Spatial and temporal characteristics of a four-wave radiation converter with due regard for Earth's gravity field acting on nanoparticles dissolved in a transparent liquid

A theoretical analysis of the dynamics of the spatial spectrum of the object wave in a degenerate four-wave mixing in a transparent solution of nanoparticles in the classical scheme with counterpropagating pump waves is carried out. It is shown that when pump waves propagate orthogonally to the gravity force, a dip arises in the modulus of the spatial spectrum of the object wave, with its half-width nonmonotonically decreasing over time and increasing in the direction of gravity force with increasing radius of the nanoparticles. There is an optimal time over which the half-width of the dip in the direction of the gravity force reaches the lowest value. This time decreases monotonically with increasing nanoparticle radius, as well as with a decrease in the solution thickness.