Freeform lens could someday provide a proof of concept for manufacturers of microelectronics and medical devices.
A lens that enables microscopic objects to be seen from nine different angles at once to create a 3D image has been developed. Other 3D microscopes use multiple lenses or cameras that move around an object; the new lens is the first single, stationary lens to create microscopic 3D images by itself.
Though the engineers milled their prototype thermoplastic lens on a precision cutting machine, the same lens could be manufactured less expensively through traditional molding techniques.
The prototype lens, which is about the size of a fingernail, looks at first glance like a gem cut for a ring, with a flat top surrounded by eight facets. But while gemstones are cut for symmetry, this lens is not symmetric. The sizes and angles of the facets vary in minute ways that are hard to see with the naked eye.
The lens is a “freeform lens,” a type of freeform optics. No matter what direction one looks at the lens, one sees a different shape. Freeform optics have been in use for more than a decade. But researchers were able to write a computer program to design a freeform lens capable of imaging microscopic objects. They used a commercially available milling tool with a diamond blade to cut the shape from a piece of the common thermoplastic material polymethyl methacrylate, a transparent plastic that is sometimes called acrylic glass. The machine shaved bits of plastic from the lens in increments of 10 nanometers, or 10 billionths of a meter — a distance about 5,000 times smaller than the diameter of a human hair.
The final lens resembled a rhinestone, with a faceted top and a wide, flat bottom. They installed the lens on a microscope with a camera looking down through the faceted side, and centered tiny objects beneath the flat side.
The lens allows scientists to see the real shape of micro-samples rather than just a two-dimensional projection. Each facet captured an image of the objects from a different angle, which can be combined on a computer into a 3D image. The engineers successfully recorded 3D images of the tip of a ballpoint pen — which has a diameter of about 1 millimeter — and a mini drill bit with a diameter of 0.2 millimeters.
In the future, this technology could be useful for manufacturers, including the medical testing industry, which is working to shrink devices that analyze fluid samples. Cutting tiny reservoirs and channels in plastic requires a clear view, and the depths must be carved with precision. Computer-controlled machines, rather than humans, do the carving. The new lens could be placed in front of equipment that is already in use. It could also simplify the design of future machine vision equipment, since multiple lenses or moving cameras would no longer be necessary.
Other devices could use the tiny lens, and the researchers have since produced a grid-shaped array of lenses made to fit an optical sensor. Another dome-shaped lens is actually made of more than 1,000 tiny lenses, similar in appearance to an insect’s eye.
This technology was done by Ohio State University, Columbus, OH. For more information, visit http://www.osu.edu.