Lens views objects from nine angles to create 3D image

Other 3D microscopes use multiple lenses or cameras that move around an object; the new lens is claimed to be the first single, stationary lens to create microscopic 3D images by itself.

Allen Yi, associate professor of integrated systems engineering at Ohio State, called the lens a proof of concept for manufacturers of microelectronics and medical devices who currently use very complex machinery to view the tiny components that they assemble.

Although the engineers milled their prototype thermoplastic lens on a precision cutting machine, the same lens could be manufactured less expensively through traditional moulding techniques, according to Yi.

The prototype freeform lens, which is about the size of a fingernail, looks like a gem cut for a ring, with a flat top surrounded by eight facets. But while gemstones are cut for symmetry, the lens is not symmetric. The sizes and angles of the facets vary in ways that are hard to see with the naked eye.

Such freeform optics have been in use for more than a decade, but postdoctoral researcher Lei Li was able to write a computer program to design the freeform lens such that it could be used to image microscopic objects.

Then, Yi and Li 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 10nm.

Next, the lens was installed on a microscope with a camera looking down through the faceted side and objects were placed beneath the flat side. Each facet captured an image of the objects from a different angle, which was 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 1mm — and a mini drill bit with a diameter of 0.2mm.

’For us, the most attractive part of this project is that we will be able to see the real shape of micro-samples instead of just a 2D projection,’ said Li.

In the future, Yi would like to develop the technology for manufacturers. He pointed to the medical testing industry, which is working to shrink devices that analyse fluid samples. Cutting tiny reservoirs and channels in plastic requires a clear view, and the depths must be carved with precision.