Title: Phase induced transparency mediated structured beam generation in a closed-loop tripod configuration,
Abstract: We present a phase induced transparency based scheme to generate structured
beam patterns in a closed four level atomic system. We employ phase structured
probe beam and a transverse magnetic field (TMF) to create phase dependent
medium susceptibility. We show that such phase dependent modulation of
absorption holds the key to formation of a structured beam. We use a full
density matrix formalism to explain the experiments of Radwell et al. [Phys.
Rev. Lett. 114,123603 (2015)] at weak probe limits. Our numerical results on
beam propagation confirms that the phase information present in the absorption
profile gets encoded on the spatial probe envelope which creates petal-like
structures even in the strong field limit. The contrast of the formed
structured beam can be enhanced by changing the strength of TMF as well as of
the probe intensity. In weak field limits an absorption profile is solely
responsible for creating a structured beam, whereas in the strong probe regime,
both dispersion and absorption profiles facilitate the generation of high
contrast structured beam. Furthermore we find the rotation of structured beams
owing to strong field induced nonlinear magneto-optical rotation (NMOR).