External Periodic Field and Skew-chG Beams for Generation of Multifocal Terahertz Radiation in Collisional Plasma

A riveting mechanism for the generation of efficient THz radiation is shown by creating an extra transverse component of the nonlinear ponderomotive force (i.e., the induced force) on the application of an external periodic electric field to the collisional plasma having density ripples. Different components of nonlinear currents are produced due to the generation of different components of the force, i.e., one beating component and two coupling components. These nonlinear currents result in the emission of THz fields, namely a beat wave THz field,
$({E}_{\mathrm{ 0THz1}})_{\mathrm{ Beating}}$
and induced THz fields,
$(\text {IE}_{\mathrm{ THz2}})_{\text {EF}}$
and
$(\text {IE}_{\mathrm{ THz3}})_{\text {EF}}$
. The multiple resonance conditions and tuning of the amplitude of emitted THz radiations are achieved by the periodicities and amplitudes of density ripples (
$\beta $
) and external electric field (
$\xi $
). A comparative study between the beat wave-enabled field and induced fields signifies that the former is
${10}^{2}$
times higher in magnitude than the latter. The collisions between electrons and neutrals mainly affect the amplitude of the emitted THz radiations when the frequency of collisions (
$\upsilon $
) is greater or equal to
$0.25\omega _{p}$
;
$\omega _{p}$
being the plasma frequency. The skew- chG beams are employed in the plasma medium due to the sharp gradient in their laser profile and the dip in their peaks that can be easily controlled by the skewness parameter. It is worth noting that the amplitude of any THz field can be tuned by changing the parameters regarding lasers, external electric field, and plasma. The emitted fields are convertible, multifocal, intensity tunable, and are highly efficient with the efficiency of
$2.25\times 10^{-4}$
.