A laser used in eye surgery emits a $2\mathrm{.}80-$mJ pulse in $1\mathrm{.}00$ ns$,$ focused to a spot $35\mathrm{.}0$m in diameter on the retina.

$($a$)$ Find $($in SI units$)$ the power per unit area at the retina. $($This quantity is called the irradiance.$)$

W$/$m$2$

$($b$)$ What energy is delivered per pulse to an area of molecular size $($say$,$ a circular area $0\mathrm{.}700$ nm in diameter$)?$

J