A laser used in eye surgery emits a $4\mathrm{.}20-mJ$ pulse in $1\mathrm{.}00$ ns $,$ focused to a spot $35\mathrm{.}0m$ in diameter on the retina.

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

$\frac{W}{m^2}$

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

Use the power per unit area you calculated for the pulse, as well as the other given information, to calculate the energy delivered to the area of molecular size. J

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