Theoretical study of arbitrary step-height measurement based on wavelength-scanning talbot effect

Recently, arbitrary multi-dimensional step-height measurement has attracted much attention. Two wavelength Talbot effect or wavelength-scanning Talbot effect is implemented for the arbitrary step-height measurement. The main advantages of the method are non-mechanical scanning, high stability because of its common-path geometry and compactness. Without any mechanical movement of the grating or the detector in the longitudinal direction, the system is free from phase ambiguity problem and measurement errors caused by it. Instead of phase information, the maximum contrast of the high visibility bands is used to judge the occurrence of Talbot image, Ronchi grating with an open ratio of 0.5 is used for the periodic structure diffraction object, step-height measurement is given by the distance of self-image planes. Since the technique measures the fringe contrast rather than absolute intensity, accuracy of the step-height measurement depends on the fringe contrast. It is important that acquirement and judgement of the maximum contrast of the high visibility bands. It is pointed out that the smaller the pitch of the grating is, the better the lateral spatial resolution of the system will be. Further, non-Ronchi grating such as sinusoidal grating or phase grating can be used to improve the maximum contrast of the high visibility bands.