Harmonic generation in multiresonant plasma films

We investigate second- and third-harmonic generation in a slab of material that displays plasma resonances at the pump and its harmonic frequencies. Near-zero refractive indices and local field enhancement can deplete the pump for kW/cm(2) incident powers, without resorting to other resonant photonic mechanisms. We show that low-threshold, highly efficient nonlinear processes are possible in the presence of losses and phase mismatch in structures that are 10(4) times shorter than typical nonlinear crystals, for relatively low irradiance values.