We analyze changes in the spatial structure of an object wave under four-wave mixing in a transparent two-component medium in schemes with opposing and concurrent pump waves. It is shown that in the spatial spectrum of the object wave there is a dip, whose position is determined by the propagation direction of the second pump wave. Angular rotation and frequency shift of the pump waves lead to a decrease in the conversion efficiency of high spatial frequencies. The bandwidth of the spatial frequencies cut out by the four-wave radiation converter decreases monotonically over time, whereas the bandwidth of the most efficiently converted spatial frequencies increases.
For a four-wave radiation converter in a two-dimensional multimode waveguide with thermal nonlinearity at a low reflection coefficient, we analyze the influence of the spatial structure of pump waves on the quality of wavefront reversal. It is shown that the half-width of modulus of the point spread function of a four-wave radiation converter decreases with decreasing radius of Gaussian pump waves on the waveguide edges, leading to an improvement in the quality of wavefront reversal. For a four-wave radiation converter in a two-dimensional waveguide with infinitely conducting surfaces, we show the presence of "generation" points, near which a sharp increase in the object wave amplitude is observed, with its form completely determined by one of the waveguide modes.
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