Method to improve the quality of Moire signals by +/- first-order Moire fringes

In an amplitude grating system of small grid pitch, the diffractive effect is distinctive. Its energy will be about 10-40% of the total energy. The di ffractive light is the root cause of deterioration of the contrast and sinu soidal property, of the Moire signal. The relations between the phase of fi rst-order Moire fringes and other factors, such as the gap of the grating p ail; are analyzed. It is proposed to use first-order Moire fringes to obtai n high-quality, signals. (C) 2001 John Wiley & Sons, Inc.