Backward output-side-grooves regulated light wave resonance in a subwavelength metallic slit and an ultrahigh energy accumulator*

Featuring conceptual breakthroughs in subwavelength wave mechanics, our work studies the output-side groove effect and finds a backward coupling mechanism. The transmitted light is scattered by the grooves and then re-enters into the slit. In one case study, this causes a phase delay of the reflected wave and is considered a reduction in the resonant film thickness. The traveling wave in the slit can be more in phase to significantly enhance the transmission. For another arrangement of the grooves, we find that the wave reflection inside the slit is raised up to 100% due to backward coupling. As the same arrangement of the grooves are patterned at the entrance side of the slit, an incident wave on the slit will be trapped in roundtrips after the transmission through the entrance. At resonance, the roundtrip wave is superposed constructively. Our analysis yields that the intensity of the time-averaged energy can be five million times that of the incident wave. This finding is groundbreaking in subwavelength optics and should have many applications in nonlinear optics, particle trapping, biomedicine, etc.