Highly focused and efficient terahertz radiation generation by photo-mixing of lasers in plasma in the presence of magnetic field

Abstract

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ω1, ω2 and wave numbers k1, k2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ω′=ω1−ω2 and wave number k′=k1−k2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ωUH=(ωp2+ωc2) (where ωc is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field.

Studies of Terahertz Sources and Their Applications

“…Kumar et al [68] studied Beat excitation of terahertz radiation from two different frequency infrared lasers of TM/TE mode propagating along z direction in a rippled density semiconductor waveguide slab in a magnetic field (applied transvers to it) and the terahertz yield is significantly higher in the TM mode laser beating than in the TE mode laser beating. Malik and Malik [69][70][71][72] investigated the role of an external DC magnetic field in tuning the frequency and power of terahertz radiation. Varshney et al [73,74] proposed a scheme for the generation of THz radiation from rippled density magnetized plasma by beating of extraordinary mode lasers.…”

Generation of terahertz radiation via cosh‐Gaussian and top‐hat laser beams in a collisional magnetized plasma

“…Utilizing the method in refs [30,31,38,[65][66][67] , the efficiency of the emitted radiation, which is the ratio of the energy of THz radiation to the energy of the incident lasers, can be derived as: eff = (Equation 1 and 2), and f ′ (y) = df (y)/dy. For the definition of G, G 1 , G 2 , G 3 , G 4 , refer to Appendix B.…”

“…[39] The other routes for THz radiation generation include transition radiation from electron beams, [40,41] gyrotrons, [42,43] plasma wakefield, [44] free electron lasers, [45,46] Schottky diodes, [47] and heterojunction barrier varactors. [65] Singh et al have reported THz generation by mixing two cosh-Gaussian laser beams in a density rippled plasma. [54,55] Solid-state electronic sources include the Gunn diode [56,57] and high-frequency transistors.…”

“…[62,63] Another way to generate THz radiation is to use semiconductor superlattice. [73] Many cited references [30,31,38,[65][66][67] study THz radiation generation by beating of two laser beams by applying a perpendicular magnetic field to the laser beams' propagation direction to achieve higher efficiency than if they have used different laser beam profile. [65] Singh et al have reported THz generation by mixing two cosh-Gaussian laser beams in a density rippled plasma.…”

Terahertz radiation generation by beating of two chirped laser pulses in a warm collisional magnetized plasma

“…The presence of an external magnetic field perpendicular to the direction of laser pulse propagation could increase the radiation efficiency up to several times more than the absence of a magnetic field. [21][22][23][24][25][26] Since the resonance excitation depends on the tuning of pulse frequency and plasma density, the different types of plasma density, for example, the ripple density, is used to increase the terahertz radiation efficiency. [27][28][29] The terahertz generation by the beating of two Gaussian laser beams for periodically modulated density in the presence of a static magnetic field has been studied by Malik et al [14] Their analytical calculations show that the resonant excitation of THz under the mentioned conditions is quite effective.…”