Ultrashort infrared 2.5-11 μm pulses: spatiotemporal profiles and absolute nonlinear response of air constituents.

We measure the detailed spatiotemporal profiles of femtosecond laser pulses in the infrared wavelength range of λ=2.5-11  μm 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.