Conversion of gyrotron output into a Gaussian beam

High frequency gyrotrons are characterized by their capacity to deliver high powers in the millimeter to the submillimeter wavelength range and their frequency step-tunability due to the alternation of the operating mode. Before these gyrotrons can be used as radiation sourced, it is necessary to convert the outputs into well-collimated, linearly-polarized beams. Gyrotrons produce hollow cone-shaped beams, which are far from what is usually required. We have constructed a quasi-optical system intended to convert the radiation of the Gyrotron FU VA into bi-Gaussian beam. The system consists of a quasi-optical antenna and an ellipsoidal mirror. The former converts the gyrotron radiation of TE0n and TE1n operating modes into linearly-polarized beam and the latter produces the far-field pattern. The measurements of the output beam have demonstrated that the system developed produces bi-Gaussians beam from the outputs of TE03 and TE13 output radiation consisting of mode rotating clockwise and counterclockwise modes, the high quality beam is obtained by matching appropriately the nodes of the radiation pattern with the step-cut of the quasi-optical antenna. This was confirmed by experiment