5. Real emission lines

5.1 Wave trains and coherence length

The notion of coherence length can be approached in a very pragmatic fashion by considering that, for an ideal transition, the light emitted during a transition consists of a wave train of finite duration τ at a single frequency (figure  1 ). Two wave trains of this type, shifted by a time interval Δ t , can interfere if Δ t  <  τ ...