Spectrally periodic pulses for enhancement of optical nonlinear effects

Nonlinear optical effects are typically weak and enhancement techniques are often required for practical applications. Here we introduce a method to enhance such effects by engineering the linear dispersion, which can be used in addition to existing methods. This allows us to generate a family of highly complex pulses consisting of several, equally spaced spectral components that are nonlinearly bound and propagate as a single unit. Our theory shows that this leads to an enhancement of the effective nonlinear parameter that increases with the number of frequency components. We experimentally demonstrate an enhancement factor of up to 3.5 in a mode-locked fibre laser that incorporates an intracavity spectral pulse shaper, with scope for achieving even higher enhancements. Our approach enables the generation of low-energy ultrashort pulses that nonetheless exhibit strong nonlinear effects.