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Study on the spectral combination characteristic of grating

Grating is well known for its dispersion characteristic. A new characteristic that we call spectral combination has been studied in this paper. It is a reverse phenomenon of grating dispersion. Light incident on a grating is dispersed into a spectrum. The same order diffracted lights of different wavelengths come from different places of the first grating converged on the second grating and outgoing beam at the same diffraction angle is spectral combination. Both using dispersion and spectral combination characteristic of grating, two gratings consist of an imaging system and a novel grating imaging phenomenon will occur. In this case, a virtual objective image can be formed after the object waves are diffracted by two gratings. This new grating imaging effect has close relation to spectral combination characteristic of grating. The characteristic is studied by theoretical analysis and numerical simulation. A relationship between the two gratings' spatial frequencies and diffraction orders that reflecting the spectral combination quality on certain condition is given. The spectral combination property of Grating on general condition is discussed by numerical calculation. To recognize the new property of grating deeply is very helpful for its application.