Phase-matched Deep Ultraviolet Chiral Bound States in the Continuum Metalens

Coherent light sources in deep ultra-violet (DUV) is essential for various applications such as biomedical imaging and biosensing. Nonlinear crystals (NLCs) generate DUV light, but limited by its bulky thickness, low transparency, and strict narrowband phase-matching conditions. Demonstrating compact, broadband, chiral, and focused DUV light integrated device is elusive. In this work, we present the first demonstration of chiral DUV third harmonic generation (THG) in a dielectric metasurface made from crystalline silicon (c-Si) of compact thickness 400 nm. Metasurface supports chiral bound states in the continuum resonance at fundamental wavelength 800 nm with experimental high Q-factor of 130 and modal phase-matched plasmonic resonance at the third harmonic wavelength for efficient THG. Generating DUV-THG power is up to 12 nW using peak power of 15 GW/cm2. Furthermore, we developed a nonlocal metalens operating in DUV for focusing the chiral DUV-THG using the same chiral BIC cavity and phase-gradient approach. Our platform creates efficient, ultracompact, and multifunctional integrated devices for future integrated DUV nanophotonics devices in MedTech, imaging, and advanced manufacturing.