  We measure the detailed spatiotemporal profiles of femtosecond laser pulses
in the infrared wavelength range {\lambda}=2.5-11{\mu}m, and the absolute
nonlinear response of major air constituents (N2, O2, and Ar) over this range.
The spatiotemporal measurements reveal wavelength-dependent pulse front tilt
and temporal stretching in the infrared pulses.
