Any image, imprinted on a wave field and propagating in free space, undergoes a paraxial diffraction spreading and eventually blurs. As was recently demonstrated, arbitrary images can be imprinted on light pulses which are dramatically slowed when traversing a medium of room-temperature atoms, via the process of electromagnetically induced transparency. In addition to the regular free-space diffraction, the slow-light images undergo diffusion due to the thermal atomic motion. Here we present an experimental demonstration of a novel technique to eliminate the paraxial free-space diffraction and the diffusion of slow-light, regardless of its position and shape [1]. The scheme is linear and occurs only in the wave-vector space, rendering elimination of diffraction for arbitrary images all throughout their propagation. By properly tuning the light-matter interaction, the diffraction can be increased, reduced, eliminated completely, or even reversed [2]. The interaction may be inverted, to accelerate the diffraction in the medium, or biased, to inflict asymmetric diffraction and deflection. Doubling the strength of the interaction surpasses the regular diffraction and effectively reverses it, allowing an implementation of a negative-diffraction lens.

1. Firstenberg, O., Shuker, M., Davidson, N. & Ron, A. Phys. Rev. Lett. 102, 043601 (2009).

2. Firstenberg, O., P. London, Shuker, M., Ron, A., Davidson, N. Nature Phys. 5, 665-668 (2009).