Hi people,(adsbygoogle = window.adsbygoogle || []).push({});

Time-dependent perturbation theory allows for transitions to excited states, through a sinusoidal perturbation whose frequency is smaller than the enegy difference between the states. (That is, [itex]P_{a \rightarrow b}=\frac{sin^{2}[(\omega_{0}-\omega)t/2]}{(\omega_{0}-\omega)^2}[/itex]. Although the transition probability falls rapidly, as incident light frequency falls below the natural frequency, it's still non-zero..)

So in the "rare" event of absorption of a photon with insufficient energy, where does the lacking energy come from? Can you comment on the energy conservation in such an event?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Excitation by photons smaller than energy interval

**Physics Forums | Science Articles, Homework Help, Discussion**