Question 40.47: The active volume of a laser constructed of the semiconducto......

Let the power of the laser beam be P and the energy of each photon emitted be E. Then, the rate of photon emission is

R=\frac{P}{E}=\frac{P}{h c / \lambda}=\frac{P \lambda}{h c}=\frac{\left(5.0 \times 10^{-3} \,W \right)\left(0.80 \times 10^{-6} \,m \right)}{\left(6.63 \times 10^{-34} \,J \cdot s \right)\left(2.998 \times 10^8\, m / s \right)}=2.0 \times 10^{16} \,s ^{-1} .