A scheme of resonant terahertz (THz) radiation generation by non-linear beating of two lasers in hot magnetized plasma with step density profile is investigated. Beating lasers of frequency difference ω1 − ω2 ≈ ωp(~1 THz) is incident obliquely on plasma surface and exerts non-linear ponderomotive force on plasma electrons. The plasma electrons start oscillating in the plane of incidence and give rise to space charge field to maintain plasma neutrality. In turn, both ponderomotive force and space charge field excites a non-linear surface current, responsible for THz radiation generation on the reflection side. The coupling between plasma wave and electromagnetic wave present (inside the plasma as well as on reflection side) becomes stronger in the presence of the transverse DC magnetic field. THz radiation amplitude is optimized at an angle of incidence θ ~ 50–70°.

This paper presents a scheme of THz generation by nonlinear photomixing of two cosh-Gaussian lasers pulses having different frequencies (ω1, ω2) and wave numbers $(\vec k_1, \vec k_2 )$ and same electrical field amplitude in a corrugated plasma embedded with transverse static magnetic field. Cosh-Gaussian laser pulses have steep gradient in intensity profile along with wider cross-section, which exerts a stronger nonlinear ponderomotive force at ω1 − ω2 and $\vec k_1 - \vec k_2 $ on plasma electrons imparting a nonlinear oscillatory velocity to plasma electrons. Oscillatory plasma electrons couple with the density ripple n′ = n α0e iαx to produce a nonlinear current, which is responsible for resonant THz radiation at frequency $\sim\left( {{\rm \omega} _{\rm c}^2 + {\rm \omega} _{\rm p}^2} \right)^{1/2} $ . The amplitude, efficiency and beam quality of THz radiation can be optimized by choosing proper corrugation factor (α of the plasma), applied magnetic field (ωc), decentered parameter (b), and beam width parameter a 0 of cosh-Gaussian lasers. An efficiency of $\sim\!10^{ - 2} - 10^{ - 1} $ is achieved for laser electric field E = 3.2 × 109 V/cm.

The acceleration of an electron beam by surface plasma waves (SPW), in the presence of external magnetic field parallel to surface and perpendicular to direction of propagation of SPW has been studied. This wave propagating along the $\hat z$ -axis is excited using Kretschmann geometry, having maximum amplitude at the metal–vacuum interface. Equations of motion have been solved for electron energy and trajectory. The electron gains and retains energy in the form of cyclotron oscillations due to the combined effect of the static magnetic field and SPW field. The energy gained by the beam increases with the strength of magnetic field and laser intensity. In the present scheme, electron beams can achieve ~15 KeV energy for the SPW amplitude A 1 = 1.6 × 1011 V/m, plasma frequency ωp = 1.3 × 1016 rad/s and cyclotron frequency ωc/ωp = 0.003.

An obliquely incident high-power laser (ω0, k 0z ) on the metallic surface can resonantly excite a surface plasma wave (SPW) (ω1, k 1z ) and a quasi-electrostatic plasma wave (ω, k z) inside the skin layer at the phase-matching conditions of frequency ω1 = ω − ω0 and wave number k 1z = k z − k 0z . The oscillating electrons in the skin layer couples with the seed SPW and exert non-linear ponderomotive force on electrons at the frequency of quasi-static mode. Density perturbations due to quasi-static mode and ponderomotive force associate with the motion of electrons (due to incident laser) and give rise to a non-linear current by feedback mechanism. At ω/k z ~ v F (where v F is the Fermi velocity of metal) this non-linear current is responsible for the growth of SPW. The maximum growth of the present process (≅1.5 × 1012 s−1) is achieved at incident angle θ = 42° for laser frequency ω0 = 2 × 1015 rad/s. Growth of SPW enhances from 1.62 × 1011 to ≅1.5 × 1012 s−1 as the magnetic field changes from 12 to 24 MG. The excited SPW can be utilized for surface heating and diagnostics purpose.

Energy enhancement by a circularly polarized laser pulse during acceleration of the electrons by a Gaussian laser pulse has been investigated. The electrons close to the temporal peak of the laser pulse show strong initial phase dependence for a linearly polarized laser pulse. The energy gained by the electrons close to the rising edge of the pulse does not show initial phase dependence for either linearly- or circularly-polarized laser pulse. The maximum energy of the electrons gets enhanced for a circularly polarized in comparison to a linearly polarized laser pulse due to axial symmetry of the circularly polarized pulse. The variation of electron energy with laser spot size, laser intensity, initial electron energy, and initial phase has been studied.

A scheme is proposed for the acceleration of electrons generated during the ionization of a gas by two laser pulses. The electrons created from the ionization of neutral atoms near the rising edge of the pulse do not gain sufficient energy. If a prepulse is used before the main pulse then the prepulse removes electrons from the outer shells, and the main laser pulse interacts with the electrons in the inner shells of high atomic number gases, such as krypton and argon. The electrons are generated close to the peak of the main laser pulse and gain energy in GeV with a small spread in the energy and low emittance angle.