Multi-aperture optical head for parallel scanning near field optical microscopy

Abstract

This paper proposes the spatial sampling of high spatial frequencies images and their conversion into sequences of diffraction limited images. That method is based on a hybrid optical head which combines a classical diffractive lens and a spatial filter directly placed in the high resolution optical field. That filter is made of a matrix of sub-wavelength apertures etched in a thin opaque screen. The distance L between apertures is large enough to be resolved by the diffractive lens. The elementary aperture size d determines the exact size of object points. If the aperture size d is much smaller than the wavelength used, near field resolutions can be expected. Each image obtained with that optical head is a sub-image (or sample matrix) of the whole high resolution image with a sampling ratio of ( d/ L) 2. The reconstruction of the entire high resolution image is based on a sequence of ( L/ d) 2 diffraction limited sub-images which are recorded during a lateral scanning of the optical head.