  We present the characterization of ultrashort laser pulses by using the
plasma-induced frequency resolved optical switching (PI-FROSt) technique,
implemented in ambient air. This recently developed method allows for a
temporal reconstruction of a pulse at its focal spot by utilizing a moderately
intense pump laser pulse for generating an ionization-induced ultrafast
defocusing lens. When propagating through the produced plasma lens, the probe
beam to characterize experiences an increase of its size in the far field. The
spectrum of the defocused probe field, measured as a function of the pump-probe
delay, allows for a comprehensive characterization of the temporal and spectral
attributes of the pulse. We report herein the ability of this technique,
initially designed for use in rare gases, to operate in ambient air conditions
with similar performance. The method is remarkably straightforward to implement
and requires no additional optical component other than a focusing mirror,
while delivering laser pulse reconstructions of high reliability.
