laser gain medium

Interpretation of the gain medium

In laser physics, the laser gain medium is the medium (usually in the form of a beam) that magnifies the power of light. In a laser, the medium requires to compensate for the loss of the resonator and is usually described as the energetic laser medium. The gain medium can likewise use it to optical fiber amplifiers. Gain refers to the level of amplification.

Considering that the gain medium raises the power of the enhanced light beam, the medium itself needs to receive the energy, that is, with a pumping procedure, generally made to either present (electric pumping) or input light wave (optical pumping), as well as the pump wavelength is smaller than that of the signal light.

Types of laser gain media

There are many type of gain media. The common ones are the following:

  • Some straight bandgap semiconductors, such as GaAs, AlGaAs, and also InGaAs, are typically pumped by an electric 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), Er: glass, Er: YAG (Erbium doped YAG), or Ti:sapphire crystal, in strong sheet form (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 transition steel ions) and pumped with light waves. Lasers utilizing these media are usually referred to as drugged insulator lasers.
  • Ceramic gain media are normally likewise doped with rare earth aspect ions.
  • A laser dye, normally a fluid service, is used in color lasers.
  • Gas lasers make use of several gases or a combination of gases, typically pumped by a discharge gadget (such as carbon dioxide as well as excimer lasers).
  • Special gain arbitrators consist of chemical gain arbitrators (which transform chemical energy right into light), nuclear pumping arbitrators, as well as oscillators in totally free electron lasers (which transfer energy from a rapid electron beam of light right into a light beam).

Important physical effects

In most cases, the physical basis of the boosting procedure is boosted radiation, in which the case photon creates more photon radiation and also the excited laser-active ion very first changes to a slightly reduced power thrilled state. There is a distinction in between the four-level gain medium and the three-level gain medium

An amplification procedure that happens much less frequently is promoted Raman spreading, which entails transforming some of the greater energy pumped photons into reduced power photons and also phonons (related to lattice resonances). If the occurrence light power is extremely high, the gain will reduce after the gain medium reaches gain saturation. The amplifier can not include an arbitrarily huge quantity of power to the occurrence beam of light at a minimal pump power. In laser amplifiers, the variety of ions in the top level decreases at saturation as a result of boosted radiation.

The gain medium has a thermal effect because part of the pump light power is exchanged warm. The resulting temperature level slope and also mechanical stress and anxiety will certainly cause the prism result as well as misshape the intensified beam. These impacts can damage the beam of light quality of the laser, lower its efficiency, and also ruin the gain medium (thermal breaking).

Related physical residential properties of laser gain medium

In laser applications, the physical buildings of several gain media are very important. It mainly includes:

  • In the laser transition procedure needing wavelength area, the very best optimal gain occurs in this region.
  • The substratum has a high level of transparency in the functioning wavelength region.
  • Good pump source of light, effective pump absorption.
  • Appropriate high-ranking life time: enough time for Q-switched applications and also brief enough for promptly modulated power.
  • High quantum performance is gotten from usual quenching effects, fired up state absorption, and comparable processes or beneficial impacts such as multiphoton changes or energy transfers.
  • Suitable four-level habits because quasi-three-level actions presents a few other additional constraints.
  • High strength as well as lengthy life, chemical security.
  • For solid-state gain media: Base media need to be of great optical high quality, can be cut or polished of very top quality (ideal hardness), allow high focus of laser-active ions to be doped without forming collections, have good chemical security, have a good thermal conductivity as well as reduced thermo-optical coefficient (weak thermal prism impact at high power procedure), resistance to mechanical anxiety, optical isotropy is normally required, Yet often birefringence (minimizing the impact of thermal depolarization) as well as gain associated with polarization is needed.
  • Low pump power threshold at a high gain: The item of radiation cross-section as well as upper-level life time is bigger.
  • The beam of light quality of the pump source of light is low: high pump absorption is needed.
  • Wavelength tuning: Needs huge gain transmission capacity
  • Ultrashort pulse generation: gain spectrum is broad as well as flat; Proper dispersion and nonlinearity.
  • Passive mode-locked lasers without Q-switching stability: completely large laser cross-sections.
  • High energy pulse boosting (favorable feedback amplifier): Effect of high optical damages threshold as well as not too high saturation on gain.