Gouy phase rotation in spectral maps of ultrashort vortex pulses

Abstract

The generation of ultrashort wavepackets with optical angular momentum (OAM) enables to combine the extreme intensity, temporal localization and spectral bandwidth of pulsed light fields with topological charges. Because of additional rotational degrees of freedom, such potential applications in optical communication, optical tweezing, microscopy, or material modification, pulses with are currently of growing interest. Rotating wavefronts are shaped by components with phase singularities like forked gratings or spiral phase plates. For few-cycle pulses, purely reflective or dispersion compensated structures are used. In all ultrafast singular optical applications with broad spectral bandwidth, spatio-spectral propagation effects have to be taken into account. Polychromatic OAM beams are known to show spectral anomalies in the vicinity of wavefront dislocations [1-3]. By measuring spectral maps of ultrashort pulses with OAM with highly sensitive (single-photon capable) detection technique at high (down to nanoscale) spatial resolution, we were able to study spectral anomalies close to phase singularities. In particular we report on the spectrally resolved Gouy effect of few-cycle pulses.