posted on 2024-01-23, 13:05authored byOmar A. M. Abdelraouf, Aravind P. Anthur, X. Renshaw Wang, Qi Jie Wang, Hong Liu
Coherent
deep ultraviolet (DUV) light sources are crucial for various
applications such as nanolithography, biomedical imaging, and spectroscopy.
DUV light sources can be generated by using conventional nonlinear
optical crystals (NLOs). However, NLOs are limited by their bulky
size, inadequate transparency at the DUV regime, and stringent phase-matching
requirements for harmonic generation. Recently, dielectric metasurfaces
support high Q-factor resonances and offer a promising
approach for efficient harmonic generation at short wavelengths. In
this study, we demonstrated a crystalline silicon (c-Si) metasurface
simultaneously exciting modal phase-matched bound states in the continuum
(BIC) resonance at the fundamental wavelength of 840 nm with a higher
degree of freedom for precise control of the BIC resonance and a plasmonic
resonance at the wavelength of 280 nm in the DUV to enhance third
harmonic generation (THG). We experimentally achieved a Q-factor of ∼180 owing to the relatively large refractive index
of the c-Si and the geometric symmetry breaking of the structure.
We realized THG at a wavelength of 280 nm with a power of 14.5 nW
by using a peak power density of 15 GW/cm2 excitation.
The measured THG power is 14 times higher than the state-of-the-art
THG dielectric metasurfaces using the same peak power density in the
DUV regime, and the maximum obtained THG power enhancement factor
is up to 48. This approach relies on the significant third-order nonlinear
susceptibility of c-Si, the interband plasmonic nature of the c-Si
in the DUV, and the strong field confinement of BIC resonance to boost
overall nonlinear conversion efficiency to 5.2 × 10–6% in the DUV regime. Our work shows the potential of c-Si BIC metasurfaces
for developing efficient and ultracompact DUV light sources using
high-efficacy nonlinear optical devices.