Controlling the spectral rotation of ultrashort vortex pulses

The large bandwidth and high intensity of ultrafast vortex pulses, i.e. pulses with orbital angular momentum (OAM), open new prospects for applications in communication, imaging or nonlinear photonics. In previous experiments, we demonstrated the peculiar spatio-spectral behavior of pulsed polychromatic vortex beams in the vicinity of phase singularities. It was shown that the rotation of characteristic, so-called "spectral eyes" and the spectral dependent Gouy phase are closely connected. For practical applications, a controlled variation of spatio-spectral distributions is required. Here we report on our most recent studies concerning the dependence of time- integrated spectral maps on key optical parameters. It is shown that the speed of rotation of spectral eyes during the propagation is essentially determined by the angular and spectral profiles. This enables to modify the spectral rotation characteristics by applying low-dispersion, adaptive optical components. The performance of reflective liquid-crystal-on silicon spatial light modulators (LCoS-SLMs) is compared to diffractive spiral gratings with variable illumination. Moreover, the generation of wavepackets with a time-dependent orbital angular momentum (self-torque) by superimposing multiple tailored vortex pulses is proposed. This allows for extending the capabilities vortex pulses by defined non-stationary spatio-spectral and topological characteristics.