Ultrafast optical control of terahertz surface plasmons in subwavelength hole-arrays at room temperature

Extraordinary optical transmission through subwavelength metallic hole-arrays has been an active research area since its first demonstration. The frequency selective resonance properties of subwavelength metallic hole arrays, generally known as surface plasmon polaritons, have potential use in functional plasmonic devices such as filters, modulators, switches, etc. Such plasmonic devices are also very promising for future terahertz applications. Ultrafast switching or modulation of the resonant behavior of the 2-D metallic arrays in terahertz frequencies is of particular interest for high speed communication and sensing applications. In this paper, we demonstrate ultrafast optical control of surface plasmon enhanced resonant terahertz transmission in two-dimensional subwavelength metallic hole arrays fabricated on gallium arsenide based substrates. Optically pumping the arrays creates a thin conductive layer in the substrate reducing the terahertz transmission amplitude of both the resonant mode and the direct transmission. Under low optical fluence, the terahertz transmission is more greatly affected by resonance damping than by propagation loss in the substrate. An ErAs:GaAs nanoisland superlattice substrate is shown to allow ultrafast control with a switching recovery time of ~10 ps. We also present resonant terahertz transmission in a hybrid plasmonic film comprised of an integrated array of subwavelength metallic islands and semiconductor hole arrays. Optically pumping the semiconductor hole arrays favors excitation of surface plasmon resonance. A large dynamic transition between a dipolar localized surface plasmon mode and a surface plasmon resonance near 0.8 THz is observed under near infrared optical excitation. The reversal in transmission amplitude from a stop-band to a pass-band and up to π/ 2 phase shift achieved in the hybrid plasmonic film make it promising in large dynamic phase modulation, optical changeover switching, and active terahertz plasmonics.