News

On-chip sampling of optical fields

03.05.2021 - New on-chip device for detecting electric-field waveforms with attosecond time resolution.

Understanding how light waves oscillate in time as they interact with materials is essential to understanding light-driven energy transfer in materials, such as solar cells or plants. Due to the fantas­tically high speeds at which light waves oscillate, however, scientists have yet to develop a compact device with enough time resolution to directly capture them. Now, a team led by MIT researchers has demons­trated chip-scale devices that can directly trace the weak electric field of light waves as they change in time. Their device, which incor­porates a microchip that uses short laser pulses and nanoscale antennas, is easy to use, requiring no special environment for operation, minimal laser parameters, and conven­tional laboratory electronics.

The team’s work may enable the development of new tools for optical measure­ments with appli­cations in areas such as biology, medicine, food safety, gas sensing, and drug discovery. “The potential applications of this technology are many,” says Phillip Donnie Keathley, group leader and Research Labora­tory of Elec­tronics (RLE) research scientist. “For instance, using these optical sampling devices, researchers will be able to better understand optical absorption pathways in plants and photovoltaics, or to better identify molecular signa­tures in complex biological systems.”

Researchers have long sought methods for measuring systems as they change in time. Tracking gigahertz waves, like those used for your phone or Wi-Fi router, requires a time resolution of less than 1 nanosecond. To track visible light waves requires an even faster time resolution – less than 1 femto­second. The MIT and DESY research teams designed a microchip that uses short laser pulses to create extremely fast electronic flashes at the tips of nanoscale antennas. The nanoscale antennas are designed to enhance the field of the short laser pulse to the point that they are strong enough to rip electrons out of the antenna, creating an electronic flash that is quickly deposited into a collecting electrode. These elec­tronic flashes are extremely brief, lasting only a few hundred atto­seconds. Using these fast flashes, the researchers were able to take snapshots of much weaker light waves oscilla­ting as they passed by the chip.

“This work shows, once more, how the merger of nano­fabrication and ultrafast physics can lead to exciting insights and new ultrafast measure­ments tools,” says Peter Hommelhoff, chair for laser physics at the University of Erlangen-Nuremberg, who was not connected with this work. “All this is based on the deep understanding of the under­lying physics. Based on this research, we can now measure ultrafast field waveforms of very weak laser pulses.” The ability to directly measure light waves in time will benefit both science and industry, say the researchers. As light interacts with materials, its waves are altered in time, leaving signatures of the molecules inside. This optical field sampling technique promises to capture these signa­tures with greater fidelity and sensi­tivity than prior methods while using compact and inte­gratable technology needed for real-world appli­cations.

Keathley’s colleagues are Mina Bionta, a senior postdoc at RLE; Felix Ritzkowsky, a graduate student at the Deutsches Elektronen-Synchro­tron (DESY) and the University of Hamburg who was an MIT visiting student; and Marco Turchetti, a graduate student in RLE. The team was led by Keathley working with Karl Berggren in the MIT Department of Electrical Engi­neering and Computer Science (EECS); Franz Kärtner of DESY and University of Hamburg in Germany; and William Putnam of the Univer­sity of California at Davis. Other co-authors are Yujia Yang, a former MIT postdoc now at École Poly­technique Fédérale de Lausanne (EFPL), and Dario Cattozzo Mor, a former visiting student. (Source: MIT)

Reference: M. R. Bionta et al.: On-chip sampling of optical fields with attosecond resolution, Nat. Phot., online 15 April 2021; DOI: 10.1038/s41566-021-00792-0

Links: Quantum Nanostructures and Nanofabrication Group, Massachusetts Institute of Technology, Cambridge, USA • Photon science, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany