  The infrared imaging detection is an important and promising technology
having wide applications. In this work, we report on the frequency
up-conversion detection of an image based on sum frequency generation in a
nonlinear crystal with a flat-top beam acting as the pump instead of a Gaussian
beam, the up-converted image at 525 nm falls in the sensitive band of visible
detectors and human eyes. Both theoretical simulations and the experimental
results clearly demonstrate that using a flat-top beam as a pump can improve
the fidelity of an image after the up-conversion compared with a Gaussian pump
beam. Our scheme will be very promising for infrared image detection based on
frequency up-conversion.
