Antennas for Angstrom Displacement Sensing

The Micro – Nano Optics and Tech­nology Research Group led by Lu Yonghua and Wang Pei from University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) realized together with dutch researchers from Delft University of Techno­logy nanometric displace­ment measurement through the inter­action between the illu­mination optical field and the optical antennas.

Schema of the near-field interaction between the antennas and incident light field. (Source: T. Zang et al.)

Optical metrology is of particular signi­ficance for it allows measure­ments of distance or displacement in a noncontact high-precision way. However, despite of the wide appli­cation in longi­tudinal displace­ment measure­ment of inter­ferometric method, such as laser radar, laser ranging and small vibration measurement, lateral displacement perpen­dicular to the direction of the beam is hard to be detected through conven­tional methods. The researchers presented a novel technique based on directional excitation of surface plasmon polaritons (SPPs).

They first excited asymmetric SPPs with a pair of optical slot antennas under the illu­mination of the focused Hermite-Gaussion (HG) (1,0) mode light. Then, by detecting the SPPs leakage at the back-focal plane of an oil-immersed objective, they sensi­tively measured the transverse displace­ment. Unlike the previous strategy to retrieve the free scat­tering signals, which remains challenging even when employing a weak measure­ment technique, the SPPs leakage pattern is spatially separated from the forward scattering of the slot antennas, and thus could be utilized to monitor displace­ments in the back-focal plane.

The reso­lution of their system reaches subwave­length level (~0.3 nm). However, the extreme resolution could be down to angstrom level. It is poten­tially applicable in super­resolution micro­scopy, semi­conductor litho­graphy, and cali­bration of nano­devices. (Source: CAS)

Reference: T. Zang et al.: Asymmetric Excitation of Surface Plasmon Polaritons via Paired Slot Antennas for Angstrom Displacement Sensing, Phys. Rev. Lett. 124, 243901 (2020); DOI: 10.1103/PhysRevLett.124.243901

Link: Dept. of Optics and Optical Engineering, University of Science and Technology of China, Hefei, China • Optics Research Group, Delft University of Technology, Department of Imaging Physics, Delft, The Netherlands

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