Enhancing THz emission from nonlinear metasurfaces by a Bragg perfect absorber

Nonlinear plasmonic metasurfaces were demonstrated recently as ultracompact tetrahertz (THz) sources, emitting relatively strong single-cycle THz pulses after femtosecond laser illumination. There has been great progress in their ability to generate controlled THz wavepackets; however, their overall emission strength has not yet been optimized. Here we numerically show that by designing a Bragg assisted perfect absorber we can improve the coupling of the pumping laser to the nonlinear metasurface. This results in over an order of magnitude enhancement of the THz signal. Moreover, we show that this method can be combined with other independent optimization schemes to further enhance the radiated THz, reaching over two orders of magnitude emission enhancement compared with previously studied plasmonic metasurfaces.