A $20\mathrm{.}0-$mW helium$$neon laser emits a beam of circular cross section with a diameter of $2\mathrm{.}15$ mm$.$

$($a$)$ Find the maximum electric field in the beam.

kN$/$C

$($b$)$ What total energy is contained in a $1\mathrm{.}00-$m length of the beam?

pJ

$($c$)$ Find the momentum carried by a $1\mathrm{.}00-$m length of the beam.