Phase shift microscopes

We report on a new class of scanning optical microscopes with twice the res olution of conventional microscopes. The new microscopes use standard compo nents to produce high intensity images, with large working distances and la rge depths of focus, without additional mechanical complexity. The microsco pes scan a focused laser beam which has passed through a pattern of phase s hifts arranged in a spiral staircase. These phase shifts generate a narrow dark spot in the center of the focused beam. The width of this central dark spot is about half the diffraction limit. The signal from this "phase shif ted" beam is subtracted from the signal produced by a conventional Gaussian beam which is simultaneously scanned. The difference between the two detec ted signals corresponds to the signal from a bright beam of width equal to the width of the dark central area. Since only linear operations on observe d optical signals are used, there is a useful improvement in resolution of about a factor of 2 This improves both the accuracy with which feature edge s may be located, as well as the resolution of small features such as the c orners of narrow lines. (C) 1998 American Vacuum Society. [S0734-211X(98)05 306-2].