Controlled-inversion-profile amplifier as soft aperture

A new method is proposed for achieving a soft aperture in controlling the transverse distribution of the intensity of a laser beam. The method is based on the use of amplifiers with a controlled transverse distribution of the population inversion. A controlled inversion profile can be produced by reducing the population inversion as a result of auxiliary lasing excited within certain parts of the active medium of the amplifier. Expenmental results are given of an investigation of an amplifier with a cylindrical neodymiumglass element (diameter 30 mm, length 320 mm) in which a controlled inversion profile is produced by stimulated emission of internal ring modes on reflection from the polished cylindrical surface of the element. The proposed method makes it possible to reduce considerably the inhomogeneity of the transverse distribution which appears as a result of diffraction by various apertures.