  We report first ns-resolved absorption measurements of the ro-vibrational
excitation of CO$_2$. The high temporal resolution of 8 ns is made possible by
a fast detector (rise-time 5 ns), sensitive in the mid-infrared region. The
resolution is achieved by a slow temperature scan of a quantum cascade laser
and a segmented data capturing scheme. A repetitively pulsed ns discharge in
10% CO$_2$ + 90% He at 150 mbar and a repetition rate of 2 kHz is investigated.
The evolution of the population densities of the different vibration modes as
well as the associated vibrational and rotational temperatures within the
discharge pulse of only 150 ns length are simultaneously determined and provide
valuable insight into the CO$_2$ excitation dynamics. A preferential excitation
in the asymmetric vibrational mode is observed in the discharge phase shortly
after the breakdown.
