Figure 40-24 shows the energy levels of two types of atoms. Atoms A are in one tube, and atoms B are in another tube. The energies (relative to ground-state energy of zero) are indicated; the average lifetime of atoms in each level is also indicated. All the atoms are initially pumped to levels higher than the levels shown in the figure. The atoms then drop down through the levels, and many become "stuck" on certain levels, leading to population inversion and lasing. The light emitted by A illuminates B and can cause stimulated emission of B. What is the energy per photon of that stimulated emission of B?

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- 11.5 eV, 3 ms 10.8 eV, 3 ms 9.5 eV, 3 ms 7.8 eV, 3 us -6.9 eV, 3 ms 6.1 eV, 3H5 4.2 eV, 3 ms 3.9 eV, 3 μs 5.4 eV, 3 ms 3.7 eV, 3 us