Tuneable nonlinearity in atomic response to a bichromatic field

An atomic response to a probe beam can be tailored by creating coherences between atomic levels with the help of another beam. Changing parameters of the control beam will change the nature of coherences and hence the nature of the atomic response as well. Such a change can depend upon intensities of both probe and control beams in a nonlinear fashion. We present a situation where this nonlinearity in dependence can be precisely controlled, to obtain different variations as desired. We also present a detailed analysis of how this nonlinear dependence arises and show that this is an interesting effect of several coherent population trap states that exist and a competition among them to trap the atomic population