The figure schematically depicts two proposed alternative versions of an instrument that amounts, in effect, to a compact, lightweight optoelectronic microscope that contains no lenses and generates a magnified video image of a specimen. The instrument was described in "Miniature Microscope Without Lenses" (NPO-20218), Vol. 22, No. 8 (August 1998), page 43. In the design and construction of the instrument, the focusing optics of a conventional microscope were replaced by a combination of a microchannel filter and a charge-coupled-device (CCD) image detector. Elimination of focusing optics reduced the size and weight of the instrument and eliminated the need for the time-consuming focusing operation. At the time of the previous article, the instrument was only at the conceptual stage of development, but since that time, a prototype of the instrument has been built and demonstrated to function as intended.
The main differences between the previous version and the present proposed versions of the lensless microscope lie in the manner in which the specimen would be illuminated. The previous version was designed for a partly transparent but highly scattering specimen. The specimen was illuminated in a transmission mode with highly collimated light that was aimed through the specimen parallel to the axes of the microchannels.
According to the present proposal, the specimen would be illuminated in either of two reflection modes. In one case, the illumination would be provided by microscopic light-emitting diodes mounted on the walls between the microchannels, facing the specimen. In the other case, the specimen would be covered by a glass plate. Illumination would be brought in from the side by total internal reflection in the glass plate. A fluid with an index of refraction equal to that of the glass would be placed between the specimen and the glass plate to couple the illumination onto the specimen. There would be a thin airgap between the glass plate and the microchannel plate. Some of the light scattered and reflected by the specimen would travel along the microchannels to the CCD, as in the other versions of this instrument.
This work was done by Yu Wang of Caltech for NASA's Jet Propulsion Laboratory.