Hollow Laser Beam Research Articles

Plasma waveguide: A concept to transfer electromagnetic energy in space

This paper studies the possibility of using a laser-generated ‘‘plasma waveguide’’ to transfer electromagnetic (EM) energy. The plasma waveguide is a cylindrical vacuum core surrounded by a plasma cladding. The analysis shows that guided-mode fields do exist inside the core. Like a general dielectric waveguide, the plasma waveguide is characterized by a ‘‘normalized frequency parameter’’ (also called the V number). Although the permittivity of the plasma varies strongly with frequency, the V number surprisingly remains constant over the entire frequency range. Because of this property, the frequency dependence of the plasma waveguide is different; it has a wider high-frequency response than the general dielectric waveguide. The EM pulse can propagate in the plasma waveguide at close to the speed of light and keep its profile and shape unchanged. When the V number is smaller than 2.4048 (the first root of the zero-order Bessel function), only the single HE11 mode exists in the plasma waveguide. Unlike the dielectric waveguide, however, there is no high-frequency limitation for single-mode propagation. The EM fields outside the core in the plasma decrease exponentially with increasing radius. Thus, practically, a plasma cladding of sufficient thickness is all that is required to confine the EM wave. Such a plasma waveguide can be generated by a hollow laser beam in upper space and used for guiding EM pulses. A brief survey on laser-generated plasmas is given.