Obvious in retrospect but optical disks use pretty high NA optics (for air) λ d NA WD CD 780 nm 780 nm 0.5 ~2 mm (+

Obvious in retrospect but optical disks use pretty high NA optics (for air) λ d NA WD CD 780 nm 780 nm 0.5 ~2 mm (+1.1 mm cover) DVD 650 nm 500 nm 0.65 ~1.5 mm (+0.6 mm cover) Blu-Ray 405 nm 240 nm 0.85 ~0.5 mm (+0.1 mm cover)