The dynamics of transient light transmission through a subwavelength slit can be intricate. Their complicated and diverse wave functions, such as beat-like, and their underlying novel physics are illuminated using a concept of step phasors and phase delay without involving nonlinearity. Step represents the change in amplitude for any non-steady function. Phase delay caused by roundtrip reflection within the slit is also critical. The two can trigger complex combinations of constructive and destructive interferences to manifest diverse consequences, which are frequently observed yet less understood. In addition to step broadening and alternative amplitude change, sinusoidal fields can be packaged together to form various wave packets, while a phase shift accumulates until steady state. Besides shedding light into new physics, our step phasor concept can also be generalized to study any form of incident light profiles and to clarify intriguing phenomena involving plasmonic metamaterials frequently occurring in nanophotonic simulations and experiments.
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