Answer
$5.24\times10^{17}$
Work Step by Step
The pulsed laser emits light at a wavelength of $694.4\;nm$
Therefore, the energy of each photon of the laser is
$E_p=\frac{ch}{\lambda}=\frac{3\times10^{8}\times6.63\times10^{-34}}{694.4\times10^{-9}}\;J=2.864\times10^{-19}\;J$
The energy per pulse is $E=0.150\;J$
Therefore, the number of photons emitted in each pulse is
$n=\frac{E}{E_p}=\frac{0.150}{2.864\times10^{-19}}=5.24\times10^{17}$
