Multiresonant metasurface for Raman spectroscopy beyond single molecule detection level

A metasurface in the metal-insulator-grating configuration is designed and optimised to support enhancement of coherent Raman signal of selected molecules orders of magnitude above the single-molecule detection threshold. The tunability is demonstrated by adjusting the structure to match selected Raman peaks of rhodamine, however, its spectral response is broad enough to cover a range of Raman shifts. Finally, the grating allows switching between distinct values of Raman shift with a single metasurface illuminated at different angles.