Join us for a seminar by Professor Shuang Zhang of the New Cornerstone Science Foundation, Department of Physics, University of Hong Kong.
Synthesizing complex-frequency waves to compensate for optical loss of polaritons
Abstract: Polaritons, including surface plasmon polaritons (SPPs) and phonon polaritons (PhPs), have emerged as a highly promising candidate for constructing nanophotonic circuits, enabling the development of ultra-compact and high-speed optical devices. Utilizing polaritons in nanophotonics provides a pathway to overcoming the diffraction limit of light, allowing for the manipulation of light at the nanoscale. However, the intrinsic losses have hindered many loss-sensitive applications based on polaritons, including bio-sensing and sub-diffractional limit imaging. Complex frequency waves with virtual gain have been proposed to counteract losses in plasmonic/phononic materials for various applications, including super-resolution imaging1,2,3, slow light4, coherent virtual absorption5, and virtual PT symmetry6. Complex frequency waves feature temporal attenuation, which requires a precise exponential decay profile in time and time-gated measurements that are challenging for experimental implementation in optics. to address this challenge, we synthesize CFW signals using a multi-frequency approach. We exploit the fact that a truncated CFW can be expressed as combination of multiple frequency components with coefficients following a Lorentzian spectral lineshape through the Fourier transformation. Based on this method, we demonstrate dramatically improved superimaging resolution with a SiC superlens2, improved sensitivity of molecular sensing with plasmonic structures7, and restoration of lossless propagation of polaritons8.
Short Bio: Shuang Zhang is a chair Professor and interim Head of the Department of Physics at the University of Hong Kong. He obtained his PhD in Electrical Engineering from the University of New Mexico. Thereafter he worked as postdoc at UIUC and UC Berkeley. He joined the University of Birmingham, UK as a Reader in 2010 and was promoted to professor in 2013. Prof. Zhang joined the University of Hong Kong as a Chair Professor in 2020. He was the recipient of IUPAP Young Scientist Award in Optics (2010), ERC consolidator grant (2015-2020), Royal Society Wolfson Research Award (2016-2021), and New Cornerstone Investigator program (2023-2028). He was elected OSA fellow in 2016, APS fellow in 2022, and has been on the list of highly cited researchers (by Clarviate) since 2018.
References:
[1] Archambault, A., Besbes, M. & Greffet, J. J. Superlens in the time domain. Phys. Rev. Lett. 109, 097405 (2012).
[2] Guan, F. et al. Overcoming losses in superlenses with synthetic waves of complex frequency. Science 771, 766–771 (2023).
[3] Kim, S., Peng, Y., Yves, S. & Alù, A. Loss Compensation and Super-Resolution with Excitations at Complex Frequencies. arxiv: 2303.17699 (2023)
[4] Kirby, E. I. et al, Evanescent gain for slow and stopped light in negative refractive index heterostructures. Phys. Rev. B – Condens. Matter Mater. Phys. 84, 041103 (2011).
[5] Baranov, D. G., Krasnok, A. & Alù, A. Coherent virtual absorption based on complex zero excitation for ideal light capturing. Optica 4, 1457 (2017).
[6] Li, H., Mekawy, A., Krasnok, A. & Alù, A. Virtual Parity-Time Symmetry. Phys. Rev. Lett. 124, 193901 (2020).
[7] Zeng, K et al, Synthesized complex-frequency excitation for ultrasensitive molecular sensing, eLight, 4, 1 (2024)
[8] Guan F. et al, Compensating losses in polariton propagation with synthesized complex frequency excitation, Nature Materials (2024) https://doi.org/10.1038/s41563-023-01787-8