In spectroscopy, the Autler–Townes effect, named after American physicists Stanley Autler and Charles Townes, is a type of the dynamical (also known as AC) Stark effect, corresponding to the case when an oscillating electric field (e.g., that of a laser) is tuned in resonance (or close) to the transition frequency of a given spectral line, and resulting in a change of the shape of the absorption/emission spectra of that spectral line.