An optical system has a light source of an optical beam, and a wavefront distortion generator that introduces a known wavefront distortion into at least one wavelength component of the optical beam prior to the formation of an intermediate image. A focusing device receives the optical beam, produces...http://www.google.com.au/patents/US6707603?utm_source=gb-gplus-sharePatent US6707603 - Apparatus and method to distort an optical beam to avoid ionization at an intermediate focus
