Illustration of a Fresnel zone plate made with plasmon-assisted etching consists of pillar-supported bowtie nanoantennas. Credit: University of Illinois
Researchers at the University of Illinois at Urbana-Champaign (USA) have developed a technique for etching flat, ultra-thin optics without hazardous chemicals and only one trip to the clean room (Nat. Commun., doi: 10.1038/ncomms10468). The new technique, called plasmon-assisted etching (PAE), can be used to create 2-D Fresnel zone plates, like the one shown here, via laser-scanning optical microscopy. Unlike standard methods, the authors say that PAE can speed up technological innovation by simplifying and reducing the cost of iterative optical component design, which could, in turn, reduce the time between basic design and fabrication.
One of the keys to their new technique is a nanostructured template—an 80 µm2 2-D array of gold pillar-supported bowtie nanoantennas on a glass substrate—that can be used to create different planar optical components. A laser from a conventional optical microscope scans a programmed pattern onto the water-submerged nanostructured template. The bowtie antennas magnify the heat from the laser, causing the gold layer to expand. The force generated by the expansion causes the gold to break away from the glass substrate, etching the template with the laser’s pattern.
Using PAE, the researchers were able to create Fresnel zone plates with a focal length of 150 µm, a diffraction grating, and a holographic mode converter using the same nanotemplate. They say that their technique can also be applied to nanotweezers and to fabricating optofluidic channels “without walls.” Team lead and OSA Senior Member Kimani Toussaint says in a press release: “We present plasmon-assisted etching as an approach to extend the do-it-yourself theme to optics with only modest tradeoff in quality, specifically, table-top fabrication of planar optical components.”