Fig. 1.

Resolution extension through the moiré effect. If an unknown sample structure (a) is multiplied by a known regular illumination pattern (b), a beat pattern (moiré fringes) will appear (c). The moiré fringes occur at the spatial difference frequencies between the pattern frequency and each spatial frequency component of the sample structure and can be coarse enough to observe through the microscope even if the original unknown pattern is unresolvable. Otherwise-unobservable sample information can be deduced from the fringes and computationally restored.