  We propose a multi-field-coupled atomic model that exhibits controllable
$symmetric$ and $asymmetric$ evolution of significantly enhanced diffraction
peaks in an opto-atomic grating at far-field regime. Such results are obtained
by the linear and nonlinear modulation of the intensities of the diffraction
peaks as a result of multi-wave-mixing-induced modification of spatially
modulated coherence in a closed four-level atomic system. Novelty of the
results lies in predicting super symmetric alignment of the diffraction peaks
due to the dominance of the amplitude part of the grating-transfer-function at
the condition of exact atom-field resonance, which is unique to the present
model. Efficacy of the present scheme is to apply it in producing nonlinear
light generated by four-wave-mixing-induced control of spatially modulated
coherence effect. The work also finds its importance for its applicability in
the field of high-precision atomic lithography.
