Achromatic system for far-field diffraction with broadband illumination

Abstract

An achromatic Fourier transformer working with spatially coherent but temporally incoherent light is described both theoretically and experimentally. The achromatic Fraunhofer diffraction pattern results from the incoherent superposition of the monochromatic diffraction patterns generated by every spectral component of light. Wavelength compensation is achieved by a specific configuration combining airspaced zone plates and lenses. Several parameters, such as the spectral resolution of the setup or the spectral broadness of the source, govern the accuracy of coincidence of the various monochromatic patterns. Experimental results demonstrate the broadband operation of the system; the error on the achromatic Fourier transformation is 2% over the visible spectrum. Applications in colored image processing are also reported.