Two gratings consist of an imaging system that forms a no-dispersion image of an object that is illuminated by white light. The process of double diffraction of the actual system is analyzed using the Fresnel diffraction approximation. One grating generates a number of spectral images of the diffraction orders of an object. The other grating combines one-order dispersive images into one and reconstructs a clear image. A bi-grating system in this case shows the same imaging capability as the lens, but its principle is completely different. An expression of the imaging rule is deduced that agrees well with experiments.
© 2009 Optical Society of America
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