Improved Ronchi lateral-shearing interferometry based on sinusoidal amplitude grating

High-precision wavefront measurement is a crucial technology in lithography systems. Ronchi lateral-shearing interferometry (LSI) has exhibited significant potential in wavefront measurement of the projection lenses in lithography systems due to its advantages of a common optical path, null testing, and reference-free interference. A conventional Ronchi interferometer applies two orthogonal Ronchi gratings sequentially as beam-splitting elements to obtain shear information in two directions. However, system errors from grating switching and higher-order parasitic diffraction complicate the accurate calculation of the wavefront under test. This paper proposes an LSI based on the sinusoidal amplitude grating. By altering the system's coherent modulation function, only the 0th and ±1st orders interfere, avoiding the effects of irrelevant diffraction orders. We establish an interference model of this novel LSI using scalar diffraction theory and used a combination of uniform phase shift and least squares to reconstruct the wavefront with high accuracy. This work simplifies the operating principle of Ronchi LSI, theoretically eliminating error sources such as higher-order parasitic diffraction and even-order harmonic diffraction, providing more possibilities for structural improvements in Ronchi LSI.