Kerr Effect

Physics: Optical Kerr effect: n = n₀ + n₂·I; silica n₂ = 2.6×10⁻²⁰ m²/W. Self-phase modulation: instantaneous phase φ(t) = γP(t)L, creating instantaneous frequency shift ω_inst(t) = ω₀ − dφ/dt. Pulse leading edge redshifts, trailing edge blueshifts — spectral broadening proportional to B-integral B = ∫γP dz. At B > π, spectral broadening becomes significant. DC Kerr effect (static E-field): birefringence change → electro-optic modulator. Kerr lensing (n₂>0): beam self-focuses; used for passive mode-locking in Ti:Sapphire lasers (KLM). Supercontinuum generation: B-integral >> 1 creates white light from femtosecond pulses in PCF.