This article describes optical pulses, nonlinearity-induced distortion, and methods to reduce nonlinearity pulse distortion.

Light pulses (especially ultrashort pulses with pulse lengths of picoseconds or femtoseconds) have high peak power and peak intensity even if the pulse energy (eg, in the order of millijoules) is moderate. Therefore, the propagation of pulses in transparent media is greatly affected by nonlinearities, such as in laser crystals, especially in optical fibers.

1. If propagating in an isotropic medium (eg, bulk crystal), its spatial properties are affected. One example is the self-focusing effect, which can cause laser-induced breakdown in extreme cases. In non-extreme cases, there are aberrations and time-dependent lenses.
2. Self-phase modulation causes strong spectral distortion, that is, the spectrum is strongly modulated and broadened.
3. The temporal shape of the pulse is also distorted: the pulse may be stretched, or become asymmetric, etc. In the extreme case, a pulse can be split into multiple pulses. Another example is obtaining higher-order soliton splitting during supercontinuum generation. A related phenomenon is wave breakup. In most cases, the temporal spectral distortion is not directly influenced by the nonlinearity, but is the result of the chromatic dispersion of the pulses from the nonlinearly broadened spectrum. For example, self-phase modulation (excluding self-jitter effects) or Raman scattering does not directly affect the temporal shape, but changes the spectrum, and then the pulse is more susceptible to dispersion effects.

In amplifiers, the gain saturation effect causes strong distortion in the pulse time shape, and the resulting flanks are then amplified, while the latter parts are not amplified much because the gain is already saturated.

Nonlinear pulse distortion is closely related to the specific situation, namely the type and strength of the nonlinearity, as well as other effects such as dispersion or waveguide effects. Calculations and analyses can be performed using the impulse propagation model.

There are also many ways to reduce nonlinear pulse distortion, such as the distortion of ultrashort pulses in amplifiers. For example, using thin (highly doped) amplifier crystals, chirped pulse amplification and sub-pulse amplification.