Optical generation of terahertz plasmons on comb-shaped surface of metal

The possibilities of a recently proposed (Opt. Express 17, 9323 (2009)) method for generating terahertz surface plasmons on a microstructured (comb-shaped) metal surface using a nonlinear polarization pulse that moves with a superluminal velocity and is induced by an ultrashort laser pulse in a strip of electrooptic material deposited on the surface are theoretically studied. For an arbitrary direction of motion of the nonlinear source along the comb-shaped surface, fields of excited terahertz plasmons and the angular spectral distribution of the radiated energy are calculated. It is shown that the spectral and energy characteristics of plasmons can be efficiently controlled by varying the direction of motion of the source. Conditions (parameters of the comb-shaped structure, direction and velocity of motion of the source) that ensure the maximal efficiency of the optical-to-terahertz conversion are found. The developed method of terahertz generation is promising for surface terahertz spectroscopy.