This study examines the ultrafast carrier dynamics of topological semimetals ${\mathrm{NiTe}}_2$ and ${\mathrm{PdTe}}_2$, highlighting the influence of their distinct electronic structures. Transient absorption spectroscopy in reflectance mode reveals that ${\mathrm{NiTe}}_2$ exhibits a sharp feature at 2.03 eV, linked to Dirac states near the Fermi level, while ${\mathrm{PdTe}}_2$ shows a broader, featureless response due to its Dirac states lying 0.5 eV below the Fermi level. In the near-infrared region, ${\mathrm{NiTe}}_2$ demonstrates rapid state filling and short-lived dynamics, whereas ${\mathrm{PdTe}}_2$ supports prolonged absorption due to accessible Dirac states. Temperature-dependent studies reveal a nonmonotonic relaxation in ${\mathrm{NiTe}}_2$, attributed to a Lifshitz transition around T*≈ 50 K, altering the Fermi surface topology. In contrast, ${\mathrm{PdTe}}_2$ exhibits conventional relaxation dynamics across temperatures. These findings underscore the role of Dirac states and topological transitions in shaping carrier dynamics, offering insights for advancing optoelectronic and thermal management technologies.

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• Carrier generation & recombination
• Electron-phonon coupling
• Lattice dynamics
• Phonons
• Dirac semimetal
• Topological materials
• Ultrafast femtosecond pump probe