Abstract
Scattering media have always been looked upon as an obstacle in imaging. Various methods, ranging from holography to phase compensation as well as to correlation techniques, have been proposed to cope with this obstacle. We, on the other hand, have a different understanding about the role of the diffusing media. In this paper we propose and demonstrate a ‘scatter-plate microscope’ that utilizes the diffusing property of the random medium for imaging micro structures with diffraction-limited resolution. The ubiquitous property of the speckle patterns permits to exploit the scattering medium as an ultra-thin lensless microscope objective with a variable focal length and a large working distance. The method provides a light, flexible and cost effective imaging device as an alternative to conventional microscope objectives. In principle, the technique is also applicable to lensless imaging in UV and X-ray microscopy. Experiments were performed with visible light to demonstrate the microscopic imaging of USAF resolution test target and a biological sample with varying numerical aperture (NA) and magnifications.
Highlights
Traditional lens-based microscope objectives have fixed focal length, short working distance, limited depth of focus and magnification, which often sets restrictions in applications
A microscope objective can be characterized by its point spread function (PSF), which is the output intensity distribution in the image plane when a point source is placed in the input plane
It can be seen that the quality of the images, in terms of resolution and contrast, of the scatter-plate microscope is almost comparable to that of a conventional microscope even though the edges look less sharp
Summary
Traditional lens-based microscope objectives have fixed focal length, short working distance, limited depth of focus and magnification, which often sets restrictions in applications. Freund proposed in 1988 an intensity-correlation-based technique, which permits lensless imaging of an object through a scattering medium by making use of the memory effect[8, 9] This principle was further exploited by combining it with phase retrieval algorithms[10, 11] for diffraction limited imaging. Microscopic imaging through diffusing media has been performed exclusively with traditional lens-based microscope objectives being combined with the above mentioned methods[23, 25, 33,34,35,36] In these approaches, the diffusing media play no constructive role but have always been treated negatively as a nuisance, except for a few instances where diffusing media have been utilized successfully for resolution enhancement in microscopy[37, 38] and speckle scanning endoscopy[39, 40].
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