Patent ID: 8618518

Claim:
An apparatus for forming a solid immersion lens (SIL) in an optical medium, comprising: a milling head configured to generate a focused ion beam; and a binary bitmap milling pattern defining locations at which the focused ion beam is projected onto a surface of the optical medium, wherein the locations at which the focused ion beam impact the surface of the optical medium are located completely within the binary bitmap milling pattern and are randomized over successive raster scans of the surface of the optical medium, wherein the binary bitmap milling pattern comprises a plurality of pixels, a first portion of the pixels defining locations where the focused ion beam impacts the surface of the optical medium and a second portion of the pixels defining locations where the focused ion beam is prevented from impacting the surface of the optical medium, each successive raster scan comprising a subsequent binary bitmap milling pattern having a different distribution of pixels that impact the surface of the optical medium and that are prevented from impacting the surface of the optical medium than a previous binary bitmap milling pattern, each different distribution of pixels comprising a functionally equivalent binary bitmap milling pattern.