A laser diode illuminator device and a method for optically conditioning the output beam radiated from such a device, so that highly-demanding illumination application requirements that call for high output powers within a specified field of illumination can be addressed. At the heart of the device is a two-dimensional stack of laser diode bars wherein the linear array of beamlets radiated by each laser diode bar is optically conditioned through its passage in a refractive-type micro-optics device followed by a cylindrical microlens. The micro-optics device performs collimation of the linear array of beamlets along the fast axis of the bars, and it also acts as a beam symmetrization device by interchanging the divergences of the laser beamlets along the fast and slow axes. The cylindrical microlens is for collimation of the beamlets along the slow axis. The optical conditioning is performed individually for each linear array of beamlets so that the radiance or brightness of the laser diode illuminator can be optimized while any specified field of illumination can be filled with an excellent uniformity of the radiant intensity.