Active Imaging

Abstract

Two general requirements for an optical maser system are the presence of an active medium for producing optical gain and also an optical cavity for the build-up of radiation energy density such that stimulated emission in the active medium can result in sustained oscillation. With the conventional Fabry–Perot, concentric, or confocal cavities the major concentration has been on the attainment of maximum energy into a single optical mode of the multi-mode cavity in the interests of maximum efficiency. In the work recorded here the mode degeneracy of the optical cavity of Fig. 1 has been used in image formation in the sense that opaque objects placed before mirror M₁ control the resultant field distributions in maser oscillation; in turn, the light generated within the cavity and partially transmitted through one mirror can be used to re-image the object. Specific attention is directed to the fact that such images may have a contrast or resolution an order of magnitude greater than would be obtained by conventional diffraction-limited image formation.