18. A ruby laser consists mostly of alumina (Al2O3) and a small amount of chromium, which is responsiblefor the red color of the ruby. This laser emits a pulse of light (λ = 685 nm) with a power of 3.00 kW overa period of 10.0 ns. How many chromium atoms undergo stimulated emission to produce this pulse?
(A) 1.03 x 1013
(B) 1.03 X 1014
(C) 1.03 X 1015
(D) 1.03 x 1016
(E) 1.03 x 1017.