An atom has two energy levels with a transition wavelength of 582 nm. At 300 K, atoms are in the lower state. (a) We have to find the number of atoms that occupy the upper state, under conditions of thermal equilibrium. (b) Suppose, instead, that atoms are pumped into the upper state, with atoms in the lower state. We have to calculate the energy that could be released in a single laser pulse.

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(a)

As the transition wavelength corresponding to the two levels is 582 nm, their energy difference is

It is given that at 300 K, atoms are in the lower state. From the Boltzmann distribution, we note that at equilibrium the number of atoms in the upper state when atoms are in the lower state will be given by the relation

This is an incredibly small number. For all purposes there are no atoms in the upper state.

(b)

We consider the situation when atoms are pumped in the upper state. Because of the laser action the energy that could be released in a single laser pulse will be