Spectral anomaly of ultrashort vortex pulses with axially oscillating twist

摘要

Spatially resolved spectroscopy of vortex beams is able to test the state of optical systems, to decode specific information or to sensitively indicate light-matter interactions. Spectral maps of ultrashort vortex pulses generated by hybrid diffractive-reflective spiral phase plates were studied experimentally and theoretically. Local spectral maps were detected by high-resolution scanning with a fiber-coupled spectrometer. Distributions of spectral centers of gravity and second moments were analyzed for femtosecond pulses. Gouy rotation of characteristic spectral features in the proximity of a phase singularity as a function of propagation distance was indicated in the spectral domain. Angular rotation was found to be modulated by weak oscillations. Analysis of spectral meta-moments indicates a fast switching and twisting behavior of spatial chirp.