Measuring spatiotemporal ultrafast field structures of pulses from multimode optical fibers

Ultrashort pulses emerging from multimode optical fibers are spatiotemporally complex, because inside these fibers the modes have different spatial intensity patterns and experience different propagation velocities and dispersions. To determine the spatiotemporal field from multimode fibers, we applied a technique for the complete measurement of the output pulses called a spatially and temporally resolved intensity and phase evaluation device: full information from a single hologram. It yields the complete electric field over space and time from multiple digital holograms, simultaneously recorded at different frequencies on a single camera frame. Using femtosecond pulses from a Ti:sapphire laser, we measured the first few linearly polarized modes (LP₀₁, LP₁₁, LP₀₂, and LP₂₁) inside several few-mode fibers. We also generate movies displaying the measured spatial, temporal, and spectral field features.