Diffusion-free image storage in hot atomic vapor

The ability to directly store optical images in atomic vapor has many potential applications, but the diffusion of atoms severely limits the image resolution and storage duration. In this paper, we report an experimental demonstration on diffusion-free storage of optical images in hot atomic vapor. By encoding two-dimensional images in incoherent light and making use of the correlation imaging technique, we overcome the effect of atomic diffusion on the all-optical image storage in atomic vapor.

Figure 1

Schematic of the experimental setup. An incoherent light beam is split into two with a polarizing beam splitter (PBS1). The reflected beam passes through the mask, is collected and is collimated with a multimode fiber, and gets stored in the atomic vapor using the EIT effect. The retrieved beam is then detected with a photodiode (PD) with no spatial resolution. The transmitted beam, which has no information about the mask, is imaged with a CCD camera. The image of the mask is reconstructed by correlating the outputs of PD and CCD which, individually, carry no information about the mask.

Figure 2

The timing sequence of the experiment. By using delayed triggering of the CCD, we achieve an effective exposure time of $4\mu \mathrm{s}$ for the CCD, and this helps to reduce the background noise.

Figure 3

Correlation images of the mask before ($0\mu \mathrm{s}$) and after ($4–12\mu \mathrm{s}$) the storage. The retrieved images exhibit no diffusion.

Figure 4

Storing two-dimensional optical images in atomic vapor. Optical images are formed with a coherent laser pulse. (a) The image plane of the mask is stored and is retrieved. (b) The Fourier transform of the mask is stored and is retrieved.

Figure 5

The image visibility as a function of storage duration. The direct image storage is affected very strongly by the atomic diffusion. The Fourier-transform storage works slightly better, but there are inherent limitations, which are reflected as the significant loss of image quality. The correlation storage offers nearly diffusion-free image storage—the visibility remains at unity for all storage durations.