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Atoms and Molecules

Quick practice

Question 1 of 5

$1.6 \times 10^{19}$ Chromium ion s cubic centimeter. All the atoms excited by the 0.4 μm radiation decay rapidly to the level $E_{2}$ which has a lifetime τ = 3ms

Assuming that there is no radiation of wavelength 0.7 μm present in the pumping cycle and that the pumping rate is R atoms per $\mathrm{cm}^{3}$ the population density in the level $N_{2}$

builds up as:

A

$N_{2}(t)=R \tau\left(e^{\frac{t}{\tau}-1}\right)$

B

$N_{2}(t)=\frac{R t^{2}}{\tau}\left(1-e^{-\frac{t}{\tau}}\right)$

C

$N_{2}(t)=R t$

D

$N_{2}(t)=R \tau\left(1-e^{-\frac{t}{\tau}}\right)$