We employ terahertz Faraday magneto-optical spectroscopy to probe the relaxation dynamics of quantized helical Caroli–de Gennes–Matricon (CdGM) states in epitaxial ${\mathrm{FeTe}}_{1-x}{\mathrm{Se}}_x$ thin films, nodeless multiband superconductors with short coherence lengths in the moderately clean limit. By exploiting polarization-selective optical transitions, we directly resolve the helicity and band origin of vortex-core quasiparticles. We observe resonant transitions between long-lived CdGM states induced by radiation with opposite helicity for electronlike and holelike bands. This enables independent, band-resolved determination of quasiparticle lifetimes, vortex masses, coherence lengths, and upper critical fields, and reveals their systematic evolution with isovalent substitution $x$. The results establish terahertz magneto-optics as a direct probe of helical vortex-core excitations and provide dynamical evidence for multiband CdGM states in iron-based superconductors.

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• Faraday effect
• Multiband superconductivity
• Vortices in superconductors
• Iron-based superconductors
• Transition metal dichalcogenides
• Terahertz spectroscopy