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Nonlinear Pulse Distortion

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Definition: distortion of the spatial, temporal or spectral characteristics of an optical pulse, resulting from optical nonlinearities

German: nichtlineare Pulsverzerrung

Categories: optical amplifiers, fiber optics and waveguides, nonlinear optics, light pulses

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Optical pulses, in particular ultrashort pulses with pulse durations of picoseconds or femtoseconds, can have very high peak powers and peak intensities even when the pulse energy is moderate, e.g. in the microjoule regime. As a consequence, such pulses can be strongly influenced by nonlinearities during propagation in transparent media, such as in laser crystals or particularly in optical fibers. Nonlinear effects can result in distortions of various kinds:

In amplifiers, the effect of gain saturation can also lead to substantial distortions of the temporal pulse shape: while the leading wing of the pulse experiences strong amplification, later parts are less strongly amplified as the gain is saturated already.

supercontinuum, time domain

Figure 1: Temporal shape of a femtosecond pulse, which has been distorted during propagation in an optical fiber.

The nature of nonlinear pulse distortions depends strongly on the circumstances, i.e., the type and strength of nonlinearity and on the occurrence of other effects such as chromatic dispersion or waveguiding. It can be investigated with pulse propagation modeling.

There are various methods to mitigate nonlinear pulse distortions, e.g. in amplifiers for ultrashort pulses. Examples are the use of thin (and highly doped) amplifier crystals, chirped-pulse amplification and divided-pulse amplification.

See also: nonlinearities, Kerr effect, pulse propagation modeling, chirped-pulse amplification
and other articles in the categories optical amplifiers, fiber optics and waveguides, nonlinear optics, light pulses

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