Through the optical Kerr effect, refractive index rises slightly with intensity, so the peak of a pulse is phase-shifted more than its edges and new frequencies appear on both sides of the spectrum. In fiber amplifiers SPM is a main limit on peak power, measured by the accumulated nonlinear phase, the B-integral. It is also exploited to broaden spectra for pulse compression and supercontinuum generation.
B-integral's past 5 radians in the last amp, all that self-phase modulation is why the spectrum has those ears.
Also heard as
- SPM
Related terms
Supercontinuum
Extremely broad, spatially coherent white-light spectrum created by sending intense pulses through a nonlinear fiber.
Chirp
A change in instantaneous frequency across a pulse, so its colors arrive spread out in time.
LMA
Large Mode Area: fiber with an enlarged core that spreads light out to raise nonlinear and damage limits.
Peak power
The highest instantaneous power reached during a laser pulse, roughly pulse energy divided by pulse duration.