Abstract
When a relativistic, femtosecond laser pulse enters a waveguide, the pulse energy is coupled into waveguide optical modes. The longitudinal laser field effectively accelerates electrons along the axis of the channel, while the asymmetric transverse electromagnetic fields tend to expel fast electrons radially outwards. At the exit of the waveguide, the ∼nC, ∼10 MeV electron bunch converts its energy to a ∼10 mJ terahertz (THz) laser pulse through coherent diffraction radiation. In this paper, we present 3D particle-in-cell simulations and theoretical analyses of the aforementioned interaction process. We investigate the process of longitudinal acceleration and radial expulsion of fast electrons, as well as the dependence of the properties of the resulting THz radiation on laser and plasma parameters and the effects of the preplasma. The simulation results indicate that the conversion efficiency of energy can be over 5% if the waveguide length is optimal and a high contrast pump laser is used. These results guide the design of more intense and powerful THz sources.
Highlights
During the last decade, terahertz (THz) sources based on laserplasma interactions have attracted considerable attention due to their potential to produce GV cm−1, mJ level THz radiation
∼1 GV cm−1, ∼1 mJ THz pulses can be obtained by adopting a tailored pump laser [9] or by obliquely irradiating an underdense plasma slab with sub-100 μm thickness [10]
Another study employs solid foil targets covered with aligned nanorod arrays in experiments; the resulting efficiency is enhanced by an order of magnitude compared to a solid foil target [20]. Among these structured targets is the microplasma waveguide (MPW); does it suppress the transverse diffraction of the pump laser, but it enhances the longitudinal acceleration field [21, 22]
Summary
Terahertz (THz) sources based on laserplasma interactions have attracted considerable attention due to their potential to produce GV cm−1, mJ level THz radiation. Another study employs solid foil targets covered with aligned nanorod arrays in experiments; the resulting efficiency is enhanced by an order of magnitude compared to a solid foil target [20] Among these structured targets is the microplasma waveguide (MPW); does it suppress the transverse diffraction of the pump laser, but it enhances the longitudinal acceleration field [21, 22]. Simulations show that high charge (∼10 nC), high energy (∼100 MeV) and well-collimated (10◦) electron bunches can be produced and accelerated by the transverse magnetic modes [30] Their energies are converted to strong THz emission through coherent diffraction radiation (CDR) when they exit the MPW.
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