Research

A major focus of our group is the development of safer, sustainable, more compact and more efficient X-ray and gamma ray sources.

We have demonstrated tunable narrowband X-ray peaks that can be continuously and precisely tuned across the entire water window regime for applications like biological imaging, overcoming restrictions that have prevented existing table-top X-ray sources from fully accessing the water window regime [Nature Photonics 18, 1203 (2024) ; Nature Photonics News & Views]. We have also demonstrated multi-color X-ray generation using van der Waals heterostructures [Science Advances 9,  eadj8584 (2023)]. Using our compact, tunable X-ray source, we experimentally demonstrated quantum recoil, a phenomenon theoretically predicted by Physics Nobel Laureate Vitaly Ginzburg in 1940 [Nature Photonics 17, 224 (2023) (Hero Image, Nature Photonics March 2023 Issue); Nature Photonics News & Views ]. 

We also pursue the application of nanophotonics to enhance X-ray and gamma ray detection [Advanced Materials (accepted); ACS Photonics 9, 3917 (2022), arXiv]

 Our breakthroughs pave the way to next-generation technologies in medical imaging, security scanning, industrial inspection, and computation, key to tackling global challenges like an aging population, sustainability, and advancing semiconductor technologies through novel imaging and lithography methods [Advanced Science 9, 2105401 (2022); Nature Photonics 14, 686 (2020), Advanced Science 7, 1901609 (2020); Nature Physics 15, 1284–1289 (2019); Light: Science & Applications 7, 64 (2018); Nature Photonics 10, 46-52, (2016); Nature Photonics News & Views]. See our featured perspective on prospects in X-ray science emerging from quantum optics and nanomaterials [Appl. Phys. Lett. 119, 130502 (2021)].

We have 4 patents on our X-ray generation techniques, with collaboration and support from local industries including CTMetrix Pte Ltd and Component Technology Pte Ltd.

Our achievements have been recognized through the 2024 Falling Walls Winner in Physical Sciences for "Breaking the Wall of Quanutm X-ray Tech".

We investigate the control and enhancement of quantum free electron-photon interactions through the quantum electron wavefunction [Science Advances 10, eadm9563 (2024); Light: Science & Applications 13, 29 (2024);   Advanced Science 10, 2205750 (2023); Nature Communications 12, 1700 (2021)] and classical electron distributions [Advanced Science, 2100925 (2021)]. We are keen on discovering new electromagnetic phenomena that can unlock new techniques in quantum information, quantum measurements, imaging, microscopy and materials processing. These phenomena may involve new types of space-time wavepackets [Optics Express 29, 30682 (2021); Advanced Science 1903377 (2020), ACS Photonics 4, 1131 (2017); ACS Photonics 4, 2257 (2017);] and new ways of shaping light with nanomaterials [Physical Review A 94, 023820 (2016)]. We have also explored efficient energy conversion techniques between electrons and light [Physical Review Letters 122, 053901 (2019); Nature Communications 7, 11880 (2016)]. 

Electron-based instrumentation -- ranging from desk-sized scanning electron microscopes to kilometers-long X-ray free electron lasers -- form a cornerstone of modern scientific progress and industrial development. The advent of ultrafast optics and nanomaterials promise more compact, versatile and cost-efficient methods of electron beam transport and control. These methods include high-gradient laser-driven electron acceleration [Scientific Reports 7, 11159 (2017); Physical Review Accelerators and Beams 19, 021303 (2016); Optics Express 21, 9792–9806 (2013); Applied Physics Letters 99, 211101 (2011); Optics Express 18, 25035–25051 (2010)] and attosecond-scale electron pulse generation [New Journal of Physics 21, 033020 (2019); New Journal of Physics 17, 013051 (2015)].

3D Dirac semimetals (DSMs) are promising solid-state platforms for highly efficient generation of extreme, THz harmonics [Communications Physics 4, 235 (2021); Phys. Rev. Research 2, 043252 (2020)], and also a promising platform for highly efficient THz generation from optical radiation [Laser & Photonics Reviews 16, 2100279; arXiv].