Extremely sharp transmission peak in optically thin aluminum film with hexagonal nanohole arrays

Extraordinary transmission is the most attractive phenomenon, that has been studied in recent decades, for optically thick metal film with nanohole arrays. On the contrary, in optically thin metal film with nanohole arrays, it has been found that the interaction between excited surface plasmon polariton and non-resonant direct propagation light introduces a strong light absorption and causes a suppressed transmission dip. Here, we explore the optical properties of a free standing optically thin aluminum film with a hexagonal large filling ratio nanohole array and find an extremely sharp extra extraordinary transmission peak within the suppressed transmission dip which is originated from the interaction of the excited surface plasmon polariton and the non-resonant directly scattered light. Simulation results show that the nanohole-array-based biosensor that were proposed have an excellent sensitivity, with a figure of merit of 87, beyond that of nanohole-array-based biosensors reported previously for normal incidence. (paper)