$[-/1$ Points$]$ SERCP$1128.$A$.$P$.048.$

A pulsed ruby laser emits light at $694\mathrm{.}3$ nm $.$ For a $14\mathrm{.}3-$ps pulse containing $3\mathrm{.}40$ J of energy, find the following.

$($a$)$ the physical length of the pulse as it travels through space

mm

$($b$)$ the number of photons in it photons

$($c$)$ If the beam has a circular cross section $0\mathrm{.}600$ cm in diameter, find the number of photons per cubic millimeter. photons $\frac{?}{m{m}^3}$

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