Ultrafast chirped pulses provide a powerful route to controlling coherent dynamics in multilevel atomic systems. In the strong field regime, however, the physical origin of spectral asymmetry is obscured by the combined effects of pulse chirp, timing linkage, and branch dependent couplings. Here we investigate the asymmetric coherent dynamics of fine structure resonances in rubidium driven by chirped femtosecond pulses. By combining femtosecond transient absorption measurements, transient-grating frequency-resolved optical gating (TG-FROG) pulse characterization, and an analytical three level model based on the Magnus expansion, we examine how chirped excitation reshapes the absorption response of the Rb D1 $\left(5p^2{P}_{1/2}\right)$ and D2 $\left(5p^2{P}_{3/2}\right)$ transitions. The measurements show that the observed spectral asymmetry depends not only on the sign of the chirp, but also on the group delay variation imposed by the compressor geometry. The asymmetry persists even after the timing linkage is compensated, which shows that it does not arise solely from the pump probe timing shift. Further analysis indicates that chirp acts mainly by modulating the phases of the relevant quantum pathways. This reshapes pathway interference and governs the asymmetric partition of the excited state population. These results establish an analytical framework for chirp based control of resonant responses in multilevel atomic systems and highlight the role of phase control in ultrafast quantum state manipulation.

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• Coherent control
• Optical pumping
• Pulse shaping
• Ultrafast optics
• Chirp
• Transient absorption spectroscopy