Lecture by Prof. Carsten Rockstuhl (KIT)
"Improved Sensing of Circular Dichroism Using Dielectric Photonic Structures"
MPSP lecture series - online webinar
Online / via videoconference
Measuring the circular dichroism (CD), i.e. the differential absorption of left and right handed circularly polarized light, from a chiral molecular solution is a canonical method to distinguish the two different enantiomers. It is particularly important in pharmacy but also in other fields of science. However, as only the difference in absorption is measured, the signal is tiny and long integration times are needed. This is undesirable and many efforts are currently put in place to explore supporting photonic materials that enhance the CD signal. Here we summarize our recent efforts in this field. We argue that a suitable photonic structure should be (a) achiral, (b) helicity preserving, and (c) optically resonant. Only if the first condition is met, the CD signal depends on the chiral absorption properties of the molecule. If the second condition is met, the enhancement of the CD signal for a given ability of the structure to enhance the field is maximized. We show that suitably shaped dielectric discs perfectly accommodate all requirements . Making cavities out of such material allows to obtain enhancement factors averaged across the cavity volume as large as 100 . The maximum enhancement in some selected spatial locations can be even as large as 2000! . Graf F. et al., ACS Photonics, (2019), 6, 482 . Feis J. et al., Physical Review Letters, (2020), 124, 033201