptly modulated power.
High quantum performance is acquired from typical quenching impacts, fired up state absorption, and similar processes or advantageous effects such as multiphoton transitions or power transfers.
Suitable four-level behavior due to the fact that quasi-three-level behavior presents a few other additional restrictions.
High stamina and lengthy life, chemical security.
For solid-state gain media: Base media require to be of great optical high quality, can be cut or polished of very excellent quality (ideal hardness), enable the high focus of laser-active ions to be doped without forming clusters, have good chemical stability, have a great thermal conductivity and reduced thermo-optical coefficient (weak thermal prism effect at high power operation), resistance to mechanical anxiety, optical isotropy is usually needed, Yet often birefringence (reducing the effect of thermal depolarization), as well as gain associated with polarization, is needed (see the polarization of laser radiation).
Low pump power limit at a high gain: The product of radiation cross-section and also high-ranking life time is larger.
The light beam quality of the pump light source is reduced: high pump absorption is called for.
Wavelength tuning: Calls for large gain transmission capacity
Ultrashort pulse generation: gain spectrum is broad as well as level; Appropriate diffusion and also nonlinearity.
Passive mode-locked lasers without Q-switching security: completely large laser cross-sections.
High power pulse amplification (favorable responses amplifier): Result of high optical damage threshold as well as not too high saturation on gain.
Note that there are situations where conflicting needs are required. For example, extremely low quantum flaws are incompatible with a four-level system. A huge gain data transfer corresponds to a smaller laser cross-section than the suitable case, and the quantum flaw is not so little. The problem in the solid-state gain medium enhances the gain bandwidth and also decreases thermal conductivity.
A short pump absorption length is advantageous yet intensifies the thermal impact.
The demands for the gain medium differ from situation to instance. Consequently, lots of gain media are really vital for applications, as well as it is necessary to select the best gain media when optimizing the design of the laser.