where is variation of index of refraction (Which is supposed to be small),
is complex field, related to the physical electric field with relation , where is vector of polarization, is wavenumber, is frequency, is transversal Laplacian; means real part.
where and 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 . 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 can be defined as ratio of the output power input power :
. It is related with gain; .
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.
In radiophysics, gain may mean logarithm of the amplification coefficient.
In many articles on laser physics, which do not use the amplification coefficient 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, exploiting the analogy between paraxial propagaition of quasi-monochromatic waves and time evolution of a dynamic system.
"Generating Laser Pulses of Narrow Spectral Linewidth Based on Chirping and Stretching of Laser Pulses and Subsequent Power Amplification" in Patent Application Approval Process
Dec 13, 2012; By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Lin, Anthony Hong...