18. A ruby laser consists mostly of alumina (Al₂O₃) and a small amount of chromium, which is responsible for the red color of the ruby. This laser emits a pulse of light (λ = 685 nm) with a power of 3.00 kW over a 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.

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