  Attosecond metrology with linearly polarized light pulses is the basis of a
highly successful research area. An even broader impact can be expected from a
generalized metrology that covers two-dimensional polarization states, enabling
notably the study of chiroptical phenomena on the electronic time scale. Here,
we introduce and demonstrate a comprehensive approach to the generation and
complete characterization of elliptically to circularly polarized attosecond
pulses. The generation relies on a simple plug-in device of unprecedented
simplicity. For the characterization, we introduce SPARROW (Stokes-Parameter
and Attosecond Resolved Reconstruction of Optical Waveforms), which encodes the
attosecond-metrology information into the photoemission angle in the
polarization plane and accesses all four Stokes parameters of the attosecond
pulses. Our study demonstrates a physically transparent scheme for attosecond
metrology with elliptical to fully circular polarizations, applicable to both
table-top and accelerator-based light sources, which will unlock studies of
chiral molecules, magnetic materials and novel chiroptical phenomena on the
most fundamental time scales.
