A general method for focusing of waves using phase and amplitude compensation

A general method for focusing of waves, based on phase and amplitude compensation, is applied to monochromatic, polychromatic and diffusive waves. Monochromatic waves may form spatially localized waves in free space, whereas polychromatic waves form non-decaying traveling evanescent modes confined to subwavelength regions in media where the frequency depends on the wavevector. We suggest an analogy between the phase compensation method and the transformation of frequencies between inertial, relativistic coordinate systems