plasmonrespons

Plasmon response, sometimes referred to as plasmonresonance or plasmon response function, describes how conduction electrons in metals or doped semiconductors collectively respond to external electromagnetic fields. This collective oscillation of the electron gas gives rise to plasmons, which couple strongly to light at nanoscale dimensions. The plasmon response largely governs the optical properties of metals, nanoparticles, and metamaterials and underpins the field of plasmonics.

The behavior is typically described by a dielectric function ε(ω) or a nonlocal ε(q, ω) that depends on frequency and wavevector. In the classical Drude model, ε(ω) = ε∞ − ω_p^2/(ω^2 + iγω), where ω_p is the bulk plasma frequency and γ is a damping rate. Bulk plasmons occur at ω ≈ ω_p in a homogeneous electron gas, while surface plasmons arise at metal–dielectric interfaces. Surface plasmon polaritons satisfy k_sp = (ω/c) sqrt(ε_m ε_d /(ε_m + ε_d)), with resonance near Re ε_m(ω) ≈ −ε_d. Localized surface plasmons in nanoparticles depend on size, shape, and the surrounding dielectric, with quantum size effects and nonlocality becoming important at very small scales.

Experimentally, plasmon response is probed by optical spectroscopy, electron energy loss spectroscopy (EELS), and refractive-index sensing. The resonance appears as peaks in extinction or scattering spectra and as features in the energy-loss function Im[−1/ε(q, ω)].

Applications of controlled plasmon response include biosensing, surface-enhanced spectroscopy, photothermal therapies, and enhanced light trapping in solar cells. Ongoing research seeks to tailor the plasmon response through material choice, nanostructure geometry, and environmental engineering.