posted on 2023-11-08, 21:29authored byLongfang Ye, Jingyan Li, Felix Ulrich Richter, Yasaman Jahani, Rui Lu, Bo Ray Lee, Ming Lun Tseng, Hatice Altug
Chirality
(C) is a fundamental property of objects,
in terms of symmetry. It is extremely important to sense and distinguish
chiral molecules in the fields of biochemistry, science, and medicine.
Vibrational circular dichroism (VCD) spectroscopy, obtained from the
differential absorption of left- and right- circularly polarized light
(CPL) in the infrared range, is a promising technique for enantiomeric
detection and separation. However, VCD signals are typically very
weak for most small molecules. Dielectric metasurfaces are an emerging
platform to enhance the sensitivity of VCD spectroscopy of chiral
molecules via superchiral field manipulation. Here, we demonstrate
a dielectric metasurface consisting of achiral germanium (Ge) tetramer
nanoresonators that provide a proper and accessible high C enhancement (CE). We
realize a maximum C enhancement (CE_max) with respect to the incident CPL
(CE_max = Cmax/CRCP) of more than 750. The volume-averaged C enhancement
(CE_ave = Cave/CRCP) is 148 in the 50 nm thick region above the sample surface
and 215 in the central region of the structure. Especially, the corresponding CE_ave values are more than
89 and 183 even when a 50 nm thick chiral lossy molecular layer is
coated on the metasurface. The metasurface benefits from geometrically
achiral nanostructure design to eliminate intrinsic background chiral-optical
signal from the substrate, which is useful in chiral sensing, enantioselectivity,
and VCD spectroscopy applications in the mid-infrared range.