  Converting the medium infrared field to the visible band is an effective
image detection method. We propose a comprehensive theory of image
up-conversion under continuous optical pumping, and discuss the relationship
between the experimental parameters and imaging field of view, resolution,
quantum efficiency, and conversion bandwidth. Theoretical predictions of
upconversion imaging results are given based on numerical simulations, which
show good agreement with experimental results. In particular, coherent and
incoherent light illumination are studied separately and the advantages and
disadvantages of their imaging performance are compared and analysed. This work
provides a study of the upconversion image detection performance of the system,
which is of great value in guiding the design of the detection system and
bringing it to practical applications.
