Design of a quasi-optical system with variable output beam size

A quasi-optical system consisting of a quasi-optical antenna and two ellipsoidal mirrors can convert the gyrotron output (TE15 mode, 354GHz) into a gaussian-like beam. The waist size of the beam produced is adjusted by moving a second ellipsoidal mirror. The second mirror with focal length of 520mm offers a tunable range from 2.0mm to 5.4mm, and those with focal lengths of 1190mm and 2390mm offer other tunable ranges from 5.1mm to 12.9mm and from 12.0mm to 25.1mm, respectively.