Abstract:
We explore the coherent control of nonlinear absorption of intense laser fields in four-level atomic systems.
For instance, in a four-level ladder system, a coupling field creates electromagnetically induced transparency
(EIT) with an Aulter-Townes doublet for the probe field while the control field is absent. A large absorption peak
appears at resonance as the control field is switched on. We show how such a large absorption leads to optical
switching. Further, this large absorption diminishes and a transparency window appears due to the saturation
effects as the strength of the probe field is increased. We further demonstrate that the threshold of the optical
bistability can be modified by suitable choices of the coupling and the control fields. In a four-level
Y
-type
configuration, the effect of the control field on saturable absorption (SA) and reverse saturable absorption (RSA)
is highlighted in the context of nonlinear absorption of the probe field. We achieve RSA and SA in a simple
atomic system just by applying a control field.
