Investigation of parametric image conversion processes in the field of a partially coherent pump wave

A theoretical and experimental investigation is reported of the influence of the polychromaticity and multimode nature of a pump wave on the resolution, contrast, and conversion efficiency of a parametric image converter. It is shown that if the width of the pump spectrum Δω_p (or the divergence Δθ_p) exceeds the phase-matching width σω_p (or the angle σΨ_p), a wide base appears in the distribution of the intensity of the converted image of a point or line object. It is also shown that when Δω_p or Δθ_p is increased, the depencence of the conversion efficiency on the pump intensity changes from oscillatory (for example in the case Δθ_p < σΨ_p) to monotonic. If Δθ_p/σ_p ≫1, the maximum conversion efficiency is 50%. The results of an experimental investigation are in agreement with the theoretical predictions. It is shown that in the most-difficult- to-analyze case of high conversion efficiencies and multimode pumping the converter resolution is practically independent of the pump intensity.