  We experimentally demonstrate the manipulation of optical diffraction,
utilizing the atomic thermal motion in a hot vapor medium of
electromagnetically-induced transparency (EIT). By properly tuning the EIT
parameters, the refraction induced by the atomic motion may completely
counterbalance the paraxial free-space diffraction and by that eliminates the
effect of diffraction for arbitrary images. By further manipulation, the
diffraction can be doubled, biased asymmetrically to induced deflection, or
even reversed. The latter allows an experimental implementation of an analogy
to a negative-index lens.
