OPTICAL-IMAGE PROCESSING BY AN ATOMIC VAPOR

ATOMIC vapours can exhibit large optical nonlinearities(1). when laser light is tuned in resonance with an atomic transition, the absorption cross-section of the atom can become very large, typically seven orde rs of magnitude larger than the cross-sectional area of its electron c loud(2). Because of these strong nonlinearities, different laser beams can interact with one another in an atomic vapour, even at intensitie s as low as a few milliwatts per cm(2). This raises the question(1) of whether atomic vapours can be used as nonlinear optical elements for parallel optical image processing. A well-known example of an all-opti cal image processor is the optical correlator: laser beams with imprin ted images interact in a nonlinear medium to produce a signal beam, th e intensity distribution of which is related to the correlation integr al of (and hence the degree of similarity between) the input images. H ere we demonstrate the use of a caesium-atom vapour as the active medi um in such an optical correlator. We show that this system compares fa vourably with others currently in use, particularly with regard to its power requirements.