  Focusing control of ultrashort pulsed beams is an important research topic,
due to its impact to subsequent interaction with matter. In this work, we study
the propagation near the focus of ultrashort laser pulses of ~25 fs duration
under diffractive focusing. We perform the spatio-spectral and spatio-temporal
measurements of their amplitude and phase, complemented by the corresponding
simulations. With them, we demonstrate that pulse shaping allows modifying in a
controlled way not only the spatio-temporal distribution of the light
irradiance in the focal region, but also the way it propagates as well as the
frequency distribution within the pulse (temporal chirp). To gain a further
intuitive insight, the role of diverse added spectral phase components is
analyzed, showing the symmetries that arise for each case. In particular, we
compare the effects, similarities and differences of the second and third order
dispersion cases.
