Self-beating

There are two kinds of nonlinear mechanism. Beat is typical for the kind involving two or more frequencies. The other kind involves only one frequency due to large wave amplitude or weak media. Considering only linear materials and processes, we discover a new mechanism of self-beating to produce a wave function that does not appear to be linear. During a pulsed light being transmitted through a plasmonic slit, a portion of the light pulse transmits as a sub-pulse, while the rest is reflected at the exit interface, propagates a round-trip, and then reaches the exit again. These linear processes repeat. The superposition of transmitted sub-pulses with a phase delay in-between produces a periodic light that beats its original light frequency. Together with the plasma effects of non-uniform dispersion and sub-pulse spreading, self-beating can explain intrigue phenomena observed. The analytical model explains the complicated simulation results.