Meta-nonlinearity and plasma effect to explain pulsed light transmissionthrough a subwavelength plasmonic metal slit*

The transmission of a light pulse through a subwavelength metal slit remains as a fundamental physics puzzle. We show that nonlinearity can be induced in this system even considering only linear materials and processes due to the roundtrip reflection within the cavity and the resultant superposition of the transmitted light sub-pulses. The superposition of sub-pulse lights with a fixed phase delay in between produces a periodic light that beats with its original light frequency and results the meta-nonlinearity that is new in additional to the well known nonlinearities from large amplitude, material nonlinearity, and two or more lights with different frequencies.  Intriguing transient behavior, step phasor, non-smoothness, nonlinear phase shift(s), nonuniform dispersion, plasma, and sub-pulse spreading are key features. The wave function of the transmitted field is highly sensitive to the phase delay due to the roundtrip reflection within the slit; especially, at half or integer periods. Analytical models are proposed to understand and explain the underneath new physics. Modeling results agree well with simulations. The academic and industrial applications are broad.