Answer
$2.01\times10^{16}\;s^{-1}$
Work Step by Step
If $\lambda$ be the wavelength of the laser, the energy of a photon emitted as laser is given by
$E=\frac{ch}{\lambda}$
$\text{Power of the laser}=\frac{\text{Total energy of the photon emitted in a given time} }{\text{time}}$
$=\frac{\text{Total number of the photon emitted in a given time}\times\text{energy of the photon}}{\text{time}}$
$=\text{Rate of photon emitted}\times\text{energy of the photon}$
Therefore,
$\text{Rate of photon emitted}=\frac{\text{Power of the laser}}{\text{energy of the photon}}=\frac{P\lambda}{ch}$
or, $\text{Rate of photon emitted}=\frac{5\times 10^{-3}\times0.8\times10^{-6}}{3\times10^{8}\times6.63\times10^{-34}}\;s^{-1}$
or, $\text{Rate of photon emitted}=2.01\times10^{16}\;s^{-1}$
Therefore, the rate of photon generated is $2.01\times10^{16}\;s^{-1}$
