Observation of a 'return' Autler-Townes effect

Abstract
In infrared-radiofrequency double resonance (IRRFDR), the IR dynamic Stark splittings is shown both theoretically and experimentally to be observable at the fixed frequency of the strong IR field itself. This is achieved by using a weakly saturating RF field and is revealed by a doublet in the IR absorption change versus the RF. As with the conventional Autler-Townes effect (1955), this phenomenon appears to be general and observable in other spectral regions.