The energy of each photon $ E = hc/ \lambda$
$ =( 6.626 \times 10^{-34} \times 3 \times 10^8 ) / 632.8 \times 10^{-9} = 3.131 \times 10^{-19}J$
Number of photons arriving per second, at a target irradiated by the beam = $n$
Equation of power, $ p = nE$
So, $ n = P/E$
$=(9.42 \times 10^{-3}) / (3.141 \times 10^{-19} )=3 \times 10^{-16}$ photon/s = $ 0.003 \times 10^{19} $ photon/s