Vortex plate retarder-based approach for the generation of sub-20 fs light pulses carrying orbital angular momentum

We use a vortex retarder-based approach to generate few optical cycles light pulses carrying orbital angular momentum (OAM) (known also as twisted light or optical vortex) from a Yb:KGW oscillator pumping a noncollinear optical parametric amplifier generating sub-10 fs linearly polarized light pulses in the near infrared spectral range (central wavelength 850 nm). We characterize such vortices both spatially and temporally by using astigmatic imaging technique and second harmonic generation-based frequency resolved optical gating, respectively. The generation of optical vortices is analyzed, and its structure reconstructed by estimating the spatio-spectral field and Fourier transforming it into the temporal domain. As a proof of concept, we show that we can also generate sub-20 fs light pulses carrying OAM and with arbitrary polarization on the first-order Poincare sphere.