Optics and Photonics Society of Iran

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In this work we theoretically and experimentally investigate the diffraction of white light beam from the radial amplitude gratings. Theoretical part of the work is resolved with the Fresnel–Kirchhoff integral. In the experimental part, a collimated wave-front of a white light beam emitting from a halogen lamp source is transmitted through a radial amplitude grating. We digitally record the diffraction pattern in various distances from the grating using a digital camera. The resulted diffraction pattern that is known "Talbot carpet at the transverse plane" has a uniform profile under propagation. The significant aspect of this pattern is the existence of a quite patternless dark area located around the optical axis and an intense rainbow-like ring in the vicinity of the patternless area. The rainbow color changes radially from the violet in the vicinity of the patternless area to red by increasing the radius. We call this phenomena "Diffraction-based rainbow". In addition, the transverse plane Talbot carpet consists colorful self-images of grating's spokes at the larger radii. The theoretical calculations and experimental results verify each other completely. The introduced diffraction-based rainbow can be utilized in determining the spectrum of the white source.

Keywords: Diffraction and gratings, Talbot Carpet and self-imaging, spectrometry.

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