Abstract
A diffractive method using a visible laser to directly monitor colloids trapped at an air/water interface under isothermal compression is discussed. Upon merely measuring the ratio of first- and second-order diffractions on the screen, the center-to-center distance of adjacent colloids can be determined. Complicated instruments such as advanced optical microscopy, geometries of the apparatus and particle tracking analysis are not necessarily required. The equation of estimation is established based on the theory of Ewald sphere construction. Fabricating and precise monitoring of a colloidal monolayer can be achieved in parallel by this noninvasive method.