Intense narrowband terahertz pulses produced by obliquely colliding laser pulses in helium gas

Abstract

A practical configuration for generating narrowband terahertz (THz) pulses based on plasma dipole oscillations (PDOs) is studied using two-dimensional particle-in-cell simulations. In this scheme, two slightly detuned laser pulses collide obliquely in a helium gas. Plasma strips are generated along the paths of the laser pulses by field ionization. The PDO created in the overlap region of the two laser pulses emits a THz pulse with a peak electric field strength of a few gigavolt per meter. An energy conversion efficiency of 0.542 x 10(-3) is achieved for laser pulse intensities 4.82 x 10(16) W=cm(2), a spot radii of 5lm, and a collision angle of 10.8 degrees. A force balance model is extended for the obliquely colliding configuration of the pulses. As the complications, such as generating plasmas separately or aligning the beams with preformed plasma, are eliminated from our new configuration, this makes a future experimental study of PDO more straightforward.