$(4$a$)$ Calculate $($a$)$ the numbers of photon, $($b$)$ wavelength, $($c$)$ free$-$space propagation constant $($wave vector$)$ and $($d$)$ the momentum of emitting photon for a $10$ mW laser

source Ga $0\mathrm{.}95$ Al $\mathrm{.}05$ As$.[$Hint: Eg$($ev$)=1\mathrm{.}42+1\mathrm{.}26$x $+0\mathrm{.}26$ x$*,$ where x $=0\mathrm{.}05].$