Radiation generated by a charge moving through a vacuum channel in a dielectric cone is analyzed. It is assumed that the charge moves through the cone from the apex side to the base side (the case of inverted cone). The cone size is supposed to be much larger than the wavelengths under consideration. We calculate the wave field outside the target using the aperture method developed in our previous papers. Contrary to the problems considered earlier, here the wave which incidences directly on the aperture is not the main wave, while the wave once reflected from the lateral surface is much more important. The general formulas for the radiation field are obtained, and the particular cases of the ray-optics area and the Fraunhofer area are analyzed. Significant physical effects including the phenomenon of “Cherenkov spotlight” are discussed. In particular it is shown that the Cherenkov spotlight regime allows for reaching the most efficient radiation for the given target with the largest intensity and smallest divergence in the far-field region. Moreover, owing to the inverted cone geometry, this effect can be realized for arbitrary charge velocity, including the ultrarelativistic case, by proper selection of the cone material and the apex angle. Typical radiation patterns in the far-field area are demonstrated.

• Received 16 April 2020
• Accepted 26 October 2020

DOI:https://doi.org/10.1103/PhysRevA.102.053514