Spot size and depth of focus in optical data storage system

Different definitions of spot size and depth of focus in optical data storage systems are analyzed and compared numerically. It ap- pears that the differences between the definitions become more signifi- cant as the numerical aperture of the optical system increases. The re- lationship between spherical aberration and axial intensity is studied, and a general definition of the depth of focus based on this analysis is proposed. © 2007 Society of Photo-Optical Instrumentation Engineers.