Generating High-Power Short Terahertz Electromagnetic Pulses with a Multifoil Radiator

We describe a multifoil cone radiator capable of generating high-field short terahertz pulses using short electron bunches. Round flat conducting foil plates with successively decreasing radii are stacked, forming a truncated cone with the $z$ axis. The gaps between the foil plates are equal and filled with some dielectric (or vacuum). A short relativistic electron bunch propagates along the $z$ axis. At sufficiently high particle energy, the energy losses and multiple scattering do not change the bunch shape significantly. When passing by each gap between the foil plates, the electron bunch emits some energy into the gap. Then, the radiation pulses propagate radially outward. For transverse electromagnetic waves with a longitudinal (along the $z$ axis) electric field and an azimuthal magnetic field, there is no dispersion in these radial lines; therefore, the radiation pulses conserve their shapes (time dependence). At the outer surface of the cone, we have synchronous circular radiators. Their radiation field forms a conical wave. Ultrashort terahertz pulses with gigawatt-level peak power can be generated with this device.

Figure 1

Short electron bunch passing through the conical foil stack. (a) After the bunch has passed through the gap between two of the foil plates, the induced electromagnetic wave propagates radially outward. (b) As the pulses reach the foil boundaries, they merge and form a conical wave.

Figure 2

Electron bunches propagating from left to right pass through the radiator. Each bunch emits a conical electromagnetic wave.

Figure 3

Function $\sqrt{2/\pi }{\int }_0^{\infty }(x-s)e^{-(x-s{)}^2/2}{s}^{-1/2}ds$ (solid line) shows the time dependence of the electric field of the pulse that is generated by an electron bunch of Gaussian shape, $\exp (-x^2/2)$ (dashed line).

Figure 4

Refraction geometry.