In a proposed optical microscope, the focusing optics of a conventional microscope would be supplanted by a combination of a microchannel filter and an advanced electronic image sensor. Elimination of focusing optics would eliminate the need for the time-consuming focusing operation, making it possible to examine different specimens in faster succession. Elimination of the focusing optics would also result in a smaller, lighter instrument.
Electronic image sensors with pixel sizes of several microns have been developed. During the next few years, pixel sizes in advanced image sensors may be reduced to < 1 μ m - close to the limit of resolution of a conventional microscope with focusing optics. In that case, and if it were possible to effect a one-to-one mapping from a point on a specimen to a pixel in such an image sensor, then the electronic output of the sensor would contain image information equivalent to that from a microscope.
The desired one-to-one mapping could be obtained by use of conventional optics to focus an image of the specimen onto the image sensor, but in this case, one seeks to avoid the use of focusing optics. Instead, according to the proposal, the following would be done: The specimen would be illuminated with highly collimated light (e.g., laser light) aimed through the specimen and toward the image sensor (see figure). Assuming that the specimen were thin enough to be partially transparent but were also highly scattering, the unscattered portion of the incident light would continue to travel along the direction of incidence, and some would be scattered in other directions.
A narrow-angle filter - a filter capable of absorbing the scattered light - would be placed between the specimen and the sensor. Such a filter could be constructed as a plate or block of opaque material with straight microchannels; more specifically, parallel microscopic-cross-section holes much longer than they are wide. The microchannels should be positioned and dimensioned so that each one is registered with a pixel on the image sensor.
The scattered light would be absorbed on the walls of the holes, and only the unscattered light would pass through. Therefore, the light arriving at each pixel on the sensor would have traveled along a straight line from a corresponding location on the specimen. Given the parallelarity of the holes and of all the optical paths in a collimated beam of light, the geometric relationship among the pixels would match that of the corresponding location in the specimen. Thus, the desired one-to-one mapping would have been effected.
This Miniature Microscope would not contain any lenses or other focusing optics. Focusing would not be necessary because the specimen would be imaged in collimated light on an electronic image sensor with microscopic pixels.
This work was done by Yu Wang of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Physical Sciences category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20218, volume and number of this NASA Tech Briefs issue, and the page number.
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Miniature microscope without lenses
(reference NPO-20218) is currently available for download from the TSP library.
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