Terahertz spectroscopy probes the low-frequency vibrational and lattice modes that are unique to a molecule's structure — the same physics behind THz security screening, pharmaceutical tablet inspection and non-destructive materials testing. This simulator models each of a molecule's THz-active modes as a damped, driven harmonic oscillator (the Lorentz oscillator model), integrates its equation of motion in real time as you sweep an incident THz field across it, and renders the resulting resonance absorption directly: dipole bands light up near each natural frequency, the transmitted beam weakens following the Beer–Lambert law, and a live spectrum plot traces out the molecule's absorption fingerprint. Switch between lactose, aspirin, an RDX-like explosive analog and glucose to see how each substance's distinct set of resonances gives it a distinct fingerprint, and raise the sample temperature to watch phonon damping blur the peaks together.