2D ACHROMATIC CORRELATION IN POLYCHROMATIC-LIGHT

A 2D achromatic correlator working in polychromatic light or with broadband illumination is demonstrated. It consists of two chromatic Fourier transformers combining zone plates set in cascade in order to cancel out chromatic blurring effects introduced by the use of several wavelengths. Each of the spectral bands resolved in the source spectrum by the zone plates works as an independent channel. Experimental results indicate that the SNR is increased by 3 db and 8 db as 5 channels (Ar** plus multiwavelength laser) and 40 channels (Xe arc lamp) are used, respectively. Practically, in pattern recognition, such a multichannel processor permits to reduce the false alarms; its discrimination capability is evaluated to be 1. 25 greater than when using a monochromatic correlator.