Gain (laser)

In laser physics, gain or amplification is a process where the medium transfers part of its energy to the emitted electromagnetic radiation, resulting in an increase in optical power. This is the basic principle of all lasers. Quantitatively, gain is a measure of the ability of a laser medium to increase optical power. However, overall a laser consumes energy.

## Contents

* 1 Definition
* 2 Gain in quasi two-level system
* 3 Alternative terminology and notations
* 4 See also
* 5 References

## Definition

The gain can be defined as the derivative of logarithm of power P as it passes through the medium. The factor by which an input beam is amplified by a medium is called the gain and is represented by G.

G=ddzln⁡(P)=dP/dzP

where z is the coordinate in the direction of propagation. This equation neglects the effects of the transversal profile of the beam.

In the quasi-monochromatic paraxial approximation, the gain can be taken into account with the following equation

2ik∂E∂z=Δ⊥E+2νE+iGE,

where ν is variation of index of refraction (Which is supposed to be small),

E is complex field, related to the physical electric field Ephys with relation Ephys=Re(e→Eexp⁡(ikz−iωt)), where e→ is vector of polarization, k is wavenumber, ω is frequency, Δ⊥=(∂2∂x2+∂2∂y2) is transversal Laplacian; Re means real part.

## Gain in quasi two-level system

In the simple quasi two-level system, the gain can be expressed in terms of populations N1 and N2 of lower and excited states:

G=σeN2−σaN1

where σe and σa are effective emission and absorption cross-sections. In the case of non-pumped medium, the gain is negative.

Round-trip gain means gain multiplied by the length of propagation of the laser emission during a single round-trip. In the case of gain varying along the length, the round-trip gain can be expressed with integral g=∫Gdz. This definition assumes either flat-top profile of the laser beam inside the laser, or some effective gain, averaged across the beam cross-section.

The amplification coefficient K can be defined as ratio of the output power Pout to the input power Pin:

K=Pout/Pin.

It is related with gain; K=exp⁡(∫Gdz).

The gain and the amplification coefficient should not be confused with the magnification coefficient. The magnification characterizes the scale of enlarging of an image; such enlargement can be realized with passive elements, without gain medium. [1]

## Alternative terminology and notations

There is no established terminology about gain and absorption. Everyone is free to use own notations, and it is not possible to cover all the systems of notations in this article.

In radiophysics, gain may mean logarithm of the amplification coefficient.

In many articles on laser physics, which do not use the amplification coefficient K defined above, the gain is called Amplification coefficient, in analogy with Absorption coefficient, which is actually not a coefficient at all; one has to multiply it to the length of propagation (thickness), change the signum, take inverse of the exponential, and only then get the coefficient of attenuation of the sample.

Some publications use term increment instead of gain and decrement instead of absorption coefficient to avoid the ambiguity,[2] exploiting the analogy between paraxial propagation of quasi-monochromatic waves and time evolution of a dynamic system.

## See also

* Round-trip gain, gain multiplied by the length of propagation of the laser emission during a single round-trip
* Disk laser
* Effective cross-sections
* McCumber relation

## References

1. ↑ A.E.Siegman (1986). Lasers. University Science Books. ISBN 0-935702-11-3. http://www.uscibooks.com/siegman.htm. Retrieved 2007-04-09.
2. ↑ D.Yu.Kuznetsov (1995). The transformation of the transverse structure of monochromatic light in the non-linear media. In book: -- Optics and Lasers. ed: G.G.Petrash.

* v
* t
* e

Lasers

* List of laser articles
* List of laser types
* List of laser applications
* Laser acronyms

* Laser types: Solid-state
* Semiconductor
* Dye
* Gas
* Chemical
* Excimer
* Ion
* Metal Vapor

Laser physics|

* Active laser medium
* Amplified spontaneous emission
* Continuous wave
* Doppler cooling
* Laser ablation
* Laser cooling
* Laser linewidth
* Lasing threshold
* Magneto-optical trap
* Optical tweezers
* Population inversion
* Resolved sideband cooling
* Ultrashort pulse

Laser optics|

* Beam expander
* Beam homogenizer
* B Integral
* Chirped pulse amplification
* Gain-switching
* Gaussian beam
* Injection seeder
* Laser beam profiler
* M squared
* Mode-locking
* Multiple-prism grating laser oscillator
* Multiphoton intrapulse interference phase scan
* Optical amplifier
* Optical cavity
* Optical isolator
* Output coupler
* Q-switching
* Regenerative amplification

Laser spectroscopy|

* Cavity ring-down spectroscopy
* Confocal laser scanning microscopy
* Laser-based angle-resolved photoemission spectroscopy
* Laser diffraction analysis
* Laser-induced breakdown spectroscopy
* Laser-induced fluorescence
* Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy
* Raman spectroscopy
* Second-harmonic imaging microscopy
* Terahertz time-domain spectroscopy
* Tunable diode laser absorption spectroscopy
* Two-photon excitation microscopy
* Ultrafast laser spectroscopy

Laser ionization|

* Above threshold ionization
* Atmospheric-pressure laser ionization
* Matrix-assisted laser desorption/ionization
* Resonance-enhanced multiphoton ionization
* Soft laser desorption
* Surface-assisted laser desorption/ionization
* Surface-enhanced laser desorption/ionization

Laser fabrication|

* Laser beam welding
* Laser bonding
* Laser converting
* Laser cutting
* Laser cutting bridge
* Laser drilling
* Laser engraving
* Laser-hybrid welding
* Laser peening
* Multiphoton lithography
* Pulsed laser deposition
* Selective laser melting
* Selective laser sintering

Laser medicine|

* Computed tomography laser mammography
* IntraLASIK
* Laser capture microdissection
* Laser hair removal
* Laser lithotripsy
* Laser coagulation
* Laser scalpel
* Laser surgery
* Laser thermal keratoplasty
* LASIK
* Low level laser therapy
* Optical coherence tomography
* Photorefractive keratectomy
* Photorejuvenation
* Soft-tissue laser surgery

Laser fusion|

* Argus laser
* Cyclops laser
* GEKKO XII
* HiPER
* ISKRA lasers
* Janus laser
* Laboratory for Laser Energetics
* Laser integration line
* Laser Mégajoule
* Long path laser
* LULI2000
* Mercury laser
* National Ignition Facility
* Nike laser
* Nova (laser)
* Novette laser
* Shiva laser
* Trident laser
* Vulcan laser

Civil applications|

* 3D laser scanner
* CD
* DVD
* Laser lighting display
* Laser pointer
* Laser printer
* Laser tag

Military applications|

* Advanced Tactical Laser
* Boeing Laser Avenger
* Dazzler (weapon)
* Electrolaser
* Laser designator
* Laser guidance
* Laser-guided bomb
* Laser guns
* Laser rangefinder
* Laser warning receiver
* Laser weapon
* LLM01
* Multiple Integrated Laser Engagement System
* Tactical High Energy Laser
* Tactical light
* ZEUS-HLONS (HMMWV Laser Ordnance Neutralization System)

* Category
* Commons

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Gain (laser). Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Physics:Gain_(laser)&oldid=421198"
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template