  Ideal absorption describes a particular means of optimizing light-matter
interactions with a host of potential applications. This work presents new
analytic formulas and describes semi-analytical methods for the design of
electric or magnetic ideal absorption in nanoparticles. These formulas indicate
that ideal absorption is attainable in homogeneous spheres with known materials
at specific sizes and frequencies. They also provide a means of designing
core-shell particles to produce ideal absorption at virtually any frequency in
the visible and near infrared range.
