Optical image processing by an atomic vapour

• Published in: Nature (London) 1994-09, Vol.371 (6495), p.318-320
• Main Authors: Biaggio, Ivan, Partanen, Jouni P, Ai, B, Knize, R. J, Hellwarth, Robert W
• Format: Article
• Language: English
• Subjects: Atoms & subatomic particles; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Humanities and Social Sciences; Image forming and processing; Imaging and optical processing; Lasers; letter; multidisciplinary; Optical elements, devices, and systems; Optical processors, correlators, and modulators; Optics; Physics; Science; Science (multidisciplinary); Vapors
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/371318a0

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 orders of magnitude larger than the cross-sectional area of its electron cloud 2 . Because of these strong nonlinearities, different laser beams can interact with one another in an atomic vapour, even at intensities 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-optical image processor is the optical correlator: laser beams with imprinted images interact in a nonlinear medium to produce a signal beam, the intensity distribution of which is related to the correlation integral of (and hence the degree of similarity between) the input images. Here we demonstrate the use of a caesium-atom vapour as the active medium in such an optical correlator. We show that this system compares favourably with others currently in use, particularly with regard to its power requirements.