Spatio-temporal couplings in ultrashort vortex pulses generated by spiral phase plates

Ultrashort laser pulses have many applications but are sensitive to distortions due to the interdependence of their temporal and spatial components, known as spatio-temporal couplings. We quantify for the first time to our knowledge the spatio-temporal couplings for ultrashort vortex pulses in the case of practical interest when they are generated by conventional and achromatic spiral phase plates. By simulating the propagation of transform-limited ultrashort Gaussian pulse and tacking chromatic dispersion of the materials into account, we obtain the fields of generated ultrashort vortices in the spectral, temporal, spatial and spatial-frequency domains and compare them to corresponding ideal Laguerre-Gauss ultrashort vortex. We found that generated pulses present spatial chirp and angular dispersion, while no pulse-front tilt was introduced as there is no temporal chirp. The achromatic spiral phase plate benefits not only from almost 3 times larger bandwidth of conversion efficiency η₀₁, but also reduces distortions induced by spatio-temporal couplings by an order of magnitude. Quantification of spatio-temporal couplings serves as an additional tool for characterization of optical components for ultrafast singular optics.