The present invention discloses a method and apparatus for the directed formation of a re-entrant micro-jet formed upon the collapse of a cavitation bubble formed proximate to a work surface placed in a fluid. A mask containing an orifice, placed between the work surface and the cavitation bubble, is utilized to direct the re-entrant micro-jet to the work surface. The cavitation bubble may be formed in the desired location by focusing an energy flow proximate to the mask. The energy flow may be obtained by radiation from laser, x-ray, or electrical discharge sources.