Ultrafast pump-probe spectroscopy is indispensable for investigating interactions, collective excitations, and nonequilibrium dynamics in superconductors and correlated electron systems. However, how a small gap opening near the Fermi surface affects the spectral changes in the high-energy interband transition region remains elusive. To address this issue, we perform systematic studies of carrier relaxation dynamics in the prototype charge-density-wave (CDW) material ${\mathrm{EuAl}}_4$. We find that the CDW gap shrinks substantially under optical pumping. This band renormalization strongly modulates interband transitions associated with the gap edge, inducing a pronounced transient reflectivity change at the corresponding probe energies. These results establish a direct link between low-energy order-parameter dynamics and high-energy spectral responses, providing a general framework for interpreting transient signals in gapped quantum materials.

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• Charge density waves
• Electronic structure
• Order parameters
• Strongly correlated systems
• Ultrafast femtosecond pump probe